Casting Ch 3

8/18/2019 Casting Ch 3

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MOLDING PROCESS AND

MATERIALS


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Classification of casting processes

• (1 San! casting• a Green"san! #ol!s

• $ Dr%"san! #ol!s• c Core"san! #ol!s

• ! Ce#ent"$on!e!"san! #ol!s

• e Loa# #ol!s

• f S&ell #ol!ing

• g Pit an! floor #ol!ing

• & All core #ol!ing


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• (' Per#anent"#ol! casting

• ( Die casting

• () Centrif*gal casting

• (+ Plaster"#ol! casting

• (, In-est#ent casting

• (. Sl*s& casting

• (/ S&ot casting

• (0 Special processes grap&ite #ol!s2 cera#ic

#ol!s3


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Categories of casting•

Expendable molds:• Ma!e of san!2 plaster2 cera#ics an! si#ilar #aterials

• 4&ic& are generall% #i5e! 4it& -ario*s $in!ers or

$on!ing agents2

• T&e #ol!s are $ro6en *p to re#o-e t&e casting3• Permanent molds:

• 7se! repeate!l% an! are

• Designe! in s*c& a 4a% t&at casting can $e easil%

re#o-e! an!

• T&e #ol! *se! for t&e ne5t casting3


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Co#posite Mol!s

• Ma!e of t4o or #ore !ifferent #aterials

(s*c& as san!2 grap&ite2 an! #etal

•Co#$ining t&e a!-antages of eacaterial3

• 7se! to i#pro-e #ol! strengt&2

• Cooling rates an!• O-erall econo#ics of t&e process3


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SAND CASTINGS• Silica san! (Si O' is *se! *ni-ersall% for

#a6ing casting t&an an% ot&er #ol!ing

#aterials3

• It is relati-el% c&eap3

• It &as goo! refractoriness3• 8on!ing agent (*s*all% cla% is #i5e! or occ*rs

nat*rall% 4it& t&e san!

• T&e #i5t*re is #oistene! 4it& 4ater• To !e-elop strengt& an! plasticit% of t&e cla% an!

to #a6e t&e aggregate s*ita$le for #ol!ing3


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• T&e flas6 is a fra#e of steel2 iron or 4oo!

in 4&ic& t&e #ol! is #a!e3

• T&e cope is t&e *pper an! t&e !rag t&elo4er &alf of t&e #ol! inter#e!iate

sections2 if *se!2 are c&ee6s3

• T&e ra##er is pro-i!e! 4it& a peen an!

$*tt en! for ra##ing san! aro*n! t&e

e!ges of t&e flas6 an! o-er t&e pattern

respecti-el%3


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• T&e pattern is t&e for# aro*n! 4&ic&

san! is ra##e!

•It #a% $e one piece or split Constr*ction2!epen!ing *pon si9e an! config*ration3

• 8otto# $oar!s are flat plates of 4oo! or

#etal *pon 4&ic& patterns is lai! $efore

ra##ing t&e !rag3


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• T&e #ol! ca-it% is t&e e#pt% s&ape left in

san! 4&en t&e pattern is re#o-e! an! into

4&ic& #etal is po*re!2 or cast2 to for# t&e

casting3

• T&e #ol! ca-it% nor#all% not $e left

co#pletel% e#pt%

• A core of fir#l% $a6e! san! #a% $e *se! tofor# t&e internal s&ape an! !i#ensions of

t&e casting3


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• C&aplets are #etal o$:ects for &ol!ing t&e core in

position against t&e 4as&ing an! lifting effect of

#olten #etal3

• Molten #etal is intro!*ce! into t&e #ol! ca-it%t&ro*g& t&e gating s%ste#2

• A po*ring c*p or po*ring $asin is eit&er place!

*pon or

• ;or#e! into t&e *pper cope s*rface2 connecting to

t&e !o4n gate2 to recei-e t&e #etal fro# t&e la!le3


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Green"san! Mol!ing• Mol!ing is often !one 4it& green san!3

• Green #ol!ing san! #a% $e !efine! as a plastic

#i5t*re of san! grains2 cla%2 4ater an! ot&er

#aterials

• $eca*se of t&e #oist*re

present an! is t&*s !isting*is&e! fro# !r% san!3

•


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Steps in green san! #ol!ing

• Preparation of t&e pattern

• Ma6ing t&e #ol!

• Core setting• Closing


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A!-antages

• Greater fle5i$ilit% as a pro!*ction process3

• Mec&anical e?*ip#ent can $e *tili9e! for

perfor#ing #ol!ing an! its allie! operations3

• ;*rt&er#ore2 green san! can $e re*se! #an%ti#es $% recon!itioning it 4it& 4ater2 cla% an!

ot&er #aterials3

• 7s*all% t&e #ost !irect ro*te fro# pattern to#ol! rea!% for po*ring is green"san! #ol!ing3


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• Advantage@ Green san! #ol!ing is or!inaril%t&e least costl% #et&o! of #ol!ing

• Disadvantages @T&in2 long pro:ections ofgreen san! in a #ol! ca-it%

• Are 4as&e! a4a% $% t&e #olten #etal or #a%

not e-en $e #ol!a$le3

• Cooling fins on air coole! engine c%lin!er $loc6san! &ea!s are an e5a#ple3

• Greater strengt& is t&en re?*ire! of t&e #ol!3

• Certain #etals an! so#e castings !e-elop!efects if po*re! into #ol! containing #oist*re3


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Dia!-antages

• More intricate castings cannot $e #a!e

• T&e !i#ensional acc*rac% an! s*rface

finis& of green"san! castings #a% not $e

a!e?*ate3

• Large castings re?*ire greater #ol!

strengt& an! resistance to erosion t&an is

a-aila$le in green san!s3


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8ASIC STEPS IN MAING A SAND MOLD

• Preparation of t&e #ol!ing san!3• In #a6ing a si#ple #ol!2 t&e $otto#

$oar! is first lai! sec*rel% on t&e $enc& or

floor3• T&e pattern is positione!2 t&e flas6 is

locate! properl%2 an! t&e san! is sie-e!

o-er t&e pattern 4it& a ri!!le3• T&e san! 4ill to*c& t&e #etal

• It is an especiall% fine an! clean -ariet% of

san!2 calle! facing san!3


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• 7se! $ac6ing san! #a% t&en $e s&o-ele!

into t&e flas6 o-er t&e facing2 an!

• T&e 4&ole ra##e! sec*rel%2

• 7sing t&e peen aro*n! t&e e!ges an! t&e

$*tt ra##er o-er t&e pattern3


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• Once t&e flas6 is ra##e! properl% a

straig&te!ge2 or stri6e2 is !ra4n across t&e

*pper s*rface to re#o-e e5cess san!

• A secon! flat $oar! is place! *psi!e !o4n

on t&e #ol! an! flas6 an! cla#pe! or &el!

in position 4&ile t&e 4&ole is o-er"t*rne!3

• T&e original $otto# $oar!2 4&ic& is no4

on t&e top2 is re#o-e!2 an! t&e !rag &alf

of t&e #ol! is essentiall% finis&e!3


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• It 4ill later $e necessar% to c*t an ingate to

t&e #ol! ca-it% *nless one is pro-i!e! as

part of t&e pattern2 as is t&e reco##en!e!

practice3

• It #a% $e necessar% to tool t&e !rag

so#e4&at2 i3e32 s#oot& t&e san! aro*n!

t&e pattern e!ges or ot&er4ise s&ape it3


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• Parting po4!er2 a 4&ite po4!er% s*$stance2

is !*ste! o-er t&e san! an! pattern2 an! t&e

cope flas6 is positione!3

• If patterns are pro-i!e! 4it& !o4n gates 2

t&ese are set in place2 as are t&e patterns

for 4&ate-er risers are *se!3

• Do4n gates are so#eti#es c*t t&ro*g& t&ecope 4it& a c%lin!rical t*$e after t&e cope is

finis&e!3


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• A la%er of facing san! is ri!!le! o-er t&e

!rag an! pattern as $efore2 an! $ac6ing

san! is a!!e! an! ra##e! soli!l%3

• A steel $ar is again *se! to stri6e off t&e

*pper s*rface of t&e cope spr*e an! riser

patterns are t&en !ra4n3

• T&e cope is re#o-e! fro# t&e !rag an!*s*all% place! asi!e for an% finis&ing

operations re?*ire!3


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• If split patterns are *se! one"&alf 4ill $e pic6e! *p 4it&

t&e cope so t&e cope is lai! *psi!e !o4n on a spare

$otto# $oar!3

• T&e patterns are t&en rappe! slig&tl% to loosen t&e#

fro# t&e san! an! are re#o-e! fro# cope an! !rag 4it&

a !ra4 spi6e

• Ingates are c*t2 t&e #ol! is patc&e! as re?*ire!2

• C&aplets an! cores are positione!2 an! #ol! is close!

$% placing t&e cope again atop t&e !rag3


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• S#all -ent &oles are #a!e t&ro*g& t&e

san! to 4it&in a fraction of an inc& of t&e

pattern to ins*re t&e escape of gases3

• Cla#ps or 4eig&ts are place! on t&e flas6

to resist t&e ten!enc% of t&e cope to float

or s&ift as #olten #etal fills t&e #ol!

ca-it%3


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Desira$le Mol! Properties an!

C&aracteristics• Strengt& " to #aintain s&ape an! resist erosion3

• Per#ea$ilit% " to allo4 &ot air an! gases to pass

t&ro*g& -oi!s in san!3

• T&er#al sta$ilit% " to resist crac6ing on contact 4it&#olten #etal3

• Collapsi$ilit% " a$ilit% to gi-e 4a% an! allo4 casting to

s&rin6 4it&o*t crac6ing t&e casting3

• Re*sa$ilit% " can san! fro# $ro6en #ol! $e re*se! to#a6e ot&er #ol!sB


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Dr%"san! Mol!s

• T&ese #ol!s are #a!e 4it& #ol!ing san!

in green con!ition3

• as goo! !r% strengt&3

• Mol!ing !one t&e sa#e 4a% as green"

san! #ol!ing3

• Refractor% coating3


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• T&e entire #ol! is !rie! in an o-en at to ,+o; or $% circ*lating &eate! air

t&ro*g& t&e #o*l!3

• T&e -ol*#e of gas for#e! 4&en t&e

casting is po*re! is #*c& less t&an 4it&

green #o*l!s3

• Casting !efects attri$*ta$le to #oist*re

s&o*l! $e a$sent3


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• T&e essential !ifference $et4een !r% san!

an! green san! #ol!ing

• T&e #oist*re in t&e #ol! san! is re#o-e!

prior to po*ring t&e #etal3

• Dr% san! #ol!ing is #ore applica$le to

#e!i*# an! large castings t&an to s#all

castings3


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• T&e #ol!s are stronger an! #ore rigi! t&an

green san! #ol!s3

• T&e% can 4it&stan! #ore &an!ling an! resist t&e

static press*re of #olten #etal2 4&ic& #a%

ca*se green san! #ol!s to !efor# or s4ell3• In a!!ition2 t&e% #a% $e e5pose! to t&e

at#osp&ere for long perio!s of ti#e 4it&o*t

!etri#ental effect3

• S*c& e5pos*re #a% $e necessar% for placing

an! fitting a large n*#$er of cores3


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S6in"!rie! Mo*l!s

• T&e effect of a !r%"san! #o*l! #a% $e partiall%

o$taine! $% !r%ing t&e #o*l! s*rface to so#e

!ept&2 to 1 in3

• S6in !r%ing #a% $e perfor#e! $% torc&es2 a$an6 of ra!iant"&eating la#ps2 or electrical

&eating ele#ents !irecte! at t&e #o*l! s*rface3

• T&ese #o*l!s #*st $e po*re! s&ortl% after

!r%ing so t&at #oist*re fro# t&e *n"!rie! san!

4ill not penetrate t&e !rie! s6in3


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;loor an! Pit Mol!ing

• Large intricate castings 4eig&ing fro# 1 to

o-er 1 tons3

• T&e s*rface finis& an! !i#ensional acc*rac%

of t&ese large castings in ferro*s allo%s is nott&at of s#aller ones2 !i#ensional tolerances

of F 11, to F in3

• $eing accepta$le *nless special e5periencesper#its closer control3


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• T&e pro$le#s of #ol! constr*ction2

&an!ling2 coring2 gating2 po*ring an!

cleaning of large castings re?*ire #*c&

engineering efforts an! control3

• T&e terrific a#o*nt of la$or2 ti#e2 an!

#aterials going into #a6ing a large

casting #a6es itcostl%3


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•


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• Mol!ing pits are concrete"line! $o5"s&ape!

&oles in t&e #ol!ing floor3

• T&e pattern is lo4ere! into pit an! #ol!ing

san! is t*c6e! an! ra##e! *n!er t&e

pattern an! *p t&e si!e 4alls to t&e parting

s*rface3

• T&e cope of t&e pit #ol! is finis&e! off 4it&cores or 4it& san! ra##e! in a cope flas63


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Dr% san! pit #ol! for stationar%

!iesel engine

.


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• S*c& large #ol!s are al4a%s !rie!3

• ;loor #ol!ing@


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• Pit #ol!ing@ E5tre#el% large castings are

fre?*entl% #ol!e! in a pit instea! of a

flas63

• T&e pit acts as t&e !rag part of t&e flas6

an! a separate cope is *se! a$o-e it3

• T&e% si!es of t&e pit are $ric6 6in!2 an! on

t&e $otto# t&ere3


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Loa# Mol!ing

• Loa# is a #ol!ing san! containing a$o*t

+ per cent san! grains an! + per cent

cla%3

• Loa# #ol!ing 4as #*c& *se! in t&e past

for #a6ing large $ron9e castings an! is

still practice! in so#e s&ops2

• partic*larl% in #a6ing &*ge #anganese"

$ron9e propellers3


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Cont""

• In t&is #et&o! a s*$strate is #a!e of

$ric6s2 4oo! an! ot&er #aterial to t&e

appro5i#ate conto*r of t&e casting3

• A -er% -isco*s sl*rr% of 4ater2 cla% an!

san! is !a*$e! o-er t&e fra#e4or6 an!

4or6e! to proper s&ape 4it& s4eeps3

• T&e #ol! is !rie! $% force! &ot air or

torc&es3


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• No pattern is re?*ire!2 as s&eet"steel

s4eeps are so s&ape! t&at t&e% generate

proper casting conto*r as t&e s4eep ar# is

#o-e! $ac6 an! fort& o-er a fi5e! spin!le3• S*c& s4eeps are *se! occasionall% in

#a6ing #ol!s for large rolling"#ill rolls

4&ere or!inar% #ol!ing san! is *se!instea! of a sl*rr%3


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• T&e c&ief a!-antages of t&is process are

sa-ings in pattern cost an! storage

• pattern storage alone is an i#portant an!

e5pensi-e ite# in #ost fo*n!ries3

• Loa# #ol!ing is slo4 an! la$orio*s2 an!

special #ol!ers are re?*ire!

• All 4or6 #*st $e !one $% &an! as t&e

process is -er% #*c& an art3


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Ce#ent"$on!e!"san! Mol!s

• Ce#ent"$on!e! #ol!ing san! is a #i5t*re

of san!2 / to 1' per cent &ig&"earl%"

strengt& &%!ra*lic ce#ent2 an! ) to , per

cent 4ater3

• T&is san! !e-elops great &ar!ness an!

strengt& $% t&e setting action of portlan!

ce#ent3


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• Core"san! or Core Mol!s (All"core Mol!ing

• So#e large castings are #a!e entirel% of

cores

• &*n!re!s of large an! s#all in!i-i!*al core

sections are fitte! toget&er in a pit

• an! finall% ra##e! sec*rel% in position 4it&

#ol!ing san! or presse! toget&er 4it&s*ita$le cla#ps3


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• T&is #et&o! is c&osen 4&ere !esign is

s*c& t&at stan!ar! patterns co*l! not $e

!ra4n fro# reg*lar #ol!s3

• In place of patterns2 core $o5es are *se!

for #a6ing all parts of t&e #ol!3

• T&e cores are $eing fitte! toget&er to

#a6e t&e #ol!2 $eing locate! $%

align#ent $osses an! &oles3


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• Core san!s *s*all% consist of #i5t*res of

san! grains an! organic $in!ers 4&ic&

!e-elop great strengt& after $a6ing at to

)+ ;3• T&e strengt& after $a6ing #a6es it possi$le

to cast #etal aro*n! t&in san! pro:ections

4it&o*t &a-ing t&e# $rea6 or ero!e$eca*se of t&e &ot #etal action3

• 3


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• T&e $a6ing operation an! t&e core"san! $in!ers

pl*s !iffic*lties in re*sing t&e san! #a6e t&e

process #ore costl%3

• o4e-er2 t&is is *s*all% :*stifie! in intricatecastings #a!e in core"san! #ol!s3

• Core"san! #ol!s are also so#eti#es #a!e 4it&

!r% #ol!ing san!s or ce#ent"$on!e! san!s

4&ere t&e great strengt& an! &eat resistance of a!r%"san! #i5t*re is re?*ire!2 as in large castings


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• S&ell Mol!ing

• S&ell #ol!ing is a special for# of san!

casting3

• S6ille! #ol!ers are not re?*ire!2 an!

process can $e &ig&l% #ec&ani9e!3


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• T&e san! *se! for s&ell #ol!ing consists

of a #i5t*re of t&e follo4ing ingre!ients@

• Dr% san! grains2 A;S fineness 0 to 1)2

!istri$*te! o-er ) to + screens3 San!s for

s&ell #ol!ing are al4a%s 4as&e! an!

gra!e! for $est res*lts fine san!s can $e

*se!2 as per#ea$ilit% of t&e t&in s&ell isnot a pro$le#3


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• ' S%nt&etic"resin $in!er2 to 1 per cent

$% 4eig&t3

• Resins 4&ic& #a% $e *se! are t&e p&enol

for#al!e&%!es2 *rea for#al!e&%!es2

al6%!s an! pol%esters3

•


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• T&e resin #*st $e a t&er#osetting plastic

since t&e strengt& !e-elope! $% t&e #ol!

!epen!s entirel% on t&e strengt& of t&e

plastic $in!er after t&e #ol! &as $een&eate!3

• Dr% po4!er an! san! are #i5e! inti#atel%

in a #*ller or ot&er s*ita$le !e-ice2 or san!#a% $e p*rc&ase! =pre"coate!> 4it& resin3


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• ii T&e s&ell2 still on t&e pattern2 can t&en

$e c*re! $% &eating it to ++ to ,+ ; for

to 1 #in*te3

• Stripping t&e s&ell fro# t&e #ol! presentsa pro$le# since t&e s&ell is -er% strong an!

grips t&e #ol! tig&tl%3 A #ol! release agent

or parting agent is necessar% so t&at t&ee:ector pins can p*s& t&e s&ell off t&e

patterns3


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• Silicone parting sol*tions spra%e! on t&e

pattern &a-e $een fo*n! satisfactor%3

• T&e s&ell &al-es #a% t&en $e asse#$le!

an! po*re!3


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• A!-antages clai#e! for s&ell #ol!ing are

e5ceptionall% goo! s*rface finis& an!

!i#ensional acc*rac%2 3 to 31 in3

per in3 -ariation $eing o$taine! in so#ecastings3

• ence2 t&e eli#ination of so#e #ac&ining

operations2 !ecrease! casting"4eig&t-ariation2 an! less cleaning cost are

t&o*g&t to $e a-aila$le3


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• Castings can $e #a!e of an% #etalallo%3

• Mol! collapsi$ilit% *s*all% a-oi!s crac6s in

casting3

• Can $e #ec&ani9e! for #ass pro!*ction3

• Disa!-antages@

• More e5pensi-e #etal pattern3• Diffic*lt to :*stif% for s#all ?*antities3


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• T&e e5tre#el% &ig& te#perat*res of casting

an! conse?*ent #ol! attrition #a6e

per#anent #ol!s *ns*ita$le for #ost steel

castings3• T&e process is li#ite! to -ol*#e pro!*ction

an! *s*all% re?*ires a contin*o*s c%cle of

#ol! preparation2 po*ring an! castinge:ection3

•


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• T&is is necessar% so t&at all steps can $e

ti#e! an! t&e #ol! t&*s 6ept 4it&in a fi5e!

operating"te#perat*re range at t&e start of

t&e po*r3• Operating te#perat*re of t&e #ol! is one

of t&e #ost i#portant factors in s*ccessf*l

per#anent"#ol! casting3


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PERMANENT MOLDS

• Mol!s 4&ic& can $e re*se! are #a!e of

#etal2 *s*all% gre% cast iron or steel2

t&o*g& so#eti#es of $ron9e2 grap&ite or

al*#in*#3• T&e #ol! ca-it% (or !ie ca-it% in a

per#anent #ol! is often cast to its ro*g&

conto*r an! t&en is #ac&ine! to its finis&e!!i#ensions3 T&e gating s%ste# as 4ell as

#ol! ca-ities are #ac&ine!3


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• T&e #ac&ine! #ol! #a6es it possi$le to

o$tain -er% goo! s*rface finis& an!

!i#ensional acc*rac% in t&e castings3

• Al*#in*#2 #agnesi*#2 9inc2 lea!2

copper"$ase allo%s an! cast irons are t&e

principal allo%s so cast


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• A*to#atic #ac&ines &a-e $een !e-elope! to

o$tain a contin*o*s c%cle3

• Coating of #ol! ca-it%3

• Car$on soot2 !eposite! fro# an acet%lenetorc&2 is *se! for iron castings3

• Refractor% s*spensions3

• Metal or san! cores #a% $e set in t&e #ol!$efore it is close!3

•


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• T&e #etal is *s*all% fe! into t&e #ol! onl%

$% gra-it% (gra-it% casting2 $*t in so#e

cases air press*re2 to 1 psi2 is *se! on

t&e spr*e after t&e casting is po*re!3


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;ig*re@ Per#anent Mol!


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;ig*re@ Per#anent Mol!

Casting


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• T&e se?*ence of operations incl*!es@

• Cleaning t&e #ol! $% $r*s&ing or $lasting

4it& 4ar# air2 an! #aintaining t&e# at

proper casting te#perat*re $% a gas or oil

fla#e t&e correct operating te#perat*re

can $e !eter#ine! onl% $% e5perience an!

-aries 4it& t&e casting• 3


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• Painting or spra%ing t&e #ol! s*rface 4it& a t&in

refractor% 4as&2 or $lac6ing it $% !epositing car$on

fro# a re!*cing gas or oil fla#e

• Inserting cores2 if *se!2 an! closing t&e #ol! $%

&an! or $% a*to#atic action

• Po*ring t&e #etal fro# a &an! la!le or a $*ll la!le

s*spen!e! on a #o-a$le trac6

• Allo4ing s*fficient ti#e for t&e casting to soli!if% an!• E:ecting t&e casting fro# t&e #ol! a*to#aticall% or

$% &an!


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A!-antages

• 8% #eans of per#anent"#ol! casting2

!i#ensional tolerances of F31 in3 on a

!i#ension for #an% castings toget&er 4it& goo!

s*rface finis& can $e o$taine!3

• T&e c&illing action of t&e #ol! pro!*ces $etter

#etal properties in #an% allo%s3

• oles can $e core! an! inserts cast into place

#ore acc*ratel% t&an is possi$le in san! #ol!s3• ig&er pro!*ction rates t&an san! casting2 $*t

#*c& slo4er t&an !ie casting3


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Li#itations

• T&e casting !esign #*st $e si#ple

eno*g& an! 4it& s*fficient !raft so t&at t&e

e:ection fro# t&e #ol! is feasi$le3

• 8eca*se of #ol! cost2 t&e process is

li#ite! to applications 4&ere t&e

a!-antages na#e! res*lt in an econo#ic

or engineering gain in preference to san!castings3


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• Applications@ car$*retor $o!ies2

refrigeration castings2 &%!ra*lic"$ra6e

c%lin!ers2 connecting ro!s2 4as&ing"

#ac&ine gears an! gear co-ers2 oil p*#p$o!ies2 t%pe4riter seg#ents2 -ac**#"

p*#p c%lin!ers2 s#all cran6s&afts2 #an%

ot&ers3


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DIE CASTING

• T&e #olten #etal is force! into t&e #ol! ca-it%

*n!er &ig& press*re2 1 to 12 psi3

• T4o principal t%pe of !ie"casting #ac&ines are*se!3

• T&e &ot"c&a#$er #ac&ine (goosenec6

• T&e col!"c&a#$er #ac&ine

•


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• In s*$#erge! &ot"c&a#$er"t%pe #ac&ine2 #olten

#etal flo4s into t&e &ot c&a#$er since it is

s*$#erge! in t&e #elt an! is t&en force! into t&e !ie

ca-it% at a$o*t 1 to ' psi3 T&is #ac&ine is *se!

for casting Hn2 Sn2 P$ an! ot&er lo4 #elting allo%s3

• In goosenec6 #ac&ine press*re #a% $e applie!

!irectl% $% #etal pl*nger or $% air3 T&e goosenec6

#a% $e fille! $% &an! or it #a% $e act*ate! $% a ca#

to alternati-el% !ip into t&e #etal an! rotate into t&eposition against t&e !ie opening $efore press*re is

applie! for t&e s&ot3


70/112

• In t&e col!"c&a#$er process 2 #etal is

la!le! into t&e s&ot c&a#$er3

• Press*re in t&e col!"c&a#$er #ac&ine

#a% go as &ig& as 2 psi3

• T&is #ac&ine is *se! for !ie"casting Al2

Mg2 C*"$ase an! ot&er &ig&"#elting

allo%s3


71/112


72/112

Die Casting in ot"C&a#$er


73/112

Die Casting in ot"C&a#$er

Process

Die Casting in Col!"C&a#$er


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Die Casting in Col! C&a#$er

Process


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• A!-antages@

• A pro!*ction rate of 1+ to '+ !ie"cast c%cles per &o*r 4it& *p to +

s&ots per &o*r possi$le3

• ig& !i#ensional tolerances2 F31 to F3inc&3

• T&in sections2 !o4n to 31+ in3 in s#all castings2 can $e cast $eca*se

of t&e press*re in-ol-e!3

• i- oles as s#all as ' ## !ia3 #a% $e core!3

• - Ma% cast t&rea!s (*p to ') inc&3

• -i Acc*rate coring an! casting of inserts is possi$le3

• -iiS*rface finis& of #an% castings is s*c& t&at t&e% can $e $*ffe!!irectl%3

• -iii Rapi! cooling rate pro!*ces &ig& strengt& an! ?*alit% in #an%

allo%s3


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Figure: Sequence of steps of operation of cold-chamber die-casting machine.

(a) The metal is ladled into the chamber, (b) the plunger forces the metal into the die cavity, the die opens, (d) the casting together !ith the gate and slug of

e"cess metal is e#ected from the die.


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• INESTMENT CASTING

• J Lost"4a5 Process or Precision Casting or Lost Pattern

• T&e ter# =in-est#ent> refers to a cloa6 or special co-ering apparel2

in t&is case a refractor% #ol!2 s*rro*n!ing a refractor%"co-ere! 4a5

pattern3

• In t&is process a 4a5 pattern #*st $e #a!e for e-er% casting an!

gating s%ste# to $e cast i3e32 1 casting re?*ire 1 patterns3

• T&e patterns are cast $% in:ection #ol!ing3

• T&e $asic steps in-ol-e! in in-est#ent casting are as $ello4@

• A #aster pattern an! !ie for casting t&e 4a5 pattern is #a!e3 T&e!ie2 *s*all% a tin"$is#*t& allo%2 #*st #a6e allo4ance for s&rin6age

of $ot& 4a5 an! later t&e #etal casting2 a$o*t 311 to 31+ in3 per

in3 total3


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•


80/112

• (iii Pre"coating@ T&e 4a5 asse#$l% is !ippe! into asl*rr% of a refractor% coating #aterial3 A t%pical sl*rr%

consists of '+"#es& silica flo*r s*spen!e! in 4ater"

et&%l silicate sol*tion of s*ita$le -iscosit% to pro!*ce a

*nifor# coating after !r%ing3 After !ipping t&easse#$l% is allo4e! to !r% for *p to 1 &o*rs3

• So#eti#es pre"coating is not *se! an! t&e 4a5

pattern is !irectl% in-este! in t&e #ol!ing #aterial3 In

t&is case2 t&e #ol!ing #i5t*re #*st $e -ac**#e! tore#o-e air $*$$les 4&ic& #a% lo!ge ne5t to t&e

pattern3


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• (i- T&e coate! 4a5 asse#$l% is ne5t in-este! in t&e #ol!3T&is is !one $% in-erting t&e 4a5 asse#$l% on a ta$le2

s*rro*n!ing it 4it& a paper"line! steel flas62 an! po*ring

t&e in-est#ent"#ol!ing #i5t*re aro*n! t&e pattern3 T&e

#ol! #aterial settles $% gra-it% an! co#pletel% s*rro*n!st&e pattern as t&e 4or6 ta$le is -i$rate!3

• T&e #ol!ing in-est#ent is co#pose! of silica or ?*art9

grains an! $in!ers3 T4o t%pes of in-est#ents are *se!2

one for lo4"te#perat*re #etals cast $elo4 ' ; an!ot&ers for #etals 4it& &ig& po*ring te#perat*res3 T&e

#ol!s are allo4e! to air"set for , to / &o*rs3


82/112

• (- De4a5ing an! pre&eating@


83/112


84/112

• A!-antages@

• Casting &ig&"po*ring"te#perat*re allo%s to

acc*rate !i#ensions3 Near net s&ape2 e5cellent

s*rface finis&2 #ini#*# #ac&ining3• Castings of great e5terior an! interior intricac% #a%

$e cast3

• T&in sections #a% $e cast e-en2 in t&e &ig&"

po*ring"te#perat*re allo%s2 $eca*se of t&e &eate!#ol!3


85/112

• Disa!-antages@

• ig& tooling cost (rec*rring2 an! la$or

cost3

• Ma53 si9e *s*all% a$o*t + g3

• Pro!*ction rate lo4 (less t&an 1&r3


86/112

;i I t t C ti


87/112

;ig*re@ In-est#ent Casting

I t t C ti


88/112

In-est#ent Casting

• One"piece #ol! K Drie! in t&e air

K eate! to 0 K 1.+ C

K el! in-erte! for 1' &rs to #elt o*t 4a5

K T&e #ol! is t&en &eate! to ,+ K 11+ C for a$o*t ) &rs

!epen!ing on t&e #etal to $e cast to !ri-e off t&e 4ater

of cr%stalli9ation

K After t&e #etal &as $een po*re! an! soli!ifie! t&e #ol!

is $ro6en *p an! t&e cast is re#o-e!

K A n*#$er of patterns can $e :oine! to #a6e one #ol!

calle! a tree 4&ic& increases pro!*ction rate


89/112

• One"piece #ol! " cont K S#all parts

• T&e tree can $e inserte! on to a flas6 an! fille! 4it& sl*rr% in-est#ent

• T&e in-est#ent is t&en place! into a c&a#$er an! e-ac*ate! to re#o-e

air $*$$les

• Ne5t it is place! in a -ac**# !ra4ing #ac&ine to pro!*ce fine !etail

K Not a c&eap process

K Pro!*ces fine !etails

K Goo! s*rface finis&

K ;e4 or no finis&ing operations K Can pro!*ce intricate parts fro# parts 4eig&ing 1g K +g

• E5 @ In-est#ent !ie casting e5a#ples


90/112


91/112

• +3 CONENTIONAL CASTINGIn t&e con-entional process2

t&e s&ell is fille! 4it& #olten

#etal $% gra-it% po*ring3 As

t&e #etal cools2 t&e parts an!

gates2 spr*e an! po*ring c*p$eco#e one soli! casting3

• ,3 NOCO7T


92/112

p ) g y y

detail and from a variety of metals.


93/112


94/112

• PLASTER MOLDS

• Casting in plaster #ol!s2 or plaster"$on!e! #ol!s2 &as

$eco#e a *sef*l casting process3

• Ag2 A*2 Mg2 C*2" an! Al K $ase allo%s #a% $e cast in plaster

#ol!s2 $*t ferro*s allo%s are not3• Plasters *se! for #ol!ing consist of #i5t*res of g%ps*# or

plaster of Paris2 CaSO)3'O2 an! ingre!ients s*c& as

talc2 as$estos fi$er2 silica flo*r2 an! ot&ers to control t&e

contraction c&aracteristics of t&e #ol! an! setting ti#e3• T&e plaster is a!!e! to 4ater an! is #i5e! to a consistenc%

of 1) to 1/3


95/112

• It is i#portant t&at t&e plaster $e a!!e! to 4ater rat&ert&an 4ater to plaster2 an! t&at an opti#*# rate of #i5ing

$e !e-elope! $% e5perience for t&e partic*lar #i5er *se!

-er% rapi! #i5ing !e-elops too #*c& air in t&e sl*rr%2

4&ic& a!-ersel% affects #ol! te5t*re2 an! #i5ing tooslo4l% #a% per#it t&e sl*rr% to &ar!en (set pre#at*rel%3

• Consistenc% is !efine! as t&e po*n!s of 4ater per 1

po*n!s of plaster in t&e #i5t*re3

• Dr% strengt& of t&e plaster !epen!s greatl% on t&econsistenc% of t&e #i52 as re-eale! in t&e ta$le fro# R3 ;3

Dalton3

$ry compression strength,

i

%onsistency,

lb &'' lb i


96/112

psi lb !ater per &'' lb mi"

&&,''' '

,''' *

+,''' +*

,'''

'' &+' - &'


97/112

• After #i5ing2 plaster in a crea#% con!ition is po*re! o-ert&e pattern an! retaine! in a flas63 A pattern parting2

stearic aci! !issol-e! in petrole*# spirits2 for e5a#ple2

#a% $e *se!3

• Generall% #etal patterns are necessar% $eca*se t&e 4aterin plaster raises grains on 4oo! patterns an! #a6es t&e#

al#ost i#possi$le to !ra43

• Matc&plate K t%pe patterns3

• Copes an! !rags #a% $e #a!e si#*ltaneo*sl% onseparate lines an! !rie! in o-ens &el! at ) " / ; ('

" )'+ C *ntil all free an! co#$ine! #oist*re is re#o-e!3


98/112

• Mol! sections are -er% fragile an! re?*ire care inasse#$ling3

• After setting ' to #in*tes t&e pattern can $e

$lo4n off t&e #ol! $% air3

• Per#ea$le (poro*s casting plaster can $e #a!e $%

$eating air $*$$les into t&e plaster sl*rr% 4it& a

#ec&anical #i5er3

•Setting of t&e plaster in-ol-es &%!ration of t&eg%ps*#@

• CaSO) 3 'O Q ' 'O CaSO)3''O Q &eat


99/112

• After setting2 t&e #ol!s are !rie! at ) ; or &ig&er3 ;oral*#in*# castings2 1 to ' &rs at ) ; is s*ita$le3

• T&e plaster can partiall% !e&%!rate! at &ig&er !r%ing

te#perat*re2 an! conse?*entl% t&e #ol! e-ol-es less

stea# 4&en t&e casting are po*re!3 o4e-er2 #ol!strengt& is lost 4it& !e&%!ration3

• It is o$-io*s t&at t&e ti#e re?*ire! for c*ring plaster #ol!s

is an *n!esira$le part of t&is process3 o4e-er2 $eca*se

of !i#ensional acc*rac% an! s*rface finis&2 #an% castingss*c& as r*$$er"tier #ol!s2 foa#"r*$$er #ol!s2 cast

#atc& plates2 an! t&e li6e are #ol!e! in t&is 4a%3


100/112

• Antioc& Process@

• A #i5t*re of san!2 g%ps*#2 as$estos2 talc2 so!i*#

silicate an! 4ater3

• San! is t&e $*l6 ingre!ient an! g%ps*# t&e $in!er3• In proportions of + parts 4ater to 1 parts !r%

ingre!ients2 4ater is a!!e! to !r% #aterial

consisting of + silica san!2 ) g%ps*#

ce#ent2 / talc2 an! s#all a#o*nt of so!i*#silicate2 portlan! ce#ent2 an! #agnesi*# o5i!e3

• Mol!ing


101/112

• In a$o*t . #in*tes !e-elops a set strengt& of a$o*t. psi in co#pression3

• After stan!ing a$o*t , &rs2 t&e #ol!s are

asse#$le! an! a*tocla-e! in stea# at a$o*t ' at#

press*re3

• Dr% in air for a$o*t 1' &rs an! finall% in o-en for 1'

to ' &rs at )+ ;3

• T&e a*tocla-ing an! !r%ing process pro!*cesper#ea$ilit%2 a$o*t '+ to + A;S per#ea$ilit%3

• Rea!% to po*r3


102/112

• A!-antages@• Non"ferro*s castings &a-ing intricate an! t&in sections can $e

#a!e 4it& goo! !i#ensional acc*rac% an! e5cellent s*rface

finis&3

• Antioc& Process """"" #ol! per#ea$ilit% an! t&e a$ilit% toincorporate c&ills in t&e #ol!

• C&ills cannot $e *se! as rea!il% in #ol!s of or!inar% #etal

casting plaster since t&e% ten! to e5pan! an! crac6 t&e $rittle

#ol! !*ring $a6ing3

• JJ Plaster casting is s*ita$le onl% for non"ferro*s castings t&e

s*lp&*r of t&e g%ps*# reacts c&e#icall% 4it& ferro*s #etals at

&ig& te#perat*re to gi-e -er% $a! casting s*rfaces3

CENTRI;7GAL CASTING


103/112

CENTRI;7GAL CASTING

• Centrif*gal force is *se! to !istri$*te t&e#olten #etal in t&e #ol!3

• Centrif*gal casting falls into t&ree

categories@

• 13 Tr*e centrif*gal casting

• '3 Se#i"centrif*gal casting

• 3 Centrif*ging


104/112

• Tr*e centrif*gal casting@ t&e #ol! is sp*n a$o*t itso4n a5is no risers are re?*ire! an! no central core is

nee!e! since centrif*gal force for#s t&e inner

!ia#eter of castings s*c& as pipe nat*rall%3

• Se#i"centrif*gal casting@ t&e o$:ect2 s*c& as 4&eel4it& spo6es2 is sp*n a$o*t its o4n a5is2 $*t risers an!

cores are nee!e!3

• Centrif*ge! casting@ t&e #ol! i#pressions are

gro*pe! aro*n! a central !o4ngate2 as in staticcasting2 an! centrif*gal force is *se! #ainl% as a

#ol!"filling !e-ice3


105/112

• 4eig&e! a#o*nt of #etal is po*re!

• Mol! coating """"" #ol! 4as&

• A!-antages@• Econo#ical for #a6ing t*$*lar o$:ects3

• No core is nee!e! to for# t&e $ore3

• Centrif*gal press*res """" force #olten #etal?*ic6l% into #ol! to pre-ent pre#at*re free9ing3

Centrif*gal Casting Process


106/112

Centrif*gal Casting Process

Figure: Schematic illustration of thecentrifugal casting process. ipes!cylinder liners! and similarly shaped

parts can be cast with this process.

Se#icentrif*gal Casting


107/112

Se#icentrif*gal Casting

Figure: (a) Schematic illustration of the semicentrifugal casting process. "heelswith spo#es can be cast by this process. (b) Schematic illustration of casting bycentrifuging. $he molds are placed at the periphery of the machine! and themolten metal is forced into the molds by centrifugal force.


108/112

SOT CASTING


109/112

SOT CASTING

• Metal s&ots """ #a!e $% !ropping #olten #etalfro# consi!era$le &eig&ts into a pool of 4ater3

• T&e !roplets $eco#e sp&erical in s&ape as t&e%

fall freel% t&ro*g& air an! free9e in t&is for# *pon

stri6ing t&e 4ater3

• Si9e of s&ot is reg*late! $% t%pe of #etal2 po*ring

te#perat*re2 rate of e5it of #etal strea#2 !istance

t&ro*g& 4&ic& t&e !roplets fall2 an! an% air :et or#ec&anical !e-ice *se! to !isperse t&e strea# as

it e5its fro# t&e control no99le3

GRAPITE MOLDS


110/112

GRAPITE MOLDS

• Non"ferro*s allo%s an! cast irons3

• 8loc6s of grap&ite #a% &a-e #ol! ca-ities

#ac&ine! into t&e#3

• Not as !*ra$le as #etal3

• Grap&ite $egins to o5i!i9e a$o-e .+ ;

an! t&e #ol! t&en $egins to s&o4 4ear3

• Mol! coating of et&%l silicate3

OTER MOLD MATERIALS


111/112

OTER MOLD MATERIALS

• Al*#in*# """ lo4 te#perat*re castingallo%s3

• Silicon car$i!e """ c&illing po4er #*c&

greater t&an san! t&o*g& not so great as#etal

Operation Se?*ence of Ma6ing


112/112

a Cera#ic Mol!

Casting Ch 3

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