UNIT3-Special casting processcasting.ppt

casting

1. UNIT-3 Special Casting Process

5. Centrifugal Casting
•Inthiscastingprocess,moltenmetal
ispouredintoarevolvingmoldand
allowedtosolidifymoltenmetalby
pressureofcentrifugalforce.
•Thisprocessmakeshollowproduct.
•Therearethreemaintypesof
centrifugalcastingprocess:
1.Truecentrifugalcastingprocess
2.Semicentrifugalcastingprocess
3.Centrifugingprocess.

6. Centrifugal Casting
1.True Centrifugal casting process:
•Thisisnormallyusedforthemakingofhollowpipes,tubes,hallowbushes,etc.
Whichareaxisymmetricwithaconcentrichole.
•Theaxisofrotationcanbeeitherhorizontal,verticaloranyanglebetween.
•Verylongpipesarenormallycastwithhorizontalaxis,whereasshortpiecesare
moreconvenientlycastwithaverticalaxis.
.

7. Process
•Incentrifugalcasting,apermanentmoldisrotatedcontinuouslyaboutitsaxisathigh
speeds(300to3000rpm)asthemoltenmetalispoured.
•Themoltenmetaliscentrifugallythrowntowardstheinsidemoldwall,whereitsolidifies
aftercooling.
•Thecastingisusuallyafine-grainedcastingwithaveryfine-grainedouterdiameter,owing
tochillingagainstthemouldsurface.
•Impuritiesandinclusionsarethrowntothesurfaceoftheinsidediameter,whichcanbe
machinedaway.
•Castingmachinesmaybeeitherhorizontalorvertical-axis.Horizontalaxismachinesare
preferredforlong,thincylinders,verticalmachinesforrings.
•Mostcastingsaresolidifiedfromtheoutsidefirst.Thismaybeusedto
encouragedirectionalsolidificationofthecasting,andthusgiveusefulmetallurgical
propertiestoit.Oftentheinnerandouterlayersarediscardedandonlythe
intermediarycolumnarzoneisused.

8. •Featuresofcentrifugalcasting
•Castingscanbemadeinalmostanylength,thicknessanddiameter.
•Differentwallthicknessescanbeproducedfromthesamesizemold.
•Eliminatestheneedforcores.
•Resistanttoatmosphericcorrosion,atypicalsituationwithpipes.
•Mechanicalpropertiesofcentrifugalcastingsareexcellent.
•Onlycylindricalshapescanbeproducedwiththisprocess.
•Sizelimitsareupto3m(10feet)diameterand15m(50feet)length.
•Wallthicknessrangefrom2.5mmto125mm(0.1-5.0in).
•Tolerancelimit:ontheODcanbe2.5mm(0.1in)ontheIDcanbe3.8mm(0.15
in).
•Surfacefinishrangesfrom2.5mmto12.5mm(0.1-0.5in)rms.

9. 9
Advantages
Goodmechanicalpropertiescanbeachieved
Nocoresarerequiredformakingconcentricholesinthe
caseoftruecentrifugalcasting.
Thereisnoneedforgatesandrunners,Whichincreases
thecastingyield,reachestoalmost100%.
Limitations
Castingswhichareaxi-symmetricandhaving
concentricholesaresuitable.
Equipmentisexpensive.

10. Materials
•Typical materials that can be cast with this process
areiron,
•steel,
•stainless steels,
•glass, and
•alloys ofaluminum,
•copperandnickel.

11. •Typical parts made by this process are
•pipes,
•boilers,
•pressure vessels ,
•flywheels,
•cylinder liners and
•other parts that are axi-symmetric.
•It is notably used to castcylinder linersandsleeve valvesfor
piston engines, parts which could not be reliably manufactured
otherwise.

14. Semi -Centrifugal Casting
•Semi –centrifugal casting is used for jobs which are more
complicated than those possible in true centrifigal casting, but are
axisymmetric in nature.
•The casting like symmetrical shape, pulley, wheel, disk, gear like
big shape products manufactured.
•More than one casting achieved.
•Here vertical axis machine is used. In center the hub is provided to
create hollow core.

16. Centrifugal Casting
3. Centrifuging:
•This process is used for
non-symmetrical castings
having intricate details
and also for precision
castings.
•The centrifugal force
provides high-fluid
pressure to force the
molten metal into mould
cavity.
•A number of similar
components can be cast
simultaneously.

18. •WHAT IS A DIE?
•A die is a specialized tool used in manufacturing industries
to cut or shape materialmostly using a press tool , mould
& die casting. Like molds, dies are generally customized to
the item they are used to create. Products made with dies
range from simple paper clips to complex pieces used in
advanced technology
•PRESS TOOL MOULD DIE CASTING
•

19. DEFINETION OF DIE CASTING
•Die casting is a metal casting process that is characterized by
forcing molten metal under high pressure into a mold
cavity.The mold cavity is created using two hardened tool
steel dies which have been machined into shape and work
similarly to an injection mold during the process.
•Most die castings are made from non-ferrous metals,
specifically
1.) zinc
2.) copper
3.) aluminium
4.) magnesium
5.) lead
6.) tin based alloys
oDepending on the type of metal being cast, a hot-or cold-
chamber machine is used.

20. Gravity die casting, also typically
known as permanent mold casting,
uses reusable molds made of metal,
like steel, graphite etc. to fabricate
metal and metal alloys. This type of
metal casting can manufacture
various parts like gears, gear
housing, pipe fittings, wheels,
engine pistons, etc.
1.Gravity Die Casting:

21. In this process, the direct pouring
of molten metal into the mold
cavity takes place under the effect
of gravity. For better coverage, the
die can be tilted to control the
filling. The molten metal is then
allowed to cool and solidifies
within the mold to form products.
As a result, this process makes
casting of materials like lead, zinc,
aluminum, and magnesium alloys,
certain bronzes, and cast iron more
common.

22. Permanent Mold Casting
Typical parts include gears, splines, wheels, gear housings,
pipe fittings, fuel injection housings, and automotive engine
pistons

23. Die Casting
2. Pressure die casting:
•In pressure die casting metal flows under high
pressure
•Also as the die is metallic, the casting rate is high
and thus mass production is possible.
The following are the types of pressure die casting
(A) Hot chamber die-casting
(B) Cold chamber die casting.

24. HOT CHAMBER DIE CASTING
•Inhotchamberdiecastingmanufacture,thesupplyofmolten
metalisattachedtothediecastingmachineandisanintegral
partofthecastingapparatusforthismanufacturing
operation.
•Themetalforcastingismaintainedatanappropriatetemperature
inaholdingfurnaceadjacentto,ifnotpartof,themachine.
•Theinjectionmechanismislocatedwithintheholdingfurnaceand
asubstantialpartofitisthereforeinconstantcontactwiththe
moltenmetal.
•Pressureistransmittedtothemetalbytheinjectionpiston,which
forcesitthroughthegooseneckandintothedie.Onthereturn
strokemetalisdrawnintothegooseneckforthenextshot.
•Inthisprocessthereisminimumcontactbetweenairandthemetal
tobeinjected,thusminimizingthetendencyforturbulent
entrainmentofairinthemetalduringinjection.Duetothe
prolongedcontactbetweenthemetalandpartsoftheinjection
systemhotchamberisrestrictedtozinc-basealloys.
•TheZincalloysarethemostwidelyusedinthediecasting
process.Theyhaveverydesirablephysical,mechanicaland
castingproperties.Theyalsohavetheabilitytobereadilyfinished
withcommercialelectroplatedororganiccoatings.

26. Some applications of Zinc Die Castings:
•Automotive Industry
•Fuel Pumps
•Carburetor Parts
•Valve Covers
•Handles
hot-chamber machines are primarily
used with zinc, tin, and lead based
alloys.

27. •Theessentialfeatureofthisprocessisthe
independentholdingandinjectionunits.In
thecoldchamberprocessmetalis
transferredbyladle,manuallyor
automatically,totheshotsleeve.
•Actuationoftheinjectionpistonforcesthe
metalintothedie.Thisisasingle-shot
operation.
•Thisprocedureminimizesthecontacttime
betweenthehotmetalandtheinjector
components,thusextendingtheiroperating
life.
•However,theturbulenceassociatedwith
high-speedinjectionislikelytoentrainairin
themetal,whichcancausegasporosityin
thecastings.
COLD CHAMBER DIE CASTING

28. •Nexttozincaluminumisthemostwidelyuseddie-casting
alloy.Theprimaryadvantageisitlightweightanditshigh
resistancetocorrosion.Magnesiumalloydie-castingsarealso
producedandareusedwhereahighstrength–to–weightratiois
desirable.
•Themoldhassections,whichincludethe“cover”orhotside
andthe“movable”orejectorside.Thediemayalsohave
additionalmoveablesegmentscalledslidesorpulls,whichare
usedtocreatefeaturessuchasundercutsorholeswhichare
paralleltothepartingline.Themachinesrunatrequired
temperaturesandpressurestoproduceaqualityparttonearnet-
shape.

29. Die Casting
•ColdChamber
Cold-chamber machines are used with
a large composition of aluminium,
magnesium and copper.
Some application for
Aluminum Die Castings:
Automotive industry
Home Appliances
Communication Equipment
Sports & Leisur

30. Advantages of die casting
•Advantages:
–Thin section (0.5 mm thickness) can be easily made.
–Impression or complicated design can be achieved on
component walls.
–The production rate is high (300 per hour approx).
–Die set can be used many times.
–All non-ferrous products are produced with this method.
–Better surface finish is achieved.

31. Disadvantages of die casting
•It is not economic for small quantity of
production.
•It is used for only small casting (10 kg weight
approx).
•Initial cost is high for die and other equipment.
•Only non-ferrous products are casted.
•If proper care is not taken then the defects like
blow hole can be possible.

32. Investment Casting
•Investmentcastingisoneoftheoldestmanufacturing
processes,datingbackthousandsofyears,inwhichmolten
metalispouredintoanexpendableceramicmold.
•Investmentcastingisoftenreferredtoas"lost-waxcasting"
becausethewaxpatternismeltedoutofthemoldafterit
hasbeenformed.
•Themoldisformedbyusingawaxpattern-adisposable
pieceintheshapeofthedesiredpart.Thepatternis
surrounded,or"invested",intoceramicslurrythathardens
intothemold.
•However,sincethemoldisdestroyedduringtheprocess,
partswithcomplexgeometriesandintricatedetailscanbe
created.

33. Investment Casting
•The following are the different
stages in Investment Casting
(1) Die making
(2) Making wax pattern
(3) Precoating the wax pattern
assembly
(4) Investment the wax pattern in
mould box
(5) Removal of wax pattern
(6) Pouring molten metal
(7) Cleaning of casting

34. •Investmentcastingrequirestheuseofametal
die,wax,ceramicslurry,furnace,molten
metal,andanymachinesneededfor
sandblasting,cutting,orgrinding.Theprocess
stepsincludethefollowing:

35. Process
•Patterncreation-Thewaxpatternsaretypically
injectionmoldedintoametaldieandareformed
asonepiece.Coresmaybeusedtoformany
internalfeaturesonthepattern.
•AssemblyofPatterns-ThePatternsareattachedto
acentralwaxstickcalledaspruetofroma
castingclusterorassembly.

36. •Moldcreation-This"patterntree"isdippedintoaslurryoffine
ceramicparticles,coatedwithmorecoarseparticles,andthendriedto
formaceramicshellaroundthepatternsandgatingsystem.This
processisrepeateduntiltheshellisthickenoughtowithstandthe
moltenmetalitwillencounter.
•Theshellisthenplacedintoanovenandthewaxismeltedout
leavingahollowceramicshellthatactsasaone-piecemold,hencethe
name"lostwax"casting.

37. Pouring-Themoldispreheatedinafurnacetoapproximately
1000°C(1832°F)andthemoltenmetalispouredfromaladleinto
thegatingsystemofthemold,fillingthemoldcavity..
Cooling-Afterthemoldhasbeenfilled,themoltenmetalis
allowedtocoolandsolidifyintotheshapeofthefinalcasting.
Coolingtimedependsonthethicknessofthepart,thicknessofthe
mold,andthematerialused.

38. •Castingremoval-Afterthemoltenmetalhascooled,themold
canbebrokenandthecastingremoved.Theceramicmoldis
typicallybrokenusingwaterjets,butseveralothermethods
exist.Onceremoved,thepartsareseparatedfromthegating
systembyeithersawingorcoldbreaking(usingliquid
nitrogen).
•Finishing-Oftentimes,finishingoperationssuchasgrinding
orsandblastingareusedtosmooththepartatthegates.Heat
treatmentisalsosometimesusedtohardenthefinalpart.

40. Products
•Turbine blades for aerospace
and power industries.
•Firearm parts such as triggers
and hammers
•Artificial orthopedic surgical
implants and parts for artificial
limbs
•Industrial pumps,, automobiles,
components, pipe fittings and
pipe elbows.

41. •Investmentcastingcanmakeuseofmostmetals,
mostcommonlyusingaluminumalloys,bronze
alloys,magnesiumalloys,castiron,stainless
steel,andtoolsteel
•Thisprocessisbeneficialforcastingmetalswith
highmeltingtemperaturesthatcannotbemoldedin
diecasting.
•Partsthataretypicallymadebyinvestmentcasting
includethosewithcomplexgeometrysuchas
turbinebladesorfirearmcomponents.

42. •Excellent surface finish.
•Tight dimensional tolerances.
•Complex and intricate shapes may be produced.
•Capability to cast thin walls.
•Low material waste.
•No parting lines
•A wide variety of material can be cast using this
method
Advantages

43. Disadvantage
•Limitations on size of casting
•Higher casting costs make it important to take
full advantage of the process to eliminate all
machining operations.
•Individual pattern is required for each
casting.

44. Casting
Defects

45. Definition
Acasting defectis an undesired irregularity in
ametal castingprocess. Some defects can be
tolerated while others can be repaired,
otherwise they must be eliminated.
The Following are the major defects which are likely to occur in sand castings.
(i)Gas defects
(ii)Shrinkage cavities
(iii)Molding Material defects
(iv)Pouring Metal defects
(v)Metallurgical defects

46. Defects in Casting
•(I)Gas defects
•Casting defects, their causes & remedies:
(1)Blow holes
These are the spherical, flattened or elongated cavities present inside
the casting or on the surfaces.
Causes: Moisture level is high in mould sand, improper baking of
core. unnecessary carbonic binder, unwanted ramming, small vent
hole, fine sand etc.
Remedies: Proper moisture level, proper baking of core, proper use
of binder, proper ramming, proper vent hole with vent rod, selection
of sand particle.

47. PINHOLES
Formationofmanysmallgascavitiesatorslightlybelow
surfaceofcastingiscalledaspinholes.
Causes:
•Sand with high moisture content.
•Absorption of hydrogen/carbon monoxide gas in the metal.
•Alloy not being properly degassed.
•Sand containing gas producing ingredients.
Remedies:
•Reducing the moisture content & increasing permeability of moulding sand.
•Employing good melting and fluxing practices.
•Improving a rapid rate of solidification.
4
7

48. Blow holes Casting Defects

49. Casting defects, their causes &
remedies
(II) Shrinkage cavities
When metal transfer from liquid to sold its volume will
decrease. During this process if it will not get more
molten metal then in the internal surface of casting voids
are developed, that is known as shrinkage.
Causes: Defective runner, gate and riser, molten metal's
pouring temperature.
Remedies : Proper arrangement of runner, riser and gate
for proper directional solidification. If required, the design
can be changed, maintaining proper molten metal
temperature.

50. Shrinkage Casting Defects

51. Casting defects, their causes & remedies
•(1) Metal Penetration: Surface of casting becomes rough due to metal penetration.
•Causes: Bigger size of sand, less ramming, low strength of moulding sand and core, higher
permeability.
•Remedies : Fine grain sand, proper ramming of mould sand, proper mixture should be used to
increase moulding and core porosity.
•(2) Lift and shift :
•Some part of casting gets distortion known as lift and shift.
•Causes: Improper alignment of pattern parts, improper support of core, improper clamping of mould
box, improper strength of mould sand.
•Remedies: By aligning the mould box with help of dowel pin, properly supporting core in mould,
properly clamping of mould box, providing proper strength mould and core sand.
•(3) Swell
•Due to molten metal the some part of mould cavity become large so the casting becomes larger than
required which known as swell.
•Causes : Pressure of molten metal on surface, improper ramming of sand, low strength of core sand.
•Remedies: By properly ramming of sand, by increasing core strength so molten metal can easily flow
in mould.
(III) Moulding Material defects

52. Casting defects, their causes & remedies
•(4) Run out: While pouring, molten metal comes out (leaks out) from casting known as run out.
•Causes: Defective mould box, defectively moulding process.
•Remedies Moulding box should be changed, modification in moulding process.
•(5) Drop: A drop occurs when cope surface cracks and breaks, thus the pieces of sand fall into the
molten metal.
•Causes Due to either low green strength or improper ramming of the cope flask, improper
reinforcement.
•Remedies: Proper mixing of binder for strength improvement, proper arrangement of steel rod for
reinforcement in core and mould, proper ramming.

53. Casting defects, their causes & remedies
•(1) Misrun and cold shut :Molten metal cannot reach in all the parts of
mould, so this improper filled casting known as misrun. Molten comes from
different sides, sometimes cannot mix each other. This defect known as
cold shut.
•Causes: Defective design of gating system, low fluidity of molten metal,
thin wall of casting, non-continues pouring of metal.
•Remedies: Modification of gating system, increasing temperature of molten
metal, continuously pouring of molten metal, increasing porosity of sand.
•(2) Warpage: After or before solidification casting may twist or change
shape known as warpage.
•Causes: Improper design, lack of directional solidification, internal stress.
•Remedies: Proper design of casting to get directional solidification. By
proper heat treatment the stress can be removed.
(IV) Pouring metal defects

54. 4) Inclusions :
•Unwanted ingredients such as metal oxide, slag, sand particles give defects known as
inclusions in metal castings.
•Causes: Improper gating system, improper pouring, low quality mouldand core sand,
improper ramming, impurity in metal charge.
•Remedies: By modifying gating system, turbulence free pouring, using good quality mould
and core, proper ramming of mouldsand, proper and pure metal charge should be used and by
using oxide free molten metal crucible.

55. Casting defects, their causes & remedies
•Hard spot: Some part of casting solidifies very fast
and that surface becomes tough, that known as hard
spot.
•Causes: Bad casting design, improper métal
composition, improper use of chills.
•Remedies: Proper design of castings so metal
solidifies in same time, proper metal Composition,
proper use of chills in design.
(V) Metallurgical defects

58. MELTING FURNACES
•Beforepouringintothemold,themetaltobecastedhastobeinthemoltenor
liquidstate.
•Furnaceisusedforcarryingoutnotonlythebasicorerefiningprocessbut
mainlyutilizedtomeltthemetalalso.
•Ablastfurnaceperformsbasicmelting(ofironore)operationtogetpigiron,
cupolafurnaceisusedforgettingcastironandanelectricarcfurnaceisusedfor
re-meltingsteel.
•Differentfurnacesareemployedformeltingandre-meltingferrousand
nonferrousmaterials.

59. What isFurnace???
•Heatingmediaordevice.
•Usedforheatingandmelting.
•Forprovidingheattochemicalreactionsfor
processeslikecracking.
•Thefurnacemaybeheatedbyfuelasinmany
furnacescokeisusedasafuel.
•someareoperatedbyelectricalenergye.g.
electricarcfurnace.

60. Furnaces for Casting Processes
•Furnaces most commonly used in foundries:
–Cupolas
–Direct fuel-fired furnaces
–Crucible furnaces
–Electric-arc furnaces
–Induction furnaces

61. FURNACES FOR MELTING DIFFERENT
MATERIALS
Grey Cast Iron
(a) Cupola
(b) Air furnace
(c) Rotary furnace
(d) Electric arc furnace
Non-ferrous Metals
(a) Reverberatoryfurnaces (fuel fired) (Al, Cu)
(i) Stationary
(ii) Tilting
(b) Rotary furnaces
(i) Fuel fired
(ii) Electrically heated
(c) Induction furnaces(Cu, Al)
(i) Low frequency
(ii) High frequency.
(d) Electric Arc furnaces (Cu)
(e) Crucible furnaces (AI, Cu)
(i) Pit type
(ii) Tilting type
(iii) Non-tilting or bale-out type
(iv) Electric resistance type (Cu)
(f) Pot furnaces (fuel fired) (Mg and AI)
(i) Stationary
(ii) Tilting
Steel
(a) Electric furnaces
(b) Open hearth furnace

62. CUPOLA FURNACE
•Cupola furnace is employed for melting scrap metal or pig iron for
production of various cast irons.
•It is also used for production of nodular and malleable cast iron.
•It is available in good varying sizes.
•The main considerations in selection of cupolas are melting
capacity, diameter of shell without lining or with lining, spark
arrester.

63. Cupola Furnace
•CupolawasmadebyRene-Antoinearound1720.
•Cupolaisameltingdevice.
•Usedinfoundriesforproductionofcastiron.
•Usedformakingbronzes.
•ItschargeisCoke,Metal,Flux.
•Scrapofblastfurnaceisremeltedincupola.
•Large cupolas may produce up to 100 tons/hour
of hot iron.

64. Construction
•Cupolaisacylindricalin
shapeandplacedvertical.
•Itsshellismadeofsteel.
•Itssizeisexpressedin
diametersandcanrangefrom
0.5to4.0m.
•Itsupportedbyfourlegs.
•Internalwallsarelinedwith
refectorybricks.
•Itsliningistemporary.

65. Parts of Cupola
•Sparkarrester.
•Chargingdoor.
•Airbox.
•Tuyeres.
•Taphole.
•Slaghole.

66. Zones
Well
•Thespacebetweenthebottom
oftheTuyeresandthesandbed.
•Moltenmetalcollectedinthis
portion.
Combustionzone
•Alsoknownasoxidizingzone.
•Combustiontakeplaceinthis
zone.
•Itislocatedbetweenwelland
meltingzone.
•Heightofthiszoneisnormally
15cmto30cm.

67. Zones
•Inthiszonethetemperature
is1540°Cto1870°C.
•Theexothermicreactions
takesplaceinthiszone
thesearefollowing.
•C+O
2→CO
2+Heat
•Si+O
2→SiO
2+Heat
•2Mn+O
2→2MnO+Heat
Reducingzone
•Locatebetweenupperlevel
ofcombustionzoneand
upperlevelofcokebed.

68. Zones
•Inthiszonetemperatureis
about1200°C.
•InthiszoneCO2changeinto
CO.
CO2+C(coke)→2CO
Meltingzone
•Inthiszonethemeltingisdone.
•Itislocatedbetweenpreheating
zoneandcombustionzone.
•Thefollowingreactiontake
placeinthiszone.
•3Fe+2CO→Fe3C+CO2.

69. Zones
Preheatingzone
•Thiszoneisstartsfromtheupper
endofthemeltingzoneand
continuesuptothebottomlevelof
thechargingdoor.
•Objectiveofthiszoneispreheatthe
chargesfromroomtemperatureto
about1090°Cbeforeenteringthe
metalchargetothemeltingzone.
Stack
•Theemptyportionofcupolaabove
thepreheatingzoneiscalledasstack.
Itprovidesthepassagetohotgases
togotoatmospherefromthecupola
furnace.

70. Charging of Cupola Furnace
•Beforetheblowerisstarted,thefurnaceisuniformly
pre-heatedandthemetal,fluxandcokecharges,lying
inalternatelayers,aresufficientlyheatedup.
•Thecoverplatesarepositionedsuitablyandtheblower
isstarted.
•Theheightofcokechargeinthecupolaineachlayer
variesgenerallyfrom10to15cm.Therequirementof
fluxtothemetalchargedependsuponthequalityofthe
chargedmetalandscarp,thecompositionofthecoke
andtheamountofashcontentpresentinthecoke.

71. Working of Cupola Furnace
•Itschargeconsistof
scrap,cokeandflux.
•Thechargeisplaced
layerbylayer.
•Thefirstlayeriscoke,
secondisfluxandthird
metal.
•Airenterthroughthe
bottomtuyeres.
•Thisincreasestheenergy
efficiencyofthefurnace.
•Cokeisconsumed.

72. Working of Cupola Furnace
•Thehotexhaustgasesriseup
throughthecharge,preheatingit.
•Thechargeismelted.
•Asthematerialisconsumed,
additionalchargescanbeaddedto
thefurnace.
•Acontinuousflowofironemerges
fromthebottomofthefurnace.
•Theslagisremovedfromslaghole.
•Themoltenmetalachievedbytap
hole.

73. Operation of Cupola
•Preparation of cupola.
•Firing the cupola.
•Soaking of iron.
•Opening of air blast.
•Pouring the molten metal.
•Closing the cupola.

74. Preparation of cupola
•Slagandmetaladheretothecupolalining
fromthepreviousrunisremovedandliningof
cupolaisremade.
•Thebottomplatesareswungtoclosing
positionsupportedbyprob.
•Thesandbedisthenpreparedwithmolding
sandsuchthatitsslopestotowardsthetap
hole.

75. Firing the Cupola
•Thecupolaisfiredbykindlingwoodatthe
bottom.
•Thisshouldbedone2.5to3hoursbeforethe
moltenmetalisrequired.
•Onthetopofthekindlingwoodabedofcoke
isbuilt.
•Theheightofthecokebedismaybevary
from50cmto125cmaccordingtothesizeof
cupola.

76. Soaking of Iron
•Whenthefurnaceischargedfullyitis
maintainforabout45minutes.
•Thechargeisslowlyheated.
•Duringthestagetheairblastisshutoffand
ironissoaked.

77. Opening of blast air
•Attheendofthesoakingperiodtheairblastis
opened.
•Thetapingholeisclosedbyaplugwhenthe
meltingproceedsandmoltenmetaliscollectat
thebottom.

78. Pouring of molten metal
•Whenthesufficientamountofmetalhas
collectedinthehearththeslagholeisopened
andtheslagisremoved.
•Thentapingholeisopenedandmoltenmetalis
flowsoutinthetable.
•Thesameprocedureisrepeateduntilthe
chargeismeltedandtheoperationisover.

79. Closing the cupola
•Whentheoperationisovertheairblastisshut
off.
•Thebottomoffurnaceisopenedbyremoving
theprop.

80. Advantages
•Itissimpleandeconomicaltooperate.
•Cupolascanrefinethemetalcharge,removing
impuritiesoutoftheslag.
•Highmeltrates.
•Easeofoperation.
•Adequatetemperaturecontrol.
•Chemicalcompositioncontrol.
•Efficiencyofcupolavariesfrom30to50%.
•Lessfloorspacerequirements.

81. Disadvantages
•Sincemoltenironandcokeareincontactwith
eachother,certainelementslikesi,Mnare
lostandotherslikesulphurarepickedup.This
changesthefinalanalysisofmoltenmetal.
•Closetemperaturecontrolisdifficultto
maintain

82. Factorsresponsiblefortheselectionoffurnace:-
(i)Considerationsofinitialcostandcostofitsoperation.
(ii)Relativeaveragecostofrepairandmaintenance.
(iii)Availabilityandrelativecostofvariousfuelsintheparticularlocality.
(iv)Meltingefficiency,inparticularspeedofmelting.
(v)Compositionandmeltingtemperatureofthemetal.
(vi)Degreeofqualitycontrolrequiredinrespectofmetalpurificationof
refining,
(vii)Cleanlinessandnoiselevelinoperation.
(viii)Personnelchoiceorsalesinfluence.

83. Electric-Arc Furnaces
Charge is melted by heat generated from an electric arc
•High power consumption, but electric-arc furnaces can be designed
for high melting capacity
•Used primarily for melting steel