tag:blogger.com,1999:blog-63020715798936455672024-02-19T09:13:19.678+05:30Mechanical Engineering DepartmentMechanical Engineering Departmenthttp://www.blogger.com/profile/12582953924770018783noreply@blogger.comBlogger76125tag:blogger.com,1999:blog-6302071579893645567.post-44492767676514766092017-08-11T15:16:00.003+05:302017-08-11T15:45:26.050+05:30ADVANCED MANUFACTURING TECHNOLOGY (UNIT-2) BY Asst. Prof. CP SAINI<div dir="ltr" style="text-align: left;" trbidi="on">
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<b><span style="font-size: 14.0pt; mso-bidi-font-size: 12.0pt;">UNIT II</span></b></div>
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<b><span style="font-size: 14.0pt; mso-bidi-font-size: 12.0pt;"><br /></span></b></div>
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<i><span style="font-size: 10pt; letter-spacing: 0.15pt;">Introduction,
Polymers, Polymerization, Addition of Polymers, Plastics, Types of plastics,
Properties of Plastics, Processing of Thermoplastic </span></i><i><span style="font-size: 10pt; letter-spacing: 0.55pt;">Plastics, Injection
Moulding, Extrusion Process, Sheet forming processes, Processing of
Thermosetting Plastics, Compression </span></i><i><span style="font-size: 10pt; letter-spacing: 0.1pt;">Moulding, Transfer Moulding, Casting of
Plastics, Machining of plastics, other processing methods of plastics</span></i><i><span style="font-size: 10.0pt;"><o:p></o:p></span></i></div>
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<i><span style="font-size: 10pt; letter-spacing: 0.1pt;">Introduction, casting,
thread chasing, Thread Rolling, Die Threading and Tapping, Thread Milling,
Thread Measurement and Inspection</span></i></div>
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<span style="background-color: transparent;"><b>2 INTRODUCTION OF PLASTICS AND
POLYMERS</b></span></div>
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<span style="font-family: inherit;">Plastics
belong to the family of organic materials. Organic materials are those materials,
which are derived directly from carbon. They consist of carbon chemically combined with hydrogen, oxygen
and other non-metallic substances, and their structures, in most cases, are
fairly complex. The large and diverse organic group includes the natural
materials: wood, coal, petroleum, natural rubber, animal fibers and food, which
have biological origins. Synthetics include the large group of solvents,
adhesives, synthetic fiber- s, rubbers, plastics, explosives, lubricants, dyes,
soaps and cutting oils etc. Which have no biological origins? Of them, plastics
and synthetic rubbers are termed as “polymers”</span><span style="font-size: 12pt;">.</span></div>
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<b><br /></b></div>
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<b>2.1 POLYMERS</b></div>
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The term
“polymer” is derived from the two Greek words: poly, meaning “many“, and meros
meaning “parts“ or “units”. Thus polymers are composed of a large number of
repeating units (small molecules) called monomers are joined together
end-to-end in a polymerization reaction. A polymer is, therefore, made up of
thousands of monomers joined tog -ether to form a large molecule of colloidal
dimension, called macromolecule. The unique characteristic of a polymer is that
each molecule is either a ling chain or a network of repeating u -nits all
covalently bonded together. Polymers are molecular materials and are generally
noncrystalline solids at ordinary temperature, but pass through a viscous stage
in course of their formation when, shaping is readily carried out.</div>
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The most common polymers are those made from compounds of carbon, but
polymers can also be made form inorganic chemicals such as silicates and
silicones. The naturally occurring polymers include: protein, cellulose,
resins, starch, shellac and lignin. They are commonly found in leather, fur,
wool, cotton, silk, rubber, rope, wood and many others. There are also
synthetic polymers such as polyethylene, polystyrene, nylon, terylene, dacron
etc., termed under plastics, fibers and elastomers. Their properties are
superior to those of the naturally occurring counter- parts. Our concern, here,
is therefore, with synthetic polymers, also called plastics (again from Greek
plastics, derived from plassein: to form, to mould) or resins.<b><o:p></o:p></b></div>
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<b>2.2 POLYMERIZATION<o:p></o:p></b></div>
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The process of linking together of monomers, that is, of obtaining
macro -molecules is called “polymerization”. It can be achieved by one of the
two processing techniques:<o:p></o:p></div>
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<b>(a) Addition Polymerization. </b>In addition or chain polymerization
under<b> </b>condition of temperature and
pressure and in the Presence of a catalyst called an initiator, the polymer is
produced by adding a second monomer to the first, then a third monomer to this
dimmer, and a fourth to the trimmer, and so on until the long polymer chain is
terminated. Polyethylene is produced by the addition polymerization of the
addition polymerization of ethylene monomers. This linear polymer can also be
converted to a branched polymer by removing a side group and replacing it with
a chain. It many such branches are formed, a network structure results.</div>
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“Co-polymerization” is the
addition polymerization of two or more different monomers. Many monomers will
not polymerize with themselves, but will copolymerize with other compounds.<b><o:p></o:p></b></div>
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<!--[if !supportLists]--><b>(b)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span>Condensation
polymerization. </b>In this process, two or more reacting compounds may<b> </b>be involved and there is a repetitive
elimination of smaller molecules, to form a by-product for example, in the case
of phenol formaldehyde (bakelite), the compounds are: formaldehyde and phenol.
Metacresol acts as a catalyst and the by- product is water. The structure of
the ‘mer’ is more complex. Also, there is the growth perpendicular to the direction of chain.
This is called ‘cross-linking’.</div>
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Size of a Polymer. The polymer chemist can control the average length
of the molecules by terminating the reaction. Thus, the molecular weight (the
average weight, in grams, of 6.02×10<sup>23</sup> molecules) or degree of
polymerization, D.P., (the number of mers in the average molecule) can be
controlled. For example, the length of molecules may range from some 700 repeat
units in low-density polyethylene to 1,70,000 repeat units in ultrahigh
molecule are weight polyethylene.<b><o:p></o:p></b></div>
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<span style="font-size: small;">2.3 ADDITIONS TO POLYMERS</span></h3>
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The properties of polymers can be
further modified by the addition of agents, which are basically of two types.
Those that enter the molecular structure are usually called “additives”,
whereas those that form a clearly defined second phase are called “fillers”.<br />
<ol>
<li><b style="text-indent: -21pt;">Plasticizers.</b><span style="text-indent: -21pt;">
Plasticizers are liquids of high boiling point and low molecular weight, which </span>are added to improve the plastic
behavior of the polymer. The board role of a plasticizer is to separate the macro- molecules
of the polymer, that is, making deformation easier. They are essentially oily
in nature. Organic solvents, resins and even water are used as plasticizers.</li>
<li><b style="text-indent: 0in;">Fillers.</b><span style="text-indent: 0in;">
Filler is used to economize on the quantity of polymer required and / or to
vary the properties to some extent, for example, mechanical strength,
electrical resistance etc. Filler, whose function is to increase mechanical
strength, is termed “reinforcing filler”. A filler is commonly fibrous in
natures and is chemically inert with respect to the polymer with </span>Which it is to be used? Common
fillers are wood flour, cellulose, cotton flock, and paper (for improving
mechanical strength); mica and asbestos (for heat resistance); talc (for acid
resistance).Wood flour is general purpose
filler. It improves mould ability, lowers the cost with fairly improved
strength of the plastics. Mica also imparts excellent electrical properties to
plastics and results in low moisture absorption. The commonly used “reinforcing
filler agents” with plastics are: fibers/filaments of glass, aramid, graphite
or boron. Reinforcing by metal and glass fibers make plastics strong, flexible
and light materials such as used in bullet proof vests. Cotton fibres improve
toughness. Carbon fibers are used for high performance installations such as
aircrafts etc. requiring high strength and stiffness.</li>
<li><b>Catalysts.</b> These are usually added to promote faster and more
complete polymerization and as such they are also called ‘accelerators’ and
‘hardeners’ e.g., ester is used as a catalyst for urea formaldehyde.</li>
<li><b>Initiators.</b>
As the name indicates, the initiators are used to initiate the reaction, that
is, to allow polymerization to begin. They stabilize the ends of the reaction
sites of the molecular chains. H<sub>2</sub>O<sub>2</sub> is a common initiator</li>
<li><b>Dyes and pigments</b>. These are added, in many cases, to impart a
desired colour to the material. For example, titanium dioxide is an excellent
white pigment; iron oxides give yellow, brown or red colour; carbon black is
not only a pigment but also a UV light absorbent. Finely divided calcium
carbonate dilutes (extends) the colour and is used in large quantities as low –
cost filler.</li>
<li><b style="text-indent: 0in;">Lubricants.</b><span style="text-indent: 0in;">
Lubricants are added to the polymers for the following purposes: to reduce
friction during processing, to prevent parts from sticking to mould walls, to
prevent polymer films from sticking to each other and to impart an elegant
finish to the final product. Commonly used lubricants include: oils, soaps and
waxes.</span></li>
<li><b style="text-indent: 0in;">Flame-retardants.</b><span style="text-indent: 0in;">
Most Plastics will ignite at sufficiently high temperatures. The
non-inflammability of the plastics can be enhanced either by producing them
from less inflammable raw materials or by adding “flame retardants”. The common
flame retardants are: compounds of chlorine, bromine and phosphorous.</span></li>
<li><b style="text-indent: 0in;">Solvents.</b><span style="text-indent: 0in;">
Solvents are useful for dissolving certain fillers or plasticizers and help in
manufacturing by allowing processing in the fluid state. For example, alcohol
is added in cellulose nitrate plastics to dissolve camphor. However,
subsequently, the solvents must be removed by evaporation.</span></li>
<li><b>Stabilizers and
anti-oxidants</b> are added to retard the degradation or polymers due to heat,
light and oxidation.</li>
<li><b style="text-indent: -0.25in;">Elastomers</b><span style="text-indent: -0.25in;">
are added to plastics to enhance their elastic properties.</span></li>
</ol>
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Note. Above, excepting fillers,
all other materials used fall under the category of “Additives”.</div>
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<b>2.4 PLASTICS<o:p></o:p></b></div>
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Polymer can be
divided in to three broad divisions: plastics, fibers and elastomers (polymer
of high elasticity, for example rubber). Synthetic resins are usually referred
to as plastics. Plastic derive their name from the fact that in a certain phase
of their manufacture, they are present in a plastic stage (that is, acquire
plasticity), which makes it possible to impart any desired shape to the product.
Plastics fall in to a category known chemically as high polymers.</div>
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Thus,
“plastics” is a term applied to composition consisting of a mixture of high
molecular compounds (synthetic polymers) is fillers, plasticizers, stains and
pigments, lubricating and other substances. Some of the plastics can contain
nothing but resin (for instance, polyethylene, polystyrene).</div>
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<b>2.4.1 TYPES OF PLASTICS:</b> Plastics are
classified on the broad basis of whether heat causes them to set
(thermosetting) or causes them to soften and melt (thermoplastic).</div>
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<b>2.4.1.1 Thermosetting plastics</b>: These
plastic undergo a no. of chemical changes on heating and cure to infusible and
practically insoluble articles, the chemical change is not reversible
Thermosetting plastics do not soften on reheating and can not be worked. They
rather become harder to completion of any leftover polymerization reaction. The
commonest thermosetting plastics are: alkyds, peroxides, melamines, polyesters,
phenolics and urea.</div>
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<b>2.4.1.2 Thermoplastic Plastics: </b>These
plastics soften under heat, harden on cooling, and can be re softened under
heat. Thus, they retain their fusibility, solubility and capability of being
repeatedly shaped. The mechanical properties of these plastics are rather
sensitive to temperature and to sunlight and exposure to temperature may cause
thermal degradation. Common thermoplastics plastics are: acrylics, poly tetra
fluoroethylene (PTFE), polyvinyl chlorides (PVC), nylons, polyethylene,
polystyrene, etc.</div>
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Thermosetting
plastics are cross-linked polymers and thermo-plastics are linear and
branched-linear polymers. The method of processing a plastic is determined
largely by whether a plastic is thermosetting or thermoplastics.</div>
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<b>2.4.2 PROPERTIES OF PLASTICS:</b> There is
great variety of physico-chemical and mechanical properties and the ease with
which they can be made into various articles have found plastics their wide
application in the engineering and other industries.<br />
<ol>
<li>Their
comparatively low density substantial mechanical strength and high anti
friction properties have enable plastics to be efficiently used as substitute
for metals, for example, non-ferrous metals and alloy bronze, lead, tin, babbit
etc., for making bearing.</li>
<li>With certain special properties (silent operation,
corrosion resistance etc), plastics can sometimes replace ferrous metals.</li>
<li>From the production point of view, their main advantage
is their relatively low melting points and their ability to flow into a mould.</li>
<li>Simple processing to obtain machine parts. Generally
there is only one production operation required to convert the chemically
manufactured plastic into a finished article.</li>
<li>In mass production, plastics substituted for ferrous
metals allow the production costs to be reduced by a factor of 1.5 to 3.5 and
for non-ferrous metals by a factor of 5 to 20.</li>
<li>Good damping capacity and good surface finished of the
product.</li>
<li>The high heat and electric insulation of plastics
permits them to be applied in the radio and electrical engineering industries
as and substitutes for porcelain, ebonite, shellac, mica, natural rubber, etc.</li>
<li>Their good chemical
stability , when subjected to the action of solvents and certain
oxidizing agents, water resistance, gas and steam proof properties, enable
plastics to be used as valuable engineering materials in the automo9bile and
tractor, ship building and other industries</li>
</ol>
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<b>2.4.3 DISADVANTAGES</b></div>
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<li><span style="font-size: 7pt; font-stretch: normal; line-height: normal; text-indent: 0in;"> </span><span style="text-indent: 0in;">Comparatively higher costs of materials.</span></li>
<li><span style="text-indent: 0in;">Inability of most plastics to withstand even moderately
high temperatures.</span></li>
</ol>
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The factors
which have determined the rapid growth of polymer materials in the recent past
are:</div>
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<ol>
<li>Ready availability of the basic raw chemical materials
in large quantities and, in general, at the low cost.</li>
<li>The large no. of available starting materials for their
production provide us with an almost continuous spectrum of composition and
structure, and hence of mechanical, optical, electrical and thermal properties
of the resulting polymers.</li>
<li>The engineer now has at his disposal many well
developed processes and machines to convert (as they from the factory and that
he can choose according to the specification of the ultimate product) into
useful goods.</li>
</ol>
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<b>2.4.4 PROCESSING OF THERMOPLASTIC PLASTICS</b></div>
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Thermoplastic
can be processed to their final shape by moulding and extrusion processes.
However, extruding is often used as an intermediate processes, for example,
vacuum forming or machining. </div>
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<b>2.4.4.1 EXTRUSION PROCESS:</b><br />
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The extrusion process,
in many cases, produces material in an intermediate form for subsequent
reprocessing to its final component form. The process is the same as for
metals, that is, the expulsion of material through a die of the required
cross-section .The earliest extrusion machines were of the ram type. The
cylinder of the machine is filled with prepared plastic and extruded through a
die under the pressure of the ram. The advantages of this machine are:
simplicity in operation and a controlled pressure which can be virtually as
high as required. If the polymer can be plasticized by pressure, then the ram
extruder is advantageous in view of its simplicity. But for plastics which
require heat, the separate pre-processing may be regarded as a drawback.
Another major drawback of this type of machine is reciprocating action of the
ram which is time wasting since the ram must be withdrawn after its power
stroke and a new dolly of material inserted in the container. Also, with many
materials the die orifice must be cleaned between each working stroke.<br />
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<b style="text-align: center;"> Fig. 2.1 Screw Extruding Machine</b><span style="text-align: left;"> </span></div>
</div>
</div>
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<span style="text-align: justify;">Now a days, the ram machine is
mainly used for “wet extrusion” that is for extruding plastics which have been
softened by the addition of solvents. Although useful in homogenizing materials
which contain hard inclusions, wet extrusion has the disadvantage of producing
a component from which the solvent has to be remolds.</span></div>
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For the extrusion of the
plastics, single-screw machine has completely replaced the ram type machine.
There are two basic types of screw extrudes: the melt extruder and the
plasticizing extruder. In the former, the material is delivered to the extruder
already melted and thus the function of the extruder is merely to push the
material to the die and through the orifice. In the plasticizing extruder the
material is in the form of granules or particle and so the extrude has to
compress and work it until it melts before delivering it, under pressure, to
the die orifice.</div>
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Complex shapes with constant
cross sections can be extruded with relatively inexpensive tooling. The
extruded product can be coiled or cut into desired lengths.</div>
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<b>2.4.4.2 SHEET –FORMING PROCESS:<o:p></o:p></b></div>
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sheet. The process resembles those for metals, but requires very low forces.
Even atmospheric pressure may be sufficient. In “Drape Forming”, the sheet is
heated to a moderate temperature. It is then clamped at the edges and stretch –
formed over a die. One of the encountered is that the portion of sheet first
touching the die will be chilled and remain thicker than the rest. This is
overcome or minimized by blowing hot air between the sheet and the die. </div>
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgq1rZUTox-oFYbccS-AaHecwZ5BWpFAx6TDtKm2KHiGoS066AJueC3oLL2gbrQQ2W3avFzw4kJ22YRVTSwm1aHAytWvdsbH17WupPdDv_bVw11EZlk8qWxGYMKmpXOuIGSyu14aCYDJWI/s1600/Untitled.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="416" data-original-width="802" height="206" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgq1rZUTox-oFYbccS-AaHecwZ5BWpFAx6TDtKm2KHiGoS066AJueC3oLL2gbrQQ2W3avFzw4kJ22YRVTSwm1aHAytWvdsbH17WupPdDv_bVw11EZlk8qWxGYMKmpXOuIGSyu14aCYDJWI/s400/Untitled.png" width="400" /></a></div>
<div class="" style="clear: both; text-align: center;">
<b>Fig. 2.2(a) Principle of Vacuum Forming Process</b><br />
<b><br /></b></div>
<div class="MsoNormal" style="text-align: justify;">
<div class="separator" style="clear: both; text-align: center;">
</div>
Vacuum
forming is a process, in which a heated plastic is changed to a desired shape
by causing it to flow against the mould surface by reducing the pressure
between one side of the sheet and mould surface. The process consist of
clamping the heat heated plastic sheet over a mould in such a way that the air
b/w the sheet and mould can be evacuated, this vacuum, of increasing intensity,
draws the sheet against the surface of the mould, where it cools and
solidifies. The solidifies will take place earliest in those resigns which
touch the mould first. This will cause differential cooling and, as a result of
non uniform temp. Distribution, there will be a marked change in thickness
along any given section of the component.</div>
<div class="separator" style="clear: both; text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiNXEo7ddrHgJf1_4YajfrYVBF7NtwFSAIlZiCVhwUcZ_uodmnl-tkEwefCF9RSQy0Rb_H_dHZvn6M7oA6lUudwfVakkRdsPkLZqR9BnLGAu4MzHBbU8btMobjeTU-zAESmE3mcs-pk2SU/s1600/Untitled.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="307" data-original-width="636" height="307" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiNXEo7ddrHgJf1_4YajfrYVBF7NtwFSAIlZiCVhwUcZ_uodmnl-tkEwefCF9RSQy0Rb_H_dHZvn6M7oA6lUudwfVakkRdsPkLZqR9BnLGAu4MzHBbU8btMobjeTU-zAESmE3mcs-pk2SU/s640/Untitled.png" width="640" /></a></div>
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<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<o:p> </o:p><b style="text-align: center;">Fig. 2.2(b) Vaccuum Forming Process</b></div>
<div class="MsoNormal" style="text-align: justify;">
<b style="text-align: center;"><br /></b></div>
<div class="MsoNormal" style="text-align: justify;">
<b>2.4.5 PROCESSING OF THERMOSETTING PLASTICS<o:p></o:p></b></div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
</div>
<div class="MsoNormal" style="text-align: justify;">
Compression molding and transfer
molding are the most common methods of processing thermosetting plastics.
Although, suitable for thermoplastics also, the main application of these
methods is to thermo sets.<br />
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>2.4.5.1
COMPRESSION MOULDING</b>:</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="separator" style="clear: both; text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEijKRyPSIF2amlxHy9LiLR0OcSOlnoEhra4_yqehnNcH2vCm_5GwzR35huQE6OBX91kH2ZFyuvAQoSRYxLJFl2PA6KSQzJgkXR1a_ZAAC9MP1GMNJHo_YSLVgvXh-mpyBxvnd7B1XpdrAo/s1600/Untitled.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="229" data-original-width="453" height="201" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEijKRyPSIF2amlxHy9LiLR0OcSOlnoEhra4_yqehnNcH2vCm_5GwzR35huQE6OBX91kH2ZFyuvAQoSRYxLJFl2PA6KSQzJgkXR1a_ZAAC9MP1GMNJHo_YSLVgvXh-mpyBxvnd7B1XpdrAo/s400/Untitled.png" width="400" /></a></div>
<br />
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<div align="center" class="MsoNormal" style="text-align: center; text-indent: -.25in;">
<b>Fig. 2.3 Compression Moulding<o:p></o:p></b></div>
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Compression moulding is the
equivalent of closed-die forging. In this process, a premature quantity of
plastic in the form of plastics or briquettes is placed in heated mould and
compressed at suitable pressure and temperature. Hydraulic pressure usually
employed to provide the pressure (which may range from 20 to 30 MPa or even
higher up to 80 MPa in same case) for compressing the plastic compound. Other
equipment, such as friction and presses, can also be used. The object of
compression moulding is to bring the plastic to virtually molten state. Thus
the process is, effectively, forming from the liquid state, the material being
healed in the mould until the curing stage is over when polymerization is
complete. The process is rather slow with the phenolics and urea resin, but
some of the newer resins have shorter curing time and this has improved the
production rates appreciably.<br />
When the plastic is completely trapped between
the male and female die, it is called as” positive mould”. Cluster tolerances
can be held if a small flash is allowed to extrude, usually along the male die
perimeter in “semi positive moulds”. More plastics is lost in “flash moulds”,
similar to those used in impression-die forging.</div>
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</div>
<div class="MsoNormal" style="text-align: justify;">
Typical product application are:
disches, handles, container caps, fitting,. Electrical and electronic
components, washing machine agitators and housing etc. </div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<!--[if gte vml 1]><v:oval id="_x0000_s1026"
style='position:absolute;left:0;text-align:left;margin-left:297pt;
margin-top:9pt;width:45pt;height:18pt;z-index:1' strokecolor="white"/><![endif]--><!--[if !vml]--><span style="height: 26px; left: 0px; margin-left: 395px; margin-top: 11px; mso-ignore: vglayout; position: absolute; width: 62px; z-index: 1;"></span><!--[endif]--><b>2.4.5.2
TRANSFER MOULDING:<o:p></o:p></b></div>
<div class="MsoNormal" style="text-align: justify;">
</div>
<div class="separator" style="clear: both; text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjv3dpv4HOwH8fIpY0rGX6dNnDR52SfqshJ-FcSLDqliqrf3960pGymXezdFJWaFZrvsjKwna_8sXr8S3TlPN9vCbqr8g5Kup7i39TrOsbnH1hg9j7HWa3DFDgqCz8AYae8zAo5OsD6_aQ/s1600/Untitled.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><i><img border="0" data-original-height="350" data-original-width="400" height="350" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjv3dpv4HOwH8fIpY0rGX6dNnDR52SfqshJ-FcSLDqliqrf3960pGymXezdFJWaFZrvsjKwna_8sXr8S3TlPN9vCbqr8g5Kup7i39TrOsbnH1hg9j7HWa3DFDgqCz8AYae8zAo5OsD6_aQ/s400/Untitled.png" width="400" /></i></a></div>
<div class="MsoNormal" style="text-align: justify;">
<b> Fig. 2.4 Transfer Moulding</b></div>
<div class="MsoNormal" style="text-align: justify;">
<b><br /></b></div>
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</v:shape><![endif]--><!--[if !vml]--><!--[endif]-->Transfer moulding is a
modification of compression moulding in which the moulding is first placed in
separate chamber (transfer pot), from which it pushed through an orifice into
the mould cavity as the mould closes. The material to be moulded is often
preheated by radio frequency methods and, where it is desired to improve toughness
and strength, reinforcing fillers may be used. </div>
<div class="MsoNormal" style="text-align: justify;">
The process has got following
advantages:</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
1. There is little pressure
inside the mould cavity until it is completely filled, at which stage the full liquid
pressure is transmitted.</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
2. The plastic acquires uniform
temperature and properties in the transfer pot prior to transfer .The plastic
is further heated by sheering through the orifice, viscosity is reduced, and
the plastic fills the intricate mould cavities.</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
</div>
<div class="MsoNormal" style="text-align: justify;">
3. It scores over normal
compression moulding in that presses can be used, since; heating of plastic is
affected, not by press itself, but by a simple heating jacket round the
transfer chamber.</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>2.4.6 CASTINGS OF
PLASTICS:</b> <o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
Casting of plastics in moulds finds application when making parts of
plastic material with a binder but no filler.
It is also used to obtain various kinds of casts thermosetting plastics,
for example, cast carbolite, as well as certain cast thermoplastic material,
such as organic glass, polystyrene and others.<o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
The method is simple and cheap since no expensive tooling or equipment is
required, and no pressure needs to be applied to fabricate the part. There are many variations of the casting
method for plastics:-<o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l1 level1 lfo1; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->(a)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span><!--[endif]-->By using flexible moulds, very intricate shapes
can be fabricated. The mould is peeled off afterwards.<o:p></o:p></div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l1 level1 lfo1; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->(b)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span><!--[endif]-->Using plate glass moulds produces thick plastic
sheets.<o:p></o:p></div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l1 level1 lfo1; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->(c)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span>Using moving stainless steel belts, which contain
and cool the resin, produces thinner plastic sheets.<o:p></o:p></div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l1 level1 lfo1; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->(d)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span><!--[endif]-->Hollow shapes can be obtained by centrifugal
casting of the molten plastic material.<o:p></o:p></div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l1 level1 lfo1; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->(e)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span><!--[endif]--><b>Potting: </b>In this method, the plastic material is cast around an electrical
component, which gets embedded in the plastic material. This is achieved by pouring the molten
plastic material in a housing or case, which is an integral part of the
component and in which the component is repositioned before pouring the
plastic.<o:p></o:p></div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l1 level1 lfo1; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->(f)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span><!--[endif]--><b>Encapsulation: </b>Here, the component is covered with a layer of cooled and solidified
plastic.<o:p></o:p></div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l1 level1 lfo1; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->(g)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span><!--[endif]-->Both potting and encapsulation are very important
to the electrical and electronics industry.
The plastic material serves as a dielectric.<o:p></o:p></div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l1 level1 lfo1; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->(h)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span><!--[endif]--><b>Foam
moulding / casting: In</b> this
method a foaming agent is mixed with the plastic resin. The mixture is placed in a mould and
heated. The foaming agent makes the
material to expand (even up to 50 times the original size) to take up the shape
of the mould. The amount of expansion
can be controlled through temperature and time. Both rigid and flexible foamed
plastics can be obtained from thermo-plastics and the thermo-setting
plastics. Rigid construction is used for
structural purposes and flexible for cushioning. Product application include: Shaped packaging
materials for cameras, appliances and electronics etc. insulating blocks, food
containers and Styrofoam cups.<o:p></o:p></div>
<div class="MsoNormal" style="margin-left: .5in; tab-stops: .5in; text-align: justify; text-indent: -.5in;">
<br /></div>
<div class="MsoNormal" style="margin-left: .5in; tab-stops: .5in; text-align: justify; text-indent: -.5in;">
<b>2.4.7 MACHINING
OF PLASTICS:<o:p></o:p></b></div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
Plastic can be machined, but in most cases, machining of plastics is not
required. Moulding and forming methods
can obtain acceptable surface quality and dimensional accuracy. However, there are certain plastics like PTFE
(Polytetra fluoroethylene) which are sintered products and are not mould able
by usual techniques, as they do not melt. For such “thermo stable plastics”
machining is a viable alternative to moulding.<o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
The machining of plastics (by operation such as turning, drilling and
milling) has special features due primarily to the structure of the
material. It also depends upon the
binder upon the binder and the filler and the method of moulding the component.
For example, the machining of thermosetting plastics allows optimum cutting
variables and tool geometry to be employed because these do not soften on
heating, whereas thermoplastic resins soften under heat. The permissible
maximum temperature in the cutting zone is 160<span style="mso-text-raise: 4.0pt; position: relative; top: -4.0pt;">0</span>C for thermo-setting resins and only 60<span style="mso-text-raise: 4.0pt; position: relative; top: -4.0pt;">0 </span>C to 100<span style="mso-text-raise: 4.0pt; position: relative; top: -4.0pt;">0</span>C for
thermoplastics.<o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
Special features of the machining of plastics are:-<br />
<br />
<ul>
<li><span style="font-family: "symbol"; text-indent: -0.25in;"><span style="font-family: "times new roman"; font-size: 7pt; font-stretch: normal; line-height: normal;"> </span></span><span style="text-indent: -0.25in;">The tendency
of certain plastics to splitting.</span></li>
<li><span style="text-indent: -0.25in;">High
elasticity (40 times as much as that of steels). Therefore, they must be
carefully supported, to avoid their deflection during machining.</span></li>
<li><span style="text-indent: -0.25in;">N</span><span style="text-indent: -0.25in;">on-homogeneous
structure of the material, with components of different hardness. This results
in poor surface finish after machining.</span></li>
<li><span style="text-indent: -0.25in;">Plastics
have a strong abrading action on cutting tools.</span></li>
<li><span style="text-indent: -0.25in;">Their low
thermal conductivity results in poor heat dissipation from the cutting zone and
in over-heating of the cutting edges.</span></li>
<li><span style="text-indent: -0.25in;">The intense
dust formation, especially for thermosetting plastics, makes it necessary to
use special dust -removing devices.</span></li>
<li><span style="text-indent: -0.25in;">T</span><span style="text-indent: -0.25in;">he hygro
scopicity of plastics excludes the use of liquid cutting fluids. Compressed air
is commonly used for cooling.</span></li>
<li><span style="text-indent: -0.25in;">Reinforced
plastics are very difficult to machine.</span></li>
</ul>
</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l0 level1 lfo2; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
Plastics can be machined with H.S.S. and cemented -carbide tools. In machining a plastic material with a filler
of glass, quartz or mica type, a satisfactory tool life can be obtained only
with carbide -tipped tools. Only diamond
tools are suitable for turning high-strength plastics of this type. The strength of cast parts of laminate
plastics is 40 to 50 percent less than that of the parts made by compression
moulding. Therefore, higher cutting
speeds and feeds can be used in their machining than for strong thermo-setting
plastics. The main trouble in turning
laminated plastics is the peeling of the surface layer.</div>
<div class="MsoNormal" style="text-align: justify;">
<o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
The cutting variables are also influenced by the life of cutting tool
which is subject to abrasive wear in machining most engineering plastics. Dulling of the cutting tool leads to a poor
surface finish and to breaking out of the material at the points the cutting tools
enters and leaves the cut. This makes it necessary to use more keenly sharpened
cutting tools for plastics. The need for
sharp cutting edges follows from the high elasticity of plastics.<o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
The selection of cutting variables is also influenced by the low heat
conductivity of the plastics, since, in machining the tool may be within a
closed volume (as in drilling) with no cooling facilities. This may lead to
charring of the machined surface.<o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
The cutting tool angles for machining plastics are made somewhat different
than those of tools for ferrous and non-ferrous metals. The rake angles are
positive and relatively larger. Because
of the visco elastic behavior of thermoplastics, some of the local elastic
deformation is regained when the load is off.
Therefore tools must be made with large relief angles (20<span style="mso-text-raise: 4.0pt; position: relative; top: -4.0pt;">0</span> to 30<span style="mso-text-raise: 4.0pt; position: relative; top: -4.0pt;">0</span>).<o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
Abrasive machining of plastics has many advantages over machining with
metal cutting tools. These include the absence of splitting and crack
formation, and the better surface finish that can be obtained.<o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
In grinding, the contact between the wheel and the surface being ground,
should be as short as possible, to avoid burns.
Organic glass is commonly ground with coated abrasive, applying an ample
amount of water as a coolant. If possible, however, grinding should be replaced
by polishing with a felt, broadcloth or flannel wheel charged with lapping
paste, the process is known as “Buffing”. The buffing wheels are of diameter
250 mm, 40 to 60 mm wide and of speed 2000 rev/min. Medium and fine lapping pastes are used as
the buffing compound for plastics. Laminate fabric base, asbestos-fiber and
glass -fiber laminate can be cut with abrasive wheels (SiC) of grain size 24 to
46 and with a 5% emulsion as the cooling fluid.<o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>2.4.8 OTHER PROCESSING METHODS FOR PLASTICS<o:p></o:p></b></div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>1. Calendering: </b> It is an
intermediate process where the extruded plastics sections are reduced to sheet
which may or may not, then be formed to final shape by vacuum forming. It is clear that the calendering process can
be used for thermoplastics and not for thermosetting plastics.<o:p></o:p></div>
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<br /></div>
<div class="MsoNormal" style="text-align: justify;">
</div>
<div class="MsoNormal" style="text-align: justify;">
Calendering is some ways similar to rolling process in that the material
is compressed between rolls and emerges as sheet (Fig 2.5a). However, there are differences. There is
appreciable thickening after the material has reached minimum thickness at the
roll gap and the pre-calendered material is not in sheet form, but of
indefinite shape. The method of producing vide sheet and foil is illustrated in
Fig (2.5b). The thermoplastic melt is fed
to a multi roll calendar. <o:p></o:p></div>
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh-VbIApW_Xpas7K3fvVUs41RIgJGqNLmvrh444NFp1tpgJhmpBCuytmB-WVHCzL-YVbhMzSVotw2k9LONI7U1W_Y5iAYGxv8_D0XZT7qyeY8ik1ybIyyVo0Nf5rGROdEI4wv3LH5rbFL4/s1600/Untitled.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="350" data-original-width="468" height="238" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh-VbIApW_Xpas7K3fvVUs41RIgJGqNLmvrh444NFp1tpgJhmpBCuytmB-WVHCzL-YVbhMzSVotw2k9LONI7U1W_Y5iAYGxv8_D0XZT7qyeY8ik1ybIyyVo0Nf5rGROdEI4wv3LH5rbFL4/s320/Untitled.png" width="320" /></a></div>
<div class="MsoNormal" style="text-align: justify;">
<b> Fig 2.5 Calendering Process</b></div>
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<b><br /></b></div>
<div class="MsoNormal" style="text-align: justify;">
The first roll gap serves as a feeder, the second as a metering device,
and the third roll gap sets the gauge of the gradually cooling plastic which is
then wound, with about 25% stretching onto a drum.<o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
Calendering is a high -production rate (typically 100 m/min) process,
mostly for flexible PVC, for example, upholstery, rainwear, shower curtains,
tapes, etc. and rigid PVC, for example, trays, credit cards, lamination. PVC is also calendered into the well known
transparent film widely used for packaging.<o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>2. Rotational Moulding: </b> In this
process, also called “rotomoulding”, large relatively thin -walled hollow (open
or closed) parts are made. A measured quantity of Polymer powder is placed in a
thin-walled metal would. The mould is closed and is rotated about two mutually
perpendicular axes as it is heated. This
causes the powder of sinter against the mould walls, building up the wall
thickness of the component. At the end
of the heating and sintering operations, the mould is cooled while it is still
rotating. Applying cold water and air to
the outside of the rotating mould does cooling. The rotation is then stopped
and the component is removed. To increase production rates, three moulds at the
end of three arms joined together to the central spindle (just like centrifuge
casting) are used, with one mould for each stage of the process, that is,
load-unload, heat and cool positions.<o:p></o:p></div>
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</div>
<div class="MsoNormal" style="text-align: justify;">
The process is simple as no pressure is employed and the part is free of
moulded in stresses. The technique is extensively used for the production of
toys in P.V.C. such as boats, horses etc.
Large containers of Polythene (or up to 20,000 liter capacity) and large
components like laminated petrol tanks for motor care are made from polythene (outer
shell) and nylon (inner shell). Other products include: Trash Cans, Boat hulls,
buckets, housings and carrying cases etc.<o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
<b><br /></b></div>
<div class="MsoNormal" style="text-align: justify;">
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</v:shape><![endif]--><!--[if !vml]--><!--[endif]--><b>3. Blow Moulding: </b> In this
process, a hot extruded tube of plastic, called a parison, is placed between
the two part open moulds (Fig 2.6 a). <o:p></o:p></div>
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgT3VxAAKhUHqGJEGJutKTQ33F48CGevX22CC9xdPv7Y647wAjHYc33c4tMnoAHt73VKVEV-IF_S30PAXLZD9sw0HdAq6Yg51cc0GlN-dvx4qKNno1wfZTxbUmUyu-ioG2tvoWdJxmo4Sw/s1600/blow-molding.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="480" data-original-width="640" height="300" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgT3VxAAKhUHqGJEGJutKTQ33F48CGevX22CC9xdPv7Y647wAjHYc33c4tMnoAHt73VKVEV-IF_S30PAXLZD9sw0HdAq6Yg51cc0GlN-dvx4qKNno1wfZTxbUmUyu-ioG2tvoWdJxmo4Sw/s400/blow-molding.png" width="400" /></a> </div>
<div class="" style="clear: both; text-align: center;">
<b>3D View of Blow Moulding</b></div>
<div class="" style="clear: both; text-align: center;">
<br /></div>
<div class="separator" style="clear: both; text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjiE3qR2k_yuRe-weoCgtbZNV-V5MoxTSnrtNGH3sCx8e8ywo28-_A20ltNZ1aaPDlJWZXELCzma0we_uWDclk0sXRUvV9B5-YeBF4_fJT08Cir-RrNDFlZH8_hCQ92vbL8NpMSRrVhKp0/s1600/Untitled.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="322" data-original-width="348" height="296" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjiE3qR2k_yuRe-weoCgtbZNV-V5MoxTSnrtNGH3sCx8e8ywo28-_A20ltNZ1aaPDlJWZXELCzma0we_uWDclk0sXRUvV9B5-YeBF4_fJT08Cir-RrNDFlZH8_hCQ92vbL8NpMSRrVhKp0/s320/Untitled.png" width="320" /></a></div>
<div class="" style="clear: both; text-align: center;">
<b>Fig 2.6 Blow Moulding</b></div>
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<br /></div>
<div class="MsoNormal" style="text-align: justify;">
The two halves of the mould move towards each other so that the mould
closes over the tube. The tube gets pinched off and welded at the bottom by the
closing <o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
</div>
<div class="MsoNormal" style="text-align: justify;">
Moulds (Fig. 2.6 b). The tube is then expended by internal pressure,
usually by hot air, which forces the tube against the walls of the mould.
(Fig2.c). The component is cooled and the mould opens to release the component
(Fig. 2d). Typical products applications are: Plastic beverage bottles and
hollow containers.<b>Fig. 2.6<o:p></o:p></b></div>
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<b><br /></b></div>
<div class="MsoNormal" style="text-align: justify;">
<b>4. Reaction Injection Moulding
(RIM) : </b> The method differs from the conventional injection moulding process in the sense
that it is not molten polymer which is
injected into a mould, but a mixture of
two or more monomers (reactants ) are
forced into a mould cavity. Chemical reaction takes place between the
constituents of the mixture giving off heat to form a plastic polymer, which
solidifies producing a thermo set component.
The major product applications include: Automotive bumpers, and fenders,
thermal insulation for refrigerators and freezers and stiffness for structural
components.<o:p></o:p></div>
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<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>5. Solid State Forming: </b> The term
is a misnomer because the temperature of the polymer is just (10<span style="mso-text-raise: 4.0pt; position: relative; top: -4.0pt;">0</span> to 20<span style="mso-text-raise: 4.0pt; position: relative; top: -4.0pt;">0</span>C) below the melting point of the
polymer. The main operations involved are: Sheet metal techniques such as
stretching, bending and deep drawing. Many food-packaging tubs and containers
are fabricated from Polypropylene.
Forging is also used mainly for producing gears.<o:p></o:p></div>
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<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>6. Cold Forming: </b> All the
cold working methods used for metals can be used for polymers. Filaments and
fibers are produced by “Cold drawing”, that is, continuous stretch
drawing. Conventional rolling can also
be used for producing fibers. In “Cold
pressing” or “Cold moulding”, the raw thermosetting material (or mixed plastic
compounds) are put in the mould and cured in an oven. Pressure applied by the press range from 14
MPa to 84 MPa. The moulds are made of abrasion resistant tool steel. The process is quite economical and the
process cycle is relative short. However, the surface quality and dimensional
accuracy of the part is not very good. <o:p></o:p></div>
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<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>7. Thermoplastic Stamping: </b>Thermoplastic Stamping or matched-die forming is
a method in which thermoplastic polymer sheet at melt temperature is worked
between mating dies. The cycle time is
greatly reduced and the spring back is minimum.<o:p></o:p></div>
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<br /></div>
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</div>
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<b>8. Spinning</b>: The extrusion process can be modified to
produce filaments, fibers and yarns. The molten thermoplastic polymer is extruded through a die containing
holes. For obtaining strands, the dies
can be rotated to produce twists and wraps.”<o:p></o:p></div>
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<b><br /></b></div>
<div class="MsoTitle" style="text-align: justify;">
<b>2.5 THREAD
MANUFACTURING<o:p></o:p></b></div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoSubtitle" style="text-align: justify;">
<b>2.5.1
INTRODUCTION</b><o:p></o:p></div>
<div class="MsoSubtitle" style="text-align: justify;">
Threads are prime importance to the engineering. These are
used as fasteners, to transmit power and motion and for adjustment. The subject
of thread manufacture has assumed a great significance because of the
ever-increasing demand for high precision fastening devices and power
transmission devices. At present, the threads are manufactured by the following
processes:<o:p></o:p></div>
<div class="MsoSubtitle" style="margin-left: .25in; mso-list: l0 level1 lfo1; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->1.<span style="font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span><!--[endif]-->Casting <o:p></o:p></div>
<div class="MsoSubtitle" style="margin-left: .25in; mso-list: l0 level1 lfo1; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->2.<span style="font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span><!--[endif]-->Thread chasing<o:p></o:p></div>
<div class="MsoSubtitle" style="margin-left: .25in; mso-list: l0 level1 lfo1; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->3.<span style="font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span><!--[endif]-->Thread rolling<o:p></o:p></div>
<div class="MsoSubtitle" style="margin-left: .25in; mso-list: l0 level1 lfo1; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->4.<span style="font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span><!--[endif]-->Die thread and tapping.<o:p></o:p></div>
<div class="MsoSubtitle" style="margin-left: .25in; mso-list: l0 level1 lfo1; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->5.<span style="font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span><!--[endif]-->Thread milling <o:p></o:p></div>
<div class="MsoSubtitle" style="margin-left: .25in; mso-list: l0 level1 lfo1; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->6.<span style="font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span><!--[endif]-->Thread grinding<o:p></o:p></div>
<div class="MsoSubtitle" style="text-align: justify;">
<br /></div>
<div class="MsoSubtitle" style="text-align: justify;">
<b>2.5.2
CASTING</b><o:p></o:p></div>
<div class="MsoSubtitle" style="text-align: justify;">
The accuracy and finish of threads made by casting will
depend upon the method of casting. Threads made by sand casting are rough and
are not used much, except sometimes in vises and rough machinery. Threads made
by die casting and permanent mould casting are very accurate and high finish,
if properly made. However, these can be made only of low melting point
non-ferrous metals and, therefore, are not fit for repeated use, being not hard
and durable. Lost wax method can produce highly accurate threads of good
finish. But the method is costly and difficult. Sewing machine vending
machines, typewriter parts and toys may have their threads cast in place by die
casting and permanent mould casting. Such parts are rarely taken apart, so, the
method is very satisfactory. The drawbacks of sand casting can overcome by
using shell molding method. Due to the inherent drawbacks of casting methods of
thread production.<o:p></o:p></div>
<div class="MsoSubtitle" style="text-align: justify;">
<br /></div>
<div class="MsoSubtitle" style="text-align: justify;">
<b>2.5.3
THREAD CHASING</b><o:p></o:p></div>
<div class="MsoSubtitle" style="text-align: justify;">
The method of cutting threads with a single point tool on a
center lathe and with a multipoint tool on a turret lathe is called “thread
chasing”. Thread chasing is a form cutting operation, with the form tool
corresponding to the profile of desired thread space.<o:p></o:p></div>
<div class="MsoSubtitle" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
</div>
<div class="MsoSubtitle" style="text-align: justify;">
<b>2.5.3.1
Thread chasing on a center lathe</b>. The first step in cutting
threads on a lathe is to get an accurately shaped and mounted tool. The form
and setting of the tool is checked with the help of a thread template or center
gauge, Fig. The job is either mounted between centers or held in a chuck (for
external threads) and held in a chuck for internal threads. When mounting the
tool in the tool post, it must be ensured that the top of the job, Fig. After
this, the second step is to establish a specific relationship between the
longitudinal movement of the tool parallel to the axis of rotation, and the
rotation, of the job. This will determine the pitch or lead of the thread. This
is achieved with the help of lead screw and a split nut. The two halves of the
split nut are fastened to the carriage. When the nut is closed on to the lead
screw, it acts as a complete nut, and the carriage starts moving as the lead
screw rotates. The lead screw is geared to the spindle and the proper speed
ratio between the two is sit by means of a gear-change box. Therefore, as the
lead screw rotates, the carriage will move a predetermined distance (depending
upon the pitch of lead of the thread) per revolution of the job. The third
requirement an exact predetermined time, for taking successive cuts, so that
the tool enters the helical groove of the cut previously produced; otherwise
the tool may remove some of the desired thread.<span style="font-size: 12pt;"><o:p></o:p></span></div>
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjqOR9iyFzYPZiC-rfG-tRm6ZcVtb6qizTT3okOqxGdf5R3uy8F61HA3HaN8fKzKinWMyHHS_xDOqdTDzB2PXsgDuFjpcqoKLRAhppeHp_V8Z-_x2KdfjlMOvCbDzofOsnxhy6sAvh_Gh0/s1600/Untitled.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="269" data-original-width="614" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjqOR9iyFzYPZiC-rfG-tRm6ZcVtb6qizTT3okOqxGdf5R3uy8F61HA3HaN8fKzKinWMyHHS_xDOqdTDzB2PXsgDuFjpcqoKLRAhppeHp_V8Z-_x2KdfjlMOvCbDzofOsnxhy6sAvh_Gh0/s1600/Untitled.png" /></a></div>
<div class="" style="clear: both; text-align: center;">
<b>Fig 2.7 Center </b><span style="text-align: left;"><b>Gauge</b></span></div>
<div class="" style="clear: both; text-align: center;">
<span style="text-align: left;"><b><br /></b></span></div>
<div class="MsoSubtitle" style="text-align: justify;">
This is achieved with the help of
a ‘thread dial’, which is mounted on the carriage and is driven by the lead
screw through a worm gear. The face of the thread dial is graduated into a even
number of full and half divisions, Fig. Whenever the lead screw rotates and the
split nut is not engaged, the thread dial rotates. The split nut must be
engaged when a particular line on the dial face coincides with the zero line.
For cutting even number of threads, the split nut should be engaged when any
line on the dial coincides with zero line, and for cutting odd-number threads, when
and homebred line coincides with zero line.<o:p></o:p></div>
<div class="MsoSubtitle" style="text-align: justify;">
</div>
<div class="MsoSubtitle" style="text-align: justify;">
To start cutting a thread, the
tool is fed inward until it first scratches the surface of the job. The
graduated dial on the cross-slide is noted or set to zero. The split nut is
then engaged and the tool moves over the desired job length. At the end of tool
travel, it is quickly withdrawn by means of cross slide. The spot nut is
disengaged and the carriage is returned to the starting portion, for the next
cut. </div>
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEizZYrpjTRcoHiHcZMpGEIehDil6-OfpaQSlIKhUQwzPJLhM_ALN9a9YYZWEWfQFmcsv-hxhD8qNdzbGBFceHtk_zC-paJM9Vr0J3EHV_-F-g8wimGXswKxqf-KURO4gzFhn8igWPrQb38/s1600/Untitled.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="236" data-original-width="476" height="196" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEizZYrpjTRcoHiHcZMpGEIehDil6-OfpaQSlIKhUQwzPJLhM_ALN9a9YYZWEWfQFmcsv-hxhD8qNdzbGBFceHtk_zC-paJM9Vr0J3EHV_-F-g8wimGXswKxqf-KURO4gzFhn8igWPrQb38/s400/Untitled.png" width="400" /></a></div>
<div class="" style="clear: both; text-align: center;">
<b><br /></b></div>
<div class="" style="clear: both; text-align: center;">
<b>Fig 2.8 Setting of Cutting Tool</b></div>
<div class="" style="clear: both; text-align: center;">
<b><br /></b></div>
<div class="MsoSubtitle" style="text-align: justify;">
These successive cuts are
continued until the thread reaches its desired depth (checked on the dial of
cross-slide). The depth of first cut is usually 0. 25 to 0.40 mm. This is
gradually decreased for the successive cuts until for the final finishing cut;
it is usually 0.027 to 0.075 mm. The tool can be fed inward either radially or
at an angle of 29 by swiveling the compound rest, Fig. <o:p></o:p></div>
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<div align="center" class="MsoSubtitle" style="text-align: center;">
<span style="font-size: 12.0pt; mso-bidi-font-weight: bold;"><b><br /></b></span></div>
<div align="center" class="MsoSubtitle" style="text-align: center;">
<span style="font-size: 12.0pt; mso-bidi-font-weight: bold;"><b>Fig. 2.9 Feeding the tool
into the job</b></span><span style="font-size: 12pt; text-align: justify;"> </span></div>
<div align="center" class="MsoSubtitle" style="text-align: center;">
<span style="font-size: 12pt; text-align: justify;"><br /></span></div>
<div class="separator" style="clear: both; text-align: center;">
</div>
<div class="MsoSubtitle" style="text-align: justify;">
The drawback of the first method
is that the absence of side and back rake will not proper cutting except on
brass and cast iron. In the second method, the cutting mainly takes place on
one face of the tool and some side rake can be provided. Also, the chip will
curl more easily. For cutting square, acme and worm threads, the first method
is used. For cutting L.H. threads, the tool is moved from left to right and for
cutting right hand threads; it is moved from right to left. Thread cutting on a
lathe is a slow process, but it is the only process of producing square threads,
as other methods develop interference on the helix.<o:p></o:p></div>
<div class="MsoSubtitle" style="text-align: justify;">
<br /></div>
<div class="MsoSubtitle" style="text-align: justify;">
<span style="font-family: "times new roman" , serif;"><b>2.5.3.2
Thread chasing on a turret lathe.</b> The main drawback of cutting
threads on a center lathe is that the operation cannot be done at higher
cutting speeds, since the permissible speed is limited by the quickness with
which the operator can withdraw the cutting tool from the job at the end of a
cut. This drawback is overcome in turret lathe, where thread-chasing attachment
is used to cut the thread. The attachment has no thread dial, which enables the
operation of the machine even by a semi-skilled worker. A simple thread chasing
attachment for a turret lathe is illustrated in Fig. From the headstock of the
machine, power is given to a short lead screw, known as the leader, by means of
change gears. The fed nut and the tool slide are carried on a shaft, which can
be engaged or disengaged to the leader by means of a hand lever. The major
advantage of the arrangement is that the fed nut can be engaged to the leader
at any portion of the work rotation. </span></div>
<div class="MsoSubtitle" style="text-align: justify;">
<span style="font-family: "times new roman" , serif;"><br /></span></div>
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjR8ZBKaKPpyLVaN6A1SR521gYZFDVnI4yrCGFWl4w5KJt5sQ37sfMi7imVEkDsQ2NVzUIUR4DHPkJDLR8hMQf-WL8TeiVbYgk3UuuMFZXRxj1trCCCxKM11Mss1HMj5q-UZFBP0BEazHI/s1600/Untitled.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="328" data-original-width="677" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjR8ZBKaKPpyLVaN6A1SR521gYZFDVnI4yrCGFWl4w5KJt5sQ37sfMi7imVEkDsQ2NVzUIUR4DHPkJDLR8hMQf-WL8TeiVbYgk3UuuMFZXRxj1trCCCxKM11Mss1HMj5q-UZFBP0BEazHI/s1600/Untitled.png" /></a></div>
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</div>
<div align="center" class="MsoSubtitle" style="text-align: center;">
<span style="font-size: 12.0pt;"><b><br /></b></span></div>
<div align="center" class="MsoSubtitle" style="text-align: center;">
<span style="font-size: 12.0pt;"><b>Fig. 2.10 Thread Chasing Attachment</b><o:p></o:p></span><br />
<span style="font-size: 12.0pt;"><b><br /></b></span>
<br />
<div class="MsoSubtitle" style="text-align: justify;">
<b>2.5.4
THREAD ROLLING</b><o:p></o:p></div>
<div class="MsoSubtitle" style="text-align: justify;">
<br /></div>
<div class="MsoSubtitle" style="text-align: justify;">
Thread rolling is a cold working
process in which a blank of diameter approximately equal to the pitch diameter
of the required thread, is rolled between hardened steel rolling dies having
the negative counter of the thread to be produced. As the thread shaped ridges
on the dies penetrate the blank material, material is displaced from the bottom
of the thread and forces radially out to form the thread crests. These are
three types of the thread rolling machine:<o:p></o:p></div>
<div class="MsoSubtitle" style="margin-left: .25in; mso-list: l1 level1 lfo1; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->1.<span style="font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->Reciprocating, flat die machines.<o:p></o:p></div>
<div class="MsoSubtitle" style="margin-left: .25in; mso-list: l1 level1 lfo1; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->2.<span style="font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->Cylindrical die machines.<o:p></o:p></div>
<div class="MsoSubtitle" style="margin-left: .25in; mso-list: l1 level1 lfo1; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->3.<span style="font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->Rotary planetary machines, having a rotary die and
one or more stationary concave-die segments.<o:p></o:p></div>
<div class="MsoSubtitle" style="text-align: justify;">
In the reciprocating, flat die
machine, one die is stationary and the other reciprocating. The part to be
threaded is rolled between the dies, as the moving die reciprocating in
reference to the stationary die. The stroke of the reciprocating die is will
depend upon the diameter of the thread being produced, since during one stroke,
the blank makes are completely revolution and the thread is completely formed.
This is highly versatile machine, since at the same time threading and knurling
can be done on a part of right and left hand threads can be rolled, by
assembling two or three sets of flat dies. This method is mainly used for the
manufacture of commercial bolts and nuts.<o:p></o:p></div>
<div class="MsoSubtitle" style="text-align: justify;">
In cylindrical die machine, the
part is to be threaded is rolled between rotating cylindrical dies. The machine
can have two rounded dies located diametrically opposite each other, or three
rounds dies usually spaced. This machine is slower than the reciprocating flat
die machine and is more suitable for large sized precision threads and for
short run production. This machine operates with the following motions:<o:p></o:p></div>
<div class="MsoSubtitle" style="margin-left: .25in; mso-list: l0 level1 lfo2; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->1.<span style="font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->Positive rotation of the both the dies (in a two die
machine) in the same direction.<o:p></o:p></div>
<br />
<div class="MsoSubtitle" style="margin-left: .25in; mso-list: l0 level1 lfo2; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->2.<span style="font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->Radial motion of one of the dies for its rapid
approach, infeed and retraction. This method has the main application of the
threads on taps.<span style="font-size: 12pt;"><o:p></o:p></span></div>
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<div align="center" class="MsoSubtitle">
<span style="font-size: 12.0pt;"><b>Fig. 2.11 Thread Rolling</b><o:p></o:p></span></div>
<div class="separator" style="clear: both; text-align: center;">
<br /></div>
<div class="MsoSubtitle" style="text-align: justify;">
In rotary planetary machine, the
job is rolled between a central die that rotates continuously about a fixed
axis, and one or more concave-shaped die segment located adjacent to the
periphery of the rotating die. This being a continuous process is the fastest
method of thread rolling.<o:p></o:p></div>
<div class="MsoSubtitle" style="text-align: justify;">
<br /></div>
<div class="MsoSubtitle" style="tab-stops: 405.0pt; text-align: justify;">
<b>2.5.4.1 Advantages of thread rolling</b><o:p></o:p></div>
<div class="MsoSubtitle" style="margin-left: .25in; mso-list: l0 level1 lfo1; tab-stops: list .25in left 405.0pt; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->1.<span style="font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->It is the fastest method of producing a thread, with
production rate more than 2000 piece per minute.<o:p></o:p></div>
<div class="MsoSubtitle" style="margin-left: .25in; mso-list: l0 level1 lfo1; tab-stops: list .25in left 405.0pt; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->2.<span style="font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->Being a chipless forming process (no material
wastage), there is lot of material saving (about 16 to 27 %).<o:p></o:p></div>
<div class="MsoSubtitle" style="margin-left: .25in; mso-list: l0 level1 lfo1; tab-stops: list .25in left 405.0pt; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->3.<span style="font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->During thread rolling, the material is strained
plastically and is work-hardened, and is, therefore, stronger against both
tension and fatigue, especially the latter.<o:p></o:p></div>
<div class="MsoSubtitle" style="margin-left: .25in; tab-stops: list .25in left 405.0pt; text-align: justify;">
Increase in tensile strength is form 10 to 20% and
that in fatigue strength is from 10 to 75%<o:p></o:p></div>
<div class="MsoSubtitle" style="margin-left: .25in; mso-list: l0 level1 lfo1; tab-stops: list .25in left 405.0pt; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->4.<span style="font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->The grain fibers remain continuous and follow the
contous of the threaded surface. Due to his, the threads are less easily
sheared off than machined threads.<o:p></o:p></div>
<div class="MsoSubtitle" style="margin-left: .25in; mso-list: l0 level1 lfo1; tab-stops: list .25in left 405.0pt; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->5.<span style="font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->The surface of rolled thread is harder than a cut
thread, so wear resistance increases. <o:p></o:p></div>
<div class="MsoSubtitle" style="margin-left: .25in; mso-list: l0 level1 lfo1; tab-stops: list .25in left 405.0pt; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->6.<span style="font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->Surface finish is better as controlled by the rolls.<o:p></o:p></div>
<div class="MsoSubtitle" style="margin-left: .25in; mso-list: l0 level1 lfo1; tab-stops: list .25in left 405.0pt; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->7.<span style="font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->Dimensional accuracy is better, as very little wear
occurs on the rolls as it would on a cutting tool.<o:p></o:p></div>
<div class="MsoSubtitle" style="tab-stops: 405.0pt; text-align: justify;">
<br /></div>
<div class="MsoSubtitle" style="tab-stops: 405.0pt; text-align: justify;">
<b>2.5.5 DIE THREADING AND TAPPING</b><o:p></o:p></div>
<div class="MsoSubtitle" style="tab-stops: 405.0pt; text-align: justify;">
<b>2.5.5.1 Die Threading.</b> Die threading is a method
of cutting external threads on cylindrical or tapered surfaces by the use of
the solid or self-opening dies. The main advantage of die threading is that it
can be performed along with other operations on turret lathes and on automatics
(in the case of self opening dies).<o:p></o:p></div>
<div class="MsoSubtitle" style="tab-stops: 405.0pt; text-align: justify;">
<br /></div>
<div class="separator" style="clear: both;">
</div>
<div class="MsoSubtitle" style="tab-stops: 405.0pt; text-align: justify;">
<b>2.2.5.2 Solid Dies</b>. In principal, a solid consists
of a hardened, threaded nut with several longitudinal grooves cut away and
shaped to provide cutting edges to the remaining portions of the thread. To
facilitate their use from either end, entry chamfers are provided at both the
ends. To cut the threads, the die is screwed on the bar upon which the threads
are to be cut. To move the die along the bar, it is held in stock. This is
rotated manually. To cut a smoother thread and to prolong the life of the die,
a suitable lubricant is used. The solid type dies are used rarely, because they
do not have any adjustment for wear. The solid adjustment can be adjust for
size and wear over a small amount by means of a screw, these dies are made of
carbon or high speed tool steel and can be used on a turret lathes with
suitable holders.<span style="font-size: 12pt;"><o:p></o:p></span></div>
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhX5C_aIMaYpnjI3VjvdgKgvZiaNrvU9Hupnjm2JthHsa0NK4TPTTVGmafexMkR42h34kqJpbJjP2EuEDKScGPSGi5goTA-621oDhlKT8sXhZtiqPeSNiDEot2jVc_7_SdpPTz-H2KDSJw/s1600/FIGURE%252B42-7%252B%2528a%2529%252BSolid%252Bthreading%252Bdie.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="403" data-original-width="906" height="283" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhX5C_aIMaYpnjI3VjvdgKgvZiaNrvU9Hupnjm2JthHsa0NK4TPTTVGmafexMkR42h34kqJpbJjP2EuEDKScGPSGi5goTA-621oDhlKT8sXhZtiqPeSNiDEot2jVc_7_SdpPTz-H2KDSJw/s640/FIGURE%252B42-7%252B%2528a%2529%252BSolid%252Bthreading%252Bdie.jpg" width="640" /></a></div>
<div align="center" class="MsoSubtitle">
<b><span style="font-size: x-small;">Fig. 2.12 Solid Threading
die</span></b><span style="font-size: 12.0pt;"><o:p></o:p></span></div>
<div align="center" class="MsoSubtitle">
<b><span style="font-size: x-small;"><br /></span></b></div>
<div class="MsoSubtitle" style="tab-stops: 405.0pt; text-align: justify;">
<b>2.2.5.3 Self-opening die heads</b>. The major
drawback of the solid type dies is that they must be unscrewed from the work
piece by reversing the machine spindle, to disengage the die from the work. Due
to this, these dies are not suitable for use on high speed production machines,
for use on high speed production machines, e.g. turret lathes and automatics.
This drawback is overcome by using self-opening die heads. When the required
length is thread is cut, the die open automatically. At the end of the turret
slide travel, the front portion of the dire head continuous to move forward by
a small amount until the chasers in the die head move outward in the body,
under the action of a scroll or a cam. This action clears the chasers from the
cut thread and enables the die head to be withdrawn without reversing the
machine spindle. The die head, while cutting threads may advance its own
guidance once it screws itself along the work, until the die trip opens.
However, for better accuracy, there is increasing use of lead screw guides. <o:p></o:p></div>
<div class="MsoSubtitle" style="tab-stops: 405.0pt; text-align: justify;">
Depending
upon the type of chaser, there are three types of die heads<o:p></o:p></div>
<div class="MsoSubtitle" style="margin-left: .25in; mso-list: l0 level1 lfo1; tab-stops: list .25in left 405.0pt; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->1.<span style="font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->Radial<o:p></o:p></div>
<div class="MsoSubtitle" style="margin-left: .25in; mso-list: l0 level1 lfo1; tab-stops: list .25in left 405.0pt; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->2.<span style="font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->Tangent<span style="font-size: 12pt;"><o:p></o:p></span></div>
<div class="MsoSubtitle" style="margin-left: .25in; mso-list: l0 level1 lfo1; tab-stops: list .25in left 405.0pt; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->3.<span style="font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->Circular<span style="font-size: 12pt;"><o:p></o:p></span></div>
<div class="MsoNormal" style="text-align: justify;">
Radial chasers can be more
rigidly, supported than other types. These are difficult to resharpen and their
life is short. Tangential chasers give a long life, because the length of the
teeth makes possible a large number of regrinds on the cutting face. Due to
this they are very suitable for heavy duty work and large batch production.
Circular chasers also have a long working life since these can be resharpened a
number of times. All the die-heads can either be stationary or revolving.</div>
<div class="MsoNormal" style="text-align: justify;">
When used on automatics, the feed
motion of the die-head is controlled by the cam rise, which can be designed
according. At the end of the return stroke, the dies are closed automatically
when the closing handle strikes a rod. Die-hands are available for cutting
threads from 6.35 mm to 114 diameter and chasers are available for any thread
form.</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>2.2.5.4 Thread tapping. </b>Taps are the tools for cutting internal
threads. A tap is similar to a threaded bolt, with one to four flutes cut
parallel to its axis. The flutes perform three functions:</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l1 level1 lfo2; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->1.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->Provide cutting edges.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l1 level1 lfo2; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->2.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->Conduct the cutting fluid to the cutting region, and </div>
<div align="center" class="MsoSubtitle">
</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l1 level1 lfo2; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->3.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->Act as channels to carry away the chips formed by the
cutting action.</div>
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiRK4XDXGvnFJ93bFcql5uvGqdZULBMLBEPAcRqjdR1TwpOXw5fNiPu45yRKdEiS5NjL65vfI1p5r8HAsmOSdJJtbBwJuKiH5LNwYJhoO4ZkfJgiv9PvnI01YIc3aU029pV9vE6SGv9MdU/s1600/FIGURE%252B42-8%252BSelf-opening%252Bdie.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="513" data-original-width="878" height="373" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiRK4XDXGvnFJ93bFcql5uvGqdZULBMLBEPAcRqjdR1TwpOXw5fNiPu45yRKdEiS5NjL65vfI1p5r8HAsmOSdJJtbBwJuKiH5LNwYJhoO4ZkfJgiv9PvnI01YIc3aU029pV9vE6SGv9MdU/s640/FIGURE%252B42-8%252BSelf-opening%252Bdie.jpg" width="640" /></a></div>
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<br /></div>
<div align="center" class="MsoNormal">
<b>Fig. 2.13 Self opening die head<o:p></o:p></b></div>
<div class="MsoNormal" style="text-align: justify;">
The flutes can be straight,
spiral, helical or spiral pointed. Taps with straight flutes are most commonly
used, since it is easier to cut and sharpen these flutes. Tapping can be dome
manually or on drilling machines, tapping machines, turret lathes and
automatics. A hole of diameter slightly larger than the minor diameter of the
thread to be cut must already exist, for thread tapping. Drilling can make the
hole, boring or casting. The two main types of taps are: solid taps and
collapsing taps.</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b><span style="font-family: "times new roman" , serif;">Solid
taps</span></b><span style="font-family: "times new roman" , serif;">. Solid taps are of one-piece construction.
These taps are usually worked manually but can also be used on machine tools,
such as lathes, drill presses and special tapping machines. Taps are made of
high carbon or high-speed steel. The shank of the taps is kept plain and the
end is squared. To operate the tap by hand (Hand taps), it is held at the
squared end with the help of a “tap wrench”, which is used to screw the tap
into the hole. To cut any particular size, hand taps are available in sets of
three: taper, plug and bottoming. The three taps are identical in size and
length, but differ in the amount of chamfer at the bottom end. The taper plug
has about 8 to 10 threads chamber at the bottom end, the plug tap has 2 to 3
threads chamfered, whereas, a bottoming tap has no taper threads at its bottom
end. The tapered are cut to the full depth gradually, so less effort is
required. If a hole is open at both ends, then, after the taper tap, plug is
used for finishing the treads as deep into the hole as its shape will permit.
Lastly, the bottoming tap is used to finish the entire thread portion. So, the
three taps should be used in the order mentioned above. The bottoming tap is
the only tap, which would nearly reach the bottom of a blind hole. The three
taps are shown in Fig. 2.14. </span></div>
</div>
<div align="center" class="MsoSubtitle" style="text-align: center;">
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<span style="font-size: 12.0pt;"><b><br /></b></span></div>
<div align="center" class="MsoSubtitle" style="text-align: center;">
<b><span style="font-family: "times new roman" , "serif"; font-size: 12.0pt;">Fig. 2.14 Solid Thread Taps</span></b></div>
<div class="MsoNormal" style="text-align: justify;">
<div class="MsoNormal">
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</v:shape><![endif]--><!--[if !vml]--><!--[endif]--> While threading a combined rotary
and axial motion is given to the tap. When using a solid tap on a drill press,
a special tapping attachment is used. This makes the tap to rotate slowly as it
is fed downward into the job. At the end of tapping, when the spindle is
raised, the tap automatically starts rotating in the reverse direction at a
higher speed to back the tap out of the hole in a shorter time. On screw
machine or turret lathe, a special holder is used for the tap, in which a pin
prevents the tap from rotating while it is fed into the job. At the end of
travel, the tap pulls the
pin so that it is free to rotate with the work. The machine spindle is then
reversed in motion and the pin again stops the tap from rotating while it is
being backed out of the hole.</div>
<div class="MsoNormal">
<b>(b) Collapsing taps</b>. For better results, a tap (or a die) should
not be backed off the thread it has just produced, because, during backing off,
they catch tiny chips which can do damage to the product. So for good finish
and to speed up openings, collapsing taps are used, which collapse inward
automatically when the thread is completed. This makes it possible to withdraw
the tap from the hole without reversing the machine spindle.</div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
<b>Nomenclature:</b> Refer to Fig. 2.15 </div>
<div class="MsoNormal">
<br /></div>
<div class="separator" style="clear: both; text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjInm9PfBFqWyvL7qPVSpAWMiqqM4pswNcOUfjXnvW9OL6a6pyebHr2H3gnU-27vVEdAVOo2yDu9rTFhRizvd6H5cqW-q_VShtHZ0WUu7j2HhBl8EKND_YOjNeh5uPVEdqtkHMFSkjUbYE/s1600/Untitled.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="326" data-original-width="370" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjInm9PfBFqWyvL7qPVSpAWMiqqM4pswNcOUfjXnvW9OL6a6pyebHr2H3gnU-27vVEdAVOo2yDu9rTFhRizvd6H5cqW-q_VShtHZ0WUu7j2HhBl8EKND_YOjNeh5uPVEdqtkHMFSkjUbYE/s1600/Untitled.png" /></a></div>
<div align="center" class="MsoNormal" style="text-align: center;">
<b>Fig. 2.15<o:p></o:p></b></div>
<div class="MsoNormal" style="margin-left: 0.25in; text-indent: -0.25in;">
<!--[if !supportLists]-->1.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]--><b>Axis.</b> It is
the longitudinal centre line through the tap.</div>
<div class="MsoNormal" style="margin-left: 0.25in; text-indent: -0.25in;">
<!--[if !supportLists]-->2.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]--><b>Body.</b> The
body of a tap is the thread and fluted part of the tap.</div>
<div class="MsoNormal" style="margin-left: 0.25in; text-indent: -0.25in;">
<!--[if !supportLists]-->3.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]--><b>Thread.</b> It
is the cutting tooth of the tap which produces the thread in a hole.</div>
<div class="MsoNormal" style="margin-left: 0.25in; text-indent: -0.25in;">
<!--[if !supportLists]-->4.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span><!--[endif]--><b>Angle of thread.</b>
It is the angle included between the sides of the thread, measured in the axial
plane.</div>
<div class="MsoNormal" style="margin-left: 0.25in; text-indent: -0.25in;">
<!--[if !supportLists]-->5.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]--><b>Crest.</b> It is
the top surface joining the two sides of a thread.</div>
<div class="MsoNormal" style="margin-left: 0.25in; text-indent: -0.25in;">
<!--[if !supportLists]-->6.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]--><b>Root.</b> It is
the bottom surface joining the sides of two adjacent threads.</div>
<div class="MsoNormal" style="margin-left: 0.25in; text-indent: -0.25in;">
<!--[if !supportLists]-->7.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]--><b>Base of thread</b>.
It is the bottom section of a thread; the greatest section</div>
<div class="MsoNormal" style="margin-left: 0.25in;">
section
between the two adjacent roots.</div>
<div class="MsoNormal" style="margin-left: 0.25in; text-indent: -0.25in;">
<!--[if !supportLists]-->8.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span><b>Depth of thread</b>.
The depth of the thread profile is the distance between the top of crest and
the base or root of thread measured perpendicular to the axis of the tap.</div>
<div class="MsoNormal" style="margin-left: 0.25in; text-indent: -0.25in;">
<!--[if !supportLists]-->9.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span><!--[endif]--><b>Side of thread.</b>
It is the surface of the thread which connects the crest with the root.</div>
<div class="MsoNormal" style="margin-left: 0.25in; text-indent: -0.25in;">
<!--[if !supportLists]-->10.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span><!--[endif]--><b>Land</b>. It is the threaded web between
flutes.</div>
<div class="MsoNormal" style="margin-left: 0.25in; text-indent: -0.25in;">
<!--[if !supportLists]-->11.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span><!--[endif]--><b>Cutting face</b>. It is the front part of
the threaded section of the land.</div>
<div class="MsoNormal" style="margin-left: 0.25in; text-indent: -0.25in;">
<!--[if !supportLists]-->12.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span><!--[endif]--><b>Hook</b>. It is the curved undercut of the
cutting face of the land.</div>
<div class="MsoNormal" style="margin-left: 0.25in; text-indent: -0.25in;">
<!--[if !supportLists]-->13.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span><!--[endif]--><b>Heel</b>. It is the back part of the
threaded section of the land.</div>
<div class="MsoNormal" style="margin-left: 0.25in; text-indent: -0.25in;">
<!--[if !supportLists]-->14.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span><b>Chamfer.</b> The tapered outside diameter
at the front end of the threaded section.</div>
<div class="MsoNormal" style="margin-left: 0.25in; text-indent: -0.25in;">
<!--[if !supportLists]-->15.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span><!--[endif]--><b>Point diameter</b>. It is the outside
diameter at the front end of the chamfered portion.</div>
<div class="MsoNormal" style="margin-left: 0.25in; text-indent: -0.25in;">
<!--[if !supportLists]-->16.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span><!--[endif]--><b>Flute</b>. It is the groove providing for
the cutting facts of the teeth, chip passage and cutting fluid.</div>
<div class="MsoNormal" style="margin-left: 0.25in; text-indent: -0.25in;">
<!--[if !supportLists]-->17.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span><!--[endif]--><b>Helix</b>. It is the curve of an ordinary
screw thread.</div>
<div class="MsoNormal" style="margin-left: 0.25in; text-indent: -0.25in;">
<!--[if !supportLists]-->18.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span><b>Helix angle.</b> It is the angle made by
the helix of the thread at the pitch diameter with a plane perpendicular to the
axis.</div>
<div class="MsoNormal" style="margin-left: 0.25in; text-indent: -0.25in;">
<!--[if !supportLists]-->19.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span><!--[endif]--><b>Shank.</b> It is the part of the tap behind
the threaded and fluted section of the tap. The tap held or located and driven
by the shank.</div>
<div class="MsoNormal" style="margin-left: 0.25in; text-indent: -0.25in;">
<!--[if !supportLists]-->20.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span><!--[endif]--><b>Square</b>. It is the squared end of the
tap.</div>
<div class="MsoNormal" style="margin-left: 0.25in; text-indent: -0.25in;">
<!--[if !supportLists]-->21.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span><b>Radial rake angle.</b> It is the angle
formed in a diametric plane between the face and a radial line from the cutting
edge at the crest of the thread from.</div>
<div class="MsoNormal" style="margin-left: 0.25in; text-indent: -0.25in;">
<!--[if !supportLists]-->22.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span><!--[endif]--><b>Chamfer angle</b>. It is the angle formed
by the tapered outside diameter at the front end with the top axis.</div>
<div class="MsoNormal" style="margin-left: 0.25in; text-indent: -0.25in;">
<!--[if !supportLists]-->23.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span><!--[endif]--><b>Web</b>. The central portion of the tap
situated between the roots of the flutes and extending along the fluted section
of the tap. Its thickness increases from the front and towards the shank end of
the flutes.</div>
<div class="MsoNormal" style="margin-left: 0.25in; text-indent: -0.25in;">
<!--[if !supportLists]-->24.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span><b>Back taper</b>. The reduction in diameter
of the tap body of the threaded portion from the front end towards the shank
end.</div>
<div class="MsoNormal" style="margin-left: 0.25in; text-indent: -0.25in;">
<!--[if !supportLists]-->25.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span><!--[endif]--><b>External Centre.</b> It is the cone-shaped
end of the tap. It is provided only for manufacturing purposes and only for
small taps and usually at the thread end.
</div>
<div class="MsoNormal" style="margin-left: 0.25in; text-indent: -0.25in;">
<!--[if !supportLists]-->26.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span><!--[endif]--><b>Internal Centre. A small</b> drilled and
countersunk hole at the end of the tap, necessary for manufacturing purposes.</div>
<div class="MsoNormal" style="margin-left: 0.25in; text-indent: -0.25in;">
<!--[if !supportLists]-->27.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span><!--[endif]--><b>Thread Relief. </b>It is the radial
clearance providing a gradual decline in the major, pitch, and minor diameters
of the lands, back of the cutting face.</div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
<b>2.5.5.5</b> <b>DESIGN FEATURES OF A
TAP<o:p></o:p></b></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
<b>A tap is ess</b>entially a screw that has been fluted to form cutting
edges. The cutting end of the tap has a relieved chamfer, which forms the
cutting edges and permits it to enter the untapped hole. The design features
are illustrated below:</div>
<div class="MsoNormal" style="margin-left: 0.25in;">
<br /></div>
<div class="MsoNormal" style="margin-left: 0.25in; text-indent: -0.25in;">
<!--[if !supportLists]-->1.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]--><b>Chamfer Diameter</b>.
The chamfer diameter, of the chamfer at the front end of the tap is made
smaller than the minor diameter of the
thread as given below:</div>
<div class="MsoNormal">
d= Minor diameter of thread – 0.10 to
0.15 mm for diameter upto 18 mm</div>
<div class="MsoNormal">
= Minor diameter of thread – 0.20 to
0.25 mm for diameter from 20 to 39 mm</div>
<div class="MsoNormal">
= Minor diameter of thread – 0.30 to
0.35 mm for diameter from 42 to 52 mm.</div>
<div class="MsoNormal">
<b><o:p></o:p></b></div>
<div align="center" class="MsoNormal" style="text-align: center;">
</div>
<div class="MsoNormal" style="margin-left: 0.25in; text-indent: -0.25in;">
<!--[if !supportLists]-->2.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span><b>Chamfer Length
and Chamfer Angle. </b>It shows the material removal in tapping threads. The
cross-hatched area represents the part of the thread groove removed in the
first revolution of the tap.</div>
<br />
<div class="separator" style="clear: both; text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhZY35Hd-La1F-fbmV-8rXYPPicm_FKSRHjDl5x3VaPPIKqxoIblcxNG9hQxDk4GQuH6NJ8J8seihZQJg2Bidm8cvtSahDopHFhGTlEcM28wGzVBTQ9-MBPhSx4jizjEdRFzyf0xdTGUjg/s1600/Untitled.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="177" data-original-width="381" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhZY35Hd-La1F-fbmV-8rXYPPicm_FKSRHjDl5x3VaPPIKqxoIblcxNG9hQxDk4GQuH6NJ8J8seihZQJg2Bidm8cvtSahDopHFhGTlEcM28wGzVBTQ9-MBPhSx4jizjEdRFzyf0xdTGUjg/s1600/Untitled.png" /></a></div>
<div align="center" class="MsoSubtitle" style="tab-stops: 405.0pt; text-align: center;">
<span style="font-size: 12.0pt;"><b>Fig. 2.16 Tap Chamfer Element</b><o:p></o:p></span></div>
<div align="center" class="MsoSubtitle" style="tab-stops: 405.0pt; text-align: center;">
<span style="font-size: 12.0pt;"><b><br /></b></span></div>
<div class="MsoNormal">
The uncut chip thickness
(measured perpendicular to the tap axis for simplicity) removed by each land
is,</div>
<div class="MsoNormal">
t = h/zf</div>
<div class="MsoNormal">
But</div>
<div class="MsoNormal">
f = <sub> </sub>L<sub>ch</sub>/p; L<sub>ch</sub>= chamfer length</div>
<div class="MsoNormal">
</div>
<div class="MsoNormal">
<span lang="FR">t = ph/z.L<sub>ch</sub> = p.tan</span>ф<span lang="FR">/z<o:p></o:p></span></div>
<div class="MsoNormal">
It is clear that,<sub><o:p></o:p></sub></div>
<div class="MsoNormal">
L<sub>ch</sub> =
h/tanф or = h/kz</div>
<div class="MsoNormal">
where</div>
<div class="MsoNormal">
h = depth of thread</div>
<div class="MsoNormal">
ф = angle of chamfer of
the tap</div>
<div class="MsoNormal">
p = pitch of the thread
being tapped.</div>
<div class="MsoNormal">
and k =t/p is a characteristic of the
construction of a tap.</div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Its values are: k = 0.012 to 0.02 for nut taps</div>
<div class="MsoNormal">
= 0.03 to 0.04
for die taps</div>
<div class="MsoNormal">
= 0.06 to 0.10
for hand and machine taps. </div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
The chamfer angle is given as,</div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
tan ф= (d<sub>o</sub>-d<sub>b</sub>)/2
L<sub>ch</sub> therefore L<sub>ch</sub> = (d<sub>o</sub>-d<sub>b</sub>
).cotф/2</div>
<div class="MsoNormal">
where</div>
<div class="MsoNormal">
d<sub>o</sub>=
major diameter of the tap thread</div>
<div align="center" class="MsoSubtitle" style="tab-stops: 405.0pt; text-align: center;">
</div>
<div class="MsoNormal">
d<sub>b</sub> =
diameter of blank hole for tapping.</div>
<div class="MsoNormal">
<b>3. Flutes</b>: Most taps have straight flutes, but special taps have
helical flutes. Changing the hand of the helical flutes on the tap can change
the direction of the chip flow. Left-handed flutes will drive the chips
forward, ahead of the tap. Left-handed flutes will drive the chips forward,
ahead of the tap, and, so, are used for tapping through holes. For tapping
blind holes, right-handed flutes are used for which the chip flow will be
towards the shank. With straight fluted taps, the chips can be made to flow
forward, ahead of the tap, by grinding a spired point on the cutting face of
each land at the chamfered end.</div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
The number of flutes may vary
from 2 to 8, the higher number is used for larger diameter taps.</div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Larger the number of flutes, better
will be the quality of the tapped thread. However, the cut chips will be
thinner, the specific cutting force and the torque will be higher.</div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
</div>
<div class="MsoNormal">
<o:p> </o:p><b>Table: 2.1 Number of Flutes</b></div>
<div class="MsoNormal">
<b><br /></b></div>
<table border="1" cellpadding="0" cellspacing="0" class="MsoNormalTable" style="border-collapse: collapse; border: none; mso-border-alt: solid windowtext .5pt; mso-border-insideh: .5pt solid windowtext; mso-border-insidev: .5pt solid windowtext; mso-padding-alt: 0in 5.4pt 0in 5.4pt; mso-yfti-tbllook: 480;">
<tbody>
<tr>
<td style="border: solid windowtext 1.0pt; mso-border-alt: solid windowtext .5pt; padding: 0in 5.4pt 0in 5.4pt; width: 167.4pt;" valign="top" width="223"><div class="MsoNormal" style="text-align: justify;">
<b><span style="font-size: 10.0pt; mso-bidi-font-size: 12.0pt;"> Type of Tap<o:p></o:p></span></b></div>
</td>
<td style="border-left: none; border: solid windowtext 1.0pt; mso-border-alt: solid windowtext .5pt; mso-border-left-alt: solid windowtext .5pt; padding: 0in 5.4pt 0in 5.4pt; width: 4.25in;" valign="top" width="408"><div class="MsoNormal" style="text-align: justify;">
<b><span style="font-size: 10.0pt; mso-bidi-font-size: 12.0pt;"> Number of
flutes<o:p></o:p></span></b></div>
<div class="MsoNormal" style="text-align: justify;">
<b><span style="font-size: 10.0pt; mso-bidi-font-size: 12.0pt;"> Major diameter, mm<o:p></o:p></span></b></div>
<div class="MsoNormal" style="text-align: justify;">
<b><span style="font-size: 10.0pt; mso-bidi-font-size: 12.0pt;">2 to 6 8 to 14 16 to 24 27 to 36 39 to 52<o:p></o:p></span></b></div>
</td>
</tr>
<tr>
<td style="border-top: none; border: solid windowtext 1.0pt; mso-border-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt; padding: 0in 5.4pt 0in 5.4pt; width: 167.4pt;" valign="top" width="223"><div class="MsoNormal">
<b><span style="font-size: 10.0pt; mso-bidi-font-size: 12.0pt;">Hand, nut and machinetaps
:<o:p></o:p></span></b></div>
<div class="MsoNormal" style="text-align: justify;">
<span style="font-size: 10.0pt; mso-bidi-font-size: 12.0pt;">For metric and inch threads<o:p></o:p></span></div>
<div class="MsoNormal" style="text-align: justify;">
<span style="font-size: 10.0pt; mso-bidi-font-size: 12.0pt;">For pipe threads<o:p></o:p></span></div>
<div class="MsoNormal" style="text-align: justify;">
<span style="font-size: 10.0pt; mso-bidi-font-size: 12.0pt;">Master taps <o:p></o:p></span></div>
</td>
<td style="border-bottom: solid windowtext 1.0pt; border-left: none; border-right: solid windowtext 1.0pt; border-top: none; mso-border-alt: solid windowtext .5pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt; padding: 0in 5.4pt 0in 5.4pt; width: 4.25in;" valign="top" width="408"><div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<span style="font-size: 10.0pt; mso-bidi-font-size: 12.0pt;">3
3 3 or 4 4 4 to 6 <o:p></o:p></span></div>
<div class="MsoNormal" style="text-align: justify;">
<span style="font-size: 10.0pt; mso-bidi-font-size: 12.0pt;">-
3 or 4 6 6 6<o:p></o:p></span></div>
<div class="MsoNormal" style="text-align: justify;">
<span style="font-size: 10.0pt; mso-bidi-font-size: 12.0pt;">3 4 6 6 6 to 8 <o:p></o:p></span></div>
</td>
</tr>
</tbody></table>
<div align="center" class="MsoSubtitle" style="tab-stops: 405.0pt; text-align: center;">
<span style="font-size: 12.0pt;"><b><br /></b></span></div>
</div>
<div class="MsoNormal" style="text-align: justify;">
</div>
<div class="MsoNormal" style="text-align: justify;">
<div class="MsoNormal">
<b>Tap geometry :<o:p></o:p></b></div>
<div class="MsoNormal">
i) <i>Rake angle.</i> of the sizing
and chamfer part is given below , depending upon the type of material to be
tapped.</div>
<div class="MsoNormal">
α = 15<sup>o</sup>,for steel with σ<sub>t </sub><600
MPa.</div>
<div class="MsoNormal">
= 10<sup>o</sup> ,
for steel with σ<sub>t</sub> 600 to 900 MPa</div>
<div class="MsoNormal">
= 5<sup>o</sup> ,for
steel with σ<sub>t</sub> >900 MPa</div>
<div class="MsoNormal">
= 5<sup>o</sup> for
Grey C.I.</div>
<div class="MsoNormal">
= 0<sup>o</sup>
for Bronze</div>
<div class="MsoNormal">
= 20<sup>o</sup> to
30<sup>o</sup>for Aluminium and its alloys.</div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
ii) <i>Relief angle</i>. Relief is provided only on the chamfer length. It is
obtained by relieving the thread only on the crests along the length of the
chamfer. Its recommended values are :</div>
<div class="MsoNormal">
γ = 8<sup>o</sup> to 10<sup>o</sup> for
machine taps</div>
<div class="MsoNormal">
= 6<sup>o</sup> to 8<sup>o</sup> for hand taps</div>
<div class="MsoNormal">
=
8<sup>o</sup> to 12<sup>o</sup> for nut and machine taps </div>
<div class="MsoNormal">
= 3<sup>o</sup> to 4<sup>o</sup> for
die calibrating taps</div>
<div class="MsoNormal">
= 4<sup>o</sup> to 8<sup>o</sup> for taps for
light alloys.</div>
<div class="MsoNormal">
The relieving over the chamfer
length will be given as,</div>
<div class="MsoNormal">
<sup><o:p></o:p></sup></div>
<div class="MsoNormal">
K = пd<sub>o</sub>.tanγ /z<sub><o:p></o:p></sub></div>
<div class="MsoNormal">
There is usually no relief on the
sizing section and at the flank of the thread. Relieving reduces the friction
between the tap and the surface of the hole.</div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
iii) <i>Back-Taper </i>: Axial back taper is provided on the tap from the front
end towards the shank end to to avoid rubbing of the tap with the surface of
the hole so as to reduce friction. It is taken as :</div>
<div class="MsoNormal">
= 0.05 mm to
0.10mm/100 mm for ground taps</div>
<div class="MsoNormal">
= 0.08 mm to 0.12
mm/100 mm for unground taps in which threads are formed by
rolling.</div>
<div class="MsoNormal">
= 0.20 mm for tapping
especially tough , high strength materials, such as heat resistant
and stainless steels and alloys and tough row-carbon steels etc.</div>
<div class="MsoNormal">
<br /></div>
<br />
<div class="MsoNormal">
iv) <i>Chamfer Angle.</i> The leading edges of a tap are chamfered to help in
starting the tap. Smaller the chamfer angle, longer will be the chamfer length.
This will result in thinner uncut chips, resulting in increase in cutting
force, eventhrough longer chamfer length provides better guiding to the tap and
the quality of the thread improves. </div>
</div>
<div class="MsoNormal" style="text-align: justify;">
<br />
<div class="MsoNormal">
<b>Table: 2.2 Chamfer Angles<o:p></o:p></b></div>
<table border="1" cellpadding="0" cellspacing="0" class="MsoNormalTable" style="border-collapse: collapse; border: none; mso-border-alt: solid windowtext .5pt; mso-border-insideh: .5pt solid windowtext; mso-border-insidev: .5pt solid windowtext; mso-padding-alt: 0in 5.4pt 0in 5.4pt; mso-yfti-tbllook: 480;">
<tbody>
<tr>
<td style="border: solid windowtext 1.0pt; mso-border-alt: solid windowtext .5pt; padding: 0in 5.4pt 0in 5.4pt; width: 2.05in;" valign="top" width="197"><div class="MsoNormal" style="text-align: justify;">
<b> Taps in a set<o:p></o:p></b></div>
</td>
<td style="border-left: none; border: solid windowtext 1.0pt; mso-border-alt: solid windowtext .5pt; mso-border-left-alt: solid windowtext .5pt; padding: 0in 5.4pt 0in 5.4pt; width: 2.05in;" valign="top" width="197"><div class="MsoNormal" style="text-align: justify;">
<b> Type of Tap<o:p></o:p></b></div>
</td>
<td style="border-left: none; border: solid windowtext 1.0pt; mso-border-alt: solid windowtext .5pt; mso-border-left-alt: solid windowtext .5pt; padding: 0in 5.4pt 0in 5.4pt; width: 2.05in;" valign="top" width="197"><div class="MsoNormal" style="text-align: justify;">
<b> ф ,degrees<o:p></o:p></b></div>
</td>
</tr>
<tr>
<td style="border-top: none; border: solid windowtext 1.0pt; mso-border-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt; padding: 0in 5.4pt 0in 5.4pt; width: 2.05in;" valign="top" width="197"><div class="MsoNormal" style="text-align: justify;">
1.<o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
2.<o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
3.<o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
</td>
<td style="border-bottom: solid windowtext 1.0pt; border-left: none; border-right: solid windowtext 1.0pt; border-top: none; mso-border-alt: solid windowtext .5pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt; padding: 0in 5.4pt 0in 5.4pt; width: 2.05in;" valign="top" width="197"><div class="MsoNormal" style="text-align: justify;">
Nut<o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
Taper<o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
Rougher<o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
Bottoming<o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
Finisher<o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
Taper<o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
Rougher<o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
Second<o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
Intermediate<o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
Bottom<o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
Finisher <o:p></o:p></div>
</td>
<td style="border-bottom: solid windowtext 1.0pt; border-left: none; border-right: solid windowtext 1.0pt; border-top: none; mso-border-alt: solid windowtext .5pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt; padding: 0in 5.4pt 0in 5.4pt; width: 2.05in;" valign="top" width="197"><div class="MsoNormal" style="text-align: justify;">
2<o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
7 <o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
7<o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
20<o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
20<o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
</div>
<div class="MsoNormal" style="text-align: justify;">
5<o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
5<o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
10<o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
10 <o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
20 <o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
20<o:p></o:p></div>
</td>
</tr>
</tbody></table>
</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b style="text-align: center;"></b><br />
<div class="MsoNormal">
<b>Cutting speeds</b>. The cutting speeds for machine taps are :</div>
<div class="MsoNormal">
<b>Table: 2.3 Cutting Speeds<o:p></o:p></b></div>
<div class="MsoNormal">
<b><br /></b></div>
<table border="1" cellpadding="0" cellspacing="0" class="MsoNormalTable" style="border-collapse: collapse; border: none; mso-border-alt: solid windowtext .5pt; mso-border-insideh: .5pt solid windowtext; mso-border-insidev: .5pt solid windowtext; mso-padding-alt: 0in 5.4pt 0in 5.4pt; mso-yfti-tbllook: 480;">
<tbody>
<tr style="height: 29.65pt; mso-yfti-firstrow: yes; mso-yfti-irow: 0;">
<td style="border: solid windowtext 1.0pt; height: 29.65pt; mso-border-alt: solid windowtext .5pt; padding: 0in 5.4pt 0in 5.4pt; width: 2.05in;" valign="top" width="197"><div class="MsoNormal" style="text-align: justify;">
<b> Work material<o:p></o:p></b></div>
</td>
<td style="border-left: none; border: solid windowtext 1.0pt; height: 29.65pt; mso-border-alt: solid windowtext .5pt; mso-border-left-alt: solid windowtext .5pt; padding: 0in 5.4pt 0in 5.4pt; width: 2.05in;" valign="top" width="197"><div class="MsoNormal" style="text-align: justify;">
<b> Lubricant<o:p></o:p></b></div>
</td>
<td style="border-left: none; border: solid windowtext 1.0pt; height: 29.65pt; mso-border-alt: solid windowtext .5pt; mso-border-left-alt: solid windowtext .5pt; padding: 0in 5.4pt 0in 5.4pt; width: 2.05in;" valign="top" width="197"><div class="MsoNormal" style="text-align: justify;">
<b> Tapping speed<o:p></o:p></b></div>
<div class="MsoNormal" style="text-align: justify;">
<b> m/min<o:p></o:p></b></div>
</td>
</tr>
<tr>
<td style="border-top: none; border: solid windowtext 1.0pt; mso-border-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt; padding: 0in 5.4pt 0in 5.4pt; width: 2.05in;" valign="top" width="197"><div class="MsoNormal" style="text-align: justify;">
Aluminium<o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
Bakelite<o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
Brass<o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
Cast Iron<o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
Steel :<o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
Mild<o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
Medium alloy<o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
Stainless<o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
Zinc die-cast<o:p></o:p></div>
</td>
<td style="border-bottom: solid windowtext 1.0pt; border-left: none; border-right: solid windowtext 1.0pt; border-top: none; mso-border-alt: solid windowtext .5pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt; padding: 0in 5.4pt 0in 5.4pt; width: 2.05in;" valign="top" width="197"><div class="MsoNormal" style="text-align: justify;">
Kerosene and hard oil<o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
Air blast<o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
Soluble or light base oil<o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
Dry or Soluble oil<o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
Soluble or sulphur based oil<o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
Sulphur-base oil<o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
Sulphur-base oil<o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
Soluble oil<o:p></o:p></div>
</td>
<td style="border-bottom: solid windowtext 1.0pt; border-left: none; border-right: solid windowtext 1.0pt; border-top: none; mso-border-alt: solid windowtext .5pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt; padding: 0in 5.4pt 0in 5.4pt; width: 2.05in;" valign="top" width="197"><div class="MsoNormal" style="text-align: justify;">
30<o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
24<o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
42 <o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
24<o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
18<o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
12<o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
6 <o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
24<o:p></o:p></div>
</td>
</tr>
</tbody></table>
</div>
<div align="center" class="MsoNormal" style="text-align: center;">
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<div align="center" class="MsoNormal" style="text-align: center;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
</div>
<div align="center" class="MsoNormal" style="text-align: center;">
<br /></div>
<div class="MsoNormal" style="tab-stops: 171.75pt; text-align: justify;">
<div class="MsoNormal">
<b>Materials</b>. Taps are usually made of carbon tool steel or H.S.S.</div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
<b>2.5.6 THREAD MILLING:<o:p></o:p></b></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
In thread milling, the threads
are cut by a revolving from milling cutter conforming to the shape of the
thread to be produced. Both external and internal threads can be cut by this
method. Thread milling has got the following characteristic:</div>
<div class="MsoNormal" style="margin-left: 0.25in; text-indent: -0.25in;">
<!--[if !supportLists]-->1)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->This is a fast thread cutting method for producing
threads usually of too large a diameter for die heads.</div>
<div class="MsoNormal" style="margin-left: 0.25in; text-indent: -0.25in;">
<!--[if !supportLists]-->2)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->The threads produced are more accurate than those cut
by dies, but less accurate than produced by grinding.</div>
<div class="MsoNormal" style="margin-left: 0.25in; text-indent: -0.25in;">
<!--[if !supportLists]-->3)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->Threads running upto a shoulder on the workpiece can be
cut without any difficulty.</div>
<div class="MsoNormal" style="margin-left: 0.25in; text-indent: -0.25in;">
<!--[if !supportLists]-->4)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->Worms and lead screws, which are too large to be cut
with a single point tool, can be milled.</div>
<div class="MsoNormal" style="margin-left: 0.25in; text-indent: -0.25in;">
<!--[if !supportLists]-->5)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->This method is desirable, when the pitch of the thread
is too coarse to be cut with a die.</div>
<div class="MsoNormal" style="margin-left: 0.25in; text-indent: -0.25in;">
<!--[if !supportLists]-->6)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->The method is more efficient than cutting thread on a
lathe; especially when the job is long or when large amounts of metal are to be
removed.</div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
For thread milling either single
or multiple cutters may be used. A single-form cutter has a single, annular row
of teeth, lying in one plane. While thread cutting with a single cutter, it is
tilted through an angle equal to the helix angle of the thread to avoid
interference while cutting. To start milling the threads, the cutter is fed
radially inward equal to the depth of the thread , while the job is stationary
, being held between centers of the machine. The job is then rotated slowly and
the cutter, while rotating, is also traversed longitudinally parallel to the
axis of the job, or vice versa , by
means of a lead screw. This operation is stopped when the thread is completed.
This method of thread milling is used for cutting coarse (large-pitch or
multiple-pitch) threads. The threading can be completed in a single cut or
roughing and finishing cuts may be used.</div>
<div class="MsoNormal">
<br /></div>
<br />
<div class="MsoNormal">
The method of cutting threads
with single-thread or single-rib milling cutters is chiefly employed to cut
long threads (chiefly of square and trapezoidal profiles) on various lead
screws and worms. Usually, the threads are cut rough by milling and then
chasing with a single-point tool or a formed grinding wheel finishes these.</div>
<div class="separator" style="clear: both; text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiWa0k3TQyYTfT1-7blNEcwN2Al1O7KfwKeBn4B0ppqjNLBTcyc9nUVd_RkPWs-JtVKo4qIZUB4SFByoswfmxuueb9jU1Hk4OcOtnbw88-0a2sCW6XfyFgczgnF2d2SBTyx4oPN1diMwPc/s1600/Untitled.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="455" data-original-width="702" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiWa0k3TQyYTfT1-7blNEcwN2Al1O7KfwKeBn4B0ppqjNLBTcyc9nUVd_RkPWs-JtVKo4qIZUB4SFByoswfmxuueb9jU1Hk4OcOtnbw88-0a2sCW6XfyFgczgnF2d2SBTyx4oPN1diMwPc/s1600/Untitled.png" /></a></div>
<div align="center" class="MsoBodyTextIndent" style="margin-bottom: .0001pt; margin-bottom: 0in; margin-left: -44.25pt; margin-right: -18.15pt; margin-top: 0in; text-align: center;">
<b>Fig. <span style="font-size: x-small;">2.17 Thread
milling with Multiple Thread Cutter; a) External Threads; b) Taper</span><o:p></o:p></b></div>
</div>
<div class="MsoNormal" style="tab-stops: 171.75pt; text-align: justify;">
<div class="MsoNormal">
Multiple cutter is used when the
thread to be cut is not too long and it is desired to cut the threads in one
revolution of the work. The width of the cutter has to be slightly more than
the length of the thread. The cutter is set parallel to the axis of the job and
is fed radially inward equal to the depth of the thread while the job is
stationary. The job is equal to depth of the thread while the job is
stationary. The job is then rotated slowly, with the cutter moving axially a
distance equal to the lead of the threads plus a small over travel to complete
the thread in one pass.<sub><o:p></o:p></sub></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
<b>2.5.7 THREAD GRINDING<o:p></o:p></b></div>
<div class="MsoNormal" style="margin-left: -0.95in;">
<br /></div>
<div class="MsoBodyTextIndent" style="text-indent: 0in;">
Thread grinding is used to produce very
accurate threads. It is also employed to cut threads on hardened materials for
which the other methods of thread cutting are not possible. The method is also
useful for materials too soft to get a good surface finish by other methods.
Thread grinding is used to cut threads on: taps, micrometer screws, lead
screws, thread gauges and milling cutters.<o:p></o:p></div>
<div class="MsoBodyTextIndent" style="text-indent: 0in;">
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</v:shape><![endif]--><!--[if !vml]--><!--[endif]-->The principle of thread grinding is similar is principle to thread
milling. The grinding wheels can be single ribbed or multi-ribbed, which are
shaped (conforming to the thread profile) by special diamond dressers. In the
case of single-ribbed wheel, the wheel turns against rotation of the job. In
addition to this rotary motion, a relative axial motion between the wheel and
the job is provided with the help of a precision lead screw. The wheel is
tilted an angle equal to the helix angle of the thread, to the axis of the job.
This method is known as ‘Traverse Thread Grinding, and is used to produce long
and coarse pitch threads. Also, the pressure on the work and hence the heat
generated during grinding is not excessive, resulting in a more accurate
thread.<o:p></o:p></div>
<div class="separator" style="clear: both; text-align: center;">
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<b>Fig. 2.18 Thread Grinding</b></div>
<div class="MsoBodyTextIndent" style="text-indent: 0in;">
<br /></div>
<div class="MsoNormal">
<span style="font-family: "times new roman" , serif;">A multi-ribbed wheel, which
is slightly longer (one or two threads) than the work, is used to cut the
entire threads in one revolution of the work. The wheel is fed into the work to
the required depth and moves axially a distance equal to the pitch of the
thread while the work revolves through one revolution. The cutter is </span><span style="text-indent: 0in;">set parallel to the axis of the job. This
method is known as ‘plunge cut grinding’. This method is employed when production
is more important than accuracy. The principle of these two methods is shown in
Fig. A thread grinding machine is similar to centre type cylindrical g</span><span style="text-indent: 0in;">rinding machine with an arrangement for
precise movement of the machine table and provision for tilting the grinding
wheel at the helix angle of the thread.</span></div>
<div class="MsoNormal">
<span style="text-indent: 0in;"><br /></span></div>
<div class="MsoBodyTextIndent" style="margin-left: -18.15pt; text-indent: 0in;">
<b><span style="font-size: 14.0pt; mso-bidi-font-size: 12.0pt;">2.6 THREAD MEASUREMENT AND INSPECTION<o:p></o:p></span></b></div>
<div class="MsoBodyTextIndent" style="margin-left: -18.15pt;">
<b> </b><span style="text-indent: 0in;">The elements to be checked for a thread are:
major diameter, pitch diameter, pitch and helix angle.</span></div>
<div class="MsoBodyTextIndent" style="text-indent: 0in;">
<o:p></o:p></div>
<div class="MsoBodyTextIndent" style="text-indent: 0in;">
<b>2.6.1 Major Diameter.</b> The major diameter of the screw or the minor
diameter of a nut can be checked by a plain snap and plug gauges respectively.
They can also be measured with micrometer and vernier calipers. To measure the
major diameter of a screw with a micrometer, the anvils should be of sufficient
diameter so as to span two threads. To eliminate the effect of errors between
the micrometer screw and the anvil faces, it is always better to first check
the instrument on a cylindrical standard of about the same diameter as the screw.<o:p></o:p></div>
<div class="MsoBodyTextIndent" style="margin-left: -44.25pt;">
<br /></div>
<div class="MsoNormal">
</div>
<div class="MsoBodyTextIndent" style="text-indent: 0in;">
<b>2.6.2 Minor Diameter.</b> Minor diameter of a
screw can be measured with a screw thread micrometer Caliper. This instrument
is similar to the ordinary micrometer, but instead of usual flat measuring
faces, it has specially designed anvil and spindle inserts.</div>
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhGicn9bXDS8AVB4JPxywLrIbtVg9ZX5ZJjRbwkqyVbj6hKDo0ujD5OmOv-5lUvq8Y6xXRhKj7q1x5l8JORQKPIzn2erzb_IoFRjSGxIaY8jnZDW6M3g_QqZZRD8t9rZ_ZWQYfkPAzCJgQ/s1600/Untitled.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="263" data-original-width="518" height="162" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhGicn9bXDS8AVB4JPxywLrIbtVg9ZX5ZJjRbwkqyVbj6hKDo0ujD5OmOv-5lUvq8Y6xXRhKj7q1x5l8JORQKPIzn2erzb_IoFRjSGxIaY8jnZDW6M3g_QqZZRD8t9rZ_ZWQYfkPAzCJgQ/s320/Untitled.png" width="320" /></a></div>
<div align="center" class="MsoBodyTextIndent" style="margin-left: -18.15pt; text-align: center; text-indent: 0in;">
<b>Fig. 2.19 Screw Thread <o:p></o:p></b><span style="text-align: justify;"><b>Micrometer</b></span></div>
<div class="MsoBodyTextIndent" style="text-indent: 0in;">
Thread pitch. To check the minor diameter of
a screw, two V-shaped inserts are used, so that their sharp apexes contact the
roots of the screw thread. </div>
<div class="MsoBodyTextIndent" style="text-indent: 0in;">
</div>
<div class="MsoBodyTextIndent" style="text-indent: 0in;">
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</v:shape><![endif]--><!--[if !vml]--><!--[endif]-->To check the pitch diameter, inserts of a type that contact the sides of
the screw thread near the pitch diameter are employed. For this, a truncated
thread form is used on the inserts.<o:p></o:p></div>
<div class="separator" style="clear: both; text-align: center;">
</div>
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<br /></div>
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</div>
<div class="MsoBodyTextIndent" style="text-indent: 0in;">
<b>2.6.3 Pitch Diameter.</b> One of the most accurate methods for
checking the pitch diameter is the ‘three-wire method’. The method consists in
placing three shall diameter cylinders
(three wires of equal and precise diameter) in the thread grooves at
opposite sides of a screw and measuring the distance W over the outer surfaces
of the wires with an ordinary micrometer caliper having flat measuring faces.
Three wires are required to prevent misalignment of the measuring faces on the
micrometer caliper. The pitch or effective diameter is calculated from the
value W in the following manner:<o:p></o:p></div>
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgd5yHWfI7zyICm9LTVrCCpfFtYoH4J1yM_mntiJaDo96B-Ifrm92F_Mg5WdCUDXMv0GKrgNr8f3hGnXvsQ7nMPYNFlzdRoNIbL4mWZqMT36cLn1bSYVa9julAHWPMwenBXAlF3dPc4si8/s1600/Untitled.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="214" data-original-width="533" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgd5yHWfI7zyICm9LTVrCCpfFtYoH4J1yM_mntiJaDo96B-Ifrm92F_Mg5WdCUDXMv0GKrgNr8f3hGnXvsQ7nMPYNFlzdRoNIbL4mWZqMT36cLn1bSYVa9julAHWPMwenBXAlF3dPc4si8/s1600/Untitled.png" /></a></div>
<div align="center" class="MsoBodyTextIndent" style="margin-left: -18.15pt; text-align: center; text-indent: 0in;">
<b>Fig. 2.20<o:p></o:p></b></div>
<div align="center" class="MsoBodyTextIndent" style="margin-left: -18.15pt; text-align: center; text-indent: 0in;">
<b><br /></b></div>
<div class="MsoBodyTextIndent" style="margin-left: -18.15pt; text-indent: 0in;">
It is clear that,
W=P+2*d/2<o:p></o:p></div>
<div class="MsoBodyTextIndent" style="margin-left: -18.15pt; text-indent: 0in;">
Where
P=pitch or effective diameter<o:p></o:p></div>
<div class="MsoBodyTextIndent" style="margin-left: -18.15pt; text-indent: 0in;">
And
d= wire size<o:p></o:p></div>
<div class="MsoBodyTextIndent" style="margin-left: -18.15pt; text-indent: 0in;">
Now AC=AD-CD=d/2cosec a/2- P/4cot a/2<o:p></o:p></div>
<div class="MsoBodyTextIndent" style="margin-left: -18.15pt; text-indent: 0in;">
Where
a=thread angle<o:p></o:p></div>
<div class="MsoBodyTextIndent" style="margin-left: -18.15pt; text-indent: 0in;">
And
p=pitch of threads`<o:p></o:p></div>
<div class="MsoBodyTextIndent" style="margin-left: -18.15pt; text-indent: 0in;">
<o:p></o:p></div>
<div class="MsoBodyTextIndent" style="margin-left: -18.15pt; text-indent: 0in;">
After simplification,
it can be seen that,<o:p></o:p></div>
<div class="MsoBodyTextIndent" style="margin-left: -18.15pt; text-indent: 0in;">
<o:p></o:p></div>
<div class="MsoBodyTextIndent" style="margin-left: -18.15pt; text-indent: 0in;">
W=p+d
(1+coseca/2)-p/4cota/2<o:p></o:p></div>
<div class="MsoBodyTextIndent" style="margin-left: -18.15pt; text-indent: 0in;">
In case of I.S.O. metric threads, a=60<sup>o</sup><o:p></o:p></div>
<div class="MsoBodyTextIndent" style="margin-left: -18.15pt; text-indent: 0in;">
W=p+3d-0.866p<o:p></o:p></div>
<div class="MsoBodyTextIndent" style="margin-left: -18.15pt; text-indent: 0in;">
P=w-3d+0.866p<o:p></o:p></div>
<div class="MsoBodyTextIndent" style="margin-left: -18.15pt; text-indent: 0in;">
Here, the pitch
diameter lies 0.3248p inside the crest of the thread that is,<o:p></o:p></div>
<div class="MsoBodyTextIndent" style="margin-left: -18.15pt; text-indent: 0in;">
P=D-0.6496p<o:p></o:p></div>
<div class="MsoBodyTextIndent" style="margin-left: -18.15pt; text-indent: 0in;">
D=Outside diameter <o:p></o:p></div>
<div class="MsoBodyTextIndent" style="margin: 0in -18.15pt 0.0001pt 1.5in; text-indent: 0in;">
D=w-3d+1.5156p<o:p></o:p></div>
<div class="MsoBodyTextIndent" style="margin-left: -18.15pt; text-indent: 0in;">
<o:p></o:p></div>
<div align="center" class="MsoBodyTextIndent" style="margin-left: -18.15pt; text-align: center; text-indent: 0in;">
</div>
<div class="MsoBodyTextIndent" style="text-indent: 0in;">
Thus, if the wire diameter d, the thread
pitch p and w are known, the pitch diameter of the screw may easily be computed
for the above relations.<o:p></o:p></div>
<div class="MsoBodyTextIndent" style="text-indent: 0in;">
<br /></div>
<div class="MsoBodyTextIndent" style="text-indent: 0in;">
<b>2.6.4 Wire Size-</b> Wire of any diameter can be used to measure the pitch diameter, provided
it makes contact on the true
flank of the thread and provided the thread angle is correct. A wire of best
size is the one that makes contact with the flanks of the tread at the pitch
diameter. The effected diameter calculated with the help of any wire touching
the true flanks of the thread will differ from the obtained by using wire of
best size if there is any error in the angle or form of the thread. In the case
of best size wire, the point B Fig (b) at which the wire touches the flank of
the thread lies on the pitch line, that is, BC lies on the pitch line and that
AB is perpendicular to the flank position of the thread. If there is a
possibility of the thread angle being incorrect, the wire of best size should
be used to determine effective diameter, since such wire will be independent of
any error in the thread angle.<o:p></o:p></div>
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<br /></div>
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</div>
<div class="MsoBodyTextIndent" style="text-indent: 0in;">
<b>2.6.5 Pitch.</b> The pitch of the thread is usually measured with “Screw pitch
gauge”. Screw pitch gauges, fig are sets of flat steel blades which are notched
on one edge according to various thread pitches represented by the gauge. The blades are pivoted at the end of a
holder. To use it, the blade with the required thread pitch is applied to the
thread being checked at the radial plane. If the pitch is correct, the gauge
will fit tightly at the thread profile and no light will pass between the gauge
and the thread profile.</div>
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjXTW9rzYguJXTFTrStIuuyPIFC9S9BfmgItQSW7Gh15rJy1MgFeTnnoe14SZfxqMhm9j-LJxldsdMAw05H5wMRecbb7ER_w2rrMBLNVXGx2qTixaiZ2PhS-CZSCqLIm00D3Gcrv9T8FrU/s1600/Untitled.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="138" data-original-width="241" height="183" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjXTW9rzYguJXTFTrStIuuyPIFC9S9BfmgItQSW7Gh15rJy1MgFeTnnoe14SZfxqMhm9j-LJxldsdMAw05H5wMRecbb7ER_w2rrMBLNVXGx2qTixaiZ2PhS-CZSCqLIm00D3Gcrv9T8FrU/s320/Untitled.png" width="320" /></a></div>
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</v:shape><![endif]--><!--[if !vml]--><!--[endif]-->To estimate the values
of the screw pitch error, screw pitch comparators are available. A comparator
comprises a frame with two or three rods ending in ball shaped contacts. The
rods are linked to a measuring tool, for example, a dial indicator and the ball
shaped contacts are inserted into the thread grooves to be checked. If the
comparator has three contacts it will align along the thread axis. A two
contact comparator checks the thread pitch in a direction perpendicular to the
helix angle. The scale of the dial indicator will indicate the accumulated
pitch error by the number of pitches. This instrument must be set up with gauge
blocks to the nominal size of the length of the measurement. Pitch measuring
machines are also available to inspect a screw for pitch. The machine consists
of a bed with centers at each end (just like a centre lathe) for supporting the
screw. Alternate means are also available for holding nuts and sleeves. A head
carrying a stylus shaped to fit in the vee of the thread is moved along the bed
with the help of an accurate micrometer. The head is provided with an indicator,
which shows when the stylus is in its lowest position in the groove that is,
bedded home centrally in the groove of the thread. When the head is moved along
the bed, the stylus seats successively in each of the threads over the length
being examined. The pitch is determined by analyzing the micrometer ending.</div>
<div class="MsoBodyTextIndent" style="text-indent: 0in;">
<br /></div>
<div class="MsoBodyTextIndent" style="text-indent: 0in;">
<b>2.6.6 Angle of thread.</b> The screw pitch gauge can also give an
indication about the correctness of the thread angle. If the angle is
incorrect, light will be seen between the gauge and the thread of the profile.
The thread angle of the screws is measured on an optical instrument, the
‘toolmakers microscope’. Checking of an internal thread is very difficult since
molded copies of the thread profile must be made.<o:p></o:p></div>
<div class="MsoBodyTextIndent" style="text-indent: 0in;">
Optical projection
methods are very convenient for inspecting the form and angle of a thread. The
screw is held between centers provided in the apparatus and tilted to the helix
angle so as to get a clear profile of the thread. When a beam of light is
thrown on the thread, the magnified image of the thread is projected on to a
screen or onto some part of the apparatus and compared with a master template.<o:p></o:p></div>
<div class="MsoBodyTextIndent" style="text-indent: 0in;">
</div>
<div class="MsoBodyTextIndent" style="text-indent: 0in;">
The angle of thread
can also be measured from the projected image with the help of a shadow
protractor provided with the apparatus. The blade of the projector is set to
each side of the thread and the angle with the vertical is measured to get the
total angle of the thread.<b> <o:p></o:p></b></div>
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<o:p></o:p></div>
</div>
</div>
Mechanical Engineering Departmenthttp://www.blogger.com/profile/12582953924770018783noreply@blogger.comtag:blogger.com,1999:blog-6302071579893645567.post-92143455513275528222017-08-11T10:57:00.000+05:302017-08-11T10:57:43.888+05:30<div dir="ltr" style="text-align: left;" trbidi="on">
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Mechanical Engineering Departmenthttp://www.blogger.com/profile/12582953924770018783noreply@blogger.comtag:blogger.com,1999:blog-6302071579893645567.post-83753198660315735232017-08-10T11:27:00.002+05:302017-08-10T11:30:38.750+05:30Question Paper HT(ME)-5th sem-(Dec'16) By Cp Saini<div dir="ltr" style="text-align: left;" trbidi="on">
QUESTION PAPER -HEAT TRANSFER-DEC'16<br />
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Mechanical Engineering Departmenthttp://www.blogger.com/profile/12582953924770018783noreply@blogger.comtag:blogger.com,1999:blog-6302071579893645567.post-7468697173338547562017-08-10T11:21:00.002+05:302017-08-10T11:21:46.227+05:30Question paper-AMT-7th sem (Dec'16) By Cp Saini<div dir="ltr" style="text-align: left;" trbidi="on">
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Mechanical Engineering Departmenthttp://www.blogger.com/profile/12582953924770018783noreply@blogger.comtag:blogger.com,1999:blog-6302071579893645567.post-13128117595359145562017-08-09T16:08:00.000+05:302017-08-11T11:46:31.636+05:30ADVANCED MANUFACTURING TECHNOLOGY(UNIT-1) BY Asst. Prof. CP SAINI<div dir="ltr" style="text-align: left;" trbidi="on">
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<span style="font-size: 20.0pt; mso-bidi-font-size: 12.0pt;">ADVANCE MANUFACTURING
TECHNOLOGY<o:p></o:p></span></h4>
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<span style="font-size: 20.0pt; mso-bidi-font-size: 12.0pt;"><b><i>SYLLABUS</i></b></span></div>
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<b>UNIT I<o:p></o:p></b></div>
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<span style="letter-spacing: 0.15pt;">Hot machining, Machining of Plastics, Unit heads,
Plastics cooling, </span><span style="letter-spacing: -0.05pt;">electro forming, Surface Cleaning and Surface
Treatments, Surface </span><span style="letter-spacing: -0.15pt;">Coatings, Paint Coating and Slushing, Adhesive Bonds,
Adhesive Bond Joints, Adhesives, Surface Coating for Tooling, Graphite Mould
Coating, Vacuum Mould Process.</span><o:p></o:p></div>
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<span style="letter-spacing: 0.15pt;">Introduction,
Types of Composites materials, Agglomerated Materials, Reinforced materials,
Laminates, Surface Coated Materials, Production </span><span style="letter-spacing: 0.05pt;">of Composite Structures, Fabrication
of particulate composite Structures, </span><span style="letter-spacing: 0.5pt;">Fabrication of reinforced Composite,
Fabrication of Laminates, </span><span style="letter-spacing: 0.1pt;">Machining, Cutting and Joining of Composites.</span><o:p></o:p></div>
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<b><span style="font-family: "times new roman" , "serif"; font-size: 12.0pt;">UNIT II<span style="font-size: 12pt;"><o:p></o:p></span></span></b></div>
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<span style="letter-spacing: 0.15pt;">Introduction,
Polymers, Polymerization, Addition of Polymers, Plastics, Types of plastics,
Properties of Plastics, Processing of Thermoplastic </span><span style="letter-spacing: 0.55pt;">Plastics,
Injection Moulding, Extrusion Process, Sheet forming processes, Processing of
Thermosetting Plastics, Compression </span><span style="letter-spacing: 0.1pt;">Moulding, Transfer Moulding, Casting of
Plastics, Machining of plastics, other processing methods of plastics.</span><o:p></o:p></div>
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<span style="letter-spacing: 0.1pt;">Introduction,
casting, thread chasing, Thread Rolling, Die Threading and Tapping, Thread
Milling, Thread Measurement and Inspection</span><o:p></o:p></div>
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<a href="https://www.blogger.com/blogger.g?blogID=6302071579893645567" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"></a><a href="https://www.blogger.com/blogger.g?blogID=6302071579893645567" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"></a><a href="https://www.blogger.com/blogger.g?blogID=6302071579893645567" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"></a><a href="https://www.blogger.com/blogger.g?blogID=6302071579893645567" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"></a><a href="https://www.blogger.com/blogger.g?blogID=6302071579893645567" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"></a><a href="https://www.blogger.com/blogger.g?blogID=6302071579893645567" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"></a><a href="https://www.blogger.com/blogger.g?blogID=6302071579893645567" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"></a><a href="https://www.blogger.com/blogger.g?blogID=6302071579893645567" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"></a><a href="https://www.blogger.com/blogger.g?blogID=6302071579893645567" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"></a><b><span style="letter-spacing: 0.55pt;">UNIT III</span></b></div>
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<a href="https://www.blogger.com/blogger.g?blogID=6302071579893645567" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"></a><a href="https://www.blogger.com/blogger.g?blogID=6302071579893645567" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"></a><a href="https://www.blogger.com/blogger.g?blogID=6302071579893645567" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"></a><a href="https://www.blogger.com/blogger.g?blogID=6302071579893645567" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"></a><span style="letter-spacing: 0.3pt;">Theoretical
basis of metal forming, classification of metal forming </span><span style="letter-spacing: 0.1pt;">processes,
cold forming, hot working, Warm working, Effect of variables </span><span style="letter-spacing: 0.15pt;">on metal
forming processes, Methods of analysis of manufacturing </span><span style="letter-spacing: 0.05pt;">processes,
Open Die forging, Rolling Power Rolling, Drawing, Extrusion. </span><br />
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<b style="background-color: transparent; text-align: center;"> UNIT IV </b></div>
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<span style="letter-spacing: 0.1pt;">Introduction,
Product Application, Limitation of Die Casting, Die Casting </span><span style="letter-spacing: 0.15pt;">Machines,
Molten metal Injection systems, Hot chamber machines, Cold chamber machines,
Die casting Design, Design of Die casting Dies, Types </span><span style="letter-spacing: 0.4pt;">of Die
casting Dies, Die design, Die material, Die Manufacture, Die </span><span style="letter-spacing: 0.15pt;">Lubrication
and Coating, Preheating of Dies, Vacuum Die Casting, Recent </span><span style="letter-spacing: 0.1pt;">trends In Die
Casting Process.</span></div>
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<span style="letter-spacing: -0.2pt;">Definition,
Cost accounting or costing, Elements of costing, cost structures, </span><span style="letter-spacing: -0.1pt;">Estimation
of cost elements, Methods of estimating, Data requirements of </span><span style="letter-spacing: 0.1pt;">cost
estimating, Steps in making cost estimate, Chief factors in cost </span><span style="letter-spacing: -0.15pt;">estimating,
Numerical examples, calculation of machining times, Estimation of total unit
time.</span><o:p></o:p></div>
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<b><span style="font-size: 18.0pt; mso-bidi-font-size: 12.0pt;">UNIT-I<o:p></o:p></span></b></div>
<h4 style="line-height: normal; text-align: justify;">
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<i><span style="font-size: 10pt; letter-spacing: 0.15pt;">Hot
machining, Machining of Plastics, Unit heads, Plastics cooling, </span></i><i><span style="font-size: 10pt; letter-spacing: -0.05pt;">electro forming,
Surface Cleaning and Surface Treatments, Surface </span></i><i><span style="font-size: 10pt; letter-spacing: -0.15pt;">Coatings, Paint
Coating and Slushing, Adhesive Bonds, Adhesive Bond Joints, Adhesives, Surface
Coating for Tooling, Graphite Mould Coating, Vacuum Mould Process.</span></i><i><span style="font-size: 10.0pt;"><o:p></o:p></span></i></div>
<div class="MsoNormal" style="background: white; margin-right: .95pt; text-align: justify;">
<i><span style="font-size: 10pt; letter-spacing: 0.15pt;">Introduction,
Types of Composites materials, Agglomerated Materials, Reinforced materials,
Laminates, Surface Coated Materials, Production </span></i><i><span style="font-size: 10pt; letter-spacing: 0.05pt;">of Composite
Structures, Fabrication of particulate composite Structures, </span></i><i><span style="font-size: 10pt; letter-spacing: 0.5pt;">Fabrication of
reinforced Composite, Fabrication of Laminates, </span></i><i><span style="font-size: 10pt; letter-spacing: 0.1pt;">Machining, Cutting and
Joining of Composites.</span></i><i><span style="font-size: 10.0pt;"><o:p></o:p></span></i></div>
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from="0,11pt" to="468pt,11pt"/><![endif]--><!--[if !vml]--><span style="height: 16px; left: -1px; mso-ignore: vglayout; position: relative; top: 14px; width: 626px; z-index: 46;"><img height="2" src="file:///C:/Users/emax/AppData/Local/Temp/msohtmlclip1/01/clip_image002.gif" v:shapes="_x0000_s1071" width="626" /></span><!--[endif]--><o:p> </o:p></h4>
<h4 style="line-height: normal; text-align: justify;">
<o:p> </o:p>1.1 HOT MACHINING</h4>
<div class="MsoNormal" style="text-align: justify;">
<o:p> </o:p>A considerable percentage of the
parts of up-to-date machinery are made of heat resisting stainless steels,
heat-resisting super alloys and similar materials. This is due to the increased
production of machines operating at high loads, pressures, speed and
temperatures, as well as in chemically active media.</div>
<div class="MsoNormal" style="text-align: justify;">
The machining of work pieces of
such materials, by conventional methods, is extremely difficult and many cases,
impossible. Very low cutting speed and feeds will have to be employed, resulting
in heavier loads on machine bearing and sides. Also, it will be quite a problem
to correctly select cutting tool materials, tool life or tool geometry.
Heat-resistant materials contain considerable amount of alloying elements, have
a tendency to weld onto the cutting
tool, loose very little of their strength, even when heated to temperatures as
high as 800<sup>o</sup>C, have a very high shear strength, combine high tensile
strength with high toughness, are susceptible to considerable work-hardening
and have low thermal conductivity. All these features lead to the development
of high cutting forces, and temperature, and to intensive cutting tool wear. In
addition, the surface finish obtained in machining is poor. Consequently, tools
for machining heat- resistant materials should be very carefully sharpened and
lapped. Tool geometry should be properly selected.</div>
<div class="MsoNormal" style="text-align: justify;">
To overcome these problems,
entirely new machining methods have been developed. Some of these : ECM, EDM
and USM have already been discussed. The method of “Hot Machining” basically
consists of applying localized heat, ahead of cutting tool, to reduce the shear
strength of the work piece metal (thus improving its machinability), and to
permit the easy formation of the cutting chip. The chip is usually produced in
the form of a long smooth chip with lessened shock to the tool.</div>
<div class="MsoNormal" style="text-align: justify;">
The application of correct amount
of heat, in the required place, is of maximum importance. Hence, the type of
heat and its application needs to be studied with care. Heating of the work piece
also influences tool wear. Therefore, heating in the cutting process improves
machinability; when the increase in tool life, due to the reduction of the work
done in cutting, is greater than the detrimental effect of the high temperature
on the tool, leading to increase wear. It has been established that the
temperature – interval in machining with heating of the work piece should be
taken 35 to 40<sup>o</sup>C lower than the temperature – interval for annealing
and aging.</div>
<div class="MsoNormal" style="text-align: justify;">
The heating temperature depends
upon the cutting speed and the rate of feed, since the amount of heat generated
in cutting increases with the speed and feed. Thus in truing a particular grade
of stainless steel, heating temperature is:</div>
<div class="MsoNormal" style="text-align: justify;">
> 500<sup>o</sup>C at cutting
speed of 19m/min</div>
<div class="MsoNormal" style="text-align: justify;">
= 350<sup>o</sup>C at cutting
speed of 300m/min</div>
<div class="MsoNormal" style="text-align: justify;">
= 230<sup>o</sup>C at cutting
speed of 375m/min</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>Advantages:<o:p></o:p></b></div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l71 level1 lfo1; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->1.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->The process id economical and in many case has reduced
the operating costs.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l71 level1 lfo1; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->2.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->Production gets increased.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l71 level1 lfo1; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->3.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span><!--[endif]-->Good surface finish can be obtained, superior to that
obtained on these materials at room temperature.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l71 level1 lfo1; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->4.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->Little evidences any adverse micro structural change.</div>
<div class="MsoNormal" style="text-align: justify;">
<a href="https://www.blogger.com/blogger.g?blogID=6302071579893645567" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"></a><a href="https://www.blogger.com/blogger.g?blogID=6302071579893645567" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"></a><a href="https://www.blogger.com/blogger.g?blogID=6302071579893645567" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"></a><a href="https://www.blogger.com/blogger.g?blogID=6302071579893645567" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"></a><a href="https://www.blogger.com/blogger.g?blogID=6302071579893645567" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"></a><a href="https://www.blogger.com/blogger.g?blogID=6302071579893645567" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"></a><a href="https://www.blogger.com/blogger.g?blogID=6302071579893645567" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"></a><a href="https://www.blogger.com/blogger.g?blogID=6302071579893645567" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"></a><a href="https://www.blogger.com/blogger.g?blogID=6302071579893645567" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"></a><b><span style="font-size: 14.0pt; mso-bidi-font-size: 12.0pt;">1.1.1 Heating
devices:</span></b><span style="font-size: 14.0pt; mso-bidi-font-size: 12.0pt;"> </span>The
work piece can be heated by various methods of heating as high-frequency
induction heating or electric – arc heating devices mounted on the carriage, by
resistance heating with the application of an electric current in the cutting
zone, by flame heating, by Plasma arc heating. Sometime, the blank is preheated
in a furnace before being loaded into the machine tool.</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<h1 style="line-height: normal; text-align: justify;">
<span style="font-size: 14.0pt; mso-bidi-font-size: 12.0pt;">1.2 UNIT HEADS<o:p></o:p></span></h1>
<div class="MsoNormal" style="text-align: justify;">
<a href="https://www.blogger.com/blogger.g?blogID=6302071579893645567" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"></a><a href="https://www.blogger.com/blogger.g?blogID=6302071579893645567" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"></a><a href="https://www.blogger.com/blogger.g?blogID=6302071579893645567" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"></a><a href="https://www.blogger.com/blogger.g?blogID=6302071579893645567" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"></a><a href="https://www.blogger.com/blogger.g?blogID=6302071579893645567" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"></a><o:p> </o:p>Basically a unit head is a power
operated slide with provisions for advancing different types of cutting tools
to the component. Unit heads are mounted on Standardized bases. A unit head
consists of a cast iron body which houses the gears driven from the motor to
rotate the spindle. The body has longitudinal movement along the base which is
affected from the main motor through a lead screw and nut.<br />
<div class="separator" style="clear: both; text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgOfAKLu4zhiF2fVXqviKhqATxkitkFDglNfTcAUH4MGqT8z8xxCZ5gYw2l2Rq0udgoXTZWFNLgSGHgslfeFboCmrVnrprkNjPPx7uhNXOZaar2z2EiNn6eT-x6xu2C3LWkhzLXFlXgfIc/s1600/Untitled.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="261" data-original-width="622" height="267" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgOfAKLu4zhiF2fVXqviKhqATxkitkFDglNfTcAUH4MGqT8z8xxCZ5gYw2l2Rq0udgoXTZWFNLgSGHgslfeFboCmrVnrprkNjPPx7uhNXOZaar2z2EiNn6eT-x6xu2C3LWkhzLXFlXgfIc/s640/Untitled.png" width="640" /></a></div>
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
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<div align="center" class="MsoNormal" style="text-align: center;">
</div>
<div align="center" class="MsoNormal" style="text-align: center;">
<a href="https://www.blogger.com/blogger.g?blogID=6302071579893645567" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"></a><a href="https://www.blogger.com/blogger.g?blogID=6302071579893645567" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"></a><a href="https://www.blogger.com/blogger.g?blogID=6302071579893645567" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"></a><a href="https://www.blogger.com/blogger.g?blogID=6302071579893645567" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"></a><b><span style="font-size: 10.0pt; mso-bidi-font-size: 12.0pt;">Fig 1.1 Unit
Head</span><o:p></o:p></b></div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
The idle motions are carried out
with the help of a traverse motor and its electrical brake. Depths of cut and
various intermittent motions are controlled by a series of trip stops secured
to the head. While a dead stop can be used to ensure the accuracy of cutter
depth. The longitudinal movement of the head can be actuated also through the
rotation of a plate or cylindrical cam, or when required for arduous duties, by
hydraulic power.</div>
<div class="MsoNormal" style="text-align: justify;">
The “Unit Head” has opened up
avenues of multiple- operation machines for the completion of components which
would need a line of machine tools, each of which would need to be fully tooled
and manned. Also inter stage handling and storage has been eliminated.</div>
<div class="MsoNormal" style="text-align: justify;">
It is possible to load one or
more components and not to remove them from the fixture on the machine until
the completion of a wide range of operations. On the completion of the
machining of these parts, the heads can be dismantled from the bases, and these
with the bases, passed into stores until required for the machining of other
components. The “Unit Heads” have made considerable headway in the production
of medium to large- scale components.</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>Advantages:<o:p></o:p></b></div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l7 level1 lfo2; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]--><a href="https://www.blogger.com/blogger.g?blogID=6302071579893645567" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"></a><a href="https://www.blogger.com/blogger.g?blogID=6302071579893645567" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"></a><a href="https://www.blogger.com/blogger.g?blogID=6302071579893645567" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"></a><a href="https://www.blogger.com/blogger.g?blogID=6302071579893645567" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"></a><a href="https://www.blogger.com/blogger.g?blogID=6302071579893645567" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"></a><a href="https://www.blogger.com/blogger.g?blogID=6302071579893645567" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"></a><a href="https://www.blogger.com/blogger.g?blogID=6302071579893645567" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"></a><a href="https://www.blogger.com/blogger.g?blogID=6302071579893645567" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"></a><a href="https://www.blogger.com/blogger.g?blogID=6302071579893645567" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"></a>1.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->Unit heads allow for maximum versatility.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l7 level1 lfo2; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->2.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->They can be mounted and remounted in a variety of
positions on standard interchangeable bases.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l7 level1 lfo2; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->3.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->High production rates, along with consistent high
accuracy.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l7 level1 lfo2; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->4.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->Number of handling times reduced.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l7 level1 lfo2; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->5.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->Less floor space needed for machines and for spring.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l7 level1 lfo2; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->6.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->Operators more fully employed.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l7 level1 lfo2; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->7.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->Physical efforts of operators reduced.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l7 level1 lfo2; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->8.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->Good economical recovery rate.</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
The unit head is available in a
wide range of sizes. Power rating of driving motors ranges from about 0.2kW to
22kW, with spindle speeds from 41 to 200 rev/min, and with feeds of 0.025 to
3.50 mm/ rev.</div>
<div class="MsoNormal" style="text-align: justify;">
Each unit head needs a control
panel and such panels can be housed in separate cabinets or enclosed within a
standard base. When a machine setup includes several heads, a combined control
board can be enclosed within the framework of the base.</div>
<div class="MsoNormal" style="text-align: justify;">
The majority of the unit heads
are designed for boring, broaching, chamfering, counter boring, countersinking,
drilling, end milling, face milling, gage milling, reaming, and sawing,
shot-facing, tapping, thread rolling and turning. The front faces of most of
the heads are provided with means to allow the fixing of multiple-spindle
drilling heads, to permit the drilling of more than one hole simultaneously.
The versatility of drilling unit heads has been discussed under art.<span style="font-size: 14pt;"> </span></div>
<h1 style="line-height: normal; text-align: justify;">
<span style="font-size: 14.0pt; mso-bidi-font-size: 12.0pt;">1.3 PLASTIC TOOLING<o:p></o:p></span></h1>
<div class="MsoNormal" style="text-align: justify;">
<o:p> </o:p>Certain types of non-cutting
tools are made nonmetallic materials including plastics. The most common
materials are epoxide resins, because of their better mechanical properties
(excellent properties when loaded in compression) than other plastic materials.</div>
<div class="MsoNormal" style="text-align: justify;">
Epoxide resins are more costly
than any other tool material. But they are lighter then other materials, being
1/4<sup>th</sup> weight of Zinc alloys and less than 1/4<sup>th</sup> weight of
cast iron. Also the cost saving due to the reduction in time and labour
involved in marking plastic tools outweighs the material cost. Other properties
of plastics have been discussed. Reinforcing with fiberglass can increase their
tensile strength.</div>
<div class="MsoNormal" style="text-align: justify;">
Epoxide resins can be poured,
cast, laminated or moulded into intricate shapes with negligible shrinkage and
finish with a minimum amount of surface finishing. Consequently, the greatest
saving in cost is obtained with tools of complex shape, for which the cost of
machining and final finishing will be very high.</div>
<div class="MsoNormal" style="text-align: justify;">
Compared with any of the tooling
metals, plastics are soft and have a much shorter life than comparable tools in
steel. It is not economical, therefore, to use plastic tools when: tool shapes
are conventional, the component material is thick and quantities and large.
Faulty handling too can damage plastic tools, more easily.</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>1.3.1 Applications: <o:p></o:p></b></div>
<div class="MsoNormal" style="text-align: justify;">
Plastic tools are being used in
many industries:</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l56 level1 lfo3; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->1.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->For drilling jigs, routing jigs and fixtures for
assembling, brazing and welding. In the majority of cases inserts are provided
to prevent endure wear.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l56 level1 lfo3; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->2.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->In plastic industry for the production of moulds for
both thermosetting and thermoplastic materials, for vacuum forming and for the
injection blow moulding of polythene products.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l56 level1 lfo3; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->3.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->In foundries for the production of patterns and core
boxes. The entry orifice of the latter is normally fitted with a hardened steel
insert to counteract the abrasive affect of the blown sand.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l56 level1 lfo3; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->4.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->Metal forming tools for drop hammers, hammers blocks
multipart press tools, piercing – punch plates, rubber press tools, spinning
chucks and stretch press formers. Most of these tools can be given extra
support by the inclusion in the mould of metal or fiber glass frames or
supports.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l56 level1 lfo3; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->5.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->Plastic tool also offer many advantages where short
runs and prototypes are required or where a set of tools is required very
quickly.</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
General tapers and blending radii
assist in producing a strong tool. The thickness of component metal should
rarely exceed about 1.5 mm while radii less than 4.75 mm are to be avoided.</div>
<div class="MsoNormal" style="text-align: justify;">
The metal formed by plastic tools
includes:</div>
<div class="MsoNormal" style="text-align: justify;">
Aluminum alloys, brass and other
copper alloys, mild steel, nimonic, stainless steel and titanium.</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>1.3.2 Production of plastic
tools:</b> Plastic tools can be produced by two methods: by Casting and
building up reinforced layers of resin and glass fiber. The casting process is
used for the production of tools of large mass, such as forming dies and
punches. Selected fillers are added to the resin to reduce the cost of the mass
and provide the properties required in the tool. Inserts and supports can be
embodied in the casting to provide strength where required. Casting is least
time – consuming and the more reproducible of the two methods.<b><o:p></o:p></b></div>
<div class="MsoNormal" style="margin-left: .5in; tab-stops: .5in; text-align: justify; text-indent: -.5in;">
<br /></div>
<div class="MsoNormal" style="margin-left: .5in; tab-stops: .5in; text-align: justify; text-indent: -.5in;">
<b>1.4 MACHINING OF PLASTICS:<o:p></o:p></b></div>
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<br /></div>
<div class="MsoNormal" style="text-align: justify;">
Plastic can be machined, but in most cases, machining of plastics is not
required. Moulding and forming methods
can obtain acceptable surface quality and dimensional accuracy. However, there are certain plastics like PTFE
(Polytetra fluoroethylene) which are sintered products and are not mould able
by usual techniques, as they do not melt. For such “thermo stable plastics”
machining is a viable alternative to moulding.<o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
The machining of plastics (by operation such as turning, drilling and
milling) has special features due primarily to the structure of the
material. It also depends upon the
binder upon the binder and the filler and the method of moulding the component.
For example, the machining of thermosetting plastics allows optimum cutting
variables and tool geometry to be employed because these do not soften on
heating, whereas thermoplastic resins soften under heat. The permissible
maximum temperature in the cutting zone is 160<sup>O</sup>C for thermo-setting
resins and only 60<sup>O</sup>C to 100<sup>O</sup>C for thermoplastics.<o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
Special features of the machining of plastics are:-<o:p></o:p></div>
<div class="MsoNormal" style="margin-left: .25in; tab-stops: .25in; text-align: justify; text-indent: -.25in;">
1. The tendency of
certain plastics to splitting.<o:p></o:p></div>
<div class="MsoNormal" style="margin-left: .25in; tab-stops: .25in; text-align: justify; text-indent: -.25in;">
2. High elasticity
(40 times as much as that of steels). Therefore, they must be carefully
supported, to avoid their deflection during machining.<o:p></o:p></div>
<div class="MsoNormal" style="margin-left: .25in; tab-stops: .25in; text-align: justify; text-indent: -.25in;">
3. Non-homogeneous
structure of the material, with components of different hardness. This results
in poor surface finish after machining.<o:p></o:p></div>
<div class="MsoNormal" style="margin-left: .25in; tab-stops: .25in; text-align: justify; text-indent: -.25in;">
4. Plastics have a
strong abrading action on cutting tools.<o:p></o:p></div>
<div class="MsoNormal" style="margin-left: .25in; tab-stops: .25in; text-align: justify; text-indent: -.25in;">
5. Their low
thermal conductivity results in poor heat dissipation from the cutting zone and
in over-heating of the cutting edges.<o:p></o:p></div>
<div class="MsoNormal" style="margin-left: .25in; tab-stops: .25in; text-align: justify; text-indent: -.25in;">
6. The intense dust
formation, especially for thermosetting plastics, makes it necessary to use
special dust -removing devices.<o:p></o:p></div>
<div class="MsoNormal" style="margin-left: .25in; tab-stops: .25in; text-align: justify; text-indent: -.25in;">
7. The hygroscopic
of plastics excludes the use of liquid cutting fluids. Compressed air is
commonly used for cooling.<o:p></o:p></div>
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8. Reinforced
plastics are very difficult to machine.<o:p></o:p></div>
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<br /></div>
<div class="MsoNormal" style="text-align: justify;">
Plastics can be machined with H.S.S. and cemented -carbide tools. In machining a plastic material with a filler
of glass, quartz or mica type, a satisfactory tool life can be obtained only
with carbide -tipped tools. Only diamond
tools are suitable for turning high-strength plastics of this type. The strength of cast parts of laminate
plastics is 40 to 50 percent less than that of the parts made by compression
moulding. Therefore, higher cutting
speeds and feeds can be used in their machining than for strong thermo-setting
plastics. The main trouble in turning
laminated plastics is the peeling of the surface layer.<o:p></o:p></div>
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The cutting variables are also influenced by the life of cutting tool
which is subject to abrasive wear in machining most engineering plastics. Dulling of the cutting tool leads to a poor
surface finish and to breaking out of the material at the points the cutting tools
enters and leaves the cut. This makes it necessary to use more keenly sharpened
cutting tools for plastics. The need for
sharp cutting edges follows from the high elasticity of plastics.<o:p></o:p></div>
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The selection of cutting variables is also influenced by the low heat
conductivity of the plastics, since; in machining the tool may be within a
closed volume (as in drilling) with no cooling facilities. This may lead to
charring of the machined surface.<o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
The cutting tool angles for machining plastics are made somewhat
different than those of tools for ferrous and non-ferrous metals. The rake
angles are positive and relatively larger.
Because of the visco elastic behavior of thermoplastics, some of the
local elastic deformation is regained when the load is off. Therefore tools must be made with large
relief angles (20<span style="mso-text-raise: 4.0pt; position: relative; top: -4.0pt;">0</span> to 30<span style="mso-text-raise: 4.0pt; position: relative; top: -4.0pt;">0</span>).<o:p></o:p></div>
<div class="MsoNormal" style="text-align: justify;">
Abrasive machining of plastics has many advantages over machining with
metal cutting tools. These include the absence of splitting and crack
formation, and the better surface finish that can be obtained.<o:p></o:p></div>
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In grinding, the contact between the wheel and the surface being ground,
should be as short as possible, to avoid burns.
Organic glass is commonly ground with coated abrasive, applying an ample
amount of water as a coolant. If possible, however, grinding should be replaced
by polishing with a felt, broadcloth or flannel wheel charged with lapping
paste, the process is known as “Buffing”. The buffing wheels are of diameter
250 mm, 40 to 60 mm wide and of speed 2000 rev/min. Medium and fine lapping pastes are used as
the buffing compound for plastics. Laminate fabric base, asbestos-fiber and
glass -fiber laminate can be cut with abrasive wheels (SiC) of grain size 24 to
46 and with a 5% emulsion as the cooling fluid. </div>
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<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b><span style="font-size: 14.0pt; mso-bidi-font-size: 12.0pt;">1.5 ELECTRO- FORMING<o:p></o:p></span></b></div>
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<br /></div>
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Electro-forming is a process of
precision metal parts that are usually thin in section, by electro-deposition
on to a form which is shaped exactly to the interior form of the product &
which is subsequently removed </div>
<div class="MsoNormal" style="text-align: justify;">
In the
process, a slab or plate of the material of the product is immersed into
electrolyte & is connected to the positive terminal of a low voltage, high
current d.c power. So it becomes an anode. A correctly prepared mandrel or a
pattern of correct shape & size is immersed at
some distance from the anode &is connected to the negative terminal. The
mandrels are made from variety of materials both metallic & non-metallic.
If the material is non-conducting, a conductive coating must first be applied
to perform electroplating. The mandrel should poses mirror like finish. When
the circuit are closed metal ion are removed from the anode, transported from
the electrolyte towards the cathode and deposited there. After the deposition
the master is removed or destroyed. A
metal shell is confirms exactly the masters. It may take hours or day to deposit
of sufficient thickness. The thickness of electroforms ranges from0.25-25 mm.
The processes very much simple electroplating with the diff. That where is the
electroplating, the deposit stays in place (on the cathode), in electroforming,
it is stripped from the form, the electroformed products are typically from
nickel, iron, copper, and more recently from copper-tin, nickel, cobalt and
nickel,</div>
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<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>1.5.1 Advantages:<o:p></o:p></b></div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l80 level1 lfo82; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->1.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->Low plant cost, cheap tooling & absence of heavy
equipment </div>
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<!--[if !supportLists]-->2.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->Low labor operating cost </div>
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<!--[if !supportLists]-->3.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span><!--[endif]-->The process can be designed to operate continuously
throughout day and night </div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l80 level1 lfo82; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->4.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span>Electro deposition can produce good dens deposit, and
compared with casting, electroforming offers high purity, freedom from porosity
with the homogeneous structure these important quality are seldom obtained to
such a degree in machine parts, stamping or forging</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l80 level1 lfo82; tab-stops: 0in list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->5.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span>There is no restriction the internal complexity of
electro-forms and this advantage eliminates in many instances, the costly
joining processes.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l80 level1 lfo82; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->6.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span>The process has no equal for the reproduction of fine
or complex details</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l80 level1 lfo82; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->7.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span>The use of inserts has widened the application of the
process. Metal inserts are attached to or are embedded in a wax or fusible
alloy master, &, when the master is melted, the inserts remain attached to
the electro-form.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l80 level1 lfo82; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->8.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->A high quality surface finish is both obtained on
interior &external surfaces of the electro forms. Accuracies as close as
.005 mm </div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l80 level1 lfo82; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->9.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span>complex thin –walled parts can be produced with
improved electrical properties</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l80 level1 lfo82; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->10.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span><!--[endif]-->Shell-like
parts can be produced </div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l80 level1 lfo82; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->11.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span><!--[endif]-->Quickly
&economically</div>
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<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b><span style="font-size: 14.0pt; mso-bidi-font-size: 12.0pt;">1.5.2. Mandrels:<o:p></o:p></span></b></div>
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<br /></div>
<div class="MsoNormal" style="text-align: justify;">
The mandrels, the mould or the matter, is the most expensive item
in the process of electro-forming. Mandrels can be made of several metallic
&non-metallic materials the metallic materials are aluminum, brass, and
carbon steel. a common feature of these mandrels is their oxide formation film –which
facilitates their separation from electro form with out any surface treatment. </div>
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Depending on shape of electro
–form mandrels are of three types-permanent; semi permanent & expandable</div>
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<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b><span style="font-size: 14.0pt; mso-bidi-font-size: 12.0pt;">1.5.2.1 </span></b><b>Permanent mandrels</b></div>
<div class="MsoNormal" style="text-align: justify;">
These mandrels are usually made of metals or
glass or rigid plastics .the surface of non-metallic mandrels is made
conductive by metalizing by electro-forming or a chemical deposition technique.
For close tolerances work such as gear &gauges, stainless steel is
recommended. Such materials can be used indefinitely, with a minimum treatment
to preserve the smooth surface. Adhesion is minimized by the application of
thin coating of a parting compound</div>
<div class="MsoNormal" style="text-align: justify;">
<b><span style="font-size: 14.0pt; mso-bidi-font-size: 12.0pt;">1.5.2.</span>2.
Semi-permanent mandrels<o:p></o:p></b></div>
<div class="MsoNormal" style="text-align: justify;">
for straight sided
components or components which have
several cuts up to about .013 mm, semi permanents mandrels are used .these are
made of steel with fusible coating, compounded usually made from wax
&graphite .,to remove electro-form the fusible layer is melted &after
removal , mandrels is cleared & rebuilt</div>
<div class="MsoNormal" style="text-align: justify;">
<b><span style="font-size: 14.0pt; mso-bidi-font-size: 12.0pt;">1.5.2.</span>3. Expendable mandrels</b></div>
<div class="MsoNormal" style="text-align: justify;">
For complex electro-form are made
from</div>
<div class="MsoNormal" style="text-align: justify;">
(1) Plaster, which after
electro-forming are removed by breaking.</div>
<div class="MsoNormal" style="text-align: justify;">
(2) Plastic resins &fusible
alloys which are melted.</div>
<div class="MsoNormal" style="text-align: justify;">
(3) Aluminum & zinc which are
dissolved chemically</div>
<div class="MsoNormal" style="text-align: justify;">
(4) Brass</div>
<div class="MsoNormal" style="text-align: justify;">
Plastic resins are commonly used
for decorative work where tolerances are wide without undercuts. The surface
finish of mandrels made from fusible metal alloys can be removed by
electroplating a layer of copper .025 to .050 this copper layer is dissolved
from electroform after fusible alloy is melted </div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b><span style="font-size: 14.0pt; mso-bidi-font-size: 12.0pt;">1.5.3 </span>Applications<o:p></o:p></b></div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l17 level1 lfo83; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->1.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->Moulds & dies feature high in the list. Moulds for
the production of artificial teeth rubber 7 glass products, & high strength
thermosetting plastics are now commonplace. The moulds can be made with
undulating parting lines which have made a considerable impact upon the
production of thermoplastic toys & novelties.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l17 level1 lfo83; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->2.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->Radar 7 electronic industries –radar wave-guides,
probes, complicated grids screens 7 meshes can be produced easily</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l17 level1 lfo83; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->3.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->Spline, thread & other types of form gauges</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l17 level1 lfo83; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->4.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->Cathode for e c m & electrodes for E D M</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l17 level1 lfo83; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->5.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->Electro-formed core boxes with inbuilt heating
elements.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l17 level1 lfo83; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->6.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span>Electro-formed precision tubing, parallel & tapered
formed to different shapes to eliminate the need for bending which the bore.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l17 level1 lfo83; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->7.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->Electrotypes floats bellows, venturi tubes, fountain
pen caps, reflectors, heat exchanger parts honey comb sandwich, parts for gas
appliances 7 musical instruments, radio parts , filter & dies .</div>
<h1 style="line-height: normal; text-align: justify;">
<span style="font-size: small;">1.5.4<span style="font-weight: normal;"> </span>Electro-Forming Is
Particularly Used For:</span></h1>
<div class="MsoNormal" style="text-align: justify;">
<span style="text-indent: -0.25in;">1.</span><span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal; text-indent: -0.25in;">
</span><span style="text-indent: -0.25in;">High cost metals</span></div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l36 level1 lfo84; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->2.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->Low production quantities</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l36 level1 lfo84; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->3.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->Quantity of identical parts, for example a multi
–impression mould</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l36 level1 lfo84; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->4.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->The possibility of using a single master for production
of a number of electro-forms</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l36 level1 lfo84; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->5.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span>Where as intricate female impression is required, son
that it would be much easier to produce a male form </div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b><o:p> </o:p><span style="font-size: 14pt;">1.6 SURFACE CLEANING AND SURFACE TREATMENTS</span></b></div>
<h1 style="line-height: normal; text-align: justify;">
<span style="font-size: small; font-weight: normal;">During the manufacture of virtually all
metal; parts, filling, fine metal chips , pieces of chips , remnants of wastage
or abrasive grit may get into holes or channels of parts . Also oil, dirt,
grease, scale, and other foreign materials remain affected to the main part
surface the purpose of surface cleaning &getting rid of all above materials
is two fold – firstly they may get into holes or channels of part.
Subsequently, in operation finished goods they may be carried by lubricants
into the bearings, where they may lead to overheating & premature wear of
the bearing & even to breakdown of the whole machine. This can be properly
avoided by cleaning. Thorough cleaning of parts is essential for high quality
of their performance.</span></h1>
<div class="MsoNormal" style="tab-stops: 33.0pt 55.5pt; text-align: justify;">
The
second purpose of surface cleaning is to prevent corrosion, & to combine a
decorative appearance with protective coating. All metals will oxide &
corrode, when expose to certain environments, unless protected with an air
thrust. Before application of any protective coating, it is essential that the
surfaces of the part be prepared by proper cleaning to good adhesion. Various surface cleaning methods are:</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="tab-stops: 68.25pt; text-align: justify;">
<b>1.6.1
CHEMICAL CLEANING METHODS</b> </div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b><i>1.6.1.</i></b><i>1</i> <b><i>Alkaline Cleaning: </i></b>In this method
dipping them in aqueous solution of alkaline silicates, caustic soda, or
similar cleaning agents cleans parts. Some type of soap is added to aid in
emulsification. Wetting may be added to the solution to help in thorough
cleaning of the parts. The method satisfactorily removes grease &oil. The
cleaning action is by emulsification of oils & grease. Special washing
machines are employed in lot &mass production. Washing m/c may be of
single, two or three chambers types. </div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
(a) In a single chamber washing
m/c, washing chamber is equipped with a bank of pipes with nozzles. A pump
delivers the cleaning fluid, drawn up from main tank to the pipes. The nozzles
are arranged so that the part or unit is washed from all sides simultaneously
with powerful streams of fluid. The parts may be transferred in washing machine
by chain conyver. The cleaning fluid is heated by a steam coil of 60 to 80,
& therefore parts ejected from the machine dry fairly soon. </div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
(b) A two-chamber washing machine
has two washing chambers. The parts are cleaned in first chamber & then
rinsed of washing solution in the second chamber. </div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
(c) In three –chamber machines
third chamber is used for drying. </div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b><i>1.6.</i><i>1.</i>2</b>. <i>Solvent<b> Cleaning:</b></i>
Small parts are cleaned of oils, dirt, grease, and fats by dipping in
commercial organic solvents, such as naphtha, acetone, carbon tetra chloride.
The parts are then rinsed once or twice in a clean solution of same solvent.
The vapors of these solvents are toxic & therefore require ventilation. The
method is particularly suitable for aluminum, brass, lead, which are chemically
active & might get attacked by alkaline cleaners</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b><i>1.6.1.</i>3. <i>Emulsion Cleaning: </i></b>In this method of
cleaning, the action of organic solvent is combined with that of an emulsifying
agent. The solvent is of generally of petroleum origin & emulsifying agent,
which are soap or a mixture of soap & kerosene oil, include nonionic
polyesters, high molecular weight sodium, amine salts of alkyl aryl
sulphonetes, acid esters of polyglycerides, glycerols & polyalcohols.
Cleaning is done either by spraying or dipping the metal parts in solution
& then rinse & drying. The method is suitable for parts & aluminium,
lead or zinc while are attached by alkaline solution </div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b><i>1.6.1.</i></b><b>4. <i>Vapor
Degreasing: </i></b>Vapor Degreasing is a similar process, except that the
solvent vapors are used as the cleaning agent. The solvent is heated to its
boiling point and the parts to9 be cleaned, are hung in its vapors. The vapor
condenses on the surface of the parts wash off the oil and grease.</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b><i>1.6.1.</i>5. <i>Pickling: </i></b>The process is used to
remove dust or oxide scale from surface of components. The parts are filled in
a tank filled with an acid solution, which is 10 to 12% of sulphuric acid in
water, & is at temp from 65 to 85 C. the solution acts to loosen the hard
scale from the components surface & removes it. The acid solution should
not react with metal while from the scale. For this an inhibitor agent is added
to9 the solution. Pickling process only removes oxide scale. </div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b><i>1.6.1.</i>6. <i>Ultra- Sonic Cleaning: </i></b>Very dirty
small parts, especially those of intricate shape with hard-to-access inside
surfaces, are difficult to clean in ordinary washing facilitates. Such parts
are cleaned much more efficiently by ultra sonic cleaning method. The method is
effected in three stages – prelimary, ultrasonic, & rinsing of parts in a
clean washing medium (kerosene, trichloroethylene) </div>
<div class="MsoNormal" style="text-align: justify;">
Ultrasonic energy is produced by
a high frequency generator, which feeds high frequency electric energy to
transducers that transforms electric energy into inaudible sound energy. The
transducers are fixed to the bottom or the sides of a stainless steel tank
designed to afford the optimum acoustic conditions. High velocities are
imparted to particles of cleaning liquid in the tank. Cavitations bubbles of
microscopic dimensions are formed on the surface of the components. The
cleaning action is done by formation of bubbles, which practically blast all contaminants
from all types of components in seconds, penetrating every crack or crevice
& removing all loose parts. The cleaning liquid includes water, water based
solutions, mild acid & caustic soda,
which are thermostatically controlled to operate at temp of about 45 C. The
effectiveness of this method is 99%. </div>
<div class="MsoNormal" style="text-align: justify;">
Rinses are required in all cases
to ensure through removal of cleaning agent before coating. After being washed,
machines parts are dried carefully. This is done by compressed air. </div>
<h1 style="line-height: normal; text-align: justify;">
<i><span style="font-size: small;">1.6.1.6.1 ADVANTAGES</span></i></h1>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l98 level1 lfo85; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->1.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->The process can be manned easily by trained labour.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l98 level1 lfo85; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->2.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->The process reduces the time element. </div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l98 level1 lfo85; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->3.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->The process produces cleaner surfaces & eliminates
many manual operations & the quality hazards. </div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l98 level1 lfo85; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->4.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->The cleaning of intricate assemblies after final assembly
can reduce testing time. </div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b><i>1.6.1.6.2 APPLICATIONS<o:p></o:p></i></b></div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
The process can be used in all
types of engineering factories, cafes, dairies, hospitals, & hotels &
by manufacturing jewellery. Components, which have been cleaned by the process,
include – ceramics, cutlery, electronic equipment, machine tool equipment,
watch parts. </div>
<div class="MsoNormal" style="text-align: justify;">
Other components, which need to
be scrupulously cleaned, include air craft, ball race assemblies, engine
components, fuel gauges, gas turbines, gears, glass components, hydraulic
devices, jet engine parts, refrigerator parts, satellite components, &
parts for semi conductors, teliprinters parts. </div>
<h1 style="line-height: normal; text-align: justify;">
<span style="font-size: small;"><i>1.6.1.7</i> <i>Surface
Polishing: </i></span><span style="font-weight: normal; mso-bidi-font-weight: bold;"><span style="font-size: small;">Mechanical
polishing of pressed or extruded metal products & many such articles is by
using a wide range of wire brushes or mops, in conjunction with specially
blended greases & oils the two non –mechanical techniques are chemical
polishing & electrolyte polishing.
Chemical polishing has made greater advantages due to increased use of aluminum
for a variety of applications. Electrolyte polishing has made less progress,
because it is more expensive to install.</span></span></h1>
<div class="MsoNormal" style="text-align: justify;">
<b>(a) Chemical Polishing<i><o:p></o:p></i></b></div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
In the process, the metallic
objects are immersed in bathtubs of selected acids. During process certain
amount of metal; mainly peaks are dissolved, producing a bright surface with
out the formation of etched pattern. For chemical polishing of aluminum alloys
the most successful of the solution used contain phosphoric, nitric acid,
sulphuric acids. Production cycle consist of following steps </div>
<div class="MsoNormal" style="tab-stops: 257.25pt; text-align: justify;">
(1) Immerse
for 1 to 3 min at 100 C. </div>
<div class="MsoNormal" style="text-align: justify;">
(2) Remove & rinse in hit
water to remove the viscous film formation. </div>
<div class="MsoNormal" style="text-align: justify;">
(3) Rinse in a mixture containing
equal amount of water & I, 42 sp. Gr. Nitric acid at Room Temperature</div>
<div class="MsoNormal" style="text-align: justify;">
(4) If anodizing required, rinse
in cold water. </div>
<div class="MsoNormal" style="text-align: justify;">
(5) If lacquering is called for,
rinse in cold water</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
The resultant surface finish is
of order of .45 to .50 with a high reflection factor of 88%. </div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<i><b>1.6.1.7.1 ADVANTAGES</b></i></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l24 level1 lfo86; tab-stops: list .25in left 45.0pt; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->1.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->The process is comparatively cheap, with low operating
cost </div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l24 level1 lfo86; tab-stops: list .25in left 45.0pt; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->2.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->The equipment has along life. </div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l24 level1 lfo86; tab-stops: list .25in left 45.0pt; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->3.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->It is very suitable for delicate, thin –walled,
embossed.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l24 level1 lfo86; tab-stops: list .25in left 45.0pt; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->4.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->Both the inside & outside surfaces are cleaned
easily </div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l24 level1 lfo86; tab-stops: list .25in left 45.0pt; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->5.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->The process can be combined with barrel – polishing to
reduce time & cost. </div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l24 level1 lfo86; tab-stops: list .25in left 45.0pt; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->6.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->The process can be included in aluminum anodizing cycle</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l24 level1 lfo86; tab-stops: list .25in left 45.0pt; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->7.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->Improved reflectivity usually is obtained. </div>
<h1 style="line-height: normal; text-align: justify;">
<span style="font-size: small;">(b) Electrolyte Polishing</span></h1>
<div class="MsoNormal" style="text-align: justify;">
<o:p> </o:p>The principle of electrolyte
polishing is the same as that of ECM. a surface layer of the work piece is
removed by anodic dissolution of the metal , leaving the component with a highly
polished surface . This depleting process is known as<b> ELECTROLYTE POLISHING</b></div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
When a metallic component is
immersed in electro polishing electrolyte, the current line leads from surface
peaks, tangentially, causing a higher current density on the peaks than on
valleys. Thus greater metal dissolution takes place on peaks to take smoother
surface than on valleys. This viscous film protects the micro valleys from the
action of current but permits minute peaks to dissolve. The rate of metal
removal is 3 to 10 microns. </div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
A wide range of metals &
alloys can be electro typically polished, but the main industrial uses of the
process are for polishing of alloys & stainless steel, copper alloys,
nickel, & aluminum alloys. </div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b><span style="font-size: 14.0pt; mso-bidi-font-size: 12.0pt;">1.7 CLEANING
AND FINISHING OF FORGINGS </span> </b></div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>1) Removal of oxide scales: </b>A thin layer of scale which is caused
by contact of heated steel with air is formed on surface of steel forgings.
Amount of scale depends upon the forging temperature & length & time of
operation. The simple way to remove the scale is by employing steam or
compressed to blow away the scale. </div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>2) Cleaning by pickling: </b>Process is used to remove hard scale from
surface of forging. It consists of immersing the forgings in a tank filled with
an acid solution, which is 12 to 15 % concentrate of sulphuric acid in water.
The acid solution should not react with clean metal while removing the scale.
For this an inhibitor is added to solution. </div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>3) Tumbling process: </b>Process is used to remove the scale & for
general cleaning of the forgings. The forging along with abrasive materials
such as coarse sand or small particle is placed in barrel. The tilted barrel is
rotated at low speed s. the forging & abrasive roll over themselves. This
action loses the scale from surface of forging & removes it along with
affecting a general cleaning of forging. </div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>4) Blast cleaning: </b>Process
consists of directing a jet of sand, grit or metallic shots against the
forging. The blast force is obtained from compressed air or centrifugal force
through suitably designed apparatus. This process removes the scale & a
smooth surface finish is imparted to the forging. </div>
<div class="MsoNormal" style="text-align: justify;">
<b><span style="font-size: 14.0pt; mso-bidi-font-size: 12.0pt;">1.7.1 CLEANING
AND FINISHING OF CASTING</span></b> </div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
After casting is solidified &
cooled down sufficiently in an expandable mould, the first is freezing the
casting from mould. The operation is called as “SHAKE OUT OPERATION” since a
great deal of heat & dust are involved in this operation, the operation is
usually mechanized. Shake out is usually done by means of vibratory knockouts,
jolting grids & vibrators. The mould is intensively jolted & broken up.
After shaking the casting out of mould, it is conveyed to the fettling shop for
cleaning and finishing. The process consists of following operations – core
removal, cleaning of surfaces, and removal of gates, risers & fins. </div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>1) CORE REMOVAL OR CORE KNOCKOUT:</b> This operation is also done
manually. Hampering & vibrations will loosen & breaks up cores.
Stationary 7 portable vibrators are employed for this purpose. To knockout from
heavy engines, it is disadvantages to use air drills. Removal of cores by hydro
blasting is more sanitary process keeping in view dust problems. The operation
consists of breaking up & washing out the cores with a jet of water
delivered at a pressure of 25 to 100 mm. </div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>2) CLEANING OF SURFACES:</b> The process involves the removal of all
adhering sand &oxide layer & produces a uniformly smooth surface.
Mechanical methods are employed for this purpose, since cleaning by hand with
wire brush is tedious & costly.</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b><i>I) Tumbling:</i></b> This method
is used for cleaning & light casting. The Castings are loaded into a
tumbler or barrel along with white iron picks. Rotation of barrel causes
casting & jack stars to tumble. Jack stars abrade the surface of casting
&also abrade surface of one another. This operation removes adhered sand
& oxide scale from the surface of the casting. The rotational speed of
barrel is 30 rev/min. </div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b><i>Ii) Sand Blasting and
Shot-Blasting:</i></b> This method is widely used to clean surfaces of light,
medium & heavy castings. In these machines, dry sands or shots is blown by
stream of compressed air against the surfaces of casting. The impact of
abrasive particles traveling at a high speed, on the surface removes adhering
sand & oxide layer. Velocity of abrasive particles leaving the nozzle of
m/c ranges from 35 to 75 m/s & pressure 0.7 MPA </div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b><i>iii) Airless Shot Blasting:</i></b>
In this shots are hurled on the surface of casting by a fast rotating paddle.
For harder castings, the shots are made up of white iron, steel, whereas for
softer non ferrous castings, these are made up of copper, bronze, glass or mild
iron,. The wheel rotates at 1800 to 2500 rev /min. The velocity of shots
striking the surface is about 60 to 72 m /s. </div>
<div class="MsoNormal" style="text-align: justify;">
<b><i>Iv)Hydro Blasting:</i></b> This
is most effective surface cleaning method. Here two operations are accomplished
simultaneously –core knockout & surface cleaning. Casting are placed on a
rotary & stationary table & high velocity jets containing about 15% sand & 85 % water under a pressure of
10 to 20 mpa . The jet velocity can be up to 100 m/s. </div>
<div class="MsoNormal" style="text-align: justify;">
<b><i>v) Removal of Gates and Risers:</i></b>
Gates, runners, risers, and spure can be removed before or after cleaning
operations. In brittle materials, these are simply broken off from the
castings. in more ductile materials , following the following methods are used
to remove them –power hacksaws , band saws , disk type cutting edges , abrasive
cut of edges , flame cutting with an oxyacetylene cutting torch & arc
cutting for heat resistant steels which are not amiable to gas cutting. </div>
<div class="MsoNormal" style="text-align: justify;">
<b><i>vi) Powder Cutting:</i></b> Process
by which risers & gates can be easily removed from castings made of
oxidation resistant alloys. Preheated iron powder is introduced in oxygen
stream. This burning iron then attacks the metal riser by a process of fluxing
& oxidation. </div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
vii) Some minor defects defected
may sometimes be repaired by welding without affecting the function of finished
castings. </div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
viii) Finished castings are
subjected to various heat treatments to modify mechanical properties or reduce
residual stress. </div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b><span style="font-size: 14.0pt; mso-bidi-font-size: 12.0pt;">1.8 SURFACE
COATING</span></b>: </div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
The various surface coating on
machine parts are used for protective, decorative, wear resistant and
processing purpose. The different types of surface coatings used for this
purpose are: metallic coatings, phosphate coatings, oxide coatings and plastic
coatings etc.</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>1.<i> </i>Electro – deposited coatings<i>:
</i></b>This process of coating also known as “electroplating”, comprises
preparation of the surface to the plated, plating itself, and degreasing of the
surface. The part to be electro-plated is made the cathode and the metal to be
deposited is made the anode and both are placed in a tank containing an
electrolyte. The process is carried out at a voltage of 10 V (D.C.) and current
density of upto 10A/dm². When the circuit is closed, metallic ions from the
anode migrate to the cathode and get deposited there. Some characteristic of
electrodeposited coatings as given below:</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>a) Copper plating: </b>Used for masking of steel parts from
carbonization a case of hardening heat treatment, plating for improved running-
in of plated surfaces as an under layer for multi-layer coatings. Coating
thickness: 5 to 25µm.<b><o:p></o:p></b></div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>b) Chrome plating</b>: Wear – resistant protective and decorative
coating. It result in improved retention of lubricant and lower co-efficient of
friction. Coating thickness: 30 – 40µm.</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>c) Cadmium plating: </b>Coating for protection against corrosion of
steel in moist atmosphere (marine corrosion) and for improved running in of
mating surfaces. Plating thickness: 15 µm.</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>d) Nickel plating: </b>Undercoat of chrome, corrosion protection for
steel, wear qualities and for decoration. Plating thickness: upto 25µm.</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>e) Lead plating: </b>Resistance to chemical corrosion<b>. <o:p></o:p></b></div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>f) Zinc plating: </b>Low- cost protection of steel and iron against
atmosphere corrosion and fro decoration. Plating thickness: upto 15µm.</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>g) Silver plating: </b>Electrical contacts. Good anti galling and
seizing qualities at high temperature. Plating thickness: 2.5 to 12.5µm.</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>h) Tin plating: </b>Coating for protection against weak acidic media,
non-toxic protection in food, for subsequent soldering and for masking in
nitriding. Plating thickness: 3 to 12µm.</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>i) Gold plating: </b>Infrared reflectors, electrical contacts,
jewellery.</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>j) Borating: </b>High hardness coating<b>. <o:p></o:p></b></div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>k) Lead-indium plating: </b>Electro-deposit of lead on a silver plated
surface followed by indium plating forms a satisfactory bearing surface.</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>l) Phosphating: </b>Anti-corrosive coating. Plating thickness: 0.5 -
1µm.</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>m) Brass plating: </b>Brass plating is frequently used as a base for
bonding rubber and rubber like materials to the metal. It improves appearance,
provides soldering surface, which is abrasive resistant. Since brass tarnishes
(it is satin yellow to bronze initially and when turns to black to green on
exposure), it must be covered with lacquer, when used for decorative purposes.
Brass plating is used on steel, zinc aluminium, and copper plate. </div>
<div class="MsoNormal" style="text-align: justify;">
<b> <o:p></o:p></b></div>
<div class="MsoNormal" style="text-align: justify;">
<b>1 8.1 Electro-less plating: </b>The method of plating differs from the
conventional method of plating that is electro-plating, in that no external
source of electricity is used in the process. The plating is obtained with the
help of chemical reaction. For example, for nickel plating, a metallic salt of
nickel, nickel chloride is reduced with the reducing agent, such as sodium
hypophosphate. Nickel metal so obtained is deposited on the work piece. Nickels
are two most commonly used metal, for this process.</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>1.8.1.1 Advantages:<o:p></o:p></b></div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l62 level1 lfo4; tab-stops: list 24.0pt; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]--><b>1.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; font-weight: normal; line-height: normal;"> </span></b><!--[endif]-->This
process can be used<b> </b>for plating
non-conducting materials<b> </b>such as
plastic and ceramics.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l62 level1 lfo4; tab-stops: list 24.0pt; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]--><b>2.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; font-weight: normal; line-height: normal;"> </span></b><!--[endif]-->This
process does not produce hydrogen embitterment.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l62 level1 lfo4; tab-stops: list 24.0pt; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]--><b>3.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; font-weight: normal; line-height: normal;"> </span></b><!--[endif]-->Cavities,
recesses and inner surface of tubes can be plated successfully.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l62 level1 lfo4; tab-stops: list 24.0pt; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]--><b>4.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; font-weight: normal; line-height: normal;"> </span></b><!--[endif]-->The
coating has excellent wear and corrosion as compared to electro-plating.</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>1.8.1.2 Disadvantages<o:p></o:p></b></div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
The process is costlier as
compared to electro-plating. Some times; some portions of the base of a work
piece are not to be electro-plated for decorative purpose or for the sake of
economy. This is known as “blacking out”. For this the complete base is
prepared for electro-plating. The base is heated to 100ºc. Paraffin wax is
applied to the portion to be black out and then the work piece is completely
cooled. After that the electro-plating is carried out.</div>
<div class="MsoNormal" style="text-align: justify;">
Electro-plated parts are usually dull and
posses little or no metallic luster. To provide finish, shine and luster to the
electro-plated parts, mops and “compos” finish them. The mop should be moved
slowly over the surface to avoid removal of any portion of electro-plated
layer, the final finish/colors be obtained by mopping with chalk. Compos, which
contain abrasive, should not be used with soft metals.</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>1.8.2. <i>Phosphate coating: </i></b>A
coating for steel as a preparation for painting, adhesive bonding or rust
proofing. The process involves the chemical development of a film, which
contains ferrous insoluble phosphate of manganese and ferrum, or ferrum and
zinc, by treatment with a dilute acid phosphate solution. Depending on the
phosphate structure and the method of surface preparation, the phosphate film
may be from 2 to 15 µm thick. A rapid phosphating process is known as
“bonderizing”. Phosphate coating can also be used for non-ferrous and light
metals.</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>1.8.3. Oxide coating: </b>Oxide coating of steel parts is done for
decoration, rust proofing and to obtain low friction surface. The coating is obtained
by thermal, chemical and electro-chemical methods.</div>
<div class="MsoNormal" style="text-align: justify;">
The thermal method involves
heating the part in air, steam or molten nitre. An oxide film 1µm thick is
formed on the part surface: the film color varies with the process temperature.
Heating in the air serves to form thin oxide films on electrical components.</div>
<div class="MsoNormal" style="text-align: justify;">
The chemical methods include
alkaline and acidic oxidation. In the first method steel parts are treated with
a hot concentrated solution of caustic alkali containing oxidants. In the
second method, solution contains ortho-phosphoric acid and oxidants. The acidic
oxidation is much quicker as compared to alkaline oxidation and provides a
stronger oxide film with improved corrosion resistance. The oxide films on
steel parts are (0.8 - 3µm) and porous, and therefore do not reliably protect
the parts from corrosion. Their corrosion – resistance can be increased by
subsequent varnishing.</div>
<div class="MsoNormal" style="text-align: justify;">
The chemical methods are used to
oxidant parts made of aluminium, manganese copper, zinc and their alloy. The
field of the process application is the manufacture of instruments, tools and
consumer goods.</div>
<div class="MsoNormal" style="text-align: justify;">
Electro-chemical oxidation of the
parts is made of ferrous and non-ferrous metals and alloy is carried out in
solutions of caustic alkali. The parts being processed form an anode. The
process runs at lower temperature and requires less chemical agents than the
chemical alkaline oxidation. Prior to treatments of parts, these are cleaned of
corrosion spots and degreased, and after oxidation they are rinsed in water.
Decorative oxidation takes from 30 to 40 min; corrosion – resistant films
require upto 1.5 – 2 hours for their formation.</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>1.8.4. The coating of nickel</b> – cobalt, zinc- cadmium and tin – lead
is obtained by methods, which are called “thermo electro- plating” or “thermo-diffusion”.
The latter consists in that individual metals are successively deposited on the
parts and in the course of subsequent heating these diffuse and form plating of
some alloy. Nickel – cobalt plating increases hardness, zinc-cadmium plating upgrades
corrosion resistance and tin-lead plating reduces porosity and improves
appearance.</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>1.8.5. Plastic coating: </b>Plastic is used as decorative,
anti-corrosive, and anti-friction coatings. These are applied in liquid and
powder form. The primary materials used are thermo-plastics such as:
polyethylene, polypropylene, polyamide, polyvinyl butyral, polyurethane,
fluroplastic and caprolactum etc. these are used in form of fine powders which
on heating. Change to plastic state. The coast thickness ranges from 0.15 to
0.35 mm. before coating the parts are heated to 180- 300ºc depending on the
plastic to be used. The treatment itself lasts from 2 to 5 s. plastic coating
makes it possible to use carbon steels or non-ferrous metals.</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>1.8.6. Metallization: </b>Metallization means spraying molten metal
with the aid to compressed air. The metal particle moving at a speed of 100 to
150m/s strike the surface of a part being coated and adhere to it, thus forming
a layer of strong, finely porous metal coating. The layer has a fairly high
compressive strength, even though it is brittle. The coating thickness varies
from a few hundredths of an mm to 3-4 mm. parts after being coated can be
turned and ground. The method is used to obtain decorative, protective,
antifriction and heat-resistant coatings, to restore worn out parts and correct
defects of castings. The metal being sprayed is melted OA flame (gas
metallization) or by electric arc (electro-metallization). The initial material
is metal wire. Sometimes uses are made of equipment operating on metable
powders. The surface to be coated is cleaned of oil and oxides. Sand blasting
and rough turning is employed for better adhesion of the metal being sprayed to
the surface.</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>1.8.7. Anodizing: </b>Anodizing or anodic coating is a process of
providing corrosion resistant and decorative films on metals, particularly
aluminium. The process is the reverse of electro-plating, in that the part to
be coated is made anode, instead of cathode, as in electro-plating. When the
circuit is closed, a layer of aluminium oxide is formed on the anode
(aluminium) by the reaction of aluminium with the electrolyte. The layer of
aluminium oxide on the surface is highly protective.</div>
<div class="MsoNormal" style="text-align: justify;">
There are two process used for
anodizing.</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>1.8.8) Chromic acid process: </b>In this process, 3% solution of
chromic acid is made as the electrolyte at a temperature of about 38ºC. This
process is applicable only to those aluminium alloys containg not more than 5%
copper or a total alloy content of more than 7½%. The process produces a light
yellow colour.</div>
<div class="MsoNormal" style="margin-left: 6.0pt; text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>1.8.9) Sulphuric acid process: </b>The electrolyte is 15 to 25%
solution of sulphuric acid. The process is applicable to aluminium alloys
containg more than 5% copper or a total alloy content of more than 7½%. The
process produces a light yellow colour. This process shall not be applied to
parts having joints or recesses in which solution may be retained. Normal
anodized coatings are 0.0050 to 0.0075 mm thick.</div>
<div class="MsoNormal" style="margin-left: 6.0pt; text-align: justify;">
</div>
<div class="MsoNormal" style="text-align: justify;">
<b>1.8.10) Hot- dip coatings: </b>Many metal parts are used for making
food containers due to the non-toxity of tin. To remove the excess tin, the
sheets are passed through rollers after these come out of the bath.</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>(i) Zinc coating: </b>Giving a coating of zinc is called “Galvanizing”.
One method of doing so is by “electro-plating”. In the hot dip method, the
parts or steel sheets are fluxed by immersing them into a solution of zinc
chloride and hydrochloric acid. After that they are dipped into a molten zinc
bath. Again, to remove excess zinc, the sheets are passed through rollers after
they leave the bath. Galvanized steel sheets (and more recently, also one sided
galvanized sheet) find increased use in automotive and appliance industry in
addition to their use for roofing.</div>
<div class="MsoNormal" style="text-align: justify;">
<span style="font-size: 6.0pt; mso-bidi-font-size: 12.0pt;"><o:p></o:p></span></div>
<div class="MsoNormal" style="text-align: justify;">
<b>(ii) Lead coating: </b>Load- coated sheet provides anticorrosion properties
in some media. Where tin coated and zinc coated sheets can not resist
corrosion. However, lead coated sheets cannot be used for food applications,
because lead is toxic. An alloy of 15% to 20% tin and the remaining lead can
also be used for this coating. Lead coating method is also called “terne”
coating.</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>(iii) Aluminum-coating: </b>Aluminum – coated sheets can resist
corrosion by hot gases. Due to this, these are suitable for heat exchanges,
automotive exhaust systems and grill parts etc.</div>
<div class="MsoNormal" style="text-align: justify;">
</div>
<div class="MsoNormal" style="text-align: justify;">
<b>1.8.11. Conversion coatings: </b>These<b> </b>are the coating produced when a film is deposited on the base
material as a result of chemical or electro-chemical reaction. Many metals
particularly steel, aluminium and zinc can be conversion coated. The coatings
can be phosphate coatings, chromate coatings oxalate coatings. After degreasing
and cleaning in alkali, the part is soaked in suitable acid bath, for example,
for chromate coatings, in chromic acid bath.</div>
<div class="MsoNormal" style="text-align: justify;">
Conversion coatings are obtained
for corrosion protection, prepainting and decorative finish. Another important
application of this coating is as a lubricant carrier in cold forming
operations, such as wire drawing.</div>
<div class="MsoNormal" style="text-align: justify;">
Oxides that form naturally on the
surface of metals are a form of conversion coating. Oxide coatings discussed
above and also “anodic coatings” fall under the category of “conversion
coatings”.</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<b><span style="font-family: "times new roman" , "serif"; font-size: 12.0pt;"><br clear="all" style="page-break-before: always;" />
</span></b>
<br />
<div class="MsoNormal" style="text-align: justify;">
<b>Bicycle wheel rim plating plant process chart<o:p></o:p></b></div>
<div class="MsoNormal" style="text-align: justify;">
The rims are loaded<b> </b>on the fixture. The fixture can carry
upto twenty rims at a time and after the loading is done, the robot is switched
on which takes control of the whole process. The rims undergo various processes
before being unloaded for use in body assembly shop. The various process of
electroplating of the rims is as in the table below:</div>
<div class="MsoNormal" style="margin-left: 6.0pt; text-align: justify;">
<br /></div>
<div class="MsoNormal" style="margin-left: 6.0pt; text-align: justify;">
<b>Table 1.1 Various process of electroplating<o:p></o:p></b></div>
<div class="MsoNormal" style="margin-left: 6.0pt; text-align: justify;">
<br /></div>
<table border="1" cellpadding="0" cellspacing="0" class="MsoNormalTable" style="border-collapse: collapse; border: none; mso-border-alt: solid windowtext .5pt; mso-padding-alt: 0in 5.4pt 0in 5.4pt; mso-table-layout-alt: fixed; width: 636px;">
<tbody>
<tr>
<td style="border: solid windowtext 1.0pt; mso-border-alt: solid windowtext .5pt; padding: 0in 5.4pt 0in 5.4pt; width: .45in;" valign="top" width="43"><div class="MsoNormal">
<b>S. No. <o:p></o:p></b></div>
</td>
<td style="border-left: none; border: solid windowtext 1.0pt; mso-border-alt: solid windowtext .5pt; mso-border-left-alt: solid windowtext .5pt; padding: 0in 5.4pt 0in 5.4pt; width: 89.75pt;" valign="top" width="120"><div class="MsoNormal" style="text-align: justify;">
<b>Process sequence<o:p></o:p></b></div>
</td>
<td style="border-left: none; border: solid windowtext 1.0pt; mso-border-alt: solid windowtext .5pt; mso-border-left-alt: solid windowtext .5pt; padding: 0in 5.4pt 0in 5.4pt; width: 135.25pt;" valign="top" width="180"><div class="MsoNormal" style="text-align: justify;">
<b>Chemical concentration<o:p></o:p></b></div>
</td>
<td style="border-left: none; border: solid windowtext 1.0pt; mso-border-alt: solid windowtext .5pt; mso-border-left-alt: solid windowtext .5pt; padding: 0in 5.4pt 0in 5.4pt; width: 85.15pt;" valign="top" width="114"><div class="MsoNormal" style="text-align: justify;">
<b>Temperature<o:p></o:p></b></div>
<div class="MsoNormal" style="text-align: justify;">
<b>(Deg. Celsius)<o:p></o:p></b></div>
</td>
<td style="border-left: none; border: solid windowtext 1.0pt; mso-border-alt: solid windowtext .5pt; mso-border-left-alt: solid windowtext .5pt; padding: 0in 5.4pt 0in 5.4pt; width: 62.9pt;" valign="top" width="84"><div class="MsoNormal" style="text-align: justify;">
<b>Density<o:p></o:p></b></div>
<div class="MsoNormal" style="text-align: justify;">
<b>(Deg. Be)<o:p></o:p></b></div>
</td>
<td style="border-left: none; border: solid windowtext 1.0pt; mso-border-alt: solid windowtext .5pt; mso-border-left-alt: solid windowtext .5pt; padding: 0in 5.4pt 0in 5.4pt; width: 71.9pt;" valign="top" width="96"><div class="MsoNormal" style="text-align: justify;">
<b>Checking <o:p></o:p></b></div>
</td>
</tr>
<tr>
<td style="border-top: none; border: solid windowtext 1.0pt; mso-border-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt; padding: 0in 5.4pt 0in 5.4pt; width: .45in;" valign="top" width="43"><div class="MsoNormal" style="text-align: justify;">
1</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
2</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
3</div>
<div class="MsoNormal" style="text-align: justify;">
4</div>
<div class="MsoNormal" style="text-align: justify;">
5</div>
<div class="MsoNormal" style="text-align: justify;">
6</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
7</div>
<div class="MsoNormal" style="text-align: justify;">
8</div>
<div class="MsoNormal" style="text-align: justify;">
9</div>
<div class="MsoNormal" style="text-align: justify;">
10</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
11</div>
<div class="MsoNormal" style="text-align: justify;">
12</div>
<div class="MsoNormal" style="text-align: justify;">
13</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
14</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
15</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
16</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
17</div>
<div class="MsoNormal" style="text-align: justify;">
18</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
19</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
20</div>
<div class="MsoNormal" style="text-align: justify;">
21</div>
<div class="MsoNormal" style="text-align: justify;">
22</div>
<div class="MsoNormal" style="text-align: justify;">
23</div>
</td>
<td style="border-bottom: solid windowtext 1.0pt; border-left: none; border-right: solid windowtext 1.0pt; border-top: none; mso-border-alt: solid windowtext .5pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt; padding: 0in 5.4pt 0in 5.4pt; width: 89.75pt;" valign="top" width="120"><div class="MsoNormal">
Kerosene oil cleaning</div>
<div class="MsoNormal">
Abrasive cleaning</div>
<div class="MsoNormal">
Water rinse</div>
<div class="MsoNormal">
Soak cleaning</div>
<div class="MsoNormal">
Water rinse</div>
<div class="MsoNormal">
Electro cleaning</div>
<div class="MsoNormal">
Water rinse</div>
<div class="MsoNormal">
Acid dipping </div>
<div class="MsoNormal">
Water rinse (1)</div>
<div class="MsoNormal">
Electro cleaning</div>
<div class="MsoNormal">
Water rinse (ii)</div>
<div class="MsoNormal">
Acid dip</div>
<div class="MsoNormal">
Water rinse (ii)</div>
<div class="MsoNormal">
Acid dip</div>
<div class="MsoNormal">
Water rinse (ii)</div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Semi-bright Ni plating(ii)</div>
<div class="MsoNormal">
Tri-Nickel plating</div>
<div class="MsoNormal">
Bright Nickel plating</div>
<div class="MsoNormal">
Drag out</div>
<div class="MsoNormal">
Water rinse (iii)</div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Chrome plating</div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Drag out</div>
<div class="MsoNormal">
Drag out</div>
<div class="MsoNormal">
Water rinse (iv)</div>
<div class="MsoNormal">
Unloading of the rim</div>
</td>
<td style="border-bottom: solid windowtext 1.0pt; border-left: none; border-right: solid windowtext 1.0pt; border-top: none; mso-border-alt: solid windowtext .5pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt; padding: 0in 5.4pt 0in 5.4pt; width: 135.25pt;" valign="top" width="180"><div class="MsoNormal" style="text-align: justify;">
M.T.kerosene oil 100%</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
Surclean-504-70-80cc/lit.</div>
<div class="MsoNormal" style="text-align: justify;">
NAON-80-100-80 ltr</div>
<div class="MsoNormal" style="text-align: justify;">
Running water</div>
<div class="MsoNormal" style="text-align: justify;">
Steelex 80-10gm/ltr</div>
<div class="MsoNormal" style="text-align: justify;">
Running water</div>
<div class="MsoNormal" style="text-align: justify;">
Ginbond- 808 </div>
<div class="MsoNormal" style="text-align: justify;">
80-100gm/ltr</div>
<div class="MsoNormal" style="text-align: justify;">
Running water</div>
<div class="MsoNormal" style="text-align: justify;">
HCI 30-40%</div>
<div class="MsoNormal" style="text-align: justify;">
Running water</div>
<div class="MsoNormal" style="text-align: justify;">
Ginbond- 808 </div>
<div class="MsoNormal" style="text-align: justify;">
80-100gm/ltr</div>
<div class="MsoNormal" style="text-align: justify;">
Running water</div>
<div class="MsoNormal" style="text-align: justify;">
Sulphuric acid 10-15%</div>
<div class="MsoNormal" style="text-align: justify;">
Running water</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
Nickel sulphate</div>
<div class="MsoNormal" style="text-align: justify;">
250-300gm/ltr</div>
<div class="MsoNormal" style="text-align: justify;">
Nickel sulphate</div>
<div class="MsoNormal" style="text-align: justify;">
250-300gm/ltr</div>
<div class="MsoNormal" style="text-align: justify;">
Nickel sulphate</div>
<div class="MsoNormal" style="text-align: justify;">
250-300gm/ltr</div>
<div class="MsoNormal" style="text-align: justify;">
D.M.water tank</div>
<div class="MsoNormal" style="text-align: justify;">
Running water</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
Chromic acid </div>
<div class="MsoNormal" style="text-align: justify;">
275-325gm/ltr</div>
<div class="MsoNormal" style="text-align: justify;">
D.M.water tank</div>
<div class="MsoNormal" style="text-align: justify;">
D.M.water tank</div>
<div class="MsoNormal" style="text-align: justify;">
Running water</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
</td>
<td style="border-bottom: solid windowtext 1.0pt; border-left: none; border-right: solid windowtext 1.0pt; border-top: none; mso-border-alt: solid windowtext .5pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt; padding: 0in 5.4pt 0in 5.4pt; width: 85.15pt;" valign="top" width="114"><div class="MsoNormal" style="text-align: justify;">
Room</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
60-80</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
Room</div>
<div class="MsoNormal" style="text-align: justify;">
60-80</div>
<div class="MsoNormal" style="text-align: justify;">
Room</div>
<div class="MsoNormal" style="text-align: justify;">
60-80</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
Room</div>
<div class="MsoNormal" style="text-align: justify;">
Room</div>
<div class="MsoNormal" style="text-align: justify;">
Room</div>
<div class="MsoNormal" style="text-align: justify;">
60-80</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
Room</div>
<div class="MsoNormal" style="text-align: justify;">
Room</div>
<div class="MsoNormal" style="text-align: justify;">
Room</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
45-55</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
45-55</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
45-55</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
Room</div>
<div class="MsoNormal" style="text-align: justify;">
Room</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
40-50</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
Room</div>
<div class="MsoNormal" style="text-align: justify;">
Room</div>
<div class="MsoNormal" style="text-align: justify;">
Room</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
</td>
<td style="border-bottom: solid windowtext 1.0pt; border-left: none; border-right: solid windowtext 1.0pt; border-top: none; mso-border-alt: solid windowtext .5pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt; padding: 0in 5.4pt 0in 5.4pt; width: 62.9pt;" valign="top" width="84"><div class="MsoNormal" style="text-align: justify;">
-</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
8-10</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
-</div>
<div class="MsoNormal" style="text-align: justify;">
8-10</div>
<div class="MsoNormal" style="text-align: justify;">
-</div>
<div class="MsoNormal" style="text-align: justify;">
8-10</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
-</div>
<div class="MsoNormal" style="text-align: justify;">
8-10</div>
<div class="MsoNormal" style="text-align: justify;">
-</div>
<div class="MsoNormal" style="text-align: justify;">
8-10</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
-</div>
<div class="MsoNormal" style="text-align: justify;">
8-10</div>
<div class="MsoNormal" style="text-align: justify;">
-</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
18-25</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
18-25</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
18-25</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
-</div>
<div class="MsoNormal" style="text-align: justify;">
-</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
24-30</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
-</div>
<div class="MsoNormal" style="text-align: justify;">
-</div>
<div class="MsoNormal" style="text-align: justify;">
-</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
</td>
<td style="border-bottom: solid windowtext 1.0pt; border-left: none; border-right: solid windowtext 1.0pt; border-top: none; mso-border-alt: solid windowtext .5pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt; padding: 0in 5.4pt 0in 5.4pt; width: 71.9pt;" valign="top" width="96"><div class="MsoNormal" style="text-align: justify;">
Once daily</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
Once daily</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
-</div>
<div class="MsoNormal" style="text-align: justify;">
Once daily</div>
<div class="MsoNormal" style="text-align: justify;">
-</div>
<div class="MsoNormal" style="text-align: justify;">
Once daily</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
-</div>
<div class="MsoNormal" style="text-align: justify;">
Once daily</div>
<div class="MsoNormal" style="text-align: justify;">
-</div>
<div class="MsoNormal" style="text-align: justify;">
Once daily</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
-</div>
<div class="MsoNormal" style="text-align: justify;">
Once daily</div>
<div class="MsoNormal" style="text-align: justify;">
-</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
Once daily</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
Once daily</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
Once daily</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
Once daily</div>
<div class="MsoNormal" style="text-align: justify;">
-</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
Once daily</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
Once daily</div>
<div class="MsoNormal" style="text-align: justify;">
Once daily</div>
<div class="MsoNormal" style="text-align: justify;">
-</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
</td>
</tr>
</tbody></table>
<div class="MsoNormal" style="margin-left: 6.0pt; text-align: justify;">
<br /></div>
<div class="MsoNormal" style="margin-left: 6.0pt; text-align: justify;">
<b>Nickel plating: i</b>s done as a protective
coating as it has excellent adhesive properties which form good base fro chrome
plating.</div>
<div class="MsoNormal" style="margin-left: 6.0pt; text-align: justify;">
Chrome plating
is corrosion resistant and also enhances the looks of the component. </div>
<div class="MsoNormal" style="margin-left: 6.0pt; text-align: justify;">
<br /></div>
<div class="MsoNormal" style="margin-left: 6.0pt; text-align: justify;">
<b><span style="font-size: 14.0pt; mso-bidi-font-size: 12.0pt;">1.9 PAINT COATING & SLUSHING</span></b><span style="font-size: 14pt;">:</span></div>
<div class="MsoNormal" style="margin-left: 6.0pt; text-align: justify;">
<span style="font-size: 14pt;"><br /></span></div>
<div class="MsoNormal" style="text-align: justify;">
Metals parts are painted to
protect their surfaces against corrosive action of surrounded medium & also
to improve their appearance. The process of coating with paints & varnishes
is carried out on 3 stages: </div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l69 level1 lfo87; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->1.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->Preparation of the surface to be coated.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l69 level1 lfo87; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->2.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->Painting.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l69 level1 lfo87; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->3.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->Drying with finishing.</div>
<div class="MsoNormal" style="text-align: justify;">
Preparation for painting consists
in cleaning & degreasing surfaces. The surface so prepared is then primed
for better adhesion of the subsequently deposited coating. Use is made of oil
varnish, oleo vituminous, water-soluble & nitro soluble primers. The prime
surface is then trited with a filter, whose layer should be as thin as
possible. Oil varnish filters & quick drawing proxylin filter are commonly
used. The clearance surfaces are painted & the preparation for painting
consists in cleaning and degreasing the surfaces, priming, luting, and
smoothing down the luted surfaces with emery clothe.</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>1.9.1 METHOD OF PAINTING</b>:</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
Following are the methods of
industrial painting:</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>a)</b> <b>Brush painting</b>: the brush painting is used in piece &
small lot production. It is done by hand & is slow cumbersome method, where
quick drawing paints are used. The method requires minimum of eq. But max. Of
labour. The point losses are upto 5%.</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>b) Spray painting</b>: The
method consists in applying fluid paint in the atomized form. This method is
the most common & productive, but requires premises equipped with exhaust
devices & spraying eq. There are various ways of painting:</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>i)</b> <b>Mechanical spraying:</b>
in this method paint is delivered to spray gun by pump.</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>ii) Air spraying:</b> the paint
I sprayed by jet of compressed air, which carries the paint mist to the surface
being painted. The method is capable of coating 30-80 mt sq. Of surface/hour
but losses is high 40-50%.</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>iii) Airless spraying:</b> in this method paint heated to 70-90C IS
FORCED through a nozzle at pressure of 2-4 n/mm sq. the production rate can be
50-200mtsq. Of surface/hour & paint losses are amt. to 25-50%.</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>iv) Electrostatic spraying</b>: in this method a negative charge
delivers paint, which gets on to the surface of charge metal part being
painted. The charging is provided by high voltage const. current source.
Setting up metal screens behind the parts can also use the method for
non-metallic parts. The paint losses are less than 5%. The method makes it
possible to improve working condition to provide for fairly high productivity.</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>c) Dip coating</b>: this
coating is used in automatic production. The method consists in dipping the
parts suspended from chain conveyor, in bathtub. The method is used in large
lot and mass prod. For painting parts of simple shape. The paint losses are 5%.</div>
<div class="MsoNormal" style="text-align: justify;">
<span style="font-size: 14pt;"><br /></span></div>
<div class="MsoNormal" style="text-align: justify;">
<b><span style="font-size: 14pt;">1.9.2 ADHISIVE BONDS </span> </b> </div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
Adhesive joints can be made by
applying adhesive in thin layer b/w the connected parts. They are fastening
metallic as well as non-metallic (textile laminate, foam plastic) materials.</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>1.9.2.1 ADVANTAGE: -</b></div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l63 level1 lfo5; tab-stops: list .25in; text-align: justify; text-indent: -19.5pt;">
<!--[if !supportLists]-->(1)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span> Reliable
connection of parts made of very thin sheet materials.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l63 level1 lfo5; tab-stops: list .25in; text-align: justify; text-indent: -19.5pt;">
<!--[if !supportLists]-->(2)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span> Dissimilar
metal can be joining.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l63 level1 lfo5; tab-stops: list .25in; text-align: justify; text-indent: -19.5pt;">
<!--[if !supportLists]-->(3)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span> The process
is used to reduce production cost</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l63 level1 lfo5; tab-stops: list .25in; text-align: justify; text-indent: -19.5pt;">
<!--[if !supportLists]-->(4)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span> It ism used
to lessen the mass of parts.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l63 level1 lfo5; tab-stops: list .25in; text-align: justify; text-indent: -19.5pt;">
<!--[if !supportLists]-->(5)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span> Highly
skilled labor is not required to bonding.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l63 level1 lfo5; tab-stops: list .25in; text-align: justify; text-indent: -19.5pt;">
<!--[if !supportLists]-->(6)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span> The process
provides for tight and corrosion free joints.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l63 level1 lfo5; tab-stops: list .25in; text-align: justify; text-indent: -19.5pt;">
<!--[if !supportLists]-->(7)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span> Smooth
bonded surface.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l63 level1 lfo5; tab-stops: list .25in; text-align: justify; text-indent: -19.5pt;">
<!--[if !supportLists]-->(8)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span> Exterior
surface remain smooth.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l63 level1 lfo5; tab-stops: list .25in; text-align: justify; text-indent: -19.5pt;">
<!--[if !supportLists]-->(9)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span>Only low
temp are involved so absence of stress or their lower concentration.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l63 level1 lfo5; tab-stops: 27.0pt; text-align: justify; text-indent: -19.5pt;">
<!--[if !supportLists]-->(10)<!--[endif]--> Heat
sensitive material can be joined easily without any damage.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l63 level1 lfo5; tab-stops: list .25in; text-align: justify; text-indent: -19.5pt;">
<!--[if !supportLists]-->(11) <!--[endif]-->Complex assemblies can be at low
cost.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l63 level1 lfo5; tab-stops: list .25in; text-align: justify; text-indent: -19.5pt;">
<!--[if !supportLists]-->(12) <!--[endif]-->Adhesive contribute towards the
shock absorption and vibration.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l63 level1 lfo5; tab-stops: list .25in; text-align: justify; text-indent: -19.5pt;">
<!--[if !supportLists]-->(13) <!--[endif]-->It can tolerate the thermal stress
of different expansion and contraction.</div>
<div class="MsoNormal" style="margin-left: .5in; mso-list: l63 level1 lfo5; tab-stops: list .5in; text-align: justify; text-indent: -.5in;">
<!--[if !supportLists]-->(14)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span><!--[endif]-->Because the adhesive bonds the entire joint area, good
load distribution and fatigue resistance are obtained.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l63 level1 lfo5; tab-stops: list .25in; text-align: justify; text-indent: -19.5pt;">
<!--[if !supportLists]-->(15) <!--[endif]-->The joints are sufficiently strong
in shear and with stand with dynamic and variable load.</div>
<div class="MsoNormal" style="margin-left: .5in; mso-list: l63 level1 lfo5; tab-stops: list .5in; text-align: justify; text-indent: -.5in;">
<!--[if !supportLists]-->(16)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span>Compared to welded soldered and riveted joints,
adhesive bonded parts have uniform spread stresses and do not tend to warp.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l63 level1 lfo5; tab-stops: list .25in; text-align: justify; text-indent: -19.5pt;">
<!--[if !supportLists]-->(17) <!--[endif]-->The process is very fast.</div>
<h1 style="line-height: normal; text-align: justify;">
<span style="font-size: small;">1.9.2.2 DISADVANTAGE: -</span></h1>
<div class="MsoNormal">
<o:p> </o:p><span style="text-align: justify; text-indent: -0.25in;">1.</span><span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal; text-align: justify; text-indent: -0.25in;">
</span><span style="text-align: justify; text-indent: -0.25in;">Comparatively low operational temp. (Maximum up to 100c
fort most adhesive).</span></div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l63 level2 lfo5; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->2.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->Low resistance to tear off.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l63 level2 lfo5; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->3.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->Reduce strength of some adhesive in the course of
timing (ageing).</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l63 level2 lfo5; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->4.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->Tendency to creep, if subjected to long-standing and
heavy load.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l63 level2 lfo5; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->5.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->The need of extended polymerization time.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l63 level2 lfo5; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<br /></div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l63 level2 lfo5; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<b>1.9.2.3 APPLICATION: -</b></div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
Adhesive have particular develop
in air –craft industry: the appearance of honeycomb structure is due to this
method. The method is used in uncritical structure such ask control surface in
aircraft body. In machine tools, adhesive are employed to bond carriage-guide
–ways to beds, and in automobile industries to fasten the friction lining to
clutch- disk brake –bands. Adhesive bonds are also used in appliance and c
consumer goods fields and also sealing, vibration damping and insulating etc.</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>1.9.3 ADHESIVE BONDED JOINTS:
-</b></div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
Adhesive-bonding of is affected
on following types of surfaces:-</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l76 level1 lfo6; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]--><a href="https://www.blogger.com/blogger.g?blogID=6302071579893645567" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"></a><a href="https://www.blogger.com/blogger.g?blogID=6302071579893645567" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"></a>(1)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->In cylindrical type of surfaces, for example, placing
bushings into the holes in the housing –types and parts discs onto the shafts,
coupling pipes together, fitting plugs and fastening lining to brake blocks.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l76 level1 lfo6; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->(2)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->On flat surface, for example, lap-type joining of sheet
parts with one or two straps and so on.</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
Typical adhesive bonded joints
are shown in figure: -</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<!--[if gte vml 1]><v:shape id="_x0000_i1026"
type="#_x0000_t75" style='width:467.25pt;height:108pt'>
<v:imagedata src="file:///C:\Users\emax\AppData\Local\Temp\msohtmlclip1\01\clip_image005.png"
o:title="" gain="112993f" blacklevel="-5898f"/>
</v:shape><![endif]--><!--[if !vml]--><!--[endif]--></div>
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<b><span style="font-size: 10.0pt; mso-bidi-font-size: 12.0pt;">Fig. 1.2 Main type of adhesive bonded joint<o:p></o:p></span></b></div>
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The strength of joints is
dependent on the amount of clearance it which is normally kept at 0.05
to1.5mm.with increased clearance the strength of joints decreases, as the
length of overlapping is increases the force need to break down teethe joints
increases asymptotically approaching a certain limit. Surface rough ewes of the
parts bonded should be held to within 6.3 to 1micro meter. Increase in curing
time has a favorable effect on the strength of adhesive-bonded joints. With cold curing the strength grows
continuously over a long period of time, the strength of bonded with old curing
adhesive increases if the polymer process is accompanied by heating. Heating also
greatly reduces the curing time.</div>
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<br /></div>
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<b>1.9.3.1 Making an Adhesive
Bonded joints</b></div>
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<br /></div>
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An adhesive-bonding process
comprises the following steps:</div>
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(1) Preparation of part surfaces.</div>
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(2) Preparation and application
of the adhesive. </div>
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(3) Assembly of parts under a pressure
of determined by the grade of adhesive.</div>
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(4) Heating of assembly product.</div>
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<b><span style="font-size: 10.0pt; mso-bidi-font-size: 12.0pt;">Fig. 1.3 Hand
Pneumatic Injector<o:p></o:p></span></b></div>
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The surface to be bonded must be
cleaned and degreased. Cleaning is done with wiping wastes, brushes or in sand
blaster. The substance used for degreasing is: acetone, trichloroethylene,
carbon tetra chloride and other organic solvents. Aluminum alloys parts are
prepared by pickling, where necessary the surface to be joined is machined to
obtain a surface finish to provide a better holding if the adhesive.</div>
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Adhesive are prepared in special
polychloroethylene or metallic containers; the will be chrome plated or varnish
with silicone. Hot curing adhesive can be stored in container for a long time.
Cold curing adhesive are prepared just before the uses there pot life is30 to
40 min.</div>
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The method of application on an
adhesive is depending upon its viscosity. Liquid adhesive, tat can be applied
with brushes and sprays are uses most commonly. Some grades of adhesive are
convenient to apply with spatulas, roller or injectors.</div>
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The adhesive can be spread in a
thin layer (0.1 to 0.2mm) with a bristle brush or a spatula. To prevent
frothing the adhesive must be applied moving the brush in one direction.</div>
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In hand pneumatic injectors,
compressed air is supplied through an inlet connection. The air extrudes the
piston by means of piston through nozzle having a dia. of 1mm.</div>
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After the application of adhesive
the parts are assembled in special fixture and clamped by means of lever
mechanism, spring or pneumatic clamping devices. Clamping force must ensure a
unit pressure of 0.05to 1MN/m2.</div>
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Lastly heat is heat is effected
in cabinets equipped with electric or gas heater. The heating temp. and the
curing temp depend upon the composition of adhesive for intake a heating temp.
of 150 to 160 c and a curing time is1.5 h is needed for a cold curing
adhesive base on epoxy resin. For a hot
curing adhesive based on epoxy resin, a curing time of 3 to 4h at 150 to 160 or
1.5 to 2h at180 to 190c is recommended.</div>
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Adhesive should be chandelled very care fully
as their constituents are toxic. The work therefore should be done with gloves
on, under proper exhaust ventilation.</div>
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<b>1.9.4 ADHISIVES: -</b></div>
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There is large variety of adhesive available for
bonding with metal and metal with non-metallic materials. They can be
classified into the following main group:</div>
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<!--[if !supportLists]--><b><i>(1)<span style="font-size: 7pt; font-stretch: normal; font-style: normal; font-variant-numeric: normal; font-weight: normal; line-height: normal;"> </span></i></b><!--[endif]--><b><i>Adhesive Based On Epoxy Resins: -<o:p></o:p></i></b></div>
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The
available epoxy resin based adhesives are both cold and hot curing. These are
used to cold and hot joining of metal ceramics plastic wood and other material.</div>
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In cold curing adhesive a curing
element such polythene polyamide</div>
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98 to10 parts by mass) or
hexamethyldiamine (20 parts by mass) is added to 100parts by mass of resin.
Maleic anhydride (40 parts by mass) is added as a curing agent to the resin in
making hot curing adhesive. There various epoxy resin are used as given below
with the curing given within the brackets: -</div>
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Epoxy (room temp. cure, 16to32c)</div>
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Epoxy (elevated temp. cure, 93 to
177c)</div>
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Epoxy nylon (121to 177c)</div>
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Epoxy phenoilic (121 to177c)</div>
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</div>
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<!--[if !supportLists]--><b><i>(2)<span style="font-size: 7pt; font-stretch: normal; font-style: normal; font-variant-numeric: normal; font-weight: normal; line-height: normal;"> </span></i></b><!--[endif]--><b><i>Phenol-Resin Based Resins: -<o:p></o:p></i></b></div>
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Various
compounds modify these. Curing take place 150cwith the joined component held
against each other. Phenol polyvinyl acetate is available readymade without
subsequent introduction of curing agent. These adhesive can sustain temp. Up to
100 c. phenolic rubber and phenolic resin based adhesive s modified by organic
solvent polymer or silicon compounds feature high temp. resistance Phenol
formaldehyde issued to bond foam plastic textile laminate. The common adhesive in
this group are: </div>
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Neoprene-phenolic
(135-177c)</div>
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Niotrile_phenolc (135-177c)</div>
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Butryl-phenolc (135-177c) </div>
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<!--[if !supportLists]--><b><i>(3)<span style="font-size: 7pt; font-stretch: normal; font-style: normal; font-variant-numeric: normal; font-weight: normal; line-height: normal;"> </span></i></b><!--[endif]--><b><i>Polyurethane Adhesive: -<o:p></o:p></i></b></div>
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These adhesive have resistance to
temp. up to 100 to 120 c and same strength as polyvinyl acetate adhesive.</div>
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<!--[if !supportLists]--><b><i>(4)<span style="font-size: 7pt; font-stretch: normal; font-style: normal; font-variant-numeric: normal; font-weight: normal; line-height: normal;"> </span></i></b><!--[endif]--><b><i>Special Grade Adhesive: - <o:p></o:p></i></b></div>
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These
are used to high temp. Resistance and poses high shearing strength.</div>
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<br /></div>
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<b>1.9.4.1
Bonding Plastic Parts: -<o:p></o:p></b></div>
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The above-discussed adhesive and
special purpose adhesive is used to bond plastic parts. For many thermoplastic
these solvent serve as a adhesive, or example dichloro ethane for organic
glass, benzol for polystyrene, acetone for viniplast etc. the scope of
automation for adhesive-bonding process is the application of adhesive to the
mating surfaces, assembly and accurate location of the parts bonded, and
subsequent curing. Adhesive can be applied with roller and feed with injector
into the clearance b/w the mating parts; dipping the mating parts into it is
also practicable.<b><o:p></o:p></b></div>
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<b><span style="font-size: 14.0pt; mso-bidi-font-size: 12.0pt;">1.10 SURFACE COATING FOR TOOLING: -</span><o:p></o:p></b></div>
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In almost every type of production
tooling the most desirable feature to have is a very hard surface on allow
strength but tough body. Toughness is needed to survive mechanical shocks that
are impact loading in interrupted cuts. Shocks occur in even continuous chip
formation process, when the counters the localized hard spot. The example of
such tooling include metal cutting tools rock drills, cutting blades, forging
die, screw for extrusion of plastic and food products and saw mills and so on.
Other application include parts of earth moving machinery, valves and valves
seat for diesel engines and many such parts involving high heat application and
in general application requiring wear resistance. The various techniques
employed for this purpose are discussed below: -</div>
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<br /></div>
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<!--[if !supportLists]--><span style="font-size: 14pt; font-weight: bold;">1.10.1</span><b><span style="font-size: 14.0pt; mso-bidi-font-size: 12.0pt;"> H</span></b><b>ard Facing: -<o:p></o:p></b></div>
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It is the
technique of depositing a layer of hard metal on component to increase the
hardness, strength of base metal. The techniques is widely used in bearings,
cam shaft, valves and valves seats, hot extrusion dies, closed dies especially
for abrasive powder, earth handling, and mining equipment of many type such as
rock drills stone crushers. Hammer mills shear blades and much type of cutting
and trimming dies.</div>
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The composing
of surfacing metal differs from that of the base metal. Hard facing materials
such include satellite and other cutting and wear resistance alloys. Tip or rod
from 5 to 10 mm thick, cat from satellite alloys, or used for hard facing of
tool y welding technique. The cutting tool material with very hard phases has
such as high alloying element concentration that they cannot be manufacture
into welding rods. The ingredients are incorporated in the flux coating or
packed inside tubular rods, and the alloys are formed in welding process
itself.</div>
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Hard facing is
by means of gas, arc or shielded arc welding techniques. Gas and shield arc
welding are more uniform composition of deposited layer. Surfacing by ordinary
a arc welding is cheaper and faster, but there is greater danger of dilution of
metal with the base metal. Deposition of tungsten carbide by an electric arc is
called spark hardening.<b> </b>When
thick layer are deposit one<b> </b>speaks of weld overlays. However the
thickness of deposit should not exceed than 2mm because the susceptibly to
cracking increase with thicker layers.</div>
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Hard facing techniques
and conditions should ensure a strong bond of the deposit with the base metal,
restrict their mixing and avoid the formation of cracks and other defects in
the deposit layer. Parts to be hard faced are first pre heated to 350 to500c;
the hard faced parts are to be cooled slowly.</div>
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Hard facing
should increase the service life of certain part by 3 to 4 times and worn parts
to be repeatedly restored.</div>
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<br /></div>
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<!--[if !supportLists]--><b><span style="font-size: 14.0pt; mso-bidi-font-size: 12.0pt;">1.10<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; font-weight: normal; line-height: normal;"> </span></span></b><!--[endif]--><b><span style="font-size: 14.0pt; mso-bidi-font-size: 12.0pt;">.2 N</span></b><b>itriding Case
Hardening: -<o:p></o:p></b></div>
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It is surface
hardening processing which the surface of steel is saturated with nitrogen. In
consist of heating the part to a temp. Of 480c to 650c inside a chamber through
which a stream of NH3 is passed ammonia gets dissociated:</div>
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2NH3 = 2N +
3H2.</div>
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The nitride
parts very high surface hardness (730 to 1100 BHN). Nitriding increase the wear
resistance in air water and water vapor.</div>
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Nitriding is
usually to medium carbon and alloy steels containing Al, Cr, Mo, and other
elements capable of forming nitrides. Prior to nitriding parts should be
hardened tempered and undergo to the complete sequence of machining process
including grinding. Only finish grinding and lapping is done after nitriding.
The nitride case is usually0.2 to 0.4 mm thick.</div>
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Nitriding done
at low temp. as compared to hardening and carburizing, so it requires more
time. But since no quenching is necessary as the high hardness is obtain
directly after the operation. The feature enables the hardening effects to be
avoided. </div>
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<br /></div>
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<!--[if !supportLists]--><b>a)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; font-weight: normal; line-height: normal;"> </span></b><b>Hard Chrome Plating</b>: Hard chrome plating is done by electrolytic
electroplating technique. It is most common process for wear resistance.</div>
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<br /></div>
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<!--[if !supportLists]--><b>b)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; font-weight: normal; line-height: normal;"> </span></b><!--[endif]--><b>Flame Plating: - </b>Flame plating is a
process develops to prolong the life of certain type of tool and there wear
applications. By this process, a carefully controlled coating of tungsten
carbide, chromium carbide (Cr3C2) or aluminum oxide is applied to a wide range
of base metals the more common material, which have been successfully,
flame-plated include: aluminium, brass, bronze, cast iron, ceramics, copper,
glass/ H.S.S., magnesium, molybdenum, nickel steel, and titanium and their
alloys.<b><o:p></o:p></b></div>
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The uses a
specially designed gun into which is admitted metered amount of oxygen and
acetylene. A change of fine particles of the selected plating mixtures is
injected into the mixture of oxygen and acetylene. Immediately a valve opens to
admit he a stream of nitrogen to protect the valve during the subsequent
detonation. The mixture is now ignited and the explosion is take place, which
plasticizes the particles and hurls in them from gun with a velocity of 750
m/s. The particle gets embedded into the surface and a microscopic welding take
place, which produces a highly tenacious bond.</div>
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Each particle
in the coating is elongated and flattened into thin disc. The coating has a
dense fine and grain laminar structure with negligible porosity and absence of
void and oxide layer.</div>
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The layer of
the plated materials about 0.006mm, this layer can build up by repeating the
explosion, to thickness ranging from0.05 to0.75mm, according to the requirement
of subsequent operations. The resultant layer well dense, hard and well bonded.</div>
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Because of the
hard dense structure of coatings, flame plating has provided industry with a
valuable tool for the solving of many abrasion, erosion and wear problem. For
example bushes for many applications, core pin for powder metallurgy, dies,
gauges, journals, mandrels, and seals for high duty pumps, have all being given
much longer lives. </div>
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The process
has influenced considerably certain type of cutting process, especially in the
glass leather, soap, and textile industries has proved to be great advantage
for component involving high heat application such as “hot-end” of gas turbine.</div>
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The coating
shows an excellent resistance to galling and corrosion. Flame-plated coating
can be ground and lapped if necessary. Resultant surface be with in the reason
of 0.025micro meter. Another advantage is that the components can be enabling
to mast the coatings to be placed preciously where required.</div>
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The mixture of
tungsten carbide coating can be consisting of cobalt ranging from 7% to17% and
rest of tungsten carbide.</div>
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Aluminum oxide
plating mixture is almost of Al2O3 (above 99%). Chromium carbide plating
consist of about 75%yo 85% of Cr3C2 and balance of (Ni-Cr).</div>
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<br /></div>
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<b><span style="font-size: 14.0pt; mso-bidi-font-size: 12.0pt;">1.10.3 </span>Chemical Vapor
Decomposition: -<o:p></o:p></b></div>
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<br /></div>
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Chemical vapor
decomposition uses volatile metal compounds, which are carried as a vapour in a
glass stream and deposit as metal upon any surface that is hot enough to
produce the desired reaction.</div>
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</div>
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Vapor phase
decomposition can be done by two methods:</div>
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i) In decomposition
method a decomposition halide is vaporized metered and transported by means of
inert carrier gas to the heated component, where it decomposes at the surface
of yield pure metal.</div>
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ii) In the second method, a
reduction process, hydrogen is used as the carrier gas through a purifier and
dry hydrogen chemically reduces the halide to pure metal on the part surface as
shown in fig. HFC, HFN. Multiple coating of Al<sub>2</sub>O<sub>3 </sub>can be
given on top of Al<sub>2</sub>O<sub>3</sub>.coating thickness is in micrometer</div>
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For depositing a layer of TiC on
carbide tool inserts a mixture of hydrogen methane and titanium trichloride gas
is form in the mixing chamber. The mixture of these gases can flow through next
chamber enrich carbide inserts are heated up to about 1000c by induction
heating or by resistance heating. The following reaction takes near the surface
of the parts:</div>
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TiCl4 +CH4 = TiC +4HCl.</div>
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TiC so produce get adhere to the
surface of the substance that is WC. The main advantage of CVD process is its
ability to produce:</div>
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a) High density coatings because
the coatings are built by atom by atom.</div>
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b) High purity materials.</div>
<div class="MsoNormal" style="text-align: justify;">
c) High strength materials.</div>
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d) And complex shapes.</div>
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<br /></div>
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<a href="https://www.blogger.com/blogger.g?blogID=6302071579893645567" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"></a><a href="https://www.blogger.com/blogger.g?blogID=6302071579893645567" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"></a><a href="https://www.blogger.com/blogger.g?blogID=6302071579893645567" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"></a>An emerging coating technology
used particularly for multiphase coatings, is medium temp. CVD (MTCVD). It is
being developed to machine ductile iron and stainless steels and to provide
higher resistance to crack propagation than conventional CVD.</div>
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<br /></div>
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgy2SD0XJycrUx55GgDPq-oyfApsh3sLhrSy7VDNMkuBizZxQlWXZzNmYEKUdYjddokqKXdJ4uC1XQHEJ_5xt3mQD12j_ywh7rX3LEw2sCiX2ZsR6YraKTls-vZXd8MIF-gf0CQf8YLNO8/s1600/Untitled.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="443" data-original-width="536" height="330" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgy2SD0XJycrUx55GgDPq-oyfApsh3sLhrSy7VDNMkuBizZxQlWXZzNmYEKUdYjddokqKXdJ4uC1XQHEJ_5xt3mQD12j_ywh7rX3LEw2sCiX2ZsR6YraKTls-vZXd8MIF-gf0CQf8YLNO8/s400/Untitled.png" width="400" /></a></div>
<br /></div>
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<b><span style="font-size: 11.0pt; mso-bidi-font-size: 12.0pt;">Fig. 1.4 Reduction Method of
CVD<o:p></o:p></span></b></div>
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</div>
<h3 style="margin-left: 0in; tab-stops: list 0in; text-align: justify;">
<span style="font-size: small;">1.10.4<span style="font-weight: normal;"> </span>Physical
Vapor Decomposition: -</span></h3>
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<b> </b>In the basic
form of PVD method applying sufficient heat with help of one of many techniques
evaporates metal or an oxide. The atom or molecule so produced move in all
direction. When they come into atomic or molecular attraction of the component
that is the substrate they condense onto it to form a uniform coating.</div>
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In a variation
of method, a cathode target is bombarded by accelerated ion. This concept
dislodges or driving of single atom or small cluster into surrounding gas for
deposition on a near by substrate surface. To increase coating adhesion and
improve film structure, the substrate surface is heated to temp. From about
200c to500c.</div>
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PVD process
particularly suited to tin coating of H.S.S. tools, because it being a
relatively low temp. Processes, the tempering temp. Point of H.S.S. is not
reached. So after the PVD process the heat treatment is not needed.</div>
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<br /></div>
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<b><span style="font-size: 14pt;">1.10.5</span><span style="font-size: 14pt;"> </span>Diffusion
Coatings: -</b></div>
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<br /></div>
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The surface
hardness of low carbon steel (with carbon lees than 2%) can be increased by
making hardneble by diffusing carbon or nitrogen into the surface. On heating or quenching the carbon-nitrogen
enriched surface is very hard but core remains tough. The surface can also be
hardened by ‘ion nitriding’ method where the steel surface is bombarded by low
energy nitrogen ions produced in plasma.</div>
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<span style="font-size: 14pt;"><br /></span></div>
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<b><span style="font-size: 14pt;">1.10.6</span><span style="font-size: 14pt;"> </span>Ion
Plating: -</b></div>
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<br /></div>
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In this method
high-energy ion are penetrated into the surface. For cutting tools, nitrogen
ions are almost commonly user. There is virtually no change in dimension in the
last two processes.<b> </b></div>
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<br /></div>
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<b><span style="font-size: 14.0pt; mso-bidi-font-size: 12.0pt;">1.11 GRAPHITE MOULD CASTING</span></b><span style="font-size: 14.0pt; mso-bidi-font-size: 12.0pt;">:<o:p></o:p></span></div>
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<br /></div>
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Graphite is
high refractory substance. Graphite moulds are used for casting metals, such as
titanium, that tends to react with many common mould materials. Graphite is
used for Moulding in much the same manner as plaster. For this graphite is
available in an investment type of mixture, which is obtained by combining
powdered graphite with cement, starch & water. This slurry is compacted
around a precision mc. metal pattern. The pattern is removed & mould is
fired at 1000 C, producing a solid graphite mould, which is then poured. After
solidification of the metal the moulds is broken for the removal of the
casting. Graphite moulds have an advantage over plaster moulds as they may be
reused. Graphite moulds can also with stand with heat of grey, ductile or
malleable metals. However the size of moulds of graphite is limited is the
order of 50 x 45 x 25cm. casting upto a mass of about 23 kg can be produced. </div>
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<br /></div>
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<b><span style="font-size: 14.0pt; mso-bidi-font-size: 12.0pt;">1.12 VACCUM MOULDING PROCESS</span></b><span style="font-size: 12.0pt;">:<o:p></o:p></span></div>
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<span style="font-size: 12.0pt;"> </span>
<o:p></o:p></div>
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Sand
can be lodged in place if air is removed from the sand mass. This principle is
employed in vacuum moulding process in which no binder is used.<o:p></o:p></div>
<div class="MsoBodyText" style="margin-left: .25in; mso-list: l46 level1 lfo88; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->1. A thin plastic sheet is draped over pattern positioned
over the mould board. Vacuum is drawn on the pattern. This makes plastic to be
tightly drawn over the pattern surface.<o:p></o:p></div>
<div class="MsoBodyText" style="margin-left: .25in; mso-list: l46 level1 lfo88; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->2.<span style="font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span>A vacuum flask is placed over the pattern & is
filted with clean unbounded sand. Pouring basin & the sprue are formed and
another plastic sheet is placed over the sand.<o:p></o:p></div>
<div class="MsoBodyText" style="margin-left: .25in; mso-list: l46 level1 lfo88; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->3.<span style="font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span>Vacuum is drawn on the sand. This makes sand very
hard.<o:p></o:p></div>
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<!--[if !supportLists]-->4.<span style="font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span>Vacuum is now released on the pattern & it is
withdrawn.<o:p></o:p></div>
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<!--[if !supportLists]-->5.<span style="font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span>Similarly the second half of the mould is made.<o:p></o:p></div>
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<br /></div>
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<br /></div>
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o:title="" gain="6.25" blacklevel="-9830f"/>
</v:shape><![endif]--><!--[if !vml]--><!--[endif]--></div>
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhiaJyEbHlUq5z1FGxmq8Q0ayQsgjnthOvf93-4KWyz36nbr8wUsty_H9uNJzdVMNIr-FUBeSrqN86fWH_ww5Q8yCTcnaPevuHPFYqrGLkKjkHeAqRCewGeeI5DG8RSoJDPH9z8IjFwcgc/s1600/Untitled.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="443" data-original-width="599" height="295" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhiaJyEbHlUq5z1FGxmq8Q0ayQsgjnthOvf93-4KWyz36nbr8wUsty_H9uNJzdVMNIr-FUBeSrqN86fWH_ww5Q8yCTcnaPevuHPFYqrGLkKjkHeAqRCewGeeI5DG8RSoJDPH9z8IjFwcgc/s400/Untitled.png" width="400" /></a></div>
<br /></div>
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<b><span style="font-size: 10.0pt; mso-bidi-font-size: 12.0pt;">Fig. 1.5
Vacuum Moulding Process<o:p></o:p></span></b></div>
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<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<a href="https://www.blogger.com/blogger.g?blogID=6302071579893645567" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"></a><a href="https://www.blogger.com/blogger.g?blogID=6302071579893645567" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"></a><a href="https://www.blogger.com/blogger.g?blogID=6302071579893645567" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"></a>The two moulds halves are
assembled & molten metal is poured. The plastic sheet will burn up. When
the casting is solidified, vacuum on the flask is released. The sand collapse
and the casting are taken out.</div>
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The process is also known as
V-process & has followed. </div>
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<br /></div>
<div class="MsoNormal" style="tab-stops: list .25in; text-align: justify;">
<b>1.12.1 Advantages<o:p></o:p></b></div>
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<!--[if !supportLists]-->1.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->Saving on the binder cost, as no binder is used in
process.</div>
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<!--[if !supportLists]-->2.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->No defect released to moisture & binder fumes.</div>
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<!--[if !supportLists]-->3.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->Any sand can be used
</div>
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<!--[if !supportLists]-->4.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->Easy shake out. However the process is quit
slowly. </div>
<span style="font-family: "times new roman" , "serif"; font-size: 12.0pt;"><br clear="all" style="page-break-before: always;" />
</span>
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<b>1. 13 </b><b><span style="font-size: 14.0pt; mso-bidi-font-size: 12.0pt;">INTRODUCTION TO COMPOSITE
MATERIALS:<o:p></o:p></span></b></div>
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<br /></div>
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Composite materials can be defined as the structures
made up of two or more distinct starting materials. The starting materials can
be organic, metals or ceramics. The components of composite materials do not
occur naturally as an alloy, but are separately manufactured before these are
combined together mechanically. Due to this, they maintain their identities,
even after a composite material is fully formed. However the starting materials
combine to rectify a weakness in one material by strength in another material.
Hence composite material exhibits properties distinctly different from those of
individual materials used, to make composite. Thus composite material or
structure possesses a unique combination of properties such as stiffness,
strength, hardness, weight, conductivity, corrosion resistance & high temp.
Performance etc. that is not possible by individual materials. Thus the search
for materials with special properties to suit some specific stringent
conditions of use has given rise to development of materials called “COMPOSITE
MATERIALS”.<span style="font-size: 12pt;"><o:p></o:p></span></div>
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<br /></div>
<div class="MsoBlockText" style="margin-left: 0in; text-align: justify;">
<b><span style="font-size: 12.0pt;">1.13.1 TYPES OF COMPOSITE MATERIALS</span></b><span style="font-size: 12.0pt;">:<o:p></o:p></span></div>
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<br /></div>
<div class="MsoBlockText" style="margin-left: 0in; text-align: justify;">
Composite materials may roughly be classified as:<o:p></o:p></div>
<div class="MsoBlockText" style="margin-left: 0in; text-align: justify;">
<br /></div>
<div class="MsoBlockText" style="margin-left: .25in; mso-list: l51 level1 lfo8; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->1)<span style="font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span><!--[endif]-->Agglomerated materials/ Particulate composites.<o:p></o:p></div>
<div class="MsoBlockText" style="margin-left: .25in; mso-list: l51 level1 lfo8; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->2)<span style="font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span><!--[endif]-->Reinforced materials.<o:p></o:p></div>
<div class="MsoBlockText" style="margin-left: .25in; mso-list: l51 level1 lfo8; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->3)<span style="font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span><!--[endif]-->Laminates.<o:p></o:p></div>
<div class="MsoBlockText" style="margin-left: .25in; mso-list: l51 level1 lfo8; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->4)<span style="font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span><!--[endif]-->Surface coated materials.<o:p></o:p></div>
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<br /></div>
<div class="MsoBlockText" style="margin-left: 0in; text-align: justify;">
The particulate composite and reinforced composites
are constituted by just two phases, the matrix phase. The aim is to improve the
strength properties of matrix material. The matrix material should be ductile
with its modulus of elasticity much lower then that of dispersed phase. Also
the bonding forces between the two phases must be very strong.<o:p></o:p></div>
<div class="MsoBlockText" style="margin-left: 0in; text-align: justify;">
In fact the particulate composite also fall in the category
of reinforced composites. Depending upon the nature of reinforced materials
(shape and size), the reinforced composites can be classified as <o:p></o:p></div>
<div class="MsoBlockText" style="margin-left: .25in; mso-list: l27 level1 lfo9; tab-stops: .25in list 76.5pt left 81.0pt; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->1.<span style="font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span><!--[endif]-->Particle reinforced composites or particulate
reinforced composites.<o:p></o:p></div>
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<!--[if !supportLists]-->2.<span style="font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span><!--[endif]-->Fiber reinforced composite.<span style="font-size: 12pt;"><o:p></o:p></span></div>
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<br /></div>
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In particulate reinforced
composites, dispersed phase is in the form of exi-axed particles, whereas in
fibre-reinforced composite, it is in the form of fibers. </div>
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<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>1.13.1.1 AGGLOMERATED
MATERIALS:<o:p></o:p></b></div>
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<br /></div>
<div class="MsoBodyText" style="text-align: justify;">
Agglomerated
materials consist of discrete particles of one material, surrounded by matrix
of another material. The material is bounded together in an integrated mass to
classic eg. Of such composite material are: concrete formed by mixing gravel,
sand, cement & water & agglomeration of asphalt & stone particles,
that is used for paving the high surfaces. Other eg. Of particulate composite
material includes:<span style="font-size: 12pt;"><o:p></o:p></span></div>
<div class="MsoBodyText" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l44 level1 lfo10; tab-stops: list .25in; text-align: justify; text-indent: -19.5pt;">
<!--[if !supportLists]-->1)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span><!--[endif]-->Grinding and cutting wheels, in which
abrasive particles (Al2O3, Sic, CBN or carbon) are held together by a vitreous
or a resin bond.<o:p></o:p></div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l44 level1 lfo10; tab-stops: list .25in; text-align: justify; text-indent: -19.5pt;">
<!--[if !supportLists]-->2)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span><!--[endif]-->Cemented carbide, in which particles of
ceramic materials such as WC, TaC, TiC & of cobalt & nickel, are
bounded together via Powder metallurgy process to produce cutting tool
materials. Many powdered metal parts & solid sintering produces various
magnetic & dielectric ceramic materials, which requires diffusion.<o:p></o:p></div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l44 level1 lfo10; tab-stops: list .25in; text-align: justify; text-indent: -19.5pt;">
<!--[if !supportLists]-->3)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span><!--[endif]-->Electrical contact point from powder of
tungsten & silver or copper is process via powder metallurgy method.<o:p></o:p></div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l44 level1 lfo10; tab-stops: list .25in; text-align: justify; text-indent: -19.5pt;">
<!--[if !supportLists]-->4)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span><!--[endif]-->Electrical Brushes for motored & heavy
duty & frictional materials for brake & clutches by combining metallic
& non-metal. Materials.<o:p></o:p></div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l44 level1 lfo10; tab-stops: list .25in; text-align: justify; text-indent: -19.5pt;">
<!--[if !supportLists]--><span lang="NL">5)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span></span><!--[endif]--><span lang="NL">Cu infilterated iron & silver, tungsten.<o:p></o:p></span></div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l44 level1 lfo10; tab-stops: list .25in; text-align: justify; text-indent: -19.5pt;">
<!--[if !supportLists]-->6)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span><!--[endif]-->Heavy metal (w+6%ni+4%cu)<o:p></o:p></div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l44 level1 lfo10; tab-stops: list .25in; text-align: justify; text-indent: -19.5pt;">
<!--[if !supportLists]-->7)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span><!--[endif]-->Electrical resistance welding electrodes from
mixture of cu & tung.<o:p></o:p></div>
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<!--[if !supportLists]-->8)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span><!--[endif]-->Shell moulding sand, using a resin binder,
which is polymerized by hot pattern.<o:p></o:p></div>
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<!--[if !supportLists]-->9)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span><!--[endif]-->Metal polymer structers (metal bearing in
filtered with nylon or PTFE).<o:p></o:p></div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l44 level1 lfo10; tab-stops: list .25in; text-align: justify; text-indent: -19.5pt;">
<!--[if !supportLists]-->10)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span><!--[endif]-->Particleboard, in which wood chips are held
together by suitable glue.<o:p></o:p></div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l44 level1 lfo10; tab-stops: list .25in; text-align: justify; text-indent: -19.5pt;">
<!--[if !supportLists]-->11)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span><!--[endif]-->Elastomers & plastics are also reinforced
with suitable particle material. The eg. Is addition of 15-30 of carbon black
in the vulcanized rubber for automobiles types?<o:p></o:p></div>
<div class="MsoBodyTextIndent" style="margin-left: .25in; mso-list: l44 level1 lfo10; tab-stops: list .25in; text-align: justify; text-indent: -19.5pt;">
<!--[if !supportLists]-->12)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->Dispersion strengthened materials: in these materials
hard, brittle and fine particles are dispersed in softer or more ductile
matrix.</div>
<div class="MsoNormal" style="text-align: justify;">
Because of their unique geometry,
the properties of particulate composite can be isotropic. This property is very
important in many engineering applications</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>1.13.1.2 </b><b>REINFORCED MATERIAL: <o:p></o:p></b></div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
Reinforced materials from the
biggest and most important group of composite materials. The purpose of
reinforcing is always to improve the strength properties. Reinforcement may
involve the use of a dispersed phase (discussed in the last article) or strong
fiber, thread or rod.</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>Fiber-reinforced materials:</b> in a larger number of applications, the
material should have high strength, along with toughness and resistance to
fatigue failure. Fiber reinforced materials, offer the solution. Stronger or
higher modulus filler, in the form of thin fibers of one material, is strongly
bonded to the matrix of another. The matrix material provides ductility and
toughness and supports and blinds the fibres together and transmits the load.
The toughness of the composite material increases, because extra energy will be
needed to break or pull out a fibre. Also, when any crack appears on the
surface of a fibre, only that fibre will fail and the crack will not propagate
catastrophically as in bulk material. Failure is often gradual, and repairs may
be possible. </div>
<div class="MsoNormal" style="text-align: justify;">
Due to the above mentioned desirable
properties of the matrix materials, the commonly used matrix materials are;
Metals and polymers, such as, Al Cu, Ni etc. and commercial polymers strong
fibers in the relatively weak matrix. Like this, it is possible to produce
parts where strength control is developing in different directions. if the part is loaded parallel to the fibers will be
much greater than in the matrix . Even if the fibre breaks, the softness of
matrix hinders the propagations of crack .The fibre direction are tailored to
the direction of loading.</div>
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<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>Reinforced Fibers:</b> A good reinforcing fibre should have: high elastic
modulus, high strength, low density, reasonable ductility and should be easily
wetted by the matrix. Metallic fibres such as patented steel; stainless steel,
tungsten and molybdenum wires are used in a metal matrix such as aluminum and
titanium. Carbon fibers and whiskers are also used in a metal ultra –high
strength composite. Fibres need not be limited to metals. Glass, ceramic and
polymer fibers are used to produce variety of composite having wide range of
properties .The high modulus of ceramic fibers make them attractive for the
reinforced of the metal. The ductile matrix materials can be aluminum
magnesium, nickel or titanium and the reinforcing fiber may be of boron ,
graphite , aluminum or SiC.</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>Forms of reinforcing fibres: </b>The fibers used for reinforcing
materials are available in different forms:</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l1 level1 lfo11; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->(a)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]--><b>Filaments:</b>
these are very long and continuous single fibres.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l1 level1 lfo11; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->(b)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]--><b>Yarns:</b> this
is twisted bundles of filaments.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l1 level1 lfo11; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->(c)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]--><b>Roving:</b>
These are untwisted bundles of gathered filaments.</div>
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<!--[if !supportLists]-->(d)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]--><b>Tows:</b> These
are bundles of thousands of filaments.</div>
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<!--[if !supportLists]-->(e)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]--><b>Woven fabrics:</b>
These are made from filaments, yarn or roving which have been woven at 90
degree to each other.</div>
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<!--[if !supportLists]-->(f)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]--><b>Mats:</b> Fibre
form is said to be mat form when the continuous fibre is deposited in a swirl
pattern or chopped fibre is deposited in a random pattern.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l1 level1 lfo11; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->(g)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]--><b>Combination mat:</b>
Here, one ply of woven roving is bonded to a ply of chopped strand mat.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l1 level1 lfo11; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->(h)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]--><b>Surface mats:</b>
These are very thin, monofilament fibre mats for better surface appearance.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l1 level1 lfo11; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->(i)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]--><b>Chopped fibre or
roving:</b> These are 3 to 50 mm in length.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l1 level1 lfo11; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->(j)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]--><b>Milled fibres:</b>
These are of brittle materials, usually 0.5 to 3 mm in length. </div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l1 level1 lfo11; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]--><b>(k)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; font-weight: normal; line-height: normal;"> </span></b><!--[endif]--><b>Whiskers:</b> whiskers are single crystal,
in the form of fine filaments, a few microns in diameter and short in length.
These single crystal whiskers are the strongest known fibers. Their high
strength is due to the high degree of perfection and the absence of dislocation
in the structure. Their strength is many times greater than that of the normal
metals. For ex The strength of an iron whisker is found to be 13450MN\m2,
compared to about 294MPa for a piece of pure iron,. Besides metal whiskers,
long non metallic, whiskers and of graphite are being produced. They are
introduced in to resin or metallic matrix for the purpose of high strength and
high stiffness at high temperatures. <b><o:p></o:p></b></div>
<div class="MsoNormal" style="margin-left: .25in; tab-stops: list .25in; text-align: justify;">
The
properties of reinforced materials will depend on:</div>
<ul style="margin-top: 0in;" type="disc">
<li class="MsoNormal" style="mso-list: l25 level1 lfo91; tab-stops: list .5in 1.0in; text-align: justify;">The properties of matrix materials.</li>
<li class="MsoNormal" style="mso-list: l25 level1 lfo91; tab-stops: list .5in 1.0in; text-align: justify;">The properties of the fibre materials.</li>
<li class="MsoNormal" style="mso-list: l25 level1 lfo91; tab-stops: list .5in 1.0in; text-align: justify;">The proportions of the reinforcement in the
composite materials. It is never less than 20% and may go up to 80% in
oriented structures.</li>
<li class="MsoNormal" style="mso-list: l25 level1 lfo91; tab-stops: list .5in 1.0in; text-align: justify;">The orientation of the fibre, relative to the
load application and relative to one another.</li>
<li class="MsoNormal" style="mso-list: l25 level1 lfo91; tab-stops: list .5in 1.0in; text-align: justify;">The degree of bonding between the fibers and
the matrix material.</li>
<li class="MsoNormal" style="mso-list: l25 level1 lfo91; tab-stops: list .5in; text-align: justify;">The length to diameter ratio of the fibers.There has
to be some minimum fibre length, known as, critical length, lc, to get the
desired strength and stiffness of the composite materials. It is given as:</li>
</ul>
<div class="MsoNormal" style="margin-left: 1.0in; text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
L<sub> c </sub>= σ<i><sub>
f </sub></i>.d / <span dir="RTL" lang="AR-SA">ح</span><span dir="LTR"></span><span dir="LTR"></span><sub><span lang="AR-SA"><span dir="LTR"></span><span dir="LTR"></span>
</span></sub></div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
Where, σ<i><sub>f </sub></i>=Tensile strength of fibre
materials</div>
<div class="MsoNormal" style="margin-left: .5in; text-align: justify;">
d =diameter of fibre</div>
<div class="MsoNormal" style="text-align: justify;">
<span dir="RTL" lang="AR-SA">ح</span><span dir="LTR"></span><span dir="LTR"></span><span dir="LTR"></span><span dir="LTR"></span>
=shear yield strength of the fibre matrix bond</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiY02_5Y1SRPs8fdbpwCjVOgpBBki5w7egIIEq-04Ztj1q3r34-2kpF-QG7V-IRbtE0Lw0DqGruqIdYDwIf6fNPvfcUg9yd2dnP1GInlNPIcJXiA5PMyN7wtYNhVjgDNyp-VaXJV2gl_0g/s1600/Untitled.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="443" data-original-width="853" height="207" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiY02_5Y1SRPs8fdbpwCjVOgpBBki5w7egIIEq-04Ztj1q3r34-2kpF-QG7V-IRbtE0Lw0DqGruqIdYDwIf6fNPvfcUg9yd2dnP1GInlNPIcJXiA5PMyN7wtYNhVjgDNyp-VaXJV2gl_0g/s400/Untitled.png" width="400" /></a></div>
<br /></div>
<div align="center" class="MsoNormal" style="text-align: center;">
<b><span style="font-size: 10.0pt; mso-bidi-font-size: 12.0pt;">Fig. 1.6
Reinforcing Fibers<o:p></o:p></span></b></div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
For example, for carbon and glass
fibers, the critical length is of the order of 1mm, which may be 20 to150 times
the diameter of the fibre.</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
The fibre reinforcement can be
done in three ways:</div>
<div class="MsoNormal" style="text-align: justify;">
1. Continuous and aligned, Fig a</div>
<div class="MsoNormal" style="text-align: justify;">
2. Discontinuous and aligned, Fig
b</div>
<div class="MsoNormal" style="text-align: justify;">
3. Continuous and randomly
oriented, Fig c</div>
<div class="MsoNormal" style="margin-left: 1.0in; text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
If the fibre length is
considerably greater than Lc e.g., 15 times or more, it is called a “continuous
fibre”, otherwise it is called “short” or “discontinuous fibre as noted above,
the properties of a composite having aligned fibre reinforcements, are highly
anisotropic, that is, they depend upon the direction in which these are
measured. Their maximum strength is along the direction of alignment. They are
very weak in the transverse direction. The arrangement is best suited for
application involving multi- direction applied stresses, for e.g., bi-axel
stresses in pressure vessel or tube. The same results can be achieved by using
bi- axially oriented or cross – ply fibers. It is apparent that the strength of
the discontinuous and aligned arrangement will be less than of the continuous
and aligned arrangement.</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>Applications:</b> As discussed in the beginning, composite structures
combine the desirable properties of two or more materials. This has greatly
expanded the scope of application of all engineering materials. This has
greatly expanded the scope of application of all engineering materials. We can
produce components with exceptional strength –to –weight and stiffness
–to-weight ratio (many composite are stronger than steel, lighter than steel
and stiffer than titanium). Also, they have low conductivity, good heat
resistance, good fatigue life, adequate wear resistance and are free from
corrosion.</div>
<div class="MsoNormal" style="text-align: justify;">
Reinforced concrete is a classic
example of reinforced materials. Steel rods used in the concrete to reinforce
the material take all tensile loads since concrete weak in tension but strong
in compression.</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l87 level1 lfo12; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]--><b>1.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; font-weight: normal; line-height: normal;"> </span></b><!--[endif]--><b>Glass- fibre reinforced Plastics:</b> Here,
we have glass fibres in a matrix of unsaturated polyester. To get better
qualities to use at high temperature, high temperature polyamide resin is used
with pure SiO<sub>2</sub> fibres. A special type of glass fibre can be used
with cement bond to form flexible type of concrete. Glass fibre reinforced
plastics are used to make: boat hulls, car bodies, truck, cabins and aircraft
fittings. The other matrix materials can be: vinyl ester and phenolic.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l87 level1 lfo12; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]--><b>2.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; font-weight: normal; line-height: normal;"> </span></b><!--[endif]--><b>C-C composites: </b>These composites have
graphite fibres in a carbon matrix. This material is being used to make: Nose
cone and leading edge of missiles and space shuttles, racing car disks brakes,
aerospace turbine and jet engine components, rocket nozzles and surgical
implants.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l87 level1 lfo12; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]--><b>3.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; font-weight: normal; line-height: normal;"> </span></b><!--[endif]--><b>Graphite fibre-</b> reinforced epoxy :<b>( Organic or Resin matrix composites): </b>This
material is being used to make many parts of a fighter plane: Wing span,
outrigger flaring. Overwing flaring, engine access doors, nose cone, forward
fuselage. Lid fence and strakes-flap. Flap slot door, aileron seals, Horizontal
stabilizer (Full span) and rubber. The other fibre-matrix combination can be:
Aramid fibre-Phenolic resin matrix, Boron fibre-Bismaleimide resin matrix.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l87 level1 lfo12; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]--><b>4.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; font-weight: normal; line-height: normal;"> </span></b><!--[endif]--><b>Automative uses:</b> Body panels, drive
shafts, spring and bumpers, Cab shell and bodies, oil pans, fan shrouds,
instrument panels and engine covers.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l87 level1 lfo12; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]--><b>5.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; font-weight: normal; line-height: normal;"> </span></b><!--[endif]--><b>Sports equipment:</b> Golf club shafts,
base ball parts, fishing rods, tennis rackets, bicycle frames, skis and pole
vaults.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l87 level1 lfo12; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]--><b>6.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; font-weight: normal; line-height: normal;"> </span></b><!--[endif]-->Rubber
used for making automobiles tyres is now reinforced with fibres of nylon, rayon
steel or Kevlar, to provide added strength and durability. Kevlar is an organic
aramid fibre with very high tensile strength and modulas of elasticity. Its
density is about half of that of aluminum and it has negative thermal
expansion. It is flame retardant to radio signals. This makes it very
attractive for military and aerospace applications. It is also being used for
making bullet proof jackets. The trade name “Kevlar” is given by Du Pont.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l87 level1 lfo12; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]--><a href="https://www.blogger.com/blogger.g?blogID=6302071579893645567" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"></a><a href="https://www.blogger.com/blogger.g?blogID=6302071579893645567" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"></a><a href="https://www.blogger.com/blogger.g?blogID=6302071579893645567" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"></a><a href="https://www.blogger.com/blogger.g?blogID=6302071579893645567" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"></a><a href="https://www.blogger.com/blogger.g?blogID=6302071579893645567" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"></a><b>7.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; font-weight: normal; line-height: normal;"> </span></b><!--[endif]-->Metal
matrix composite (MMC): As already noted, these composites are obtained by
impregnating high-strength fibres (of stainless steel, boron, tungusten,
molybdenum, graphite, AL<sub>2</sub>O<sub>3</sub>, SiC and Si<sub>3</sub>N<sub>4</sub>
etc.) with molten metal ( aluminuim , titanium, Ni and cobalt etc). These
composites offer higher strength and stiffness especially at elevated
temperatures and lower co-efficient of thermal expansion as compared to metals.
And as compared to Organic-matrix composites, these composites offer grater
heat resistance and improved thermal and electric conductivity. Hence metal
matrix composites are used where operation temperature is high or extreme
strength is desired. These will find applications in a variety segments like
automobiles and machinery.</div>
<div class="MsoNormal" style="text-align: justify;">
Aluminum oxide reinforced
aluminum is used for making automotive connecting rods. Aluminum reinforced
with SiC whiskers is used to make air craft wing panels. Fibre reinforced super
alloys are used for making turbine blades. Graphite fibres in aluminum matrix
are used for Satellite, missile, helicopter structures.Graphite fibres in
magnesium matrix is used for space and satellite structures. Graphite fibres in
lead matrix are used for Strong –battery plates. A graphite fibre in copper
matrix is used for bearings and electrical contacts. Other e.g. of MMC is:</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l87 level2 lfo12; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->(a)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->Boron fibre in aluminum: Compressor blades and
structural supports.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l87 level2 lfo12; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->(b)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->““ “ magnesium : Antenna structures. </div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l87 level2 lfo12; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->(c)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->“””” Titanium: Jet-engine fan blades.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l87 level2 lfo12; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->(d)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->Alumina ““
Lead: Strong-battery plates.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l87 level2 lfo12; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->(e)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->““ “ Magnesium: Helicopter transmission
structures.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l87 level2 lfo12; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->(f)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->SiC “‘ Super
alloy (Cobalt based): High temperature engine components.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l87 level2 lfo12; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->(g)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->Tungsten and Molybundum fibres in Super alloy matrix:
High temperature engine components.</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="margin-left: 0in; mso-list: l87 level1 lfo12; tab-stops: list .25in; text-align: justify; text-indent: 0in;">
<!--[if !supportLists]--><b>8.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; font-weight: normal; line-height: normal;"> </span></b><!--[endif]--><b>Ceramic-matrix composites: </b>(CMC): AS
already noted, ceramics are strong, stiff, can resist high temperatures, but
generally lack toughness. Ceramic matrix materials are: AL<sub>2</sub>O<sub>3</sub>,
SiC and Si<sub>3</sub>N<sub>4</sub>, and mullite (a compound of Al, Si, and O<sub>2</sub>).
They can retain their strength upto 1700 degree C, and also resist corrosive
environments.<b> </b></div>
<div class="MsoNormal" style="text-align: justify;">
Typical product applications of
ceramic matrix<b> composite</b> are: in jet
and automotive engines, deep-sea mining equipment, pressure vessels, structural
components’ cutting tools, and dies for extrusion and drawing operations.</div>
<div class="MsoNormal" style="text-align: justify;">
Composite in development stage:</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l42 level1 lfo13; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->1.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->Advance bismaleinmide resin matrix series for high
temperature service.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l42 level1 lfo13; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->2.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->Polyether ether ketone thermoplastic matrix series for
higher temperature service.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l42 level1 lfo13; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->3.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->Hybrid reinforcements and Knitted/stacked ply fabrics
and three-dimensional woven fabric reinforcements. </div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l42 level1 lfo13; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->4.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]-->Selective stitching of collated ply kits.</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b><span style="font-size: 14.0pt; mso-bidi-font-size: 12.0pt;">1.14
LAMINATES: <o:p></o:p></span></b></div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
Laminates or laminar composites
are those structures which have alternate layers of materials bonded together
in some manner some common examples of laminar composites are given below:</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l37 level1 lfo14; tab-stops: list .25in .75in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->1.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]--><b>Plywood:</b> it
is most common material under this category. Here, thin layer of wood veneer
are bonded with adhesives. The successive layers have different orientations of
the grain or fibre; Structural parts capable of carrying a load are made of
multi-plywood board from 25 to 30 mm thick. </div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l37 level1 lfo14; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->2.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]--><b>Bimetallic</b>
strips used in thermostats & other heat sensing application.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l37 level1 lfo14; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->3.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]--><b>Safety glass </b></div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l37 level1 lfo14; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->4.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span><!--[endif]--><b>Sandwich
material:</b> Here, low density core is placed between thin, high strength</div>
<div class="MsoNormal" style="margin-left: .25in; tab-stops: list .25in; text-align: justify;">
High-density
surfaces, for example, corrugated cardboard. Cores of polymer foam or honeycomb
structures can be used. Wood substitutes based on red mud polymer have been
developed to be used for door shutters, windows, partitions and false ceilings.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l37 level1 lfo14; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->5.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]--><b>Roll cladding
(bonding) and explosive cladding (welding) of one metal upon another</b>: The
main aim of clad material is to improve corrosion resistance while retaining
low cost, high strength and /or lightweight. Mild steel –stainless steel
combination, copper stainless steel combination are examples of metal-to-metal
laminates. Another example is “Alclad”, which is formed by cladding duralumin
with thin sheets of pure aluminium. The material is high strength composite in
which aluminium cladding provides galvanic protection for the more corrosive
duralumin. The above claddings are done by “hot roll bonding” method.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l37 level1 lfo14; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->6.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;">
</span><!--[endif]--><b>Laminated
Plastic Sheet:</b> This structure is usually made from sheets of paper or cloth and suitable resin. The resin used
includes: phenolics, polyster,silicones and epoxide. The paper and cloth provides bulk of strength, while the resin
acts as a semi rigid binder. Laminated plastic sheet can be machined, drilled,
punched and pressed to shaped. It is used in the production of gears, bearings,
electrical components, and small cabinets. Laminate fabric base gears have the
advantages over metal gears of being silent in operation and stable against the
attack of various. Aggressive media. In many cases, laminated fabric base gears
have completely replaced nonferrous gears. They are employed to transmit
rotation from electric motor in high-speed machine tools; they are mounted on
the camshafts of internal-combustion engines etc. In chemical industry,
laminate fabric base gears are used in various apparatus & instruments
where they resist corrosive attack much more efficiently then gears of bronze
brass or leather. In addition to gears, certain other transporting devices:
roller, rings etc. are also made of laminated fabric base. Laminated sheets
/plates are available in sizes of: 900*900 mm, 900 *1800 mm, and 1200*2400 mm.
The minimum thickness of sheet is 0.8 mm & it varies as follows: -</div>
<div class="MsoNormal" style="margin-left: .5in; text-align: justify; text-indent: -.25in;">
</div>
<div class="MsoNormal" style="margin-left: .5in; text-align: justify; text-indent: -.25in;">
<span style="font-size: x-small;">Thickness
range (mm) 0.8-1.6 1.6-4.8 6.4-9.6 12.8- 19.2 25.6- 38.4</span></div>
<div class="MsoNormal" style="margin-left: .5in; text-align: justify; text-indent: -.25in;">
<span style="font-size: x-small;"> Step(mm) 0.4 0.8 1.6 3.2 6.4</span></div>
<ol start="7" style="margin-top: 0in;" type="1">
<li class="MsoNormal" style="mso-list: l37 level1 lfo14; tab-stops: list .5in; text-align: justify;"><b>Tufnol:</b> this
is a laminated material consisting of layers of woven textiles impregnated
with a thermosetting resin. The polymer imparts rigidity, while the woven
textile provides great tensile strength. Paper or asbestos may also be
used as alternative reinforcements. The material (with woven textile) can
be used for making seat covers &carpets.</li>
<li class="MsoNormal" style="mso-list: l37 level1 lfo14; tab-stops: list .5in; text-align: justify;"><b>Laminated
carbides:</b> In laminated carbides, laminates consisting of a hard thin
surface layer TiCand the form of throw away tips, are bonded by epoxy
resin to the rake face of a tip body of WC. This increases the crater wear
of WC cutting tool.</li>
<li class="MsoNormal" style="mso-list: l37 level1 lfo14; tab-stops: list .5in; text-align: justify;"><b>Laminated wood</b>
: this sheets of wood (veneer ) , impregnated with special resins &
compressed hot , form what is called ‘laminated wood ‘, which find
extensive application in textile machinery & electric engineering , as
well as substitute for nonferrous metal in bearing of hydraulic machinery
&mechanisms operating in abrasive media . Parts of wood are machined
in ordinary machine tools &wood working machinery.</li>
</ol>
<div class="MsoNormal" style="margin-left: .25in; text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>Surface coated materials:</b> the surface coating is applied to the
materials for various purposes: - protection of the material against corrosion;
for decorative, wear resistant &processing purpose. They may also be used
to :(i) improve visibility through luminescence & better reflectivity (ii)
provide electrical insulation , & (iii) improve the appearance. Surface
coating are usually classified as: metallic coatings, inorganic chemical
coating & organic chemical coating </div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l13 level1 lfo89; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->1.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span>Metallic coating: metallic coating of copper, chromium
nickel, zinc, lead & tin etc. are
applied by hot dipping , electro- plating or spraying techniques to protect the
base metal from corrosion & for other purpose .</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l13 level1 lfo89; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->2.<span style="font-size: 9.33333px;"> </span>Inorganic chemical coating: This surface coating may be
divided into: Phosphate coating, oxide coating & vitreous coating. Oxide
& phosphate coating are done to make iron or steel surface free from rust
& this is done by chemical action. These coating also provide protection
against corrosion. Vitreous coating are commonly applied to steel in the form of
a powder or frit & are then used to the steel surface by heat. These
coating are relatively brittle, but offer absolute protection against
corrosion. Enamel is an example of ceramic coating on metal & glaze on
tiles is an example of glassy ceramic on crystalline ceramic base. The glazing
as a protective coating on porcelain & stoneware ceramic is performed for
the purpose of protection from moisture absorption in ceramic materials.
Coating of TiC , TiN , Al2o3 or HFN on WC base are examples of ceramics on
ceramic & coatings of TiC & TiN on HSS base are examples of ceramics on
steel. These coatings increase the life of cutting tools.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l13 level1 lfo89; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]-->3.<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; line-height: normal;"> </span><!--[endif]-->Organic Coatings:
It includes paint, varnishes, enamels & lacquers. They serve to protect the base
metal & to improve its appearance. </div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
Polymer coating on paper are used
for making milk cartons. Polymer coated textiles are used for making seat
covers & carpets. Polymer Coatings on metals act as wire insulation.
Polymer coated metals are used for making beverage cans.</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b><span style="font-size: 14.0pt; mso-bidi-font-size: 12.0pt;">1.15
PRODUCTION OF COMPOSITE STRUCTURES<o:p></o:p></span></b></div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>Fabrication of particulate
composites</b>: As discussed in above art. A majority of the particulate
composites are made via the powder metallurgy route. So, for details readers
should refer to chapter 10. However, a few particulate composites are made by
dispersing the particles in the matrix materials through introduction into
slurry or into a liquid melt (agglomeration of asphalt and stone particles). </div>
<h1 style="line-height: normal; text-align: justify;">
<span style="font-size: small;">Fabrication of Fibre
reinforced Composites: </span><span style="font-weight: normal;"><span style="font-size: small;">Many processes have been developed to fabricate
fibre-reinforced composite structures. Their aim is to combine the fibre and
the matrix into a unified form. The various fabrication techniques depend on:
the size and the form of the fibres and their orientation in the matrix
material; the shape, size and form of the product. The common fabrication
processes are: Open-Mould process, Filament winding, Pultrusion and
Matched-die-Moulding, and Laminating. Before these processes are discussed, the
following terms should be understood:</span><o:p></o:p></span></h1>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l53 level1 lfo92; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]--><span style="font-family: "symbol"; mso-bidi-font-family: Symbol; mso-fareast-font-family: Symbol;">·<span style="font-family: "times new roman"; font-size: 7pt; font-stretch: normal; line-height: normal;">
</span></span><!--[endif]--><b>Prepergs: </b>Prepergs means “Preimpregnated<b>
with resin</b>”. It is ready to mould material in the sheet form. Impregnated
rovings and mats make these with resin matrix under the condition in which the
resin undergoes only a partial cure. These are stored for subsequent use. These
are supplied to the fabricator, who lays up the finished shape in stacks, which
is subjected to heat and pressure. This completes the curing of the resin into
a continues solid matrix. “Lay-up” is positioning of the reinforcement
material, sometimes resin-impregnated, in the mould.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l53 level1 lfo92; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]--><span style="font-family: "symbol"; mso-bidi-font-family: Symbol; mso-fareast-font-family: Symbol;">·<span style="font-family: "times new roman"; font-size: 7pt; font-stretch: normal; line-height: normal;">
</span></span><!--[endif]--><b>BMCs: </b>are
“<b>Bulk Moulding Compounds</b>”. These are thermosetting resins mixed with
chopped reinforcements or filters and made into a viscous compound for compressing
moulding.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l53 level1 lfo92; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]--><span style="font-family: "symbol"; mso-bidi-font-family: Symbol; mso-fareast-font-family: Symbol;">·<span style="font-family: "times new roman"; font-size: 7pt; font-stretch: normal; line-height: normal;">
</span></span><!--[endif]--><b>SMCs: </b>are “<b>Sheet Moulding Compounds</b>”.
These comprise chopped fibres and resin in the sheet form approx. 2.5 mm thick.
These are3 processed further to fabricate large sheet like parts. They can
replace sheet metal, where lightweight, corrosion resistance and integral
colour are attractive features.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l53 level1 lfo92; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]--><span style="font-family: "symbol"; mso-bidi-font-family: Symbol; mso-fareast-font-family: Symbol;">·<span style="font-family: "times new roman"; font-size: 7pt; font-stretch: normal; line-height: normal;">
</span></span><!--[endif]--><b>Thick Moulding Compounds: </b>Thick Moulding
Compounds (TMC) combines the lower cost of BMC and higher strength of SMC.
These are usually injection moulded using chopped fibres of various lengths.
Used for electrical components due to their high electrical strength.</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>1) Open – Mould Process ~ </b>In this process, only one mould (Die) is
employed to fabricate the reinforced part. The mould may be made of: wood,
plaster or reinforced plastic material. The various techniques in this category
are:-</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l16 level1 lfo16; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]--><b>a)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; font-weight: normal; line-height: normal;"> </span></b><!--[endif]--><b><i>Hand lay-up technique</i>: </b>In this
method, the successive layers of reinforcement mat or web (which may or may not
be impregnated with resin) are positioned on a mould by hand. Resin in used to
impregnate or coat the reinforcement. Curing the resin to permanently fix the
shape then follows it. Curing may be at room temperature or heating may speed
it up. The technique in which resin-saturated reinforcements are placed in the
mould is called “Wet lay-up”.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l16 level1 lfo16; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]--><b>b)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; font-weight: normal; line-height: normal;"> </span></b><!--[endif]--><b><i>Bag Moulding</i>: </b>This is a technique of moulding reinforced
plastics composites by using a flexing cover (bag) over a rigid mould. The
composite material is positioned in the mould and covered with the plastic film
(bag). Pressure is then applied by a : Vacuum, auto-clave, press or by inflating the bag . An auto-clave is a
closed pressure vessel for inducing a resin cure or other operation under heat
and pressure.</div>
<div class="MsoNormal" style="margin-left: .25in; mso-list: l14 level1 lfo17; tab-stops: list .25in; text-align: justify; text-indent: -.25in;">
<!--[if !supportLists]--><b>i)<span style="font-size: 7pt; font-stretch: normal; font-variant-numeric: normal; font-weight: normal; line-height: normal;">
</span></b><!--[endif]--><b><i>Vacuum-</i></b><b><i>bag</i></b><i> <b>moulding</b></i><b>: </b>In this technique for moulding
reinforced plastics, a sheet of flexible, transparent material is placed over
the lay-up on the mould. After sealing the edges the entrapped air between the
sheet and the lay-up is mechanically worked out and removed by the vacuum.
Finally, the part is cured.</div>
<div class="MsoNormal" style="margin-left: 2.0in; text-align: justify;">
<br /></div>
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiEdGPqks0aqT98lxtMwknssMTbcFCd9KfjNTVLgRTv8krbDUL2qRqzQQWR6If538zpkQoVk1VAw7FyhhAqIEsWp8p5MOiu3bRukCgqfYP-uvQmgoVNEHnrhZN6Fzf9HEQvKDj7SMn-UE8/s1600/Untitled.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="154" data-original-width="252" height="244" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiEdGPqks0aqT98lxtMwknssMTbcFCd9KfjNTVLgRTv8krbDUL2qRqzQQWR6If538zpkQoVk1VAw7FyhhAqIEsWp8p5MOiu3bRukCgqfYP-uvQmgoVNEHnrhZN6Fzf9HEQvKDj7SMn-UE8/s400/Untitled.png" width="400" /></a></div>
<br /></div>
<div align="center" class="MsoNormal" style="text-align: center;">
<b><span style="font-size: 10.0pt; mso-bidi-font-size: 12.0pt;">Fig. 1.7
Vacuum Bag Moulding</span></b><b><span style="font-size: 11.0pt; mso-bidi-font-size: 12.0pt;"><o:p></o:p></span></b></div>
<div class="MsoNormal" style="text-align: justify;">
<b>ii) Pressure-bag Moulding: It</b> is a process for moulding reinforced
plastics in which a tailored, flexible bag is placed over the contact lay-up on
the mould, sealed and clamped in placed. Compressed air forces the bag against
the part to apply pressure while the part cures.</div>
<div class="MsoNormal" style="text-align: justify;">
<b>iii) Spray-up: </b>In this technique, a spray gun supplies resin in two
converging streams into which chopped roving fiber is forced with the help of a
chopper. The composite material stream is then deposited against the walls of
the mould cavity. It is a low-cost method of fabricating medium strength
composite structures.</div>
<div class="MsoNormal" style="text-align: justify;">
All the above open-mould
techniques are extensively used for fabricating parts such as: boats, tanks,
swimming pools, ducts and truck bodies.</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b>2) Matched-die moulding: </b>Matched metal dies are used for moulding
composite structure when: production quantities are large, tolerances are close
and surface quality has to be the best. The dies are heated to complete the
curing of the product during the moulding process.</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
i) Compression Moulding is
essentially employed for moulding BMCs.</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
ii) <b>Resin- Transfer Moulding or Resin Injection Moulding: </b>In this
technique (RTM or RIM), two piece matched cavity dies are used with one or
multiple injection points and breather holes. The reinforcing material, which
is either chopped or continuous strand material is cut to shape and draped in
the die-cavity. The die-halves are clamped together and a polyester resin is
pumped through an injection port in the die. The pressure used in the die is
low, which allows use of low cost tooling. The method is used for moulding
small non-load bearing parts.</div>
<div class="MsoNormal" style="text-align: justify;">
In a variant of the above
technique, instead of the injection of only resin into the die-cavity, the
reinforcement (flake glass) is mixed with the resin in a mixing head and the mixture
is injected into the closed heated two-piece die. Flake glass is preferred to
avoid directionality of reinforcement. This method is known as “Reaction
Injection Moulding” and is being increasingly used for BMCs.</div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
iii) SMCs cut to size, are
fabricated into parts by methods similar to metal pressing. However, curing of
the part takes place outside the press.
</div>
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<br /></div>
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<b><span style="font-size: 11.0pt; mso-bidi-font-size: 12.0pt;">Fig. 1.8
Compression Moulding<o:p></o:p></span></b></div>
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</div>
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<b>3) Pultrusion: </b>This is the process of extrusion of
resin-impregnated roving ( a bundle of fibres ) to manufacture rods, tubes and
structural shapes (Channels, I-beams and Z- Sections etc.) o0f a constant
cross-section. After passing through the resin-dip tank, the roving is dawn
through a heated die (where curing takes place) and cured to form the desired
cross-section, as it continuously runs through the machine. After the Puller
rolls, a saw cutter cuts the extruded section to the required lengths.</div>
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In “ Pulmoulding”, the process
begins with pultruding; then the part is placed in a compression mould.</div>
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Product applications are: - Golf
club shafts, because of their high damping capacity, and structural members for
vehicle and aerospace applications.</div>
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<b><span style="font-size: 11.0pt; mso-bidi-font-size: 12.0pt;">Fig. 1.9
Pultrusion<o:p></o:p></span></b></div>
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<br /></div>
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<b>4) Filament Winding: </b>In this process, resin impregnated strands are
applied over a rotating mandrel, to produce high strength, reinforced
cylindrical shapes. Fibers or tapes are drawn through a resin bath and wound
onto a rotating mandrel. The process is relatively slow, but the fiber
direction can be controlled and the diameter can be varied along the length of
the piece. In a variation, the Fiber bundle (made up of several thousand carbon
fibers) is first coated with the matrix material, to make a prepreg tape (endless
strip with width equal to several cms, by a meter). With both the fiber and
tape winding processes, the finished part is cured in an autoclave and later
removed from the mandrel. In axial winding, the filaments are parallel to the
axis and in circumferential winding; these are essentially perpendicular to the
axis of rotation.</div>
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Cylindrical, spherical and other
shapes are made by filament winding, for example, pressure bottles, missile
canisters, industrial storage tanks and automobile drive shafts C- fibers with
epoxy- basin resin composite is used for fabricating strength- critical
aerospace structures. </div>
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<b><span style="font-size: 11.0pt; mso-bidi-font-size: 12.0pt;">Fig. 1.10
Filament Winding Process<o:p></o:p></span></b></div>
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<b>5) Laminating: </b>In this
process, composite parts are produced by combining layers of resin-impregnated
material in a press under heat and pressure. The parts include, standard for
comparatively flat pieces. Two principal steps in the manufacture of laminated
fiber-reinforced composite materials are:- </div>
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(a) Lay-up, which consists of
arranging fibers in layers.</div>
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(b) Curing</div>
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We start with a preperg material
(partially cured composite with the fibers aligned parallel to each other). A
pattern of product’s shape is cut out the preperg material is then stacked in
layers into the desired laminate geometry. Curing the stacked pile under heat
and pressure in an autoclave makes a final product, or by tool press moulding,
winding the impregnated fibre on a mandrel of suitable diameter produces tubes.
The assembly is then cured in a moulding press and then the mandrel is removed.</div>
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<b><span style="font-size: 14.0pt; mso-bidi-font-size: 12.0pt; mso-bidi-font-style: italic;">1.16 FABRICATION OF MMC:</span></b><b><i><u><span style="font-size: 14.0pt; mso-bidi-font-size: 12.0pt;"><o:p></o:p></span></u></i></b></div>
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Basically, three approaches are
followed for fabricating MMC</div>
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1. <b>Liquid phase approach: </b>In this technique, the matrix material is
the molten phase and the reinforcement is in the solid state. Either one of the
conventional casting process can be used to fabricate MMC or “Pressure
infiltration casting method “can be used. In this method, a perform is made
(usually a sheet or wire) of reinforcing fibres and the liquid metal matrix is
forced into it with the help of a pressurized gas.</div>
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<br /></div>
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<b>2. Solid phase technique: </b>Here the Powder Metallurgy route is used
to fabricate MMC. The best example is of manufacturing WC tool material where
cobalt is used as the matrix material.</div>
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<br /></div>
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3. <b>Two phase Processing</b>: Here the metal matrix contains both the solid
and liquid phases. The reinforcing fibres are mixed with the matrix. The
mixture is then atomized when it leaves the nozzles and is sprayed and
deposited over the surface of a mould cavity to fabricate MMC.</div>
<h1 style="line-height: normal; text-align: justify;">
<span style="font-size: 14.0pt; mso-bidi-font-size: 12.0pt; mso-bidi-font-style: italic;">PROCESSING OF CMC</span> </h1>
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The most common method of fabricating
CMC is of “Slurry infiltration”. A perform of reinforcing fibres is prepared
which is then hot pressed. Slurry containing matrix powder, a carrier liquid
and an organic binder is prepared. The perform is then impregnated with the
slurry to fabricate CMC.</div>
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<br /></div>
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<b><span style="font-size: 14.0pt; mso-bidi-font-size: 12.0pt;">1.17 MACHINING
CUTTING AND JOINING OF COMPOSITES<o:p></o:p></span></b></div>
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<br /></div>
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Conventional processes and tools
are generally not suited for machining, cutting and joining of composites.
Therefore, special methods are employed to the final processing operations for
the composites.</div>
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<b>1. Machining: </b>Machining of composite materials should ensure that
there is no splintering, cracking, fraying or delaminating of cured composite
edges. Standard machine tools can be used with appropriate modifications.
Cutting tools for composites include: drills, reamers, countersinks, cut-of
wheels and router bits. Common cutting tool materials are: HSS and WC. However,
poly-crystalline diamond insert tool performs satisfactory and is cost
effective. Tools must be kept sharp, to provide quality cuts and avoid
de-lamination. Tool and its geometry should be carefully selected. Cutting
speeds and feeds will depend on the type of composite material, its thickness
and the cutting method.</div>
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<br /></div>
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<b>2. Cutting: </b>The conventional methods for cutting uncured composites,
such as preperg ply include: manual cutting with Carbide disk cutter, scissors
and power shears. For cutting uncured composites, the main techniques are:
reciprocating knife cutting, high pressure water jet cutting, ultrasonic knife
cutting and laser cutting.</div>
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<br /></div>
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<b>3. Joining: </b>The common joints provided for composites structures
are: Bolted joints and Adhesive bonded joints. </div>
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Prepared
By- Er. CP SINGH</div>
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(Asst.
Prof)</div>
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(Mech
Engg Dept)</div>
<br />
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E-Max
Group of Institutions, Ambala</div>
</div>
Mechanical Engineering Departmenthttp://www.blogger.com/profile/12582953924770018783noreply@blogger.comtag:blogger.com,1999:blog-6302071579893645567.post-18070619414792237882017-08-09T14:30:00.001+05:302017-08-09T14:36:10.309+05:30Industrial Engineering Notes ( Unit 3)<div dir="ltr" style="text-align: left;" trbidi="on">
Forcasting<br />
<div class="style5" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
<b>Introduction</b></div>
<div align="justify" class="style5" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
The growing competition, frequent changes in customer's demand and the trend towards automation demand that decisions in business should not be based purely on guesses rather on a careful analysis of data concerning the future course of events. More time and attention should be given to the future than to the past, and the question 'what is likely to happen?' should take precedence over 'what has happened?' though no attempt to answer the first can be made without the facts and figures being available to answer the second. When estimates of future conditions are made on a systematic basis, the process is called forecasting and the figure or statement thus obtained is defined as forecast.</div>
<div align="justify" class="style5" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
In a world where future is not known with certainty, virtually every business and economic decision rests upon a forecast of future conditions. Forecasting aims at reducing the area of uncertainty that surrounds management decision-making with respect to costs, profit, sales, production, pricing, capital investment, and so forth. If the future were known with certainty, forecasting would be unnecessary. But uncertainty does exist, future outcomes are rarely assured and, therefore, organized system of forecasting is necessary. The following are the main functions of forecasting:</div>
<ul style="color: #000066; font-family: Arial, Helvetica, sans-serif;">
<li class="style5 style15" style="color: black; font-size: 12px;">The creation of plans of action.</li>
<li class="style5" style="color: black; font-size: 12px;">The general use of forecasting is to be found in monitoring the continuing progress of plans based on forecasts.</li>
<li class="style5" style="color: black; font-size: 12px;">The forecast provides a warning system of the critical factors to be monitored regularly because they might drastically affect the performance of the plan.</li>
</ul>
<div align="justify" style="color: #000066; font-family: Arial, Helvetica, sans-serif;">
<span class="style5" style="color: black; font-size: 12px;">It is important to note that the objective of business forecasting is not to determine a curve or series of figures that will tell exactly what will happen, say, a year in advance, but it is to make analysis based on definite statistical data, which will enable an executive to take advantage of future conditions to a greater extent than he could do without them. In forecasting one should note that it is impossible to forecast the future precisely and there always must be some range of error allowed for in the forecast.</span></div>
<div class="style5" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
<b>Dependent versus Independent Demand</b></div>
<div align="justify" class="style5" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
Demand of an item is termed as independent when it remains unaffected by the demand for any other item. On the other hand, when the demand of one item is linked to the demand for another item, demand is termed as dependent. It is important to mention that only independent demand needs forecasting. Dependent demand can be derived from the demand of independent item to which it is linked.</div>
<div class="style5" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
<b>Business Time Series</b></div>
<div align="justify" class="style5" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
The first step in making a forecast consists of gathering information from the past. One should collect statistical data recorded at successive intervals of time. Such a data is usually referred to as time series. Analysts plot demand data on a time scale, study the plot and look for consistent shapes and patterns. A time series of demand may have constant, trend, or seasonal pattern ( <a href="http://nptel.ac.in/courses/112107142/part3/forcasting/lecture1.htm#">Figure 1 </a>) or some combination of these patterns. The forecaster tries to understand the reasons for such changes, such as,</div>
<ul style="color: #000066; font-family: Arial, Helvetica, sans-serif;">
<li class="style12 style14" style="color: black; font-size: 12px;"><div align="justify" class="style15">
Changes that have occurred as a result of general tendency of the data to increase or decrease, known as secular movements.</div>
</li>
<li class="style5" style="color: black; font-size: 12px;"><div align="justify">
Changes that have taken place during a period of 12 months as a result in changes in climate, weather conditions, festivals etc. are called as seasonal changes.</div>
</li>
<li class="style5" style="color: black; font-size: 12px;"><div align="justify">
Changes that have taken place as a result of booms and depressions are called as cyclical variations.</div>
</li>
<li class="style13" style="color: black; font-size: 12px;"><div align="justify" class="style15">
Changes that have taken place as a result of such forces that could not be predicted (like flood, earthquake etc.) are called as irregular or erratic variations.</div>
</li>
</ul>
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<div align="left" class="style5" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
<b>uantitative Approaches of Forecasting</b></div>
<div align="justify" class="style5" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
Most of the quantitative techniques calculate demand forecast as an average from the past demand. The following are the important demand forecasting techniques.</div>
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<li class="style16 style3" style="font-size: 12px;"><div align="justify">
Simple average method: A simple average of demands occurring in all previous time periods is taken as the demand forecast for the next time period in this method.</div>
</li>
</ul>
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<div class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px; font-weight: bold; text-align: start;">
Simple Average :</div>
<div align="justify" class="style2" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
A XYZ television supplier found a demand of 200 sets in July, 225 sets in August & 245 sets in September. Find the demand forecast for the month of october using simple average method.</div>
<div align="center" class="style2" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
The average demand for the month of October is</div>
<div align="center" class="style2" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
<img src="http://nptel.ac.in/courses/112107142/part3/forcasting/image/ex1.gif" height="116" width="140" /></div>
<div align="center" class="style2" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
<br /></div>
<div align="center" class="style2" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
<span style="text-align: justify;">Simple moving average method: In this method, the average of the demands from several of the most recent periods is taken as the demand forecast for the next time period. The number of past periods to be used in calculations is selected in the beginning and is kept constant (such as 3-period moving average).</span></div>
<div class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px; font-weight: bold; text-align: start;">
Simple Moving Average :</div>
<div align="justify" class="style2" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
A XYZ refrigerator supplier has experienced the following demand for refrigerator during past five months.</div>
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<strong><span class="style4" style="font-family: "arial" , "helvetica" , sans-serif; font-size: 12px;">Month</span></strong></div>
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<strong><span class="style4" style="font-family: "arial" , "helvetica" , sans-serif; font-size: 12px;">Demand</span></strong></div>
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<span class="style4" style="font-family: "arial" , "helvetica" , sans-serif; font-size: 12px;">February</span></div>
</td><td><div align="center">
<span class="style4" style="font-family: "arial" , "helvetica" , sans-serif; font-size: 12px;">20</span></div>
</td></tr>
<tr><td><div align="center">
<span class="style4" style="font-family: "arial" , "helvetica" , sans-serif; font-size: 12px;">March </span></div>
</td><td><div align="center">
<span class="style4" style="font-family: "arial" , "helvetica" , sans-serif; font-size: 12px;">30</span></div>
</td></tr>
<tr><td><div align="center">
<span class="style4" style="font-family: "arial" , "helvetica" , sans-serif; font-size: 12px;">April</span></div>
</td><td><div align="center">
<span class="style4" style="font-family: "arial" , "helvetica" , sans-serif; font-size: 12px;">40</span></div>
</td></tr>
<tr><td><div align="center">
<span class="style4" style="font-family: "arial" , "helvetica" , sans-serif; font-size: 12px;">May</span></div>
</td><td><div align="center">
<span class="style4" style="font-family: "arial" , "helvetica" , sans-serif; font-size: 12px;">60</span></div>
</td></tr>
<tr><td><div align="center">
<span class="style4" style="font-family: "arial" , "helvetica" , sans-serif; font-size: 12px;">June</span></div>
</td><td><div align="center" class="style4" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
45</div>
</td></tr>
</tbody></table>
<div style="text-align: start;">
<span class="style4" style="font-family: "arial" , "helvetica" , sans-serif; font-size: 12px;">Find out the demand forecast for the month of July using five-period moving average & three-period moving average using simple moving average method.</span></div>
<blockquote style="text-align: start;">
<blockquote>
<div align="center">
<img src="http://nptel.ac.in/courses/112107142/part3/forcasting/image/ex2.gif" height="233" width="208" /></div>
</blockquote>
</blockquote>
<span style="font-family: "arial" , "helvetica" , sans-serif; font-size: 12px;">Weighted moving average method: In this method, unequal weights are assigned to the past demand data while calculating simple moving average as the demand forecast for next time period. Usually most recent data is assigned the highest weight factor</span><br />
<table border="0" style="color: black; width: 100%px;"><tbody>
<tr><td><div align="center" class="style1 style3 style2" style="color: #000099; font-family: Arial, Helvetica, sans-serif; font-size: 12px; font-weight: bold;">
Example 3</div>
<div class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px; font-weight: bold;">
Weighted Moving Average Method :</div>
<div align="justify" class="style3" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
The manager of a restaurant wants to make decision on inventory and overall cost. He wants to forecast demand for some of the items based on weighted moving average method. For the past three months he exprienced a demand for pizzas as follows:</div>
<div align="justify" class="style3" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
</div>
<table align="center" border="1" cellpadding="0" cellspacing="0" style="width: 33%px;"><tbody>
<tr bgcolor="#CC9999"><td width="51%"><div align="center" class="style5" style="color: #330000;">
<strong><span class="style3" style="font-family: "arial" , "helvetica" , sans-serif; font-size: 12px;">Month</span></strong></div>
</td><td width="49%"><div align="center" class="style5" style="color: #330000;">
<strong><span class="style3" style="font-family: "arial" , "helvetica" , sans-serif; font-size: 12px;">Demand</span></strong></div>
</td></tr>
<tr><td><div align="center">
<span class="style3" style="font-family: "arial" , "helvetica" , sans-serif; font-size: 12px;">October</span></div>
</td><td><div align="center">
<span class="style3" style="font-family: "arial" , "helvetica" , sans-serif; font-size: 12px;">400</span></div>
</td></tr>
<tr><td><div align="center">
<span class="style3" style="font-family: "arial" , "helvetica" , sans-serif; font-size: 12px;">November </span></div>
</td><td><div align="center">
<span class="style3" style="font-family: "arial" , "helvetica" , sans-serif; font-size: 12px;">480</span></div>
</td></tr>
<tr><td><div align="center">
<span class="style3" style="font-family: "arial" , "helvetica" , sans-serif; font-size: 12px;">December</span></div>
</td><td><div align="center">
<span class="style3" style="font-family: "arial" , "helvetica" , sans-serif; font-size: 12px;">550</span></div>
</td></tr>
</tbody></table>
<span class="style3" style="font-family: "arial" , "helvetica" , sans-serif; font-size: 12px;">Find the demand for the month of January by assuming suitable weights to demand data.</span><br />
<div align="center">
<img src="http://nptel.ac.in/courses/112107142/part3/forcasting/image/ex3.gif" height="182" width="241" /></div>
<div align="center">
<span style="font-family: "arial" , "helvetica" , sans-serif; font-size: 12px; text-align: justify;">Exponential smoothing method: In this method, weights are assigned in exponential order. The weights decrease exponentially from most recent demand data to older demand data</span></div>
<table border="0" style="color: black; width: 100%px;"><tbody>
<tr><td><div align="center" class="style1 style3 style2" style="color: #000099; font-family: Arial, Helvetica, sans-serif; font-size: 12px; font-weight: bold;">
<br /></div>
<div class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px; font-weight: bold;">
Exponential Smoothing :</div>
<div align="justify" class="style3" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
One of the two wheeler manufacturing company exprienced irregular but usually increasing demand for three products. The demand was found to be 420 bikes for June and 440 bikes for July. They use a forecasting method which takes average of past year to forecast future demand. Using the simple average method demand forecast for June is found as 320 bikes (Use a smoothing coefficient 0.7 to weight the recent demand most heavily) and find the demand forecast for August.</div>
<blockquote>
<blockquote>
<blockquote>
<div align="left" class="style3" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
<img src="http://nptel.ac.in/courses/112107142/part3/forcasting/image/ex4.gif" height="260" width="273" /></div>
</blockquote>
</blockquote>
</blockquote>
<span style="text-align: justify;">Regression analysis method: In this method, past demand data is used to establish a functional relationship between two variables. One variable is known or assumed to be known; and used to forecast the value of other unknown variable (i.e. demand)</span><br />
<table border="0" style="color: black; width: 100%px;"><tbody>
<tr><td><div align="center" class="style1 style3 style2" style="color: #000099; font-family: Arial, Helvetica, sans-serif; font-size: 12px; font-weight: bold;">
Example 5</div>
<div class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px; font-weight: bold;">
Regression Analysis :</div>
<div align="justify" class="style3" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
Farewell Corporation manufactures Integrated Circuit boards(I.C board) for electronics devices. The planning department knows that the sales of their client goods depends on how much they spend on advertising, on account of which they receive in advance of expenditure. The planning department wish to find out the relationship between their clients advertising and sales, so as to find demand for I.C board.</div>
<div class="style3" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
The money spend by the client on advertising and sales (in dollar) is given for different periods in following table :</div>
<table align="center" border="1" cellpadding="0" cellspacing="0" style="width: 56%px;"><tbody>
<tr bgcolor="#CC9999"><td width="13%"><div align="center" class="style18" style="font-weight: bold;">
<span class="style3" style="font-family: "arial" , "helvetica" , sans-serif; font-size: 12px;">Period(t)</span></div>
</td><td width="17%"><div align="center" class="style10 style19" style="font-weight: bold;">
<span class="style3" style="font-family: "arial" , "helvetica" , sans-serif; font-size: 12px;">Advertising (<span class="style8" style="font-size: 18px;"><span class="style9" style="font-size: 12px;">X<sub>t</sub>)</span></span></span><br />
<div class="style3" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
$(1,00,000)</div>
</div>
</td><td width="15%"><div align="center" class="style18" style="font-weight: bold;">
<div class="style3" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
Sales (<span class="style8" style="font-size: 18px;"><span class="style9" style="font-size: 12px;">D<sub>t</sub>)</span></span></div>
<div class="style3" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
$(1,000.000)</div>
</div>
</td><td width="14%"><div align="center" class="style7 style10" style="color: #330000; font-weight: bold;">
<span class="style3" style="font-family: "arial" , "helvetica" , sans-serif; font-size: 12px;"><span class="style8" style="font-size: 18px;"><span class="style20" style="color: black; font-size: 12px;">D<sub>t</sub><sup>2</sup></span></span></span></div>
</td><td width="14%"><div align="center">
<span class="style21 style6" style="font-family: "arial" , "helvetica" , sans-serif; font-size: 12px; font-weight: bold;">X</span><span class="style9" style="font-size: 12px;"><span class="style9"><span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;"><span class="style19 style10" style="font-weight: bold;"><sub>t</sub><sup>2</sup></span></span></span></span></div>
</td><td width="14%"><div align="center" class="style18" style="font-weight: bold;">
<div class="style3" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
<span class="style20">X<sub>t</sub>D<sub>t</sub></span></div>
</div>
</td></tr>
<tr><td><div align="center">
<span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;"><span class="style9" style="font-size: 12px;">1</span></span></div>
</td><td><div align="center">
<span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;"><span class="style9" style="font-size: 12px;">20</span></span></div>
</td><td><div align="center">
<span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;"><span class="style9" style="font-size: 12px;">6</span></span></div>
</td><td><div align="center">
<span class="style3" style="font-family: "arial" , "helvetica" , sans-serif; font-size: 12px;">36</span></div>
</td><td><div align="center">
<span class="style9" style="font-size: 12px;"><span class="style9"><span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;">400</span></span></span></div>
</td><td><div align="center">
<span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;"><span class="style9" style="font-size: 12px;">120</span></span></div>
</td></tr>
<tr><td><div align="center">
<span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;"><span class="style6"><span class="style9" style="font-size: 12px;">2</span></span></span></div>
</td><td><div align="center">
<span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;"><span class="style9" style="font-size: 12px;">25</span></span></div>
</td><td><div align="center">
<span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;"><span class="style9" style="font-size: 12px;">8</span></span></div>
</td><td><div align="center">
<span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;"><span class="style9" style="font-size: 12px;">64</span></span></div>
</td><td><div align="center">
<span class="style9" style="font-size: 12px;"><span class="style9"><span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;">625</span></span></span></div>
</td><td><div align="center">
<span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;"><span class="style9" style="font-size: 12px;">200</span></span></div>
</td></tr>
<tr><td><div align="center">
<span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;"><span class="style6"><span class="style9" style="font-size: 12px;">3</span></span></span></div>
</td><td><div align="center">
<span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;"><span class="style9" style="font-size: 12px;">15</span></span></div>
</td><td><div align="center">
<span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;"><span class="style9" style="font-size: 12px;">7</span></span></div>
</td><td><div align="center">
<span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;"><span class="style9" style="font-size: 12px;">49</span></span></div>
</td><td><div align="center">
<span class="style9" style="font-size: 12px;"><span class="style9"><span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;">225</span></span></span></div>
</td><td><div align="center">
<span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;"><span class="style9" style="font-size: 12px;">105</span></span></div>
</td></tr>
<tr><td><div align="center">
<span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;"><span class="style6"><span class="style9" style="font-size: 12px;">4</span></span></span></div>
</td><td><div align="center">
<span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;"><span class="style9" style="font-size: 12px;">18</span></span></div>
</td><td><div align="center">
<span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;"><span class="style9" style="font-size: 12px;">7</span></span></div>
</td><td><div align="center">
<span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;"><span class="style9" style="font-size: 12px;">49</span></span></div>
</td><td><div align="center">
<span class="style9" style="font-size: 12px;"><span class="style9"><span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;">324</span></span></span></div>
</td><td><div align="center">
<span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;"><span class="style9" style="font-size: 12px;">126</span></span></div>
</td></tr>
<tr><td><div align="center">
<span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;"><span class="style6"><span class="style9" style="font-size: 12px;">5</span></span></span></div>
</td><td><div align="center">
<span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;"><span class="style9" style="font-size: 12px;">22</span></span></div>
</td><td><div align="center">
<span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;"><span class="style9" style="font-size: 12px;">8</span></span></div>
</td><td><div align="center">
<span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;"><span class="style9" style="font-size: 12px;">64</span></span></div>
</td><td><div align="center">
<span class="style9" style="font-size: 12px;"><span class="style9"><span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;">484</span></span></span></div>
</td><td><div align="center">
<span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;"><span class="style9" style="font-size: 12px;">176</span></span></div>
</td></tr>
<tr><td><div align="center">
<span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;"><span class="style6"><span class="style9" style="font-size: 12px;">6</span></span></span></div>
</td><td><div align="center">
<span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;"><span class="style9" style="font-size: 12px;">25</span></span></div>
</td><td><div align="center">
<span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;"><span class="style9" style="font-size: 12px;">9</span></span></div>
</td><td><div align="center">
<span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;"><span class="style9" style="font-size: 12px;">81</span></span></div>
</td><td><div align="center">
<span class="style9" style="font-size: 12px;"><span class="style9"><span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;">625</span></span></span></div>
</td><td><div align="center">
<span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;"><span class="style9" style="font-size: 12px;">225</span></span></div>
</td></tr>
<tr><td><div align="center">
<span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;"><span class="style6"><span class="style9" style="font-size: 12px;">7</span></span></span></div>
</td><td><div align="center">
<span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;"><span class="style9" style="font-size: 12px;">27</span></span></div>
</td><td><div align="center">
<span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;"><span class="style9" style="font-size: 12px;">10</span></span></div>
</td><td><div align="center">
<span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;"><span class="style9" style="font-size: 12px;">100</span></span></div>
</td><td><div align="center">
<span class="style9" style="font-size: 12px;"><span class="style9"><span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;">729</span></span></span></div>
</td><td><div align="center">
<span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;"><span class="style9" style="font-size: 12px;">270</span></span></div>
</td></tr>
<tr><td><div align="center">
<span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;"><span class="style6"><span class="style9" style="font-size: 12px;">8</span></span></span></div>
</td><td><div align="center">
<span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;"><span class="style9" style="font-size: 12px;">23</span></span></div>
</td><td><div align="center">
<span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;"><span class="style9" style="font-size: 12px;">7</span></span></div>
</td><td><div align="center">
<span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;"><span class="style9" style="font-size: 12px;">49</span></span></div>
</td><td><div align="center">
<span class="style9" style="font-size: 12px;"><span class="style9"><span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;">529</span></span></span></div>
</td><td><div align="center">
<span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;"><span class="style9" style="font-size: 12px;">161</span></span></div>
</td></tr>
<tr><td><div align="center">
<span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;"><span class="style6"><span class="style9" style="font-size: 12px;">9</span></span></span></div>
</td><td><div align="center">
<span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;"><span class="style9" style="font-size: 12px;">16</span></span></div>
</td><td><div align="center">
<span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;"><span class="style9" style="font-size: 12px;">6</span></span></div>
</td><td><div align="center">
<span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;"><span class="style9" style="font-size: 12px;">36</span></span></div>
</td><td><div align="center">
<span class="style9" style="font-size: 12px;"><span class="style9"><span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;">256</span></span></span></div>
</td><td><div align="center">
<span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;"><span class="style9" style="font-size: 12px;">96</span></span></div>
</td></tr>
<tr><td><div align="center">
<span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;"><span class="style6"><span class="style9" style="font-size: 12px;">10</span></span></span></div>
</td><td><div align="center">
<span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;"><span class="style9" style="font-size: 12px;">20</span></span></div>
</td><td><div align="center">
<span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;"><span class="style9" style="font-size: 12px;">8</span></span></div>
</td><td><div align="center">
<span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;"><span class="style9" style="font-size: 12px;">64</span></span></div>
</td><td><div align="center">
<span class="style9" style="font-size: 12px;"><span class="style9"><span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;">400</span></span></span></div>
</td><td><div align="center">
<span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;"><span class="style9" style="font-size: 12px;">120</span></span></div>
</td></tr>
<tr bgcolor="#E1C8C8"><td><div align="center">
<span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;"><span class="style6"><span class="style9" style="font-size: 12px;"><img src="http://nptel.ac.in/courses/112107142/part3/forcasting/image/ex5.gif" height="26" width="30" /></span></span></span></div>
</td><td><div align="center">
<strong><span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;"><span class="style9" style="font-size: 12px;">211</span></span></strong></div>
</td><td><div align="center">
<strong><span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;"><span class="style9" style="font-size: 12px;">76</span></span></strong></div>
</td><td><div align="center">
<strong><span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;"><span class="style9" style="font-size: 12px;">592</span></span></strong></div>
</td><td><div align="center">
<strong><span class="style9" style="font-size: 12px;"><span class="style9"><span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;">4597</span></span></span></strong></div>
</td><td><div align="center">
<strong><span class="style6" style="font-family: "arial" , "helvetica" , sans-serif;"><span class="style9" style="font-size: 12px;">1599</span></span></strong></div>
</td></tr>
</tbody></table>
<div align="center">
<img src="http://nptel.ac.in/courses/112107142/part3/forcasting/image/ex5.3.gif" height="294" width="365" /><br />
<br />
<br /></div>
</td></tr>
</tbody></table>
<br />
<div align="left" class="style5" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
<b>Error in Forecasting</b></div>
<div align="justify" class="style5" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
Error in forecasting is nothing but the numeric difference in the forecasted demand and actual demand. <a href="http://nptel.ac.in/courses/112107142/part3/forcasting/lecture2.htm#">MAD</a> (Mean Absolute Deviation) and <a href="http://nptel.ac.in/courses/112107142/part3/forcasting/lecture2.htm#">Bias</a> are two measures that are used to assess the accuracy of the forecasted demand. It may be noted that MAD expresses the magnitude but not the direction of the error<br />
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<br />
<b>Inventory </b><br />
<div class="style1" style="font-family: Arial, Helvetica, sans-serif; text-align: start;">
<b>Introduction</b></div>
<div align="justify" class="style1" style="font-family: Arial, Helvetica, sans-serif;">
The amount of material, a company has in stock at a specific time is known as inventory or in terms of money it can be defined as the total capital investment over all the materials stocked in the company at any specific time. Inventory may be in the form of,</div>
<ul style="font-family: "Times New Roman"; font-size: medium; text-align: start;">
<li><span class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">raw material inventory</span></li>
<li class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">in process inventory</li>
<li class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">finished goods inventory</li>
<li class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">spare parts inventory</li>
<li class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">office stationary etc.</li>
</ul>
<div align="justify" class="style1" style="font-family: Arial, Helvetica, sans-serif;">
As a lot of money is engaged in the inventories along with their high carrying costs, companies cannot afford to have any money tied in excess inventories. Any excessive investment in inventories may prove to be a serious drag on the successful working of an organization. Thus there is a need to manage our inventories more effectively to free the excessive amount of capital engaged in the materials.</div>
<div class="style1" style="font-family: Arial, Helvetica, sans-serif; text-align: start;">
<b>Why Inventories?</b></div>
<div align="justify" class="style1" style="font-family: Arial, Helvetica, sans-serif;">
Inventories are needed because demand and supply can not be matched for physical and economical reasons. There are several other reasons for carrying inventories in any organization.</div>
<ul style="font-family: "Times New Roman"; font-size: medium; text-align: start;">
<li class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;"><div align="justify">
To safe guard against the uncertainties in price fluctuations, supply conditions, demand conditions, lead times, transport contingencies etc.</div>
</li>
<li class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;"><div align="justify">
To reduce machine idle times by providing enough in-process inventories at appropriate locations.</div>
</li>
<li class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;"><div align="justify">
To take advantages of quantity discounts, economy of scale in transportation etc.</div>
</li>
<li class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;"><div align="justify">
To decouple operations i.e. to make one operation's supply independent of another's supply. This helps in minimizing the impact of break downs, shortages etc. on the performance of the down stream operations. Moreover operations can be scheduled independent of each other if operations are decoupled.</div>
</li>
<li class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;"><div align="justify">
To reduce the material handling cost of semi-finished products by moving them in large quantities between operations.</div>
</li>
<li class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;"><div align="justify">
To reduce clerical cost associated with order preparation, order procurement etc.</div>
</li>
</ul>
<div class="style1" style="font-family: Arial, Helvetica, sans-serif; text-align: start;">
<b>Inventory Costs</b></div>
<div align="justify" class="style1" style="font-family: Arial, Helvetica, sans-serif;">
In order to control inventories appropriately, one has to consider all cost elements that are associated with the inventories. There are four such cost elements, which do affect cost of inventory.</div>
<ul style="font-family: "Times New Roman"; font-size: medium; text-align: start;">
<li class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;"><div align="justify">
Unit cost: it is usually the purchase price of the item under consideration. If unit cost is related with the purchase quantity, it is called as discount price.</div>
</li>
<li class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;"><div align="justify">
Procurement costs: This includes the cost of order preparation, tender placement, cost of postages, telephone costs, receiving costs, set up cost etc.</div>
</li>
<li class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;"><div align="justify">
Carrying costs: This represents the cost of maintaining inventories in the plant. It includes the cost of insurance, security, warehouse rent, taxes, interest on capital engaged, spoilage, breakage etc.</div>
</li>
<li class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;"><div align="justify">
Stockout costs: This represents the cost of loss of demand due to shortage in supplies. This includes cost of loss of profit, loss of customer, loss of goodwill, penalty etc.</div>
</li>
</ul>
<div class="style1" style="font-family: Arial, Helvetica, sans-serif; text-align: start;">
If one year planning horizon is used, the total annual cost of inventory can be expressed as:</div>
<div class="style1" style="font-family: Arial, Helvetica, sans-serif; text-align: start;">
<strong>Total annual inventory cost = Cost of items + Annual procurement cost + Annual carrying cost + Stockout cost</strong></div>
<div class="style1" style="font-family: Arial, Helvetica, sans-serif; text-align: start;">
<strong>Variables in Inventory Models</strong></div>
<blockquote style="font-family: "Times New Roman"; font-size: medium; text-align: start;">
<div class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
D = Total annual demand (in units)</div>
<div class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
Q = Quantity ordered (in units)</div>
<div class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
Q* = Optimal order quantity (in units)</div>
<div class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
R = Reorder point (in units)</div>
<div class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
R* = Optimal reorder point (in units)</div>
<div class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
L = Lead time</div>
<div class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
S = Procurement cost (per order)</div>
<div class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
C = Cost of the individual item (cost per unit)</div>
<div class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
I = Carrying cost per unit carried (as a percentage of unit cost C)</div>
<div class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
K = Stockout cost per unit out of stock</div>
<div class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
P = Production rate or delivery rate</div>
<div class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
d<sub>l</sub> = Demand per unit time during lead time</div>
<div class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
D<sub>l</sub> = Total demand during lead time</div>
<div class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
TC = Total annual inventory costs</div>
<div class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
TC* = Minimum total annual inventory costs</div>
</blockquote>
<div class="style7" style="font-family: Arial, Helvetica, sans-serif; font-weight: bold; text-align: start;">
Number of orders per year = <img align="absmiddle" height="40" src="http://nptel.ac.in/courses/112107142/part3/inventory/image/equ1.gif" width="132" /></div>
<div style="font-family: "Times New Roman"; font-size: medium; text-align: start;">
<span class="style7" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px; font-weight: bold;">Total procurement cost per year =</span> <span class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">S.D / Q</span></div>
<div style="font-family: "Times New Roman"; font-size: medium; text-align: start;">
<span class="style7" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px; font-weight: bold;">Total carrying cost per year = </span><span class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">Carrying cost per unit * unit cost * average inventory per cycle</span></div>
<div style="font-family: "Times New Roman"; font-size: medium; text-align: start;">
<img height="76" src="http://nptel.ac.in/courses/112107142/part3/inventory/image/equ2.gif" width="90" /></div>
<div style="font-family: "Times New Roman"; font-size: medium; text-align: start;">
<span class="style7" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px; font-weight: bold;">Cost of items per year = </span><span class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">Annual demand * unit cost</span></div>
<div class="style1" style="font-family: Arial, Helvetica, sans-serif; text-align: start;">
= D.C</div>
<div class="style7" style="font-family: Arial, Helvetica, sans-serif; font-weight: bold; text-align: start;">
Total annual inventory cost (TC) = <img align="absmiddle" height="37" src="http://nptel.ac.in/courses/112107142/part3/inventory/image/equ3.gif" width="356" /></div>
<div align="justify" class="style1" style="font-family: Arial, Helvetica, sans-serif;">
The objective of inventory management team is to minimize the total annual inventory cost. A simplified graphical presentation in which cost of items, procurement cost and carrying cost are depicted is shown in <a href="http://nptel.ac.in/courses/112107142/part3/inventory/lecture1.htm#">Figure 1 </a>. It can be seen that large values of order quantity Q result in large carrying cost. Similarly, when order quantity Q is large, fewer orders will be placed and procurement cost will decrease accordingly. The total cost curve indicates that the minimum cost point lies at the intersection of carrying cost and procurement cost curves.</div>
<div class="style1" style="font-family: Arial, Helvetica, sans-serif; text-align: start;">
<b>Inventory Operating Doctrine</b></div>
<div class="style1" style="font-family: Arial, Helvetica, sans-serif; text-align: start;">
When managing inventories, operations manager has to make two important decisions:</div>
<ul style="font-family: "Times New Roman"; font-size: medium; text-align: start;">
<li class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;"><div align="justify">
When to reorder the stock (i.e. time to reorder or reorder point)</div>
</li>
<li class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;"><div align="justify">
How much stock to reorder (i.e. order quantity)</div>
</li>
</ul>
<div align="justify" class="style1" style="font-family: Arial, Helvetica, sans-serif;">
Reorder point is usually a predetermined inventory level, which signals the operations manager to start the procurement process for the next order. Order quantity is the order size.</div>
<div>
<div class="style1" style="font-family: Arial, Helvetica, sans-serif; text-align: start;">
<b>nventory Modelling</b></div>
<div class="style1" style="font-family: Arial, Helvetica, sans-serif; text-align: start;">
This is a quantitative approach for deriving the minimum cost model for the inventory problem in hand.</div>
<div class="style1" style="font-family: Arial, Helvetica, sans-serif; text-align: start;">
<b>Economic Order Quantity (EOQ) Model</b></div>
<div align="justify" class="style1" style="font-family: Arial, Helvetica, sans-serif;">
This model is applied when objective is to minimize the total annual cost of inventory in the organization. Economic order quantity is that size of the order which helps in attaining the above set objective. EOQ model is applicable under the following conditions.</div>
<ul style="font-family: "Times New Roman"; font-size: medium; text-align: start;">
<li class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;"><div align="justify">
Demand per year is deterministic in nature</div>
</li>
<li class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;"><div align="justify">
Planning period is one year</div>
</li>
<li class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;"><div align="justify">
Lead time is zero or constant and deterministic in nature</div>
</li>
<li class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;"><div align="justify">
Replenishment of items is instantaneous</div>
</li>
<li class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;"><div align="justify">
Demand/consumption rate is uniform and known in advance</div>
</li>
<li class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;"><div align="justify">
No stockout condition exist in the organization</div>
</li>
</ul>
<div class="style1" style="font-family: Arial, Helvetica, sans-serif; text-align: start;">
The total annual cost of the inventory (TC) is given by the following equation in EOQ model.</div>
<div class="style1" style="font-family: Arial, Helvetica, sans-serif; text-align: start;">
<img height="198" src="http://nptel.ac.in/courses/112107142/part3/inventory/image/equ4.gif" width="293" /></div>
<div class="style1" style="font-family: Arial, Helvetica, sans-serif; text-align: start;">
The graphical representation of the EOQ model is shown in</div>
<div style="font-family: Arial, Helvetica, sans-serif; font-weight: bold; text-align: -webkit-center;">
Figure 2: Economic Order Quantity Model (EOQ Model)</div>
<div style="font-family: Arial, Helvetica, sans-serif; font-weight: bold; text-align: -webkit-center;">
<img height="304" src="http://nptel.ac.in/courses/112107142/part3/inventory/image/fig2.jpg" width="477" /></div>
<div style="font-family: Arial, Helvetica, sans-serif; font-weight: bold; text-align: -webkit-center;">
<br /></div>
<div style="font-family: Arial, Helvetica, sans-serif; font-weight: bold; text-align: -webkit-center;">
<br /></div>
<div class="style1" style="color: #000099; font-family: Arial, Helvetica, sans-serif; font-size: medium; font-weight: bold; text-align: -webkit-center;">
Example 1</div>
<div align="left" style="font-family: "Times New Roman"; font-size: medium;">
<div align="justify" class="style5" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
<span class="style7">ABC</span> manufacturers produces 1,25,000 oil seals each year to satisfy the requirement of their client. They order the metal for the bushing in lot of 30,000 units. It cost them $40 to place the order. The unit cost of bushing is $0.12 and the estimated carrying cost is 25% unit cost. Find out the economic order quantity? <span class="style7">What percentage of increases or decrease in order quantity is required so that the ordered quantity is Economic order quantity ?</span></div>
<div align="center">
<img height="316" src="http://nptel.ac.in/courses/112107142/part3/inventory/image/ex1.gif" width="628" /></div>
</div>
</div>
</div>
<div align="justify" class="style3" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
</div>
</td></tr>
</tbody></table>
</td></tr>
</tbody></table>
<div class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px; text-align: start;">
<b>Economic Production Quantity (EPQ) Model</b></div>
<div align="justify" class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
In EOQ model supply was instantaneous, which may not be the case in all industrial applications. If supply of items is gradual to satisfy a continuous demand, then supply line will be depicted by a slanted line</div>
<div style="font-family: Arial, Helvetica, sans-serif; font-size: 12px; font-weight: bold; text-align: -webkit-center;">
Figure 3 : Economic Production Quantity Model (EPQ Model)</div>
<div style="font-family: Arial, Helvetica, sans-serif; font-size: 12px; font-weight: bold; text-align: -webkit-center;">
<img height="315" src="http://nptel.ac.in/courses/112107142/part3/inventory/image/fig3.jpg" width="461" /></div>
<div align="justify" class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
In this situation, when the order is placed, the supplier begins producing the units and supplies them continuously. While new units are added to inventory, other units are being used. Thus, if delivery rate (P) > demand rate (D), the net result will be a net increase in the inventory level. The slope of replenishment line will thus be (P-D). Simillarly the slope of demand line will be (-D). The average inventory carried per year is</div>
<div align="justify" class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
<img height="280" src="http://nptel.ac.in/courses/112107142/part3/inventory/image/equ5.gif" width="394" /></div>
<table border="0" style="color: black; width: 100%px;"><tbody>
<tr><td><div align="center">
<div class="style1" style="color: #000099; font-family: Arial, Helvetica, sans-serif; font-size: 16px; font-weight: bold;">
Example 2</div>
<div align="left">
<span class="style4" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">The XYZ Company produces wheat flour as one of their product. The wheat flour </span><span class="style4" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">is produced in the pack of 1kg. The demand for wheat flour is 40,000 packs/year & the production rate is 50,000 packs/year. Wheat flour 1kg pack cost $0.50 each to make. The Procurement cost is $5. The carrying cost is high because the product gets spoiled in few week times span. It is nearly 50 percent of cost of one pack. Find out the operating doctrine.</span><br />
<div align="center">
<img height="168" src="http://nptel.ac.in/courses/112107142/part3/inventory/image/ex2.gif" width="229" /></div>
</div>
</div>
</td></tr>
</tbody></table>
</div>
</div>
</div>
Mechanical Engineering Departmenthttp://www.blogger.com/profile/12582953924770018783noreply@blogger.comtag:blogger.com,1999:blog-6302071579893645567.post-865217402194216342017-08-09T14:22:00.001+05:302017-08-09T14:22:29.734+05:30Industrial Engineering Notes (Unit1)<div dir="ltr" style="text-align: left;" trbidi="on">
<div align="justify" class="style11" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
<strong>Work Study</strong></div>
<div align="justify" class="style11" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
<strong>Definition: </strong>Work study may be defined as the analysis of a job for the purpose of finding the preferred method of doing it and also determining the standard time to perform it by the preferred (or given) method. Work study, therefore, comprises of two areas of study: method study (motion study) and time study (work measurement).</div>
<div align="justify" class="style11" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
<strong>Role of Work Study in Improving Productivity</strong></div>
<div align="justify" class="style11" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
In order to understand the role of work study, we need to understand the role of method study and that of time study.</div>
<div align="justify" class="style11" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
Method study (also sometimes called Work Method Design) is mostly used to improve the method of doing work. It is equally applicable to new jobs. When applied to existing jobs and existing jobs, method study aims to find better methods of doing the jobs that are economical and safe, require less human effort, and need shorter make-ready / put-away time. The better method involves the optimum use of best materials and appropriate manpower so that work is performed in well organized manner leading to increased resource utilization, better quality and lower costs.</div>
<div align="justify" class="style11" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
It can therefore be stated that through method study we have a systematic way of developing human resource effectiveness, providing high machine and equipment utilization, and making economical use of materials.</div>
<div align="justify" class="style11" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
Time study, on the other hand, provides the standard time, that is the time needed by worker to complete a job by the standard method. Standard times for different jobs are necessary for proper estimation of</div>
<div align="justify">
<ul class="style11" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
<li>manpower, machinery and equipment requirements</li>
<li>daily, weekly or monthly requirement of materials</li>
<li>production cost per unit as an input to better make or buy decision</li>
<li>labor budgets</li>
<li>worker's efficiency and make incentive wage payments.</li>
</ul>
</div>
<div align="justify" class="style11" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
By the application of method study and time study in any organization, we can thus achieve greater output at less cost and of better quality, and hence achieve higher productivity.</div>
<div align="justify" class="style11" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
<strong>Work Study and Ergonomics</strong></div>
<div align="justify" class="style11" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
The work study and the ergonomics are the two areas of study having the same objective: design the work system so that for the operator it is safe, and the work is less fatiguing and less time taking.</div>
<div align="justify" class="style11" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
<strong>Historical Developments</strong></div>
<div align="justify" class="style11" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
<strong>The Work of Taylor</strong></div>
<div align="justify" class="style11" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
Frederick W. Taylor is generally considered to be the founder of modern method and time study, although time studies were conducted in Europe many years before Taylor 's time. In 1760, Jean Rodolphe Perronet, a French engineer, made extensive time studies on the manufacture of No. 6 common pins.</div>
<div align="justify" class="style11" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
Taylor began his time study work in 1881 while associated with the Midvale Steel Company in U.S.A.. He evolved a system based on the “task”, and proposed that the work of each employee be planned out by the management in advance. Each job was to have a standard time, deter mined by time studies made by experts. In the timing process, Taylor advocated dividing the work into small divisions of effort known as "ele ments." Experts were to time these individually and use their collective values to determine the allowed time for the task.</div>
<div align="justify" class="style11" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
Early presentations of Taylor 's findings were received with little enthusiasm, because many interpreted his findings to be somewhat new piece-rate system rather than a technique for analyzing work and improving methods. Both management and employees were skeptical of piece rates, because many standards were earlier typically based on the supervisor's guess or even sometimes inflated by bosses to protect the performance of their departments.</div>
<div align="justify" class="style11" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
In June 1903, at the American Society of Mechanical Engineers meeting, Taylor presented his famous paper, "Shop Management," which included the elements of scientific management: time study, standardization of all tools and tasks, use of a planning department, use of slide rule and similar timesaving implements, instruction cards for workers, bonuses for successful per formance, differential rates, mnemonic systems for classifying products, routing systems, and modern cost systems. Taylor 's techniques were well received by many factory managers, and by 1917, of 113 plants that had installed "scientific manage ment," 59 considered their installations completely successful, 20 partly successful, and 34 failures.</div>
<div align="justify" class="style11" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
In 1898, while at the Bethlehem Steel Company <em>, </em>Taylor carried out the pig-iron experiment that became the most celebrated demonstrations of his principles. He established the correct method, along with financial incentives, and workers carrying 92-pound pigs of iron up a ramp onto a freight car were able to increase their productivity from an average of 12.5 tons per day to between 47 and 48 tons per day. This work was performed with an increase in the daily rate of $1.15 to $1.85. Taylor claimed that workmen per formed at the higher rate "without bringing on a strike among the men, without any quarrel with the men and were happier and better contented."</div>
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Another of Taylor 's Bethlehem Steel studies that became famous was on shovel ing work. Workers who shoveled at Bethlehem would use the same shovel for any job—lifting heavy iron ore to lifting light rice coal. Taylor designed shovels to fit the different loads: short- handled shovels for iron ore, long-handled scoops for light rice coal, and showed their usefulness in improving productivity.</div>
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Not as well known as his engineering contributions is the fact that in 1881, he was a U.S. tennis doubles champion. Here he used an odd-looking racket he had designed with a spoon curved handle.</div>
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<strong>The Work of Gilbreths</strong></div>
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Frank and Lilian Gilbreth are considered as the founders of the modern motion study technique, which may be defined as the study of the body motions used in performing an oper ation, for the purpose of improving the operation by eliminating unnecessary motions, simplifying necessary motions, and then establishing the most favorable motion sequence for maximum efficiency. Frank Gilbreth originally implemented ideas into the bricklayer's trade in which he was employed. After introducing meth ods improvements through motion study, including an adjustable scaffold that he had invented, as well as operator training, he was able to increase the average num ber of bricks laid from 120 to 350 per worker per hour.</div>
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More than anyone else, the Gilbreths were responsible for industry's recogni tion of the importance of a detailed study of body motions to arrive at the best method of performing an operation that would increase production, reduce operator fatigue. They developed the technique of filming motions for study, known as micromotion study.</div>
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The Gilbreths also developed the cyclegraphic and chronocyclegraphic analysis techniques for studying the motion paths made by an operator. The cycle- graphic method involves fixing small electric light bulb to the finger or part of the body being studied and then photographing the motion while the operator is performing the operation. The resulting picture gives a permanent record of the motion pattern employed and can be analyzed for possible improvement. The chrono- cyclegraph is similar to the cyclegraph, but its electric circuit is interrupted regularly, causing the light to flash. Instead of showing solid lines of the motion patterns, the resulting photograph shows short dashes of light spaced in proportion to the speed of the body motion being photographed. Consequently, with the chronocyclegraph it is possible to determine direction and compute velocity, acceleration, and deceleration, in addition to study of body motions.</div>
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<strong>The Work of Others</strong></div>
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Carl G. Barth, an associate of Frederick W. Taylor, developed a production slide rule for estimating the most efficient combinations of speeds and feeds for cutting metals of various hardnesses, considering the depth of cut, size of tool, and life of the tool. He is also known for his work on estimation of allowances by establishing the number of foot-pounds of work a worker could do in a day. He developed a relationship in which a certain push or pull on a worker's arms was equated with the amount or weight that worker could handle for a certain percentage of the day.</div>
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Harrington Emerson applied scientific methods to work on the Santa Fe Railroad and wrote a book, <em>Twelve Principles of Efficiency, </em>in which he made an attempt to lay down procedures for efficient operation. He reorganized the company, integrated its shop procedures, installed standard costs and a bonus plan, and introduced Hollerith tabulating machines for the accounting work. This effort resulted in annual saving of $ 1.5 million and recognition of his approach, called <em>efficiency engineering </em>.</div>
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In 1917, Henry Laurence Gantt developed simple graph that would present performance while visually showing projected schedules. This production control tool was adopted by the shipbuilding industry during World War I. For the first time, this tool demonstrated the possibility of comparing actual performance against the original plan, and to adjust daily schedules in accordance with capacity, back log, and customer requirements. Gantt is also known for his wage payment system that rewarded workers for above-standard performance, eliminated any penalty for failure, and offered the boss a bonus for every worker who per formed above .standard. Gantt advocated human relations and promoted scientific management in the back drop of an inhuman "speedup" of labor.</div>
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Motion and time study received added stimulus during World War II when Franklin D. Roosevelt, through the U.S. Department of Labor, attempted to establish standards for increasing production. The stated policy advocated greater pay for greater output but without an increase in unit labor costs, incentive schemes to be collectively bargained between labor and management, and the use of time study for setting production standards.</div>
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<strong>Method Study</strong></div>
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Method study, aims to achieve the better method of doing work, and for this reason method study is sometimes called Work Method Design.</div>
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<strong>Definition: </strong>Method study can be defined as the procedure for systematic recording, analysis and critical examination of existing or proposed method of doing work for the purpose of development and application of easier and more effective method.</div>
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<strong>Method Study Procedure</strong></div>
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The following general steps describe the procedure for making a method study.</div>
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<li>Select the job – on which method study is to be applied.</li>
<li>Obtain information and record.</li>
<li>Examine the information critically.</li>
<li>Develop the most practical, economical and effective method by considering real limitations of the situation.</li>
<li>Install the new method as standard practice.</li>
<li>Maintain the standard practice by regular follow up.</li>
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Let us consider these steps in some detail.</div>
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<strong>Selection of Job for Method Study</strong></div>
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Practically, any activity or a job is a potential project for improvement but as the work study engineer is to sell his ideas and maintain his existence in the organisation, he should always attempt to select those jobs for improvement which are unpopular among employees or are considered “dirty” by them.</div>
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By improving such jobs, he would earn goodwill from the employees as well as the management, and can expect their full cooperation for other studies in the future.</div>
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Considerations may be given to the following factors while selecting a job for method study</div>
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• Economic Factors</div>
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• Technical Factors</div>
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• Human Factors</div>
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<strong>Economic Factors:</strong></div>
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If the economic importance of a job is small, it is not wise to start or continue a long study. Priorities should be given to those types of job which offer greater potential for cost reduction. Such jobs are easily identifiable, as they have</div>
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• High labour content, i.e. they consume more time</div>
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• excessive machine or man idleness</div>
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• higher frequency of occurrence, i.e. they have large demand</div>
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• bottlenecks in production line</div>
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• higher proportion of accidents</div>
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• movement of material or men over long distance</div>
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• high scrap and reprocessing costs</div>
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• high payment of overtime bills.</div>
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<strong>Technical Factors: </strong>The method study engineer must have the necessary technical knowledge about the job to be studied. Only surface knowledge about the subject may not lead to the right solution to the real problem. To illustrate, consider that a particular machine tool in proving bottleneck. The output from this machine is not reaching the assembly line in the required quantity. Through a preliminary study, it is found that it is running at lower speed and feed than that recommended for the pair of work and tool material used. Just increase in speed or feed may not be the solution of this problem. It may be possible that the machine itself is not rigid enough to operate at higher speeds or take a deeper cut. Just increase in speed may increase the output but the quality of job may be seriously affected. Technical expertise in machine tools and metal cutting process would be essential to solve problem of this kind.</div>
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<strong>Human Factors: </strong>Emotional reaction of the workers to the method study and changes in method are important considerations. If the study of a particular job is suspected to cause unrest or ill feeling, it should not be undertaken, however useful it may be from the economic point of view. It is always better to take up first those jobs which are considered ‘dirty', unsafe, unpleasant, boring, or highly fatiguing, and improvements brought about as a result of method study. This would possibly ensure cooperative from the workers for the other jobs as well.</div>
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After it is recognized that a problem exists, the first step is to properly formulate it. From the general statements like “Costs are too high“, “Increase the production”, “Reduce shop floor accidents”, it is necessary to determine just what the real problem is. After it is ascertained that the problem merits consideration, it is decided whether this is the proper time to solve it, and how much time can be spent in solving it. The problem may then be defined broadly giving minimum constraints at this stage, as it will permit the use of imagination and creativity in finding a solution. It may sometimes be desirable to divide the complete problem into a couple of small problems and solve them.</div>
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<strong>Information Collection and Recording</strong></div>
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<strong>Information Collection Techniques:</strong></div>
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The accuracy of data about the method study problem is important for the development of improved method. The following techniques are used for the collection of information / data about the task under consideration. These are not exclusive of each other, and for any particular method study problem, some or all the techniques may be employed.</div>
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• Observation. It is a common technique used for collecting information about the present method or the existing problem. The method study person visits the site where the work is currently being done and observes various steps in the method being followed. There are many instances where all the data needed is obtained by only observing the work or work site.</div>
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• Discussion. Discussion with those who do or who supervise the work can frequently provide information not obtainable by observation. The discussion technique is commonly used where irregular work is involved or where one is trying to analyze past work in order to improve efficiency of work to be done in future.</div>
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Even where observation by itself may accomplish the data collection task, discussion may be used for developing good human relations.</div>
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• Records. Valuable information can be obtained from past records concerning production, cost, time, inventory and sub-contracts. For certain type of information concerning the past practice, sometimes this is the only way to obtain authentic data.</div>
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• Motion Pictures or video Films. Accurate and most detailed information can be obtained by taking motion pictures or video film. Information obtained by this procedure can easily be transmitted / forwarded to all levels in the organization and if needed, can be used directly for training purposes. The film can be used to focus attention at particular point or motion in an operation. For obtaining information concerning those types of work that involve large crew size, it is probably the only procedure.</div>
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<strong>Information Recording Techniques:</strong></div>
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There are three main types of information recording techniques. These are</div>
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• Process Charts</div>
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• Diagrams</div>
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• Templates</div>
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A <strong>Process Chart </strong>is a graphic means of representing the activities that occur during a manufacturing or servicing job.</div>
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There are several types of process charts. These can be divided into two groups.</div>
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(i) Those which are used to record a process sequence (i.e. series of events in the order in which they occur) but do not depict the events to time scale.</div>
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Charts falling in this group are</div>
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• Operation process chart</div>
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• Flow process chart – (man / material / equipment type)</div>
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• Operator chart (also called Two Handed Process Chart)</div>
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(ii) Those which record events in the sequence in which they occur on a time scale so that the interaction of related events can be more easily studied. Charts falling in this group are</div>
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• Multiple activity chart</div>
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• Simo chart</div>
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Diagrams. A diagram gives pictorial view of the layout of workplace or floor on which locations of different equipment, machines, etc. are indicated. The movement of subject (man or material) is then indicated on the diagram by a line or a string. The diagrams are valuable in highlighting the movement so that analyst can take steps to simplify or reduce it and thus effect saving in time or reduction in collisions / accidents.</div>
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Two types of diagrams are common: <a href="http://nptel.ac.in/courses/112107142/part1/lecture3.htm#">Flow diagram</a> and string diagram.</div>
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<strong>Templates and 3-D models:</strong></div>
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Two-dimensional cut outs made from thin card sheet representing machinery, furniture, etc. can be used for developing new layouts and methods. The templates may have pieces of permanent magnet attached to them, so that when used on iron board; they remain glued on the board whenever placed.</div>
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A scaled 3-D model of a working area helps easy understanding of lighting, ventilation, maintenance and safety aspects that may be important in a method. Such models are often of great value in demonstrating the advantages of the proposed changes to all concerned. However, their use is limited because of higher cost involved. Some computer softwares are available which help in constructing the layout and possibility of visualizing the working of process in a systematic way.</div>
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Before taking up descriptions of these charts or diagrams, it is necessary to know the various elements of work.</div>
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<strong>Elements of Work:</strong></div>
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There are five basic elements of work: Operation, Inspection, Transportation, Delay, and storage. <a href="http://nptel.ac.in/courses/112107142/part1/lecture3.htm#">Table</a> gives the definitions and symbols by which these elements are represented. Also given in the Table are examples of each element.</div>
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Sometimes, more than one element occur simultaneously. It is shown as combined element with combined symbol. Examples are “Operation in combination will inspection”, and “Inspection in combination with Transportation”.</div>
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<strong>Operation Process Chart:</strong></div>
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An <a href="http://nptel.ac.in/courses/112107142/part1/lecture3.htm#">operation process chart</a> provides the chronological sequence of all operations and inspections that occur in a manufacturing or business process. It also shows materials used and the time taken by operator for different elements of work. Generally a process chart is made for full assembly, that is, it shows all the operations and inspections that occur from the arrival of raw material to the packaging of the finished product.</div>
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<strong>Flow Process Chart:</strong></div>
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A flow process chart is used for recording greater detail than is possible in an operation process chart. It is made for each component of an assembly rather than for the whole assembly.</div>
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A flow process chart shows a complete process in terms of all the elements of work. There are two main types of flow charts: <a href="http://nptel.ac.in/courses/112107142/part1/lecture3.htm#">product or material type</a>, and the <a href="http://nptel.ac.in/courses/112107142/part1/lecture3.htm#">operator type</a> . The product type records the details of the events that occur to a product or material, while the operator flow chart details how a person performs an operational sequence.</div>
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An important and valuable feature of this chart is its recording of non-productive hidden costs, such as delays, temporary storages, unnecessary inspections, and unnecessary long distances traveled. When the time spent on these non productive activities is highlighted, analyst can take steps to minimize it and thus reduce costs.</div>
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<strong><a href="http://nptel.ac.in/courses/112107142/part1/lecture3.htm#">Operator Process Chart</a> :</strong></div>
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It is also called Left Hand – Right Hand chart and shows the activities of hands of the operator while performing a task. It uses four elements of hand work: Operation, Delay (Wait), Move and Hold. Its main advantage lies in highlighting un-productive elements such as unnecessary delay and hold so that analyst can take measures to eliminate or shorten them.</div>
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<strong>Multiple Activity Chart:</strong></div>
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<a href="http://nptel.ac.in/courses/112107142/part1/lecture3.htm#">Worker-Machine process chart </a>and gang process chart fall in the category of multiple activity charts. A worker-machine chart is used for recording and analyzing the working relationship between operator and machine on which he works. It is drawn to time scale. Analysis of the chart can help in better utilization of both worker and machine time. The possibility of one worker attending more than one machine is also sought from the use of this chart.</div>
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A gang process chart is similar to worker-machine chart, and is used when several workers operate one machine. The chart helps in exploring the possibility of reducing both the operator time and idle machine time.</div>
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<strong>Simo Chart:</strong></div>
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A <a href="http://nptel.ac.in/courses/112107142/part1/lecture3.htm#">Simo chart </a>is another Left-Hand Right-Hand chart with the difference that it is drawn to time scale and in terms of basic motions called therbligs. It is used when the work cycle is highly repetitive and of very short duration.</div>
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<strong>CRITICAL EXAMINATION</strong></div>
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Critical examination of the information recorded about the process in charts / diagrams is the most important phase of the method study. In this, each element of the work, as presently being done and recorded on the chart is subjected to a systematic and progressive series of questions with the purpose of determining true reasons for which it is done. Based on the reasons, improvements are found and adopted into a new method, called better method. This examination, thus requires exhaustive collaboration with everyone whose contribution can prove useful, and also full use of all available sources of technical information. The use of questioning technique reduces the possibility of missing any information which may be useful for the development of better method.</div>
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A popular procedure of carrying out critical examination uses two sets of questions: Primary questions (answers to these show up the necessity of carrying out the activity), and Secondary questions (answers to these allow considerations to alternative methods of doing the activity). Selection of the best way of doing each activity is later determined to develop new method which is introduced as a standard practice.</div>
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A general-purpose set of primary and secondary questions is given below:</div>
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<strong>Primary Questions:</strong></div>
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<strong>1. Purpose. </strong>The need of carrying out the activity is challenged by the questions-What is achieved? Is it necessary? Why?</div>
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The answers to these questions determine whether the particular activity will be included in the proposals of new method for the process.</div>
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<strong>2. Means. </strong>The means of carrying out the activity are challenged by the questions- 'How is it done?' and 'Why that way'?</div>
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<strong>3. Place. </strong>The location of carrying out the activity is challenged by the questions- 'Where is it done'? and 'Why there'?</div>
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<strong>4. Sequence. </strong>The time of carrying out the activity is challenged by the questions- 'When is it done'? and 'Why then'?</div>
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<strong>5. Person. </strong>The level of skill and experience of the person performing the activity is challenged by the questions- 'Who does it'? and 'Why that person'?</div>
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The main object of the primary questions is to make sure that the reasons for every aspect of the presently used method are clearly understood. The answers to these questions should clearly bring out any part of the work which is unnecessary or inefficient in respect of means, sequence, person or place.</div>
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<strong>Secondary Questions:</strong></div>
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The aim of secondary questions is to arrive at suitable alternatives to the presently used method:</div>
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<strong>1. Purpose. </strong>If the answer to the primary question 'Is the activity necessary"? is convincingly 'Yes', alternatives to achieve the object of carrying nut the activity are considered by the question— 'What else could be done'?</div>
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<strong>2. Means. </strong>All the alternative means to achieve the object are considered by the question— 'How else could it be done'?</div>
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<strong>3. Place. </strong>Other places for carry ing out the activity are considered by the question— 'Where else could it be done'?</div>
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<strong>4. Sequence. </strong>The secondary question asked under this heading is— 'When else could it be clone'?</div>
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<strong>5. Person. </strong>The possibilities for carrying out the activity by other persons are considered by asking the question- 'Who else should do it' ?</div>
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This phase involves the search of alternative possibilities within the imposed restrictions of cost, volume of production, and the like. For this the method study man uses his own past experience with same or similar problems or refers to text books, handbooks, etc.</div>
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The answers to the following questions are then sought through evaluation of the alternatives.</div>
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'What should be done'?</div>
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'How should it be done'?</div>
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'Where should it be done'?</div>
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'When should it be done'? and</div>
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'Who should do it'?</div>
</blockquote>
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These answers form the basis of the proposals for the improved method. The evaluation phase requires the work study man to consider all the possibilities with respect to the four factors—economic, safety, work quality and human factors—the economic factor being the most important in most situations.</div>
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Economic considerations to any alternative refer to determination of 'How much will it cost'? and 'How much will it save'? The purpose of evaluating safety factor is to ensure that the alternative selected shall not make the work less safe. The evaluation of quality factor shall determine whether the alternative selected shall make for better product quality or quality control.</div>
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And lastly human factors considerations shall ensure that the new method will be interesting, easy to learn, safe, less monotonous and less fatiguing to the operator.</div>
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<a href="http://nptel.ac.in/courses/112107142/part1/lecture4.htm#">Figure</a> shows a sample sheet used for critical examination the use of which can be quite helpful in this phase of method study.</div>
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<strong>Developing Better Method:</strong></div>
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With the present method or procedure for the job in mind, the application of ‘critical analysis' highlights the essential part of the job, for which alternative ways for its carrying out are developed .</div>
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When developing alternative ways for doing a task the following may be considered.</div>
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• Where and how to use ‘man' in the process?</div>
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• What better work procedure be adopted?</div>
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• What better equipment be used?</div>
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• What better layout of work station, shop or factory be used?</div>
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In deciding whether a particular element of work (operation, inspection, or transportation) be carried out manually or with the help of a device, method study engineer must be well aware of things which man cannot do or does in inferior fashion than machine. Examples of such things are:</div>
<ol type="a">
<li class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">Exert large amount of force, as needed in metal cutting.</li>
<li class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">Exert force precisely or smoothly at a fixed rate as needed in metal forming.</li>
<li class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">Do high speed computations of complex nature.</li>
<li class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">Perform repetitive tasks without suffering from side effects like boredom, fatigue, etc.</li>
<li class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">Move at high speeds for hours together.</li>
<li class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">Carry out several tasks simultaneously.</li>
<li class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">Respond fast to frequently changing control signals.</li>
<li class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">Perform satisfactorily in an environment where conditions relating to cold, heat, noise, dampness, etc. are extreme.</li>
</ol>
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In contrast, machines prove inferior generally when for carrying out a task it is necessary to</div>
<blockquote>
<ol class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;" type="a">
<li>Think creatively or inductively</li>
<li>Learn</li>
<li>Generalize</li>
<li>Cope will unexpected events.</li>
</ol>
</blockquote>
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In most cases, the relative roles of man and machine vary from one extreme end in which entire process is manual to the other extreme in which the process is completely mechanized with the presence of man only for monitoring, trouble shooting, maintenance, and the like.</div>
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Man is readily available and extremely flexible tool, who has the capability of doing a large number and type of tasks with learning and practice that is generally less expensive than the cost of creating devices for the same purpose. Man is therefore considered a strong competitor for low, medium and even some high volume production tasks.</div>
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When an activity is decided to be carried out manually, the best work procedure is determined by considering the principles of Motion Economy.</div>
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Equipped will the various alternative ways of carrying out essential elements of task, method study engineer has now to choose the best alternative method. He decides upon the criteria, which may be additional fixed costs involved, running cost, production rate, operator's fatigue, operator learning time, and the like. The weight to each criterion is fixed and performance is predicted of each alternative with respect to each criteria. The one which gets the maximum points is selected for adoption as a standard method.</div>
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Detailed specifications of this method are prepared with the description of procedure, workplace layout and material/equipment to be used. This is important for</div>
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• Communication of the proposed work method to those responsible for its approval</div>
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• Communication of the proposed method to those concerned with its installation, for example instructors and supervisors who are actually responsible for instructions to operators and setting up the machinery and work place layouts.</div>
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• Official record of the work method.</div>
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<strong>Installation of Improved Method:</strong></div>
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When the proposals of the improved method for a job are approved by the management of the company, the next step is to put this method into practice. Installation of method requires necessary prior preparation for which the active support of everyone concerned is very important.</div>
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The activities of the installation phase include:</div>
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1. Gaining acceptance of the change by the workers involved and their representatives. The method change may affect the routine and paper work of wages, costs, planning, and even purchase department. It may require displacement of staff from one section to another of the organisation. Adjustments of this type need to be carried out very carefully so that the least possible hardship or inconvenience is caused.</div>
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2. Retraining the workers. The extent to which workers need retraining will depend on the nature of the job and the changes involved. It is much more for those jobs which have a high degree of manual dexterity and where the workers have been doing the work by traditional methods. The use of films demonstrating the advantages of new method as compared to traditional one are often very useful in retraining the workers.</div>
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3. Arranging the requirements of the new method. This involves -</div>
<blockquote>
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(i) arranging the necessary plant, tools and equipment at all the workplaces,</div>
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(ii) arranging building-up of necessary stocks of new raw materials, and running-down of old stocks,</div>
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(iii) checking up the availability and continuity of all supplies and services, and</div>
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(iv) arranging any clerical records which may be required for purposes of control and comparison.</div>
</blockquote>
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4. Taking other necessary actions. These will depend upon situation to situation. For example, if changes in working hours are involved, necessary instructions should be passed on to auxiliary services such as transport, canteen, water supply, etc. If change in wages is involved, information concerning the date of installation must reach the costing department. Necessary instructions should be passed on to every one concerned about the time table for the installation of the change in method.</div>
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5. Giving a trial run to the new method. It is important that all departments affected by the change are represented at the rehearsal. It is often advantageous to conduct the rehearsal while the old method is still operating. It should usually take place outside normal working hours; say at week-end or at holiday time so that there is no interference with normal production. The suggestions for minor variations in the proposed method if they are worth while and cost effective should be accepted and incorporated.</div>
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It is obvious that the method analyst has to be extra tactful and keep restraint throughout the period of installation. The installation is considered complete when the new method starts running smoothly.</div>
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<strong>Follow-up:</strong></div>
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The work of method study man is not complete with the installation of the improved method; the maintenance of the new method in its specified form is also part of his activities. The main aim of maintenance of the new method is to ensure that the workers do not slip back into old method, or introduce elements which are not part of the proposed method.</div>
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For effective maintenance it is important to define and specify the new method very clearly. An operator chart giving adequate details of the tools, equipment, and workplace layout and operator-motion pattern is often helpful.</div>
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The workers have tendencey to drift away from the method laid down. The purpose of the method-maintenance is to check this tendency. But if it is found that the change from the method specified is in fact an improvement which can be made in the method, this should be officially incorporated.</div>
</div>
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<strong>Motion Study</strong></div>
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Motion study is a technique of analyzing the body motions employed in doing a task in order to eliminate or reduce ineffective movements and facilitates effective movements. By using motion study and the principles of motion economy the task is redesigned to be more effective and less time consuming.</div>
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The Gilbreths pioneered the study of manual motions and developed basic laws of motion economy that are still relevant today. They were also responsible for the development of detailed motion picture studies, termed as Micro Motion Studies, which are extremely useful for analyzing highly repetitive manual operations. With the improvement in technology, of course, video camera has replaced the traditional motion picture film camera.</div>
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In a broad sense, motion study encompasses micro motion study and both have the same objective: job simplification so that it is less fatiguing and less time consuming. While motion study involves a simple visual analysis, micro motion study uses more expensive equipment. The two types of studies may be compared to viewing a task under a magnifying glass versus viewing the same under a microscope. The added detail revealed by the microscope may be needed in exceptional cases when even a minute improvement in motions matters, i.e. on extremely short repetitive tasks.</div>
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Taking the cine films @ 16 to 20 frames per second with motion picture camera, developing the film and analyzing the film for micro motion study had always been considered a costly affair. To save on the cost of developing the film and the cost of film itself, a technique was used in which camera took only 5 to 10 frames per minute. This saved on the time of film analysis too. In applications where infrequent shots of camera could provide almost same information, the technique proved fruitful and acquired the name Memo Motion Study.</div>
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Traditionally, the data from micro motion studies are recorded on a Simultaneous Motion (simo) Chart while that from motion studies are recorded on a Right Hand - Left Hand Process Chart.</div>
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<strong>Therbligs</strong></div>
<div align="justify">
On analysing the result of several motion studies conducted, Gilbreths concluded that any work can be done by using a combination of some or all of 17 basic motions, called Therbligs (Gilbreth spelled backward). These can be classified as effective therbligs and ineffective therbligs. Effective therbligs take the work progress towards completion. Attempts can be made to shorten them but they cannot be eliminated. Ineffective therbligs do not advance the progress of work and therefore attempts should be made to eliminate them by applying the Principles of Motion Economy. <a href="http://nptel.ac.in/courses/112107142/part1/lecture6.htm#">Table</a>gives different therbligs along with their symbols and descriptions.</div>
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<strong>SIMO Chart</strong></div>
<div align="justify">
It is a graphic representation of an activity and shows the sequence of the therbligs or group of therbligs performed by body members of operator. It is drawn on a common time scale. In other words, it is a two-hand process chart drawn in terms of therbligs and with a time scale, see <a href="http://nptel.ac.in/courses/112107142/part1/lecture6.htm#">Figure</a>.</div>
<div align="justify">
Making the Simo Chart. A video film or a motion picture film is shot of the operation as it is carried out by the operator. The film is analyzed frame by frame. For the left hand, the sequence of therbligs (or group of therbligs) with their time values are recorded on the column corresponding to the left hand. The symbols are added against the length of column representing the duration of the group of therbligs. The procedure is repeated for the right hand and other body members (if any) involved in carrying out the operation.</div>
<div align="justify">
It is generally not possible to time individual therbligs. A certain number of therbligs may be grouped into an element large enough to be measured as can be seen in <a href="http://nptel.ac.in/courses/112107142/part1/lecture6.htm#">Figure</a>.</div>
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<strong>Uses of Simo Chart</strong></div>
<div align="justify">
<div style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
From the analysis shown about the motions of the two hands (or other body members) involved in doing an operation, inefficient motion pattern can be identified and any violation of the principle of motion economy can be easily noticed. The chart, therefore, helps in improving the method of doing an operation so that balanced two-handed actions with coordinated foot and eye motions can be achieved and ineffective motions can be either reduced or eliminated. The result is a smoother, more rhythmic work cycle that keeps both delays and operator fatigue to the minimum extent.</div>
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<strong>Cycle graph and Chrono cycle graph</strong></div>
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These are the techniques of analyzing the paths of motion made by an operator and were originally developed by the Gilbreths. To make a cycle graph , a small electric bulb is attached to the finger, hand, or any other part of the body whose motion is to be recorded. By using still photography, the path of light of bulb (in other words, that of the body member) as it moves through space for one complete cycle is photographed. The working area is kept relatively less illuminated while photograph is being taken. More than one camera may be used in different planes to get more details. After the film is developed, the resulting picture (cycle graph) shows a permanent record of the motion pattern employed in the form of a closed loop of white continuous line with the working area in the background. A cycle graph does not indicate the direction or speed of motion.</div>
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It can be used for</div>
<div align="justify">
<ul class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
<li>Improving the motion pattern, and</li>
<li>Training purposes in that two cycle graphs may be shown with one indicating a better motion pattern than the other.</li>
</ul>
</div>
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The chrono cycle graph is similar to the cycle graph, but the power supply to the bulb is interrupted regularly by using an electric circuit. The bulb is thus made to flash. The procedure for taking photograph remains the same. The resulting picture (chrono cycle graph), instead of showing continuous line of motion pattern, shows short dashes of line spaced in proportion to the speed of the body member photographed. Wide spacing would represent fast moves while close spacing would represent slow moves. The jumbling of dots at one point would indicate fumbling or hesitation of the body member. A chrono cycle graph can thus be used to study the motion pattern as well as to compute velocity, acceleration and retardation experienced by the body member at different locations. Figures show a cycle graph and a chrono cycle graph.</div>
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The world of sports has extensively used this analysis tool, updated to video, for the purpose of training in the development of form and skill.</div>
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<strong>Principles of Motion Economy:</strong></div>
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These principles can be considered under three different groups.</div>
<blockquote style="text-align: start;">
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• Those related to the use of the human body.</div>
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• Those related to the workplace arrangement, and</div>
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• Those related to the design of tools and equipment.</div>
</blockquote>
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<strong>1. Principles related to the use of human body:</strong></div>
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(i) Both hands should begin and end their basic divisions of activity simultaneously and should not be idle at the same instant, except during the rest periods.</div>
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(ii) The hand motions should be made symmetrically and simultaneously away from and toward the centre of the body.</div>
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• Momentum should be employed to assist the worker wherever possible, and it should be reduced to a minimum if it must be overcome by muscular effort.</div>
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• Continuous curved motions should be preferred to straight line motions involving sudden and sharp changes in the direction.</div>
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• The least number of basic divisions should be employed and these should be confined to the lowest practicable classifications. These classifications, summarized in ascending order of time and fatigue expended in their performance, are:</div>
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• Finger motions</div>
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• Finger and wrist motions.</div>
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• Finger, wrist, and lower arm motions.</div>
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• Finger, wrist, lower arm, and upper arm motions.</div>
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• Finger, wrist, lower arm, upper arm motions and body motions.</div>
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• Work that can be done by the feet should be arranged so that it is done together with work being done by the hands. It should be recognized, however, that it is difficult to move the hand and foot simultaneously.</div>
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• The middle finger and the thumb should be used for handling heavy loads over extended periods as these are the strongest working fingers. The index finger, fourth finger, and little finger are capable of handling only light loads for short durations.</div>
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• The feet should not be employed for operating pedals when the operator is in standing position.</div>
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• Twisting motions should be performed with the elbows bent.</div>
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• To grip tools, the segment of the fingers closed to the palm of the hand should be used.</div>
</blockquote>
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<strong>2. Principles related to the arrangement and conditions of workplace:</strong></div>
<blockquote style="text-align: start;">
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• Fixed locations should be provided for all tools and materials so as to permit the best sequence and eliminate <em>search </em>and <em>select </em>.</div>
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• Gravity bins and drop delivery should be used to reduce <em>reach </em>and <em>move </em>times. Use may be made of ejectors for removing finished parts.</div>
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• All materials and tools should be located within the normal working area in both the vertical and horizontal plane ( see <a href="http://nptel.ac.in/courses/112107142/part1/lecture7.htm#">Figure</a> ), and as close to the point of use as possible.</div>
<div align="justify" class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
• Work table height should permit work by the operator in alternately sitting and standing posture.</div>
<div align="justify" class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
• Glare-free adequate illumination, proper ventilation and proper temperature should be provided.</div>
<div align="justify" class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
• Dials and other indicators should be patterned such that maximum information can be obtained in minimum of time and error.</div>
</blockquote>
<div align="justify" class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
<strong>3. Principles related to the design of tools and equipment:</strong></div>
<blockquote style="text-align: start;">
<div align="justify" class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
• Use colour, shape or size coding to maximize speed and minimize error in finding controls.</div>
<div align="justify" class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
• Use simple on/off, either/or indicators whenever possible. If simple on/off indicator is not sufficient, use qualitative type indicator, and use quantitative type indicator only when absolutely essential.</div>
<div align="justify" class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
• All levers, handles, wheels and other control devices should be readily accessible to the operator and should be designed so as to give the best possible mechanical advantage and utilize the strongest available muscle group. Their direction of motion should conform to stereo-typed reactions.</div>
<div align="justify" class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
• Use quick acting fixture to hold the part or material upon which the work is being performed.</div>
<div align="justify" class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
• Use stop guides to reduce the control necessary in positioning motions.</div>
<div align="justify" class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
• Operating, set-up and emergency controls should be grouped according to the function.</div>
</blockquote>
<div align="justify" class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
<strong>Design of Workplace Layout</strong></div>
<div align="justify" class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
The design of workplace layout involves the following</div>
<div align="justify">
<ul class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
<li>Determination of work surface height</li>
<li>Design of operator chair (if work is to be done in sitting posture), or allowing the use of antifatigue mats for standing operator</li>
<li>Determination of location of tools, materials, controls, displays and other devices.</li>
</ul>
</div>
<div align="justify" class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
We shall consider these briefly.</div>
<div align="justify" class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
<strong>Work Place Height</strong></div>
<div align="justify" class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
This should be decided from the standpoint of comfortable working posture for the operator. Generally, it is equal to the elbow height of operator whether work is done in standing or sitting posture. However, for work involving lifting of heavy parts, it is useful to lower the work surface height by as much as 20 cm. This would reduce the fatigue to the trunk of operator. Similarly, it may be useful to raise the work surface height when work involves visual examination of minute details of fine parts. This would reduce the eye fatigue to the operator. Alternatively, the work surface may be inclined by 15 degrees or so. Work surface height may also be made adjustable in situations where operator is permitted to do work in alternatively sitting and standing postures.</div>
<div align="justify" class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
<strong>Design of Operator Chair</strong></div>
<div align="justify" class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
A seated posture is better than standing posture from the standpoint of stress reduction on the feet and the overall energy expenditure. A well-designed seat should</div>
<div align="justify">
<ul class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
<li>Provide trunk stabilization so that a good posture is maintained,</li>
<li>Permit change of posture, and</li>
<li>Not unduly press the thigh tissues.</li>
</ul>
</div>
<div align="justify" class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
This requires the use of ergonomic considerations and anthropometric dimensions of operator so that appropriate dimensions are chosen for the following features of chair</div>
<blockquote style="text-align: start;">
<div align="justify" class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
(i) Seat Height</div>
<div align="justify" class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
(ii) Seat Depth</div>
<div align="justify" class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
(iii) Seat Width</div>
<div align="justify" class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
(iv) Seat Inclination</div>
<div align="justify" class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
(v) Arm Rests</div>
<div align="justify" class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
(vi) Back Rest</div>
<div align="justify" class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
(vii) Foot Rest</div>
</blockquote>
<div align="justify" class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
It is necessary to provide adjustability, particularly with respect to seat height, in order that the same seat (or chair) is useable by many operators doing same job.</div>
<div align="justify" class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
Standing for long periods of time on a cemented floor is fatiguing. If operator has to work only in standing posture, it is essential to provide resilient anti-fatigue floor mats. Such mats allow small muscle contractions in the legs and force the blood to keep circulating.</div>
<div align="justify" class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
<strong>Determination of location of tools, materials, controls, displays and other devices.</strong></div>
<div align="justify" class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
We all know that greater the distance through which operator moves his body member while doing work, larger is the requirement of muscular effort, control and time. This means that all tools, materials, controls, etc need to be located within close reach of the operator. In this context, two areas can be identified: normal working area and maximum working area. <a href="http://nptel.ac.in/courses/112107142/part1/lecture7.htm#">Figure</a> identifies these areas in horizontal and vertical planes.</div>
<div align="justify" class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
Within these areas, all tools, materials, controls, displays and other devices must be located on the basis of any of the following principles.</div>
<div align="justify" class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
(i) Importance Principle. According to this principle, the most important item or group of items is first located within the normal area in the best position. The next important component item or group of items is then selected and located in the best location within the remaining area. In this way, all the items are located.</div>
<div align="justify" class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
(ii) Frequency of Use Principle. According to this principle, the item with the greatest frequency of use has the highest priority for location at the optimum position. From within the remaining items to be located in the remaining area, the same principle can then be applied repetitively.</div>
<div align="justify" class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
(iii) Functional Principle. This principle provides for grouping of items according to their function. For instance, all controls that are functionally related may be grouped together and located at one place.</div>
<div align="justify" class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
(iv) Sequence of Use Principle. According to this principle, items are located according to sequence of their use. For illustration, let us consider the case of assembly. As we know, an assembly is made by assembling the sub-assemblies in a specific order. From motion economy or production efficiency point of view, it would be better if sub-assemblies and other items are located in the sequence in which they are to be used in assembly.</div>
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Further, for better productivity, it is important that location of all tools, materials and controls be fixed so that their "search" and “select" is minimized</div>
<div align="justify">
<strong>Work Measurement</strong></div>
<div align="justify">
Work measurement refers to the estimation of standard time for an activity, that is the time allowed for completing one piece of job by using the prescribed method. Standard time can be defined as the time taken by an average experienced worker for the job with provisions for delays beyond the worker's control.</div>
<div align="justify">
There are several techniques used for estimation of standard time in industry. These include time study, work sampling, standard data, and predetermined motion time system.</div>
<div align="justify">
<strong>Applications:</strong></div>
<div align="justify">
Standard times for operations are useful for several applications in industry, like</div>
<div align="justify">
• Estimating material, machinery, and equipment requirements.</div>
<div align="justify">
• Estimating production cost per unit as an input to</div>
<ul>
<li>Preparation of budgets</li>
<li>Determination of selling price</li>
<li>Make or buy decision</li>
</ul>
<div align="justify">
• Estimating manpower requirements.</div>
<div align="justify">
• Estimating delivery schedules and planning the work</div>
<div align="justify">
• Balancing the work of operators working in a group.</div>
<div align="justify">
• Estimating performance of workers and using that as the basis for incentive payment to those direct and indirector labor who show greater productivity.</div>
<div align="justify">
We will study some of the popular techniques of work measurement.</div>
<div align="justify">
TIME STUDY. It is the most versatile and the most widely used technique of work measurement.</div>
<div align="justify">
<strong>Definition:</strong></div>
<div align="justify">
Time study is a technique to estimate the time to be allowed to a qualified and well-trained worker working at a normal pace to complete a specified task by using specified method.</div>
<div align="justify">
This technique is based on measuring the work content of the task when performed by the prescribed method, with the allowance for fatigue and for personal and unavoidable delays.</div>
<div align="justify">
<strong>Time Study Procedure:</strong></div>
<div align="justify">
The procedure for time study can best be described step-wise, which are self explanatory.</div>
<div align="justify">
<strong>Step 1: </strong>Define objective of the study. This involves statement of the use of the result, the precision desired, and the required level of confidence in the estimated time standards.</div>
<div align="justify">
<strong>Step 2: </strong>Verify that the standard method and conditions exist for the operation and the operator is properly trained. If need is felt for method study or further training of operator, the same may be completed before starting the time study.</div>
<div align="justify">
<strong>Step 3: </strong>Select operator to be studied if there are more than one operator doing the same task.</div>
<div align="justify">
<strong>Step 4: </strong>Record information about the standard method, operation, operator, product, equipment, and conditions on the Time Study observation sheet.</div>
<div align="justify">
<strong>Step 5: </strong>Divide the operation into reasonably small elements, and record them on the Time Study observation sheet.</div>
<div align="justify">
<strong>Step 6: </strong>Time the operator for each of the elements. Record the data for a few number of cycles on the Time Study observation sheet. Use the data to estimate the total number of observations to be taken.</div>
<div align="justify">
<strong>Step 7: </strong>Collect and record the data of required number of cycles by timing and rating the operator.</div>
<div align="justify">
<strong>Step 8: </strong>Calculate the representative watch time for each element of operation. Multiply it by the rating factor to get normal time.</div>
<div align="justify">
Normal time = Observed time x Rating factor</div>
<div align="justify">
Calculate the normal time for the whole operation by adding the normal time of its various elements.</div>
<div align="justify">
<strong>Step 9: </strong>Determine allowances for fatigue and various delays.</div>
<div align="justify">
<strong>Step 10: </strong>Determine standard time of operation.</div>
<div align="justify">
Standard time = Normal time + allowances</div>
<div align="justify">
<strong>Selection of job for Time Study</strong></div>
<div align="justify">
Time Study is conducted on a job</div>
<blockquote>
<div align="justify">
• which has not been previously time-studied.</div>
<div align="justify">
• for which method change has taken place recently.</div>
<div align="justify">
• for which worker(s) might have complained as having tight time standards.</div>
</blockquote>
<div align="justify">
<strong>Selection of Worker for Time Study</strong></div>
<div align="justify">
The selection of worker for time study is a very important factor in the success of the study. If there is only one person on the job, as usually is, then there is no choice. But if more than one person is performing the same operation, the time study man may time one or more of the workers. If all the workers are using the same method for doing the job and there is different in the rate of their doing it, it is necessary to select a suitable worker for the study. The worker on which time study should be conducted must</div>
<div align="justify">
<ul>
<li>have necessary skill for the job.</li>
<li>have sufficient experience with the given method on the job (that is, he should have crossed the learning stage).</li>
<li>be an ‘average' worker as regards the speed of working.</li>
<li>be temperamentally suited to the study (those who can't work in normal fashion when watched, are not suitable for the study).</li>
<li>have knowledge about the purpose of study.</li>
</ul>
</div>
<div align="justify">
<strong>Time Study Equipment</strong></div>
<div align="justify">
The following equipment is needed for time study work.</div>
<blockquote>
<div align="justify">
• Timing device</div>
<div align="justify">
• Time study observation sheet</div>
<div align="justify">
• Time study observation board</div>
<div align="justify">
• Other equipment</div>
</blockquote>
<div align="justify">
<strong>Timing Device. </strong>The stop watch ( see <a href="http://nptel.ac.in/courses/112107142/part1/lecture8.htm#">Figure </a>) is the most widely used timing device used for time study, although electronic timer is also sometimes used. The two perform the same function with the difference that electronic timer can measure time to the second or third decimal of a second and can keep a large volume of time data in memory.</div>
<div align="justify">
<strong>Time Study Observation Sheet. </strong>It is a printed form with spaces provided for noting down the necessary information about the operation being studied, like name of operation, drawing number, and name of the worker, name of time study person, and the date and place of study. Spaces are provided in the form for writing detailed description of the process (element-wise), recorded time or stop-watch readings for each element of the process, performance rating(s) of operator, and computation. <a href="http://nptel.ac.in/courses/112107142/part1/lecture8.htm#">Figure</a> shows a typical time study observation sheet.</div>
<div align="justify">
<strong>Time Study Board. </strong>It is a light -weight board used for holding the observation sheet and stopwatch in position. It is of size slightly larger than that of observation sheet used. Generally, the watch is mounted at the center of the top edge or as shown in <a href="http://nptel.ac.in/courses/112107142/part1/lecture8.htm#">Figure</a> near the upper right-hand corner of the board. The board has a clamp to hold the observation sheet. During the time study, the board is held against the body and the upper left arm by the time study person in such a way that the watch could be operated by the thumb/index finger of the left hand. Watch readings are recorded on the observation sheet by the right hand.</div>
<div align="justify">
<strong>Other Equipment. </strong>This includes pencil, eraser, device like tachometer for checking the speed, etc.</div>
<div align="justify">
<strong>Dividing Work into Short Elements</strong></div>
<div align="justify">
Timing a complete task as one element is generally not satisfactory. For the purpose of time study the task is normally broken<br />into short elements and each element is timed separately, for the following<br />reasons:</div>
<div align="justify">
(1) To separate unproductive part of task from the productive one.</div>
<div align="justify">
(2) To improve accuracy in rating. The worker may not work at the<br />same speed throughout the cycle. He may perform some elements faster and<br />some slower. Breaking of task into short elements permits rating of each<br />element separately which is more realistic than just rating once for the complete<br />cycle.</div>
<div align="justify">
(3) To identify elements causing high fatigue. Breaking of task into short elements permits giving appropriate rest allowances to different elements.</div>
<div align="justify">
(4) To have detailed job specifications. This helps in detection of any variation in the method that may occur after the time standard is established.</div>
<div align="justify">
(5) To prepare standard data for repeatedly occurring elements.</div>
<div align="justify">
The following guidelines should be kept in mind while dividing a task into elements.</div>
<div align="justify">
(1) The elements should be of as short duration as can be accurately timed. (This in turn, depends on the skill of the time study man, method of timing and recording, and many other factors. Generally, with the stop watch, elements of duration less than 0.03 to 0.05 minute are difficult to time accurately. The elements should not normally be longer than 0.40 min.).</div>
<div align="justify">
(2) Manually performed elements should be separated from machine paced elements. (Time for machine paced elements can be determined by calculation). Machine elements are not rated against a normal. This rule also helps in recognition of delays.</div>
<div align="justify">
(3) Constant elements should be separated from variable elements.<br />(Constant elements are those elements which are independent of the size, weight,<br />length, or shape of the workpiece. For example, the time to pick screw driver<br />from its place and bring it to the head of a screw is constant, whereas the time<br />to tighten or loosen the screw is a variable, depending upon the length and<br />size of the screw).</div>
<div align="justify">
(4) The beginnings and endings of elements should be easily distinguishable. These should preferably be associated with some kind of sound.</div>
<div align="justify">
(5) Irregular elements, those not repeated in every cycle, should be separated from regular elements. For example, if the jig is cleaned off after every ten parts produced, "cleaning" is an irregular element, and its time should be spread over ten cycles.</div>
<div align="justify">
(6) Unnecessary motions and activities should be separated from those considered essential.</div>
<div align="justify">
(7) Foreign or accidental elements should be listed separately. Such elements are generally of non-repetitive type.</div>
<div align="justify">
<strong>Number of cycles to be timed.</strong></div>
<div align="justify">
The following general principles govern the number of cycles to get the representative average cycle time.</div>
<div align="justify">
(1) Greater the accuracy desired in the results, larger should be the number of cycles observed.</div>
<div align="justify">
(2) The study should be continued through sufficient number of cycles so that occasional elements such as setting-up machine, cleaning of machine or sharpening of tool are observed for a good number of times.</div>
<div align="justify">
(3) Where more than one operator is doing the same job, short study (say 10 to 15 cycles) should be conducted on each of the several operators than one long study on a single operator.</div>
<div align="justify">
It is important that enough cycles are timed so that reliable average is obtained.</div>
<div align="justify">
Following techniques are used to determine the number of cycles to be timed.</div>
<div align="justify">
<strong>(i) Use of Tables: </strong>On the consideration of the cost of obtaining the data and the desired accuracy in results, most companies have prepared their own tables for the use of time study people, which indicate the number of cycles to be timed as a function of the cycle time and the frequency of occurrence of the job in the company. For example, one Company uses the <a href="http://nptel.ac.in/courses/112107142/part1/lecture8.htm#">Table</a> for such purposes.</div>
<div align="justify">
<strong>(ii) Statistical methods: </strong>On the basis of the requirements of the particular situation involved, <em>accuracy </em>and <em>confidence level </em>are decided (An accuracy of a confidence level of 95% is considered reasonable in most cases). A preliminary study is conducted in which some (say <em>N) </em>cycles are timed. Standard deviation o of these <em>(N) </em>observations is calculated as</div>
<div align="justify">
<img height="281" src="http://nptel.ac.in/courses/112107142/part1/image/ex7.gif" width="728" /></div>
<div align="justify">
<strong>(iii) Mundel Method:</strong> In this method the following steps are followed.</div>
<div align="justify">
<strong>Step 1. </strong>Take a few good watch readings of the work cycle. (Generally, 10 readings are taken if cycle time is less than 2 minutes, otherwise 5 readings).</div>
<div align="justify">
<strong>Step 2. </strong>Find the ratio <img align="absmiddle" height="36" src="http://nptel.ac.in/courses/112107142/part1/image/ex6.gif" width="34" />, where H and L are respectively the highest and the lowest value of the leading.</div>
<div align="justify">
<strong>Step 3. </strong>Corresponding to the value of the ratio, determine the number of observations from the <a href="http://nptel.ac.in/courses/112107142/part1/lecture8.htm#">Table</a>.</div>
<div align="justify">
<strong>Normal Performance</strong></div>
<div align="justify">
There is no universal concept of Normal Performance. However, it is generally defined as the working rate of an average qualified worker working under capable supervision but not under any incentive wage payment scheme. This rate of working is characterized by the fairly steady exertion of reasonable effort, and can be maintained day after day without undue physical or mental fatigue.</div>
<div align="justify">
The level of normal performance differs considerably from one company to another. What company a calls 100 percent performance, company B may call 80 percent, and company C may call 125 percent and so on. It is important to understand that the level that a company selects for normal performance is not critical but maintaining that level uniform among time study persons and constant with the passage of time within the company is extremely important.</div>
<div align="justify">
There are, of course, some universally accepted benchmark examples of normal performance, like dealing 52 cards in four piles in 0.5 minute, and walking at 3 miles per hour (4.83 km/hr). In order to make use of these benchmarks, it is important that a complete description about these be fully understood, like in the case of card dealing, what is the distance of each pile with respect to the dealer, technique of grasping, moving and disposal of the cards.</div>
<div align="justify">
<div style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
Some companies make use of video films or motion pictures for establishing what they consider as normal speed or normal rate of movement of body members. Such films are made of typical factory jobs with the operator working at the desired normal pace. These films are found to be useful in demonstrating the level of performance expected from the operators and also for training of time study staff.</div>
<div>
<div align="justify" class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px; font-weight: bold;">
Performance Rating</div>
<div align="justify" class="style2 style5" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
During the time study, time study engineer carefully observes the performance of the operator. This performance seldom conforms to the exact definition of normal or standard. Therefore, it becomes necessary to apply some 'adjustment' to the mean observed time to arrive at the time that the normal operator would have taken to do that job when working at an average pace. This 'adjustment' is called Performance Rating.</div>
<div align="justify" class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
Determination of performance rating is an important step in the work measurement procedure. It is based entirely on the experience, training, and judgment of the work-study engineer. It is the step most subjective and therefore is subject to criticism.</div>
<div align="justify" class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
Performance Rating can be defined as the procedure in which the time study engineer compares the performance of operator(s) under observation to the Normal Performance and determines a factor called Rating Factor.</div>
<div align="center" class="style2" style="font-size: 12px;">
<img height="37" src="http://nptel.ac.in/courses/112107142/part1/image/ex8.gif" width="238" /> <strong> </strong></div>
<span class="style2" style="font-size: 12px; text-align: start;"></span><span style="text-align: start;"></span><div align="justify" class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
<strong>System of Rating</strong></div>
<div align="justify" class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
There are several systems of rating the performance of operator on a job.</div>
<div align="justify" class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
These are:</div>
<div align="justify" class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
• Pace Rating</div>
<div align="justify" class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
• Westinghouse System of Rating</div>
<div align="justify" class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
• Objective Rating</div>
<div align="justify" class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
• Synthetic Rating</div>
<div align="justify" class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
A brief description of each rating method follows.</div>
<div align="justify" class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
<strong>Pace Rating</strong></div>
<div align="justify" class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
Under this system, operator's performance is evaluated by considering his rate of accomplishment of the work. The study person measures the effectiveness of the operator against the concept of normal performance and then assigns a percentage to indicate the ratio of the observed performance to normal or standard performance.</div>
<div align="justify" class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
In this method, which is also called the speed rating method, the time study person judges the operators speed of movements, i.e. the rate at which he is applying himself, or in other words "how fast" the operator performs the motions involved.</div>
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<strong>Westinghouse System of Rating</strong></div>
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This method considers four factors in evaluating the performance of operator: skill, effort, conditions, and consistency.</div>
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Skill may be defined as the proficiency at of an individual in following the given method. It is demonstrated by co-ordination of mind and hands. A person's skill in a given operation increases with his experience on the job, because increased familiarity with work brings speed, smoothness of motions and freedom from hesitations.</div>
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The Westinghouse system lists six classes of each factor. For instance the classes of skill are poor, fair, average, good, excellent and superskill, as given in a <a href="http://nptel.ac.in/courses/112107142/part1/lecture9.htm#">Table</a> . Each class has further two degrees. The time study person evaluates the skill displayed by the operator. And puts it in one of the six classes and also decides the degree in that class, higher or lower, i.e. 1 or 2. As equivalent % value of each class of skill is provided in the Table, the rating is translated into its equivalent percentage value, which ranges from +15 % (for super skill of higher degree) to -22 % (for poor skill of lower degree).</div>
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In a similar fashion, the ratings for effort, conditions, and consistency are given using the Table for each of the factors. By algebraically combining the ratings with respect to each of the four factors, the final performance-rating factor is estimated.</div>
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<strong>Objective Rating</strong></div>
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In this system, speed of movements and job difficulty are rated separately and the two estimates are combined into a single value. Rating of speed or pace is done as discussed earlier, and the rating of job difficulty is done by selecting adjustment factors corresponding to characteristics of operation with respect to (i) amount of body used, (ii) foot pedals, (iii) bimanual ness, (iv) eye-hand co-ordination, (v) handling requirements and (vi) weight handled or resistance encountered. Mundel and Danner have given <a href="http://nptel.ac.in/courses/112107142/part1/lecture9.htm#">Table</a> of % values (adjustment factors) for the effects of various difficulties in the operation performed.</div>
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For an operation under study, a numerical value for each of the six factors is assigned, and the algebraic sum of the numerical values called job difficulty adjustment factor is estimated.</div>
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The rating factor R can be expressed as</div>
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R = P x D</div>
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Where: P = Pace rating factor, and</div>
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D = Job difficulty adjustment factor.</div>
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<strong>Synthetic Rating</strong></div>
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This method of rating has two main advantages over other methods. These are (i) it does not rely on the judgment of time study person and (ii) it gives consistent results.</div>
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The time study is made as usual. Some manually controlled elements of the work cycle are selected. Using a PMT system (Pre-determined motion time system), the times for these selected elements are determined. The times of these elements as determined are compared with the actual observed times and the performance factor is estimated for each of the selected elements.</div>
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Performance or Rating Factor, R = P / A</div>
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Where P = Predetermined motion time of the element, and</div>
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A = Average actual observed time of the element.</div>
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The overall rating factor is the mean of rating factors determined for the selected elements. This is applied uniformly to all the manually controlled elements of the work cycle.</div>
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<strong>Example</strong></div>
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A work cycle has been divided into 8 elements and time study has been conducted. The average observed times for the elements are given in the following Table:</div>
<div align="justify" class="style5" style="font-family: Arial, Helvetica, sans-serif;">
<table align="center" border="1" bordercolor="#000000" cellpadding="0" cellspacing="0"><tbody>
<tr><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
Element No.</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
1</div>
<div align="center">
<br /></div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
2</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
3</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
4</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
5</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
6</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
7</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
8</div>
</td></tr>
<tr><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
Element Type</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
M</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
M</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
P</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
M</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
M</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
M</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
M</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
M</div>
</td></tr>
<tr><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
Average actual time (minutes)</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
0.14</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
0.16</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
0.30</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
0.52</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
0.26</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
0.45</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
0.34</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
0.15</div>
</td></tr>
</tbody></table>
</div>
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M = Manually Controlled, P = Power Controlled</div>
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Total observed time of work cycle = 2.32 min.</div>
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Suppose we select three elements 2, 5 and 8 (These must be manually controlled elements). By using some PMT system, suppose we determine the times of these elements as</div>
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<table align="center" border="1" bordercolor="#000000" cellpadding="0" cellspacing="0"><tbody>
<tr><td class="style2" style="font-size: 12px;" valign="top" width="148"><div align="center">
Elements No.</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="148"><div align="center">
2</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="148"><div align="center">
5</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="148"><div align="center">
8</div>
</td></tr>
<tr><td class="style2" style="font-size: 12px;" valign="top" width="148"><div align="center">
PMT System times (min)</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="148"><div align="center">
0.145</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="148"><div align="center">
0.255</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="148"><div align="center">
0.145</div>
</td></tr>
</tbody></table>
</div>
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Rating factor for element 2 = 0.145 / 0.16 = 90.62 %.</div>
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Rating factor for element 5 = 0.255 / 0.26 = 98.08 %.</div>
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Rating factor for element 8 = 0.145 / 0.15 = 96.66 %.</div>
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The mean of the rating factors of selected elements = 95.12 % or say 95 % is the rating factor that will be used for all the manual elements of the work cycle.</div>
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The normal time of the cycle can than be calculated as.</div>
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<table align="center" border="1" bordercolor="#000000" cellpadding="0" cellspacing="0"><tbody>
<tr><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
Element No.</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
1</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
2</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
3</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
4</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
5</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
6</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
7</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
8</div>
</td></tr>
<tr><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
Element Type</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
M</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
M</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
P</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
M</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
M</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
M</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
M</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
M</div>
</td></tr>
<tr><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
Average actual time (min)</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
0.14</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
0.16</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
0.30</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
0.52</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
0.26</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
0.45</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
0.34</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
0.15</div>
</td></tr>
<tr><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
PMT system time (min)</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
<br /></div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
0.145</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
<br /></div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
<br /></div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
0.255</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
<br /></div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
<br /></div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
0.145</div>
</td></tr>
<tr><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
Performance Rating Factor</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
95</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
95</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
100</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
95</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
95</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
95</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
95</div>
</td><td class="style2" style="font-size: 12px;" valign="top" width="66"><div align="center">
95</div>
</td></tr>
</tbody></table>
</div>
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Normal Cycle Time</div>
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= 0.95(0.14+0.16+0.52+0.26+0.45+0.34+0.15) +1.00(0.30)</div>
<div align="justify" class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
=1.92+0.30</div>
<div align="justify" class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
=2.22 minutes</div>
<div align="justify" class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
It is to be noted that power controlled (or machine-paced) elements are always given 100% rating.</div>
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<strong>Allowances</strong></div>
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The readings of any time study are taken over a relatively short period of time. The normal time arrived at, therefore, does not include unavoidable delay and other legitimate lost time, for example, in waiting for materials, tools or equipment; periodic inspection of parts; interruptions due to legitimate personal needs, etc. It is necessary and important that the time study person applies some adjustment, or allowances, to compensate for such losses so that fair time standard is established for the given job.</div>
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Allowances are generally applied to total cycle time as some percentage of it, but sometimes these are given separately for machine time as some % and for manual effort time some other %. However, no allowances are given for interruptions which may be due to factors which are within the operator's control or which are avoidable.</div>
<div align="justify" class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
Most companies allow the following allowances to their employees.</div>
<blockquote style="text-align: start;">
<div align="justify" class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
• Constant allowances (for personal needs and basic fatigue)</div>
<div align="justify" class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
• Delay Allowance (for unavoidable delays)</div>
<div align="justify" class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
• Fatigue Allowance (for job dependent fatigue)</div>
<div align="justify" class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
• Personal Allowance</div>
<div align="justify" class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
• Special Allowance <strong> </strong></div>
</blockquote>
<div align="center" class="style2" style="font-size: 12px;">
<span class="style6" style="font-family: Arial, Helvetica, sans-serif;"><strong></strong></span><strong><img height="358" src="http://nptel.ac.in/courses/112107142/part1/image/chart1.jpg" width="542" /></strong></div>
<div align="justify" class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
<strong>Delay Allowance</strong></div>
<div align="justify" class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
This time allowance is given to operator for the numerous unavoidable delays and interruptions that he experiences every day during the course of his work. These interruptions include interruptions from the supervisor, inspector, planners, expediters, fellow workers, production personnel and others. This allowance also covers interruptions due to material irregularities, difficulty in maintaining specifications and tolerances, and interference delays where the operator has to attend to more than one machine.</div>
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<strong>Fatigue Allowance</strong></div>
<div align="justify" class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
This allowance can be divided into two parts: (i) basic fatigue allowance and (ii) variable fatigue allowance. The basic fatigue allowance is given to the operator to compensate for the energy expended for carrying out the work and to alleviate monotony. For an operator who is doing light work while seated, under good working conditions and under normal demands on the sensory or motor system, a 4% of normal time is considered adequate. This can be treated as a constant allowance.</div>
<div align="justify" class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
The magnitude of variable fatigue allowance given to the operator depends upon the severity of conditions, which cause extra (more than normal) fatigue to him. As we know, fatigue is not homogeneous. It ranges from strictly physical to purely psychological and includes combinations of the two. On some people it has a marked effect while on others, it has apparently little or no effect. Whatever may be the kind of fatigue-physical or mental, the result is same-it reduces the work output of operator. The major factors that cause more than just the basic fatigue includes severe working conditions, especially with respect to noise, illumination, heat and humidity; the nature of work, especially with respect to posture, muscular exertion and tediousness, and like that.</div>
<div align="justify" class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
It is true that in modern industry, heavy manual work, and thus muscular fatigue is reducing day by day but mechanization is promoting other fatigue components like monotony and mental stress. Because fatigue in totality cannot be eliminated, proper allowance has to be given for adverse working conditions and repetitiveness of the work.</div>
<div align="justify" class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
<strong>Personal Allowance</strong></div>
<div align="justify" class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
This is allowed to compensate for the time spent by worker in meeting the physical needs, for instance a periodic break in the production routine. The amount of personal time required by operator varies with the individual more than with the kind of work, though it is seen that workers need more personal time when the work is heavy and done under unfavorable conditions.</div>
<div align="justify" class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
The amount of this allowance can be determined by making all-day time study or work sampling. Mostly, a 5 % allowance for personal time (nearly 24 minutes in 8 hours) is considered appropriate.</div>
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<strong>Special Allowances</strong></div>
<div align="justify" class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
These allowances are given under certain special circumstances. Some of these allowances and the conditions under which they are given are:</div>
<div align="justify" class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
Policy Allowance: Some companies, as a policy, give an allowance to provide a satisfactory level of earnings for a specified level of performance under exceptional circumstance. This may be allowed to new employees, handicap employees, workers on night shift, etc. The value of the allowance is typically decided by management.</div>
<div align="justify" class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
Small Lot Allowance: This allowance is given when the actual production period is too short to allow the worker to come out of the initial learning period. When an operator completes several small-lot jobs on different setups during the day, an allowance as high as 15 percent may be given to allow the operator to make normal earnings.</div>
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Training Allowance: This allowance is provided when work is done by trainee to allow him to make reasonable earnings. It may be a sliding allowance, which progressively decreases to zero over certain length of time. If the effect of learning on the job is known, the rate of decrease of the training allowance can be set accordingly.</div>
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Rework Allowance: This allowance is provided on certain operation when it is known that some percent of parts made are spoiled due to factors beyond the operator's control. The time in which these spoiled parts may be reworked is converted into allowance.</div>
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Different organizations have decided upon the amount of allowances to be given to different operators by taking help from the specialists / consultants in the field and through negotiations between the management and the trade unions. ILO has given its recommendations about the magnitude of various allowances, as shown in <a href="http://nptel.ac.in/courses/112107142/part1/lecture9.htm#">Table</a>.</div>
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<strong>Example:</strong></div>
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In making a time study of a laboratory technician performing an analysis of processed food in a canning factory, the following times were noted for a particular operation.</div>
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<table align="center" border="1" bordercolor="#000000" cellpadding="0" cellspacing="0"><tbody>
<tr><td class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;" valign="top" width="45"><div align="center">
Run</div>
</td><td class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;" valign="top" width="45"><div align="center">
1</div>
</td><td class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;" valign="top" width="45"><div align="center">
2</div>
</td><td class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;" valign="top" width="45"><div align="center">
3</div>
</td><td class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;" valign="top" width="45"><div align="center">
4</div>
</td><td class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;" valign="top" width="45"><div align="center">
5</div>
</td><td class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;" valign="top" width="45"><div align="center">
6</div>
</td><td class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;" valign="top" width="45"><div align="center">
7</div>
</td><td class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;" valign="top" width="45"><div align="center">
8</div>
</td><td class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;" valign="top" width="45"><div align="center">
9</div>
</td><td class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;" valign="top" width="45"><div align="center">
10</div>
</td><td class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;" valign="top" width="45"><div align="center">
11</div>
</td><td class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;" valign="top" width="45"><div align="center">
12</div>
</td></tr>
<tr><td class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;" valign="top" width="45"><div align="center">
Operation time (sec.)</div>
</td><td class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;" valign="top" width="45"><div align="center">
21</div>
</td><td class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;" valign="top" width="45"><div align="center">
21</div>
</td><td class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;" valign="top" width="45"><div align="center">
16</div>
</td><td class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;" valign="top" width="45"><div align="center">
19</div>
</td><td class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;" valign="top" width="45"><div align="center">
20</div>
</td><td class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;" valign="top" width="45"><div align="center">
16</div>
</td><td class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;" valign="top" width="45"><div align="center">
20</div>
</td><td class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;" valign="top" width="45"><div align="center">
19</div>
</td><td class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;" valign="top" width="45"><div align="center">
19</div>
</td><td class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;" valign="top" width="45"><div align="center">
20</div>
</td><td class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;" valign="top" width="45"><div align="center">
40</div>
</td><td class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;" valign="top" width="45"><div align="center">
19</div>
</td></tr>
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Run</div>
</td><td class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;" valign="top" width="45"><div align="center">
13</div>
</td><td class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;" valign="top" width="45"><div align="center">
14</div>
</td><td class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;" valign="top" width="45"><div align="center">
15</div>
</td><td class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;" valign="top" width="45"><div align="center">
16</div>
</td><td class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;" valign="top" width="45"><div align="center">
17</div>
</td><td class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;" valign="top" width="45"><div align="center">
18</div>
</td><td class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;" valign="top" width="45"><div align="center">
19</div>
</td><td class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;" valign="top" width="45"><div align="center">
20</div>
</td><td class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;" valign="top" width="45"><div align="center">
21</div>
</td><td class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;" valign="top" width="45"><div align="center">
22</div>
</td><td class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;" valign="top" width="45"><div align="center">
23</div>
</td><td class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;" valign="top" width="45"><div align="center">
24</div>
</td></tr>
<tr><td class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;" valign="top" width="45"><div align="center">
Operation time (sec.)</div>
</td><td class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;" valign="top" width="45"><div align="center">
21</div>
</td><td class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;" valign="top" width="45"><div align="center">
18</div>
</td><td class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;" valign="top" width="45"><div align="center">
23</div>
</td><td class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;" valign="top" width="45"><div align="center">
19</div>
</td><td class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;" valign="top" width="45"><div align="center">
15</div>
</td><td class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;" valign="top" width="45"><div align="center">
18</div>
</td><td class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;" valign="top" width="45"><div align="center">
18</div>
</td><td class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;" valign="top" width="45"><div align="center">
19</div>
</td><td class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;" valign="top" width="45"><div align="center">
21</div>
</td><td class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;" valign="top" width="45"><div align="center">
20</div>
</td><td class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;" valign="top" width="45"><div align="center">
20</div>
</td><td class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;" valign="top" width="45"><div align="center">
19</div>
</td></tr>
</tbody></table>
</div>
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If the technician's performance has been rated at 120 percent, and the company policy for allowance (personal, fatigue, etc.) stipulates 13 percent,</div>
<blockquote style="text-align: start;">
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• Determine the normal time.</div>
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• Determine the standard time.</div>
</blockquote>
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Watch readings falling 50 % above and 25 % below the average may be considered as abnormal.</div>
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<strong>Ans:</strong></div>
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<img height="248" src="http://nptel.ac.in/courses/112107142/part1/image/ex1.gif" width="464" /></div>
</div>
<div>
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<strong>Work Sampling</strong></div>
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Work Sampling (also sometimes called ratio delay study) is a technique of getting facts about utilization of machines or human beings through a large number of instantaneous observations taken at random time intervals. The ratio of observations of a given activity to the total observations approximates the percentage of time that the process is in that state of activity. For example, if 500 instantaneous observations taken at random intervals over a few weeks show that a lathe operator was doing productive work in 365 observations and in the remaining 135 observations he was found 'idle' for miscellaneous reasons, then it can be reliably taken that the operator remains idle (135/500) x 100 = 27 % 0f the time. Obviously, the accuracy of the result depends on the number of observations. However, in most applications there is usually a limit beyond which greater accuracy of data is not economically worthwhile.</div>
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<strong>Use of Work Sampling for Standard Time Determination</strong></div>
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Work sampling can be very useful for establishing time standards on both direct and indirect labor jobs. The procedure for conducting work sampling study for determining standard time of a job can be described step-wise.</div>
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<strong>Step 1 </strong>. Define the problem.</div>
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• Describe the job for which the standard time is to be determined.</div>
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• Unambiguously state and discriminate between the two classes of activities of operator on the job: what are the activities of job that would entitle him to be in 'working" state.</div>
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This would imply that when operator will be found engaged in any activity other than those would entitle him to be in "Not Working" state.</div>
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<strong>Step 2. </strong>Design the sampling plan.</div>
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• Estimate satisfactory number of observations to be made.</div>
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• Decide on the period of study, e.g. two days, one week, etc.</div>
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• Prepare detailed plan for taking the observations.</div>
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This will include observation schedule, exact method of observing, design of observation sheet, route to be followed, particular person to be observed at the observation time, etc.</div>
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<strong>Step 3. </strong>Contact the persons concerned and take them in confidence regarding conduct of the study.</div>
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<strong>Step 4. </strong>Make the observations at the pre-decided random times about the working / not working state of the operator. When operator is in working state, determine his performance rating. Record both on the observation sheet.</div>
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<strong>Step 5. </strong>Obtain and record other information. This includes operator's starting time and quitting time of the day and total number of parts of acceptable quality produced during the day.</div>
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<strong>Step 6. </strong>Calculate the standard time per piece.</div>
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We will now briefly discuss some important issues involved in the procedure.</div>
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<strong>Number of Observations</strong></div>
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As we know, results of study based on larger number of observations are more accurate, but taking more and more observations consumes time and thus is costly. A cost-benefit trade-off has thus to be struck. In practice, the following methods are used for estimation of the number of observations to be made.</div>
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(i) Based on judgment. The study person can decide the necessary number of observations based on his judgment. The correctness of the number may be in doubt but estimate is often quick and in many cases adequate.</div>
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(ii) Using cumulative plot of results. As the study progresses the results of the proportion of time devoted to the given state or activity, i.e. Pi from the cumulative number of observations are plotted at the end of each shift or day. A typical plot is shown in <a href="http://nptel.ac.in/courses/112107142/part1/lecture10.htm#">Figure</a>. Since the accuracy of the result improves with increasing number of observations, the study can be continued until the cumulative Pi appears to stabilize and collection of further data seems to have negligible effect on the value of Pi.</div>
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(iii) Use of statistics. In this method, by considering the importance of the decision to be based on the results of study, a maximum tolerable sampling error in terms of confidence level and desired accuracy in the results is specified. A pilot study is then made in which a few observations are taken to obtain a preliminary estimate of Pi. The number of observations N necessary are then calculated using the following expression.</div>
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The number of observations estimated from the above relation using a value of Pi obtained from a preliminary study would be only a first estimate. In actual practice, as the work sampling study proceeds, say at the end of each day, a new calculation should be made by using increasingly reliable value of Pi obtained from the cumulative number of observations made.</div>
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<strong>Determination of Observation Schedule</strong></div>
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The number of instantaneous observations to be made each day mainly depends upon the nature of operation. For example, for non-repetitive operations or for operations in which some elements occur in-frequently, it is advisable to take observations more frequently so that the chance of obtaining all the facts improves. It also depends on the availability of time with the person making the study. In general, about 50 observations per day is a good figure. The actual random schedule of the observations is prepared by using random number table or any other technique.</div>
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<strong>Design of Observation Sheet</strong></div>
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A sample observation sheet for recording the data with respect to whether at the pre-decided time, the specified worker on job is in 'working' state or 'non-working' state is shown in <a href="http://nptel.ac.in/courses/112107142/part1/lecture10.htm#">Figure</a>. It contains the relevant information about the job, the operators on job, etc. At the end of each day, calculation can be done to estimate the percent of time workers on the job (on an average) spend on activities, which are considered as part of the job.</div>
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<strong>Conducting Work Sampling Study</strong></div>
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At the predecided times of study, the study person appears at the work site and observes the specific worker (already randomly decided) to find out what is he doing. If he is doing activity which is part of the job, he is ticked under the column 'Working' and his performance rating is estimated and recorded. If he is found engaged in an activity which is not a part of job, he is ticked under the column 'Not Working'. At the end of day, the number of ticks in 'Working' column is totaled and average performance rating is determined.</div>
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The observed time (OT) for a given job is estimated as</div>
<div align="justify" class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
<img height="137" src="http://nptel.ac.in/courses/112107142/part1/image/ex2.gif" width="589" /></div>
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The normal time (NT) is found by multiplying the observed time by the average performing index (rating factor).</div>
<blockquote style="text-align: start;">
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<img height="33" src="http://nptel.ac.in/courses/112107142/part1/image/ex4.gif" width="109" /></div>
</blockquote>
<div align="justify" class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
Where =<img align="absmiddle" height="21" src="http://nptel.ac.in/courses/112107142/part1/image/ex4.1.gif" width="16" /> is average rating factor to be determined as <img align="absmiddle" height="41" src="http://nptel.ac.in/courses/112107142/part1/image/ex9.gif" width="37" />, <a href="http://nptel.ac.in/courses/112107142/part1/lecture10.htm#">Figure</a></div>
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The standard time is determined by adding allowances to the normal time.</div>
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<strong>Example</strong></div>
<div align="justify" class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
A work sampling study was made of a cargo loading operation for the purpose of developing its standard time. The study was conducted for duration of 1500 minutes during which 300 instantaneous observations were made at random intervals. The results of study indicated that the worker on the job was working 80 percent of the time and loaded 360 pieces of cargo during the study period. The work analyst rated the performance at 90 %. If the management wishes to permit a 13 % allowance for fatigue, delays and personal time, what is the standard time of this operation?</div>
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<strong>Ans:</strong></div>
<div align="justify" class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">
Here, total study period = 1500 minutes</div>
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Working fraction = 80 percent</div>
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Average rating = 90 percent</div>
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Number of units loaded = 360</div>
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Allowances = 13 %</div>
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<strong>Advantages and Disadvantages of Work Sampling in Comparison with Time Study.</strong></div>
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<strong>Advantages</strong></div>
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<em>Economical</em></div>
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• Many operators or activities which are difficult or uneconomical to measure by time study can readily be measured by work sampling.</div>
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• Two or more studies can be simultaneously made of several operators or machines by a single study person. Ordinarily a work study engineer can study only one operator at a time when continuous time study is made.</div>
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• It usually requires fewer man-hours to make a work sampling study than to make a continuous time study. The cost may also be about a third of the cost of a continuous time study.</div>
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• No stopwatch or other time measuring device is needed for work sampling studies.</div>
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• It usually requires less time to calculate the results of work sampling study. Mark sensing cards may be used which can be fed directly to the computing machines to obtain the results just instantaneously.</div>
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<em>Flexible</em></div>
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6. A work sampling study may be interrupted at any time without affecting the results.</div>
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7. Operators are not closely watched for long period of time. This decreases the chance of getting erroneous results for when a worker is observed continuously for a long period, it is probable that he will not follow his usual routine exactly during that period.</div>
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<em>Less Erroneous</em></div>
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8. Observations may be taken over a period of days or weeks. This decreases the chance of day-to-day or week-to-week variations that may affect the results.</div>
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<em>Operators Like It</em></div>
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9. Work sampling studies are preferred to continuous time study by the operators being studied. Some people do not like to be observed continuously for long periods of time.</div>
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<em>Observers Like It</em></div>
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10. Work sampling studies are less fatiguing and less tedious to make on the part of time study engineer.</div>
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<strong>Disadvantages</strong></div>
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• Work sampling is not economical for the study of a single operator or operation or machine. Also, work-sampling study may be uneconomical for studying operators or machines located over wide areas.</div>
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• Work sampling study does not provide elemental time data.</div>
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• The operator may change his work pattern when he sees the study person. For instance, he may try to look productive and make the results of study erroneous.</div>
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• No record is usually made of the method being used by the operator. Therefore, a new study has to be made when a method change occurs in any element of operation.</div>
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• Compared to stop watch time study, the statistical approach of work sampling study is difficult to understand by workers.</div>
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<strong>Computerized Work Sampling</strong></div>
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Use of a computer can save as much as 30 to 40 percent of the total work sampling study cost. This is because too much clerical effort is involved in summarizing work sampling data, e.g. in determining the number of observations required, determining the daily observations required, determining the number of trips to the area being studied per day, determining the time of each observation, calculating the accuracy of results, plotting data on control charts and like that. Computers can be used for mechanization of the repetitive calculations, display of control charts and calculation of daily as well as cumulative results.</div>
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<strong>Predetermined Motion Time System</strong></div>
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A predetermined motion time system (PMTS) may be defined as a procedure that analyzes any manual activity in terms of basic or fundamental motions required to perform it. Each of these motions is assigned a previously established standard time value and then the timings for the individual motions are synthesized to obtain the total time needed for performing the activity.</div>
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The main use of PMTS lies in the estimation of time for the performance of a task before it is performed. The procedure is particularly useful to those organizations which do not want troublesome performance rating to be used with each study.</div>
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Applications of PMTS are for</div>
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(i) Determination of job time standards.</div>
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(ii) Comparing the times for alternative proposed methods so as to find the economics of the proposals prior to production run.</div>
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(iii) Estimation of manpower, equipment and space requirements prior to setting up the facilities and start of production.</div>
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(iv) Developing tentative work layouts for assembly lines prior to their working in order to minimize the amount of subsequent re-arrangement and re-balancing.</div>
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(v) Checking direct time study results.</div>
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A number of PMTS are in use, some of which have been developed by individual organizations for their own use, while other organizations have developed and publicized for universal applications.</div>
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Some commonly used PMT systems are:</div>
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<li class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">Work factor (1938)</li>
<li class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">Method Time Measurement (1948)</li>
<li class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">Basic Motion Time (1951)</li>
<li class="style1" style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">Dimension Motion Time (1954)</li>
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Important considerations which may be made while selecting a PMT system for application to particular industry are:</div>
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Cost of Installation. This consists mainly of the cost of getting expert for applying the system under consideration.</div>
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Application Cost. This is determined by the length of time needed to set a time standard by the system under consideration.</div>
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Performance Level of the System. The level of performance embodied in the system under consideration may be different from the normal performance established in the industry where the system is to be used. However, this problem can be overcome by 'calibration' which is nothing but multiplying the times given in the PMT Tables by some constant or by the application of an adjustment allowance.</div>
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Consistency of Standards. Consistency of standards set by a system on various jobs is a vital factor to consider. For this, the system can be applied on a trial basis on a set of operations in the plant and examined for consistency in the so obtained operation times.</div>
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Nature of Operation. Best results are likely to be achieved if the type and nature of operations in the plant are similar to the nature and type of operations studied during the development of the system under consideration.</div>
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<strong>Advantages and limitations of using PMT systems</strong></div>
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<strong>Advantages</strong></div>
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Compared to other work measurement techniques, all PMT systems claim the following advantages:</div>
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<li>There is no need to actually observe the operation running. This means the estimation of time to perform a job can be made from the drawings even before the job is actually done. This feature is very useful in production planning, forecasting, equipment selection, etc.</li>
<li>The use of PMT eliminates the need of troublesome and controversial performance rating. For the sole reason of avoiding performance rating, some companies have been using this technique.</li>
<li>The use of PMT forces the analyst to study the method in detail. This sometimes helps to further improve the method.</li>
<li>A bye-product of the use of PM times is a detailed record of the method of operation. This is advantageous for installation of method, for instructional purposes, and for detection and verification of any change that might occur in the method in future.</li>
<li>The PM times can be usefully employed to establish elemental standard data for setting time standards on jobs done on various types of machines and equipment.</li>
<li>The basic times determined with the use of PMT system are relatively more consistent.</li>
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<strong>Limitations</strong></div>
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There are two main limitations to the use of PMT system for establishing time standards. These are: (i) its application to only manual contents of job and (ii) the need of trained personnel. Although PMT system eliminates the use of rating, quite a bit of judgment is still necessarily exercised at different stages.</div>
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<strong>Physiological Methods for Work Measurement</strong></div>
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The physiological cost to an operator of performing any given physical work results from the activities of the muscles of arms, legs, back and other parts of the body and is, therefore, affected by the number and type of muscles involved in either moving the body member(s) or controlling antagonist contraction.</div>
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The activities of body muscles cause changes in oxygen consumption, heart rate, body temperature, lactic acid concentration in blood, 17-ketosteroid excretion in urine, pulmonary ventilation, and other factors. Studies have shown that some of these factors are only slightly affected by muscular activity. The important factors which have linear correlation with the physiological cost of work performed by an individual are oxygen consumption, heart rate, and pulmonary ventilation.</div>
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<strong>Increase in Heart Rate</strong></div>
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When a person is at rest, his heart rate is at a fairly steady level (generally at about 70 beats/minute). Then when he starts doing some muscular work his pulse rate increases rapidly to about 110 beats/minute and remains near to this level during the working period. When work ends, the recovery begins and his heart rate drops off and finally returns to the original resting level ( <a href="http://nptel.ac.in/courses/112107142/part1/lecture11.htm#">Figure</a> ).</div>
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The increase in heart rate during work has been used as an index of the physiological cost of the job. Some physiologists have also proposed the use of 'the rate of recovery immediately after work stops' for the evaluation of physiological cost of certain types of work. It is to be noted that the total physiological cost of a task consists of the energy expenditure during work and the energy expenditure above the resting rate during the recovery period. It is generally agreed that the optimum limit of industrial performance is reached when the average pulse rate during the work lies 30 beats/minute above the resting pulse rate.</div>
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<strong>Measurement. </strong>With every heart beat, a small electric potential is generated. This signal can be picked up by placing silver electrodes on either side of the chest, and transmitted to a receiver, where these can be counted directly or recorded continuously on a ruled graph paper or integrated over time to measure in units of beats per minute with the help of a cardiotachometer.</div>
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Another method of getting the heart beat signals is through the use of an ear lobe unit, which is a photo duodiode with a light source. This unit is mounted on an ear of the subject in such a way that the duodiode is on one side and the light source is on the other side of the ear. As the capacity of the ear lobe changes due to the blood surges through the ear with beats of the heart, impulses are created which are transmitted and recorded.</div>
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A simple method to get the heart beat rate is through the use of a stethoscope and stop watch. Studies have shown that the data obtained in this manner are fairly reliable and also easy to obtain.</div>
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<strong>Oxygen Consumption. </strong>It may be defined as the volume of oxygen which a person extracts from the air he inhales. Increase in the rate of oxygen consumption from the resting level to the working level is also taken as a measure of the physiological cost of the work done. The oxygen consumption per unit time is usually measured indirectly. To do this the volume of air exhaled by a person in a certain time is collected and the oxygen content of this air is determined. For this, use is made of a portable respirometer. It is a lightweight gas meter which is worn on the back of the subject. A mask is fitted on the face of the subject, and the exhaled air is collected in the respirometer through a rubber tube. The respirometer directly shows the volume of exhaled air in litres.</div>
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A sample of the exhaled air is taken out at random intervals into a rubber bladder and an analysis is carried out of its content. Comparison is then made between the oxygen content of the two samples-drawn from the exhaled air and another from the room air. For each litre of oxygen consumed by the human body, there is an average energy turnover of 4.8 Kcal.</div>
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<a href="http://nptel.ac.in/courses/112107142/part1/lecture11.htm#">Table</a> gives the general values of oxygen consumption, lung ventilation, rectal temperature and heart beats at the different work loads.</div>
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Physiological measurements can be used to compare the energy cost to the operator on a job for which no time standard exists, with the energy cost to the same operator on a similar operation for which a satisfactory time standard already exists. By this comparison it is possible to establish the time standard on the job for which it does not exist already. For the sake of illustration, consider a job of lifting boxes weighing 2-3 kgs. from the floor level and placing it on a conveyor belt. For this job a time standard of 6 seconds (10 boxes/min.) is being used. When energy measurements were taken, it was found that to Mr. Singh, the operator on the job, the energy cost of this job was 300 W. Let us suppose now that there is another jab, similar to the first one, with the difference that here, the weight of the boxes is 5-6 kgs. If it is required to establish the t ime standard for this job, we need Mr. Singh to do this job of handling 5-6 kg. boxes at various speeds. From the energy cost data collected on him, we can select the speed of working that gives an energy cost of 300 W. So, by keeping the energy cost of the two jobs same, the time standard (the number of 5-6 kg. boxes/min.) can be determined.</div>
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Mechanical Engineering Departmenthttp://www.blogger.com/profile/12582953924770018783noreply@blogger.comtag:blogger.com,1999:blog-6302071579893645567.post-8354838227677717202017-08-09T14:13:00.000+05:302017-08-09T14:13:41.344+05:30Kinematics of Machine Notes<div dir="ltr" style="text-align: left;" trbidi="on">
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Mechanisms</div>
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A mechanism is a combination of rigid or restraining bodies so shaped and connected that they move upon each other with a definite relative motion. A simple example of this is the <a class="plinks" href="http://nptel.ac.in/courses/Webcourse-contents/IIT-Delhi/Kinematics%20of%20Machine/site/basickinematics/anims/slider_crank.htm" style="color: #3366ff; font-size: 11pt; font-weight: bolder; text-decoration-line: none;" target="_blank">slider crank mechanism</a> used in an internal combustion or reciprocating air compressor.</div>
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Machine</div>
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A machine is a mechanism or a collection of mechanisms which transmits force from the source of power to the resistance to be overcome,and thus perform a mechanical work.</div>
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Kinematic Pairs</div>
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A mechanism has been defined as a combination so connected that each moves with respect to each other.A clue to the behaviour lies in in the nature of connections,known as kinetic pairs.<br />
The degree of freedom of a kinetic pair is given by the number independent coordinates required to completely specify the relative movement.</div>
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Lower Pairs</div>
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A pair is said to be a lower pair when the connection between two elementsis through the area of contact.Its 6 types are :</div>
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<li style="padding: 3px;"><a href="http://nptel.ac.in/courses/Webcourse-contents/IIT-Delhi/Kinematics%20of%20Machine/site/basickinematics/pair01.htm" style="color: #3366ff; text-decoration-line: none;">Revolute Pair</a></li>
<li style="padding: 3px;"><a href="http://nptel.ac.in/courses/Webcourse-contents/IIT-Delhi/Kinematics%20of%20Machine/site/basickinematics/pair02.htm" style="color: #3366ff; text-decoration-line: none;">Prismatic Pair</a></li>
<li style="padding: 3px;"><a href="http://nptel.ac.in/courses/Webcourse-contents/IIT-Delhi/Kinematics%20of%20Machine/site/basickinematics/pair03.htm" style="color: #3366ff; text-decoration-line: none;">Screw Pair</a></li>
<li style="padding: 3px;"><a href="http://nptel.ac.in/courses/Webcourse-contents/IIT-Delhi/Kinematics%20of%20Machine/site/basickinematics/pair04.htm" style="color: #ff5500; letter-spacing: 1px; text-decoration-line: none;">Cylindrical Pair</a></li>
<li style="padding: 3px;"><a href="http://nptel.ac.in/courses/Webcourse-contents/IIT-Delhi/Kinematics%20of%20Machine/site/basickinematics/pair05.htm" style="color: #3366ff; text-decoration-line: none;">Spherical Pair</a></li>
<li style="padding: 3px;"><a href="http://nptel.ac.in/courses/Webcourse-contents/IIT-Delhi/Kinematics%20of%20Machine/site/basickinematics/pair06.htm" style="color: #3366ff; text-decoration-line: none;">Planar Pair</a></li>
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Higher Pairs</div>
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A higher pair is defined as one in which the connection between two elements has only a point or line of contact. A cylinder and a hole of equal radius and with axis parallel make contact along a surface. Two cylinders with unequal radius and with axis parallel make contact along a line. A point contact takes place when spheres rest on plane or curved surfaces (ball bearings) or between teeth of a skew-helical gears. in roller bearings, between teeth of most of the gears and in cam-follower motion. The degree of freedom of a kinetic pair is given by the number independent coordinates required to completely specify the relative movement.</div>
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Wrapping Pairs</div>
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Wrapping Pairs comprise belts, chains, and other such devices.</div>
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To define a mechanism we define the basic elements as follows :</div>
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Link</div>
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A material body which is common to two or more kinematic pairs is called a <em>link</em>.</div>
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Kinematic Chain</div>
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A <em>kinematic chain</em> is a series of links connected by kinematic pairs. The chain is said to be <em>closed chain</em> if every u link is connected to atleast two other links, otherwise it is calledan <em>open chain</em>. A link which is connected to only one other link is known as <em>singular link</em>.If it is connected to two other links, it is called <em>binary link</em>.If it is connected to three other links, it is called <em>ternary link</em>, and so on. A chain which consists of only binary links is called <em>simple chain</em>. A type of kinematic chain is one with <em>constrained motion</em>, which means that a definite motion of any link produces unique motion of all other links. Thus motion of any point on one link defines the relative position of any point on any other link.So it has one degree of freedom.</div>
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The process of fixing different links of a kinematic chain one at a time to produce distinct mechanisms is called kinematic inversion.Here the relative motions of the links of the mechanisms remain unchanged.<br />
First, let us consider the simplest kinematic chain,i.e., achain consisting of four binary links and four revolute pairs. The four different mechanisms can be obtained by four different inversions of the chain.</div>
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<img alt="Figure" class="float_right" src="http://nptel.ac.in/courses/Webcourse-contents/IIT-Delhi/Kinematics%20of%20Machine/site/basickinematics/pics/slider_crank.gif" style="float: right; font-size: 14.6667px; padding-left: 25px;" /></div>
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Slider Crank mechanism</div>
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It has four binary links, three revolute pairs, one prismatic pair.By fixing links 1, 2, 3 in turn we get various inversions.</div>
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Double Slider Crank mechanism</div>
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It has four binary links, two revolute pairs, two sliding pairs.Its various types are :</div>
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Scotch Yoke mechanism:</div>
<span style="background-color: white; font-size: 14.6667px;"></span><br />
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Here the constant rotation of the crank produces harmonic translation of the yoke.Its four binary links are :</div>
<ol class="numlist" style="font-size: 14.6667px; margin-bottom: 0px; margin-top: 0px;">
<li style="padding: 3px;">Fixed Link </li>
<li style="padding: 3px;">Crank </li>
<li style="padding: 3px;">Sliding Block </li>
<li style="padding: 3px;">Yoke </li>
</ol>
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The four kinematic pairs are :</div>
<ul class="numlist" style="font-size: 14.6667px; list-style-type: decimal; margin-bottom: 0px; margin-top: 0px;">
<li style="padding: 3px;">revolute pair (between 1 & 2) </li>
<li style="padding: 3px;">revolute pair (between 2 & 3) </li>
<li style="padding: 3px;">prismatic pair (between 3 & 4) </li>
<li style="padding: 3px;">prismatic pair (between 4 & 1) </li>
</ul>
<div>
<img alt="Figure" src="http://nptel.ac.in/courses/Webcourse-contents/IIT-Delhi/Kinematics%20of%20Machine/site/basickinematics/pics/double_slider.gif" /></div>
<div>
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Oldhams Coupling:</div>
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It is used for transmitting anbgular velocity between two parallel but eccentric shafts</div>
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Elliptical Trammel:</div>
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<div class="tdata" style="font-size: 14.6667px; margin-left: 5px; margin-right: 5px;">
Here link 4 is fixed. Any point on the link 2 describes an ellipse as it moves.The mid-point of the link 2 will obiviously describe a circle.</div>
</div>
<div>
<img alt="Figure" src="http://nptel.ac.in/courses/Webcourse-contents/IIT-Delhi/Kinematics%20of%20Machine/site/basickinematics/pics/trammels.gif" /></div>
<div>
<span style="background-color: white; font-size: 14.6667px;">Very often a mechanism with higher pair can be replaced by an equivalent mechanism with lower pair.This equivalence is valid for studying only the instantaneous characteristics.The equivalent lower-pairmechanism facilitates analysis as a certain amount of sliding takes place between connecting links in a higher-pair mechanism.</span><br />
<span style="background-color: white; font-size: 14.6667px;">Another example of an equivalent lower-pair mechanism for a cam-follower system is shown.The sliding block is the additional link and thebhigher pair is replaced by two lower pairs, one revoluteand other prismatic. C is the center of curvature of the cam surface at the point of contact between the cam and the follower</span></div>
<div>
<img alt="Figure" src="http://nptel.ac.in/courses/Webcourse-contents/IIT-Delhi/Kinematics%20of%20Machine/site/basickinematics/pics/equi_link.gif" /></div>
<div>
<h3 style="color: #660000; font-family: "Book Antiqua"; font-style: italic; margin: 0px; text-transform: uppercase;">
KINEMATICS AND DYNAMICS : MOBILITY AND RANGE OF MOVEMENT</h3>
</div>
<div>
<span style="background-color: white; font-size: 14.6667px;">Let n be the no. of links in a mechanism out of which, one is fixed, and let j be the no. of simple hinges(ie, those connect two links.) Now, as the (n-1) links move in a plane, in the absence of any connections, each has 3 degree of freedom; 2 coordinates are required to specify the location of any reference point on the link and 1 to specify the orientation of the link. Once we connect the linmks there cannot be anyrelative translation betweenthem and only one coordinate is necessary to specify their relative orientation.Thus, 2 degrees of freedom (translation) are lost, and only one degree of freedom (rotational) is left. So, no. of degrees of freedom is:</span><br />
<span style="background-color: white; font-size: 14.6667px;">F=3(n-1)-2j</span><br />
<span style="background-color: white; font-size: 14.6667px;">Most mechanisms are constrained, ie F=1. Therefore the above relation becomes,</span><br />
<span style="background-color: white; font-size: 14.6667px;">2j-3n+4=0</span><br />
<span style="background-color: white; font-size: 14.6667px;">,this is called Grubler's Criterion.</span><br />
<span style="background-color: white; font-size: 14.6667px;">Failure of Grubler's criterion</span><br />
<span style="background-color: white; font-size: 14.6667px;">A higher pair has 2 degrees of freedom .Following the same argument as before, The degrees of freedom of a mechanism having higher pairs can be written as,</span><br />
<span style="background-color: white; font-size: 14.6667px;">F=3(n-1)-2j-h</span><br />
<span style="background-color: white; font-size: 14.6667px;">Often some mechanisms have a redundant degree of freedom. If a link can move without causing any movement in the rest of the mechanism, then the link is said to have a redundant degree of freedom.</span><br />
<span style="background-color: white; font-size: 14.6667px;">Example of redundant degree of freedom </span></div>
<div>
<a href="http://nptel.ac.in/courses/Webcourse-contents/IIT-Delhi/Kinematics%20of%20Machine/site/coursecontent/cntmod03.htm" style="background-color: white; color: #3366ff; font-size: 14.6667px; text-decoration-line: none; text-indent: 10px;">Displacement analysis of plane mechanisms.</a></div>
<div>
<span style="background-color: white; font-size: 14.6667px;">The objective of kinematic analysis is to determine the kinematic quantities such as displacements, velocities, and accelerations of the elements of a mechanism when the input motion is given. It establishes the relationship between the motions of various components of the linkage</span></div>
<div>
<h3 style="color: #660000; font-family: "Book Antiqua"; font-style: italic; margin: 0px; text-transform: uppercase;">
DISPLACEMENT ANALYSIS</h3>
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When the kinematic dimensions and the configurations of the input link of a mechanism are prescribed, the configurations of all the other links are determined by displacement analysis.</div>
<ol class="numlist" style="font-size: 14.6667px; margin-bottom: 0px; margin-top: 0px;">
<li style="padding: 3px;">Graphical Method</li>
<li style="padding: 3px;">Analytical Method</li>
</ol>
<div>
<h3 style="color: #660000; font-family: "Book Antiqua"; font-style: italic; margin: 0px; text-transform: uppercase;">
GRAPHICAL METHOD</h3>
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In a graphical method of displacement analysis, the mechanism is drawn to a convenient scale and the desired unknown quantities are determined through suitable geometrical constructions and calculations.</div>
<ol class="numlist" style="font-size: 14.6667px; margin-bottom: 0px; margin-top: 0px;">
<li style="padding: 3px;">The configurations of a rigid body in plane motion are completely defined by the locations of any two points on it.</li>
<li style="padding: 3px;">Two intersecting circles have two points of intersection and one has to be careful, when necessary, to choose the correct point for the purpose in hand.</li>
<li style="padding: 3px;">The use of tracing paper, as an overlay, is very convenient and very often provides an unambiguous and quick solution.</li>
<li style="padding: 3px;">The graphical method fails if no closed loop with four links exists in the mechanism.</li>
</ol>
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<h3 style="color: #660000; font-family: "Book Antiqua"; font-style: italic; margin: 0px; text-transform: uppercase;">
ANALYTICAL METHOD</h3>
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<img alt="Figure 1" class="float_right" src="http://nptel.ac.in/courses/Webcourse-contents/IIT-Delhi/Kinematics%20of%20Machine/site/kinematics/pics/image001.png" style="float: right; font-size: 14.6667px; padding-left: 25px;" /><br />
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An analytical method of displacement analysis, is preferred whenever </div>
<ol class="numlist" style="font-size: 14.6667px; margin-bottom: 0px; margin-top: 0px;">
<li style="padding: 3px;">high level of accuracy is required</li>
<li style="padding: 3px;">a large number of configurations have to be solved</li>
<li style="padding: 3px;">The graphical method fails.</li>
</ol>
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In this method every link is represented by two dimensional are represented by two dimensional vectors expressed through complex notation. Considering each closed loop in the mechanism, a vector equation is established. Separating the real and imaginary parts , sufficient number of nonlinear algebraic equations are obtained to solve for the unknown quantities.</div>
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Let us consider a 4R linkage of given link lengths, viz.,<em> i</em>=1, 2, 3, and 4. The configuration of the input link (2) is also prescribed by the angle <em>θ<sub>2</sub></em>, and we have to determine the configurations of the other two links, namely, the coupler and the follower, expressed by the angles <em>θ<sub>3</sub></em> and <em>θ<sub>4</sub></em>.</div>
<div class="tdata" style="font-size: 14.6667px; margin-left: 5px; margin-right: 5px;">
<a href="http://nptel.ac.in/courses/Webcourse-contents/IIT-Delhi/Kinematics%20of%20Machine/site/coursecontent/cntmod04.htm" style="background-color: white; color: #3366ff; font-size: 14.6667px; text-decoration-line: none; text-indent: 10px;">Introduction to Instantaneous centre and velocity analysis.</a></div>
<h3 style="color: #660000; font-family: "Book Antiqua"; font-style: italic; margin: 0px; text-transform: uppercase;">
TRANSMISSION ANGLE</h3>
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<img alt="Figure 3" class="float_right" src="http://nptel.ac.in/courses/Webcourse-contents/IIT-Delhi/Kinematics%20of%20Machine/site/kinematics/pics/image003.png" style="float: right; font-size: 14.6667px; padding-left: 25px;" /></div>
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For a 4R linkage, the transmission angle ( μ ) is defined as the acute angle between the coupler (AB) and the follower ).<sub>4</sub>B), as indicated in Fig. 2.11. If ( - ABO<sub>4</sub>) is acute (Fig.2.11), then μ =- ABO<sub>4</sub>. On the other hand, if - ABO<sub>4</sub> is obtuse, then μ =Π-- ABO<sub>4</sub>. As explained in this figure, if μ = Π /2, then the entire coupler force is utilized to drive the follower. For good transmission quality, the minimum value of μ(μ<sub>min</sub>)>300. For a crank-rocker mechanism, the minimum value of μ occurs when the crank becomes collinear with the frame, i.e.,<img alt="inlinesymbol" class="inlinesymbol" src="http://nptel.ac.in/courses/Webcourse-contents/IIT-Delhi/Kinematics%20of%20Machine/site/kinematics/eqn/eqn5_1.gif" style="display: inline; font-size: 11pt; font-style: italic; vertical-align: middle;" />. If the swing angle (<img alt="inlinesymbol" class="inlinesymbol" src="http://nptel.ac.in/courses/Webcourse-contents/IIT-Delhi/Kinematics%20of%20Machine/site/kinematics/eqn/eqn5_2.gif" style="display: inline; font-size: 11pt; font-style: italic; vertical-align: middle;" />) of the rocker is increased maintaining the same quick-return ratio, then the maximum possible value of μ <sub>min</sub> decreases. If the forward and return strokes of the rocker take equal time, then (μ<sub>min</sub>)max is restricted to <img alt="inlinesymbol" class="inlinesymbol" src="http://nptel.ac.in/courses/Webcourse-contents/IIT-Delhi/Kinematics%20of%20Machine/site/kinematics/eqn/eqn5_3.gif" style="display: inline; font-size: 11pt; font-style: italic; vertical-align: middle;" /> (see Problem 2.6). Therefore, such a crank rocker will have a poor transmission quality if <img alt="inlinesymbol" class="inlinesymbol" src="http://nptel.ac.in/courses/Webcourse-contents/IIT-Delhi/Kinematics%20of%20Machine/site/kinematics/eqn/eqn5_4.gif" style="display: inline; font-size: 11pt; font-style: italic; vertical-align: middle;" />.</div>
<div class="tdata" style="font-size: 14.6667px; margin-left: 5px; margin-right: 5px;">
<a href="http://nptel.ac.in/courses/Webcourse-contents/IIT-Delhi/Kinematics%20of%20Machine/site/coursecontent/cntmod05.htm" style="background-color: white; color: #3366ff; font-size: 14.6667px; text-decoration-line: none; text-indent: 10px;">Introduction to Velocity and Acceleration diagrams.</a></div>
<h3 style="color: #660000; font-family: "Book Antiqua"; font-style: italic; margin: 0px; text-transform: uppercase;">
VELOCITY AND ACCELERATION IMAGES</h3>
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The concept of velocity and acceleration images is used extensively in the kinematic analysis of mechanisms having ternary, quaternary, and higher-order links. If the velocities and accelerations of any two points on a link are known, then, with the help of images the velocity and acceleration of any other point on the link can be easily determined. An example is illustrated below:</div>
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A rigid link BCDE having four hinges is sown in figure. Let the angular velocity and acceleration of this be ω and α. The absolute velocity vectors of the E, B, C and D are shown in the figure as V<sub>E</sub>, V<sub>B</sub>, V<sub>C</sub>, and V<sub>D</sub> respectively. The velocity difference vectors are</div>
<div class="tdata" style="font-size: 14.6667px; margin-left: 5px; margin-right: 5px;">
<img alt="equation" class="equation" src="http://nptel.ac.in/courses/Webcourse-contents/IIT-Delhi/Kinematics%20of%20Machine/site/kinematics/eqn/eqn9_1.gif" style="display: inline; font-size: 14.6667px; font-style: italic; margin-left: 50px; vertical-align: middle;" /></div>
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And their magnitudes are, respectively,</div>
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<img alt="equation" class="equation" src="http://nptel.ac.in/courses/Webcourse-contents/IIT-Delhi/Kinematics%20of%20Machine/site/kinematics/eqn/eqn9_3.gif" style="display: inline; font-size: 14.6667px; font-style: italic; margin-left: 50px; vertical-align: middle;" /></div>
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So,</div>
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<img alt="equation" class="equation" src="http://nptel.ac.in/courses/Webcourse-contents/IIT-Delhi/Kinematics%20of%20Machine/site/kinematics/eqn/eqn9_2.gif" style="display: inline; font-size: 14.6667px; font-style: italic; margin-left: 50px; vertical-align: middle;" /></div>
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Hence the velocity diagram <i>bcde</i> is a scale drawing of the link BCDE. The figure <i>bcde</i> is called the <i>velocity image</i> of the link BCDE. The velocity image is rotated through 90o in the direction ω, as all the velocity difference vectors are perpendicular to the corresponding lined. The scale of the image is determined by and therefore the scale will be different for each link of a mechanism. The letters identifying the end points of the image are in the same sequence as that in the link diagram BCDE. The absolute velocity any point X on the link is obtained by joining the image of X(x) with the pole of the velocity diagram o.</div>
<h3 style="color: #660000; font-family: "Book Antiqua"; font-style: italic; margin: 0px; text-transform: uppercase;">
VELOCITY ANALYSIS (GRAPHICAL)</h3>
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<ol class="numlist" style="font-size: 14.6667px; margin-bottom: 0px; margin-top: 0px;">
<li style="padding: 3px;">Instantaneous Centre Method</li>
<li style="padding: 3px;">Relative Velocity Method</li>
</ol>
<div>
<h3 style="color: #660000; font-family: "Book Antiqua"; font-style: italic; margin: 0px; text-transform: uppercase;">
INSTANTANEOUS CENTRE METHOD</h3>
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<ol class="numlist" style="font-size: 14.6667px; margin-bottom: 0px; margin-top: 0px;">
<li style="padding: 3px;">First determine the number of instantaneous centers (N) by using the relation<br /><img alt="equation" class="equation" src="http://nptel.ac.in/courses/Webcourse-contents/IIT-Delhi/Kinematics%20of%20Machine/site/kinematics/eqn/eqn11_1.gif" style="display: inline; font-size: 11pt; font-style: italic; margin-left: 50px; vertical-align: middle;" /></li>
<li style="padding: 3px;">Make a list of all the instantaneous centers in the mechanism.</li>
<li style="padding: 3px;">Locate the fixed and permanent instantaneous centers by inspection.</li>
<li style="padding: 3px;">Locate the remaining neither fixed nor permanent instantaneous centers by Kennedy’s theorem. This can be done by circle diagram. Mark points on a circle equal to the number of links in a mechanism.</li>
<li style="padding: 3px;">Join the points by solid lines to show that these circles are already found. In the lines indicate the instantaneous centers corresponding to those particular two points.</li>
<li style="padding: 3px;">In order to find the remaining instantaneous centers, join two such points that the line joining them forms two adjacent triangles in the circle diagram. The line which is responsible for completing two triangles should be a common side to the two triangles. </li>
</ol>
<div>
<h3 style="color: #660000; font-family: "Book Antiqua"; font-style: italic; margin: 0px; text-transform: uppercase;">
RELATIVE VELOCITY METHOD</h3>
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The relative velocity method is based upon the velocity of the various points of the link.</div>
<div class="tdata" style="font-size: 14.6667px; margin-left: 5px; margin-right: 5px;">
Consider two points A and B on a link. Let the absolute velocity of the point A i.e. VA is known in magnitude and direction and the absolute velocity of the point B i.e. VB is known in direction only. Then the velocity of B may be determined by drawing the velocity diagram as shown.</div>
<img alt="Figure 5" class="float_right" src="http://nptel.ac.in/courses/Webcourse-contents/IIT-Delhi/Kinematics%20of%20Machine/site/kinematics/pics/image005.png" style="float: right; font-size: 14.6667px; padding-left: 25px;" /><br />
<ol class="numlist" style="font-size: 14.6667px; margin-bottom: 0px; margin-top: 0px;">
<li style="padding: 3px;">Take some convenient point o, known as the pole.</li>
<li style="padding: 3px;">Through o, draw oa parallel and equal to VA, to some convenient scale.</li>
<li style="padding: 3px;">Through a, draw a line perpendicular to AB. This line will represent the velocity of B with respect to A, i.e.</li>
<li style="padding: 3px;">Through o, draw a line parallel to VB intersecting the line of VBA at b.</li>
<li style="padding: 3px;">Measure ob, which gives the required velocity of point B to the scale.</li>
</ol>
<div>
<ul style="background-color: white; color: #660000; font-family: Century; font-size: 14.6667px; text-align: left;">
<li style="padding: 3px;"><a href="http://nptel.ac.in/courses/Webcourse-contents/IIT-Delhi/Kinematics%20of%20Machine/site/cams/cam01.htm" style="color: #3366ff; text-decoration-line: none;">Introduction to Cams</a></li>
</ul>
<div style="text-align: left;">
<h3 style="color: #660000; font-family: "Book Antiqua"; font-style: italic; margin: 0px; text-align: justify; text-transform: uppercase;">
INTRODUCTION</h3>
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Cams come under higher pair mechanisms. As we already know that in higher pair the contact between the two elements is either point or line contact, instead of area in the case of lower pairs.</div>
<img alt="Figure 1" class="fig_center" src="http://nptel.ac.in/courses/Webcourse-contents/IIT-Delhi/Kinematics%20of%20Machine/site/cams/pics/image001.gif" style="display: block; font-size: 14.6667px; text-align: center;" /><br />
<div class="tdata" style="font-size: 14.6667px; margin-left: 5px; margin-right: 5px; text-align: justify;">
In CAMs, the driving member is called the cam and the driven member is referred to as the <i>follower</i>. CAM is used to impart desired motion to the follower by direct contact. Generally the CAM is a rotating or reciprocating element, where as the follower may de rotating, reciprocating or oscillating element. Using CAMs we can generate complex, coordinate movements that are very difficult with other mechanisms. And also CAM mechanisms are relatively compact and easy it design. Cams are widely used in automatic machines, internal combustion engines, machine tools, printing control mechanisms and so on. Along with <i>cam</i> and <i>follower</i> one <i>frame</i> also will be there with will supports the <i>cam</i> and guides the follower.</div>
<h3 style="color: #660000; font-family: "Book Antiqua"; font-style: italic; margin: 0px; text-align: justify; text-transform: uppercase;">
CLASSIFICATION OF FOLLOWERS</h3>
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<div class="theadings" style="color: #000066; font-size: 14.6667px; font-weight: bold; margin: 2px; text-align: justify;">
A follower can be classified in three ways</div>
<ol class="numlist" style="font-size: 14.6667px; margin-bottom: 0px; margin-top: 0px; text-align: justify;">
<li style="padding: 3px;">According to the motion of the follower.</li>
<li style="padding: 3px;">According to the nature of contact.</li>
<li style="padding: 3px;">According to the path of motion of the follower.</li>
</ol>
<div style="text-align: justify;">
<h3 style="color: #660000; font-family: "Book Antiqua"; font-style: italic; margin: 0px; text-transform: uppercase;">
CLASSIFICATION OF FOLLOWERS</h3>
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<div class="theadings" style="color: #000066; font-size: 14.6667px; font-weight: bold; margin: 2px;">
According to the motion of the follower</div>
<ol class="numlist" style="font-size: 14.6667px; margin-bottom: 0px; margin-top: 0px;">
<li style="padding: 3px;"><div class="tsheadings" style="color: teal; display: inline; font-weight: bold; text-decoration-line: underline;">
Reciprocating or Translating follower</div>
: When the follower reciprocates in guides as the can rotates uniformly, it is known as reciprocating or translating follower.</li>
<li style="padding: 3px;"><div class="tsheadings" style="color: teal; display: inline; font-weight: bold; text-decoration-line: underline;">
Oscillating or Rotating follower</div>
: When the uniform rotary motion of the cam is converted into predetermined oscillatory motion of the follower, it is called oscillating or rotating follower.</li>
</ol>
<div>
<h3 style="color: #660000; font-family: "Book Antiqua"; font-style: italic; margin: 0px; text-transform: uppercase;">
CLASSIFICATION OF FOLLOWERS</h3>
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<div class="theadings" style="color: #000066; font-size: 14.6667px; font-weight: bold; margin: 2px;">
According to the nature of contact:</div>
<ol class="numlist" style="font-size: 14.6667px; margin-bottom: 0px; margin-top: 0px;">
<li style="padding: 3px;"><div class="tsheadings" style="color: teal; display: inline; font-weight: bold; text-decoration-line: underline;">
The Knife-Edge follower</div>
: When contacting end of the follower has a sharp knife edge, it is called a knife edge follower. This cam follower mechanism is rarely used because of excessive wear due to small area of contact. In this follower a considerable thrust exists between the follower and guide.</li>
<li style="padding: 3px;"><div class="tsheadings" style="color: teal; display: inline; font-weight: bold; text-decoration-line: underline;">
The Flat-Face follower</div>
: When contacting end of the follower is perfectly flat faced, it is called a flat faced follower. The thrust at the bearing exerted is less as compared to other followers. The only side thrust is due to friction between the contact surfaces of the follower and the cam. The thrust can be further reduced by properly offsetting the follower from the axis of rotation of cam so that when the cam rotates, the follower also rotates about its axis. These are commonly used in automobiles.</li>
<li style="padding: 3px;"><div class="tsheadings" style="color: teal; display: inline; font-weight: bold; text-decoration-line: underline;">
The Roller follower</div>
: When contacting end of the follower is a roller, it is called a roller follower. Wear rate is greatly reduced because of rolling motion between contacting surfaces. In roller followers also there is side thrust present between follower and the guide. Roller followers are commonly used where more space is available such as large stationary gas or oil engines and aircraft engines.</li>
<li style="padding: 3px;"><div class="tsheadings" style="color: teal; display: inline; font-weight: bold; text-decoration-line: underline;">
The Spherical-Faced follower</div>
: When contacting end of the follower is of spherical shape, it is called a spherical faced follower. In flat faced follower’s high surface stress are produced. To minimize these stresses the follower is machined to spherical shape.</li>
</ol>
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<div class="theadings" style="color: #000066; font-size: 14.6667px; font-weight: bold; margin: 2px;">
According to the path of motion of the follower:</div>
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<li style="padding: 3px;"><div class="tsheadings" style="color: teal; display: inline; font-weight: bold; text-decoration-line: underline;">
Radial follower</div>
: When the motion of the follower is along an axis passing through the centre of the cam, it is known as radial follower.</li>
<li style="padding: 3px;"><div class="tsheadings" style="color: teal; display: inline; font-weight: bold; text-decoration-line: underline;">
Off-set follower</div>
: When the motion of the follower is along an axis away from the axis of the cam centre, it is called off-set follower.</li>
</ol>
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A Cam can be classified in two ways:</div>
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<li style="padding: 3px;"><div class="tsheadings" style="color: teal; display: inline; font-weight: bold; text-decoration-line: underline;">
Radial or Disc cam</div>
: In radial cams, the follower reciprocates or oscillates in a direction perpendicular to the cam axis.</li>
<li style="padding: 3px;"><div class="tsheadings" style="color: teal; display: inline; font-weight: bold; text-decoration-line: underline;">
Cylindrical cam</div>
: In cylindrical cams, the follower reciprocates or oscillates in a direction parallel to the cam axis. The follower rides in a groove at its cylindrical surface.</li>
</ol>
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<h3 style="color: #660000; font-family: "Book Antiqua"; font-style: italic; margin: 0px; text-transform: uppercase;">
CAM DESIGN: RADIAL CAM NOMENCLATURE</h3>
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<img alt="Figure 2" class="float_right" src="http://nptel.ac.in/courses/Webcourse-contents/IIT-Delhi/Kinematics%20of%20Machine/site/cams/pics/image002.png" style="float: right; font-size: 14.6667px; padding-left: 25px;" /><br />
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The various terms we will very frequently use to describe the geometry of a radial <em>cam</em>are defined as fallows.</div>
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<li style="padding: 3px;"><div class="tsheadings" style="color: teal; display: inline; font-weight: bold; text-decoration-line: underline;">
Base Circle</div>
: It is the smallest circle, keeping the center at the <em>cam</em>center, drawn tangential to <em>cam</em> profile. The base circle decides the overall size of the <em>cam</em> and thus is fundamental feature.</li>
<li style="padding: 3px;"><div class="tsheadings" style="color: teal; display: inline; font-weight: bold; text-decoration-line: underline;">
Trace Point</div>
: It is a point on the follower, and it is used to generate the pitch curve. Its motion describing the movement of the follower. For a knife-edge follower, the trace point is at knife-edge. For a roller follower the trace point is at the roller center, and for a flat-face follower, it is a t the point of contact between the follower and the <em>cam </em>surface when the contact is along the base circle of the cam. It should be note that the trace point is not necessarily the point of contact for all other positions of the <em>cam</em></li>
</ol>
<div class="imgcaption" style="color: olive; font-size: 8pt; text-align: center;">
[The figure on the right shows a radial <em>cam </em>with radial-translating roller follower.]</div>
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<h3 style="color: #660000; font-family: "Book Antiqua"; font-style: italic; margin: 0px; text-transform: uppercase;">
CAM DESIGN: RADIAL CAM NOMENCLATURE</h3>
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The various terms we will very frequently use to describe the geometry of a radial <em>cam </em>are defined as fallows.</div>
<ol class="numlist" start="3" style="font-size: 14.6667px; margin-bottom: 0px; margin-top: 0px;">
<li style="padding: 3px;"><div class="tsheadings" style="color: teal; display: inline; font-weight: bold; text-decoration-line: underline;">
Pitch Curve</div>
: It is the curve drawn by the trace point assuming that the <em>cam </em>is fixed, and the trace point of the follower rotates around the cam, i.e. if we hold the <em>cam </em>fixed and rotate the follower in a direction opposite to that of the cam, then the curve generated by the locus of the trace point is called <em>pitch curve</em>.<br />For a knife-edge follower, the pitch curve and the <em>cam </em>profile are same where as for a roller follower they are separated by the radius of the roller.</li>
<li style="padding: 3px;"><div class="tsheadings" style="color: teal; display: inline; font-weight: bold; text-decoration-line: underline;">
Pressure Angle</div>
: It is the measure of steepness of the <em>cam </em>profile. The angle between the direction of the follower movement and the normal to the pitch curve at any point is called <em>pressure angle</em>. Pressure angle varies from maximum to minimum during complete rotation. Higher the pressure angle higher is side thrust and higher the chances of jamming the translating follower in its guide ways. The pressure angle should be as small as possible within the limits of design. The pressure angle should be less than 450 for low speed <em>cam </em>mechanisms with oscillating followers, whereas it should not exceed 300 in case of cams with translating followers. The pressure angle can be reduced by increasing the <em>cam </em>size or by adjusting the offset.</li>
<li style="padding: 3px;"><div class="tsheadings" style="color: teal; display: inline; font-weight: bold; text-decoration-line: underline;">
Pitch Point</div>
: The point corresponds to the point of maximum pressure angle is called <em>pitch point</em>, and a circle drawn with its centre at the <em>cam </em>centre, to pass through the pitch point, is known as the <em>pitch circle</em>.</li>
<li style="padding: 3px;"><div class="tsheadings" style="color: teal; display: inline; font-weight: bold; text-decoration-line: underline;">
Prime Circle</div>
: The <em>prime circle</em> is the smallest circle that can be drawn so as to be tangential to the pitch curve, with its centre at the <em>cam </em>centre. For a roller follower, the radius of the prime circle will be equal to the radius of the base circle plus that of the roller where as for knife-edge follower the prime circle will coincides with the base circle.</li>
</ol>
<div>
<a href="http://nptel.ac.in/courses/Webcourse-contents/IIT-Delhi/Kinematics%20of%20Machine/site/coursecontent/cntmod10.htm" style="background-color: white; color: #ff5500; font-size: 14.6667px; letter-spacing: 1px; text-decoration-line: none; text-indent: 10px;">Introduction to Cams & its classification, basic terminology of cams, analysis of follower motion.</a></div>
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<h3 style="color: #660000; font-family: "Book Antiqua"; font-style: italic; margin: 0px; text-transform: uppercase;">
INTRODUCTION</h3>
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A gear is a toothed element commonly used for transmitting rotary motion from one shaft to another if the centre to center distance is relatively less. It is a higher-pair mechanism. The power transmitting capacity for gears is high when compared to the other power transmitting elements. Gears are used widely in our day to day life, automobile industry to meet different speed requirements for the same power.</div>
<h3 style="color: #660000; font-family: "Book Antiqua"; font-style: italic; margin: 0px; text-transform: uppercase;">
FUNDAMENTAL LAW OF GEARING</h3>
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When two parallel shafts are connected to each other by a pair of toothed wheels (gears), the number of teeth from each gear passing through the engagement zone in a given period of time is equal. If this number be <em>N</em> for a period of 1 second and the number of teeth on the two gears 1 an 2 be <em>N1</em> and <em>N2</em>, respectively, then gars 1 and 2 make (<em>N / N1</em>) and (<em>N / N2</em>) revolutions, respectively. Hence, the average angular velocities of these two gears can be written as</div>
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<img alt="equation" class="equation" src="http://nptel.ac.in/courses/Webcourse-contents/IIT-Delhi/Kinematics%20of%20Machine/site/gear/eqn/eqn3_1.gif" style="display: inline; font-size: 14.6667px; font-style: italic; margin-left: 50px; vertical-align: middle;" /><br />
<img alt="equation" class="equation" src="http://nptel.ac.in/courses/Webcourse-contents/IIT-Delhi/Kinematics%20of%20Machine/site/gear/eqn/eqn3_2.gif" style="display: inline; font-size: 14.6667px; font-style: italic; margin-left: 50px; vertical-align: middle;" /><span style="background-color: white; font-size: 14.6667px;"></span></div>
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The ratio of these average angular velocities in</div>
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<img alt="equation" class="equation" src="http://nptel.ac.in/courses/Webcourse-contents/IIT-Delhi/Kinematics%20of%20Machine/site/gear/eqn/eqn3_3.gif" style="display: inline; font-size: 14.6667px; font-style: italic; margin-left: 50px; vertical-align: middle;" /></div>
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However, the ratio of the instantaneous angular speeds in general is not a constant and takes the form</div>
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<img alt="equation" class="equation" src="http://nptel.ac.in/courses/Webcourse-contents/IIT-Delhi/Kinematics%20of%20Machine/site/gear/eqn/eqn3_4.gif" style="display: inline; font-size: 14.6667px; font-style: italic; margin-left: 50px; vertical-align: middle;" /></div>
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Where <em>P(t)</em> is a periodic function of time with zero average. This relation suggests that, for a given constant driving speed, the rotation of the driven gear is not uniform rotation. This results in harmful effects, and proper gearing action requires the tooth profile to be so chosen that, for a constant droving speed, the driven shat also rotates uniformly. Thus, proper gearing action implies</div>
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<img alt="equation" class="equation" src="http://nptel.ac.in/courses/Webcourse-contents/IIT-Delhi/Kinematics%20of%20Machine/site/gear/eqn/eqn3_5.gif" style="display: inline; font-size: 14.6667px; font-style: italic; margin-left: 50px; vertical-align: middle;" /></div>
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To attain the above condition the gear pair must satisfy the condition “The common normal <em>AB</em> to the involutes at the point of contact <em>Q</em> (called the line of action) meets the line of centres <em>O<sub>1</sub>O<sub>2</sub></em> at the (fixed) pitch point <em>P</em>. this is the condition required for maintaining a constant angular velocity ratio and is known as the <strong><em>fundamental law of gearing</em></strong>”</div>
<h3 style="color: #660000; font-family: "Book Antiqua"; font-style: italic; margin: 0px; text-transform: uppercase;">
: CHARACTERISTICS OF INVOLUTE ACTION</h3>
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<img alt="Figure 3" class="float_right" src="http://nptel.ac.in/courses/Webcourse-contents/IIT-Delhi/Kinematics%20of%20Machine/site/gear/pics/image003.png" style="float: right; font-size: 14.6667px; padding-left: 25px;" /></div>
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Here we are going in to the quantitative analysis of some important aspects relating to involute gears.</div>
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Contact Ratio</div>
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To transit rotational motion continuously, there must be at least one pair of teeth in contact at all times. In the actual case, certain amount of overlap exists between the actions of two consecutive pairs of teeth. The term contact ratio is used to provide a quantitative measure of the amount of this overlap. Figure shows a pair of teeth at the beginning and end of contact. So, at the point <em>E</em> ( on the line of action ,i.e., the common tangent to the base circles of the two gears), the contact begins and at <em>F</em> the contact ends. The points <em>S</em> and <em>T</em> are the points on a tooth of gear2 (on its base circle) at the start and end of contact, respectively. Since <em>E</em> and <em>F</em> are two points on two involutes with the same base circle, the length EF (called the length of action) will be equal to <em>ST</em>. now, the ratio (<em>ST/ base pitch</em> ) is a measure of the <strong>contact ratio</strong>, <em>m<sub>c</sub></em>. So,</div>
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<img alt="equation" class="equation" src="http://nptel.ac.in/courses/Webcourse-contents/IIT-Delhi/Kinematics%20of%20Machine/site/gear/eqn/eqn6_1.gif" style="display: inline; font-size: 14.6667px; font-style: italic; margin-left: 50px; vertical-align: middle;" /></div>
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The base pitch of gear 2 can be expressed as <img alt="inlinesymbol" class="inlinesymbol" src="http://nptel.ac.in/courses/Webcourse-contents/IIT-Delhi/Kinematics%20of%20Machine/site/gear/eqn/eqn6_2.gif" style="display: inline; font-size: 11pt; font-style: italic; vertical-align: middle;" />, where <em>rb<sub>2</sub></em> is the base circle radius of gear 2 and <em>N<sub>2</sub></em> is the number of teeth on this gear. The above figure shows the essential dimensions of the gears in contact. From those figure, the length of action.</div>
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<img alt="equation" class="equation" src="http://nptel.ac.in/courses/Webcourse-contents/IIT-Delhi/Kinematics%20of%20Machine/site/gear/eqn/eqn6_3.gif" style="display: inline; font-size: 14.6667px; font-style: italic; margin-left: 50px; vertical-align: middle;" /><span style="background-color: white; font-size: 14.6667px;"></span></div>
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If <em>ro<sub>1</sub></em> and <em>roOfc</em> are the outer circle (same as the addendum circle ) radii, then this relation yields</div>
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<img alt="equation" class="equation" src="http://nptel.ac.in/courses/Webcourse-contents/IIT-Delhi/Kinematics%20of%20Machine/site/gear/eqn/eqn6_4.gif" style="display: inline; font-size: 14.6667px; font-style: italic; margin-left: 50px; vertical-align: middle;" /><span style="background-color: white; font-size: 14.6667px;"></span></div>
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Where <em>C= rp<sub>1</sub> + rp<sub>2</sub></em> ( = centre distance) and <em>rb<sub>1</sub></em> is the base circle radius of gear 1, <em>rp<sub>1</sub></em> and <em>rpfc</em> being the pitch circle radii with α as the pressure angle. So, the expression for contact ratio becomes</div>
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<img alt="equation" class="equation" src="http://nptel.ac.in/courses/Webcourse-contents/IIT-Delhi/Kinematics%20of%20Machine/site/gear/eqn/eqn6_5.gif" style="display: inline; font-size: 14.6667px; font-style: italic; margin-left: 50px; vertical-align: middle;" /><span style="background-color: white; font-size: 14.6667px;"></span></div>
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Normally, the contact ratio is not a whole number. If the ratio is 1.3 it means that there alternately, one pair and two pairs of teeth in contact and the time average is 1.3. In practice, a value of 1.4 is recommended for m c for smooth and good performance. It cam de seen from figure (3) that by increasing the addendum the </div>
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length of the path of contact <em>EF</em> can de increased , resulting in a larger value of the contact ratio. But increasing the addendum can lead to some problems.</div>
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Mechanical Engineering Departmenthttp://www.blogger.com/profile/12582953924770018783noreply@blogger.comtag:blogger.com,1999:blog-6302071579893645567.post-52290577715618869022017-07-27T14:04:00.000+05:302017-07-27T14:04:34.072+05:30Fluid Machines Notes<div dir="ltr" style="text-align: left;" trbidi="on">
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<strong>INTRODUCTION</strong></div>
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A fluid machine is a device which converts the energy stored by a fluid into mechanical energy or <em>vice versa </em>. The energy stored by a fluid mass appears in the form of potential, kinetic and intermolecular energy. The mechanical energy, on the other hand, is usually transmitted by a rotating shaft. Machines using liquid (mainly water, for almost all practical purposes) are termed as hydraulic machines. In this chapter we shall discuss, in general, the basic fluid mechanical principle governing the energy transfer in a fluid machine and also a brief description of different kinds of hydraulic machines along with their performances. Discussion on machines using air or other gases is beyond the scope of the chapter.</div>
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<strong>CLASSIFICAITONS OF FLUID MACHINES</strong></div>
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The fluid machines may be classified under different categories as follows:</div>
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<strong>Classification Based on Direction of Energy Conversion.</strong></div>
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The device in which the kinetic, potential or intermolecular energy held by the fluid is converted in the form of mechanical energy of a rotating member is known as a <em>turbine </em>. The machines, on the other hand, where the mechanical energy from moving parts is transferred to a fluid to increase its stored energy by increasing either its pressure or velocity are known as <em>pumps, compressors, fans or blowers </em>.</div>
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<strong>Classification Based on Principle of Operation</strong></div>
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The machines whose functioning depend essentially on the change of volume of a certain amount of fluid within the machine are known as <em>positive displacement machines </em>. The word positive displacement comes from the fact that there is a physical displacement of the boundary of a certain fluid mass as a closed system. This principle is utilized in practice by the reciprocating motion of a piston within a cylinder while entrapping a certain amount of fluid in it. Therefore, the word reciprocating is commonly used with the name of the machines of this kind. The machine producing mechanical energy is known as reciprocating engine while the machine developing energy of the fluid from the mechanical energy is known as reciprocating pump or reciprocating compressor.</div>
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The machines, functioning of which depend basically on the principle of fluid dynamics, are known as <em>rotodynamic machines </em>. They are distinguished from positive displacement machines in requiring relative motion between the fluid and the moving part of the machine. The rotating element of the machine usually consisting of a number of vanes or blades, is known as rotor or impeller while the fixed part is known as stator. Impeller is the heart of rotodynamic machines, within which a change of angular momentum of fluid occurs imparting torque to the rotating member.</div>
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For turbines, the work is done by the fluid on the rotor, while, in case of pump, compressor, fan or blower, the work is done by the rotor on the fluid element. Depending upon the main direction of fluid path in the rotor, the machine is termed <em>as radial flow or axial flow machine </em>. In radial flow machine, the main direction of flow in the rotor is radial while in axial flow machine, it is axial. For radial flow turbines, the flow is towards the centre of the rotor, while, for pumps and compressors, the flow is away from the centre. Therefore, radial flow turbines are sometimes referred to as radially <em>inward flow machines </em>and radial flow pumps as radially outward flow machines. Examples of such machines are the Francis turbines and the centrifugal pumps or compressors. The examples of axial flow machines are Kaplan turbines and axial flow compressors. If the flow is party radial and partly axial, the term <em>mixed-flow machine</em> is used. Figure 1.1 (a) (b) and (c) are the schematic diagrams of various types of impellers based on the flow direction.</div>
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<img src="http://nptel.ac.in/courses/112104117/chapter_1/fig1.1.gif" style="text-align: left;" /></div>
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<strong>Classification Based on Fluid Used</strong></div>
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The fluid machines use either liquid or gas as the working fluid depending upon the purpose. The machine transferring mechanical energy of rotor to the energy of fluid is termed as a pump when it uses liquid, and is termed as a compressor or a fan or a blower, when it uses gas. The compressor is a machine where the main objective is to increase the static pressure of a gas. Therefore, the mechanical energy held by the fluid is mainly in the form of pressure energy. Fans or blowers, on the other hand, mainly cause a high flow of gas, and hence utilize the mechanical energy of the rotor to increase mostly the kinetic energy of the fluid. In these machines, the change in static pressure is quite small.</div>
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For all practical purposes, liquid used by the turbines producing power is water, and therefore, they are termed <em>as water turbines or hydraulic turbines </em>. Turbines handling gases in practical fields are usually referred to as <em>steam turbine, gas turbine, and </em><em>air turbine</em> depending upon whether they use steam, gas (the mixture of air and products of burnt fuel in air) or air.</div>
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<strong>ROTODYNAMIC MACHINES</strong></div>
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In this section, we shall discuss the basic principle of rotodynamic machines and the performance of different kinds of those machines. The important element of a rotodynamic machine, in general, is a rotor consisting of a number of vanes or blades. There always exists a relative motion between the rotor vanes and the fluid. The fluid has a component of velocity and hence of momentum in a direction tangential to the rotor. While flowing through the rotor, tangential velocity and hence the momentum changes.</div>
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The rate at which this tangential momentum changes corresponds to a tangential force on the rotor. In a turbine, the tangential momentum of the fluid is reduced and therefore work is done by the fluid to the moving rotor. But in case of pumps and compressors there is an increase in the tangential momentum of the fluid and therefore work is absorbed by the fluid from the moving rotor.</div>
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<strong>Basic Equation of Energy Transfer in Rotodynamic Machines</strong></div>
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The basic equation of fluid dynamics relating to energy transfer is same for all rotodynamic machines and is a simple form of " Newton 's Laws of Motion" applied to a fluid element traversing a rotor. Here we shall make use of the momentum theorem as applicable to a fluid element while flowing through fixed and moving vanes. Figure 1.2 represents diagrammatically a rotor of a generalised fluid machine, with 0-0 the axis of rotation and <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_1a_clip_image002.gif" /> the angular velocity. Fluid enters the rotor at 1, passes through the rotor by any path and is discharged at 2. The points 1 and 2 are at radii <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_1a_clip_image004.gif" /> and <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_1a_clip_image006.gif" /> from the centre of the rotor, and the directions of fluid velocities at 1 and 2 may be at any arbitrary angles. For the analysis of energy transfer due to fluid flow in this situation, we assume the following:</div>
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<span class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">(a)</span> <span class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">The flow is steady, that is, the mass flow rate is constant across any section (no storage or depletion of fluid mass in the rotor).</span></div>
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(b) The heat and work interactions between the rotor and its surroundings take place at a constant rate.</div>
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(c) Velocity is uniform over any area normal to the flow. This means that the velocity vector at any point is representative of the total flow over a finite area. This condition also implies that there is no leakage loss and the entire fluid is undergoing the same process.</div>
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The velocity at any point may be resolved into three mutually perpendicular components as shown in Fig 1.2. The axial component of velocity <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_1a_clip_image002_0000.gif" /> is directed parallel to the axis of rotation , the radial component <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_1a_clip_image004_0000.gif" /> is directed radially through the axis to rotation, while the tangential component <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_1a_clip_image006_0000.gif" /> is directed at right angles to the radial direction and along the tangent to the rotor at that part.</div>
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The change in magnitude of the axial velocity components through the rotor causes a change in the axial momentum. This change gives rise to an axial force, which must be taken by a thrust bearing to the stationary rotor casing. The change in magnitude of radial velocity causes a change in momentum in radial direction</div>
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<img src="http://nptel.ac.in/courses/112104117/chapter_1/gif1.gif" /></div>
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However, for an axisymmetric flow, this does not result in any net radial force on the rotor. In case of a non uniform flow distribution over the periphery of the rotor in practice, a change in momentum in radial direction may result in a net radial force which is carried as a journal load. The tangential component <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_1b_clip_image002_0000.gif" /> only has an effect on the angular motion of the rotor. In consideration of the entire fluid body within the rotor as a control volume, we can write from the moment of momentum theorem</div>
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<tr><th scope="row"><img height="19" src="http://nptel.ac.in/courses/112104117/chapter_1/1_1b_clip_image004_0000.gif" width="150" /></th><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;"><div align="right">
(1.1)</div>
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where<em> T</em> is the torque exerted by the rotor on the moving fluid, <em>m</em> is the mass flow rate of fluid through the rotor. The subscripts 1 and 2 denote values at inlet and outlet of the rotor respectively. The rate of energy transfer to the fluid is then given by</div>
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<tr><th scope="row"><img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_1b_clip_image002_0001.gif" /></th><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;"><div align="right">
(1.2)</div>
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where <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_1b_clip_image004_0001.gif" /> is the angular velocity of the rotor and <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_1b_clip_image006_0000.gif" /> which represents the linear velocity of the rotor. Therefore <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_1b_clip_image008_0000.gif" /> and <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_1b_clip_image010_0000.gif" /> are the linear velocities of the rotor at points 2 (outlet ) and 1 (inlet) respectively (Fig. 1.2). The Eq, (1.2) is known as Euler's equation in relation to fluid machines. The Eq. (1.2) can be written in terms of head gained '<em>H</em>' by the fluid as</div>
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<tr><th scope="row" width="410"><img src="http://nptel.ac.in/courses/112104117/chapter_1/1_1b_clip_image012_0000.gif" /></th><td width="30"><div align="right" class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
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(1.3)</div>
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In usual convention relating to fluid machines, the head delivered by the fluid to the rotor is considered to be positive and vice-versa. Therefore, Eq. (1.3) written with a change in the sign of the right hand side in accordance with the sign convention as</div>
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<tr><th scope="row" width="410"><img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_1b_clip_image014_0000.gif" /></th><td width="30"><div align="center" class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
(1.4)</div>
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<span class="style11" style="font-style: italic; font-weight: bold;">Components of Energy Transfer</span> It is worth mentioning in this context that either of the Eqs. (1.2) and (1.4) is applicable regardless of changes in density or components of velocity in other directions. Moreover, the shape of the path taken by the fluid in moving from inlet to outlet is of no consequence. The expression involves only the inlet and outlet conditions. A rotor, the moving part of a fluid machine, usually consists of a number of vanes or blades mounted on a circular disc. Figure 1.3a shows the velocity triangles at the inlet and outlet of a rotor. The inlet and outlet portions of a rotor vane are only shown as a representative of the whole rotor.</div>
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<tr><th scope="row"><span class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; font-weight: normal; text-align: justify;"><img align="absmiddle" height="444" src="http://nptel.ac.in/courses/112104117/chapter_1/gif2.gif" width="595" /></span></th></tr>
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<strong>(a)</strong></div>
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<strong>(b)</strong></div>
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<tr><th class="BodyText" scope="row" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; font-weight: normal; text-align: justify;" width="81"><span class="BodyText style6" style="color: #990000;"><strong>Fig 1.3 (a)</strong></span></th><td width="359"><span class="BodyText style6" style="color: #990000; font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;"><strong>Velocity triangles for a generalised rotor vane</strong></span></td></tr>
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<tr><th class="BodyText" scope="row" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; font-weight: normal; text-align: justify;" width="81"><span class="BodyText style6" style="color: #990000;"><strong>Fig 1.3 (b)</strong></span></th><td width="359"><span class="BodyText style6" style="color: #990000; font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;"><strong>Centrifugal effect in a flow of fluid with rotation</strong></span></td></tr>
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Vector diagrams of velocities at inlet and outlet correspond to two velocity triangles, where <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_1b_clip_image016_0000.gif" /> is the velocity of fluid relative to the rotor and <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_1b_clip_image018_0000.gif" /> are the angles made by the directions of the absolute velocities at the inlet and outlet respectively with the tangential direction, while <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_1b_clip_image020_0000.gif" /> and <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_1b_clip_image022_0000.gif" /> are the angles made by the relative velocities with the tangential direction. The angles <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_1b_clip_image020_0001.gif" /> and <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_1b_clip_image022_0001.gif" /> should match with vane or blade angles at inlet and outlet respectively for a smooth, shockless entry and exit of the fluid to avoid undersirable losses. Now we shall apply a simple geometrical relation as follows:</div>
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From the inlet velocity triangle,</div>
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<span class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; font-weight: normal; text-align: justify;">or</span>, <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_1b_clip_image027.gif" /></div>
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(1.5)</div>
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Similarly from the outlet velocity triangle.</div>
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<span class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; font-weight: normal; text-align: justify;">or, </span><img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_1b_clip_image002_0002.gif" /></div>
</th><td width="30"><div align="right" class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
(1.6)</div>
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Invoking the expressions of <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_1b_clip_image033_0000.gif" /> and <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_1b_clip_image035_0000.gif" /> in Eq. (1.4), we get <em>H</em> (Work head, i.e. energy per unit weight of fluid, transferred between the fluid and the rotor as) as</div>
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<div align="right">
(1.7)</div>
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The Eq (1.7) is an important form of the Euler's equation relating to fluid machines since it gives the three distinct components of energy transfer as shown by the pair of terms in the round brackets. These components throw light on the nature of the energy transfer. The first term of Eq. (1.7) is readily seen to be the change in absolute kinetic energy or dynamic head of the fluid while flowing through the rotor. The second term of Eq. (1.7) represents a change in fluid energy due to the movement of the rotating fluid from one radius of rotation to another.</div>
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More About Energy Transfer in Turbomachines</div>
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Equation (1.7) can be better explained by demonstrating a steady flow through a container having uniform angular velocity <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_2_clip_image002.gif" /> as shown in Fig.1.3b. The centrifugal force on an infinitesimal body of a fluid of mass d<em>m </em>at radius <em>r </em>gives rise to a pressure differential d<em>p</em> across the thickness d<em>r </em>of the body in a manner that a differential force of d<em>p</em>d<em>A</em> acts on the body radially inward. This force, in fact, is the centripetal force responsible for the rotation of the fluid element and thus becomes equal to the centrifugal force under equilibrium conditions in the radial direction. Therefore, we can write</div>
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<span class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px;">with d<em>m </em>= d<em>A</em> d</span><span class="style7" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; font-style: italic;">r</span><span class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px;"> ρ where ρ is the density of the fluid, it becomes</span></div>
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For a reversible flow (flow without friction) between two points, say, 1 and 2, the work done per unit mass of the fluid (i.e., the flow work) can be written as</div>
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The work is, therefore, done on or by the fluid element due to its displacement from radius <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_2_clip_image002_0003.gif" /> to radius <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_2_clip_image004.gif" /> and hence becomes equal to the energy held or lost by it. Since the centrifugal force field is responsible for this energy transfer, the corresponding head (energy per unit weight) <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_2_clip_image006.gif" /> is termed as centrifugal head. The transfer of energy due to a change in centrifugal head <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_2_clip_image008.gif" /> causes a change in the static head of the fluid.</div>
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The third term represents a change in the static head due to a change in fluid velocity relative to the rotor. This is similar to what happens in case of a flow through a fixed duct of variable cross-sectional area. Regarding the effect of flow area on fluid velocity <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_2_clip_image010.gif" /> relative to the rotor, a converging passage in the direction of flow through the rotor increases the relative velocity <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_2_clip_image012.gif" />and hence decreases the static pressure. This usually happens in case of turbines. Similarly, a diverging passage in the direction of flow through the rotor decreases the relative velocity <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_2_clip_image014.gif" />and increases the static pressure as occurs in case of pumps and compressors.</div>
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The fact that the second and third terms of Eq. (1.7) correspond to a change in static head can be demonstrated analytically by deriving Bernoulli's equation in the frame of the rotor.</div>
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In a rotating frame, the momentum equation for the flow of a fluid, assumed "inviscid" can be written as</div>
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where <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_2_clip_image002_0004.gif" /> is the fluid velocity relative to the coordinate frame rotating with an angular velocity <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_2_clip_image004_0000.gif" />.</div>
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<span class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">We assume that the flow is steady in the rotating frame so that</span> <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_2_clip_image002_0006.gif" />. <span class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">We choose a cylindrical coordinate system <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_2_clip_image004_0001.gif" /> with z-axis along the axis of rotation. Then the momentum equation reduces to</span></div>
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where <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_2_clip_image008_0001.gif" /> and <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_2_clip_image010_0001.gif" /> are the unit vectors along <em>z </em>and <em>r </em>direction respectively. Let <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_2_clip_image012_0001.gif" /> be a unit vector in the direction of <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_2_clip_image014_0001.gif" />and <em>s </em>be a coordinate along the stream line. Then we can write</div>
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<span class="Black_Heading" style="color: black; font-size: 14px;">More About Energy Transfer in Turbomachines</span></div>
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Taking scalar product with <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_3_clip_image002.gif" /> it becomes</div>
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We have used <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_3_clip_image006.gif" />. With a little rearrangement, we have</div>
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Since <em>v </em>is the velocity relative to the rotating frame we can replace it by <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_3_clip_image010.gif" />. Further <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_3_clip_image012.gif" /> is the linear velocity of the rotor. Integrating the momentum equation from inlet to outlet along a streamline we have</div>
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<tr><th scope="row" width="410"><span class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; font-weight: normal; text-align: justify;">or,</span> <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_3_clip_image016.gif" /></th><td width="30"><div align="right" class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
<div align="right">
(2.1)</div>
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Therefore, we can say, with the help of Eq. (2.1), that last two terms of Eq. (1.7) represent a change in the static head of fluid.</div>
<span class="Black_Heading" style="font-family: Arial, Helvetica, sans-serif; font-size: 14px; font-weight: bold;"><strong>Energy Transfer in Axial Flow Machines</strong> </span><span class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;"><br />For an axial flow machine, the main direction of flow is parallel to the axis of the rotor, and hence the inlet and outlet points of the flow do not vary in their radial locations from the axis of rotation. Therefore, <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_3_clip_image018.gif" /> and the equation of energy transfer Eq. (1.7) can be written, under this situation, as</span><br />
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(2.2)</div>
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Hence, change in the static head in the rotor of an axial flow machine is only due to the flow of fluid through the variable area passage in the rotor.</div>
<span class="Black_Heading" style="font-family: Arial, Helvetica, sans-serif; font-size: 14px; font-weight: bold;"><strong>Radially Outward and Inward Flow Machines</strong><strong></strong></span><span class="style10" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;"><strong><br /></strong></span><span class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">For radially outward flow machines, <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_3_clip_image022.gif" />, and hence the fluid gains in static head, while, for a radially inward flow machine, <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_3_clip_image002_0003.gif" /> and the fluid losses its static head. Therefore, in radial flow pumps or compressors the flow is always directed radially outward, and in a radial flow turbine it is directed radially inward.</span><br />
<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
<span class="Heading" style="color: #993300; font-size: 16px; font-weight: bold;">Impulse and Reaction Machines </span>The relative proportion of energy transfer obtained by the change in static head and by the change in dynamic head is one of the important factors for classifying fluid machines. The machine for which the change in static head in the rotor is zero is known as <em>impulse machine </em>. In these machines, the energy transfer in the rotor takes place only by the change in dynamic head of the fluid. The parameter characterizing the proportions of changes in the dynamic and static head in the rotor of a fluid machine is known as degree of reaction and is defined as the ratio of energy transfer by the change in static head to the total energy transfer in the rotor.</div>
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Therefore, the degree of reaction,</div>
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<div align="right">
(2.3)</div>
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<span class="Heading" style="color: #993300; font-size: 16px; font-weight: bold;">Impulse and Reaction Machines</span></div>
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For an impulse machine <em>R = 0 </em>, because there is no change in static pressure in the rotor. It is difficult to obtain a radial flow impulse machine, since the change in centrifugal head is obvious there. Nevertheless, an impulse machine of radial flow type can be conceived by having a change in static head in one direction contributed by the centrifugal effect and an equal change in the other direction contributed by the change in relative velocity. However, this has not been established in practice. Thus for an axial flow impulse machine <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_4_clip_image002.gif" />. For an impulse machine, the rotor can be made open, that is, the velocity <em>V<sub>1</sub></em> can represent an open jet of fluid flowing through the rotor, which needs no casing. A very simple example of an impulse machine is a paddle wheel rotated by the impingement of water from a stationary nozzle as shown in Fig.2.1a.</div>
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<tr><th scope="row"><span class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; font-weight: normal; text-align: justify;"><img align="absmiddle" height="299" src="http://nptel.ac.in/courses/112104117/chapter_1/1.gif" width="529" /></span></th></tr>
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<tr><th class="BodyText" scope="row" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; font-weight: normal; text-align: justify;" width="53"><span class="BodyText style15" style="color: #990000;"><strong>Fig 2.1</strong></span></th><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;" width="387"><span class="BodyText style15" style="color: #990000;"><strong>(a) Paddle wheel as an example of impulse turbine</strong></span></td></tr>
<tr><th scope="row"> </th><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;"><span class="BodyText style15" style="color: #990000;"><strong>(b) Lawn sprinkler as an example of reaction turbine</strong></span></td></tr>
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<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
A machine with any degree of reaction must have an enclosed rotor so that the fluid cannot expand freely in all direction. A simple example of a reaction machine can be shown by the familiar lawn sprinkler, in which water comes out (Fig. 2.1b) at a high velocity from the rotor in a tangential direction. The essential feature of the rotor is that water enters at high pressure and this pressure energy is transformed into kinetic energy by a nozzle which is a part of the rotor itself.</div>
<span class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">In the earlier example of impulse machine (Fig. 2.1a), the nozzle is stationary and its function is only to transform pressure energy to kinetic energy and finally this kinetic energy is transferred to the rotor by pure impulse action. The change in momentum of the fluid in the nozzle gives rise to a reaction force but as the nozzle is held stationary, no energy is transferred by it. In the case of lawn sprinkler (Fig. 2.1b), the nozzle, being a part of the rotor, is free to move and, in fact, rotates due to the reaction force caused by the change in momentum of the fluid and hence the </span><span class="style14" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">word</span><span class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;"><strong><em> reaction machine </em></strong>follows.</span><br />
<span class="Heading" style="color: #993300; font-family: Arial, Helvetica, sans-serif; font-size: 16px; font-weight: bold;">Efficiencies </span><span class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;"><br />The concept of efficiency of any machine comes from the consideration of energy transfer and is defined, in general, as the ratio of useful energy delivered to the energy supplied. Two efficiencies are usually considered for fluid machines-- the hydraulic efficiency concerning the energy transfer between the fluid and the rotor, and the overall efficiency concerning the energy transfer between the fluid and the shaft. The difference between the two represents the energy absorbed by bearings, glands, couplings, etc. or, in general, by pure mechanical effects which occur between the rotor itself and the point of actual power input or output.</span><br />
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Therefore, for a pump or compressor,</div>
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(2.4b)</div>
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For a turbine,</div>
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(2.5a)</div>
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<br />
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(2.5b)</div>
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<span class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">The ratio of rotor and shaft energy is represented by mechanical efficiency</span> <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_4_clip_image012.gif" />.<br />
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Therefore</div>
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<br /></div>
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Principle of Similarity and Dimensional Analysis</div>
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The principle of similarity is a consequence of nature for any physical phenomenon. By making use of this principle, it becomes possible to predict the performance of one machine from the results of tests on a geometrically similar machine, and also to predict the performance of the same machine under conditions different from the test conditions. For fluid machine, geometrical similarity must apply to all significant parts of the system viz., the rotor, the entrance and discharge passages and so on. Machines which are geometrically similar form a homologous series. Therefore, the member of such a series, having a common shape are simply enlargements or reductions of each other. If two machines are kinematically similar, the velocity vector diagrams at inlet and outlet of the rotor of one machine must be similar to those of the other. Geometrical similarity of the inlet and outlet velocity diagrams is, therefore, a necessary condition for dynamic similarity.</div>
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Let us now apply dimensional analysis to determine the dimensionless parameters, i.e., the π terms as the criteria of similarity for flows through fluid machines. For a machine of a given shape, and handling compressible fluid, the relevant variables are given in Table 3.1</div>
<blockquote>
<blockquote>
<blockquote>
<div align="left" class="BodyText style12" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; font-weight: bold; text-align: justify;">
Table 3.1 Variable Physical Parameters of Fluid Machine</div>
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</blockquote>
</blockquote>
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<strong>Variable physical parameters</strong></div>
</th><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;" width="176"><div align="center">
<strong>Dimensional formula</strong></div>
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<tr><th scope="row"> </th><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;"><div align="center">
</div>
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<em>D </em>= any physical dimension of the machine as a measure of the machine's size, usually the rotor diameter</div>
</th><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;"><div align="center" class="BodyText">
<div align="left">
<blockquote>
L</blockquote>
</div>
</div>
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<div align="left">
<em>Q </em>= volume flow rate through the machine</div>
</div>
</th><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;"><blockquote>
<div align="center" class="BodyText">
L<sup>3</sup> T <sup>-1</sup></div>
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<em>N </em>= rotational speed (rev/min.)</div>
</th><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;"><div align="center" class="BodyText">
<div align="left">
<blockquote>
T <sup>-1</sup></blockquote>
</div>
</div>
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<tr class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;"><th class="BodyText" scope="row" style="font-weight: normal; text-align: justify;"><em>H </em>= difference in head (energy per unit weight) across the machine. This may be either gained or given by the fluid depending upon whether the machine is a pump or a turbine respectively</th><td class="BodyText"><div align="left">
<blockquote>
L</blockquote>
</div>
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<span class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; font-weight: normal; text-align: justify;"><em><img src="http://nptel.ac.in/courses/112104117/chapter_1/1_2_clip_image002_0008.gif" /></em></span>=<span class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; font-weight: normal; text-align: justify;">density of fluid</span></div>
</th><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;"><div align="left">
<blockquote>
ML<sup>-3</sup></blockquote>
</div>
</td></tr>
<tr><th scope="row"><div align="left">
<img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_5_clip_image002_0002.gif" /> <span class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; font-weight: normal; text-align: justify;">= viscosity of fluid</span></div>
</th><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;"><blockquote>
<div align="center" class="BodyText">
ML<sup>-1</sup> T <sup>-1</sup></div>
</blockquote>
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<tr><th class="BodyText" scope="row" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; font-weight: normal; text-align: justify;"><em>E </em>= coefficient of elasticity of fluid</th><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;"><blockquote>
<div class="BodyText">
ML<sup>-1</sup> T<sup>-2</sup></div>
</blockquote>
</td></tr>
<tr><th class="BodyText" scope="row" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; font-weight: normal; text-align: justify;"><em>g </em>= acceleration due to gravity</th><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;"><blockquote>
LT <sup>-2</sup></blockquote>
</td></tr>
<tr><th class="BodyText" scope="row" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; font-weight: normal; text-align: justify;"><em>P</em> = power transferred between fluid and rotor (the difference between <em>P</em> and <em>H</em> is taken care of by the hydraulic efficiency <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_5_clip_image002_0003.gif" /></th><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;"><blockquote>
ML<sup>2</sup> T<sup>-3</sup></blockquote>
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<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
In almost all fluid machines flow with a free surface does not occur, and the effect of gravitational force is negligible. Therefore, it is more logical to consider the energy per unit mass <em>gH </em>as the variable rather than <em>H </em>alone so that acceleration due to gravity does not appear as a separate variable. Therefore, the number of separate variables becomes eight: <em>D, Q, N, gH, ρ, µ, </em><em>E </em>and <em>P </em>. Since the number of fundamental dimensions required to express these variable are three, the number of independent π terms (dimensionless terms), becomes five. Using Buckingham's π theorem with <em>D, N </em>and ρ as the repeating variables, the expression for the terms are obtained as,</div>
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<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
We shall now discuss the physical significance and usual terminologies of the different π terms. All lengths of the machine are proportional to <em>D </em>, and all areas to D<sup>2</sup>. Therefore, the average flow velocity at any section in the machine is proportional to <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_5_clip_image006_0000.gif" />. Again, the peripheral velocity of the rotor is proportional to the product <em>ND </em>. The first π term can be expressed as</div>
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<span class="Heading" style="font-size: 16px;">Similarity and Dimensional Analysis</span><strong></strong></div>
<div class="BodyText" style="background-color: white; font-family: Arial, Helvetica, sans-serif; font-size: 13px; font-weight: normal; text-align: justify;">
Thus, <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_6_clip_image002.gif" /> represents the condition for kinematic similarity, and is known as <em>capacity </em><em>coefficient </em>or <em>discharge coefficient </em>The second <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_6_clip_image004.gif" /> term <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_6_clip_image006.gif" /> is known as the <em>head </em><em>coefficient </em>since it expresses the head <em>H </em>in dimensionless form. Considering the fact that <em>ND</em> <img src="http://nptel.ac.in/courses/112104117/chapter_1/1_6_clip_image008.gif" /> rotor velocity, the term <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_6_clip_image006_0000.gif" /> becomes <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_6_clip_image011.gif" />, and can be interpreted as the ratio of fluid head to kinetic energy of the rotor, Dividing <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_6_clip_image006_0001.gif" /> by the square of <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_6_clip_image002_0000.gif" /> we get</div>
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<div class="BodyText" style="background-color: white; font-family: Arial, Helvetica, sans-serif; font-size: 13px; font-weight: normal; text-align: justify;">
The term <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_6_clip_image002_0002.gif" /> can be expressed as <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_6_clip_image004_0000.gif" /> and thus represents the Reynolds number with rotor velocity as the characteristic velocity. Again, if we make the product of <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_6_clip_image006_0002.gif" /> and <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_6_clip_image002_0003.gif" />, it becomes <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_6_clip_image002_0015.gif" /> which represents the Reynolds's number based on fluid velocity. Therefore, if <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_6_clip_image006_0003.gif" /> is kept same to obtain kinematic similarity, <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_6_clip_image002_0004.gif" /> becomes proportional to the Reynolds number based on fluid velocity.</div>
<div class="BodyText" style="background-color: white; font-family: Arial, Helvetica, sans-serif; font-size: 13px; font-weight: normal; text-align: justify;">
The term <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_6_clip_image012.gif" /> expresses the power <em>P </em>in dimensionless form and is therefore known as <em>power coefficient </em>. Combination of <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_6_clip_image014.gif" /> and <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_6_clip_image016.gif" /> in the form of <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_6_clip_image018.gif" /> gives <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_6_clip_image020.gif" />. The term 'PQgH' represents the rate of total energy given up by the fluid, in case of turbine, and gained by the fluid in case of pump or compressor. Since <em>P</em> is the power transferred to or from the rotor. Therefore <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_6_clip_image018_0000.gif" /> becomes the hydraulic efficiency <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_6_clip_image025.gif" />for a turbine and <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_6_clip_image027.gif" /> for a pump or a compressor. From the fifth <img src="http://nptel.ac.in/courses/112104117/chapter_1/1_6_clip_image029.gif" /> term, we get</div>
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<tr><th scope="row"><img src="http://nptel.ac.in/courses/112104117/chapter_1/1_6_clip_image002_0005.gif" /></th></tr>
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<div class="BodyText" style="background-color: white; font-family: Arial, Helvetica, sans-serif; font-size: 13px; font-weight: normal; text-align: justify;">
Multiplying <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_6_clip_image002_0006.gif" />, on both sides, we get</div>
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<tr><th scope="row"><img src="http://nptel.ac.in/courses/112104117/chapter_1/1_6_clip_image002_0016.gif" /></th></tr>
</tbody></table>
<div class="BodyText" style="background-color: white; font-family: Arial, Helvetica, sans-serif; font-size: 13px; font-weight: normal; text-align: justify;">
Therefore, we find that <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_6_clip_image002_0008.gif" /> represents the well known <em>Mach number </em>, Ma.</div>
<div class="BodyText" style="background-color: white; font-family: Arial, Helvetica, sans-serif; font-size: 13px; font-weight: normal; text-align: justify;">
For a fluid machine, handling incompressible fluid, the term <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_6_clip_image004_0001.gif" /> can be dropped. The effect of liquid viscosity on the performance of fluid machines is neglected or regarded as secondary, (which is often sufficiently true for certain cases or over a limited range).Therefore the term <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_6_clip_image006_0004.gif" /> can also be dropped.The general relationship between the different dimensionless variables ( <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_6_clip_image008_0000.gif" /> terms) can be expressed as</div>
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<tr><th scope="row"><img src="http://nptel.ac.in/courses/112104117/chapter_1/1_6_clip_image002_0009.gif" /></th><td><div align="right" class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
<div align="right">
(3.1)</div>
</div>
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<div class="BodyText" style="background-color: white; font-family: Arial, Helvetica, sans-serif; font-size: 13px; font-weight: normal; text-align: justify;">
<br /></div>
<div class="BodyText" style="background-color: white; font-family: Arial, Helvetica, sans-serif; font-size: 13px; font-weight: normal; text-align: justify;">
Therefore one set of relationship or curves of the <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_6_clip_image002_0013.gif" /> terms would be sufficient to describe the performance of all the members of one series.</div>
<div class="BodyText" style="background-color: white; font-family: Arial, Helvetica, sans-serif; font-size: 13px; font-weight: normal; text-align: justify;">
<br /></div>
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<tr><td><div class="Heading" style="color: #993300; font-family: Arial, Helvetica, sans-serif; font-size: 16px; font-weight: bold;">
<span class="Heading">Similarity and Dimensional Analysis</span><strong></strong><strong></strong></div>
<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
or, with another arrangement of the π terms,</div>
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<tr><th scope="row"><img height="56" src="http://nptel.ac.in/courses/112104117/chapter_1/1_6_clip_image002_0011.gif" width="225" /></th><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;"><div align="right">
(3.2)</div>
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If data obtained from tests on model machine, are plotted so as to show the variation of dimensionless parameters <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_6_clip_image002_0012.gif" /> with one another, then the graphs are applicable to any machine in the same homologous series. The curves for other homologous series would naturally be different.</div>
<div class="Heading" style="color: #993300; font-family: Arial, Helvetica, sans-serif; font-size: 16px; font-weight: bold;">
<span class="Black_Heading" style="color: black; font-size: 14px;">Specific Speed </span><span class="BodyText" style="color: black; font-size: 13px; font-weight: normal; text-align: justify;"><br />The performance or operating conditions for a turbine handling a particular fluid are usually expressed by the values of <em>N </em>, <em>P </em>and <em>H </em>, and for a pump by <em>N </em>, <em>Q </em>and <em>H </em>. It is important to know the range of these operating parameters covered by a machine of a particular shape (homologous series) at high efficiency. Such information enables us to select the type of machine best suited to a particular application, and thus serves as a starting point in its design. Therefore a parameter independent of the size of the machine <em>D </em>is required which will be the characteristic of all the machines of a homologous series. A parameter involving <em>N </em>, <em>P </em>and <em>H </em>but not <em>D </em>is obtained by dividing <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_6_clip_image004_0002.gif" /> by <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_6_clip_image006_0005.gif" />. Let this parameter be designated by <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_6_clip_image008_0001.gif" /> as</span></div>
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<tr><th scope="row"><img src="http://nptel.ac.in/courses/112104117/chapter_1/1_7_clip_image002_0014.gif" /></th><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;"><div align="right">
(3.3)</div>
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<div align="left" class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
Similarly, a parameter involving <em>N </em>, <em>Q </em>and <em>H </em>but not <em>D </em>is obtained by divining <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_7_clip_image002_0000.gif" /> by <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_7_clip_image004.gif" /> and is represented by <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_7_clip_image006.gif" /> as</div>
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<tr><th scope="row"><img height="53" src="http://nptel.ac.in/courses/112104117/chapter_1/1_7_clip_image002_0015.gif" width="232" /></th><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;"><div align="right">
(3.4)</div>
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<div align="left" class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
Since the dimensionless parameters <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_7_clip_image002_0002.gif" /> and <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_7_clip_image004_0000.gif" /> are found as a combination of basic π terms, they must remain same for complete similarity of flow in machines of a homologous series. Therefore, a particular value of <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_7_clip_image002_0003.gif" /> or <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_7_clip_image004_0001.gif" />relates all the combinations of <em>N </em>, <em>P </em>and <em>H </em>or <em>N </em>, <em>Q </em>and <em>H </em>for which the flow conditions are similar in the machines of that homologous series. Interest naturally centers on the conditions for which the efficiency is a maximum. For turbines, the values of <em>N </em>, <em>P </em>and <em>H </em>, and for pumps and compressors, the values of <em>N </em>, <em>Q </em>and <em>H </em>are usually quoted for which the machines run at maximum efficiency.</div>
<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
The machines of particular homologous series, that is, of a particular shape, correspond to a particular value of <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_7_clip_image009.gif" /> for their maximum efficient operation. Machines of different shapes have, in general, different values of <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_7_clip_image009_0000.gif" />. Thus the parameter <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_7_clip_image011.gif" /> is referred to as the <em>shape factor </em>of the machines. Considering the fluids used by the machines to be incompressible, (for hydraulic turbines and pumps), and since the acceleration due to gravity dose not vary under this situation, the terms <em>g </em>and <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_7_clip_image013.gif" /> are taken out from the expressions of <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_7_clip_image002_0004.gif" /> and <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_7_clip_image004_0002.gif" />. The portions left as <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_7_clip_image015.gif" /> and <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_7_clip_image017.gif" /> are termed, for the practical purposes, as the <em>specific </em>speed <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_7_clip_image019.gif" /> for turbines or pumps. Therefore, we can write,</div>
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<tr><th scope="row"><img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_7_clip_image002_0016.gif" /> <span class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; font-weight: normal; text-align: justify;">(specific speed for turbines) = <img src="http://nptel.ac.in/courses/112104117/chapter_1/1_7_clip_image002_0006.gif" /></span></th><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;"><div align="right">
(3.5)</div>
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<tr><th scope="row" width="403"><div align="center">
<img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_7_clip_image002_0017.gif" /> <span class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; font-weight: normal; text-align: justify;">(specific speed for turbines) = <img src="http://nptel.ac.in/courses/112104117/chapter_1/1_7_clip_image002_0009.gif" /></span></div>
</th><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;" width="37"><div align="right">
(3.6)</div>
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<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
The name specific speed for these expressions has a little justification. However a meaning can be attributed from the concept of a hypothetical machine. For a turbine, <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_7_clip_image002_0010.gif" /> is the speed of a member of the same homologous series as the actual turbine, so reduced in size as to generate unit power under a unit head of the fluid. Similarly, for a pump, <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_7_clip_image004_0003.gif" /> is speed of a hypothetical pump with reduced size but representing a homologous series so that it delivers unit flow rate at a unit head. The specific speed <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_7_clip_image006_0001.gif" /> is, therefore, not a dimensionless quantity.</div>
<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
The dimension of <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_7_clip_image006_0002.gif" /> can be found from their expressions given by Eqs. (3.5) and (3.6). The dimensional formula and the unit of specific speed are given as follows:</div>
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<span class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; font-weight: normal; text-align: justify;">Specific speed</span></div>
</th><td width="166"><div align="center">
<span class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">Dimensional formula</span></div>
</td><td width="145"><div align="center" class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
<div align="center">
Unit (SI)</div>
</div>
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<tr><th scope="row" width="126"><div align="center">
<img src="http://nptel.ac.in/courses/112104117/chapter_1/1_7_clip_image002_0011.gif" /><span class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; font-weight: normal; text-align: justify;">(turbine)</span></div>
</th><td width="165"><div align="center" class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
<div align="center">
M <sup>1/2</sup> T <sup>-5/2</sup> L<sup>-1/4</sup></div>
</div>
</td><td width="145"><div align="center">
<span class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">kg<sup> 1/2</sup>/ s<sup>5/2</sup> m<sup>1/4</sup></span></div>
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<tr><th scope="row" width="128"><div align="center">
<img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_7_clip_image002_0012.gif" /><span class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; font-weight: normal; text-align: justify;">(pump)</span></div>
</th><td width="165"><div align="center" class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
<div align="center">
L <sup>3/4</sup> T<sup>-3/2</sup></div>
</div>
</td><td width="143"><div align="center" class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
<div align="center">
m <sup>3/4</sup> / s<sup>3/2</sup></div>
</div>
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<div align="left" class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
The dimensionless parameter <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_7_clip_image002_0013.gif" /> is often known as the dimensionless specific speed to distinguish it from <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_1/1_7_clip_image004_0004.gif" />.</div>
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<div class="Heading" style="color: #993300; font-family: Arial, Helvetica, sans-serif; text-align: justify;">
<br /></div>
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<strong>IMPULSE TURBINE</strong></div>
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<tr><th scope="row"><img height="359" src="http://nptel.ac.in/courses/112104117/chapter_7/PeltonWheel.gif" width="600" /></th></tr>
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<span class="style2" style="color: #990000;"><strong>Figure 26.1 Typical PELTON WHEEL with 21 Buckets</strong></span></div>
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<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
Hydropower is the longest established source for the generation of electric power. In this module we shall discuss the governing principles of various types of hydraulic turbines used in hydro-electric power stations.</div>
<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
<strong><em>Impulse Hydraulic Turbine </em>: </strong><strong>The Pelton Wheel</strong></div>
<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
The only hydraulic turbine of the impulse type in common use, is named after an American engineer Laster A Pelton, who contributed much to its development around the year 1880. Therefore this machine is known as Pelton turbine or Pelton wheel. It is an efficient machine particularly suited to high heads. The rotor consists of a large circular disc or wheel on which a number (seldom less than 15) of spoon shaped buckets are spaced uniformly round is periphery as shown in Figure 26.1. The wheel is driven by jets of water being discharged at atmospheric pressure from pressure nozzles. The nozzles are mounted so that each directs a jet along a tangent to the circle through the centres of the buckets (Figure 26.2). Down the centre of each bucket, there is a splitter ridge which divides the jet into two equal streams which flow round the smooth inner surface of the bucket and leaves the bucket with a relative velocity almost opposite in direction to the original jet.</div>
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<tr><th scope="row"><img height="349" src="http://nptel.ac.in/courses/112104117/chapter_7/4.gif" width="533" /></th></tr>
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<span class="style2" style="color: #990000;"><strong>Figure 26.2 A Pelton wheel</strong></span></div>
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<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
For maximum change in momentum of the fluid and hence for the maximum driving force on the wheel, the deflection of the water jet should be <img src="http://nptel.ac.in/courses/112104117/chapter_7/7_1_clip_image002.gif" />. In practice, however, the deflection is limited to about <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_1_clip_image004.gif" /> so that the water leaving a bucket may not hit the back of the following bucket. Therefore, the camber angle of the buckets is made as <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_1_clip_image004_0000.gif" /><img align="absmiddle" height="23" src="http://nptel.ac.in/courses/112104117/chapter_7/7_1_clip_image006.gif" width="66" />. Figure(26.3a)</div>
<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
The number of jets is not more than two for horizontal shaft turbines and is limited to six for vertical shaft turbines. The flow partly fills the buckets and the fluid remains in contact with the atmosphere. Therefore, once the jet is produced by the nozzle, the static pressure of the fluid remains atmospheric throughout the machine. Because of the symmetry of the buckets, the side thrusts produced by the fluid in each half should balance each other.</div>
<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
<strong><em>Analysis of force on the bucket and power generation </em></strong>Figure 26.3a shows a section through a bucket which is being acted on by a jet. The plane of section is parallel to the axis of the wheel and contains the axis of the jet. The absolute velocity of the jet <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_1_clip_image002_0000.gif" /> with which it strikes the bucket is given by</div>
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<tr><th scope="row"><img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_1_clip_image002_0005.gif" /></th></tr>
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<tr><th scope="row"><img height="216" src="http://nptel.ac.in/courses/112104117/chapter_7/1.gif" width="367" /></th></tr>
</tbody></table>
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<tr><th scope="row"><img height="72" src="http://nptel.ac.in/courses/112104117/chapter_7/2.gif" width="287" /></th><td><img height="136" src="http://nptel.ac.in/courses/112104117/chapter_7/3.gif" width="241" /></td></tr>
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<tr><th class="BodyText" rowspan="3" scope="row" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; font-weight: normal; text-align: justify;" width="138"><span class="style2" style="color: #990000;"><strong>Figure 26.3</strong></span></th><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;" width="302"><span class="style2" style="color: #990000;"><strong>(a)Flow along the bucket of a pelton wheel</strong></span></td></tr>
<tr><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;"><span class="style2" style="color: #990000;"><strong>(b) Inlet velocity triangle</strong></span></td></tr>
<tr><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;"><span class="style2" style="color: #990000;"><strong>(c)Outlet velocity triangle</strong></span></td></tr>
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<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
where, <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_1_clip_image002_0001.gif" /> is the coefficient of velocity which takes care of the friction in the nozzle. <em>H </em>is the head at the entrance to the nozzle which is equal to the total or gross head of water stored at high altitudes minus the head lost due to friction in the long pipeline leading to the nozzle. Let the velocity of the bucket (due to the rotation of the wheel) at its centre where the jet strikes be <em>U </em>. Since the jet velocity <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_1_clip_image004_0001.gif" /> is tangential, i.e. <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_1_clip_image004_0002.gif" /> and <em>U </em>are collinear, the diagram of velocity vector at inlet (Fig 26.3.b) becomes simply a straight line and the relative velocity is given by</div>
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<tr><th scope="row"><img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_1_clip_image002_0002.gif" /></th></tr>
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<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
It is assumed that the flow of fluid is uniform and it glides the blade all along including the entrance and exit sections to avoid the unnecessary losses due to shock. Therefore the direction of relative velocity at entrance and exit should match the inlet and outlet angles of the buckets respectively. The velocity triangle at the outlet is shown in Figure 26.3c. The bucket velocity <em>U </em>remains the same both at the inlet and outlet. With the direction of <em>U </em>being taken as positive, we can write. The tangential component of inlet velocity (Figure 26.3b)</div>
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<tr><th scope="row"><img src="http://nptel.ac.in/courses/112104117/chapter_7/7_1_clip_image002_0003.gif" /></th></tr>
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<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
and the tangential component of outlet velocity (Figure 26.3c)</div>
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</td></tr>
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<div class="BodyText" style="background-color: white; font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
<br /></div>
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<tr><th scope="row"><img src="http://nptel.ac.in/courses/112104117/chapter_7/7_2_clip_image002.gif" /></th></tr>
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<div align="left" class="BodyText" style="background-color: white; font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
where <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_2_clip_image002_0000.gif" /> and <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_2_clip_image004.gif" /> are the velocities of the jet relative to the bucket at its inlet and outlet and <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_2_clip_image006.gif" /> is the outlet angle of the bucket.</div>
<div class="BodyText" style="background-color: white; font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
From the Eq. (1.2) (the Euler's equation for hydraulic machines), the energy delivered by the fluid per unit mass to the rotor can be written as</div>
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<tr><th scope="row"><img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_2_clip_image002_0024.gif" /></th></tr>
</tbody></table>
<table align="center" border="0" style="background-color: white; width: 450px;"><tbody>
<tr><th scope="row" width="184"> </th><td width="218"><img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_2_clip_image002_0025.gif" /></td><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;" width="34">(26.1)</td></tr>
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<div class="BodyText" style="background-color: white; font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
(since, in the present situation, <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_2_clip_image002_0004.gif" /></div>
<div class="BodyText" style="background-color: white; font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
The relative velocity <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_2_clip_image002_0005.gif" /> becomes slightly less than <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_2_clip_image004_0000.gif" /> mainly because of the friction in the bucket. Some additional loss is also inevitable as the fluid strikes the splitter ridge, because the ridge cannot have zero thickness. These losses are however kept to a minimum by making the inner surface of the bucket polished and reducing the thickness of the splitter ridge. The relative velocity at outlet <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_2_clip_image002_0006.gif" /> is usually expressed as <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_2_clip_image006_0000.gif" /> where, K is a factor with a value less than 1. However in an ideal case ( in absence of friction between the fluid and blade surface) K=1. Therefore, we can write Eq.(26.1)</div>
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<tr><th scope="row" width="402"><img src="http://nptel.ac.in/courses/112104117/chapter_7/7_2_clip_image002_0026.gif" /></th><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;" width="38">(26.2)</td></tr>
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<div class="BodyText" style="background-color: white; font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
If Q is the volume flow rate of the jet, then the power transmitted by the fluid to the wheel can be written as</div>
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<tr><th scope="row"><div align="center">
<img src="http://nptel.ac.in/courses/112104117/chapter_7/7_2_clip_image002_0008.gif" /></div>
</th></tr>
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<table align="center" border="0" style="background-color: white; width: 450px;"><tbody>
<tr><th scope="row" width="146"> </th><td width="272"><img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_2_clip_image002_0009.gif" /></td><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;" width="18">(26.3)</td></tr>
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<div class="BodyText" style="background-color: white; font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
The power input to the wheel is found from the kinetic energy of the jet arriving at the wheel and is given by <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_2_clip_image002_0010.gif" />. Therefore the wheel efficiency of a pelton turbine can be written as</div>
<blockquote style="background-color: white;">
<blockquote>
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<tr><th scope="row"><img src="http://nptel.ac.in/courses/112104117/chapter_7/7_2_clip_image002_0011.gif" /></th></tr>
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<table align="center" border="0" style="width: 450px;"><tbody>
<tr><th scope="row" width="137"> </th><td width="281"><img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_2_clip_image002_0027.gif" /></td><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;" width="18">(26.4)</td></tr>
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<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
It is found that the efficiency <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_2_clip_image002_0013.gif" /> depends on <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_2_clip_image004_0001.gif" /> and <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_2_clip_image006_0001.gif" /> For a given design of the bucket, i.e. for constant values of <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_2_clip_image008.gif" /> and K, the efficiency <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_2_clip_image002_0014.gif" />becomes a function of <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_2_clip_image011.gif" /> only, and we can determine the condition given by <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_2_clip_image011_0000.gif" /> at which <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_2_clip_image002_0015.gif" /> becomes maximum.</div>
<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
For <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_2_clip_image002_0016.gif" /> to be maximum,</div>
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<tr><th scope="row"><img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_2_clip_image002_0017.gif" /></th></tr>
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<tr><th class="BodyText" scope="row" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; font-weight: normal; text-align: justify;" width="165">or,</th><td width="232"><img src="http://nptel.ac.in/courses/112104117/chapter_7/7_2_clip_image002_0018.gif" /></td><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;" width="39">(26.5)</td></tr>
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<img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_2_clip_image002_0019.gif" /><span class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;"> is always negative.</span><br />
<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
Therefore, the maximum wheel efficiency can be written after substituting the relation given by eqn.(26.5) in eqn.(26.4) as</div>
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<tr><th scope="row"><img src="http://nptel.ac.in/courses/112104117/chapter_7/7_2_clip_image002_0022.gif" /></th><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;"><div align="right">
(26.6)</div>
<div>
<br /></div>
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</blockquote>
</blockquote>
<div class="BodyText" style="background-color: white; font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
The condition given by Eq. (26.5) states that the efficiency of the wheel in converting the kinetic energy of the jet into mechanical energy of rotation becomes maximum when the wheel speed at the centre of the bucket becomes one half of the incoming velocity of the jet. The overall efficiency <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_3_clip_image002.gif" /> will be less than <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_3_clip_image004.gif" /> because of friction in bearing and windage, i.e. friction between the wheel and the atmosphere in which it rotates. Moreover, as the losses due to bearing friction and windage increase rapidly with speed, the overall efficiency reaches it peak when the ratio <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_3_clip_image006.gif" /> is slightly less than the theoretical value of 0.5. The value usually obtained in practice is about 0.46. The Figure 27.1 shows the variation of wheel efficiency <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_3_clip_image004.gif" /> with blade to jet speed ratio <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_3_clip_image006.gif" /> for assumed values at k=1 and 0.8, and <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_4_clip_image002_0004.gif" /> . An overall efficiency of 85-90 percent may usually be obtained in large machines. To obtain high values of wheel efficiency, the buckets should have smooth surface and be properly designed. The length, width, and depth of the buckets are chosen about 2.5.4 and 0.8 times the jet diameter. The buckets are notched for smooth entry of the jet.</div>
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<tr><th scope="row"><img height="225" src="http://nptel.ac.in/courses/112104117/chapter_7/1_1.jpg" width="368" /></th></tr>
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<tr><th class="BodyText" scope="row" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; font-weight: normal; text-align: justify;"><div align="center">
<span class="style4" style="color: #990000;"><strong>Figure 27.1 Theoretical variation of wheel efficiency for a Pelton turbine with blade speed to jet speed ratio for different values of k</strong></span></div>
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<div class="BodyText" style="background-color: white; font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
<strong><em>Specific speed and wheel geometry </em></strong><em>. </em>The specific speed of a pelton wheel depends on the ratio of jet diameter <em>d </em>and the wheel pitch diameter. <em>D </em>(the diameter at the centre of the bucket). If the hydraulic efficiency of a pelton wheel is defined as the ratio of the power delivered <em>P </em>to the wheel to the head available <em>H </em>at the nozzle entrance, then we can write.</div>
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<tr><th scope="row" width="407"><img src="http://nptel.ac.in/courses/112104117/chapter_7/7_3_clip_image002_0000.gif" /></th><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;" width="33">(27.1)</td></tr>
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<div align="center" style="background-color: white;">
<span class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">Since [ </span><img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_3_clip_image002_0001.gif" /> <span class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">and</span> <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_3_clip_image004_0000.gif" /></div>
<span class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">The specific speed</span><span style="background-color: white;"> </span><img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_3_clip_image002_0002.gif" /><span class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;"> = <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_3_clip_image004_0001.gif" /></span><br />
<table align="center" border="0" cellpadding="0" cellspacing="0" style="width: 98%px;"><tbody>
<tr><td><div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
The optimum value of the overall efficiency of a Pelton turbine depends both on the values of the specific speed and the speed ratio. The Pelton wheels with a single jet operate in the specific speed range of 4-16, and therefore the ratio D/d lies between 6 to 26 as given by the Eq. (15.25b). A large value of D/d reduces the rpm as well as the mechanical efficiency of the wheel. It is possible to increase the specific speed by choosing a lower value of D/d, but the efficiency will decrease because of the close spacing of buckets. The value of D/d is normally kept between 14 and 16 to maintain high efficiency. The number of buckets required to maintain optimum efficiency is usually fixed by the empirical relation.</div>
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<tr><th scope="row" width="405"><span class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; font-weight: normal; text-align: justify;">n(number of buckets)</span> = <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_5_clip_image002.gif" /></th><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;" width="35">(27.2)</td></tr>
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<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
<span class="style4" style="font-style: italic; font-weight: bold;">Govering of Pelton Turbine </span><strong>:</strong> First let us discuss what is meant by governing of turbines in general. When a turbine drives an electrical generator or alternator, the primary requirement is that the rotational speed of the shaft and hence that of the turbine rotor has to be kept fixed. Otherwise the frequency of the electrical output will be altered. But when the electrical load changes depending upon the demand, the speed of the turbine changes automatically. This is because the external resisting torque on the shaft is altered while the driving torque due to change of momentum in the flow of fluid through the turbine remains the same. For example, when the load is increased, the speed of the turbine decreases and <em>vice versa </em>. A constancy in speed is therefore maintained by adjusting the rate of energy input to the turbine accordingly. This is usually accomplished by changing the rate of fluid flow through the turbine- the flow in increased when the load is increased and the flow is decreased when the load is decreased. This adjustment of flow with the load is known as the governing of turbines.</div>
<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
In case of a Pelton turbine, an additional requirement for its operation at the condition of maximum efficiency is that the ration of bucket to initial jet velocity <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_5_clip_image002_0000.gif" /> has to be kept at its optimum value of about 0.46. Hence, when U is fixed. <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_5_clip_image004.gif" /> has to be fixed. Therefore the control must be made by a variation of the cross-sectional area, A, of the jet so that the flow rate changes in proportion to the change in the flow area keeping the jet velocity <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_5_clip_image004_0000.gif" /> same. This is usually achieved by a spear valve in the nozzle (Figure 27.2a). Movement of the spear and the axis of the nozzle changes the annular area between the spear and the housing. The shape of the spear is such, that the fluid coalesces into a circular jet and then the effect of the spear movement is to vary the diameter of the jet. Deflectors are often used (Figure 27.2b) along with the spear valve to prevent the serious water hammer problem due to a sudden reduction in the rate of flow. These plates temporarily defect the jet so that the entire flow does not reach the bucket; the spear valve may then be moved slowly to its new position to reduce the rate of flow in the pipe-line gradually. If the bucket width is too small in relation to the jet diameter, the fluid is not smoothly deflected by the buckets and, in consequence, much energy is dissipated in turbulence and the efficiency drops considerably. On the other hand, if the buckets are unduly large, the effect of friction on the surfaces is unnecessarily high. The optimum value of the ratio of bucket width to jet diameter has been found to vary between 4 and 5.</div>
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<tr><th scope="row"><img height="131" src="http://nptel.ac.in/courses/112104117/chapter_7/6.gif" width="609" /></th></tr>
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<tr><th scope="row"><img height="197" src="http://nptel.ac.in/courses/112104117/chapter_7/1_2.jpg" width="516" /></th></tr>
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<tr><th class="BodyText" rowspan="2" scope="row" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; font-weight: normal; text-align: justify;"><span class="style3" style="color: #990000;"><strong>Figure 27.2</strong></span></th><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;"><span class="style3" style="color: #990000;"><strong>(a) Spear valve to alter jet area in a Pelton wheel</strong></span></td></tr>
<tr><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;"><span class="style3" style="color: #990000;"><strong>(b) Jet deflected from bucket</strong></span></td></tr>
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<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
<strong>Limitation of a Pelton Turbine: </strong>The Pelton wheel is efficient and reliable when operating under large heads. To generate a given output power under a smaller head, the rate of flow through the turbine has to be higher which requires an increase in the jet diameter. The number of jets are usually limited to 4 or 6 per wheel. The increases in jet diameter in turn increases the wheel diameter. Therefore the machine becomes unduly large, bulky and slow-running. In practice, turbines of the reaction type are more suitable for lower heads.</div>
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<tr><td><div class="Heading" style="color: #993300; font-family: Arial, Helvetica, sans-serif; font-size: 16px; font-weight: bold;">
Francis Turbine</div>
<div class="style6" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
<strong>Reaction Turbine:</strong> The principal feature of a reaction turbine that distinguishes it from an impulse turbine is that only a part of the total head available at the inlet to the turbine is converted to velocity head, before the runner is reached. Also in the reaction turbines the working fluid, instead of engaging only one or two blades, completely fills the passages in the runner. The pressure or static head of the fluid changes gradually as it passes through the runner along with the change in its kinetic energy based on absolute velocity due to the impulse action between the fluid and the runner. Therefore the cross-sectional area of flow through the passages of the fluid. A reaction turbine is usually well suited for low heads. A radial flow hydraulic turbine of reaction type was first developed by an American Engineer, James B. Francis (1815-92) and is named after him as the Francis turbine. The schematic diagram of a Francis turbine is shown in Fig. 28.1</div>
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<tr><th scope="row"><img height="358" src="http://nptel.ac.in/courses/112104117/chapter_7/1_3.jpg" width="324" /></th></tr>
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<tr><th class="BodyText" scope="row" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; font-weight: normal; text-align: justify;"><div align="center" class="style5" style="color: #990000;">
<strong>Figure 28.1 A Francis turbine</strong></div>
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<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
A Francis turbine comprises mainly the four components:</div>
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(i) sprical casing,</div>
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(ii) guide on stay vanes,</div>
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(iii) runner blades,</div>
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(iv) draft-tube as shown in Figure 28.1 .</div>
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<strong>Spiral Casing : </strong>Most of these machines have vertical shafts although some smaller machines of this type have horizontal shaft. The fluid enters from the penstock (pipeline leading to the turbine from the reservoir at high altitude) to a spiral casing which completely surrounds the runner. This casing is known as scroll casing or volute. The cross-sectional area of this casing decreases uniformly along the circumference to keep the fluid velocity constant in magnitude along its path towards the guide vane.</div>
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<tr><th scope="row"><img height="289" src="http://nptel.ac.in/courses/112104117/chapter_7/1_4.jpg" width="422" /></th></tr>
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<strong>Figure 28.2 Spiral Casing</strong></div>
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This is so because the rate of flow along the fluid path in the volute decreases due to continuous entry of the fluid to the runner through the openings of the guide vanes or stay vanes.</div>
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<strong>Guide or Stay vane:</strong></div>
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The basic purpose of the guide vanes or stay vanes is to convert a part of pressure energy of the fluid at its entrance to the kinetic energy and then to direct the fluid on to the runner blades at the angle appropriate to the design. Moreover, the guide vanes are pivoted and can be turned by a suitable governing mechanism to regulate the flow while the load changes. The guide vanes are also known as wicket gates. The guide vanes impart a tangential velocity and hence an angular momentum to the water before its entry to the runner. The flow in the runner of a Francis turbine is not purely radial but a combination of radial and tangential. The flow is inward, i.e. from the periphery towards the centre. The height of the runner depends upon the specific speed. The height increases with the increase in the specific speed. The main direction of flow change as water passes through the runner and is finally turned into the axial direction while entering the draft tube.</div>
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<strong>Draft tube:</strong></div>
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The draft tube is a conduit which connects the runner exit to the tail race where the water is being finally discharged from the turbine. The primary function of the draft tube is to reduce the velocity of the discharged water to minimize the loss of kinetic energy at the outlet. This permits the turbine to be set above the tail water without any appreciable drop of available head. A clear understanding of the function of the draft tube in any reaction turbine, in fact, is very important for the purpose of its design. The purpose of providing a draft tube will be better understood if we carefully study the net available head across a reaction turbine.</div>
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<strong>Net head across a reaction turbine and the purpose to providing a draft tube </strong>. The effective head across any turbine is the difference between the head at inlet to the machine and the head at outlet from it. A reaction turbine always runs completely filled with the working fluid. The tube that connects the end of the runner to the tail race is known as a draft tube and should completely to filled with the working fluid flowing through it. The kinetic energy of the fluid finally discharged into the tail race is wasted. A draft tube is made divergent so as to reduce the velocity at outlet to a minimum. Therefore a draft tube is basically a diffuser and should be designed properly with the angle between the walls of the tube to be limited to about 8 degree so as to prevent the flow separation from the wall and to reduce accordingly the loss of energy in the tube. Figure 28.3 shows a flow diagram from the reservoir via a reaction turbine to the tail race.</div>
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The total head <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_7_clip_image002.gif" /> at the entrance to the turbine can be found out by applying the Bernoulli's equation between the free surface of the reservoir and the inlet to the turbine as</div>
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<tr><th scope="row" width="403"><img src="http://nptel.ac.in/courses/112104117/chapter_7/7_7_clip_image002_0000.gif" /></th><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;" width="37">(28.1)</td></tr>
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<span class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; font-weight: normal; text-align: justify;">or,</span></div>
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<img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_7_clip_image002_0001.gif" /></div>
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(28.2)</div>
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where <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_7_clip_image002_0002.gif" /> is the head lost due to friction in the pipeline connecting the reservoir and the turbine. Since the draft tube is a part of the turbine, the net head across the turbine, for the conversion of mechanical work, is the difference of total head at inlet to the machine and the total head at discharge from the draft tube at tail race and is shown as <em>H </em>in Figure 28.3</div>
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<tr><th class="BodyText" scope="row" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; font-weight: normal; text-align: justify;"><div align="center" class="style5" style="color: #990000;">
<strong>Figure 28.3 Head across a reaction turbine</strong></div>
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Therefore, <em>H </em>= total head at inlet to machine (1) - total head at discharge (3)</div>
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<tr><th scope="row" width="407"><img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_7_clip_image002_0003.gif" /></th><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;" width="33">(28.3)</td></tr>
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<tr><th scope="row" width="407"><img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_7_clip_image002_0004.gif" /></th><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;" width="33">(28.4)</td></tr>
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The pressures are defined in terms of their values above the atmospheric pressure. Section 2 and 3 in Figure 28.3 represent the exits from the runner and the draft tube respectively. If the losses in the draft tube are neglected, then the total head at 2 becomes equal to that at 3. Therefore, the net head across the machine is either <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_7_clip_image002_0005.gif" /> or <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_7_clip_image004.gif" />. Applying the Bernoull's equation between 2 and 3 in consideration of flow, without losses, through the draft tube, we can write.</div>
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<tr><th scope="row" width="405"><img src="http://nptel.ac.in/courses/112104117/chapter_7/7_7_clip_image002_0006.gif" /></th><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;" width="35">(28.5)</td></tr>
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<tr><th scope="row" width="406"><img src="http://nptel.ac.in/courses/112104117/chapter_7/7_7_clip_image002_0009.gif" /></th><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;" width="34"><div align="right">
(28.6)</div>
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Since <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_7_clip_image002_0008.gif" />, both the terms in the bracket are positive and hence <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_7_clip_image004_0000.gif" />is always negative, which implies that the static pressure at the outlet of the runner is always below the atmospheric pressure. Equation (28.1) also shows that the value of the suction pressure at runner outlet depends on z, the height of the runner above the tail race and <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_7_clip_image006.gif" />, the decrease in kinetic energy of the fluid in the draft tube. The value of this minimum pressure <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_7_clip_image008.gif" />should never fall below the vapour pressure of the liquid at its operating temperature to avoid the problem of cavitation. Therefore, we fine that the incorporation of a draft tube allows the turbine runner to be set above the tail race without any drop of available head by maintaining a vacuum pressure at the outlet of the runner.</div>
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<br /></div>
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<strong>Runner of the Francis Turbine</strong></div>
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The shape of the blades of a Francis runner is complex. The exact shape depends on its specific speed. It is obvious from the equation of specific speed that higher specific speed means lower head. This requires that the runner should admit a comparatively large quantity of water for a given power output and at the same time the velocity of discharge at runner outlet should be small to avoid cavitation. In a purely radial flow runner, as developed by James B. Francis, the bulk flow is in the radial direction. To be more clear, the flow is tangential and radial at the inlet but is entirely radial with a negligible tangential component at the outlet. The flow, under the situation, has to make a 90<sup>o</sup> turn after passing through the rotor for its inlet to the draft tube. Since the flow area (area perpendicular to the radial direction) is small, there is a limit to the capacity of this type of runner in keeping a low exit velocity. This leads to the design of a mixed flow runner where water is turned from a radial to an axial direction in the rotor itself. At the outlet of this type of runner, the flow is mostly axial with negligible radial and tangential components. Because of a large discharge area (area perpendicular to the axial direction), this type of runner can pass a large amount of water with a low exit velocity from the runner. The blades for a reaction turbine are always so shaped that the tangential or whirling component of velocity at the outlet becomes zero <img align="middle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_8_clip_image002.gif" />. This is made to keep the kinetic energy at outlet a minimum.</div>
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Figure 29.1 shows the velocity triangles at inlet and outlet of a typical blade of a Francis turbine. Usually the flow velocity (velocity perpendicular to the tangential direction) remains constant throughout, i.e. <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_8_clip_image004.gif" /> and is equal to that at the inlet to the draft tube.</div>
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The Euler's equation for turbine [Eq.(1.2)] in this case reduces to</div>
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<tr><th scope="row"><img src="http://nptel.ac.in/courses/112104117/chapter_7/7_8_clip_image002_0000.gif" /></th><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;"><div align="right">
(29.1)</div>
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where, <em>e </em>is the energy transfer to the rotor per unit mass of the fluid. From the inlet velocity triangle shown in Fig. 29.1</div>
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<tr><th scope="row"><img src="http://nptel.ac.in/courses/112104117/chapter_7/7_8_clip_image002_0001.gif" /></th><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;"><div align="right">
(29.2a)</div>
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<tr><th class="BodyText" scope="row" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; font-weight: normal; text-align: justify;" width="93">and</th><td width="324"><img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_8_clip_image002_0002.gif" /></td><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;" width="19">(29.2b)</td></tr>
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Substituting the values of <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_8_clip_image002_0003.gif" /> and <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_8_clip_image004_0000.gif" /> from Eqs. (29.2a) and (29.2b) respectively into Eq. (29.1), we have</div>
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<tr><th scope="row"><img src="http://nptel.ac.in/courses/112104117/chapter_7/7_8_clip_image002_0004.gif" /></th><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;"><div align="right">
(29.3)</div>
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<tr><th scope="row"><img height="336" src="http://nptel.ac.in/courses/112104117/chapter_7/21.gif" width="232" /></th></tr>
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<tr><th class="BodyText" scope="row" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; font-weight: normal; text-align: justify;"><div align="center" class="style4" style="color: #990000;">
<strong>Figure 29.1 Velocity triangle for a Francis runner</strong></div>
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The loss of kinetic energy per unit mass becomes equal to <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_8_clip_image002_0005.gif" />. Therefore neglecting friction, the blade efficiency becomes</div>
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<table align="center" border="0" style="width: 450px;"><tbody>
<tr><th scope="row" width="191"> </th><td width="249"><div align="center">
<img src="http://nptel.ac.in/courses/112104117/chapter_7/7_8_clip_image002_0012.gif" /></div>
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<tr><th class="BodyText" scope="row" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; font-weight: normal; text-align: justify;" width="113">since</th><td width="198"><div align="center">
<img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_8_clip_image002_0008.gif" /></div>
</td><td width="125"><div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
can be written as</div>
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<tr><th scope="row"><img src="http://nptel.ac.in/courses/112104117/chapter_7/7_8_clip_image002_0009.gif" /></th></tr>
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<div align="left" class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
The change in pressure energy of the fluid in the rotor can be found out by subtracting the change in its kinetic energy from the total energy released. Therefore, we can write for the degree of reaction.</div>
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<span class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; font-weight: normal; text-align: justify;">[since </span><img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_8_clip_image002_0011.gif" /></div>
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<br /></div>
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<br /></div>
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Using the expression of <em>e </em>from Eq. (29.3), we have</div>
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(29.4)</div>
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<div align="left" class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
The inlet blade angle <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_9_clip_image002_0000.gif" /> of a Francis runner varies <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_9_clip_image004.gif" /> and the guide vane angle angle <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_9_clip_image006.gif" /> from <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_9_clip_image008.gif" />. The ratio of blade width to the diameter of runner B/D, at blade inlet, depends upon the required specific speed and varies from 1/20 to 2/3.</div>
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Expression for specific speed. The dimensional specific speed of a turbine, can be written as</div>
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<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
Power generated <em>P </em>for a turbine can be expressed in terms of available head <em>H </em>and hydraulic efficiency <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_9_clip_image002_0002.gif" /> as</div>
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<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
Hence, it becomes</div>
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(29.5)</div>
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<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
Again, <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_9_clip_image002_0005.gif" />,</div>
<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
Substituting <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_9_clip_image002_0006.gif" /> from Eq. (29.2b)</div>
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<tr><th scope="row"><img src="http://nptel.ac.in/courses/112104117/chapter_7/7_9_clip_image002_0007.gif" /></th><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;"><div align="right">
(29.6)</div>
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<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
Available head <em>H </em>equals the head delivered by the turbine plus the head lost at the exit. Thus,</div>
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<table align="center" border="0" style="width: 450px;"><tbody>
<tr><th class="BodyText" scope="row" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; font-weight: normal; text-align: justify;" width="31">since</th><td width="409"><div align="center">
<img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_9_clip_image002_0009.gif" /></div>
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<table align="center" border="0" style="width: 450px;"><tbody>
<tr><th scope="row"><img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_9_clip_image002_0010.gif" /></th></tr>
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<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
with the help of Eq. (29.3), it becomes</div>
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<tr><th scope="row"><img src="http://nptel.ac.in/courses/112104117/chapter_7/7_9_clip_image002_0011.gif" /></th></tr>
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<tr><th class="BodyText" scope="row" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; font-weight: normal; text-align: justify;" width="94">or,</th><td width="329"><div align="center">
<img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_9_clip_image002_0012.gif" /></div>
</td><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;" width="13">(29.7)</td></tr>
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<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
Substituting the values of H and N from Eqs (29.7) and (29.6) respectively into the expression <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_9_clip_image002_0013.gif" /> given by Eq. (29.5), we get,</div>
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<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
Flow velocity at inlet <img align="middle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_9_clip_image002_0015.gif" /> can be substituted from the equation of continuity as</div>
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<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
where B is the width of the runner at its inlet</div>
<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
Finally, the expression for <img align="middle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_9_clip_image002_0017.gif" /> becomes,</div>
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<tr><th scope="row"><img src="http://nptel.ac.in/courses/112104117/chapter_7/7_9_clip_image002_0019.gif" /></th><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;"><div align="right">
(29.8)</div>
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For a Francis turbine, the variations of geometrical parameters like <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_9_clip_image002_0020.gif" /> have been described earlier. These variations cover a range of specific speed between 50 and 400. Figure 29.2 shows an overview of a Francis Turbine. The figure is specifically shown in order to convey the size and relative dimensions of a typical Francis Turbine to the readers.</div>
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<img height="661" src="http://nptel.ac.in/courses/112104117/chapter_7/Water_turbine_grandcoulee.jpg" width="713" /></div>
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</div>
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<strong>Figure 29.2 Installation of a Francis Turbine</strong></div>
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<br /></div>
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<tr><td><div class="Heading" style="color: #993300; font-family: Arial, Helvetica, sans-serif; font-size: 16px; font-weight: bold;">
<strong>KAPLAN TURBINE</strong></div>
<div class="Heading" style="color: #993300; font-family: Arial, Helvetica, sans-serif; font-size: 16px; font-weight: bold;">
I<span class="Black_Heading" style="color: black; font-size: 14px;">ntroduction</span></div>
<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
Higher specific speed corresponds to a lower head. This requires that the runner should admit a comparatively large quantity of water. For a runner of given diameter, the maximum flow rate is achieved when the flow is parallel to the axis. Such a machine is known as axial flow reaction turbine. An Australian engineer, Vikton Kaplan first designed such a machine. The machines in this family are called Kaplan Turbines.(Figure 30.1)</div>
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<span class="style2" style="color: #990000;"><strong>Figure 30.1 A typical Kaplan Turbine</strong></span></div>
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<div class="Black_Heading" style="font-family: Arial, Helvetica, sans-serif; font-size: 14px; font-weight: bold;">
Development of Kaplan Runner from the Change in the Shape of Francis Runner with Specific Speed</div>
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Figure 30.2 shows in stages the change in the shape of a Francis runner with the variation of specific speed. The first three types [Fig. 30.2 (a), (b) and (c)] have, in order. The Francis runner (radial flow runner) at low, normal and high specific speeds. As the specific speed increases, discharge becomes more and more axial. The fourth type, as shown in Fig.30.2 (d), is a mixed flow runner (radial flow at inlet axial flow at outlet) and is known as Dubs runner which is mainly suited for high specific speeds. Figure 30.2(e) shows a propeller type runner with a less number of blades where the flow is entirely axial (both at inlet and outlet). This type of runner is the most suitable one for very high specific speeds and is known as Kaplan runner or axial flow runner.</div>
<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
From the inlet velocity triangle for each of the five runners, as shown in Figs (30.2a to 30.2e), it is found that an increase in specific speed (or a decreased in head) is accompanied by a reduction in inlet velocity <em><img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_10_clip_image002.gif" /></em>. But the flow velocity <em><img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_10_clip_image002_0000.gif" /></em> at inlet increases allowing a large amount of fluid to enter the turbine. The most important point to be noted in this context is that the flow at inlet to all the runners, except the Kaplan one, is in radial and tangential directions. Therefore, the inlet velocity triangles of those turbines (Figure 30.2a to 30.2d) are shown in a plane containing the radial ant tangential directions, and hence the flow velocity <em><img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_10_clip_image002_0000.gif" /> </em>represents the radial component of velocity.</div>
<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
In case of a Kaplan runner, the flow at inlet is in axial and tangential directions. Therefore, the inlet velocity triangle in this case (Figure 30.2e) is shown in a place containing the axial and tangential directions, and hence the flow velocity <em><img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_10_clip_image002_0000.gif" /></em> represents the axial component of velocity <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_10_clip_image002_0002.gif" /> .The tangential component of velocity is almost nil at outlet of all runners. Therefore, the outlet velocity triangle (Figure 30.2f) is identical in shape of all runners. However, the exit velocity <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_10_clip_image002_0001.gif" /> is axial in Kaplan and Dubs runner, while it is the radial one in all other runners.</div>
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<tr><th scope="row"><span class="BodyText style2" style="color: #990000; font-family: Arial, Helvetica, sans-serif; font-size: 13px; font-weight: normal; text-align: justify;"><strong>(a) Francis runner for low specific speeds</strong></span></th></tr>
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<span class="style2" style="color: #990000;"><strong>(b) Francis runner for normal specific speeds</strong></span></div>
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<tr><th scope="row"><img height="192" src="http://nptel.ac.in/courses/112104117/chapter_7/24.gif" width="518" /></th></tr>
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<span class="style2" style="color: #990000;"><strong>(c) Francis runner for high specific speeds</strong></span></div>
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<tr><th class="BodyText" scope="row" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; font-weight: normal; text-align: justify;"><div align="center" class="style2" style="color: #990000;">
<strong>(d) Dubs runner</strong></div>
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<tr><th scope="row"><img height="161" src="http://nptel.ac.in/courses/112104117/chapter_7/26.gif" width="412" /></th></tr>
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<tr><th scope="row"><span class="BodyText style2" style="color: #990000; font-family: Arial, Helvetica, sans-serif; font-size: 13px; font-weight: normal; text-align: justify;"><strong>(e) Kalpan runner</strong></span></th></tr>
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<tr><th class="BodyText" scope="row" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; font-weight: normal; text-align: justify;" width="195"><span class="style3" style="color: #660000;"><strong>(<span class="style2" style="color: #990000;">f) For allreaction (Francis as well as Kaplan) runners</span></strong></span></th><td width="245"><img height="156" src="http://nptel.ac.in/courses/112104117/chapter_7/27.gif" width="174" /></td></tr>
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<span class="style3" style="color: #660000;"><strong>Outlet velocity triangle</strong></span></div>
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<tr><th scope="row"><span class="BodyText style2" style="color: #990000; font-family: Arial, Helvetica, sans-serif; font-size: 13px; font-weight: normal; text-align: justify;"><strong>Fig. 30.2 Evolution of Kaplan runner form Francis one</strong><div class="BodyText" style="background-color: white; color: black;">
Figure 30.3 shows a schematic diagram of propeller or Kaplan turbine. The function of the guide vane is same as in case of Francis turbine. Between the guide vanes and the runner, the fluid in a propeller turbine turns through a right-angle into the axial direction and then passes through the runner. The runner usually has four or six blades and closely resembles a ship's propeller. Neglecting the frictional effects, the flow approaching the runner blades can be considered to be a free vortex with whirl velocity being inversely proportional to radius, while on the other hand, the blade velocity is directly proportional to the radius. To take care of this different relationship of the fluid velocity and the blade velocity with the changes in radius, the blades are twisted. The angle with axis is greater at the tip that at the root.</div>
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<tr><th scope="row"><span class="BodyText style2" style="color: #990000; font-family: Arial, Helvetica, sans-serif; font-size: 13px; font-weight: normal; text-align: justify;"><strong>Fig. 30.3 A propeller of Kaplan turbine</strong></span></th></tr>
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<div align="justify" style="background-color: white; color: black; font-family: "Times New Roman"; font-size: medium;">
<span class="style5" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px;"><strong>Different types of draft tubes incorporated in reaction turbines </strong></span><span class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px;">The draft tube is an integral part of a reaction turbine. Its principle has been explained earlier. The shape of draft tube plays an important role especially for high specific speed turbines, since the efficient recovery of kinetic energy at runner outlet depends mainly on it. Typical draft tubes, employed in practice, are discussed as follows.</span></div>
<div align="justify" style="background-color: white; color: black; font-family: "Times New Roman"; font-size: medium;">
<span class="style5" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px;"><strong>Straight divergent tube</strong> </span><span class="style4" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; font-weight: bold;">[Fig. 30.4(a)]</span><span class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px;"> The shape of this tube is that of frustum of a cone. It is usually employed for low specific speed, vertical shaft Francis turbine. The cone angle is restricted to 8 0 to avoid the losses due to separation. The tube must discharge sufficiently low under tail water level. The maximum efficiency of this type of draft tube is 90%. This type of draft tube improves speed regulation of falling load.</span></div>
<div style="background-color: white; color: black; font-family: "Times New Roman"; font-size: medium; text-align: start;">
<span class="style5" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;"><strong>Simple elbow type (Fig. 30.4b)</strong></span><span class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;"> The vertical length of the draft tube should be made small in order to keep down the cost of excavation, particularly in rock. The exit diameter of draft tube should be as large as possible to recover kinetic energy at runner's outlet. The cone angle of the tube is again fixed from the consideration of losses due to flow separation. Therefore, the draft tube must be bent to keep its definite length. Simple elbow type draft tube will serve such a purpose. Its efficiency is, however, low(about 60%). This type of draft tube turns the water from the vertical to the horizontal direction with a minimum depth of excavation. Sometimes, the transition from a circular section in the vertical portion to a rectangular section in the horizontal part (Fig. 30.4c) is incorporated in the design to have a higher efficiency of the draft tube. The horizontal portion of the draft tube is generally inclined upwards to lead the water gradually to the level of the tail race and to prevent entry of air from the exit end.</span></div>
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<strong>Figure 30.4 Different types of draft tubes</strong></div>
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<div style="background-color: white; color: black; font-family: "Times New Roman"; font-size: medium; text-align: start;">
<br /></div>
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<tr><td><div class="Heading" style="color: #993300; font-family: Arial, Helvetica, sans-serif; font-size: 16px; font-weight: bold;">
Cavitation in reaction turbines</div>
<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
If the pressure of a liquid in course of its flow becomes equal to its vapour pressure at the existing temperature, then the liquid starts boiling and the pockets of vapour are formed which create vapour locks to the flow and the flow is stopped. The phenomenon is known as cavitation. To avoid cavitation, the minimum pressure in the passage of a liquid flow, should always be more than the vapour pressure of the liquid at the working temperature. In a reaction turbine, the point of minimum pressure is usually at the outlet end of the runner blades, i.e at the inlet to the draft tube. For the flow between such a point and the final discharge into the trail race (where the pressure is atmospheric), the Bernoulli's equation can be written, in consideration of the velocity at the discharge from draft tube to be negligibly small, as</div>
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<tr><th scope="row"><img src="http://nptel.ac.in/courses/112104117/chapter_7/7_12_clip_image002_0001.gif" /></th><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;"><div align="right">
(31.1)</div>
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<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
where, <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_12_clip_image002.gif" /> and <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_12_clip_image004.gif" /><em></em> represent the static pressure and velocity of the liquid at the outlet of the runner (or at the inlet to the draft tube). The larger the value of <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_12_clip_image004_0000.gif" />, the smaller is the value of <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_12_clip_image002_0000.gif" /> and the cavitation is more likely to occur. The term <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_12_clip_image006.gif" /> in Eq. (31.1) represents the loss of head due to friction in the draft tube and z is the height of the turbine runner above the tail water surface. For cavitation not to occur <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_12_clip_image008.gif" /> where <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_12_clip_image010.gif" /> is the vapour pressure of the liquid at the working temperature.</div>
<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
An important parameter in the context of cavitation is the available suction head (inclusive of both static and dynamic heads) at exit from the turbine and is usually referred to as the net positive suction head 'NPSH' which is defined as</div>
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<tr><th scope="row"><img src="http://nptel.ac.in/courses/112104117/chapter_7/7_12_clip_image002_0002.gif" /></th><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;"><div align="right">
(31.2)</div>
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<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
with the help of Eq. (31.1) and in consideration of negligible frictional losses in the draft tube <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_12_clip_image002_0003.gif" />, Eq. (31.2) can be written as</div>
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<tr><th scope="row"><img src="http://nptel.ac.in/courses/112104117/chapter_7/7_12_clip_image002_0004.gif" /></th><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;"><div align="right">
(31.3)</div>
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<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
A useful design parameter <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_12_clip_image002_0005.gif" /> known as Thoma's Cavitation Parameter (after the German Engineer Dietrich Thoma, who first introduced the concept) is defined as</div>
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<tr><th scope="row"><img src="http://nptel.ac.in/courses/112104117/chapter_7/7_12_clip_image002_0006.gif" /></th><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;"><div align="right">
(31.4)</div>
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<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
For a given machine, operating at its design condition, another useful parameter <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_12_clip_image002_0007.gif" /> known as critical cavitaion parameter is define as</div>
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<tr><th scope="row"><img src="http://nptel.ac.in/courses/112104117/chapter_7/7_12_clip_image002_0008.gif" /></th><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;"><div align="right">
(31.5)</div>
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<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
Therefore, for cavitaion not to occur <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_12_clip_image002_0009.gif" /> (since, <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_12_clip_image004_0001.gif" /></div>
<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
If either <em>z </em>or <em>H </em>is increased, <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_12_clip_image006_0000.gif" /> is reduced. To determine whether cavitation is likely to occur in a particular installation, the value <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_12_clip_image006_0001.gif" />of may be calculated. When the value of <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_12_clip_image006_0002.gif" /> is greater than the value of <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_12_clip_image010_0000.gif" /> for a particular design of turbine cavitation is not expected to occur.</div>
<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
In practice, the value of <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_7/7_12_clip_image002_0010.gif" /> is used to determine the maximum elevation of the turbine above tail water surface for cavitation to be avoided. The parameter of increases with an increase in the specific speed of the turbine. Hence, turbines having higher specific speed must be installed closer to the tail water level.</div>
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<strong>Performance Characteristics of Reaction Turbine</strong></div>
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It is not always possible in practice, although desirable, to run a machine at its maximum efficiency due to changes in operating parameters. Therefore, it becomes important to know the performance of the machine under conditions for which the efficiency is less than the maximum. It is more useful to plot the basic dimensionless performance parameters (Fig. 31.1) as derived earlier from the similarity principles of fluid machines. Thus one set of curves, as shown in Fig. 31.1, is applicable not just to the conditions of the test, but to any machine in the same homologous series under any altered conditions.</div>
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<strong>Figure 31.1 performance characteristics of a reaction turbine (in dimensionless parameters)</strong></div>
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Figure 31.2 is one of the typical plots where variation in efficiency of different reaction turbines with the rated power is shown.</div>
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<strong>Figure 31.2 Variation of efficiency with load</strong></div>
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<strong style="text-align: left;">Comparison of Specific Speeds of Hydraulic Turbines</strong></div>
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Specific speeds and their ranges of variation for different types of hydraulic turbines have already been discussed earlier. Figure 32.1 shows the variation of efficiencies with the dimensionless specific speed of different hydraulic turbines. The choice of a hydraulic turbine for a given purpose depends upon the matching of its specific speed corresponding to maximum efficiency with the required specific speed determined from the operating parameters, namely, <em>N </em>(rotational speed), <em>p </em>(power) and <em>H </em>(available head).</div>
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<tr><th class="BodyText" scope="row" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; font-weight: normal; text-align: justify;"><span class="style2" style="color: #990000;"><strong>Figure 32.1 Variation of efficiency with specific speed for hydraulic turbines</strong></span></th></tr>
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<strong class="Black_Heading" style="font-family: Arial, Helvetica, sans-serif; font-size: 14px;">Governing of Reaction Turbines </strong><span class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px;">Governing of reaction turbines is usually done by altering the position of the guide vanes and thus controlling the flow rate by changing the gate openings to the runner. The guide blades of a reaction turbine (Figure 32.2) are pivoted and connected by levers and links to the regulating ring. Two long regulating rods, being attached to the regulating ring at their one ends, are connected to a regulating lever at their other ends. The regulating lever is keyed to a regulating shaft which is turned by a servomotor piston of the oil</span></div>
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<strong>Figure 32.2 Governing of reaction turbine</strong><strong style="color: #993300; font-size: medium; text-align: justify;">Pumps</strong></div>
<div align="left" class="Black_Heading" style="font-size: 14px; font-weight: bold;">
<strong>Rotodynamic Pumps</strong></div>
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A rotodynamic pump is a device where mechanical energy is transferred from the rotor to the fluid by the principle of fluid motion through it. The energy of the fluid can be sensed from the pressur and velocity of the fluid at the delivery end of the pump. Therefore, it is essentially a turbine in reverse. Like turbines, pumps are classified according to the main direction of fluid path through them like (i) radial flow or centrifugal, (ii) axial flow and (iii) mixed flow types.</div>
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<strong>Centrifugal Pumps</strong></div>
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The pumps employing centrifugal effects for increasing fluid pressure have been in use for more than a century.The centrifugal pump, by its principle, is converse of the Francis turbine. The flow is radially outward, and the hence the fluid gains in centrifugal head while flowing through it. Because of certain inherent advantages,such as compactness, smooth and uniform flow, low initial cost and high efficiency even at low heads, centrifugal pumps are used in almost all pumping systems. However, before considering the operation of a pump in detail, a general pumping system is discussed as follows.</div>
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<strong>General Pumping System and the Net Head Developed by a Pump</strong></div>
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The word pumping, referred to a hydraulic system commonly implies to convey liquid from a low to a high reservoir. Such a pumping system, in general, is shown in Fig. 33.1. At any point in the system, the elevation or potential head is measured from a fixed reference datum line. The total head at any point comprises pressure head, velocity head and elevation head. For the lower reservoir, the total head at the free surface is <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_1_clip_image002.gif" /> and is equal to the elevation of the free surface above the datum line since the velocity and static pressure at <em>A </em>are zero. Similarly the total head at the free surface in the higher reservoir is ( <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_1_clip_image004.gif" />) and is equal to the elevation of the free surface of the reservoir above the reference datum.</div>
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The variation of total head as the liquid flows through the system is shown in Fig. 33.2. The liquid enters the intake pipe causing a head loss <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_1_clip_image006.gif" /> for which the total energy line drops to point <em>B </em>corresponding to a location just after the entrance to intake pipe. The total head at <em>B </em>can be written as</div>
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As the fluid flows from the intake to the inlet flange of the pump at elevation <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_1_clip_image002_0001.gif" /> the total head drops further to the point C (Figure 33.2) due to pipe friction and other losses equivalent to <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_1_clip_image002_0016.gif" /> . The fluid then enters the pump and gains energy imparted by the moving rotor of the pump. This raises the total head of the fluid to a point D (Figure 33.2) at the pump outlet (Figure 33.1).</div>
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In course of flow from the pump outlet to the upper reservoir, friction and other losses account for a total head loss or<img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_1_clip_image002_0017.gif" /> down to a point <em>E </em>. At <em>E </em>an exit loss <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_1_clip_image008.gif" /> occurs when the liquid enters the upper reservoir, bringing the total heat at point <em>F </em>(Figure 33.2) to that at the free surface of the upper reservoir. If the total heads are measured at the inlet and outlet flanges respectively, as done in a standard pump test, then</div>
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<strong>Figure 33.1 A general pumping system</strong></div>
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<strong>Figure 33.2 Change of head in a pumping system</strong></div>
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Total inlet head to the pump = <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_1_clip_image002_0002.gif" /></div>
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Total outlet head of the pump = <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_1_clip_image004_0001.gif" /></div>
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where <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_1_clip_image006_0001.gif" /> and <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_1_clip_image008_0000.gif" /> are the velocities in suction and delivery pipes respectively.</div>
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<span class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">Therefore, the total head developed by the pump,</span></div>
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The head developed <em>H </em>is termed as <em>manometric head </em>. If the pipes connected to inlet and outlet of the pump are of same diameter, <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_1_clip_image002_0005.gif" /> and therefore the head developed or manometric head <em>H </em>is simply the gain in piezometric pressure head across the pump which could have been recorded by a manometer connected between the inlet and outlet flanges of the pump. In practice, ( <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_1_clip_image004_0003.gif" />) is so small in comparison to <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_1_clip_image006_0003.gif" /> that it is ignored. It is therefore not surprising o find that the static pressure head across the pump is often used to describe the total head developed by the pump. The vertical distance between the two levels in the reservoirs <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_1_clip_image008_0002.gif" /> is known as static head or static lift. Relationship between <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_1_clip_image008_0003.gif" />, the static head and <em>H </em>, the head developed can be found out by applying Bernoulli's equation between <em>A </em>and <em>C </em>and between <em>D </em>and <em>F </em>(Figure 33.1) as follows:</div>
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(33.2)</div>
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Between <em>D </em>and <em>F </em>,</div>
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(33.3)</div>
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substituting <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_1_clip_image002_0008.gif" /> from Eq. (33.2) into Eq. (33.3), and then with the help of Eq. (33.1),</div>
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we can write</div>
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<tr><th scope="row" width="131"> </th><td width="275"><img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_1_clip_image002_0010.gif" /></td><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;" width="30">(33.4)</td></tr>
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Therefore, we have, the total head developed by the pump = static head + sum of all the losses.</div>
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<span style="background-color: white; font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">The simplest from of a centrifugal pump is shown in Figure 33.3. It consists of three important parts: (i) the rotor, usually called as impeller, (ii) the volute casing and (iii) the diffuser ring. The impeller is a rotating solid disc with curved blades standing out vertically from the face of the disc. The impeller may be single sided (Figure 33.4a) or doublesided (Figure 33.4b). A double sided impeller has a relatively small flow capacity.</span><br />
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Figure 33.3 A centrifugal pump</div>
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The tips of the blades are sometimes covered by another flat disc to give shrouded blades (Figure 33.4c), otherwise the blade tips are left open and the casing of the pump itself forms the solid outer wall of the blade passages. The advantage of the shrouded blade is that flow is prevented from leaking across the blade tips from one passage to another.</div>
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<tr><th scope="row" width="56"><img height="200" src="http://nptel.ac.in/courses/112104117/chapter_8/34.gif" width="182" /></th><td width="183"><img height="198" src="http://nptel.ac.in/courses/112104117/chapter_8/35.gif" width="165" /></td><td width="197"><div align="right">
<img height="198" src="http://nptel.ac.in/courses/112104117/chapter_8/36.gif" width="197" /></div>
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<span class="style7" style="color: #990000; font-weight: bold;">(a) Single sided impeller</span></div>
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<span class="style7" style="color: #990000; font-weight: bold;">(b) Double sided impeller</span></div>
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<span class="style7" style="color: #990000; font-weight: bold;">(c) Shrouded impeller</span></div>
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Figure 33.4 Types of impellers in a centrifugal pump</div>
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As the impeller rotates, the fluid is drawn into the blade passage at the impeller eye, the centre of the impeller. The inlet pipe is axial and therefore fluid enters the impeller with very little whirl or tangential component of velocity and flows outwards in the direction of the blades. The fluid receives energy from the impeller while flowing through it and is discharged with increased pressure and velocity into the casing. To convert the kinetic energy or fluid at the impeller outlet gradually into pressure energy, diffuser blades mounted on a diffuser ring are used.</div>
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The stationary blade passages so formed have an increasing cross-sectional area which reduces the flow velocity and hence increases the static pressure of the fluid. Finally, the fluid moves from the diffuser blades into the volute casing which is a passage of gradually increasing cross-section and also serves to reduce the velocity of fluid and to convert some of the velocity head into static head. Sometimes pumps have only volute casing without any diffuser.</div>
<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
Figure 34.1 shows an impeller of a centrifugal pump with the velocity triangles drawn at inlet and outlet. The blades are curved between the inlet and outlet radius. A particle of fluid moves along the broken curve shown in Figure 34.1.</div>
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<strong>Figure 34.1 Velocity triangles for centrifugal pump Impeller</strong></div>
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<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
Let <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_2_clip_image002.gif" /> be the angle made by the blade at inlet, with the tangent to the inlet radius, while <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_2_clip_image004.gif" /> is the blade angle with the tangent at outlet. <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_2_clip_image006.gif" /> and <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_2_clip_image008.gif" /> are the absolute velocities of fluid at inlet an outlet respectively, while <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_3_clip_image002_0015.gif" /> and <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_3_clip_image002_0016.gif" />are the relative velocities (with respect to blade velocity) at inlet and outlet respectively. Therefore,</div>
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<tr><th scope="row"><span class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; font-weight: normal; text-align: justify;">Work done on the fluid per unit weight</span> = <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_3_clip_image002_0024.gif" /></th><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;"><div align="right">
(34.1)</div>
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<div align="left" class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
A centrifugal pump rarely has any sort of guide vanes at inlet. The fluid therefore approaches the impeller without appreciable whirl and so the inlet angle of the blades is designed to produce a right-angled velocity triangle at inlet (as shown in Fig. 34.1). At conditions other than those for which the impeller was designed, the direction of relative velocity <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_3_clip_image002_0000.gif" /> does not coincide with that of a blade. Consequently, the fluid changes direction abruptly on entering the impeller. In addition, the eddies give rise to some back flow into the inlet pipe, thus causing fluid to have some whirl before entering the impeller. However, considering the operation under design conditions, the inlet whirl velocity <img src="http://nptel.ac.in/courses/112104117/chapter_8/8_3_clip_image004.gif" />and accordingly the inlet angular momentum of the fluid entering the impeller is set to zero. Therefore, Eq. (34.1) can be written as</div>
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<tr><th scope="row"><span class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; font-weight: normal; text-align: justify;">Work done on the fluid per unit weight </span>= <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_3_clip_image002_0025.gif" /></th><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;"><div align="right">
(34.2)</div>
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<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
We see from this equation that the work done is independent of the inlet radius. The difference in total head across the pump known as manometric head, is always less than the quantity <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_3_clip_image002_0026.gif" /> because of the energy dissipated in eddies due to friction.</div>
<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
The ratio of manometric head <em>H </em>and the work head imparted by the rotor on the fluid <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_3_clip_image002_0027.gif" /> (usually known as Euler head) is termed as manometric efficiency <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_3_clip_image004_0000.gif" />. It represents the effectiveness of the pump in increasing the total energy of the fluid from the energy given to it by the impeller. Therefore, we can write</div>
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<tr><th scope="row" width="403"><img src="http://nptel.ac.in/courses/112104117/chapter_8/8_3_clip_image002_0029.gif" /></th><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;" width="37"><div align="right">
(34.3)</div>
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<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
The overall efficiency <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_3_clip_image002_0005.gif" /> of a pump is defined as</div>
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<tr><th scope="row" width="407"><img src="http://nptel.ac.in/courses/112104117/chapter_8/8_3_clip_image002_0006.gif" /></th><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;" width="33"><div align="right">
(34.4)</div>
</td></tr>
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<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
where, <em>Q </em>is the volume flow rate of the fluid through the pump, and <em>P </em>is the shaft power, i.e. the input power to the shaft. The energy required at the shaft exceeds <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_3_clip_image002_0028.gif" /> because of friction in the bearings and other mechanical parts. Thus a mechanical efficiency is defined as</div>
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<tr><th scope="row" width="407"><img src="http://nptel.ac.in/courses/112104117/chapter_8/8_3_clip_image002_0030.gif" /></th><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;" width="33"><div align="right">
(34.5)</div>
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<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
so that</div>
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<tr><th scope="row" width="405"><img src="http://nptel.ac.in/courses/112104117/chapter_8/8_3_clip_image002_0009.gif" /></th><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;" width="35"><div align="right">
(34.6)</div>
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</tbody></table>
</td></tr>
</tbody></table>
<div class="Heading" style="color: #993300; font-family: Arial, Helvetica, sans-serif; font-weight: bold; text-align: justify;">
<br /></div>
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<tr><td height="576" valign="top"><div class="Black_Heading" style="font-family: Arial, Helvetica, sans-serif; font-size: 14px; font-weight: bold;">
Slip Factor</div>
<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
Under certain circumstances, the angle at which the fluid leaves the impeller may not be the same as the actual blade angle. This is due to a phenomenon known as fluid slip, which finally results in a reduction in <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_4_clip_image002_0009.gif" /> the tangential component of fluid velocity at impeller outlet. One possible explanation for slip is given as follows.</div>
<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
In course of flow through the impeller passage, there occurs a difference in pressure and velocity between the leading and trailing faces of the impeller blades. On the leading face of a blade there is relatively a high pressure and low velocity, while on the trailing face, the pressure is lower and hence the velocity is higher. This results in a circulation around the blade and a non-uniform velocity distribution at any radius. The mean direction of flow at outlet, under this situation, changes from the blade angle at outlet <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_4_clip_image004.gif" /> to a different angle <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_4_clip_image006.gif" /> as shown in Figure 34.2 Therefore the tangential velocity component at outlet <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_4_clip_image002_0010.gif" /> is reduced to <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_4_clip_image002_0011.gif" /> , as shown by the velocity triangles in Figure 34.2, and the difference <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_4_clip_image010.gif" /> is defined as the slip. The slip factor <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_4_clip_image012.gif" /> is defined as</div>
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<tr><th scope="row" width="434"><img src="http://nptel.ac.in/courses/112104117/chapter_8/8_4_clip_image002_0012.gif" /></th><td width="10"> </td></tr>
</tbody></table>
<table align="center" border="0" style="width: 450px;"><tbody>
<tr><th scope="row"><img height="344" src="http://nptel.ac.in/courses/112104117/chapter_8/20.gif" width="524" /></th></tr>
</tbody></table>
<table align="center" border="0" style="width: 522px;"><tbody>
<tr><th class="BodyText" scope="row" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; font-weight: normal; text-align: justify;" width="516"><div align="center" class="style3" style="color: #990000;">
<strong>Figure 34.2 Slip and velocity in the impeller blade passage of a centrifugal pump</strong></div>
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<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
With the application of slip factor <img align="baseline" src="http://nptel.ac.in/courses/112104117/chapter_8/8_4_clip_image002_0002.gif" />, the work head imparted to the fluid (Euler head) becomes <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_4_clip_image002_0013.gif" /> . The typical values of slip factor lie in the region of 0.9.</div>
<div align="left" class="Black_Heading" style="font-family: Arial, Helvetica, sans-serif; font-size: 14px; font-weight: bold;">
<strong>Losses in a Centrifugal Pump</strong></div>
• <span class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">Mechanical friction power loss due to friction between the fixed and rotating parts in the bearing and stuffing boxes.</span><br />
<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
• Disc friction power loss due to friction between the rotating faces of the impeller (or disc) and the liquid.</div>
<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
• Leakage and recirculation power loss. This is due to loss of liquid from the pump and recirculation of the liquid in the impeller. The pressure difference between impeller tip and eye can cause a recirculation of a small volume of liquid, thus reducing the flow rate at outlet of the impeller as shown in Fig. (34.3).</div>
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<tr><th scope="row"><img height="223" src="http://nptel.ac.in/courses/112104117/chapter_8/42.gif" width="488" /></th></tr>
</tbody></table>
<table align="center" border="0" style="width: 450px;"><tbody>
<tr><th class="BodyText" scope="row" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; font-weight: normal; text-align: justify;"><div align="center" class="style3" style="color: #990000;">
<strong>Figure 34.3 Leakage and recirculation in a centrifugal pump</strong></div>
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<div class="Heading" style="color: #993300; font-family: Arial, Helvetica, sans-serif; font-weight: bold; text-align: justify;">
<br /></div>
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<tr><td height="576" valign="top"><div class="Heading" style="color: #993300; font-family: Arial, Helvetica, sans-serif; font-size: 16px; font-weight: bold;">
<strong>Characteristics of a Centrifugal Pump</strong></div>
<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
With the assumption of no whirl component of velocity at entry to the impeller of a pump, the work done on the fluid per unit weight by the impeller is given by Equation( 34.2). Considering the fluid to be frictionless, the head developed by the pump will be the same san can be considered as the theoretical head developed. Therefore we can write for theoretical head developed <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_5_clip_image002.gif" /> as</div>
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<tr><th scope="row"><img src="http://nptel.ac.in/courses/112104117/chapter_8/8_5_clip_image002_0010.gif" /></th><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;"><div align="right">
(35.1)</div>
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<div align="left" class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
From the outlet velocity triangle figure( 34.1)</div>
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<tr><th scope="row"><img src="http://nptel.ac.in/courses/112104117/chapter_8/8_5_clip_image002_0001.gif" /></th><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;"><div align="right">
(35.2)</div>
</td></tr>
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<div align="left" class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
where <em>Q </em>is rate of flow at impeller outlet and <em>A </em>is the flow area at the periphery of the impeller. The blade speed at outlet <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_5_clip_image002_0002.gif" /> can be expressed in terms of rotational speed of the impeller <em>N </em>as</div>
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<tr><th scope="row"><img src="http://nptel.ac.in/courses/112104117/chapter_8/8_5_clip_image002_0003.gif" /></th></tr>
</tbody></table>
<div align="left" class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
Using this relation and the relation given by Eq. (35.2), the expression of theoretical head developed can be written from Eq. (35.1) as</div>
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<tr><th scope="row"><img src="http://nptel.ac.in/courses/112104117/chapter_8/8_5_clip_image002_0004.gif" /></th></tr>
</tbody></table>
<table align="center" border="0" style="width: 450px;"><tbody>
<tr><th scope="row" width="377"><img src="http://nptel.ac.in/courses/112104117/chapter_8/8_5_clip_image002_0005.gif" /></th><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;" width="63"><div align="right">
(35.3)</div>
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<div align="left" class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
where, <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_5_clip_image002_0006.gif" /> and <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_5_clip_image004.gif" /></div>
<div align="justify">
<span class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px;">For a given impeller running at a constant rotational speed. <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_5_clip_image002_0007.gif" /> and <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_5_clip_image004_0000.gif" /> are constants, and therefore head and discharge bears a linear relationship as shown by Eq. (35.3). This linear variation of <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_5_clip_image006.gif" /> with <em>Q </em>is plotted as curve </span><span class="style14" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px;">I</span><span class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px;">in Fig. 35.1.</span></div>
<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
If slip is taken into account, the theoretical head will be reduced to <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_5_clip_image008.gif" />. Moreover the slip will increase with the increase in flow rate <em>Q </em>. The effect of slip in head-discharge relationship is shown by the curve II in Fig. 35.1. The loss due to slip can occur in both a real and an ideal fluid, but in a real fluid the shock losses at entry to the blades, and the friction losses in the flow passages have to be considered. At the design point the shock losses are zero since the fluid moves tangentially onto the blade, but on either side of the design point the head loss due to shock increases according to the relation</div>
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<tr><th scope="row"><img src="http://nptel.ac.in/courses/112104117/chapter_8/8_5_clip_image002_0008.gif" /></th><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;"><div align="right">
(35.4)</div>
</td></tr>
</tbody></table>
<table align="center" border="0" style="width: 450px;"><tbody>
<tr><th scope="row"><table align="center" border="0" style="width: 450px;"><tbody>
<tr><th scope="row"><img height="322" src="http://nptel.ac.in/courses/112104117/chapter_8/lecture35.jpg" width="361" /></th></tr>
</tbody></table>
</th></tr>
</tbody></table>
<table align="center" border="0" style="width: 450px;"><tbody>
<tr><th class="BodyText" scope="row" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; font-weight: normal; text-align: justify;"><div align="center" class="style13" style="color: #990000;">
<strong>Figure 35.1 Head-discharge characteristics of a centrifugal pump</strong></div>
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<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
where <img align="middle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_6_clip_image002.gif" /> is the off design flow rate and <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_6_clip_image004.gif" /> is a constant. The losses due to friction can usually be expressed as</div>
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<tr><th scope="row" width="407"><img src="http://nptel.ac.in/courses/112104117/chapter_8/8_6_clip_image002_0000.gif" /></th><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;" width="33"><div align="right">
(35.5)</div>
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<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
where, <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_6_clip_image002_0001.gif" /> is a constant.</div>
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<div class="Heading" style="color: #993300; font-family: Arial, Helvetica, sans-serif; font-weight: bold; text-align: justify;">
<br /></div>
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<tr><td height="576" valign="top"><div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
Equation (35.5) and (35.4) are also shown in Fig. 35.1 (curves III and IV) as the characteristics of losses in a centrifugal pump. By subtracting the sum of the losses from the head in consideration of the slip, at any flow rate (by subtracting the sum of ordinates of the curves III and IV from the ordinate of the curve II at all values of the abscissa), we get the curve V which represents the relationship of the actual head with the flow rate, and is known as head-discharge characteristic curve of the pump.</div>
<div align="left" class="Black_Heading" style="font-family: Arial, Helvetica, sans-serif; font-size: 14px; font-weight: bold;">
<strong>Effect of blade outlet angle</strong></div>
<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
The head-discharge characteristic of a centrifugal pump depends (among other things) on the outlet angle of the impeller blades which in turn depends on blade settings. Three types of blade settings are possible (i) the forward facing for which the blade curvature is in the direction of rotation and, therefore, <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_6_clip_image002_0002.gif" />(Fig. 35.2a), (ii) radial, when <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_6_clip_image004_0000.gif" /> (Fig. 35.2b), and (iii) backward facing for which the blade curvature is in a direction opposite to that of the impeller rotation and therefore, <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_6_clip_image006.gif" /> (Fig. 35.2c). The outlet velocity triangles for all the cases are also shown in Figs. 35.2a, 35.2b, 35.2c. From the geometry of any triangle, the relationship between <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_6_clip_image008.gif" /> and <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_6_clip_image010.gif" /> can be written as.</div>
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<tr><th scope="row"><img src="http://nptel.ac.in/courses/112104117/chapter_8/8_6_clip_image002_0003.gif" /></th></tr>
</tbody></table>
<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
which was expressed earlier by Eq. (35.2).</div>
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<tr><th scope="row"><img height="181" src="http://nptel.ac.in/courses/112104117/chapter_8/16.gif" width="621" /></th></tr>
</tbody></table>
<table align="center" border="0" style="width: 450px;"><tbody>
<tr><th class="BodyText" scope="row" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; font-weight: normal; text-align: justify;"><div align="center" class="style13" style="color: #990000;">
<strong>Figure 35.2 Outlet velocity triangles for different blade settings in a centrifugal pump</strong></div>
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<div align="left" class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
In case of forward facing blade, <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_6_clip_image002_0004.gif" />and hence cot <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_6_clip_image004_0001.gif" /> is negative and therefore <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_6_clip_image006_0000.gif" /> is more than <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_6_clip_image008_0000.gif" />. In case of radial blade, <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_6_clip_image010_0000.gif" />and <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_6_clip_image012.gif" />In case of backward facing blade, <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_6_clip_image014.gif" />and <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_6_clip_image016.gif" />Therefore the sign of <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_6_clip_image018.gif" />, the constant in the theoretical head-discharge relationship given by the Eq. (35.3), depends accordingly on the type of blade setting as follows:</div>
F<span class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">or forward curved blades <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_6_clip_image020.gif" /></span><br />
<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
For radial blades <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_6_clip_image022.gif" /></div>
<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
For backward curved blades <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_6_clip_image024.gif" /></div>
<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
With the incorporation of above conditions, the relationship of head and discharge for three cases are shown in Figure 35.3. These curves ultimately revert to their more recognized shapes as the actual head-discharge characteristics respectively after consideration of all the losses as explained earlier Figure 35.4.</div>
<div class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;">
For both radial and forward facing blades, the power is rising monotonically as the flow rate is increased. In the case of backward facing blades, the maximum efficiency occurs in the region of maximum power. If, for some reasons, <em>Q</em>increases beyond <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_6_clip_image002_0005.gif" /> there occurs a decrease in power. Therefore the motor used to drive the pump at part load, but rated at the design point, may be safely used at the maximum power. This is known as self-limiting characteristic. In case of radial and forward-facing blades, if the pump motor is rated for maximum power, then it will be under utilized most of the time, resulting in an increased cost for the extra rating. Whereas, if a smaller motor is employed, rated at the design point, then if <em>Q </em>increases above <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_6_clip_image002_0006.gif" /> the motor will be overloaded and may fail. It, therefore, becomes more difficult to decide on a choice of motor in these later cases (radial and forward-facing blades).</div>
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<tr><th scope="row"><img height="238" src="http://nptel.ac.in/courses/112104117/chapter_8/17.gif" width="561" /></th></tr>
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<strong>Figure 35.3 Theoretical head-discharge characteristic curves of a centrifugal pump for different blade settings</strong></div>
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<tr><th scope="row"><img height="329" src="http://nptel.ac.in/courses/112104117/chapter_8/18.gif" width="391" /></th></tr>
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<strong>Figure 35.4 Actual head-discharge and power-discharge characteristic curves of a centrifugal pump</strong></div>
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<br /></div>
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<br /></div>
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<strong>Flow through Volute Chambers</strong></div>
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Apart from frictional effects, no torque is applied to a fluid particle once it has left the impeller. The angular momentum of fluid is therefore constant if friction is neglected. Thus the fluid particles follow the path of a free vortex. In an ideal case, the radial velocity at the impeller outlet remains constant round the circumference. The combination of uniform radial velocity with the free vortex ( <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_7_clip_image002.gif" /> =constant) gives a pattern of spiral streamlines which should be matched by the shape of the volute. This is the most important feature of the design of a pump. At maximum efficiency, about 10 percent of the head generated by the impeller is usually lost in the volute.</div>
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<strong>Vanned Diffuser</strong></div>
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A vanned diffuser, as shown in Fig. 36.1, converts the outlet kinetic energy from impeller to pressure energy of the fluid in a shorter length and with a higher efficiency. This is very advantageous where the size of the pump is important. A ring of diffuser vanes surrounds the impeller at the outlet. The fluid leaving the impeller first flows through a vaneless space before entering the diffuser vanes. The divergence angle of the diffuser passage is of the order of 8-10 ° which ensures no boundary layer separation. The optimum number of vanes are fixed by a compromise between the diffusion and the frictional loss. The greater the number of vanes, the better is the diffusion (rise in static pressure by the reduction in flow velocity) but greater is the frictional loss. The number of diffuser vanes should have no common factor with the number of impeller vanes to prevent resonant vibration.</div>
<table align="center" border="0" style="width: 450px;"><tbody>
<tr><th scope="row"><img height="346" src="http://nptel.ac.in/courses/112104117/chapter_8/19.gif" width="424" /></th></tr>
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<strong>Figure 36.1 A vanned diffuser of a centrifugal pump</strong></div>
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<strong>Cavitation in centrifugal pumps</strong></div>
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Cavitation is likely to occur at the inlet to the pump, since the pressure there is the minimum and is lower than the atmospheric pressure by an amount that equals the vertical height above which the pump is situated from the supply reservoir (known as sump) plus the velocity head and frictional losses in the suction pipe. Applying the Bernoulli's equation between the surface of the liquid in the sump and the entry to the impeller, we have</div>
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<tr><th scope="row"><img src="http://nptel.ac.in/courses/112104117/chapter_8/8_7_clip_image002_0000.gif" /></th><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;"><div align="right">
(36.1)</div>
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where, <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_7_clip_image002_0001.gif" /> is the pressure at the impeller inlet and <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_7_clip_image004.gif" /> is the pressure at the liquid surface in the sump which is usually the atmospheric pressure, <em>Z1 </em>is the vertical height of the impeller inlet from the liquid surface in the sump, <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_7_clip_image006.gif" />is the loss of head in the suction pipe. Strainers and non-return valves are commonly fitted to intake pipes. The term <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_7_clip_image006_0000.gif" />must therefore include the losses occurring past these devices, in addition to losses caused by pipe friction and by bends in the pipe.</div>
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In the similar way as described in case of a reaction turbine, the net positive suction head 'NPSH' in case of a pump is defined as the available suction head (inclusive of both static and dynamic heads) at pump inlet above the head corresponding to vapor pressure.</div>
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Therefore,</div>
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<tr><th scope="row"><img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_7_clip_image008.gif" /></th><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;"><div align="right">
(36.2)</div>
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Again, with help of Eq. (36.1), we can write</div>
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The Thomas cavitation parameter s and critical cavitation parameter <img align="absmiddle" src="http://nptel.ac.in/courses/112104117/chapter_8/8_7_clip_image002_0003.gif" /> are defined accordingly (as done in case of reaction turbine) as</div>
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<tr><th scope="row" width="401"><img src="http://nptel.ac.in/courses/112104117/chapter_8/8_7_clip_image002_0004.gif" /></th><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;" width="39"><div align="right">
(36.3)</div>
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and</div>
</th><td><img src="http://nptel.ac.in/courses/112104117/chapter_8/8_7_clip_image002_0005.gif" /></td><td class="BodyText" style="font-family: Arial, Helvetica, sans-serif; font-size: 13px; text-align: justify;"><div align="right">
(36.4)</div>
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We can say that for cavitation not to occur,</div>
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In order that s should be as large as possible, <em>z </em>must be as small as possible. In some installations, it may even be necessary to set the pump below the liquid level at the sump (i.e. with a negative vale of <em>z </em>) to avoid cavitation.</div>
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Mechanical Engineering Departmenthttp://www.blogger.com/profile/12582953924770018783noreply@blogger.comtag:blogger.com,1999:blog-6302071579893645567.post-17349046686179787422017-01-24T13:58:00.002+05:302017-01-24T13:58:56.341+05:30DOM UNIT1<div dir="ltr" style="text-align: left;" trbidi="on">
<a href="https://drive.google.com/file/d/0BylRye1I0XbHS1Q1VzV0Rmh1RkU/view?usp=sharing" target="_blank">UNIT !</a><br /></div>
Mechanical Engineering Departmenthttp://www.blogger.com/profile/12582953924770018783noreply@blogger.comtag:blogger.com,1999:blog-6302071579893645567.post-26909327337850550222017-01-24T13:52:00.001+05:302017-01-24T13:52:56.270+05:30Unit 4 (AUTOMOTIVE ENGINE)<div dir="ltr" style="text-align: left;" trbidi="on">
<a href="https://drive.google.com/file/d/0BylRye1I0XbHbWlwY19VcFhDYlk/view?usp=sharing" target="_blank">Emission Control Methods</a><br /></div>
Mechanical Engineering Departmenthttp://www.blogger.com/profile/12582953924770018783noreply@blogger.comtag:blogger.com,1999:blog-6302071579893645567.post-70861542217649626812017-01-24T13:48:00.002+05:302017-01-24T13:48:46.511+05:30UNIT 2-3 LUBRICATION SYSTEM (AUTOMOTIVE ENGINES)<div dir="ltr" style="text-align: left;" trbidi="on">
<a href="https://drive.google.com/file/d/0BylRye1I0XbHNFNwbkFLRm1tUlU/view?usp=sharing" target="_blank">LUBRICATION SYSTEM</a><br /></div>
Mechanical Engineering Departmenthttp://www.blogger.com/profile/12582953924770018783noreply@blogger.comtag:blogger.com,1999:blog-6302071579893645567.post-36166087059883034382017-01-24T13:43:00.002+05:302017-01-24T13:43:35.005+05:30Automotive Engine UNIT -1(Heat Engine)<div dir="ltr" style="text-align: left;" trbidi="on">
<a href="https://drive.google.com/file/d/0BylRye1I0XbHUDNnaFh3azB3SXM/view?usp=sharing" target="_blank">Heat Engine</a></div>
Mechanical Engineering Departmenthttp://www.blogger.com/profile/12582953924770018783noreply@blogger.comtag:blogger.com,1999:blog-6302071579893645567.post-87882931382691162102017-01-23T12:16:00.004+05:302017-01-23T12:27:33.844+05:30MOTOR VEHICLE & ENVIRONMENT PROTECTION <div dir="ltr" style="text-align: left;" trbidi="on">
UNIT-1<br />
<b>EMISSION STANDARD & REGULATIONS MEASURMENT & TESTING PROCEDURES</b><br />
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<span style="background-color: white;">Vehicular Pollution Control</span><br />
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INTRODUCTION<br />
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Human activities generate three broad sources of air pollution: stationary or point, mobile, and indoor. In developing countries especially in the rural area, indoor air pollution from using open fires for cooking and heating may be a serious problem. Industries, power plants etc. are the cause of stationary air pollution. But in urban areas –both developing and developed countries, it is predominantly mobile or vehicular pollution that contributes to overall air quality problem. In Delhi, the data shows that of the total 3,000 metric tonnes of pollutants1 belched out everyday, close to two-third (66%) is from vehicles. Similarly, the contribution of vehicles to urban air pollution is 52% in Bombay and close to one-third in Calcutta.2 Katz (1994) has estimated that in Santiago, Chile, wherever pollution concentration exceeds ambient standards, mobile sources or vehicles are the cause. Similarly, in case of Budapest, Hungary, transport is the dominant source of emissions except sulphur dioxide (SO2), contributing 57% of Oxides of Nitrogen (NOx), 80% of lead (Pb), 81% of carbon monoxide (CO) and 75% of hydrocarbon (HC) emissions (Lehoczki, 2000).</div>
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A number of countries have targeted vehicles and associated sectors (such as, fuel) to curb the menace. Notable successful initiatives are: conversion of public transport from diesel to CNG in Delhi, switching of Vikrams (tuk-tuks) from diesel to electricity in Kathmandu valley, shifting from leaded to unleaded gasoline in many countries etc. Still the pollution problem in urban cities may continue to loom large due to ever-burgeoning vehicular population, which is outpacing any such measure and road network development. Following data gives a glimpse of such skewed growth. Against 1.9 million vehicular population in 1990 in Delhi, it rose to nearly 3.6 million in the year 2001 (i.e., an increase of nearly 87%). During the same period, Delhi’s population has increased by only 43% (from 9.5 million to 13.8 million) and road-length by merely 14% (from 22,000 Km to 25,000 Km) respectively. Situation is similar across a number of cities in India and the developing world. This indicates the exigency of controlling vehicular pollution.</div>
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The worst thing about vehicular pollution is that it cannot be avoided as the emissions are emitted at the near-ground level where we breathe. Pollution from vehicles gets reflected in increased mortality and morbidity and is revealed through symptoms like cough, headache, nausea, irritation of eyes, various bronchial problems and visibility. The pollution from vehicles are due to discharges like CO, unburned HC, Pb compounds, NOx, soot, suspended particulate matter (SPM) and aldehydes, among others, mainly from the tail pipes. A recent study reports that in Delhi one out of every 10 school children suffers from asthma that is worsening due to vehicular pollution.3 Similarly, two of the three most important health related problems in Bangkok are caused by air pollution and lead contamination, both of which are contributed greatly by motor vehicles.4 Situation is same in a number of other mega-cities across the globe – be it Mexico City, Sao Paulo and Santiago in Latin America or Bangkok, Jakarta, Manila, Dhaka in Asia or Ibadan and Lagos in Africa or in cities of Eastern Europe, the erstwhile USSR and the Middle East.</div>
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According to the World Health Organisation (WHO), 4 to 8% of deaths that occur annually in the world are related to air pollution and of its constituents, the WHO has identified SPM as the most sinister in terms of its effect on health.</div>
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The SPM is not homogeneous. It has a number of constituents. As a result, it is measured and characterised in various ways: (i) TSP (Total suspended particulates) with particle diameters < 50-100 μm is the fraction sampled with high-volume samplers. (ii) PM: Inhalable particles having a diameter <10 μm penetrates through the nose, by breathing. (iii) Thoracic particles: are approximately equal to PM particles. (iv) PM: ‘Fine fraction’ with a diameter <2.5 μm penetrates to the lungs; and (v) Black smoke: a measure of the blackness of a particle sample gives a relative value for the soot content of the sample. Due to their high health damaging potential10102.5 recent studies have started paying more attention to PM10 and PM2.5 particles.</div>
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The different air pollutants due to vehicles can have effects at all the three levels – local (e.g., smoke affecting visibility, ambient air, noise etc.), regional (such as smog, acidification) and global (i.e., global warming). The vehicles besides being the prominent source of air pollutants also account for a number of external effects, such as congestion, noise, accidents, road wear and tear, and ‘barrier effects.</div>
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Under this background this note investigates what is the economics of vehicular pollution control and what policy instruments / initiatives can be employed to control the vehicular pollution. For a prescription to yield desired results, it should hit the right source of pollution. Section 2 gives in brief the contribution of different sources to vehicular air pollution problem. This is followed by the economics of vehicular pollution control in Section 3. The section also explores the instruments that can be applied to control vehicular pollution. </div>
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The major difference between developing and developed countries lies in the fact that institutions are in place and information of health impacts are known to the policy makers. For developing countries, the challenge rests on devising suitable policy instruments that fully take into account the damage caused by the polluting source. A discussion of complexity involved in estimating the damage function is given in Section 4. Section 5 gives under what conditions a particular instrument will be more appropriate, especially in the case of mega cities of developing world followed by India’s experience in combating vehicular pollution. The concept note concludes in Section 6. It is to be stated at the outset that the note covers mainly the environmental consequences of transport and does not investigate the other important external effects of the sector such as barrier effect, congestion effect etc.</div>
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<b>VEHICULAR AIR POLLUTION – CAUSES OF EMISSIONS</b></div>
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Vehicular pollution sources are not homogenous, as there is a complete range of technological mix. The mix could be in terms of fuel used – gasoline or diesel or natural gas; or engine type – 2-stroke or 4-stroke and/or a combination of these. Emissions from Gasoline Vehicles Gasoline-powered engines are of two types: 4-stroke and 2-stroke. gives the various sources of emissions in the two cases. The exhaust emissions from gasoline-run vehicles consist of CO, HC, NOx, SO2, and partial oxides of aldehydes, besides particulate matters including lead salts.</div>
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EMISSION TESTING IN VARIOUS VEHICLE:</div>
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<span style="background-color: white;"><b>Motor vehicle exhaust emissions are a significant source of pollution, including carbon monoxide, nitrogen oxides and hydrocarbons. These pollutants can be harmful to human health and the environment and lead to the formation of ground level ozone (smog). Exhaust emissions from cars and trucks are one of the single greatest sources of air pollution in the Chicago and Metro-East St. Louis areas.</b></span></div>
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<span style="background-color: white;"><b>The Illinois EPA's vehicle emissions inspection program plays an important role in improving air quality and public health in Illinois. The federal Clean Air Act (42 U.S.C. § 7511a) requires vehicle emissions inspection programs in large, urbanized areas that do not meet the National Ambient Air Quality Standards (NAAQS) for ozone. Although Illinois has made significant strides to clean its air, levels of air pollution in the Chicago and Metro-East St. Louis areas still exceed the ozone NAAQS. Additionally, the Illinois Vehicle Emissions Inspection Law of 2005 (625 ILCS 5/13C) requires a vehicle emissions inspection program to reduce air pollution from motor vehicles in these areas of Illinois. For these reasons, the vehicle emissions inspection program is part of Illinois EPA’s strategy to reduce air pollution in Illinois and bring the Chicago and Metro-East areas into attainment of the ozone NAAQS.</b></span></div>
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<span style="background-color: white;"><b>Through the On-Board Diagnostic (OBD) test, vehicle emissions inspections in Illinois identify malfunctioning emission control systems that often result in vehicles exceeding federal emission standards. Requiring repairs on such vehicles helps clean the air while improving the vehicle's performance and fuel economy.</b></span></div>
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<span style="background-color: white;"><b>Most 1996 and newer gasoline-powered passenger vehicles are subject to emissions inspections after they are four years old (e.g. 2012 vehicles are being inspected in 2016 for the first time). The inspection month coincides with the expiration date of the vehicle license plate. Typically, even model-year vehicles are inspected during even years, and odd model-year vehicles are inspected in odd years.</b></span></div>
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<span style="background-color: white;"><span style="color: #404040; font-weight: bold;">The Illinois EPA oversees its vehicle emissions inspection program that is operated by its contractor. The Illinois EPA enforces the vehicle emissions inspection requirement by partnering with the Illinois Secretary of State’s Office to deny vehicle license plate registrations to non-complying </span>vehicles.</span></div>
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<span style="background-color: white;">Automobile pollution sources effect and control of automobile pollution </span>Air Pollution from Motor Vehicles Standards and Technologies for Controlling Emissions Controlling Emissions from In-Use Vehicles Inspection and maintenance (I/M) measures to control emissions from in-use vehicles are an essential complement to emission standards for new vehicles. Although difficult to implement, an effective inspection and maintenance program can significantly reduce emissions from uncontrolled vehicles. I/M programs are also needed to ensure that the benefits of new-vehicle control technologies are not lost through poor maintenance and tampering with emission controls. I/M programs for gasoline vehicles commonly include measurement of hydrocarbon and carbon monoxide concentrations in the exhaust. These have limited effectiveness but can identify gross malfunctions in emission control systems. Newer programs such as the IM240 procedure developed in the United States use dynamometers and constant volume sampling to measure emissions in grams per kilometer over a realistic driving cycle. Inspection and maintenance of high-technology, computer-controlled vehicles can be enhanced substantially with on-board diagnostic systems. For diesel vehicles, smoke opacity measurements in free acceleration are the most common inspection method. This approach also has limited effectiveness but can identify serious emission failures. Opacity measurements can also be used to control white smoke emissions from twostroke <span style="font-family: "roboto" , "trebuchet ms" , "helvetica" , "arial" , sans-serif;">motorcycles.</span>On-road emission checks can improve the effectiveness of periodic I/M programs. Checks for smoke emissions from two-stroke and diesel vehicles can be made more effective by visual prescreening. The effectiveness of on-road checks for hydrocarbons and carbon monoxide can be enhanced by remote sensing the concentrations of these pollutants in the vehicle exhaust.</div>
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There are two main types of I/M programs: centralized programs, in which all inspections are done in high-volume test facilities operated by the government or contracted to competitively-selected private operators, and decentralized programs, in which both emissions testing and repairs are done in private garages.<br />
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Mechanical Engineering Departmenthttp://www.blogger.com/profile/12582953924770018783noreply@blogger.comtag:blogger.com,1999:blog-6302071579893645567.post-76016063883881141062017-01-23T11:44:00.001+05:302017-01-23T11:44:10.301+05:30Automobile Engineering Previous Years Question Papers<div dir="ltr" style="text-align: left;" trbidi="on">
<a href="https://drive.google.com/drive/folders/0BylRye1I0XbHazdXeEY5SXAxcmM?usp=sharing" target="_blank">AE previous year question papers</a><br /></div>
Mechanical Engineering Departmenthttp://www.blogger.com/profile/12582953924770018783noreply@blogger.comtag:blogger.com,1999:blog-6302071579893645567.post-81740777348260585382017-01-23T11:14:00.006+05:302017-01-23T11:14:59.551+05:30<div dir="ltr" style="text-align: left;" trbidi="on">
<a href="https://drive.google.com/file/d/0BylRye1I0XbHWlkxSGZiUmdlOXc/view?usp=sharing" target="_blank">rac3</a><br /></div>
Mechanical Engineering Departmenthttp://www.blogger.com/profile/12582953924770018783noreply@blogger.comtag:blogger.com,1999:blog-6302071579893645567.post-1347017240434896582017-01-23T11:13:00.002+05:302017-01-23T11:13:31.651+05:30<div dir="ltr" style="text-align: left;" trbidi="on">
<a href="https://drive.google.com/file/d/0BylRye1I0XbHenF5QlZCYUQ4UWs/view?usp=sharing" target="_blank">RAC2</a><br /></div>
Mechanical Engineering Departmenthttp://www.blogger.com/profile/12582953924770018783noreply@blogger.comtag:blogger.com,1999:blog-6302071579893645567.post-55011671613878424592017-01-23T11:12:00.002+05:302017-01-23T11:12:34.902+05:30<div dir="ltr" style="text-align: left;" trbidi="on">
<a href="https://drive.google.com/file/d/0BylRye1I0XbHenF5QlZCYUQ4UWs/view?usp=sharing" target="_blank">RAC 1</a></div>
Mechanical Engineering Departmenthttp://www.blogger.com/profile/12582953924770018783noreply@blogger.comtag:blogger.com,1999:blog-6302071579893645567.post-14571093122044273002017-01-23T11:02:00.001+05:302017-01-23T11:02:07.286+05:30MANEGEMENT INFORMATION SYSTEM (ME-432-E) 8TH SEM<div dir="ltr" style="text-align: left;" trbidi="on">
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<b>UNIT-1 MIS</b></div>
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<b>what is mis ? Decision support system</b></div>
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INTRODUCTION:<br />
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Management information systems encompass a broad and complex topic. To make this topic more manageable, boundaries will be defined. First, because of the vast number of activities relating to management information systems, a total review is not possible. Those discussed here is only a partial sampling of activities, reflecting the author's viewpoint of the more common and interesting developments. Likewise where there were multiple effects in a similar area of development, only selected ones will be used to illustrate concepts. This is not to imply one effort is more important than another. Also, the main focus of this paper will be on information systems for use at the farm level and to some lesser extent systems used to support researchers addressing farm level problems (e.g., simulation or optimization models, geographic information systems, etc.) and those used to support agribusiness firms that supply goods and services to agricultural producers and the supply chain beyond the production phase.</div>
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Secondly, there are several frameworks that can be used to define and describe management information systems. More than one will be used to discuss important concepts. Because more than one is used, it indicates the difficult of capturing the key concepts of what is a management information system. Indeed, what is viewed as an effective and useful management information system is one environment may not be of use or value in another.</div>
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Lastly, the historical perspective of management information systems cannot be ignored. This perspective gives a sense of how these systems have evolved, been refined and adapted as new technologies have emerged, and how changing economic conditions and other factors have influenced the use of information systems.</div>
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Before discussing management information systems, some time-tested concepts should be reviewed. Davis offers a commonly used concept in his distinction between data and information. Davis defines data as raw facts, figures, objects, etc. Information is used to make decisions. To transform data into information, processing is needed and it must be done while considering the context of a decision. We are often awash in data but lacking good information. However, the success achieved in supplying information to decision makers is highly variable. Barabba, expands this concept by also adding inference, knowledge and wisdom in his modification of Haechel's hierarchy which places wisdom at the highest level and data at the lowest. As one moves up the hierarchy, the value is increased and volume decreased. Thus, as one acquires knowledge and wisdom the decision making process is refined. Management information systems attempt to address all levels of Haechel's hierarchy as well as converting data into information for the decision maker. As both Barabba and Haechel argue, however, just supplying more data and information may actually be making the decision making process more difficult. Emphasis should be placed on increasing the value of information by moving up Haechel's hierarchy.</div>
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Another important concept from Davis and Olsen is the value if information. They note that “in general, the value of information is the value of the change in decision behavior caused by the information, less the cost of the information.” This statement implies that information is normally not a free good. Furthermore, if it does not change decisions to the better, it may have no value. Many assume that investing in a “better” management information system is a sound economic decision. Since it is possible that the better system may not change decisions or the cost of implementing the better system is high to the actual realized benefits, it could be a bad investment. Also, since before the investment is made, it is hard to predict the benefits and costs of the better system, the investment should be viewed as one with risk associated with it.Another approach for describing information systems is that proposed by Harsh and colleagues. They define information as one of four types and all these types are important component of a management information system. Furthermore, the various types build upon and interact with each other.Descriptive information can also be used as inputs to secure other needed types of information.</div>
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<b>MANAGEMENT INFORMATION & SYSTEM APPROACH</b></div>
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“what is” information is needed for supplying restraints in analyzing farm adjustment alternatives. It can also be used to identify problems other than the “what is” condition. Descriptive information is necessary but not completely sufficient in identifying and addressing farm management problems.</div>
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The second type of information is diagnostic information, This information portrays this “what is wrong” condition, where “what is wrong” is measured as the disparity between “what is” and “what ought to be.” This assessment of how things are versus how they should be (a fact-value conflict) is probably our most common management problem. Diagnostic information has two major uses. It can first be used to define problems that develop in the business. Are production levels too low? Is the rate earned on investment too low? These types of question cannot be answered with descriptive information alone (such as with financial and production records). A manager may often be well supplied with facts about his business, yet be unable to recognize this type of problem. The manager must provide norms or standards which, when compared with the facts for a particular business, will reveal an area of concern. Once a problem has been identified, a manager may choose an appropriate course of action for dealing with the problem (including doing nothing). Corrective measures may be taken so as to better achieve the manager’s goals. Several pitfalls are involved for managers in obtaining diagnostic information. Adequate, reliable, descriptive information must be available along with appropriate norms or standards for particular business situations. Information is inadequate for problem solving if it does not fully describe both “what is” and “what ought to be.”As description is concerned with “what is” and diagnostics with ”what is wrong,” prediction is concerned with “what if...?” Predictive information is generated from an analysis of possible future events and is exceedingly valuable with “desirable” outcomes. With predictive information, one either defines problems or avoids problems in advance. Prediction also assists in analysis. When a problem is recognized, a manager will analyze the situation and specify at least one alternative (including doing nothing) to deal with it. Predictive information is needed by managers to reduce the risk and uncertainty concerning technology, prices, climate, institutions, and human relationships affecting the business. Such information is vital in formulating production plans and examining related financial impacts. Predictive information takes many forms. What are the expected prices next year? What yields are anticipated? How much capital will be required to upgrade production technologies? What would be the difference in expected returns in switching from a livestock farm to a cropping farm? Management has long used various budgeting techniques, simulation models, and other tools to evaluate expected changes in the business.</div>
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Without detracting from the importance of problem identification and analysis in management, the crux of management tasks is decision making. For every problem a manager faces, there is a “right” course of action. However, the rightness of a decision can seldom, if ever, be measured in absolute terms. The choice is conditionally right, depending upon a farm manager’s knowledge, assumptions, and conditions he wishes to impose on the decision. Prescriptive information is directed toward answering the “what should be done” question. Provision of this information requires the utilization of the predictive information. Predictive information by itself is not adequate for decision making. An evaluation of the predicted outcomes together with the goals and values of the manger provides that basis for making a decision. For example, suppose that a manager is considering a new changing marketing alternative. The new alternative being considered has higher “predicted” returns but also has higher risks and requires more management monitoring. The decision as to whether to change plans depends upon the managers evaluation of the worth of additional income versus the commitment of additional time and higher risk. Thus, the goals and values of a farm manager will ultimately enter into any decision.</div>
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<b>EVOLUTION OF AN INFORMATION SYSTEM</b></div>
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HISTORICAL PERSPECTIVE</div>
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The importance of management information systems to improve decision making has long been understood by farm management economists. Financial and production records have long been used by these economists as an instrument to measure and evaluate the success of a farm business. However, when computer technology became more widely available in the late 1950s and early 1960s, there was an increased enthusiasm for information systems to enhance management decision processes. At an IBM hosted conference, Ackerman, a respected farm management economist, stated that:</div>
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“The advances that have taken place in calculating equipment and methods make it possible to determine the relationship between ultimate yields, time of harvest and climatic conditions during the growing season. Relationship between the perspective and actual yields and changing prices can be established. With such information at hand the farmer should be in a position to make a decision on his prediction with a high degree of certainty at mid-season regarding his yield and income at harvest time.”</div>
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This statement, made in 1963, reflects the optimism that prevailed with respect to information systems. Even though there was much enthusiasm related to these early systems they basically concentrated on accounting activities and production records. Examples include the TelFarm electronic accounting system at Michigan State University and DHIA for dairy operations. These early systems relieved on large mainframe computers with the data being sent to a central processing center and the reports send back to the cooperating businesses. </div>
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<b>TYPES OF INFORMATION SYSTEM</b></div>
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limited data analysis capabilities beyond calculating typical ratios (e.g., return on assets, milk per cow, etc.). By the mid 1960s it became clear that the accounting systems were fairly effective in supplying descriptive and diagnostic information but they lacked the capacity to provide predictive and prescriptive information. Thus, a new approach was needed – a method of doing forward planning or a management information system that was more model oriented. Simulation models for improving management skills and testing system interaction were developed. As an example, Kuhlmann, Giessen University, developed a very robust and comprehensive whole farm simulation model (SIMPLAN) that executed on a mainframe computer. This model was based on systems modeling methods that could be used to analyze different production strategies of the farm business. To be used by managers, however, they often demanded that the model developer work closely with them in using the model.</div>
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Another important activity during this period was the “Top-Farmer Workshops” developed by Purdue University. They used a workshop setting to run large linear-programming models on mainframe computers (optimization models) to help crop producers find more efficient and effective ways to operate their business.</div>
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As mainframe timeshare computers emerged in the mid-1960's, I became possible to remotely access the computer with a terminal and execute software. Systems such TelPlan developed by Michigan State University made it possible for agricultural producers to run a farm related computer decision aids. Since this machine was shared by many users, the cost for executing an agriculturally related decision aid was relatively inexpensive and cost effective. These decision aids included optimization models (e.g., least cost animal rations) budgeting and simulation models, and other types of decision aids. These decision aids could be accessed by agricultural advisor with remote computer terminals (e.g., Teletype machine or a touch-tone telephone). These advisors used these computer models at the farm or at their own office to provide advice to farm producers.</div>
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These were exciting times with many people becoming involved in the development, testing, refining, and implementation of information systems for agriculture. Computer technology continued to advance at a rapid pace, new communication systems were evolving and the application of this technology to agriculture was very encouraging. Because of the rapid changes occurring, there were international conferences held where much of the knowledge learned in developing these systems was shared. One of the first of these was held in Germany in the mid-1980s.</div>
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It was also clear from these early efforts that the data oriented systems where not closely linked to the model oriented systems. Information for the data oriented systems often did not match the data needed for the model oriented systems. For example, a cash-flow projection model was not able to directly use financial data contained in the accounting system. In most cases, the data had to be manually extracted from the accounting system and re-entered into the planning model. This was both a time consuming and error prone process</div>
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Because of the lack of integration capabilities of various systems, they were devoid of many of the desirable characteristics of an evolving concept describes as decision support systems (DSS). These systems are also known as Executive Support Systems, and Management Support System, and Process Oriented Information Systems . The decision support system proposed by Sprague and Watson (House, ed.) Has as its major components a database, a modelbase, a database/modelbase management system and a user interface (see Figure 3). The database has information related to financial transactions, production information, marketing records, the resource base, research data, weather data and so forth. It includes data internally generated by the business (e.g., financial transactions and production data) and external data (e.g., market prices). These data are stored in a common structure such that it is easily accessible by other database packages as well as the modelbase.</div>
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The modelbase component of the system has decision models that relate to operational, tactical and strategic decisions. In addition, the modelbase is able to link models together in order to solve larger and more complex problems, particularly semi-structured problems. The database/modelbase management system is the bridge between database and modelbase components. It has the ability to extract data from the database and pass it to the modelbase and vice versa. The user interface, one of the more critical features of the system, is used to assist the decision maker in making more efficient and effective use of the system. Lastly, for these systems to be effective in supporting management decision, the decision maker must have the</div>
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<b>Decision Support System</b></div>
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skills and knowledge on how to correctly use these systems to address the unique problem situation at hand.</div>
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Several follow-up international conferences were held to reflect these new advances in management information systems. The first of these conferences focused on decision support systems was held in Germany. This conference discussed the virtues of these systems and the approach used to support decisions. Several prototype systems being developed for agriculture were presented. From these presentations, it was clear that the decision support systems approach had many advantages but the implementation in agriculture was going to be somewhat involved and complex because of the diversity of agricultural production systems. Nevertheless, there was much optimism for the development of such systems.</div>
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A couple of years later, another conference was held in Germany that focused on knowledge-based systems with a major emphasis on expert systems and to a lesser extent optimum control methods and simulation models. Using Alter’s scheme to describe information systems, for the</div>
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most part these would be described as suggestion models. It was interesting to note that the prototype knowledge-based systems for the most part did not utilize the concepts of decisions support systems which was the focus of the earlier conference. Perhaps this was related to the fact that many of the applications were prototypes.</div>
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The international conference that followed in France focused on the low adaption rate of management information systems. This was a topic of much discussion but there were few conclusions reached except the systems with the highest adaption rate were mainly data-oriented ones (e.g., accounting systems, field record systems, anaimal production and health records, etc.) which provide mainly descriptive and diagnostic information.</div>
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The international conferences that followed had varying themes. One of the major themes was precision agriculture with several conferences held. These conferences extolled the use of geographic information systems (GIS) in conjunction with geographic positioning systems (GPS) to record and display data regarding cropping operations (e.g., yields obtained) and to control production inputs (e.g., fertilizer levels). Other conference addressed the use of information systems to more tightly control agriculture production such as those developed for greenhouse businesses.</div>
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To briefly summarize the historical developments, there have been significant efforts devoted to improving the management information systems from the early computerized activities forty years earlier. The decision aids available have grown in number and they are more sophisticated. There has been some movement toward integration of the data oriented systems and the model oriented systems. An examination of our current usage of management information systems, however, suggests that we have not nearly harnessed the potential of the design concepts contained modern management information systems.</div>
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<b>CURRENT STATUS OF INTERNAL INFORMATION SYSTEMS</b></div>
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The current status of management information systems is remains dynamic. Several adoption surveys and personal experiences lead to some interesting observations. These observations will be reviewed in the context of a decision support system as defined by Spraque and Watson.</div>
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On-Farm Information Systems -- Computer Hardware</div>
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The percentage of farms owning a computer continues to grow. Most commercial farms now own a computer and have access to the Internet, many with high speed connections. Most of the computers are of recent vintage with large data storage and memory capacity. It is safe to state that the hardware is not the bottleneck with respect to management information systems.</div>
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<b>On-Farm Database and Modelbase Applications</b></div>
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The decision support system literature stressed that the database and modelbase remain separate entities. They should be bridged by the database/modelbase management system. In examining much of the software developed for on-farm usage, it appears that most of it does not currently employ this design concept. Indeed most of the software is a stand-alone product with the database an integral part of the modelbase. However, some packages have the ability to export and import data, allowing for the sharing of data across the various packages, but these data sharing features are usually rather narrow in scope and flexibility.</div>
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<b>ROLE OF MIS IN PPC (PRODUCTION PLANNING & CONTROL)</b></div>
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The most common software packages used by agricultural producers are data oriented with the most common being one designed for financial accounting. Accounting packages explicitly designed for agricultural businesses and general business accounting packages are used for keeping the financial records. Because of their rather low cost relative to the agricultural specific packages, the general purpose packages are growing in market share. These financial accounting systems are used beyond completing tax documents. They are also important for providing information to creditors and for planning and control. Production management also accounts for a significant proportion of computer usage. There are many software packages available that address livestock problems. Some are database programs to keep track of animal related data and/or feed inventories. There are models to address operational and tactical decisions such as ration balancing, culling decisions, alternative replacements options, etc.</div>
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However, many livestock producers also use off-farm production records processing such as using the DHIA service bureau for processing dairy records. These service bureaus provide a downloading feature so the data can be moved to the on-farm computer.</div>
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For cropping operations, there are similarities in software availability. Database systems are available for keeping track of information on fields and sub-fields, particularly fertilizers and pesticides applied, varieties planted and yields achieved.</div>
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Though there is increasing interest in geographic information systems by agricultural producers, the main usage is for yield monitoring and mapping. This approach is used to evaluate the effectiveness of alternative management practices employed in the production of the crop (e.g., comparison of varieties, seeding rates, pest control measures, tillage systems, etc.) and to identify field problems (e.g., soil compaction, drainage problems, etc.). This yield monitoring approach is finding the greatest acceptance and this may be in part because the yield monitoring and mapping systems are common option on grain harvesting equipment. One of the real concerns with using yield monitoring and mapping systems relates to the issue of arriving at the correct inference of what causes the variation in yields noted. The potential layers of data (e.g., pH, precious crops grown, soil structure, planting date, nutrients applied, variety grown, pesticides used, rainfall, etc.) has been suggested to exceed 100. To be able to handle the large number of data layers in an effective manner would suggest a full-feature geographic information system (GIS) might be needed. However, few agricultural producers have access to a full-feature GIS and/or training to utilize these systems, and there are substantial costs related to capturing and storing various data layers. Nevertheless, the more obvious observations originating from these systems (e.g., such as poor drainage and soil compaction) have resulted in sound investments being made in corrective measures.</div>
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To a limited extent, some agricultural producers are starting to make use of remote sensing data to identify problems related to the growing crop such as an outbreak of a disease. Those using remote sensing feel they are able to more quickly identify the problems and take corrective action, minimizing the damage done.</div>
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Precision agriculture applied to the animal industries is on a different scale. Information systems are playing a major role on the integrated mega-farms. When using information systems to carefully track genetic performance, balance rations, monitor health problems, facilities scheduling, control the housing environment and so forth, it is generally acknowledged that it is possible to achieve a fairly significant reduction in cost per unit of output (10-15%) over that of more traditional, smaller farming operations. These are proprietary information systems and the information from these systems are used to gain a strategic competitive advantage.</div>
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Lastly, the general purpose spreadsheet is the most common software used for planning purposes. Some of these applications are very sophisticated and address complex problems.</div>
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User Interface .The user interface has improved in greatly in quality. Most agricultural software now uses the windowing environment. This environment makes it easier for the user to use and access data and information, and to move data from one application to another or to link applications. However, this still remains a user-initiated task and in some cases can be complex. Also most of the data contained in the software package is unique to that package and not easily shared with other software packages. Thus, from a DSS viewpoint there are still significant shortcomings. </div>
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The Decision Maker An often overlooked component of a decision support system is the decision maker. Prior surveys suggest that the primary user of the on-farm computer system is the farm operator. Operators that are younger and college educated were much more likely to routinely use the computer. Also large farms were more likely to utilize a computer in their farming operation. It is also observed that there is a fair amount of “learning cost” related to use of on-farm information systems. These cost can be large enough to hinder the adoption of management information systems.</div>
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<b>CURRENT STATUS OF EXTERNAL INFORMATION SYSTEMS</b></div>
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There is increased interest and excitement about the role external information systems available to agricultural producers, particularly Internet and satellite data transmission systems. Each of these technologies is a vast resource of data which can be used to enhance the various levels (e.g., information, intelligence, knowledge, wisdom) of Haechel's Hierarchy for an individual or organization. Another information source is the outside advisor. As the complexity and breadth of the farm level decision process has increased, the use of consultants and advisors has grown. This is particularly true of the larger farming operations.</div>
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The growth in Internet is phenomenal. The growth in its use by agricultural producers is also phenomenal. Email is a common communication tool used by agricultural business. The same is true for the world-wide-web (WWW). They made extensive use of the web to find information that fit their unique requirement. Even though they find it a major source of information for their operation, it takes good skills to locate the information desired. One of the common complaints is the amount of time it takes to utilize the Internet effectively and the lack of depth of information. One of the critical questions relates to how effective Internet is in addressing the higher levels of Haechel's hierarchy.</div>
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Other Internet resources available to agriculture include sites for downloading agricultural software. Much of the economic data compiled by the government is now available on-line. Lastly, in some cases it is being used as a marketing tool for products produced by the business.</div>
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Satellite Data Transmission Systems</div>
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The satellite data transmission systems are widely used by producers. These systems are passive data acquisition systems from the user's viewpoint. Data is continuously broadcast to the leased data terminal from a satellite. The data is automatically stored in the data terminal and can be accessed by a menuing process. These systems provide current data/information on a number of topics. Amounts and types of data/information received depends upon the options purchased. The basic subsystem provides for the latest market prices and news, weather maps (e.g., rainfall, jet streams, severe weather, crop soil moisture index, soil temperature, air temperature, etc.), government reports on market developments, long- and short-term weather forecasts, political developments that pertain to agriculture, and product information. Premium service options add even more features.</div>
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<b>Outside Advisors</b></div>
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Several recent studies suggest that use of outside advisory services by farmers to enhance and supplement their on-farm information systems was fairly prevalent. The tax preparer is the</div>
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advisory most commonly used. Other important sources of information include the local Extension agents, veterinary consultants, accountants, crop/pest management consultants, and livestock management advisors (e.g., a nutritionist).</div>
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The outside advisors utilize many different software packages to help provide advice to producers. FINPAK developed by the University of Minnesota is an example of a software package widely used by outside advisors with farmers. This financial analysis and related projection package helps evaluate the financial process being made by the farm and compares alternative future business options. This package (an accounting type model) is widely used in the U.S.</div>
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FURURE SYSTEM OF MIS </div>
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Predicting the future is not an exact science. But with the structural changes occurring in agriculture today, the management problems are significantly different from the problems of yesterday. Earlier emphasis in information systems was on improving production management decisions. Today, major issues that are commonly faced in management relate to financial, human resource, and marketing management. These management areas and their importance are identified in the strategic management workshops I have conducted with agricultural producers. Thus, managers will have less time to address production issues because more time and effort are being focused in the other management areas. This will have an impact on information systems to address production management.</div>
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Addressing Structured Decisions In the future information systems to address production management will likely be of five general types: 1) software for systems analysis, 2) theory testing, software for teaching purposes, 3) software for advisors, 4) software for use by producers, and 5) software to control and monitor the supply chain.</div>
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Software for systems analysis and theory testing will be developed with the primary objective of defining the structure and studying the dynamics and interaction of the various system components. Its main use is in research. These models are fairly complex and often have robust data requirements. Their utilization often depends upon availability of the developers to run the model or assist in the use of the model. This software is very useful in testing various hypotheses regarding system dynamics </div>
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These models play a vital role in generating a better understanding of the overall system and can give valuable insight on how to manage the system. They are also useful in identifying areas for further research. The results from these models are communicated in various ways (e.g., journal articles, trade journals, and advisory service publications and conferences) and these communicated results are often used by producers to adjust production practices. However, direct use by producers to evaluate their own unique situations is not common with these models. There are several reasons for this limited use including a poor user interface or lacking the data to drive the model. Also, it is generally unlikely that transformation of a model of this nature into one that is to be used by the producers will be successful.</div>
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Software developed for teaching purposes is likely to continue. Sometimes these software packages are referred to as simulation games. Because these models teach concepts and principles, they are often a simplification of reality. They tend to use the case analysis approach, making it difficult to use the model to analyze various options and alternatives utilizing actual business data. The models are often used in an interactive mode (e.g., in a classroom or workshop environment) where knowledge is gained by testing “what if” questions, then observing the results. These models can be very powerful teaching tools, but are rarely used to analyze actual business situations. Producers often lose interest in using this software because it is too simplistic, takes too much time and effort to extract knowledge for better decision-making, or it does not adequately reflect the reality of the business.</div>
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Software for advisors is a class of software that is used by agricultural advisors (e.g., Extension staff, consultants, and agribusiness firms) to assist producers in making decisions. The advisor is a necessary intermediary, because the software could demand a thorough understanding of a difficult set of concepts (e.g., long range planning) or it may be rather demanding of the user’s time and effort (e.g., a large amount of data has to be collected, entered and analyzed), or the time and effort to become proficient in the use of the model is considered excessive. This type of software will grow in importance as the use of outside consultants and advisory services by agricultural businesses grows. These outside advisors and consulting services will increasingly use many different software packages to help provide advice to the producer. The package they use depends upon their area of specialization. For instance, those that are offering production advise may use one of several production decision aid models.</div>
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Advisors also serve as an intermediary to extracting information from Internet (external data). They often subscribe to threaded discussion groups. They use these groups for posting problems and receiving back suggested solutions. They also learn from the exchange of ideas between others using the system. Also, advisors more readily see the merit of using a software program designed for systems analysis for enhancing their personal knowledge and skills and solving problems for their clients. This is particularly true if the software has a good user interface.</div>
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Software for use by producers is and will continue to be some of the most demanding software to develop. As indicated earlier, a large amount of software has been written, but much of it has fallen short of expected usage rate. One reason is the decision makers have found the software fails to address their problems. The software must be fairly easy to utilize, and the producer expects it to provide information that has a perceived value greater than the cost of attaining that information.</div>
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<b>ROLE OF SOFTWALE IN MIS:</b></div>
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Software being used by producers can be grouped into two subcategories. The first subcategory is used to process transaction data and meet regulatory requirements. These are the software applications most used by the actual businesses. They must keep accounting, personnel and crop production records (e.g., pesticides used) because of government regulation. They also use software to reduce the time, effort and cost of processing the transaction records. This is why payroll packages, and shipping and billing systems are commonly employed on these operations. This usage will continue to grow in importance.</div>
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The other subcategory of software is used for management purposes. This currently accounts for a lesser portion of the computer usage. A large growth in this usage of this software is unlikely. The time and effort to master this software is major commitment. Since management time is being diverted to areas other than production management, they will have less and less time to become proficient in the use of this software. Thus, very thorough and sophisticated systems (e.g., the SAP software system) currently being employed by large companies are not likely to be common on farm businesses because of their complexity and cost.</div>
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Software for process control is used to control and automate many of the structured-operational decisions of the business enterprises, such as controlling temperature, light, irrigation and fertility in greenhouses. These models are generally of a closed-loop optimal control design. The process control models are generally knowledge based systems and have been developed using knowledge from many sources including the systems analysis models discussed earlier. The use of process control systems will grow in importance and acceptance. This acceptance implies that the managers have confidence in the models and that they improve the efficiency and effectiveness of the business. These models also free them to concentrate on more complex decisions.</div>
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Software to control and monitor the supply chain will greatly grow in importance. The will be many factors driving this grow including concerns about food safely, country of origin labeling, organic foods, foods to meet special dietary requirements, and concerns about product liability suits. In will likely become commonplace that a food item purchased by the consumer at the retail level will have attached its entire history, including identity preservation and traceability, included with the purchase. The new advances in RFID chips and the requirements by certain major retailers to label all products with these chips will impact agricultural businesses including those engaged in producing farm products. The system imposed upon the entire supply chain will likely be designed by the retailers and the entire chain will need to adjust to the defined information structure. To adapt to the defined information structure may mean a major restructuring of the information system currently being used by the business with substantial costs associated with the conversion.</div>
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-tructured and Unstructured Decisions</div>
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To address the management areas related to human resources, finances, and marketing, suggest information systems that can address ill-structured or unstructured problems. Some would state that we are in the process of moving from the “old economy” to “new economy.” With this</div>
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paradigm shift, among the changes is a movement from resource based to idea based wealth creation, from a stable comparative advantage to a dynamic one, from investment in physical assets to investment in human capital, from protected to open markets, from subsidies to encouragement to adapt, from hierarchal organizations to strategies alliances and partnerships. In addition agriculture will move from commodity markets to product markets and it will become more environmentally friendly, concerned with food safety, and quality and supply coordination.</div>
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If this transition from the “old economy” to the “new economy” occurs for agriculture, then the information systems of the past will not be adequate for the future. They will need to be much broader and more comprehensive than the current systems. </div>
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The future systems must:</div>
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• address the larger scope of financial management rather than financial record keeping, tax reporting, and analysis.</div>
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• help define marketing strategies and alliances.</div>
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• help identify potential niche markets rather than supplying data on current commodity market trends;</div>
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• support the creation of new ideas.</div>
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• nurture the growth of knowledge since this will become a major source of wealth creation.</div>
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• deal with the many dimensions and complexity of human resource management.</div>
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• signal needed production changes in an overall system of supply chain management.</div>
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• assist in negotiating contractual arrangements.</div>
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• help the producer adopt to an economic climate that has more risk and uncertainty because of less government intervention in markets.</div>
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• provide the capacity to track the identify of a product from its genetics to the consumer.</div>
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• assist in producing a product that meets customer desires rather than the production of a commodity.</div>
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Developing farm-level information systems to fulfill these needs will be a major challenge. It will take a major rethinking with regard to the role of management information systems. It will involve more than enhancing hardware, communications infrastructure, and software components of the information system. An equally important consideration will be the analytical skills, knowledge, wisdom, and interests of the agricultural decision maker.</div>
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The information system of the future will need to concentrate more on the upper levels of Haechel's hierarchy -- knowledge and wisdom. As Honaka and Hirotaka observe, knowledge has two forms, tacit (subjective) and explicit (objective). Tacit knowledge is gained from experiences and practice, whereas explicit knowledge is based more on theory and rationality. As decision makers address problems, they convert knowledge between the two forms. An information system that focuses only on one form will have shortcomings. The information system of the future must have both forms of knowledge, and encourage the conversion of knowledge between the forms as a continuous process. Only by this process will the manager's knowledge base grow in size and function.</div>
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Information systems of the past have tended to concentrate on explicit knowledge (e.g., linear programming to balance a ration) and, to lesser extent tacit knowledge. Many of the problems of the future will involve tacit knowledge. The challenge will be designing information systems that will allow for an easier and more effective means of sharing tacit knowledge. The Internet will no doubt play a key role in meeting this challenge. Perhaps a system for documenting experiences (e.g., structured case studies) can be used to enhance the sharing of tacit knowledge.</div>
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Mechanical Engineering Departmenthttp://www.blogger.com/profile/12582953924770018783noreply@blogger.comtag:blogger.com,1999:blog-6302071579893645567.post-58605015989462832032017-01-19T15:11:00.001+05:302017-01-19T15:11:59.436+05:30Previous Year Question Papers 4th Semester Mecahanical<div dir="ltr" style="text-align: left;" trbidi="on">
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Mechanical Engineering Departmenthttp://www.blogger.com/profile/12582953924770018783noreply@blogger.comtag:blogger.com,1999:blog-6302071579893645567.post-10088150829654110652017-01-19T15:08:00.002+05:302017-01-19T15:09:19.148+05:30Previous Year Question Papers 6th Semester (Mechanical)<div dir="ltr" style="text-align: left;" trbidi="on">
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Mechanical Engineering Departmenthttp://www.blogger.com/profile/12582953924770018783noreply@blogger.comtag:blogger.com,1999:blog-6302071579893645567.post-7825018363064500362017-01-19T14:09:00.001+05:302017-01-19T14:25:47.881+05:30Previous Year Question Papers (8th Semester (Mechanical)<div dir="ltr" style="text-align: left;" trbidi="on">
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Mechanical Engineering Departmenthttp://www.blogger.com/profile/12582953924770018783noreply@blogger.comtag:blogger.com,1999:blog-6302071579893645567.post-65603709281692251882016-11-04T16:08:00.001+05:302017-08-10T11:09:29.554+05:30AUTO FUELS & LUBRICATION (UNIT IV) By Asst. Prof CP SAINI<div dir="ltr" style="text-align: left;" trbidi="on">
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Mechanical Engineering Departmenthttp://www.blogger.com/profile/12582953924770018783noreply@blogger.comtag:blogger.com,1999:blog-6302071579893645567.post-32470988173378516042016-11-04T15:40:00.002+05:302016-11-04T16:09:47.967+05:30AUTOMOTIVE FUEL AND LUBRICATION UNIT I& III-(BY-Asst. Prof. C.P. SINGH)<div dir="ltr" style="text-align: left;" trbidi="on">
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<span style="color: red; font-size: x-large;"><b>UNIT III</b></span></div>
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Mechanical Engineering Departmenthttp://www.blogger.com/profile/12582953924770018783noreply@blogger.comtag:blogger.com,1999:blog-6302071579893645567.post-86392159702699044172016-11-04T14:03:00.001+05:302016-11-04T14:43:57.452+05:30Mechanics of solids by R.K RAJPUT<div dir="ltr" style="text-align: left;" trbidi="on">
<a href="https://www.scribd.com/doc/107076408/Strength-of-Materials-Mechanics-of-solids-R-K-RAJPUT-S-CHAND" target="_blank">Mechanics-of-solids BY R-K-RAJPUT-S-CHAND</a><br />
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<b> Unit-I</b>
Introduction: Force, types of forces, Characteristics of a force, System of forces,
Composition and resolution of forces, forces in equilibrium, principle and laws of
equilibrium, Free body diagrams, Lami's Theorem, equations of equilibrium, Concept of
center of gravity and centroid, centroid of various shapes: Triangle, circle, semicircle and
trapezium, theorem of parallel and perpendicular axes, moment of inertia of simple
geometrical figures, polar moment of inertia. Numerical Problems<br />
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Simple stresses &strains : Concept & types of Stresses and strains, Polson’s ratio, stresses
and strain in simple and compound bars under axial loading, stress strain diagrams, Hooks
law, elastic constants & their relationships, temperature stress & strain in simple &
compound bars under axial loading, Numerical problems.<br />
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<b> Unit-II</b>
Principle stresses: Two dimensional systems, stress at a point on a plane, principal stresses
and principal planes, Mohr’s circle of stresses,<br />
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Numerical
Shear Force & Bending Moments : Definitions, SF & BM diagrams for cantilevers, simply
supported beams with or without over-hang and calculation of maximum BM & SF and the
point of contraflexture under (i) concentrated loads, (ii) uniformly distributed loads over
whole span or a part of it, (iii)combination of concentrated loads and uniformly distributed
loads, (iv) uniformly varying loads and (v) application of moments, relation between the rate
of loading, the shear force and the bending moments, Numerical Problems.
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<b>Unit-III
</b>Torsion of circular Members: Derivation of equation of torsion, Solid and hollow circular
shafts, tapered shaft, stepped shaft & composite circular shafts, Numerical problems.<br />
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Flexural and shear stresses – Theory of simple bending, Assumptions, derivation of
equation of bending, neutral axis, determination of bending stresses, section modulus of
rectangular & circular (solid & hollow), I,T, Angle, channel sections, composite beams, shear
stresses in beams with derivation, shear stress distribution across various beam sections like
rectangular, circular, triangular, I, T, angle sections. Combined bending and torsion,
equivalent torque,. Numerical problems.<br />
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<b>Unit-IV</b>
Columns & Struts: Column under axial load, concept of instability and buckling,
slenderness ratio, derivation of Euler's formula for crippling load for columns of different
ends, concept of equivalent length, eccentric loading, Rankine formulae and other empirical
relations, Numerical problems.<br />
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Slope &Deflection : Relationship between bending moment, slope & deflection, moment
area method, method of integration, Macaulay’s method, calculations for slope and deflection
of (i) cantilevers and (ii) simply supported beams with or without overhang under
concentrated load, Uniformly distributed loads or combination of concentrated and uniformly
distributed loads, Numerical problems. <br />
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Mechanical Engineering Departmenthttp://www.blogger.com/profile/12582953924770018783noreply@blogger.com