下載本文檔
版權(quán)說(shuō)明:本文檔由用戶提供并上傳,收益歸屬內(nèi)容提供方,若內(nèi)容存在侵權(quán),請(qǐng)進(jìn)行舉報(bào)或認(rèn)領(lǐng)
文檔簡(jiǎn)介
MajorQulityIlkiiJta
Fig.1.Majorcastngqualityissuesinaluminum,grayiron,ductileiron,andsteelcastings,basedon121responsestoquestionnaire.
Castingisasolidificationprocess,whichmeansthesolidificationphenomenoncontrolsmostofthepropertiesofthecasting.Moreover,mostofthecastingdefectsoccurduringsolidification,suchasgasporosityandsolidificationshrinkage.^4
Solidificationoccursintwosteps:nucleationandcrystalgrowth.Inthenucleationstagesolidparticlesformwithintheliquid.Whentheseparticlesformtheirinternalenergyislowerthanthesurroundedliquid,whichcreatesanenergyinterfacebetweenthetwo.Theformationofthesurfaceatthisinterfacerequiresenergy,soasnucleationoccursthematerialactuallyundercools,thatisitcoolsbelowitsfreezingtemperature,becauseoftheextraenergyrequiredtoformtheinterfacesurfaces.Itthenrecalescences,orheatsbackuptoitsfreezingtemperature,forthecrystalgrowthstage.Notethatnucleationoccursonapre-existingsolidsurface,becausenotasmuchenergyisrequiredforapartialinterfacesurface,asisforacompletesphericalinterfacesurface.Thiscanbeadvantageousbecausefine-grainedcastingspossessbetterpropertiesthancoarse-grainedcastings.Afinegrainstructurecanbeinducedbygrainrefinementorinoculation,whichistheprocessofaddingimpuritiestoinducenucleation.島
Allofthenucleationsrepresentacrystal,whichgrowsastheheatoffusionisextractedfromtheliquiduntilthereisnoliquidleft.Thedirection,rate,andtypeofgrowthcanbecontrolledtomaximizethepropertiesofthecasting.Directionalsolidificationiswhenthematerialsolidifiesatoneendandproceedstosolidifytotheotherend;thisisthemostidealtypeofgraingrowthbecauseitallowsliquidmaterialtocompensateforshrinkage.^
CoreandMoldGasEvolution
Accordingtoasurveyof121productengineers,designengineers,metallurgists,laboratorypersonnel,andothersassociatedwiththedesign,production,anduseofcastings,themetalcastingindustry'sgreatestneedfoioVenpientliesineliminatingporosityincastings.Byconsensus,thisappliestoaluminum,grayiron,andductileiron,andtoalltypesofsteelcastings.ThedistributionofqualityissuesbasedonthisbroadsurveyisshowninFigure1.Concernsoverporosityratedtwiceashighasanyotherissueinthesurvey.
OneresearcheraddressingthisconcernisLeonardWinardi,aPh.D.candidateattheUniversityofAlabama-Birmingham.Hehasdevelopedthreetechniquesfordetermininggaspressureinmolds:insertingaprobeattachedtoapressuretransducerincores;immersingsamplesinmoltenmetaltovariousdepths,dependingonthecalculatedgaspressureinthemoldorcore;andobservingwhetherornotbubblesareejected,andobservinggasevolutionfromcoresduringpouringinareal-timeX-rayunit.Anyorallofthesethreetechniquesmaybeusedtodeterminepeakpressures,atleastinsimplecores.
Winardimeasuredthevolumeandrateofgasevolutionfromacoreproducedinacommercialfoundry,andcalculatedthepressureinsidethecoreasafunctionoftime(seeFig.2).Thebinderbeingusedproducedtwogas-evolutionpeakswhichresultedintwogas-pressurepeaks.Thepeakcalculatedpressurewasalmostidenticaltothepeakmeasuredpressure.Furtherimprovementsintheshapeofthepressurecurvesmaybeobtainedwhenmoreaccurateinformationonthecompositionofthegasesproducedisobtained.
Flore4.
Nucleationistheextremelylocalizedbuddingofadistinctthermodynamicphase.Someexamplesofphasesthatmayformvianucleationinliquidsaregaseousbubbles,crystals,orglassyregions.Creationofliquiddropletsinsaturatedvaporisalsocharacterizedbynucleation(seeCloudcondensationnuclei).Nucleationofcrystalline,amorphous,andevenvacancyclustersinsolidmaterialsisalsoimportant,forexampletothesemiconductorindustry.Mostnucleationprocessesarephysical,ratherthanchemical,butfewexceptionsdoexist(e.g.electrochemicalnucleation).AgoodexamplewouldbethefamousDietCokeandMentoseruption.Nucleationnormallyoccursatnucleationsitesonsurfacescontactingtheliquidorvapor.Suspendedparticlesorminutebubblesalsoprovidenucleationsites.
Thisiscalledheterogeneousnucleation.Nucleationwithoutpreferentialnucleationsitesishomogeneousnucleation.Homogeneousnucleationoccursspontaneouslyandrandomly,butitrequiressuperheatingorsupercoolingofthemedium.Nucleationisinvolvedinsuchprocessesascloudseedingandininstrumentssuchasthebubblechamberandthecloudchamber.
Homogeneousnucleation
Nucleationgenerallyoccurswithmuchmoredifficultyintheinteriorofauniformsubstance,byaprocesscalledhomogeneousnucleati.oTnhecreationofanucleusimpliestheformationofaninterfaceattheboundariesofanewphase.
Heterogeneousnucleation
Heterogeneousnucleationoccursmuchmoreoftenthanhomogeneousnucleation.Itformsatpreferentialsitessuchasphaseboundariesorimpuritieslikedustandrequireslessenergytothanhomogeneousnucleation.Atsuchpreferentialsites,theeffectivesurfaceenergyislower,thusdiminishedthefreeenergybarrierandfacilitatingnucleation.
Segregationincastings
Whencastinganalloy,segregationoccurs,wherebytheconcentrationofsoluteisnotconstantthroughoutthecasting.Thiscanbecausedbyavarietyofprocesses,whichcanbeclassifiedintotwotypes:
Microsegregation;whichoccursoverdistancescomparabletothesizeofthedendritearmspacing.Thisoccursasaresultofthefirstsolidformedbeingofalowerconcentrationthanthefinalequilibriumconcentration,resultinginpartitioningoftheexcesssoluteintotheliquid,sothatsolidformedlaterhasahigherconcentration.MoreaboutmicrosegregationcanbefoundintheTLPonSolidificationofalloys.
Die-castingissimilartopermanentmoldcastingexceptthatthemetalisinjectedintothemoldunderhighpressureof10-210Mpa(1,450-30,500)psi.Thisresultsinamoreuniformpart,generallygoodsurfacefinishandgooddimensionalaccuracy,asgoodas0.2%ofcastingdimension.Formanyparts,post-machiningcanbetotallyeliminated,orverylightmachiningmayberequiredtobringdimensionstosize.
Die-castingcanbedoneusingacoldchamberorhotchamberprocess.
Aluminum,ZincandCopperalloysarethematerialspredominantlyusedindiecasting.Ontheotherhand,pureAluminumisrarelycastduetohighshrinkage,andsusceptibilitytohotcracking.ItisalloyedwithSilicon,whichincreasesmeltfluidity,reducesmachinability.Copperisanotheralloyingelement,whichincreaseshardness,reducesductility,andreducescorrosionresistance.
Aluminumiscastatatemperatureof650°C(1200°F).ItisalloyedwithSilicon9%andCopperabout3.5%toformtheAluminumAssociation380alloy(UNSA03800).Siliconincreasesthemeltfluidity,reducesmachinability,Copperincreaseshardnessandreducestheductility.BygreatlyreducingtheamountofCopper(lessthan0.6%)thechemicalresistanceisimproved;thus,AA360(UNSA03600)isformulatedforuseinmarineenvironments.Ahighsiliconalloyisusedinautomotiveenginesforcylindercastings,AA390(UNSA03900)with17%Siliconforhighwearresistance.Commonaluminumalloysfordiecastingaresummarizedasfollows:
Material
Silicon
Copper
TensileStrengthMPa(ksi)
Properties
AA380
8.5%
3.5%
324
Faireasytofill
(UNSA03800)
(47)
AA384
11%
4%
331
Easytofill
(UNSA03840)
(48)
AA386
9.5%
0.6%
317
Goodcorrosionresistanee
(UNSA03860)
(46)
AA390
17%
4.5%
283
Goodwearresistanee
(UNSA03900)
(41)
ZinccanbemadetoclosetolerancesandwiththinnerwallsthanAluminum,duetoitshighmeltfluidity.ZincisalloyedwithAluminum(4%),whichaddsstrengthandhardness.Thecastingisdoneatafairlylowtemperatureof425°C(800°F)sothepartdoesnothavetocoolmuchbeforeitcanbeejectedfromthedie.This,incombinationwiththefactthatZinccanberunusingahotchamberprocessallowsforafastfill,fastcooling(andejection)andashortcycletime.Zincalloysareusedinmakingprecisionpartssuchassprockets,gears,andconnectorhousings.
Copperalloysareusedinplumbing,electricalandmarineapplicationswherecorrosionandwearresistanceisimportant.
Minimumwallthicknessesan
溫馨提示
- 1. 本站所有資源如無(wú)特殊說(shuō)明,都需要本地電腦安裝OFFICE2007和PDF閱讀器。圖紙軟件為CAD,CAXA,PROE,UG,SolidWorks等.壓縮文件請(qǐng)下載最新的WinRAR軟件解壓。
- 2. 本站的文檔不包含任何第三方提供的附件圖紙等,如果需要附件,請(qǐng)聯(lián)系上傳者。文件的所有權(quán)益歸上傳用戶所有。
- 3. 本站RAR壓縮包中若帶圖紙,網(wǎng)頁(yè)內(nèi)容里面會(huì)有圖紙預(yù)覽,若沒(méi)有圖紙預(yù)覽就沒(méi)有圖紙。
- 4. 未經(jīng)權(quán)益所有人同意不得將文件中的內(nèi)容挪作商業(yè)或盈利用途。
- 5. 人人文庫(kù)網(wǎng)僅提供信息存儲(chǔ)空間,僅對(duì)用戶上傳內(nèi)容的表現(xiàn)方式做保護(hù)處理,對(duì)用戶上傳分享的文檔內(nèi)容本身不做任何修改或編輯,并不能對(duì)任何下載內(nèi)容負(fù)責(zé)。
- 6. 下載文件中如有侵權(quán)或不適當(dāng)內(nèi)容,請(qǐng)與我們聯(lián)系,我們立即糾正。
- 7. 本站不保證下載資源的準(zhǔn)確性、安全性和完整性, 同時(shí)也不承擔(dān)用戶因使用這些下載資源對(duì)自己和他人造成任何形式的傷害或損失。
最新文檔
- 2024屆湖南省永州市高三第二次模擬考試化學(xué)試卷
- 多重困境長(zhǎng)者幫扶個(gè)案服務(wù)項(xiàng)目“關(guān)愛(ài)困境家庭社工案例計(jì)劃”
- 2.1 設(shè)計(jì)的創(chuàng)造性思維和工程思維 課件高中技術(shù)粵科版(2019)必修 技術(shù)與設(shè)計(jì)1
- 早發(fā)性卵巢功能不全的臨床診療-
- 村生態(tài)農(nóng)業(yè)綜合科技園區(qū)開(kāi)發(fā)項(xiàng)目實(shí)施方案
- 八年級(jí)教學(xué)計(jì)劃
- 2024年CPA注冊(cè)會(huì)計(jì)師考試稅法必考重要知識(shí)點(diǎn)全套復(fù)習(xí)匯編
- 餐飲員工試用期總結(jié)5篇
- 部門(mén)月度的工作總結(jié)
- 軟件開(kāi)發(fā)技術(shù)基礎(chǔ) 第4版 課件 2.查找和排序
- 割蘆葦施工方案
- 監(jiān)理部質(zhì)量評(píng)估報(bào)告
- 柔性電子技術(shù)方案
- 贛南師范大學(xué)外國(guó)語(yǔ)學(xué)院《621綜合英語(yǔ)(含英漢互譯)》歷年考研真題及詳解
- 籃球比賽分組循環(huán)積分表
- 高中英語(yǔ)詞匯3500詞(必背)-excel版
- 博物館陳列布展互動(dòng)多媒體軟件設(shè)計(jì)開(kāi)發(fā)技術(shù)方案框架
- 《13875界面設(shè)計(jì)》自考復(fù)習(xí)必備試題庫(kù)(含答案)
- 游戲綜合YY頻道設(shè)計(jì)模板
- 2022湖北國(guó)際物流機(jī)場(chǎng)限公司招聘【105人】上岸筆試歷年難、易錯(cuò)點(diǎn)考題附帶參考答案與詳解
- 特殊的比較級(jí)最高級(jí)單詞歸納匯總表格(較全)
評(píng)論
0/150
提交評(píng)論