铸造和铸造过程外文文献翻译中英文翻译材料加工铸造外文翻译Word下载.docx
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外文原文
Castinganditsprocesses
Introduction
ManufacturingprocesscanbeclassifiedintotwogeneralgroupsknownasprimaryandsecondaryprocessesTheprimaryprocessesnamelycastingforgingcoldheadingcoldextrudingbrakeformingandsoonarethosethatconvertrawmaterialintoshapesTheseformingmethodsincludebothhotandcoldworkingprocessesandingeneralwillstillrequirefurtherfinishingoperationsinordertoobtainanendproduct
ThesecondaryprocessesarethosethatbringtheparttothedimensionsandsurfacefinishspecifiedOnemayalsoincludeinthesecondaryprocessessuchoperationsasheattreatingandsurfacetreatmentsforcorrosionresistancehardnessandappearanceSecondaryprocessesareplanningturningmillingdrillingboringreamingbroachinggrindinghoninglappingpolishingandspecialmethodsofmetalremovalsuchaselectrochemicalmachiningOperationslikescrewcuttingtappingthreadmillinggearcuttingandsoonaresecondaryprocessesthataremerelyadaptationsofoneoftheaforementionedprocessesthataremerelyadaptionofoneoftheaforementionedprocesses
AcompletediscussionoftheseproceduresisbeyondthescopeofthistextThereforewewillconfineourselvestosuccinctdescriptionsofthemostprominenttechniques
12Castings
CastingsareidentifiedbythetypeofmoldortheforcerequiredtoyfillthemoldMoldsareeitherpermanentorexpendableThepatternofsandshellandplastermoldshowevercanbeusedrepeatedlyformakingnewmoldsAsthemetalcoolsittakestheshapeofthecavityThebasiccastingmethodsaredescribedbelow
Sandcastings
1ThegreensandprocessisoneinwhichmostbondedsandspackedaroundawoodormetalpatternThepatternisthenremovedandmoltenmetalispouredintothecavityWhenthemetalsolidifiesthemoldisbrokenandthecastingisremovedAlmostanymetalcanbeusedwithvirtuallynolimitastothesizeorshapeofthepartThemethodpermitscastingcomplexcomponentsatalowtoolingcostandisthemostdirectroutefrompatterntocasting
SomemachiningisalwaysnecessarywiththegreensandprocessandlargecastingshaveroughsurfacefinishClosetolerancesaredifficulttoachieveandlongthinprojectionsshouldnotbecastItispossiblehowevertodesignforbossesundercutsandinsertsTheminimumcoreholediameteradvisablearealuminum31614inandtheminimumsectionthicknessesadvisablearealuminum316incooper332iniron332inmagnesium5332inandsteel1412in
2ThedrysandprocessissimilartothegreensandprocessexceptthatcoreboxesareusedinplaceofpatternsThismethodisusuallylimitedtosmallerpartsthanmethod1Thesandisbondedwithasettingbinderandthecoreisthenovenbakedat300400toremovethemoisture
3ThecarbendioxidesandprocessisoneinwhichthesandmoldsarebondedwhitsodiumsilicatesolutionsandsetbyforcingcarbondioxidegasthroughthesandThistypeofmoldisstrongandpermitstheproductionofbetterdimensionallycontrolledcastingsthaneithermethod1or2
4Thecoresandmoldprocessisonewherethemoldsareputtogethercompletelyfromovenbakedcoressetwithorganicbinderssuchasoilordextrines
ShellMoldCastingThisisaprocesswherethemoldsaremadebycoatingthesandwithathermosettingplasticThemoldisthensupportedontheoutsaidbysandorshotandmoltenmetalispouredWhenthemetalhassolidifiedthemoldisbrokenawayfromthefinishedcasting
ShellmoldingproducescastingwithsmoothsurfacesuniformgrainstructurehighdimensionalaccuracyrapidproductionrateandminimalamountoffinishingoperationsTheminimumsectionthicknisscastableis11614inbutsectiondifferenceswheretheimum–minimumratioisgreaterthan5to1shouldbeavoidedBossesundercutsandinsertsareeasilycastandtheminimumcoredholediameteris1814inThemethodisrelativelycostlyislimitedtofewmetals
Full-MoldCastingAprocessinwhichagreensandorcold-settingresinbondedispackedaroundafoamedplasticpatternforexamplepolystyreneTheplasticpatternisvaporizedwiththepouringofthemoltenmetalintothemoldAnimprovedcastingsurfacecanbeobtainedbyputtingarefractorytypeofcoatingonthepatternsurfacebeforesandpackingThepatterncanbeonepieceorseveralpiecesdependinguponthecomplexityoftheparttobecast
TheplasticpatternsarehandledeasilyTheydonotrequireanydraftandproducenoflashonthecastingForsmallquantityproductionthismethodcanbeexpensivedependinguponthesizeandcomplexityofthecastingTheminimumrecommendedsectionthicknessis01inandtheimumsectionthicknessisunlimitedBossesundercutsandinsertspresentnoprobleminthistypeofcastingTheminimumcoredholediameteris14in
PermanentMoldCastingsTheseareformedbyamoldthatcanbeusedrepeatedlySomeapplicationshavereportedasmanyas25000castingsbeingmadefromthesamemoldUsuallythemoldrequiressomeredressingafterabout3000usesThemoldsaremachinedofmetalforexamplegrayironforcastingnonferrousmetalsandcastitonsMachinedgraphitemoldsareusedtocaststeel
ThismethodproducescastingsthathaveagoodsurfacefinishaswellasagoodgrainstructurelowporosityandhighdimensionalaccuracyTheinitialmoldcostisrelativelyexpensivebutcastingsweighingaslittleasseveralouncestocastingsarelimitedtorelativelysimpleshapesandformsTheimumrecommendedsectionthicknessisabout20inTheminimumthicknesshoweverdependsuoonthematerialbeingcastasfollows316inforiton33218inforaluminum532informagnesiumand332–516inforcopperTheminimumcastableholesare31614inindiameter
DieCastingAprocessusedextensivelyinthequantityproductionofintricatelyshapedzincalumimumleadandmagnesiumalloysThemethodislimitedinusewithtinandcopperalloys
Castingsareformedbyforcingmoltenmetalunderpressuresof1500-25000psiintoanaccuratelymachinedsteeldieThesteeldiewhichiswatercooledisheldtogetherbyahydraulicpressuntilthemetalcastingssolidifiesToeasetheejectionofthecastpartsalubricantissprayedonthedieformingsurfaceandtheejectionpinsForsmalldiecastcomponentsmultiplecavitydiesareused
ThesurfacefinishoftheresultingcastingsisquitesmoothandhasexcellentdimensionalaccuracyAlthoughthecostofproductionisrelativelycheaptheinitialdiecostishighDiecastingislimitedtononferrousmetalsandbythesizeofthepartthatcanbecastTheimumwallsectionthicknessisusuallyrestrictedto316inbutcertainlytonogreaterthan050in
PlasterMoldCastingThesearemadebypouringanonferrousalloyforexamplealuminumcopperorzincalloyintoaplastermoldwhichisthenbrokentoremovethesolidifiedcastingThecastingsproducedbythisprocessaresmoothhavehighdimensionalaccuracylowporosityandcanbemadeinmanyintricateshapesThemethodhoweverhasdisadvantagesinthatislimitedtononferrousmetalssmallcastingsandalsorequiresarelativelylongtimetomakethemoldsTheminimumwallsectionthicknessis0040-0060inforacastareathatislessthan2sqinForlargercastareastheminimumwallthicknessincreasedaccordingly
TheshowprocessdevelopedwithinthelastdecadeisacostpromisingmethodItemploystheuseofplastermoldsThisprocedureproducescastingswithfinedetailandexcellentdimensionalaccuracyandsurfacefinish
CeramicMoldCastingThisprocessusesamoldmadeofaceramicpowderbinderandgellingagentThemoldcanalsobemadeofaceramicfacingreinforcedwithasandbackingThemethodisrestrictedtocastingintricatepartsrequiringfinedetailclosetolerancesandsmoothfinishesTheminimumwallthicknessrecommendedis0025-0050inThereishowevernolimittotheimumwallthickness
InvestmentCastingThesearemadewhenpartsaredesiredthatareintricateinshapehaveexcellentsurfacefinishandrequireahighdegreeofdimensionalaccuracyInadditionthismethodofcastingpermitstheuseofavarietyofmetalalloysanddoesnothaveInadditionthismethodofcastingpermitstheuseofavarietyofmetalalloysanddoesnothaveanymetalflashingtoberemovedfromthefinishescasting
ThetechniqueofinvestmentcastingrequirescarefulworkmanshipandexpensivepatternsandmothsTheminimumcastablewallthicknessisabout0025-0050inandtheimumthicknessshouldnotexceed3in
CentrifugalCastingThisisamethodofcastingashapebypoutingthemoltenmetalintoarotatingfladkcontainingthemoldThemoldsaremadeofsandmetalorgraphitedependingonthemetalcastandarerotatedabouttheiraxialcenterseitherinahorizontalorverticalposition
RelativelylargediameterandbulkycomponentsaremadearepipegunbarrelshollowshaftsmachinerydriverollslongsleevestubingandsoonWherethediametertolengthratioisratherlargetherotationalaxiscanbeverticallymountedmoldsthemethodiscalledsemmicentrifugalcastinganditisusedtomakepartssuchaswheelsturbosuperchargerdiaphragmsdisksflywheelsandsoonFigure1-5-2showsaschematicsectionofasemicentrifugalcastingofacoredflywheel
GenerallythemethodofcentrifugalcastingisexpensiveandisalsolimitedintheshapeswhichcanbecastHoweverthecastingsmadebythismehodareverysoundandhavegooddimensionalaccuracyItshouldalsobenotedthatthismethodistheonlywaytoobtainalargecylindricalpart
ContinuousCastingThisisamethodwherebyamoltenmetaliscontinuouslygravityfedfromaladleintoaningotmoldofadesiredshapewhichisopenatbothendsAs