铸造专业英语文选.docx
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铸造专业英语文选.docx
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铸造专业英语文选
LessononeCasting
Theword“casting”isusedtodescribeboththeprocessandthecomponentorpartthatresultswhenmoltenmetalispouredintoamold.Casting,thenistheprocessbywhichmoltenmetalistransformedinonestepintoapartacomponent.Thepartorcomponentproducediscalledacasting.
Thecastingprocessisbasicallysimple.First,acavityisformedinamold.Theshapeofthecavitydeterminestheshapeofthecasting.
Liquid(ormolten)metalispouredintothemold,thenisallowedtocoolandbecomesolid.Afterthemetalhassolidified,thecastingcanberemovedfromthemold.Theprocedurecanberepeatedforproductionofduplicateparts.Agivenshapemaybeproducedinquantitiesinthemillions.
Animportantcharacteristicofcastingisthatevenanintricatepartcanoftenbeproducedinonepiece.Asimilarpartpreparedbyweldingorboltingwouldhavetobeassembledformanypieces.
Thereareavarietyofspecifictechniquesformakingacasting,buttheyallrequireamold.Themoldsmaybeoftwokinds:
sandmoldsandmetalmolds.
Ofallcastmetals,themostcommoniscastiron.Mostcastironismeltedinacupola.Itwillmeltatapropertemperatureandwillbefluidwhenitismolten.Castironcanbemadeveryfluid,soitcanbecastintocomplicatedshapesbyusingamold.
LessonTwoPatternsforCastings
thefirststepinmakingacastingistoprepareapattern.Mostpatternsaremadeofwoodbecauseofitscheapnessandabilitytobeworkedeasily.Whenhighproductionofsandcastingsisrequired,moredurableandstrongermaterials,suchasferrousandnonferrousmetals,areemployedtomakepatterns.Brass,aluminumalloy,andmagnesiumalloypattersarerecommendedformediumandlightcastings.Ferrousalloysarefrequentlyusedforlargepatterns.Ifmetalpatternsaredecidesupon,thefirstormasterpatternsareusuallymadefromsuitablewoodand,thereafter,themetalpatternsarecastfromthesewoodpatterns.Inmakingpatterns,additionalpatternallowancesmustbeprovidedinordertoobtainsandcastingsofthedesireddimensions.
Thequalityofthefinalproductsdependsuponintelligentplanningofthepatternbythepatternmaker.Beforeapatternismade,thepatternmakermustvisualizefromtheblueprintwhatthecastingwilllooklikewhencompletedandhowitcanbebestmolded.Thispreliminaryestimateisimportant,sincethemoldingexpenseinthefoundrydependstoagreatextentonproperpatternconstruction.
Lesson3moldingsands
Sandistheprincipalbasicmoldingmaterialusedbythefoundryman,whetheritisforiron,steel,non-ferrousorlight-alloycastings.Foreverytonofironcastingsproduceditisestimatedthatonetonofsandisused.
Moldingsandsmustpossessmanyusefulproperties.Theyarefineness,plasticity,strengthorbond,permeability,refractorinessanddurability.Allnaturalmoldingsandshavethesevariousqualitiesindifferentdegrees.Thechiefconstituentsinsandsaresilicagrains,whichresisttheheat,andaluminumsilicate,orclay,whichservesasabinderandmakesmoldingpossible.Otherbindersarefrequentlypresentinnaturalsands,andartificialbindersareoftenadded.
Finenessisrequired,particularlyforgreensandwork,toensureasmoothsurfaceinthecasting.Plasticityisnecessarytoobtainacleanimpressionofthepatternorstrikle.Ingreensandmolding,thisdemandscorrectproportioningwithwater.
Strengthorbondistheabilityofthesandtoholdorbindtogether.Therearetwokindsofbond,i.e.greenbondanddriedbond.Permeabilityisameasureoftheeasewithwhichairorgascanpassthroughrammedsand.Refractorinessisrequiredtoavoidthefusingofthesandatthemouldfaceontothecasting,soastoleaveasmoothcleanskinonthecasting.Durabilityisanimportantpropertyofthesand,itrelatestotheabilityofthesandtowithstandperiodsofservice.
Lesson4Greensandmolding
Ofallthemethodsintheproductionofcastings,themostcommonisthegreensandmoldingprocess.Thegreensandmoldscanbemadebyhandormachinery.Thesandiscalledgreenbecauseitdependsonmoistureforbond.Moldingsandshavethreeprincipalingredients:
silicasandofspecifiedgrainsize,shape,anduniformity;greenbondofdesiredplasticity;andmoisture.Thesandisnotsuitableforthickcross-sections,beingreadilywashedoffbythemetalstream,buttheexpenseofdryingisavoided,greatercollapsibilityensured,andthemoldingboxesareusableseveraltimesaday.
Medium-sizedgreensandmoldsareenclosedinflasksthatconsistoftwoparts,theupperhalforcope,andthelowerhalfordrag.
Theplaneseparatingthecopeanddragiscalledpartingline.Theshapeofthedesiredcastingissimulatedbyapatternaroundwhichthemoldingsandidformed.Whenthepatternisremoved,theshapeofthemoldcavityisidenticalwiththeshapeofthepattern.Sufficienttaper,calleddraft,isplacedonthesidesofthepatterntofacilitatewithdrawalofthepatternwithoutdamagetothemoldcavity.
Theverticalpassagewaythroughwhichmoltenmetalflowsdowntothepartingplaneiscalledthesprue.Thehorizontalconnectioninthepartingplanebetweenthemoldcavityandthesprueisthegate.
Formaximumventing,thesandshouldbehighlypermeable,withopengrains,andprovidedwithplentifulvents.
Lesson5drysandmolds
Drysandmoldsareover-driedtoadepthof1/2inch,ormore.(thedriedlayerisusuallydeeperthan1/2inch,dependingonsectionthickness,andmayextendclearthroughthesection.)themoldsarebakedat300℉to700℉for8to48hours,dependingonthebindersusedinthesandmixtureandtheamountofsandsurfacetobedried,andontherequirementsoftheproductioncycles.Drysandmoldsgenerallyusedareusedinpreferencetogreensandmoldsformakingmedium-sizetolargecastings,suchaslargerolls(滚筒机,碾压机),housings(壳体,机架),gearsandmachinerycomponents.
Advantagesofdrysandmoldsare:
1.Theyarestrongerthangreensandmolds,andthusarelesssusceptibletodamageinhandling.
2.Over-alldimensionalaccuracyofthemoldisbetterthanforgreensandmolds.
3.Surfacefinishofcastingsisbetter,mainlybecausedrysandmoldsarecoatedwithawash.
Disadvantagesofdrysandmoldsare:
1.Castingsaremoresusceptibletohottears.(热纹)
2.Distortionisgreaterthanforgreensandmolds,becausethebaking.
3.Moreflaskequipmentisneededtoproducethesamenumberoffinishedpieces,becauseprocessingcyclesarelongerthanforgreensandmolds.
4.Productionisslowerthanforgreensandmolds.
Lesson6core
Ifthecastingistobeholloworhaveaholethroughit,acoremustbeused.Thecorewillbeplacedinthemold,positionedbycoreprints(芯头),andthemoltenmetalallowedtosolidifyaroundit.Theexternalshapeofthecorethusbecomestheinternalshapeofthecasting.
Coremaybemadeofmetal,plaster,andinvestmentandceramicmaterialsaswellassand.Sandcores,alongwithmolding,arethemostfrequentlyused.
Mostcoresaremadeofcore-sandmixtureconsistingofsandgrainsandorganicbinderswhichprovidegreenstrength,bakedstrengthandcollapsibility.Greenstrengthisrequiredsothatthecoresandmaybemoldedtoshape,i.e.forcore-making.Thecoreobtainsitsrealstrengthandhardnesswhenitisbakedinacoreoven.However,becausethestrengthcomesfromcoreoil,thestrengthislostandthecorebecomescollapsiblewhenhotmetalispouredaroundthecore.
Core-makingisdonemanuallyandwithmachines.Makingsmallcores,whicharemadebyhand-fillingcoreboxeswiththecoresand,usuallyisdoneatcorebenches(制芯台).Inthiscase,onlyacoreplateisrequiredasequipment.Thecoreisfilledwithcoresand,rammed,andsruckoff.Thenitistransferredtoacoreplateforbaking.
Forquantityproduction,acoreblowingmachine(吹芯机)canbeused.Atwo-partcorebox(芯盒),designedtoformthecoreinonepieceisarrangedsothatsandcanbemobbedintoitunderairpressure.
Lesson7moldingmachine
Moldingmachineshavebeendesignedtodopartoftheworkthatamolderpreviouslyhasdonebyhand.Nosatisfactoryautomaticmoldingmachinehasbeendevelopeduptothepresenttime.
Thechiefoperationsperformedbymoldingmachinesconsistoframmingthesandintothemold,rollingthemoldover,anddrawingthepattern.Rammingthesandintothemoldbyhandisaslowprocess.Thepneumatic(气动的,气体的)rammerincreasestheamountoframmingamancando.Inmoldingmachinesthewholeflaskmayberammedatonetime,orthefillingandrammingmaybeaccomplishedatonetime.
Ifnoconsiderationweretakenofthelargeincreaseinproductionpossiblebytheiruse,theimprovementinqualityofcastingsalonewouldoftentimeswarranttheirinstallation,asthedecreaseincostofmachiningcastingsproducedbythismethodpaysgooddividendsontheinvestment.Theuseofunskilledworkmenonthesemachinesisnosmallitemintheirfavor.
Severaltypesofmoldingmachineshavebeendevelopedtoramthesandintothemold.Thethreetypesoframmingmachinesthathavesurvivedarethesqueezer(压实造型机),thejarorjoltrammachine(震实造型机),andthesandslinger(抛砂机).Thesqueezerislimitedtosmall,shallowflasksthatarehandledbyhand.Thejarorjoltrammachineisbestadaptedtomoldsthatarelargerandtoodeeptosqueeze.Thesandslingerisamachinethatisusedformediumandheavywork.
Lesson8Sand-slinger
Uniformpackingofthesandinmoldsisanimportantoperationintheproductionsocastings.Toaccomplishthisoperationinasatisfactorymanner,particularlyforlargemolds,amechanicaldeviceknownasthesand-slingerhadbeendeve
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