FromFraBurmeisterogWain'sIronFoundry,byPederSeverinKryer,1885.

FoundryFromWikipedia,thefreeencyclopedia

Thisarticleisaboutmetalfoundries.Forotheruses,seeFoundry(disambiguation)."Ironfoundry"redirectshere.ForthemusiccompositionbySovietcomposerAlexanderMosolov,seeIronFoundry.

Afoundryisafactorythatproducesmetalcastings.Metalsarecastintoshapesbymeltingthemintoaliquid,pouringthemetalinamold,andremovingthemoldmaterialorcastingafterthemetalhassolidifiedasitcools.Themostcommonmetalsprocessedarealuminiumandcastiron.However,othermetals,suchasbronze,brass,steel,magnesium,andzinc,arealsousedtoproducecastingsinfoundries.Inthisprocess,partsofdesiredshapesandsizescanbeformed.

Contents

1Process1.1Melting

1.1.1Furnace1.2Degassing1.3Moldmaking1.4Pouring1.5Shakeout1.6Degating1.7Heattreating1.8Surfacecleaning1.9Finishing

2Seealso3References4Externallinks

Process

Mainarticle:Casting(metalworking)

AFoundryman,picturedbyDanielA.Wehrschmidtin1899.

Meltingmetalinacrucibleforcasting

Inmetalworking,castinginvolvespouringliquidmetalintoamold,whichcontainsahollowcavityofthedesiredshape,andthenallowingittocoolandsolidify.Thesolidifiedpartisalsoknownasacasting,whichisejectedorbrokenoutofthemoldtocompletetheprocess.Castingismostoftenusedformakingcomplexshapesthatwouldbedifficultoruneconomicaltomakebyothermethods.[1]

Melting

Meltingisperformedinafurnace.Virginmaterial,externalscrap,internalscrap,andalloyingelementsareusedtochargethefurnace.Virginmaterialreferstocommerciallypureformsoftheprimarymetalusedtoformaparticularalloy.Alloyingelementsareeitherpureformsofanalloyingelement,likeelectrolyticnickel,oralloysoflimitedcomposition,suchasferroalloysormasteralloys.Externalscrapismaterialfromotherformingprocessessuchaspunching,forging,ormachining.Internalscrapconsistsofgates,risers,defectivecastings,andotherextraneousmetaloddmentsproducedwithinthefacility.

Theprocessincludesmeltingthecharge,refiningthemelt,adjustingthemeltchemistryandtappingintoatransportvessel.Refiningisdonetoremovedeleteriousgasesandelementsfromthemoltenmetaltoavoidcastingdefects.Materialisaddedduringthemeltingprocesstobringthefinalchemistrywithinaspecificrangespecifiedbyindustryand/orinternalstandards.Certainfluxesmaybeusedtoseparatethemetalfromslagand/ordrossanddegassersareusedtoremovedissolvedgasfrommetalsthatreadilydissolvecertaingasses.Duringthetap,finalchemistryadjustmentsaremade.

Furnace

Severalspecialisedfurnacesareusedtomeltthemetal.Furnacesarerefractorylinedvesselsthatcontainthematerialtobemeltedandprovidetheenergytomeltit.Modernfurnacetypesincludeelectricarcfurnaces(EAF),inductionfurnaces,cupolas,reverberatory,andcruciblefurnaces.Furnacechoiceisdependentonthealloysystemquantitiesproduced.ForferrousmaterialsEAFs,cupolas,andinductionfurnacesarecommonlyused.Reverberatoryandcruciblefurnacesarecommonforproducingaluminium,bronze,andbrasscastings.

Furnacedesignisacomplexprocess,andthedesigncanbeoptimizedbasedonmultiplefactors.Furnacesinfoundriescanbeanysize,rangingfromsmallonesusedtomeltpreciousmetalstofurnacesweighingseveraltons,designedtomelthundredsofpoundsofscrapatonetime.Theyaredesignedaccordingtothetypeofmetalsthataretobemelted.Furnacesmustalsobedesignedbasedonthefuelbeingusedtoproducethedesiredtemperature.Forlowtemperaturemeltingpointalloys,suchaszinc

Ametaldiecastingrobotinanindustrialfoundry

ortin,meltingfurnacesmayreacharound500C.Electricity,propane,ornaturalgasareusuallyusedtoachievethesetemperatures.Forhighmeltingpointalloyssuchassteelornickelbasedalloys,thefurnacemustbedesignedfortemperaturesover1600C.Thefuelusedtoreachthesehightemperaturescanbeelectricity(asemployedinelectricarcfurnaces)orcoke.

Themajorityoffoundriesspecializeinaparticularmetalandhavefurnacesdedicatedtothesemetals.Forexample,anironfoundry(forcastiron)mayuseacupola,inductionfurnace,orEAF,whileasteelfoundrywilluseanEAForinductionfurnace.Bronzeorbrassfoundriesusecruciblefurnacesorinductionfurnaces.Mostaluminiumfoundriesuseeitherelectricresistanceorgasheatedcruciblefurnacesorreverberatoryfurnaces.

Degassing

Seealso:Hydrogengasporosity

Inthecaseofaluminiumalloys,adegassingstepisusuallynecessarytoreducetheamountofhydrogendissolvedintheliquidmetal.Ifthehydrogenconcentrationinthemeltistoohigh,theresultingcastingwillbeporousasthehydrogencomesoutofsolutionasthealuminiumcoolsandsolidifies.Porosityoftenseriouslydeterioratesthemechanicalpropertiesofthemetal.

Anefficientwayofremovinghydrogenfromthemeltistobubbleargonornitrogenthroughthemelt.Todothat,severaldifferenttypesofequipmentareusedbyfoundries.Whenthebubblesgoupinthemelt,theycatchthedissolvedhydrogenandbringittothetopsurface.Therearevarioustypesofequipmentwhichmeasuretheamountofhydrogenpresentinit.Alternatively,thedensityofthealuminiumsampleiscalculatedtocheckamountofhydrogendissolvedinit.

Incaseswhereporositystillremainspresentafterthedegassingprocess,porositysealingcanbeaccomplishedthroughaprocesscalledmetalimpregnating.

Moldmaking

Inthecastingprocessapatternismadeintheshapeofthedesiredpart.Simpledesignscanbemadeinasinglepieceorsolidpattern.Morecomplexdesignsaremadeintwoparts,calledsplitpatterns.Asplitpatternhasatoporuppersection,calledacope,andabottomorlowersectioncalledadrag.Bothsolidandsplitpatternscanhavecoresinsertedtocompletethefinalpartshape.Coresareusedtocreatehollowareasinthemoldthatwouldotherwisebeimpossibletoachieve.Wherethecopeanddragseparatesiscalledthepartingline.

Whenmakingapatternitisbesttotapertheedgessothatthepatterncanberemovedwithoutbreakingthemold.Thisiscalleddraft.Theoppositeofdraftisanundercutwherethereispartofthepatternunderthemoldmaterial,makingitimpossibletoremovethepatternwithoutdamagingthemold.

Adiagramofdraftonapattern

Adiagramofanundercutinamold

Diagramsoftwopatterntypes

Bronzepouredfromacrucibleintoamold,usingtheancientlostwaxcastingprocess

Thepatternismadeoutofwax,wood,plasticormetal.Themoldsareconstructedbyseveraldifferentprocessesdependentuponthetypeoffoundry,metaltobepoured,quantityofpartstobeproduced,sizeofthecastingandcomplexityofthecasting.Thesemoldprocessesinclude:

SandcastingGreenorresinbondedsandmold.LostfoamcastingPolystyrenepatternwithamixtureofceramicandsandmold.InvestmentcastingWaxorsimilarsacrificialpatternwithaceramicmold.CeramicmoldcastingPlastermold.VprocesscastingVacuumisusedinconjunctionwiththermoformedplastictoformsandmolds.Nomoisture,clayorresinisneededforsandtoretainshape.DiecastingMetalmold.

Billet(ingot)castingSimplemoldforproducingingotsofmetalnormallyforuseinotherfoundries.

Pouring

Inafoundry,moltenmetalispouredintomolds.Pouringcanbeaccomplishedwithgravity,oritmaybeassistedwithavacuumorpressurizedgas.Manymodernfoundriesuserobotsorautomaticpouringmachinesforpouringmoltenmetal.Traditionally,moldswerepouredbyhandusingladles.

Shakeout

Thesolidifiedmetalcomponentisthenremovedfromitsmold.Wherethemoldissandbased,thiscanbedonebyshakingortumbling.Thisfreesthecastingfromthesand,whichisstillattachedtothemetalrunnersandgateswhicharethechannelsthroughwhichthemoltenmetaltraveledtoreachthecomponentitself.

Degating

Degatingistheremovaloftheheads,runners,gates,andrisersfromthecasting.Runners,gates,andrisersmayberemovedusingcuttingtorches,bandsawsorceramiccutoffblades.Forsomemetaltypes,andwithsomegatingsystemdesigns,thesprue,runnersandgatescanberemovedbybreakingthemawayfromthecastingwithasledgehammerorspeciallydesignedknockoutmachinery.Risersmustusuallyberemovedusingacuttingmethod(seeabove)butsomenewermethodsofriserremovaluseknockoffmachinerywithspecialdesignsincorporatedintotheriserneckgeometrythatallowtherisertobreakoffattherightplace.

Thegatingsystemrequiredtoproducecastingsinamoldyieldsleftovermetal,includingheads,risersandsprue,sometimescollectivelycalledsprue,thatcanexceed50%ofthemetalrequiredtopourafullmold.Sincethismetalmustberemeltedassalvage,theyieldofaparticulargatingconfigurationbecomesanimportanteconomicconsiderationwhendesigningvariousgatingschemes,tominimizethecostofexcesssprue,andthusmeltingcosts.

Heattreating

Heattreatingisagroupofindustrialandmetalworkingprocessesusedtoalterthephysical,andsometimeschemical,propertiesofamaterial.Themostcommonapplicationismetallurgical.Heattreatmentsarealsousedinthemanufactureofmanyothermaterials,suchasglass.Heattreatmentinvolvestheuseofheatingorchilling,normallytoextremetemperatures,toachieveadesiredresultsuchashardeningorsofteningofamaterial.Heattreatmenttechniquesincludeannealing,casehardening,precipitationstrengthening,temperingandquenching.Itisnoteworthythatwhilethetermheattreatmentappliesonlytoprocesseswheretheheatingandcoolingaredoneforthespecificpurposeofalteringpropertiesintentionally,heatingandcoolingoftenoccurincidentallyduringothermanufacturingprocessessuchashotformingorwelding.

Surfacecleaning

Afterdegatingandheattreating,sandorothermoldingmediamayadheretothecasting.Toremovethisthesurfaceiscleanedusingablastingprocess.Thismeansagranularmediawillbepropelledagainstthesurfaceofthecastingtomechanicallyknockawaytheadheringsand.Themediamaybeblownwithcompressedair,ormaybehurledusingashotwheel.Themediastrikesthecastingsurfaceathighvelocitytodislodgethemoldingmedia(forexample,sand,slag)fromthecastingsurface.Numerousmaterialsmaybeusedasmedia,includingsteel,iron,othermetalalloys,aluminiumoxides,glassbeads,walnutshells,bakingpowderamongothers.Theblastingmediaisselectedtodevelopthecolorandreflectanceofthecastsurface.Termsusedtodescribethisprocessincludecleaning,beadblasting,andsandblasting.Shotpeeningmaybeusedtofurtherworkhardenandfinishthesurface.

Finishing

Thefinalstepintheprocessusuallyinvolvesgrinding,sanding,ormachiningthecomponentinordertoachievethedesireddimensionalaccuracies,physicalshapeandsurfacefinish.

Removingtheremaininggatematerial,calledagatestub,isusuallydoneusingagrinderorsanding.Theseprocessesareusedbecausetheirmaterialremovalratesareslowenoughtocontroltheamountofmaterial.Thesestepsaredonepriortoanyfinalmachining.

Aftergrinding,anysurfacesthatrequiretightdimensionalcontrolaremachined.ManycastingsaremachinedinCNCmillingcenters.Thereasonforthisisthattheseprocesseshavebetterdimensionalcapabilityandrepeatabilitythanmanycastingprocesses.However,itisnotuncommontodayformanycomponentstobeusedwithoutmachining.

Modernfoundry(about2000)

WikimediaCommonshasmediarelatedtoFoundries.

Afewfoundriesprovideotherservicesbeforeshippingcomponentstotheircustomers.Paintingcomponentstopreventcorrosionandimprovevisualappealiscommon.Somefoundrieswillassembletheircastingsintocompletemachinesorsubassemblies.Otherfoundriesweldmultiplecastingsorwroughtmetalstogethertoformafinishedproduct.[2]

Moreandmoretheprocessoffinishingacastingisbeingachievedusingroboticmachineswhicheliminatetheneedforahumantophysicallygrindorbreakpartinglines,gatingmaterialorfeeders.Theintroductionofthesemachineshasreducedinjurytoworkers,costsofconsumableswhilstalsoreducingthetimenecessarytofinishacasting.Italsoeliminatestheproblemofhumanerrorsoastoincreaserepeatabilityinthequalityofgrinding.Withachangeoftoolingthesemachinescanfinishawidevarietyofmaterialsincludingiron,bronzeandaluminium.[3]

Seealso

BellfoundingCoremakingFoundrysandtestingSmeltingInclusionsinaluminiumcastings

References1. Degarmo,E.PaulBlack,JT.Kohser,RonaldA.(2003),MaterialsandProcessesinManufacturing(9th

ed.),Wiley,ISBN0471656534,p.277.2. Beeley,Peter(2001),FoundryTechnology(2nded.),Oxford,UK:ButterworthHeinemann,ISBN9780

7506456763. Campbell,John(2003),Castings(2nded.),Oxford,UK:ButterworthHeinemann,ISBN978075064790

8

ExternallinksFreeinfosandarticlesinSpanishandEnglishofmagazineFUNDIDORES(http://metalspain.com/FUNDIDORESFoundry.html/)TheInstituteofIndianFoundrymen(http://www.indianfoundry.org/)AmericanFoundrySociety(http://www.afsinc.org/)WorldFoundryOrganization(http://www.thewfo.com/)Photographicdocumentationofthefoundingprocess(http://heroldgefrees.de/en/foundry/process)

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