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1、SANDCASTINGMostmetalcastingsaremadebypouringmoltenmetalintoapreparedcavityandallowingittosolidify.Theprocessdatesfromantiquity.ThelargestbronzestatueinexistencetodayisthegreatSunBuddhainNara,Japan.Castintheeighthcentury,itweighs551tons(500metrictons)andismo
2、rethan71ft(21m)high.ArtisansoftheShangDynastyinChina(1766-1222B.C.)createdartworksofbronzewithdelicatefiligreeassophisticatedasanythingthatisdesignedandproducedtoday.Therearemanycastingprocessesavailabletoday,andselectingthebestonetoproduceaparticularpartde
3、pendsonseveralbasicfactors,suchascost,size,productionrate,finish,tolerance,sectionthickness,physical-mechanicalproperties,intricacyofdesign,machinability,andweldability.Sandcasting,theoldestandstillthemostwidelyusedcastingprocess,willbepresentedinmoredetail
4、thantheotherprocessessincemanyoftheconceptscarryoverintothoseprocessesaswell.GreenSandGreensandgenerallyconsistsofsilicasandandadditivescoatedbyrubbingthesandgrainstogetherwithclayuniformlywettedwithwater.Morestableandrefractorysandshavebeendeveloped,suchas
5、fusedsilica,zircon,andmullite,whichreplacelower-costsilicasandandhaveonly2%linearexpansionatferrousmetaltemperatures.Also,relativelyunstablewaterandclaybondsarebeingreplacedwithsyntheticresins,whicharemuchmorestableatelevatedtemperatures.Greensandmoldingisu
6、sedtoproduceawidevarietyofcastingsinsizesoflessthanapoundtoaslargeasseveraltons.Thisversatileprocessisapplicabletobothferrousandnonferrousmaterials.Greensandcanbeusedtoproduceintricatemoldssinceitprovidesforrapidcollapsibility;thatis,themoldismuchlessresist
7、anttothecontractionofthecastingasitsolidifiesthanareothermoldingprocesses.Thisresultsinlessstressandstraininthecasting.Thesandisrammedorcompactedaroundthepatternbyavarietyofmethods,includinghandorpneumatic-toolramming,jolting(abruptmechanicalshaking),squeez
8、ing(compressingthetopandbottommoldsurfaces),anddrivingthesandintothemoldathighvelocities(sandslinging).Sandslingersareusuallyreservedforuseinmakingverylargestingswheregreatvolumesofsandarehandled.Forsm
