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PartII:Metal-CastingProcessesandEquipment

金屬鑄造工藝與設(shè)備

Inthispart,someimportantandfundamentalknowledgeaboutcastingmustbe

understood.Forthischapter,weshouldknowthedifferencesofChinesemeaningsfor

theseprofessionalEnglishwords,andIwilladdresstheseimportantparts.

Forming:成型Ornament:裝飾物

Molding:造型Intricate:復(fù)雜的

Powdermetallurgy:粉末冶金Hollow:中空的

Pouring:澆注

Fig.II.1Castpartsinatypicalautomobile圖2.1一個(gè)典型的汽車中的鑄造部件

Waterpump:水泵Lettering:編字碼

Pulley:滑輪Differentialhousing:差速機(jī)殼

Grill:柵欄Transmissionhousing:變速機(jī)殼

Intakeandexhaustmanifold:進(jìn)氣和排Engineblock:汽缸體

氣管Carburetor:化油器

Diskbrake:剎車片Piston:陽模

Brakedrum:制動(dòng)鼓Alternatorhousing:同步發(fā)電機(jī)殼

Brakecylinder:閘缸

Fig.IL2.Outlineofmetal-castingprocessesdescribedinpartII.

Shell

PressureSingle-crystal

Expandablepattern

Dieturbineblades

Plaster

CentrifugalDirectional

Ceramic

Squeezesolidification

InvestmentSemisolid

鍛壓

消耗性的圖形定向凝固

離心

高聚物

擠壓

陶瓷

半凝固

圍模料

圖II.2.在第二章中所描述的金屬鑄造工藝概要

Chapter10FundamentalsofMetal-Casting

金屬鑄造基礎(chǔ)

Forthischapter,itwasdividedintotheseparts:

1.Introduction:簡介

2.Solidificationofmetals:金屬的凝固

3.Fluidflow:流體流動(dòng)

4.Fluidityofmoltenmetal:熔融金屬的流動(dòng)性

5.Heattransfer:熱傳遞

6.Defects:缺陷

First,1.Introduction

Thecastingprocessbasicallyinvolvesthreesteps:

a.pouringmoltenmetalintoamoldpatternedaftertheparttobemanufactured;（把

熔融金屬澆注到加工好的模具型腔）

b.allowingittocoolandsolidify（冷卻和凝固）

c.removingthemetalfromthemold（從模具中取出金屬）

Asweknow,thecastingistheoldestprocesstomanufacturepartoftoolinthehuman

being'shistory,becauseithasmanyadvantagescomparedwithothermanufactured

processesasfollows:

/complexshapes,suchasdifferentialhousing（差速機(jī)殼）usedintheautomobile,

crankshaft（曲軸）andsoon;

/Verylargepart,suchasenginehousingusedintheshipmaking.

/Utilizetheworkpiecesthatothermanufacturedprocessescannotproduceof

uneconomic,suchasturbineblade（渦輪機(jī)葉片）.

So,itisessentialforustounderstandthefundamentalsofmetalcastingbystudying

thisbookhard.

Therearesomeimportantconsiderationsinthecastingoperationasfollows:

令Theflowofthemoltenmetalintothemoldcavity:熔融金屬流入模具型腔,

Fluidity.

令Thecoolingandsolidificationofmetalinthemold:金屬在模具中的冷卻和凝

[SI:heattransfer:熱傳導(dǎo).

令Theinfluenceofdifferenttypeofmoldmaterials,differentheattransferring

ability,不同的模具材料具有不同的熱傳導(dǎo)能力.

Inthispart,wetalkedaboutsomeintroductionsofmetalcasting;inthenext,wewill

talkthesecondpart:solidificationofmetals.

2.Solidificationofmetals

Asweknow,fordifferentmetals,suchaspuremetalsandalloys,thesolidification

processesaredifferent,sotheywillbedividedintopuremetalandalloytobe

discusseddifferentsolidificationprocesses.

1,Puremetals

Forpuremetal,themeltingpointisconstant,so,thesolidificationislikethisone:

熔化潛熱Releaseoflatent

heatoffusion

Afterreachingmeltingpointsolidificationfrominterfaceandthen

tocenterwithdifferentgraintypeandsize

/ChillzoneEquiaxed

（a）J/Columnarzone（c）struciure

Fig.10.1Schematicillustration

ofthreecasterstructureof

metalssolidifiedinasquare

mold;a,puremetals;b,

solid-solutionalloys;c,

structuredobtainedbyusing

nucleatingagents（孕育劑）.

Chillzone:極冷區(qū)，白口區(qū)，grainsizeduetoveryhighcoolingrate.

Columnarzone:柱狀區(qū)，largegrainsizeduetolowercoolingrateandheterogeneous

nucleation.

Equiaxedzone:等軸晶區(qū)，homogeneousnucleation.

Fig.10.2.Developmentofapreferredtexture（擇優(yōu)質(zhì)構(gòu)）atacoolmoldwall.Note

thatonlyfavorablyorientedgrainsgrowawayfromthesurfaceofthemold.

Wecansee,differentmetalshavedifferentsolidifiedstructures,andthenucleation

agentsaffectit.

Fig.10.3.Schematicillustrationof

alloysolidificationandtemperature

distributioninthesolidifying

metal.Notetheformationof

dendritesinthemushyzone（多空

隙的區(qū)域）.

Ondniei

10.2.2alloys

ThesolidificationprocessofalloyscanbeschematicallyillustratedfromFig.10.3.

Fromthisfigure,wecansee,thesolidificationtakesplaceinatemperaturerange,T1

andTs.Thesolidificationprocessofthistypealloycanbeillustratedasfollow:

Chillzoneformation

RelnwTlBetweenT1andTsBelowTs

個(gè)

?Solidificationbegin>DendriteformationComplete

Forthistypedendrite,itcanbenamedascolumnardendrite,withthree-dimensional

armsandbranches.

Thestructureofdendriteinfluencesthepropertiesofcastingseriously,soitis

essentialtofindandstudytheeffectorsonitsstructure.

Asmentionedabove,thestructureofdendriteisaffectedbythemushyzone;inother

word,itcanbedescribedasdifferentmushyzoneduringsolidification,andthemushy

zonecanbenamedasfreezingrange,asthis:

n

a)當(dāng)曲

8n

Minutesafterpouring

(b)0.05-0.10%c0.25-0.30%C0.55060%C

SteelSteelSteel

SandChillChillSandChill

moldmoldmoldmoldmold

口口

522162

Minutesafterpouring

Fig.10.4(a)Solidificationpatternsforgraycastironina180mmsquarecasting.

Notethatafter11min.ofcooling,dendritesreacheachother,butthecastingisstill

mushythroughout.(b)Solidificationofcarbonsteelinsandandchill(metal)molds.

Notethedifferenceinsolidificationpatternsasthecarboncontentincreases

Freezingrange=Tl-Ts,thetemperaturedifferencebetweenT1andTsduring

solidification.

Forexample:forpuremetalsandeutecticalloys,freezingrange=0,so,nomushy

zone,nodendriteformation.

Usually,theshortfreezingrange<50°C,forexample,Fe-basealloys.

Thelongrangefreezingrang>110℃,example,AlandMg-basealloys,andthese

alloysareinamushystatethroughoutmostofsolidificationprocess.

Effectofcoolingrate

Thecastingstructureisaffectedseriouslybythecoolingrate:

Usually,fbrslowcoolingrate(<102K/s),coarsedendriteformation;

Fastercoolingrate(ontheorderof104K/s),finerdendriteformation;

Highercoolingrate(106-108K/s),amorphousformation.

Ascoolingrateincreases,thegrainsizedecreases,sostrengthandductilityenhanced,

thatishall-petchformula.

Forthesolidifiedstructure,itcanbecertifiedbytheratioofG/R,whereGisthermal

gradientattheinterfaceofliquidandsolid,andRistherateatwhichtheliquid-solid

interfacemoves.TypicalvaluesfbrGrangefrom102to103K/mandforRfrom10'3

to10-4m/s.Dendritictypestructures(Figs.5.5aandb)typicallyhaveanratiointhe

rangeof105to10',whereasratiosofIO10to1012produceaplane-front,nondendritic

liquid-solidinterface(Fig.10.6).

Fig.10.5.Schematicillustrationofthreebasictypesofcaststructures:(a)columnar

dendritic;(b)equaiaxeddendritic;and(c)equiaxednondendritic.

Fig.10.6.Schematicofcast

structuresin(a)planefront,

singlephase,and(b)planefront,

twophases.

10.2.3.structure-propertyrelationship

Allcastingsarehopedtomeetdesignandservicerequirements.Usually,theproperty

isuptostructure.Thecompositionsofdendritesandtheliquidmetalaregivenbythe

phasediagramsofparticularalloys,usuallybinaryalloys.Ascoolingrateverylow,

dendritewithuniformcompositiondevelops.Normal（fast）coolingrate,core

dendritesdevelopwithdifferentcompositionatsurfaceandcenter,knownas

concentrationgradient（濃度梯度）：highercontentofalloyingelementinthesurface

layerthanthatofcenter.Thatisduetosoluterejectionduringsolidifiedprocess,

resultinginmicrosegregation（微觀偏析）.

Macrosegregation（宏觀偏析）involvesdifferencesincompositionthroughoutthe

casting.

Normalsegregation（正常偏析）,versesegeration（反向偏析）,thereasonisthatliquid

metal（havingahigherconcentrationofalloyingelements）entersthecavities

developedfromsolidificationshrinkage（收縮）inthedendriticarmswhichsolidified

sooner.

Gravitysegregation（重力偏析）describestheprocesswherebyhigher-density

inclusions（夾雜）orcompositionssink（下沉）andlighterelements（suchasantimony

inantimony-leadalloy（睇-鉛））float（上浮）tosurface.

Inoculants（孕育劑I）inducethenucleationofthegrainsthroughouttheliquidinduced

heterogeneousnucleation.

Convectionpromotestheformationofanouterchillzone,refinesgrainsizeand

acceleratesthetransitionfromcolumnartoequiaxedgrains.

Dendritemultiplication:枝晶增殖,rheocasting:流變鑄造

Inthispart,wetalkedaboutthesolidificationprocessfordifferentmetalsandthe

property-structurerelation;next,thefluidflowwillbetalked.

10.3.Fluidflow

Thefluidflowismostimportantfactorincasting.Asshowninfig.10.7,thecasting

processisdescribedas:themoltenmetalispouredthroughapouringbasin（轉(zhuǎn)包，澆

注槽）orcup.Itthenflowsthroughthegatingsystem（澆注系統(tǒng)）（sprue,runnersand

gates,注流口，流道，內(nèi)澆道）intothemoldcavity.Sprueisaverticalchannel

throughwhichmoltenmetalflowsdownwardinthemold.Runnersarethechannels

thatcarrythemoltenmetalfromthespruetothemoldcavity,orconnectthesprueto

thegate.Thegateisthatportionoftherunnerthroughwhichthemoltenmetalenters

themoldcavity.Risers（冒口）serveasreservoirs（儲(chǔ)液槽）tosupplythemoltenmetal

necessarytopreventshrinkageduringsolidification,asshowninFig.10.7.

Fig.10.7.Schematicillustration

ofatypicalriser-gatedcasting.

Risersserveasreservoirs,

supplyingmoltenmetaltothe

castingasitshrinksduring

solidification.

Trapcontaminant:捕獲雜質(zhì)，prematurecooling:過早冷去|J,gasentrapment:夾氣

Gatingsystemdesignisthemostimportantparttogethighqualitycastings.

Twobasicprinciplesoffluidflowarerelevanttogatingdesign:Bernoulli'stheorem

andlawofmasscontinuity.

Bernoulli'stheorem:百努利定律

,pv2

h+--1=constant10.2

Pg2g

Where:

h:theelevationaboveacertainplane,p:pressureatthatelevation,v:velocityofthe

liquidatatelevation,p:thedensityofthefluid,g:gravitationalconstant.

Conservationofenergyrequiresthat,ataparticularlocation,inthissystem,the

relationshipissatisfied:

22

h.+—+—=h+—+—+f10.3

Pg2g2pg2g

Where,subscripts（下標(biāo)）1and2representtwodifferentelevations,andfrepresents

thefrictionallossintheliquidasittravelsdownwardthroughthesystem.

Continuity（連續(xù)性）

Thelawofmasscontinuity（質(zhì)量連續(xù)性）statesthatforincompressible（不可壓縮的）

liquidandinasystemwithimpermeable（不可滲透的）wall,therateofflowis

constant:

Q=4%=A2v210.4

Where

Q:therateofflow,A:thecross-sectionalareaoftheliquid,andv:theaverage

velocityoftheliquidinthatcross-sectionallocation.Thedescription1and2referto

twodifferentlocationsinthesystem.

Forexample,fbrspruedesign:—=J—10.5

A2）h2

so,theareaofthebottominthesprueissmallerthanthatoftop,thatmeanstapered

sprue（圓錐型鑄道）.

Aspiration:吸出，choke:節(jié)流口，縮頸

Recallthatinafree-fallingliquid（suchaswaterfromafaucet:水龍頭）the

cross-sectionareaofthestreamdecreasesasitgainsvelocitydownward.Ifwedesign

aspruewithaconstantcross-sectionareaandpourthemoltenmetalintoit,regions

maydevelopwheretheliquidlosscontactwiththespruewalls.Asaresultaspiration,

aprocesswherebyairissuckedinorentrappedintheliquid,maytakeplace.Onthe

otherhand,taperedspruesarenowreplacedinmanysystemsbystraight-sidedsprures

withachoketoallowthemetaltoflowsmoothly.

回想自由落下的水流（例如從水龍頭流下的水），其橫截面積隨其獲得的向下的

速度而減小。如果我們設(shè)計(jì)一個(gè)截面積不變的直澆道并向其澆注金屬液，可能會(huì)

出現(xiàn)液流接觸不到澆道壁的區(qū)域。由于有吸氣作用，在澆注過程中可能卷入空氣。

另一方面，錐形的直澆道現(xiàn)在在許多系統(tǒng)中被帶節(jié)流口的平直直澆道所取代，以

使金屬液平穩(wěn)地流動(dòng)。

Flowcharacteristics:

Animportantconsiderationinthefluidflowingatingsystemsisthepresenceof

turbulence（湍流）asopposedtothelaminarflow（層流）.WeusetheReynolds

number（雷諾系數(shù)）,Re,toquantify（定量）thisaspect（方面）offluidflow;It

representstherationtheinertia（慣性）totheviscousforces（粘滯力）influidflow,

andisdefinedas:

Re=^10.6

7

Where,v:velocity,D:diameterofthechannel;pandr|densityandviscosity（粘度）.

Re<2000,laminarflow,good;

2000~20000,mixtureoflaminarandturbulentflow,butnoharmless.

>200000,severeturbulentflow,resultinginairentrainmentandtheformationdross

（熔渣）（thescum（浮渣）thatformsonthesurfaceofthemoltenmetal）fromthe

reactionoftheliquidmetalwithairandothergases.Techniquesfbrminimizing

turbulencegenerallyinvolveavoidanceofsuddenchangesinflowdirectionandinthe

geometryofchannelcross-sectionsingatingsystemdesign.

Mitigate:緩和，減小

Skimming:擋渣

10.4Fluidityofmoltenmetal

Thecapability（能力，本領(lǐng)）ofthemoltenmetaltofillmoldcavitiesiscalledfluidity

（流動(dòng)性）;itconsists（包括）oftwobasicfactors:（1）characteristicsofthemolten

metal,and（2）castingparameters.Thefollowingcharacteristicsofmoltenmetal

influencefluidity:

a,viscosityincreasing,fluiditydecreasing;

b,surfacetension（表面張力）increasing,fluiditydecreasing;

c,inclusion（夾雜）increasing,fluiditydecreasing;

d,solidificationpatternofthealloy,freezingrangeincreasing,fluiditydecreasing.

Thefollowingcastingparametersinfluencefluidityandalsoinfluencethefluidflow

andthennalcharacteristicsofthesystem:

a.Molddesign,thedesignanddimensionsofsprue,runnerandrisersallinfluence

fluidity;

b.Moldmaterialsanditssurfacecharacteristics:thermalconductivityandsurface

roughincreasing,fluiditydecreasing;

c.Degreeofsuperheat（過熱）increasing,fluidityincreasing;

d.Rateofpouringdecreasing,fluiditydecreasing;

e.Heattransfer.Thisfactordirectlyaffectstheviscosityoftheliquidmetal.

Castabilty（可鑄，性）：theeasewithwhichametalcanbecasttoobtainapartwith

goodquality,includesnotonlyfluiditybutalsocastingparametersaswell.

10.4.1Testsforfluidity

Pouringcup

Sprue

Fig.10.8Atestmethodforfluidity

Fluidityindex

usingaspiralmold（螺旋模）.The

fluidityindex（流動(dòng)性指數(shù)）isthe

lengthofthesolidifiedmetalinthe

spiralpassage（通道，通路）.

Thegreaterthelengthofthesolidifiedmetal,thegreaterisitsfluidity.

10.5Heattransfer

Animportantconsiderationincastingistheheattransferduringthecompletecycle

frompouringtosolidificationandcoolingtoroomtemperature.Forinstance,in

castingthinsections,themetalflowratesmustbehighenoughtoavoidpremature（早

期的）chillingandsolidification.However,theflowratemustnotbesohighasto

causeexcessive（過多的）turbulencewithitsdetrimental（有害的）effectsonthe

castingprocess.

Theshapeofthecurvedependsonthethermalpropertiesofthemoltenmetalandthe

mold.

Fig.10.9Temperature

Solid-

distributionatthe

interfaceofthemoldwall

Meltingandtheliquidmetal

point

duringsolidificationof

Atmetal?mmetalsincasting.

-"interface

Room

temp.

Distance

10.5.1.Solidificationtime

Duringearlystagesofsolidification,athin,solidifiedskinbeginstoformatthecool

moldwallsand,astimepasses,theskinthickens.Withflatmoldwall,thisthickness

isproportionaltothesquarerootoftime.

Thesolidificationtimeisafunctionofthevolumeofacastinganditssurfacearea

（Chvorinovsfrule）;thatis,

Solidificationtime=C（——）210.7

surfacearea

Where,C:aconstantthatreflectsmoldmaterial,metalproperties（includelatentheat）,

andtemperature.Thatmeans,thesolidificationtimeisinverseproportionaltospecific

area.

Notethattheskinthicknessincreaseswithelapsedtime,butthattheskinisthinnerat

internalangel（內(nèi)切角）thanatexternalangels（外切角）.Thislatterconditionis

causedbyslowercoolingatinternalangelsthanatexternalangels.

B

Fig.10.10Solidifiedskin

昌onasteelcasting

5sA1minA2minA6min

Forexample,samevolumefbrsphere,cubeandcylinder,thesequenceofsurfacearea

is:sphere<cylinder<cube,sospherehasfastestsolidificationrate.

10.5.2.Shrinkage(收縮)

Shrinkageistheresultofthefollowingthreeevents:

a.contraction(收縮)ofthemoltenmetalasitcoolspriortoitssolidification;

b.contractionofthemetalduringphasechangefromliquidtosolid(latentheatof

fusion);

c.Contractionofthesolidifiedmetal(thecasting)asitstemperaturedropsto

ambienttemperature.

TABLE10.1SolidificationContractionforvariousCastMetals

MetaloralloyVolumetricMetaloralloyVolumetric

solidificationsolidification

contraction(%)contraction(%)

Aluminum6.670%Cu-30%Zn4.5

A145%Cu6.390%Cu-10%Al4

Al-12%Si3.8GrayironExpansionto2.5

Carbonsteel2.5-3Magnesium4.2

1%carbonsteel4Whiteiron4?5.5

copper4.9zinc6.5

Thelargestamountofshrinkageoccursduringcoolingofthecasting.Notethatgray

castironexpands,duetothatgraphitehasarelativelyhighspecificvolume,andwhen

itprecipitatesasgraphiteflakes（薄片，片狀的）duringsolidification,itcausesanet

expansionofthemetal.

10.6Defects

SevenbasiccategoriesofcastingdefectsnamedbytheInternationalcommitteeof

FoundryTechnicalAssociationsareshownasfollows:

A.Metallicprojection（突出,隆起），consistingoffins（毛刺）,flash（E刺），or

massiveprojectionsasswells（隆起）androughsurface（粗燥表面，鑄疵）；

B.Cavities（空洞，凹起），consistingofrounded（滾圓的）orrough（粗燥的）or

exposed（外露的）cavities,includingblow-holes（砂眼）,pinholes（弓I孔線,針孔,

氣孔），andshrinkagecavities（收縮孔），hottear（熱撕裂），exothermicpadding

（發(fā)熱貼片）.

C.Discontinuities（不連續(xù)性，間斷），suchascracks,coldorhottearing,andcold

shuts（冷疤）；

D.Defectivesurface,suchassurfacefolds（表面褶皺），laps（褶皮），scars（凍結(jié)物）,

adheringsandlayers,andoxidescale（氧化皮）；

E.Incompletecasting,suchasmisruns（鑄件不滿），insufficientvolumeofthemetal

pouredandrunout,reason:moltenmetalwithlowtemperatureorlowspeedof

pour;

F.Incorrectdimensionsorshape,owingtofactorssuchasimpropershrinkage

allowance,patternmountingerror,irregularcontraction,definedpattern,or

warpedcasting（翅曲，凹凸）；

G.Inclusion俠雜），whichformduringmelting,solidificationandmolding,spalling

（漲裂，剝落）.

HoltearHot(ear

Fig.10.11Examplesofhottears.Thesedefectsoccurbecausethecastingcannot

shrinkfreelyduringcooling,owingtoconstraintsinvariousportionsofthemoldsand

cores.Exothermic(heatproduction)compoundsmaybeused(asexothermicpadding)

tocontrolcoolingatcriticalsectiontoavoidhottearing.

Fig.10.12Examplesof

commondefectsincastings.

Thesedefectscanbe

minimizedoreliminatedby

properdesignandpreparation

ofmoldsandcontrolof

pouringprocedures.

10.6.1.Porosity(氣孑L,

Fig.10.13Varioustypesof

(a)internaland(b)

externalchills,usedin

castingstoeliminate

porositycausedby

shrinkage.Chillsare

歸國￥Vplacedinregionswhere

thereisalargervolumeof

CMImg

metal,asshownin(c).

Porosityinacastingmaybecausedbyshrinkageorgasesorboth,itdeducesthe

strengthandductilityofthecastingorevenfailed.

Porositycausedbyshrinkagecanbereducedoreliminatedbyvariousmeans.

Adequateliquidmetalshouldbeprovidedtoavoidcavitiescausedbyshrinkage.

Internalorexternalchills(冷鐵，冷模，冷卻片)，arealsoeffectivemeanstoreduce

shrinkageporosity.Thefunctionofchillsistoincreasetherateofsolidificationin

criticalregions.

Liquidmetalshavemuchgreatersolubility（溶解度）fbrgasesthandosolidmetals,as

showninFig.10.14.Whenametalbeginstosolidify,thedissolved（溶入的）gases

areexpelled（擠出）fromthesolution.Gasesmayalsoresultfromreactionsofthe

moltenmetalwiththemoldmaterials.Gaseseitheraccumulate（聚集）inregionsof

existingporosity（suchasininterdendriticregions）ortheycasemicroporosityinthe

casting,particularlyincastiron,AlandCu.

>Fig.10.14Solubilityof

三

nqhydrogen（H）inaluminum

so

U（Al）.Notethesharpdecrease

Q

ginsolubilityasthemolten

p

A

Hmetalbeginstosolidify.

Dissolvedgasesmayberemovedfromthemoltenmetalbyflushing（吹）orpurging

（吹洗）withan山e片gos（'懵'性氣體），orbymeltingandpouringthemetalinavacuum.

Ifthedissolvedgasisoxygen（O）,themoltenmetalcanbedeoxidized（脫氧）.Steelis

usuallydeoxidizedwithAl,Cu-basedalloyswithphosphoruscopper（磷銅），titanium

（Ti）,andzirconium-bearingmaterials.

Whethermicroposityisaresultofshrinkageoriscausedbygasesmaybedifficultto

determine.Iftheporosityissphericalandhassmoothwalls,itisgenerallyfromgases.

Ifthewallsareroughandangular.Porosityislikelyfromshrinkagebetweendendrites.

Gross（粗的、大的）porosity（isfromshrinkageandisusuallycalledshrinkagecavity

（收縮孔）.

SUMMARY

?Castingisasolidificationprocessinwhichmoltenmetalispouredintoamold

andallowedtocool.Themetalmayflowthroughavarietyofpassages(including

pouringbasins,sprues,risers,andgatingsystem)beforereachingthefinalmold

cavity.Bernoulli'stheorem,thecontinuitylaw,andtheReynoldsnumberarethe

analyticaltoolsusedindesign,withthegoalsofanappropriateflowrateandthe

eliminationofdefectsassociatedwithfluidflow.

鑄造是一種凝固工藝方法。這種工藝方法是將熔化的金屬澆注到鑄型中并使

之冷卻。金屬液可能流經(jīng)各種通道(包括澆口池，直流道，橫流道，冒口和

內(nèi)澆口)才達(dá)到最終型腔。利用百努利定律，連續(xù)性定理和雷諾系數(shù)作為設(shè)

計(jì)中的分析工具，以達(dá)到適當(dāng)?shù)牧魉倭髁?，消除因流體流動(dòng)性不足而引起的

缺陷。

?Solidificationofpuremetalstakesplaceataconstanttemperature;solidification

ofalloysoccursoverarangeoftemperature,dependingoncomposition.Phase

diagramsareimportanttoolsforidentifyingthesolidificationpointorpointsfor

technologicallyimportantmaterials.

純金屬在確定的溫度凝固；依賴其成分，合金的凝固是在一個(gè)溫度區(qū)間進(jìn)行

的。相圖示用于取代工藝材料凝固點(diǎn)的重要工具。

?Compositionandcoolingratesofthemeltaffectthesizeandtheshapeofgrains

anddendritesinthesolidifiedcasting.Solidificationtimeisafunctionofvolume

ofacastinganditssurfacearea(Chvorinov9srule).

金屬的成分和冷卻速率影響鑄件凝固后的晶粒和枝晶的尺寸和形狀。凝固時(shí)

間是鑄件體積和表面積的函數(shù)(契維瑞諾夫定則)。

?Thegrainstructureofcastingscanbecontrolledbyvariousmeanstoobtainthe

desiredproperties.Becausemetalscontractduringsolidificationandcooling,

cavitiescanforminthecasting.Porositycausedbygasesevolvedduring

solidificationcanbeasignificantproblem,particularlybecauseofitsadverse

effectonthemechanicalpropertiesofthecastings.Variousdefectscandevelopin

castingsfromlackofcontrolofmaterialandprocessvariables.

可以通過各種方法來對鑄件的晶粒組織進(jìn)行控制以獲得所期望的性能。由于

金屬在凝固和冷卻期間與型腔接觸，所以型腔能夠形成鑄件。凝固期間析出

的氣體引起的氣孔施工嚴(yán)重的問題，特別是對鑄件的機(jī)械性能有負(fù)面的影

響。由于缺乏對材料和工藝變量的控制，而在鑄件中形成各種缺陷。

?Althoughmostmetalsshrinkduringsolidification,graycastironandaluminum

alloysactuallyexpand.Dimensionalchangesandcracking(hottearing)and

difficultieswhichcanariseduringsolidificationandcooling.Sevenbasic

categoriesofcastingdefectshavebeenidentified.