mm imp questions

8/12/2019 Mm Imp Questions

http://slidepdf.com/reader/full/mm-imp-questions 1/43

1

1. List the various lattice defects.

Ans:

The List of various Lattice defects is1) Point Defects: Point defects include a) Vacancies b) Self-interstitial atoms

c) Substitutional impurity atoms and d) Interstitial impurity atoms!) Linear Defects: linear defects include dislocations these are a) "d#e dislocation and b) Scre$ dislocation

%) Planar Defects: Planar defects include a) &rain boundaries b) T$in boundaries c) Stac'in# faults

2. Differentiate between Slip and Twinning.

Sl.No. Slip Twinning

1 The parallel movement of t$o ad(acentcrystal planes relative to one another isslip

T$innin# is a homo#eneous shear $hichreorients the deformed lattice into a mirrorima#e of the parent lattice across the plane oft$innin#

! The orientation of atoms above and belo$ the slip plane is the same afterslip deformation

T$innin# produces an orientation differenceacross the t$in plane

% Slip usually occurs in discrete multiplesof atomic spacin#

In t$innin# atoms move only a fraction of interatomic distance

The stress re*uired to initiate slip is lessthan to propa#ate it

The stress re*uired to propa#ate t$innin# isappreciably less than that re*uired to initiate it

+ There is a time la# for slip T$innin# occurs in micro seconds

3. ,hat are the variables $hich influence the ecrystalisation temperature of a material.

Ans:

The variables $hich influence the ecrystalisation temperature of a material are:1) Time at a constant temperature!) /mount of cold $or'in#%) Purity of metal) 0ri#inal #rain sie+) Temperature of deformation2) 3eltin# point of metal4)

. List out the forging !"uip#ent.

Ans:

5or#in# e*uipment may be classified $ith respect to the principle of operation1) 5or#in# hammers: The force is supplied by fallin# $ei#ht or ram The follo$in# are for#in#

hammersa &ravity drop hammer or 6oard hammers

b Po$er drop hammer !) 5or#in# presses: these are t$o types

a 3echanical Presses: the force is supplied by an eccentric cran' $hich translates rotarymotion of a fly $heel into reciprocatin# linear motion of the press slide

b 7ydraulic presses: the force is supplied by movin# piston $hich feeds on hydraulic pressure of a fluid

$. Draw a planetar% #ill and #ention its i#portance.



2

Ans:

Drawing of a planetar% #ill:

&#portance of planetar% #ill:1) It hot reduces a slab directly to strip in one pass throu#h the mill!) "ach planetary roll #ives an almost constant reduction to the slab%) The action in the planetary mill is more li'e for#in# than rollin#

'. Differentiae between Direct and &ndirect !(trusion.

Ans:

Sl8o Direct "9trusion Indirect "9trusion

1

5lo$ of billet metal is in for$ard

direction and in the same direction asram

5lo$ of metal ta'es place in a direction opposite

to that of ram movement

!There is a relative motion bet$een billetand container $alls and hence friction is

prevalent $hile e9trudin# the billet

Since there is no relative movement bet$een thecontainer $all and the billet frictional forces arelo$er

% Lubrication is a problem particularly$hen hot e9trusion ;direct) is done

"9tensive lubrication is not needed

Pressure re*uired increases $ith thelen#th of the billet

Pressure remains constant up to (ust to the end ofthe e9trusion process

+

3ore turbulence of billet metal occurs$ithin the billet hence lot of ener#y #ets$asted This re*uires more po$erconsumption to e9trude the billet metal

Turbulence of billet metal is minimum henceflo$ of metal is more uniform $ithin the billethence ener#y loss is minimum This re*uiresless po$er consumption to e9trude the billetmetal

2There is no practical limitation to use this

processThere are practical limitations because use ofhollo$ ram limits the load $ithstandin#capacity

4 7andlin# the e9trudin# metal comin# outthrou#h the movin# ram is not a problem

7andlin# the e9trudin# metal comin# outthrou#h the movin# ram is a problem

). List the various steps involved in the production of *+ower ,etallurg%* parts.

Ans:



3

The various steps involved in the production of *+ower ,etallurg%* parts are:

1) Production of metal po$ders: 0btainin# the metal po$ders in a suitable de#ree of fineness and purity

!) 3i9in# and 6lendin#: Intermin#lin# of various po$ders accordin# to the composition

%) <ompaction: Sub(ectin# the mi9ed po$ders to a sufficient pressure in a suitable mould to causecohesion) Sinterin#: heatin# under controlled atmosphere at a temperature hi#h enou#h to cause diffusion

and inter #ranular crystal #ro$th to occur+) 5inishin# operations: these include siin# impre#nation inspection etc

-. ive the classification of *Ther#o #echanical treat#ent* #ethods.

Ans: Dependin# on the temperature at $hich deformation of austenite ta'es place thermo-mechanicaltreatments can be classified as

7i#h temperature thermo-mechanical treatment ;7T3T)1) Lo$ temperature thermo-mechanical treatment ;LT3T)

/nother method of classifyin# the treatment is based on the deformation temperature in relation tothe critical temperature of steel namely

1) Supercritical ;deformin# steel in austenite condition)!) Intercritical ;deformin# ferrite and austenite mi9ture)%) Subcritical ;deformation of austenite belo$ the lo$er critical temperature)

"9amples of Thermo mechanical treatments:1) /usformin#!) Isoformin# and%) 3arformin#

/. !(plain about Shearing process.

Ans:

Shearing is the separation of metal by two moving blades. In this process a narrow strip of

metal is severely plastically deformed to a point of fracture at the surface in contact with the

blades. The fracture then propagates inwards to provide complete separation. Clearance

between the blades is an important variable in the shearing process.

5orce re*uired to shear a metal is the product of the len#th ;l) cut the sheet thic'ness ;t) and

the

Shearin# stren#th ;=) of the metal"mpirically the ma9imum punch force needed to producethe shearin# is #iven by

P ma9 > ?4@utl

,here

@u is the ultimate tensile stren#th of the metal



4

10. Distinguish between ot woring and cold woring.

Sl.No. old woring ot woring

1,or'in# of metals and alloys belo$ theirrecrystallisation temperature

,or'in# of metals and alloys above theirrecrystallisation temperature

!

Strain ;$or') hardenin# ta'es place Strain ;$or') hardenin# is removed byrecrystallisation

%Increase in hardness and tensile stren#th$hile ductility decreases

8o chan#e in mechanical properties

3icrostructure sho$s distorted #rainsalon# the direction of $or'in#

3icrostructure sho$s e*uia9ed and usuallyrefined #rains

+Stress and ener#y re*uired for plasticdeformation is more

Stress and ener#y re*uired for plasticdeformation is less

2 8o o9idation of metal occurs and hence pic'lin# is not re*uired

7eavy o9idation of metal occurs and hence pic'lin# is re*uired

4Surface decarburiation in steels does notoccur

Surface decarburiation in steels is li'ely tooccur

A 3etals and alloys do not #et embrittled byo9y#en

eactive metals #et severely embrittled byo9y#en

B Surface finish is #ood Surface finish is not so #ood

1?"asy to control the dimensions $ithin thetolerance limits

Difficult to control the dimensions $ithin thetolerance limits

11 etains chemical hetero#eneity if present educes chemical hetero#eneity of in#ots

11 Define a4 Dispersion hardening b4 Strain ageing

Ans:

a4 Dispersion hardening



/ stren#thenin# mechanism in $hich the stren#th of the material is increased by theresistance offered to the movin# dislocations as a result of uniformly dispersed hi#h hard andhi#h elastic particles in a plastic matri9b4 Strain ageing

Strain /#ein# is the increase in stren#th and decrease in ductility of a metal on heatin# at arelatively lo$ temperature after cold $or'in# Strain /#ein# is a type of behaviour usually

associated $ith yield point phenomenon

12 a4 !(plain *5auschenger*s effect*.

6b4 !(plain and differentiate edge and screw dislocations.

Ans:

5auschenger*s effect:

The phenomenon of decreased yield stren#th $hen the deformation in one direction is follo$ed bydeformation in opposite direction is called 6auschen#erCs effect

The initial yield stress of the material in tension is / The yield stren#th of the material incompression $ould be 6 8e$ specimen is loaded in tension past the yield stress to < alon# the path0-/-< If the specimen is un loaded it $ill follo$ the path <-D If no$ a compressive stress is

applied plastic flo$ $ill be#in at the stress correspondin# to point " /bove stress is appreciablylo$er than stress in tensionThe decrease in stress $ith the chan#e in direction of loadin# is called 6auschen#erCs effect6auschen#erCs effect can have important conse*uence in metal formin# applications 5or e9ample itcan be important in bendin# of steel plates

6b4 !dge and screw dislocations.

!dge dislocation:

These are disturbed re#ions bet$een t$o perfect parts of a crystal created by interleavin# of an e9trahalf atomic plane /n ed#e dislocation can be associated $ith compressive and tensile stresses

/tomic arran#ementaround a scre$ dislocation



!

Screw dislocation:

It is the disturbed re#ion bet$een t$o perfect parts of a crystal <haracteried by a spiral ramp$indin# / Scre$ dislocation is associated $ith shear strains

/tomic arran#ement around a scre$dislocation

13 Differences between edge and screw dislocations:



"

1. 6a4 !(plain about Twinning.6b4 List out twin planes of 5...7 8...7 and ..+. cr%stals.

Ans:

6a4 Twinning:

The second important mechanism by $hich metals deform is the process 'no$n as t$innin#T$innin# results $hen a portion of the crystal ta'es up an orientation that is related to the orientationof the rest of the unt$inned lattice in a definite symmetrical $ay

The t$inned portion of the crystal is a mirror ima#e of the parent crystal The plane ofsymmetry bet$een the t$o portions is called the t$innin# plane. 5i#ure 1 illustrates the classical

atomic picture of t$innin# 5i#ure ! represents a section perpendicular to the surface in a cubic lattice$ith a lo$-inde9 plane parallel to the paper and oriented at an an#le to the plane of polish Thet$innin# plane is perpendicular to the paper If a shear stress is applied the crystal $ill t$in about thet$innin# plane ;5i# !) The re#ion to the ri#ht of the t$innin# plane is undeformed To the left of this

plane the planes of atoms have sheared in such a $ay as to ma'e the lattice a mirror ima#e across thet$in plane In a simple lattice such as this each atom in the t$inned re#ion moves by a homo#eneousshear a distance proportional to its distance from the t$in plane

5i#ure1 5i#ure !

6b4 List of twin planes of 5...7 8...7 and ..+. cr%stals:

Sl.No. +ropert% !dge dislocation Screw dislocation

16ur#erCs vector

Perpendicular to dislocationline

Parallel to dislocation line

!Dislocation movementrelative to 6ur#erCs vector

Dislocation moves parallelto 6ur#erCs vector

Dislocation movesPerpendicular to 6ur#erCs

vector%

Slip direction/toms move parallel to6ur#erCs vector

/toms move parallel to6ur#erCs vector

3ovement of dislocationrelative to slip direction

/toms move parallel tomotion of dislocation

/toms move perpendicularto 6ur#erCs vector

+ 3ethod of leavin# slip plane 6y climb up or do$n 6y cross slip

2 Velocity of motion 5aster than scre$ dislocation Slo$er than ed#e dislocation

4 Strain ener#y of dislocation 3ore Less

A Strain fields arounddislocation

<ompression and Tension Shear



#

T$innin# occurs in a definite direction on a specific crystallo#raphic plane and for eachcrystal structure The follo$in# Table lists the common t$in planes and t$in directions

It is not 'no$n $hether or not there is a critical resolved shear stress for t$innin# 7o$evert$innin# is not a dominant deformation mechanism in metals $hich possess many possible slipsystems T$innin# #enerally occurs $hen the slip systems are restricted or $hen somethin# increasesthe critical resolved shear stress so that the t$innin# stress is lo$er than the stress for slip

1$4 ive the classification of forging operations and e(plain the principle of *9p setting

8orging*.

Ans:

lassification of forging operations:

The t$o broad cate#ories of for#in# processes are 1) open-die for#in# !) closed-die for#in# and%) pset for#in#

14 opendie forging

0pen-die for#in# is carried out bet$een flat dies or dies of very simple shape The process isused mostly for lar#e ob(ects or $hen the number of parts produced is small 0ften open-die for#in#

is used to perform the $or' piece for closed-die for#in#

Se"uence in opendie forging

24 closeddie forging

In closed-die for#in# the $or' piece is deformed bet$een t$o die halves $hich carry theimpressions of the desired final shape The $or' piece is deformed under hi#h pressure in a closedcavity and thus precision for#in#s $ith close dimensional tolerances can be produced

Sl.No. r%stal structure Twin plane Twin direction

1 6 < < ;11!) E111F

! 5 < < ;111) E11!F

% 7 < P ;1?G1!) EG1?11F



$

Sche#atics of the closed die forging process

34 9pset forging

It is the process of increasin# the cross section by decreasin# the len#th This process $asori#inally developed for headin# bolts but today its scope has been $idened to produce a lar#e varietyof components the mechanical properties of $hich benefit considerably from the for#ed structureobtained

+rocess of 9pset forging

The len#th of bar to be headed is first heated at the end and then inserted bet$een the (a$s ofthe fi9ed die until it meets a HstopH This stop is so placed that the re*uired amount of metal to producethe head protrudes beyond the (a$s of the fi9ed die The machine is no$ set in motion

The #rippin# die closes and immediately the movin# die stri'es the heated end of the rod sofor#in# it to shape The movin# die is shaped to produce a head of the re*uired dimensions /fterheadin# has ta'en place the machine continues its cycle and the movin# die retracts as the #rippin#die opens

Stages in Typical Upset ForgingProcesses

The principle of 9psetting 8orging:

In the desi#n of dies for upset for#in# three rules formulated ori#inally by " 5rost are follo$ed:

;1) The len#th L , of unsupported metal $hich can be upset at one stro'e $ithout ris' of serious buc'lin# must not be more than three times the diameter D , of the bar ;5i#) In practice L is usually'ept belo$ 2.$D

;!) ,here the len#th L7 of unsupported metal is not #reater than three times the diameter D , of the bar the ma9imum increase in cross-section obtainable at a sin#le stro'e is 1.$D /#ain in practice alo$er fi#ure of 1.D is #enerally used

;%) / len#th of metal more than three times the diameter of the bar can be upset in one stro'e provided that a die of the follo$in# type is used



1%

7ere the diameter of the die impression must not e9ceed 1.$D and the len#th of bar 6L ; L14

pro(ectin# beyond the die face must be less than the diameter of the bar D.

In practice L1 < L ; D=2

1' List out the forging !"uip#ent.

Ans:

5or#in# e*uipment may be classified $ith respect to the principle of operation

%) 5or#in# hammers: The force is supplied by fallin# $ei#ht or ram The follo$in# are for#in#hammers

a &ravity drop hammer or 6oard hammers

b Po$er drop hammer

) 5or#in# presses: these are t$o types

a 3echanical Presses: the force is supplied by an eccentric cran' $hich translates rotarymotion of a fly $heel into reciprocatin# linear motion of the press slide

b 7ydraulic presses: the force is supplied by movin# piston $hich feeds on hydraulic pressure of a fluid

1). !(plain the production of Sea#less tubes b% !(trusion #ethod.

Ans:



11

Pipe and tubin# may be classified as seamless or $elded dependin# on the method of manufacture,elded tubin# is formed from strip and $elded by hot-formin# fusion or electric $eldin# "9trusionis an e9cellent method of producin# seamless pipe and tubin# especially for metals $hich aredifficult to $or'

;a) 3annesmann mill ;b) plu# rollin# mill ;c) three-roll piercin# mill ;d) reelin# mill

The 3annesmann mill ;5i# a) is used e9tensively for the rotary piercin# of steel and copper billets The process employs t$o barrel-shaped driven rolls $hich are set at an an#le to each other /na9ial thrust is developed as $ell as rotation to the billet This assists in openin# up the center of the

billet as it flo$s around the piercin# point to create the tube cavity Piercin# is the most severe hot-$or'in# operation customarily applied to metals

The 3annesmann mill does not provide sufficiently lar#e $all reduction and elon#ation to produce finished hot-$or'ed tubes Various types of plu# rollin# mills $hich drive the tube over alon# mandrel containin# a plu# ;5i#b) have evolved

The /ssel elon#ator $hich uses three conical driven rolls has been $idely adopted This ledto the development of three-roll piercin# machines ;5i# c) $hich produce more concentric tubes $ithsmoother inside and outside surfaces than the older 3annesmann desi#n

/ reelin# mill ;5i#d) $hich burnishes the outside and inside surfaces and removes the sli#htoval shape is usually one of the last steps in the production of pipe or tubin#

1-. >hat are the advantages7 applications and li#itations of +owder ,etallurg%

Ans:

Advantages of +owder ,etallurg%:



12

The po$der metallur#y process has certain basic advanta#es over conventional meltin# and castin#method of producin# metals alloys and finished articles These advanta#es include:;1) 5reedom to produce components of any composition;%) "conomy #reater accuracy ;ie closed dimensional tolerance in the finished part) and smooth

surfaces

;) <leaner and *uieter operations and lon#er life;2) <ontrol of #rain sie and relatively much uniform structure;4) "9cellent reproducibility;A) Improved physical properties;B) "limination of numerous machinin# operations since pJm parts can be net or near net shaped;1?) Possibility of producin# ne$ materials composition of metals and non-metals $hich are *uite

impossible to prepare by normal) methods ;1!) 8o re*uirement of hi#hly *ualified or s'illed personnel

Applications of +owder ,etallurg%:

Some typical applications of PJ3 are:

1) Production of net-shape or near-net shape parts made of e9pensive materials PJ3 Process iscapable of less than %K scrap losses

!) Parts $ith porosity such as filters can be made

%) 6earin#s especially so-called permanently lubricated bearin#s in $hich air pores in the PJ3 parts

are filled $ith oil ;process of impre#nation)

+) Parts of certain metals and metal alloys that are difficult to fabricate by other methods ;<arbide

tool inserts tun#sten ceramics etc)

2) Parts of materials $ith special and uni*ue properties ;alloys that cannot be produced by other

processes)

4) ?efractor% ,etals: <omponents made of tun#sten molybdenum and tantalum by Po$dermetallur#y are $idely used in the electric li#ht bulbs radio valves oscillator Valves mercury arc

rectifiers and -ray tubes in the form of filament

A) Auto#otive Applications: In the developed countries it is the motor industry $hich relies

heaviest upon po$der metallur#ical components In the motor car industry the porous bearin#s

include starters screen $ipers slidin# roofs vehicle dynamos clutches bra'es Slide bearin#

materials are used for hi#her loads and hi#h runnin# speeds Self-lubricatin# bearin#s are mostly

employed in motor cars truc's buses tractors

B) Aerospace Applications: 3etal po$ders are playin# an important role in roc'et missilessatellites and space vehicles Tun#sten parts employed in plasma (et en#ines 3a#netic materials such

as /lnico in communication systems

1?) Ato#ic !nerg% Applications: PJ3 has played a si#nificant role in the development of nuclear

po$er reactors <omposite materials are applied in various fuel elements and control rod systems

Dispersion stren#thened materials are used in atomic reactors and roc'ets ma#neto-hydro-dynamic

#enerators hi#h temperature #as turbines

Li#itations of +owder ,etallurg%:

There are limitations and disadvanta#es associated $ith PJ3 processin# These include:1) 7i#h toolin# costs!) "9pensive ra$ materials ;po$ders)%) Variation in material density and mechanical properties across the volume



13

) elatively lon# parts are difficult to manufacture+) Difficult storin# and handlin# of po$ders ;de#radation $ith time and fire haard $ith Particular metallic po$ders)2) <orrosion resistance is poor for pJm parts

1/. !(plain *?edrawing* operation and classif% the operations with suitable diagra#s.

Ans:

educin# a cup or dra$n part to a smaller diameter and increased hei#ht is 'no$n as redra$in#

Since the avera#e ma9imum reduction in deep dra$in# is about +? percent to ma'e tallslender cups ;such as cartrid#e cases and closed-end tubes) it is necessary to use successive dra$in#operations for this redra$in# is necessary

The t$o basic methods of redra$in# are

• direct7 or regular redrawing and

• ?everse7 or indirect7 redrawing ;see the fi#ures belo$)

In direct redra$in# the ori#inal outside surface of the cup remains the outside surface of theredra$n cup

In reverse redra$in# the cup is turned inside out so that the outside surface of the dra$n cup becomes the inside surface of the redra$n shell

edra$in# methods (a) Direct redra$in# (b) direct redra$in# $ith tapered die ; c) reverseredra$in#

The reduction obtained by redra$in# is al$ays less than that obtainable on the initial dra$ because of the hi#her friction inherent in the redra$in# process &enerally the reduction is decreasedfor each successive redra$in# operation to allo$ for strain hardenin# &reater reductions are ofcourse possible if annealin# is carried out bet$een redra$s 3ost metals $ill permit a total reductionof +? to A? percent before annealin#

20. !(plain about the following: 6a4 ross slip 6b4 all+etch e"uation. Ans:

6a4 ross slip:

It is the movement by $hich a scre$ dislocation can chan#e its slip planeThe process of cross slip is illustrated in the follo$in# fi#ure In the fi#ure small loop of

dislocation line $ith b > aoJ!EG1?1F is movin# on a ;111) plane in a fee crystal The dislocation loop



1

+) 5ailure at the punch radius

14 @range peel effect

The surface *uality of the deep-dra$n component depends very lar#ely on the #rain sie of

the sheet from $hich it is blan'ed and dra$n <oarse #rain $ill often manifest itself as a rou#h or

rumpled surface on those parts of the component $hich have under#one the #reatest amount of deep

dra$in# and $hich have not been in contact $ith the die face ;see the fi#ure) This rou#hness

resembles to some e9tent the surface of an oran#e and is commonly referred to as the Horan#e-peel

effectH

0ran#e peel effect

?e#ed%

The oran#e peel effect occurs in sheet metal of relatively lar#e #rain sie This condition is

best corrected by usin# finer-#rain-sie sheet metal so that the #rains deform more nearly as a $hole

and the individual #rains are difficult to distin#uish $ith the eye

24 Stretcher strains

Stretcher strains or $orms is a serious surface defect that is commonly found in lo$-carbonsheet Steel This defect sho$s up as a flame li'e pattern of depressions in the surface ;see the fi#ure)

resultin# in a uniform rou#h surface



1!

Stretcher strains inlo$-carbon steel

sheet.

?e#ed%

The e9istence of stretcher strains is directly associated $ith the presence of a yield point inthe stress-strain curve and the non uniform deformation $hich results from the yield-point elon#ationThe usual solution to this problem is to #ive the sheet steel a small cold reduction usually Q to !

percent reduction in thic'ness Such a temper-rollin# or s'in-rollin# treatment cold-$or's the metalsufficiently to eliminate the yield point and hence is a remedy for stretcher strains

34 !aring

"arin# is the formation of a $avy ed#e on-the top of a dra$n cup "arin# is caused bydirectional properties in the sheet from $hich the cup $as dra$n <old-$or'in# tends to produce

preferred orientation in sheet materials and this leads to varyin# properties in different directions sothat the metal deforms more easily in some directions than in others thus formin# ears on the deep-dra$n parts "arin# is illustrated in the follo$in# fi#ures

?e#ed%

"arin# can be minimied by avoidin# e9cessive deformation in the deep dra$in# Process and by annealin# treatment 5urther the shape and sie of the ears can be controlled to some e9tent byvaryin# the shape of the blan' to oval or even s*uare instead of circular

4 >rinling or pucering

,rin'lin# is formation of $avy flan#e or $avy ed#es of the cup resultin# from buc'lin# ofthe sheet as a result of the hi#h circumferential compressive stresses ,rin'lin# is sho$n in thefi#ure



1"

?e#ed%

To prevent this defect it is necessary to use sufficient hold-do$n pressure to suppress the buc'lin#

$4 8ailure at the punch radius

The follo$in# fi#ure sho$s a cup $hich has failed at the punch radius This occurs $hen thinnin# ofthe $all in that re#ion has ta'en place to such an e9tent that the stress set up in the metal has e9ceededits tensile stren#th

?e#ed%

<learly the ma9imum dra$in# force must not e9ceed the tensile stren#th of the material multiplied by

the annular area of the shell at its thinnest section "9cessive blan'-holdin# pressure $hich hasrestricted the flo$ of metal in the blan' and caused it to thin drastically at the punch radius maycause failure in this ,ay /lternatively insufficient clearance bet$een punch and die or inade*uateradius of punch or die may also lead to failure of this type

22 Define a4 Low angle grain boundar% b4 Dislocation.

Ans:

a4 Low angle grain boundar%

Lo$ an#le #rain boundaries are boundaries bet$een ad(acent crystals of same structure but $ith smalldifference in crystal orientations The an#le bet$een orientations of t$o ad(acent #rains is less than

1??

They contain a relatively simple arran#ement of dislocations The t$o lattices can be maintainedcontinuity by periodic addition of an ed#e dislocationb4 Dislocation



1#

The dislocation is a boundary bet$een the slipped re#ion and the unslipped re#ion and lies in the slip plane The dislocations belon# to one dimensional imperfection Therefore dislocations are called asline defects

"d#e dislocation

23 +rove B tan C where E B coefficient of friction CE B Angle of bite

Ans:

5orces actin# durin# rollin# are sho$n in the follo$in# fi#ure

5or the $or' piece to enter into the throat of the roll5 cos R Pr sin R

,here

5 cos R is the horiontal component of the friction force $hich acts to$ard the roll #apPr sin R is the horiontal component of the normal force $hich acts a$ay from the roll #ap

Therefore the limitin# condition for unaided entry of a slab into the rolls is5 cos R > Pr sin R

5JPr > tan R > tan R ;5 > Pr)



1$

,here MC is coefficient of friction

2 Differentiate between Direct and &ndirect !(trusion.

Ans:

Sl8o Direct "9trusion Indirect "9trusion

15lo$ of billet metal is in for$arddirection and in the same direction asram

5lo$ of metal ta'es place in a direction oppositeto that of ram movement

!There is a relative motion bet$een billetand container $alls and hence friction is

prevalent $hile e9trudin# the billet

Since there is no relative movement bet$een thecontainer $all and the billet frictional forces arelo$er

% Lubrication is a problem particularly$hen hot e9trusion ;direct) is done

"9tensive lubrication is not needed

Pressure re*uired increases $ith thelen#th of the billet

Pressure remains constant up to (ust to the end ofthe e9trusion process

+

3ore turbulence of billet metal occurs$ithin the billet hence lot of ener#y #ets$asted This re*uires more po$erconsumption to e9trude the billet metal

Turbulence of billet metal is minimum henceflo$ of metal is more uniform $ithin the billethence ener#y loss is minimum This re*uiresless po$er consumption to e9trude the billetmetal

2There is no practical limitation to use this

processThere are practical limitations because use ofhollo$ ram limits the load $ithstandin#capacity

4 7andlin# the e9trudin# metal comin# outthrou#h the movin# ram is not a problem

7andlin# the e9trudin# metal comin# outthrou#h the movin# ram is a problem

2$ Define a4 Ther#o #echanical treat#ents b4 Ausfor#ing

a4 Ther#o #echanical treat#ents

Thermo mechanical treatments refer to the treatment processes in $hich plastic deformationis carried out in such a manner that phase transformation is affected by it6y plastic deformation production of vacancies dislocations and other defects occurs andthese defects severely affects the phase transformation in metals and alloys by providin#

nucleation sites 7ence durin# this treatment t$o processes heat treatment and mechanicaldeformation simultaneously ta'es place

b4 Ausfor#ing

/usformin# is a thermo mechanical treatment in $hich the steel is heated above <T ;uppercritical temperature) to #et austenite and this austenite is super cooled to a temperature belo$recrystallisation temperature of steel The austenite so obtained is heavily deformed and then*uenched to obtain martensite structure

2' List the #ethods to produce powders of #etals.

Ans:

,echanical processes:

3achinin#



2%

<rushin#3illin# and/tomiation

+h%sicohe#ical processes:

<ondensation

Thermal decomposition ;<arbonyl process)

<hemical reduction and

"lectro-deposition method

2) List the various strengthening #echanis#s.

Ans:

1) <old $or'in# or strain hardenin#

!) Solid solution stren#thenin#

%) &rain boundary stren#thenin#

) Precipitation hardenin#

+) Dispersion hardenin#

2) Strain /#ein# ;yield point phenomenon)

2- Differences between edge and screw dislocations:



21

2/ a4 ,ention the conditions for +recipitation hardening and !(plain +recipitation

hardening inter#s of b4 Solutionising c4 Fuenching and d4 Ageing.

Ans:

The conditions for precipitation hardening are:

1 The solubility of the solute in the solvent must decrease in decrease in temperature! The precipitate that separates from the matri9 should be coherent

% /fter choosin# a proper composition of the alloy

The steps in precipitation hardening are

• Solutionisin#

• Uuenchin#

• /#ein#

Solutionising:

•

It is the process of heatin# the alloy (ust above the solvus temperature to obtain asin#le phase solid solution MRC• The alloy should not be heated above solidus temperature as meltin# and o9idation

shall occur to cause adverse effect on ductility

Fuenching:

• The solutionised alloy is cooled fast to retain the hi#h temperature sin#le phase solidsolution at room temperature as metastable supersaturated solid solution

• The alloy can be easily cold rolled under this condition

Ageing:

Sl.No. +ropert% !dge dislocation Screw dislocation

16ur#erCs vector

Perpendicular to dislocationline

Parallel to dislocation line

!Dislocation movementrelative to 6ur#erCs vector

Dislocation moves parallelto 6ur#erCs vector

Dislocation movesPerpendicular to 6ur#erCs

vector%

Slip direction/toms move parallel to6ur#erCs vector

/toms move parallel to6ur#erCs vector

3ovement of dislocationrelative to slip direction

/toms move parallel tomotion of dislocation

/toms move perpendicularto 6ur#erCs vector

+ 3ethod of leavin# slip plane 6y climb up or do$n 6y cross slip

2 Velocity of motion 5aster than scre$ dislocation Slo$er than ed#e dislocation

4 Strain ener#y of dislocation 3ore Less

A Strain fields arounddislocation

<ompression and Tension Shear



22

• It is the process of controlled decomposition of supersaturated solid solution to formfinely-dispersed-precipitates usually at one and some intermediate temperatures for asuitable time period

• /#ein# is t$o types 1) 8atural a#ein# !) /rtificial a#ein#

Natural Ageing: It is the process of a#e hardenin# the *uenched alloy at room temperature

Artificial Ageing: It is the process of a#e-hardenin# by holdin# the Uuenched alloy atsli#htly

30 !(plain about ?olling Gariables.

Ans:

,ain variables in rolling are:

The roll diameter

The deformation resistance of the metal as influenced by metallur#y temperature andstrain rate The friction bet$een the rolls and the $or' piece The presence of front tension and J or bac' tension in the plane of the sheet

?oll dia#eter

ollin# load increases $ith roll diameter at a rate #reater than D1J! dependin# on thecontribution from the friction hill

The roll diameter has an important influence on determinin# the minimum possible #a#esheet that can be rolled $ith a particular mill

6oth rollin# load and len#th of arc of contact decrease $ith decreasin# roll diameter Therefore $ith smaller diameter rolls properly stiffened a#ainst deflection by bac'up

rolls it is possible to produce a #reater reduction

The defor#ation resistance of the #etal as influenced b% #etallurg%7 te#perature and

strain rate.

Durin# rollin# eventually a point is reached $here the deformation resistance of the sheetis #reater than the roll pressure $hich can be applied and no further reduction inthic'ness can be achieved

This occur $hen the rolls in contact $ith the sheet are both severely elastically deformed The mean flo$ stress for cold rollin# does not depend much on the strain rate or roll

speed 7o$ever in hot rollin# chan#es in strain rate can produce si#nificant chan#es in the flo$

stress of the metal The relation bet$een flo$ stress and strain rate is

Stress ;@) > WXm

,hereW > constantX > strain ratem > strain rate sensitivity constant

The friction between the rolls and the wor piece

5rictional force is needed to pull the metal in to the rolls



23

5or cold rollin# $ith lubricants MC varies from about ??+ to ?1? 5or hot rollin# MC varies from about ?! up to the stic'in# condition are common The minimum thic'ness sheet that can be rolled on a #iven mill is directly related to MC 7i#h friction results in hi#h rollin# load a steep friction hill and #reat tendency for ed#e

crac'in#

The presence of front tension and = or bac tension in the plane of the sheet

If bac' tension is applied #radually to the sheet the neutral point shifts to$ard e9it plane The presence of tension in the plane of the sheet can materially reduce the rollin# load

ie The roll pressure reduced is in direct proportion to the tension in the plane of the sheet This results in less $ear of the rolls and improved flatness and uniformity of thic'ness

across the $idth of the sheet

31 !(plain the production of Sea#less pipes b% !(trusion #ethod

Ans:

Pipe and tubin# may be classified as seamless or $elded dependin# on the method of manufacture,elded tubin# is formed from strip and $elded by hot-formin# fusion or electric $eldin# "9trusionis an e9cellent method of producin# seamless pipe and tubin# especially for metals $hich aredifficult to $or'

;a) 3annesmann mill ;b) plu# rollin# mill ;c) three-roll piercin# mill ;d) reelin# mill

The 3annesmann mill ;5i# a) is used e9tensively for the rotary piercin# of steel and copper

billets The process employs t$o barrel-shaped driven rolls $hich are set at an an#le to each other /n

a9ial thrust is developed as $ell as rotation to the billet This assists in openin# up the center of the

billet as it flo$s around the piercin# point to create the tube cavity Piercin# is the most severe hot-

$or'in# operation customarily applied to metals



24

The 3annesmann mill does not provide sufficiently lar#e $all reduction and elon#ation to

produce finished hot-$or'ed tubes Various types of plu# rollin# mills $hich drive the tube over a

lon# mandrel containin# a plu# ;5i#b) have evolved

The /ssel elon#ator $hich uses three conical driven rolls has been $idely adopted This led

to the development of three-roll piercin# machines ;5i# c) $hich produce more concentric tubes $ith

smoother inside and outside surfaces than the older 3annesmann desi#n

/ reelin# mill ;5i#d) $hich burnishes the outside and inside surfaces and removes the sli#ht

oval shape is usually one of the last steps in the production of pipe or tubin#

32 !(plain an% si( forging defects with their re#edies

Ans:

Defects $hich occur in a for#in# may be due to faults in the structure or composition of the alloyfrom $hich it $as made or they may arise durin# the heatin# process before the $or'-piece is ta'ento the for#in# hammer /lternatively defects may be produced due to poor for#in# techni*ue or to theuse of badly desi#ned die e*uipment

The more serious defects $hich may arise durin# the actual for#in# operations are:

614 old shut: / cold shut is a discontinuity produced $hen t$o surfaces of metal folda#ainst each other $ithout $eldin# completely These are usually caused by poor die desi#n orsometimes by the incorrect positionin# of the $or'-piece in the die cavity The effects of one aspectof bad die desi#n are sho$n in 5i# The sharp corner at H cause the metal to flo$ across the die ratherthan follo$ its contours and as the die closes a fold is produced in the metal #ivin# rise to a coldshut as indicated

The 8or#ation of a old Shut.

624 ourse grain: ,hich may be present in the final for#in# due to the finishin# temperatures bein#

too hi#h This $ill be less important in the case of steel if a normaliin# treatment is to follo$for#in#

34 A poor i#pression This may be caused by the metal not fillin# the die cavity correctly and may be due to the $or'-piece bein# of inade*uate sie or bein# for#ed at too Io$a temperature/lternatively the die desi#n may be poor so that the metal has been unable to flo$ sufficiently

4 5reaing of the fibre flow: This $ill be revealed $hen a macro section of a for#in# is e9amined6ro'en fibre results in poor mechanical properties and is caused by the metal flo$in# too rapidly atri#ht an#les to the ori#inal direction of the fibres durin# for#in#

6$4 ,is#atched forgings: ,hich are produced $hen theupper and lo$er die bloc's are out of ali#nment durin# thehammerin# process

'4 8lashline cracs sometimes develop if the reduction inthic'ness durin# for#in# is e9cessive 5lash crac's insteel for#in#s ;5i# A1A) may develop after for#in# or



2

even after subse*uent heat-treatment The flash of a for#in# $hich under#oes considerable reductionin thic'ness durin# the process develops as a result a fibre structure $hich is $ea' in the normaldirection /ny undue strain in this direction may therefore cause fracture If a for#in# tends to developflash crac's these may be prevented by reducin# the amount of metal in the for#in# or limitin# thereduction $hich ta'es place in the flash itself

The 8or#ation of a 8lashline rac

334 Draw a4 61004 b4 61104 planes in a si#ple cubic lattice.

Ans:a4 !dge dislocation

This is the disturbed re#ion bet$een t$o perfect parts of a crystal created by interleavin# of an e9tra

half atomic plane

b4 Gacanc%

If an atom is missin# from its re#ular site the defect produced is called vacancy

3 Differentiate between Twinning and Slip

2. Ans:

&acancy

'(tra half atomic

plane



2!

Sl.No. Slip Twinning

1 The parallel movement of t$o ad(acent

crystal planes relative to one another is

slip

T$innin# is a homo#eneous shear $hich

reorients the deformed lattice into a mirror

ima#e of the parent lattice across the plane of

t$innin#! The orientation of atoms above and

belo$ the slip plane is the same after

slip deformation

T$innin# produces an orientation difference

across the t$in plane

% Slip usually occurs in discrete multiples

of atomic spacin#

In t$innin# atoms move only a fraction of inter

atomic distance The stress re*uired to initiate slip is less

than to propa#ate it

The stress re*uired to propa#ate t$innin# is

appreciably less than that re*uired to initiate it+ There is a time la# for slip T$innin# occurs in micro seconds

3$ Define a4 Solid solution strengthening b4 +recipitation hardening

Ans:

a4 Solid solution strengthening

Stren#thenin# produced by dissolution of a solute in the lattice of solvent is called solid solution

stren#thenin#

Solid solutions offer a #reater resistance to dislocation motion than pure crystals The stress fields

around solute atoms interact $ith the stress field of a movin# dislocation Thereby increasin# the

stress re*uired for plastic deformation

b4 +recipitation hardening

Increase in stren#th and hardness of produced by precipitation of a second phase in a fine form

throu#hout the matri9 of the parent phase is called precipitation hardenin#

The precipitate particles offer much resistance to the movin# dislocations there by producin# the

solution stren#thenin#

3' Define a4 ?olling b4 >rite the li#iting condition for rolling.

Ans:

a4 ?olling



2"

The process of plastically deformin# metal by passin# it bet$een the rolls is 'no$n as rollin#

b4 The li#iting condition for rolling.

5or the $or' piece to enter into the throat of the roll

5 cos R Pr sin R

,here

5 cos R is the horiontal component of the friction force $hich acts to$ard the roll #ap

Pr sin R is the horiontal component of the normal force $hich acts a$ay from the roll #ap

Therefore the limitin# condition for unaided entry of a slab into the rolls is

5 cos R > Pr sin R5JPr > tan R

I B tan C ;since 5 > Pr)

,here MC is coefficient of friction

3) List the #ain rolling variables.

Ans:


The roll diameter

The deformation resistance of the metal as influenced by metallur#y temperature and

strain rate

The friction bet$een the rolls and the $or' piece

The presence of front tension and J or bac' tension in the plane of the sheet

3- List the variables in !(trusion.

Ans:

The e9trusion variables are:

• Type of e9trusion ; direct or indirect)



2#

• "9trusion ratio

• The $or'in# temperature

• Speed of deformation

• 5rictional conditions at billet and the e9trusion container

3/ Define a4 8orging b4 lassif% the forging processes

Ans:

a4 8orging

/ direct compression type of 3echanical $or'in# process $here the $or' is shaped by plastic

deformation achieved either by hammerin# or pressin# is called for#in#

b4 lassif% the forging processes

Ans:

Depending upon the co#ple(it% of die

@pen die forging process: Dies of simple shape employed

losed die forging process: 7ollo$ dies of comple9 internal shapes are employed

Depending upon the te#perature

ot forging: ,or'in# temperature above recrystallisation temp

od forging: ,or'in# temperature belo$ recrystallisation temp

0 lassif% Ther#o #echanical treat#ents.

Ans:

Depending on the te#perature at which defor#ation of austenite taes place7 ther#o

#echanical treat#ents can be

Forgin

g



2$

7i#h temperature thermo-mechanical treatment ;7T3T)

Lo$ temperature thermo-mechanical treatment ;LT3T)

Depending on the defor#ation te#perature in relation to the critical te#perature of steel

Supercritical ;deformin# steel in austenite condition)

Intercritical ;deformin# ferrite and austenite mi9ture)

Subcritical ; deformation of austenite belo$ the L<T)

1 List the various steps involved in powder #etallurg%.

The various steps involved in the production of PJ3 parts are:;1) Production of metal po$ders

;!) 6lendin# and mi9in# of po$ders

;%) <ompaction

;) Sinterin# and

;+) a number of optional and finishin# secondary operations such as Siin# <oinin# Impre#nation

Infiltration 7eat treatin# Platin# and Paintin# etc

2 List the various strengthening #echanis#s.

Ans:

• <old $or'in# or strain hardenin#

• Solid solution stren#thenin#

• &rain boundary stren#thenin#

• Precipitation hardenin#

• Dispersion hardenin#

• Strain /#ein# ;yield point phenomenon)

3 6a4 List the slip s%ste#s for 87 57 and + r%stals. 6b4 Derive the e"uation for

ritical ?esolved Shear Stress.

Ans:

6a4 List the slip s%ste#s for 87 57 and + r%stals.



3%

Slip system is the combination of slip plane and slip direction such that the direction lies in the slip

plane

r%stal Structure +lane Directions No. of Slip S%ste#s

8

J111K 110< 12

5J110K 111< 12

J112K 111< 12

J123K 111< 2

+J0001K 1120< 03

6b4 Derive the e"uation for ritical ?esolved Shear Stress.

Ans:

<onsider a sin#le crystal under a tensile force 5 The an#le bet$een the normal to the slip plane and

the tensile a9is be Y The an#le bet$een the slip direction and the tensile a9is is Z

If M/C is the cross sectional area of the specimen

Then the area of the slip plane inclined at an an#le MYC is > /J<0S Y

The component of the a9ial force 5 actin# alon#

the slip direction is > 5 <os Z

7ence the critical resolved shear stress is

#iven by

T > 5 <os J /J<os Y

> 5J/ <os Z <osY

> @ <os Z <osY

,here M@C is the applied stress



31

!(plain various stages of the flow curve of 8 single cr%stals.

Ans:

Stress-strain curves for sin#le crystals are plotted as resolved shear stress vs shear strain

The flo$ curve of 5<< sin#le crystal is sho$n belo$

This flo$ curve can be divided into three sta#es

Sta#e I the re#ion of easy #lide

Sta#e II the re#ion of strain hardenin#

Sta#e III the re#ion of dynamic recovery

Stage &:



34

Two high 6nonreversing4 #ill

olls of e*ual sie are rotated only in one direction

The stoc' is returned to the entrance or rear of the rolls for further reduction

Two high reversing #ill

,or' can be passed bac' and forth throu#h the rolls by reversin# their direction

Three high #ill.

<onsists of an upper and lo$er driven roll and amiddle roll $hich rotates by friction



3

8our high #ill

Smaller diameter rolls are supported by lar#er diameter bac'up rolls for stren#th and ri#idity

Very thin sheet can be rolled to close tolerances

?oll cluster #ill

"ach of the $or' rolls is supported by t$o bac'in# rolls



3!

8our stand continuous #ill

The speed of each set of rolls is synchronied

The uncoiler and $indup reel supply bac' tension and front tension

) !(plain a4 !dging b4 8ullering c4 Swaging d4 Drawing down e4 +unching and f4

+iercing.

Ans:

a4 !dging: The open die for#in# operation $hich is used to shape the ends of the bars and to #ather

metal /s is sho$n in 5i# a and b the metal is confined by the die from flo$in# in the horiontal

direction but it is free to flo$ laterally to fill the die "d#in# is performed by the ed#in# dies

b4 8ullering: The open die for#in# operation used to reduce the cross-sectional area of a portion of

the stoc' The metal flo$s are out$ard and a$ay from the center of the fullerin# die ;5i#c) /n

e9ample of the use of this type of operation $ould be in the for#in# of a connectin# rod for an

internal-combustion en#ine

c4 Swaging: educin# the sie of for#in# stoc' alternately for#in# in semi contoured dies to

len#then a blan';or) The dra$in#-do$n operation carried out $ith concave dies ;5i# e) so as to

produce a bar of smaller diameter it is called s$a#in#

d4 Drawing down: The reduction in cross section of the $or' $ith concurrent increase in len#th is

called dra$in# do$n or dra$in# out ;5i# d)

e4 +unching: The open die for#in# operation $hich is used to ma'e holes in the $or' is called

punchin# ;fi# #)

f4 +iercing: The open die for#in# operation in $hich the $or' is forced to ta'e the shape of the

contour of a simple die ;fi# f)



3"

5or#in# operations ;a b) "d#in# ;c) 5ullerin# ;d) dra$in# ;e) s$a#in# ;f) piercin# ;#) punchin#.

- !(plain the characteristics of #etal powders.

Ans:

The basic characteristics of a metal po$der are:

;I) <hemical composition and purity

;II) Particle sie and its distribution

;III) Particle shape

;IV) Particle microstructure

Specific surface apparent Density tap density flo$ rate as $ell as its compactin# and

sinterin# characteristics are the other characteristics $hich are dependent entirely on the

above primary properties of metal po$ders

6&4 he#ical co#position and purit%

The chemical composition of po$ders is the outstandin# characteristic It usually

reveals the type and percenta#e of impurity and determines the particle hardness and

compressibility The term impurity refers to some elements or compounds $hich has an

undesirable effect Impurities influence not only the mechanical properties of the po$dercompacts but also their chemical electrical cal and ma#netic properties The chemical

composition of a po$der is determined by the $ell established standard techni*ues of

chemical analysis

6&&4 +article siPe and its distribution



3$

In the same $ay dendritic po$ders result in reduced apparent density and poor flo$ rate

6&G4 +article #icrostructure

The metallo#raphic microstructure e9amination of these po$ders $ill reveal not only

various phases inclusions impurities fissures and internal porosity but also the particle

sie relative sie distribution and particle shape

/ Na#e an% four lattice defects.

Ans:

1) Vacancy !) interstitial impurity%) Substitutional impurity ) self interstitial or interstitialcy

+) Dislocations 2) &rain boundary 4) T$in boundary A) Stac'in# fault

$04 Draw a4 61004 b4 61104 planes in a si#ple cubic lattice.

Ans:

a4

b)



4%

$1 Define a4 Solid solution strengthening b4 +recipitation hardening

Ans:

a4 Solid solution strengthening

Stren#thenin# produced by dissolution of a solute in the lattice of solvent is called solid solution

stren#thenin#

b4 +recipitation hardening

Increase in stren#th and hardness produced by precipitation of a second phase in a fine form

throu#hout the matri9 of the parent phase is called precipitation hardenin#

$2 Define a4 Qield point pheno#enon b4 Strain ageing

Ans:

a4 Qield point pheno#enon

The hetero#eneous plastic deformation durin# elastic to plastic deformation is called yield point

phenomenon

b4 Strain ageing

Strain /#ein# is the increase in stren#th and decrease in ductility of a metal on heatin# at a relatively

lo$ temperature after cold $or'in#

$3 Define ?olling with a neat setch.



41

Ans:

c4 ?olling

The process of plastically deformin# metal by passin# it bet$een the rolls is 'no$n as rollin#

Setch

$ List the #ain rolling variables.

Ans:


The roll diameter

The deformation resistance of the metal as influenced by metallur#y temperature and

strain rate

The friction bet$een the rolls and the $or' piece

The presence of front tension and J or bac' tension in the plane of the sheet

$$ List the variables in !(trusion.

Ans:

The e9trusion variables are:

• Type of e9trusion ; direct or indirect)

• "9trusion ratio

• The $or'in# temperature

• Speed of deformation

• 5rictional conditions at billet and the e9trusion container



42

$' Define 8orging with a neat setch

Ans:

a4 8orging

/ direct compression type of 3echanical $or'in# process $here the $or' ;Ie metal) is shaped by

plastic deformation achieved either by hammerin# or by pressin#

S'etch

$) lassif% Ther#o #echanical treat#ents.

Ans:

Dependin# on the temperature at $hich deformation of austenite ta'es place thermo-mechanical

treatments can be

7i#h temperature thermo-mechanical treatment ;7T3T)

Lo$ temperature thermo-mechanical treatment ;LT3T)

Dependin# on the deformation temperature in relation to the critical temperature of steel

Supercritical ;deformin# steel in austenite condition)

Intercritical ;deformin# ferrite and austenite mi9ture)

Subcritical ; deformation of austenite belo$ the L<T)

$- List the #ain steps involved in powder #etallurg%.

The main steps involved in the production of PJ3 parts are:

;1) Production of metal po$ders

Forging



43

;!) 6lendin# and mi9in# of po$ders

;%) <ompaction and

;) Sinterin#

$/ !(plain the production of #etal powders through a4 Ato#isation b4 arbon%l

process.

Ans:

a4 Ato#isation

6asically atomiation consists of mechanically disinte#ratin# a stream of molten metal into the fine

particles by means of a (et of compressed air inert #ases or $ater

Li*uid metal is forced throu#h a small orifice by the application of air or inert #as <ompressed air

causes the li*uid metal to disinte#rate in to small drop lets $hich on subse*uent coolin# in air or inert

#as produce finely divided po$der

/nother variation of atomiation is rotary atomiation In rotary atomiation the front end of the

rotatin# electrode is heated by arc and allo$ed to melt The li*uid drop lets are thro$n off due to

centrifu#al force action and cooled in to po$der in inert #as

b4 arbon%l process.

<arbonyls are volatile li*uids e# 5e ;<0)+ 8i;<0) etc

These are produced by reaction bet$een metal and <0 #as for e#

8i;s) N <0;#) ] 8i;<0)

5e;s) N +<0;#) ] 5e;<0)+

These reactions occur fastly at !??-!4? 0< and 4?-!?? atm and are reversible at 1+?-?? 0< and

1atm pressure

pon decomposin# the above carbonyls pure po$ders are obtained

Iron po$ders produced by this process are pure and *uite spherical

mm imp questions

Documents