金属铸造过程外文翻译Word格式.docx
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金属铸造过程外文翻译Word格式.docx
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Metal-CastingProcesses
Abstract-Followingadescriptionofthefundamentalsofsolidificationofmetalsintheprecedingchapterandtherolesoffluidflowandheattransferinmolds,wenowdescribeindetail:
●Characteristicsofexpendable-moldandpermanent-moldprocesses.
Applicationsadvantages,andlimitationsofcommoncastingprocesses.
●Castingofsinglecrystals.
●Inspectiontechniquesforcastings.
●Briefreviewoffoundriesandtheirautomation.
Typicalproductsmadebycasting:
engineblocks,crankshafts,hubcaps,powertools,turbineblades,plumbing,zipperteeth,diesandmolds,gears,railroadwheels,propellers,officeequipment,statues,andhousings.
Alternativeprocesses:
forging,powdermetallurgy,machining,andfabrication.
11.1Introduction
Thefirstmetalcastingsweremadeduringtheperiodfrom4000to3000B.C.,usingstoneandmetalmoldsforcastingcopper.Variouscastingprocesseshavebeendevelopedovertime,eachwithitsowncharacteristicsandapplications(seealsoFig.1.7a),tomeetspecificengineeringandservicerequirements(Table11.1).Alargevarietyofpartsandcomponentsaremadebycasting,suchasengineblocks,crankshafts,automotivecomponentsandpowertrains(Fig.11.1),agriculturalandrailroadequipment,pipesandplumbingfixtures,powertools,gunbarrels,fryingpans,officeequipment,andverylargecomponentsforhydraulicturbines.
Twotrendshavehadamajorimpactonthecastingindustry.Thefirstisthemechanizationandautomationofthecastingprocess,whichhasledtosignificantchangesintheuseofequipmentandlabor.Advancedmachineryandautomatedprocess-controlsystemshavereplacedtraditionalmethodsofcasting.Thesecondmajortrendhasbeentheincreasingdemandforhigh-qualitycastingswithclosedimensionaltolerances.
Thischapterisorganizedaroundthemajorclassificationsofcastingpractices(seeFig.Ⅱ.2intheIntroductiontoPartⅡ).Theseclassificationsarerelatedtomoldmaterials,moldingprocesses,andmethodsoffeedingthemoldwithmoltenmetal.
Themajorcategoriesareasfollows:
1.Expendablemolds,whichtypicallyaremadeofsand,plaster,ceramics,andsimilarmaterialsandgenerallyaremixedwithvariousbinders(bondingagents)forimprovedproperties.Atypicalsandmoldconsistsof90%sand,7%clay,and3%water.AsdescribedinChapter8,thesematerialsarerefractories(thatis,theyarecapableofwithstandingthehightemperaturesofmoltenmetals).Afterthecastinghassolidified,themoldisbrokenuptoremovethecasting.
2.Permanentmolds,whicharemadeofmetalsthatmaintaintheirstrengthathightemperatures.Asthenameimplies,theyareusedrepeatedlyandaredesignedinsuchawaythatthecastingcanberemovedeasilyandthemoldusedforthenextcasting.Metalmoldsarebetterheatconductorsthanexpendablenonmetallicmolds(seeTable3.1);
hence,thesolidifyingcastingissubjectedtoahigherrateofcooling,whichinturnaffectsthemicrostructureandgrainsizewithinthecasting.
3.Compositemolds,whicharemadeoftwoormoredifferentmaterials(suchassand,graphite,andmetal)combiningtheadvantagesofeachmaterial.Thesemoldshaveapermanentandanexpendableportionandateusedinvariouscastingprocessestoimprovemoldstrength,controlthecoolingrates,andoptimizetheoveralleconomicsofthecastingprocess.
ThegeneralcharacteristicsofsandcastingandothercastingprocessesaregiveninTable11.2.Almostallcommerciallyusedmetalscanbecast.Thesurfacefinishobtainedislargelyafunctionofthemoldmaterial;
although,asexpected,sandcastingsgenerallyhaverough,grainysurfaces.Dimensionaltolerancesgenerallyarenotasgoodasthoseinmachiningandothernet-shapeprocesses.However,intricateshapescanbemadebycasting,suchascast-ironengineblocksandverylargepropellersforoceanliners.
Becauseoftheiruniquecharacteristicsandapplications,particularlyinmanufacturingmicroelectronicdevices(PartⅤ),basiccrystal-growingtechniquesalsoaredescribedinthischapter,whichconcludeswithabriefoverviewofmodernfoundries.
11.2Expendable-MoldCastingProcesses
Themajorcategoriesofexpendable-moldcastingaresand,shellmold,plastermold,ceramicmold,evaporativepattern,andinvestmentcasting.
11.2.1Sandcasting
Thetraditionalmethodofcastingmetalsisinsandmoldsandhasbeenusedformillennia.Sandcastingisstillthemostprevalentformofcasting;
intheUnitedStatesalone,about15milliontonsofmetalarecastbythismethodeachyear.Typicalapplicationsofsandcastingincludemachinebases,largeturbineimpellers,propellers,plumbingfixtures,andnumerouscomponentsforagriculturalandrailroadequipment.ThecapabilitiesofsandcastingaregiveninTable11.2.
Basically,sandcastingconsistsof(a)placing
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