机械制造专业英语第7章SAND CASTING砂型铸造.docx
- 文档编号:10298202
- 上传时间:2023-02-09
- 格式:DOCX
- 页数:10
- 大小:153.33KB
机械制造专业英语第7章SAND CASTING砂型铸造.docx
《机械制造专业英语第7章SAND CASTING砂型铸造.docx》由会员分享,可在线阅读,更多相关《机械制造专业英语第7章SAND CASTING砂型铸造.docx(10页珍藏版)》请在冰豆网上搜索。
机械制造专业英语第7章SANDCASTING砂型铸造
SANDCASTING
Mostmetalcastingsaremadebypouringmoltenmetalintoapreparedcavityandallowingittosolidify.Theprocessdatesfromantiquity.ThelargestbronzestatueinexistencetodayisthegreatSunBuddhainNara,Japan.Castintheeighthcentury,itweighs551tons(500metrictons)andismorethan71ft(21m)high.ArtisansoftheShangDynastyinChina(1766-1222B.C.)createdartworksofbronzewithdelicatefiligreeassophisticatedasanythingthatisdesignedandproducedtoday.
Therearemanycastingprocessesavailabletoday,andselectingthebestonetoproduceaparticularpartdependsonseveralbasicfactors,suchascost,size,productionrate,finish,tolerance,sectionthickness,physical-mechanicalproperties,intricacyofdesign,machinability,andweldability.
Sandcasting,theoldestandstillthemostwidelyusedcastingprocess,willbepresentedinmoredetailthantheotherprocessessincemanyoftheconceptscarryoverintothoseprocessesaswell.
GreenSand
Greensandgenerallyconsistsofsilicasandandadditivescoatedbyrubbingthesandgrainstogetherwithclayuniformlywettedwithwater.Morestableandrefractorysandshavebeendeveloped,suchasfusedsilica,zircon,andmullite,whichreplacelower-costsilicasandandhaveonly2%linearexpansionatferrousmetaltemperatures.Also,relativelyunstablewaterandclaybondsarebeingreplacedwithsyntheticresins,whicharemuchmorestableatelevatedtemperatures.
Greensandmoldingisusedtoproduceawidevarietyofcastingsinsizesoflessthanapoundtoaslargeasseveraltons.Thisversatileprocessisapplicabletobothferrousandnonferrousmaterials.
Greensandcanbeusedtoproduceintricatemoldssinceitprovidesforrapidcollapsibility;thatis,themoldismuchlessresistanttothecontractionofthecastingasitsolidifiesthanareothermoldingprocesses.Thisresultsinlessstressandstraininthecasting.
Thesandisrammedorcompactedaroundthepatternbyavarietyofmethods,includinghandorpneumatic-toolramming,jolting(abruptmechanicalshaking),squeezing(compressingthetopandbottommoldsurfaces),anddrivingthesandintothemoldathighvelocities(sandslinging).Sandslingersareusuallyreservedforuseinmakingverylargestingswheregreatvolumesofsandarehandled.
Forsmallercastings,atwo-partmetalboxorflaskreferredtoasacopeanddragisused.Firstthepatternispositionedonamoldboard,andthedragorlowerhalfoftheflaskispositionedoverit.Partingpowderissprinkledonthepatternandtheboxisfilledwithsand.Ajoltsqueezemachinequicklycompactsthesand.Theflaskisthenturnedoverandagainpartingpowderisdustedonit.Thecopeisthenpositionedonthetophalfoftheflaskandisfilledwithsand,andthetwo-partmoldwiththepatternboardsandwichedinbetweenissqueezed.
Patterns
Patternsforsandcastinghavetraditionallybeenmadeofwoodormetal.However,ithasbeenfoundthatwoodpatternschangeasmuchas3%duetoheatandmoisture.Thisfactoralonewouldputmanycastingsoutofacceptabletoleranceformoreexactingspecifications.Now,patternsareoftenmadefromepoxiesandfromcold-settingrubberwithstabilizinginserts.Patternsofsimpledesign,withoneormoreflatsurface,canbemoldedinonepiece,providedthattheycanbewithdrawnwithoutdisturbingthecompactedsand.Otherpatternsmaybesplitintotwoormorepartstofacilitatetheirremovalfromthesandwhenusingtwo-partflasks.Thepatternmustbetaperedtopermiteasyremovalfromthesand.Thetaperisreferredtoasdraft.Whenapartdoesnothavesomenaturaldraft,itmustbeadded.Amorerecentinnovationinpatternsforsandcastinghasbeentomakethemoutoffoamedpolystyrenethatisvaporizedbythemoltenmetal.Thistypeofcasting,knownasthefull-moldprocess,doesnotrequirepatterndraft.
Sprues,Runners,andGates.
Accesstothemoldcavityforentryofthemoltenmetalisprovidedbysprues,runners,andgates,asshowninFig.7-1.Apouringbasincanbecarvedinthesandatthetopofthesprue,orapourbox,whichprovidesalargeopening,maybelaidoverthespruetofacilitatepouring.Afterthemetalispoured,itcoolsmostrapidlyinthesandmold.Thustheoutersurfaceformsashellthatpermitsthestillmoltenmetalnearthecentertoflowtowardit.Asaresult,thelastportionofthecastingtofreezewillbedeficientinmetaland,intheabsenceofasupplementalmetal-feedsource,willresultinsomeformofshrinkage.Thisshrinkagemaytaketheformoflshrinkage(largecavities)orthemoresubtlemicroshrinkage(finelydispersedporosity).Theseporousspotscanbeavoidedbytheuseofrisers,asshowninFig.7-1,whichProvidemoltenmetaltomakeupforshrinkagelosses.
Fig.7-1Sectionalviewofacastingmold
Cores
Coresareplacedinmoldswhereveritisnecessarytopreservethespaceitoccupiesinthemoldasavoidintheresultingcastings.AsshowninFig.7-11thecorewillbeputinplaceafterthepatternisremoved.Toensureitsproperlocation,thepatternhasextensionsknownascoreprintsthatleavecavitiesinthemoldintowhichthecoreisseated.Sometimesthecoremaybemoldedintegrallywiththegreensandandisthenreferredtoasagreen-sandcore.Generally,thecoreismadeofsandbondedwithcoreoil,someorganicbondingmaterials,andwater.Thesematerialsarethoroughlyblendedandplacedinamoldorcorebox.Afterforming,theyareremovedandbakedat350°to450°F(177°to232°C).Coresthatconsistoftwoormorepartsarepastedtogetherafterbaking.
CO2Cores
CO2coresaremadebyrammingupmoistsandinacorebox.Sodiumsilicateisusedasabinder,whichisquicklyhardenedbyblowingCO2gasoverit.TheCO2systemhastheadvantageofmakingthecoresimmediatelyavailable.
PouringtheMetal
Severaltypesofcontainersareusedtomovethemoltenmetalfromthefurnacetothepouringarea.Largecastingsofthefloor-and-pittypearepouredwithaladlethathasapluginthebottom,or,asitiscalled,abottom-pouringladle.Itisalsoemployedinmechanizedoperationswherethemoldsaremovedalongalineandeachispouredasitismomentarilystoppedbeneaththelargebottom-pourladle.
Ladlesusedforpouringferrousmetalsarelinedwithahighalumina-contentrefractory.Afterlonguseandoxidation,itcanbebrokenoutandreplaced.Ladlesusedinhandlingferrousmetalsmustbepreheatedwithgasflamestoapproximately2600°to2700°F(1427°to1482°C)beforefilling.Oncetheladleisfilled,itisusedconstantlyuntilithasbeenemptied.
Fornonferrousmetals,simpleclay-graphitecruciblesareused.Whiletheyarequitesusceptiblebreakage,theyareveryresistanttothemetalandwillholdupalongtimeundernormalconditions.Theyusuallydonotrequirepreheating,althoughcaremustbetakentoavoidmoisturepickup.Forthisreasontheyaresometimesbakedouttoassuredryness.
Thepouringprocessmustbecarefullycontrolled,sincethetemperatureofthemeltgreatlyaffectsthedegreeofliquidcontractionbeforesolidification,therateofsolidification,whichinturnaffectstheamountofcolumnargrowthpresentatthemoldwall,theextentandnatureofthedendriticgrowth,thedegreeofalloyburnout,andthefeedingcharacteristicsoftheriseringsystem.
FinishingOperations
Afterthecastingshavesolidifiedandcooledsomewhat,theyareplacedonashakeouttableorgratingonwhichthesandmoldisbrokenup,leavingthecastingfreetobepickedout.Thecastingisthentakentothefinishingroomwherethegatesandrisersareremoved.Smallgatesandrisersmaybebrokenoffwithahammerifthematerialisbrittle.Largeronesrequiresawing,cuttingwithatorch,orshearing.Unwantedmetalprotrusionssuchasfins,bosses,andsmallportionsofgatesandrisersneedtobesmoothedofftoblendwiththesurface.Mostofthisworkisdonewithaheavy-dutygrinderandtheprocessisknownassnaggingorsnaggrinding.Onlargecastingsitiseasiertomovethegrinderthanthework,soswing-typegrindersareused.Smallercastingsarebroughttostand-orbench-typegrinders.Handandpneumaticchiselsarealsousedtotrimcastings.Amorerecentmethodofremovingexcessmetalfromferrouscastingsiswithacarbon-airtorch.Thisconsistsofacarbonrodandhigh-amperagecurrentwithastreamofcompressedairblowingatthebaseofit.Thisoxidizesandremovesthemetalassoonasitismolten.Inmanyfoundriesthismethodhasreplacednearlyallchippingandgrindingoperations.
NewWords
castingn.铸造,铸件
cavityn.空腔,型腔
solidifyvt.凝固
antiquityn.古代
Buddhan.佛
Naran.奈良市
artisann.工匠
filigreen.精细之作
finishn.光洁度
tolerancen.公差
intricacyn.复杂
machinabilityn.(可)切削性
weldabilityn.(可)焊接性
silican.石英
additiven.添加剂
clayn.粘土
refractorya.难熔的,耐火的
fusevt.使熔化
zirconn.锆石
mulliten.富铝红柱石
ferrousa.铁的
resinn.树脂,松香
moldingn.铸型,造型
versatilea.多用途的
nonferrousa.非铁的
intricatea.复杂的
collapsibilityn.退让性
contractionn.收缩
ramvt.夯实
patternn.模型,木模
pneumatica.气动的
joltvi.振动,摇动
slingn.抛(砂)
flaskn.砂箱
copen.上砂箱
dragn.下砂箱
sprinklevt.撒
epoxyn.环氧树脂(胶)
tapern.锥度,起模斜度
draftn.起模斜度
foameda.泡沫的
polystyrenen.聚苯乙烯
spruen.直浇口
runnern.内浇口,横浇口
basinn.浇口杯
deficienta.不足的,缺乏的
shrinkagen.收缩
subtlea.细微的
porosityn.多孔,缩松
porousa.多孔的
voidn.空间
integrallyad.整体地
organica.有机的
bondingn.粘结剂
sodiumn.钠
silicaten.硅酸盐
plugn.塞
ladlen.浇勺,铁水包
aluminan.氧化铝
linev.做内衬
susceptiblea.容易的
columnara.柱状的
dendritica.树枝状的
burnoutn.熔蚀
riseringn.冒口
protrusionn.凸出物
finn.周缘翅边
bossn.表面凸出部分
snagn.毛刺,凸出物;vt.清除
- 配套讲稿:
如PPT文件的首页显示word图标,表示该PPT已包含配套word讲稿。双击word图标可打开word文档。
- 特殊限制:
部分文档作品中含有的国旗、国徽等图片,仅作为作品整体效果示例展示,禁止商用。设计者仅对作品中独创性部分享有著作权。
- 关 键 词:
- 机械制造专业英语第7章SAND CASTING砂型铸造 机械制造 专业 英语 SAND CASTING 砂型 铸造