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ID:10723822
大小:55.50 KB
页数:11页
时间:2018-07-07
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1、附录附录1SandCastingThefirststageintheproductionofsandcastingsmustbethedesignandmanufactureofasuitablepattern.Castingpatternsaregenerallymadefromhardwordandthepatternhastobemadelargerthanthefinishedcastingsizetoallowfortheshrinkagethattakesplaceduringsolidi
2、ficationandcooling.Theextentofthisshrinkagevarieswiththetypeofmetaloralloytobecast.Forallbutthesimplestshapesthepatternwillbemadeintwoormorepiecestofacilitatemoulding.Ifahollowcastingistobemadethepatterndesignwillincludeextensionpiecessothatspacestoacce
3、ptthesandcorearemouldedintosand.Theseadditionalspacesinthemouldaretermedcoreprints.Sandmouldsfortheproductionofsmallandmedium-sizedcastingsaremadeinamouldingbox.Themouldismadeintwoormorepartsinorderthatthepatternmayberemoved.Thedraghalfofthemouldboxispl
4、acedonaflatfirmboardandthedraghalfofthepatternplacedinposition.Facingsandissprinkledoverthepatternandthenthemouldboxisfilledwithmouldingsand.Thesandisrammedfirmlyaroundthepattern.Thisprocessoffillingandrammingmaybedonebyhandbutmouldproductionisautomated
5、inalargefoundrywiththemouldboxesmovingalongaconveyor,firstlytobefilledwithsandfromhoppersandthentopassundermechanicalhammersforramming.Whenrammingofthesandiscomplete,excesssandisremovedtoleaveasmoothsurfaceflushwiththeedgesofthemouldingbox.Thecompletedd
6、ragisnowturnedoverandtheupper,orcope,portionofthemouldingboxpositionedoverit.Thecopehalfofthepatternisplacedinposition,correctalignmentbeingensuredbymeansofsmalldowelpins.Patternsforthenecessaryfeeder,runnerandrisersarealsoplacedsoastogiveanevendistribu
7、tionofmetalintothemouldcavity.Therisersshouldcoincidewiththehighestreadilyescapefromthemould.Thesizesofrisersshouldbesuchthatthemetalinthemdoesnotfreezetoorapidly.Animportantfunctionofariseristoactasreservoirofliquidmetaltofeedsolidificationwithinthemou
8、ld.Athincoatingofdrypartingsandissprinkledintomouldatthisstage.Thisistopreventthecopeanddragstickingtogetherwhenthecopehalfismoulded.Thecopeisnowfilledwithmouldingsandandthisisrammedfirmlyintoshapeinthesamemannerasinthemakingofth
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