欢迎来到人人文库网! | 帮助中心 人人文档renrendoc.com美如初恋!
人人文库网
全部分类
  • 图纸下载>
  • 教育资料>
  • 专业文献>
  • 应用文书>
  • 行业资料>
  • 生活休闲>
  • 办公材料>
  • 毕业设计>
  • ImageVerifierCode 换一换
    首页 人人文库网 > 资源分类 > PDF文档下载  

    外文翻译--热塑性塑料注射模中焊缝形成的流体分析 英文版.pdf

    • 资源ID:97465       资源大小:373.53KB        全文页数:6页
    • 资源格式: PDF        下载积分:5积分
    扫码快捷下载 游客一键下载
    会员登录下载
    微信登录下载
    三方登录下载: 微信开放平台登录 支付宝登录   QQ登录   微博登录  
    二维码
    微信扫一扫登录

    手机扫码下载

    请使用微信 或支付宝 扫码支付

    • 扫码支付后即可登录下载文档,同时代表您同意《人人文库网用户协议》

    • 扫码过程中请勿刷新、关闭本页面,否则会导致文档资源下载失败

    • 支付成功后,可再次使用当前微信或支付宝扫码免费下载本资源,无需再次付费

    账号:
    密码:
      忘记密码?
        
    友情提示
    2、PDF文件下载后,可能会被浏览器默认打开,此种情况可以点击浏览器菜单,保存网页到桌面,就可以正常下载了。
    3、本站不支持迅雷下载,请使用电脑自带的IE浏览器,或者360浏览器、谷歌浏览器下载即可。
    4、本站资源(1积分=1元)下载后的文档和图纸-无水印,预览文档经过压缩,下载后原文更清晰。
    5、试题试卷类文档,如果标题没有明确说明有答案则都视为没有答案,请知晓。

    外文翻译--热塑性塑料注射模中焊缝形成的流体分析 英文版.pdf

    IntroductionWeldlinesareformedduringmoldfillingwhenevertwoseparatedmeltstreamsrecombine.Thisoccurseitherduetoinjectionthroughmultiplegatesorasaconse-quenceofflowaroundanobstacle.Twomaintypesofweldlinesareusuallydistinguished.Coldorstagnat-ingweldlineisformedbyahead-onimpingementoftwomeltfrontswithoutadditionalflowafterthat.Hotorflowingweldlinesoccurwhentwomeltstreamscontinuetoflowaftertheirlateralmeeting.Sinceweldlinesoftenresultinreducedmechanicalstrengthsand/orpooropticalsurfaceappearanceofinjectionmoldedpartstherehavebeenagreatnumberofinvestigationsabouttheeectofprocessingcondi-tionsontheweldlines.MalguarneraandManisali(1981)measuredtheweldlinestrengthforseveraltypesofpolymersandfoundthatmeltandmoldtemperaturehadaremarkableinfluenceontheweldlinestrength.CriensandMosle´(1983)investigatedtheinfluenceofdesignandprocessingparametersonthemechanicalpropertiesofaplatewithhole.Theyrec-ognizedthattheeectofmelttemperaturechangesfrompolymertopolymer.KimandSuh(1986)haveshownthatincreasingmelttemperaturecanleadtoadeteriorationofweldlinestrengthjustbelowthedegradationtemperature.Injectionpressure,injectionspeed,holdingtimeandholdingpressurehavealsobeeninvestigatedandonlylittleeecthasbeenobserved(PiccaroloandSaiu1988).Recently,Liuetal.(2000)designedtheirexperimentsaccordingtotheTaguchiC213smethodandshowedagainthatthemeltandmoldtemperaturearetheprinciplefactorsaect-ingweldlinepropertiesofinjectionmoldedthermo-plastics.Itshouldbenotedthatthesensibilityofweldlinesdependsnotonlyonthematerialpropertiesandtheprocessingconditions,butalsoonthetestingmethodsapplied(Selde´n1997).Althoughintheliteraturemechanicalweaknessofweldlinesisusuallyexplainedby(1)lackofdiusionThamNguyen-ChungFlowanalysisoftheweldlineformationduringinjectionmoldfillingofthermoplasticsReceived:10February2003Accepted:22October2003Publishedonline:19December2003C211Springer-Verlag2003AbstractTostudytheweldlineformationofcollidingflowfrontsthefillingofamoldcavitywassim-ulated.Thethermo-rheologicalfindingswereusedtoinvestigatethesourcesofweldlineweakness.Inthiswaycriticalareasoftheinter-faceinregardtothelackofinter-diusionandtheinappropriatemolecularorientationwerefoundtobeplacednearthesurfaceofthefinishedparts.ThemainsourcefortheweldlineweaknessseemstobetheV-notchthatarisesduetothepoorlybondedregionnearthesur-faceincombinationwiththelargeshrinkageasaresultofextremelyhighmolecularorientationsinducedattheendofthefilling.Further-more,theempiricalknowledgewasconfirmedthatweldlinesarerathermoresensitivetothelocalflowsit-uationthantheglobalprocessingconditions.Meltandmoldtemper-aturescanbeconsideredtobethemostimportantfactorswhichinflu-encetheweldlinestrength.KeywordsPolymerÆInjectionmoldingÆThermoplasticsÆWeldlineÆSimulationRheolActa(2004)43:240245DOI10.1007/s00397-003-0339-2ORIGINALCONTRIBUTIONInpartpresentedatthe6thEuropeanCon-ferenceonRheology,Erlangen,2002T.Nguyen-ChungInstitutfu¨rAllgemeinenMaschinenbauundKunststotechnik,ChemnitzUniversityofTechnology,09107Chemnitz,GermanyE-mail:tham.nguyen.chungmb.tu-chemnitz.deofpolymermolecules,(2)unfavorablemolecularori-entationattheinterface,and(3)formationofaV-notchatthesurfaceofinjectionmoldedparts(KimandSuh1986;Fellahietal.1995),littlewasknownabouttheinterrelationshipbetweenthesefactors.KimandSuh(1986)analyzedthefirstandsecondfactorsseparatelyandthenintegratedthemtopredictthestrengthofweldlines.Intheirtheoreticalapproachforthediusionprocessthetemperaturegradientacrossthepartthicknesswasneglected.Tomarietal.(1990)clarifiedtheV-notchstructureanditseectonthestrengthofgeneralpurposepolystyreneinjectionmol-dings.Theymeasuredtheweldstrengthofdogbonetypetensilespecimensthesurfaceofwhichwaspar-tiallyeliminatedbymilling.TheirresultssuggestedthattheV-notcheectiscausedratherbyapoorlybondedlayernearthesurfacethanthefinegrooveonthesurface.ItisalsoworthnotingthattheV-notchmaybealsoattributedtotheairentrappedattheinterfacebetweentheflowfronts(Hagerman1973)orvolumetricshrinkageduringcooling(PiccaroloandSaiu1988).Todate,modelingoftheweldlinemainlyfocusesonpredictingtheweldlinepositionandinvestigatingtheinfluenceofthethermo-rheologicalsituationonthemeasuredweldlinestrengths.However,mostofthesimulationisbasedonthepressuredropformulation,whichdoesnotgivedetailedinformationabouttheflowsituationattheadvancingfront.Therehavebeenonlyafewpapersonsimulationoftheweldlinefor-mationconsideringthefullflowhistory.Weietal.(1987)calculatedthestresswhichaviscoelasticmeltexhibitsinaflowpastobstaclesbyassumingthatthekinematicsareclosetothoseofashear-thinningfluidsuchastheCarreaumodel.Thecalculatedvaluesofmolecularorientationshowedahighlyorientedregionsurroundingtheweldinterfacejustdownstreamoftheobstacle,whichwasverifiedbyexperimentsusingtherheo-opticalmethod.Mavridisetal.(1988)simulatedthesituationofcollidingflowfrontsforaNewtonianfluidandshowedthattheorientationofpolymermoleculesatastagnatingweldlineismainlydeter-minedbythefountainflowbeforethecollisionoccurs.Recently,Nguyen-Chungetal.(1998)investigatedtheflowmechanismsbehindanobstacleclarifyingtheinfluenceofthethermo-rheologicalhistoryofthemeltontheperformanceoftheweldline.Thepresentedpaperrepresentsanon-isothermalsimulationoftheweldlineformationduetocollisionoftwoflowfronts.Thiswaytheaforementionedsourcesoftheweldlineweaknessandtheirinterrelationshipcanbeinvesti-gatedwithregardtotheflowhistoryandthethermo-rheologicalsituation,whichasawholeenablesabetterunderstandingofthemechanismsoftheweldlineformation.SimulationSimulationhasbeencarriedoutofaviscousfluidfillingarectan-gularcavityfrombothends(Fig.1).Byconsideringthesymmetryaquarterofthecavitywasmodeledastwo-dimensionalgeometry.Neglectinggravityandsurfacetensionmeansthatthefreesurfacescanbeassumedtobeinitiallyflat,thefluidbeingatrest.Themass,momentumandenergyconservationequationsforanincompressiblefluidcanbewrittenasfollows:rC1t¼0ð1ÞqttþtC1rtC18C19¼C0rpþrC1C0sð2ÞqcpTtþtC1rTC18C19¼rC1krTðÞþC0s:_C0cð3Þwheret,t,T,p,C0s,_C0c,q,cpandkdenotetime,velocityvector,temperature,hydrostaticpressure,deviatoricstresstensor,rateofdeformationtensor,density,specificheatandheatconductivityrespectively.TheconstitutiveequationforageneralizedNewtonianfluidwasused:C0s¼2gT;_cðÞ_C0c;_C0c¼12rtþrtTðÞð4ÞwiththeviscositygivenbytheBird-Carreaumodel(Birdetal.1977):g¼g01þkc_cðÞ2hinC012;_c¼2_C0c:_C0cpð5ÞFortemperaturedependencetheArrheniusmodelwasappliedontheviscosityatareferencetemperatureT0:g_c;TðÞ¼aTgaT_c;T0ðÞ;aT¼expa1TC01T0C18C19C20C21ð6ÞFig.1Initialstate(top)andboundaryconditions(bottom)forafillingsimulationofarectangularcavity241Thefollowingboundaryconditionscompletethestatementoftheproblem:attheinletaconstantvelocityandaconstanttem-peratureofthemeltareassumed;no-slipconditionandaconstantmoldtemperatureareimposedonthewall(Table1);atthesym-metrylinessymmetryconditionsareapplied;attheflowfrontzerosurfacetractionisappliedandheattransportthroughthissurfaceisneglected.WiththecommercialcodeFIDAP(Fluent1998),theGalerkinfiniteelementmethodwasusedtosolvethecontinuity,momentum,andenergyequationswhicharediscretizedbystandardprocedures,usingamixedformulationinwhichpressureisinterpolatedoneorderlowerthanvelocityandtemperature.ThefreesurfacesaretrackedbyusingtheVOFmethodappliedonafixedmesh(HirtandNichols1981).Anadditionalequationistobesolvedtogetherwiththegoverningflowequations:FtþtC1rF¼0ð7ÞwherebyFisdefinedasamaterialdensityfunction.Ithasavalueofunityinafilledsectionoftheflowdomainandiszerooutsideofthefluid.Atthefreesurfaceitselfthisfunctionhasavaluebetween0and1.Asmaterial,polystyrene165H(suppliedbyBASF,Ludwigshafen,Germany)hasbeenused.Thethermo-rheologicalpropertiesandthecoecientsoftheviscositymodelareshowninTable2.ResultsResultswillbeshownusingthenon-dimensionalizedvariablesasfollows:vC3¼vv0;tC3¼tt0;tC3¼tt0v0;_cC3¼_cv0t0;pC3¼pv0g0T0ðÞt0ð8Þwithacharacteristiclengthv0=0.004m,acharacteristicvelocitym0=0.1m/s,andazero-shear-rateviscosityg0(T0)=3760Pas.Theflowfrontsatdierenttimes(Fig.2)showthattheweldlineisformedasexpectedfromthemiddleofthecavitytowardsthewall.InFig.3thepathlinesofselectedmaterialelementscanbeobservedwhichareoriginallypositionedontheflatflowfront.Thedistancebetweentheoriginallyflatflowfrontandtheweldlinepositionislargeenoughsothattheflowfronthasbeenfullydevelopedbeforetheweldlineisformed.Itcanbeseenthattheweldlineconsistsofthematerialelementscomingfromthecoreregionofthecavitywheretheygenerallydidnothaveexperiencedlargedeformations(Nguyen-ChungandMennig2001).Onlyduringthetransitionfromtheflattothefullydevelopedflowfrontmaydeformationsoccur,butthatisratheranexceptionduetothespecificproblemdefinition.Onthewhole,deformationsattheweldlinemustbemostlysubjectedtothelocalflowsituation.Attheinterfacethematerialelementschangetheirflowdirectionandcontinuetomovealongthethicknessdirection.Duringthesetimesinterdiusionmayoccur.Inthecorethecontacttimeabovethesolidificationtemperatureislongerthanintheouterregionsothatastrongerdegreeofinterdiusioncanbeexpectedthere.Bycontrast,inthelayernearthewall,thecontacttimeisveryshortsincethematerialelementsarrivingtherewillbefrozen-inimmediatelybeforecontactwiththeircounterpartscanbeestablished(forexamplethemate-rialelementnumbered8).ThisresultsinalayerwithpoorbondingasfoundbyTomarietal.(1990).Themolecularorientationhasbeenfrequentlyinvestigatedbytracingagreatnumberofmaterialele-mentswhicharefirstlyplacedonastraightline(Coyleetal.1987).However,inthatwayitisnotpossibletodistinguishbetweentheabsolutedeformationsthatstronglydependontheobservationtimeandtherelativedeformationsthatareameasurementformolecularorientation.Inthiswork,severalgroupsofmaterialTable1ProcessingparametersParametersValuesMelttemperatureTF503C176KMouldtemperatureTW333C176KInletvelocityv00.1m/sTable2Materialpropertiesofpolystyrene165HPropertiesValuesMeltdensityq892kg/m3Specificheatcp1968J/kgKThermalconductivityk0.14W/mKReferencetemperatureT0503C176KZero-shear-rateviscosityg0(T0)3760PasTimeconstantk0.15sPowerlawindexn0.23Arrheniuscoecienta10,842Fig.2Developmentoftheflowfronts242elementsweretraced.Eachgroupformsacircleandlocatesoriginallyonthestraightflowfront(Fig.4).Bycomparingthedeformationsofthecirclesatdierenttimestherelativedeformationsofthemeltandsothedevelopmentoftheflowinducedmolecularorientationcanbevisualized.Itshowsagainthatthehighorienta-tionattheweldlineisaresultofratherthelocaldeformationsalongtheinterfacethanofthegeneraldeformationattheflowfront.Inthepast,Mavridisetal.(1988)alsorecognizedthattherewassignificantexten-sionaldeformationatthesurfaceoftheadvancingflowfrontwhichwouldleadtoaperpendicularorientationtothewall.TheauthorspointedouttheanalogyofthecollidingflowfrontstotheplanarstagnationflowwhichwasoriginallyusedbyTadmor(1974)asamodeltodescribethefountainflow.However,inthesamepaperMavridisetal.(1988)comparedthestretchingofmaterialbandsattheflowfrontwiththoseattheweldlineandrecognizedthatthestretchingduetofountainflowismuchlargerleadingtotheassumptionthatthefountainflowmaybemostlyresponsiblefortheanisotropyatweldlinesofinjectionmoldedparts.Thisassumptionisnotquitecorrectduetothefactthatdif-ferenttrackingtimeswerecomparedtoeachother,i.e.,thematerialbandsatthefountainflowweretracedlongerthanthoseatthecollidingflowfronts.Actually,Fig.4showsthatthefountainflow,whichleadstohighdeformationsatthemoldwall(Nguyen-ChungandMennig2001)producingpronouncedmolecularorien-tationparalleltothewall,aectsonlytheregionsfarawayfromtheweldline.Asthetwoflowfrontsmeet,theextensionalongtheweldlinecanbeconsideredtobethemainsourceforthemolecularorientationperpen-diculartothewall.Furthermore,thelargestextensionratewasfoundtooccurnearthecavitysurfacejustbeforethecavityhasbeenfullyfilled(Fig.5).Inthecoretheextensionratesareatalowerlevelallthetimelikeincaseofasteady-stateplanarextensionalflow.Fig.3PathlinesofmaterialelementsoriginallypositionedonthestraightflowfrontFig.4DeformationsofcircularvolumeelementsFig.5Extensionratesalongtheweldlinejustbeforetheendoffilling243

    注意事项

    本文(外文翻译--热塑性塑料注射模中焊缝形成的流体分析 英文版.pdf)为本站会员(上***)主动上传,人人文库网仅提供信息存储空间,仅对用户上传内容的表现方式做保护处理,对上载内容本身不做任何修改或编辑。 若此文所含内容侵犯了您的版权或隐私,请立即通知人人文库网(点击联系客服),我们立即给予删除!

    温馨提示:如果因为网速或其他原因下载失败请重新下载,重复下载不扣分。




    关于我们 - 网站声明 - 网站地图 - 资源地图 - 友情链接 - 网站客服 - 联系我们

    网站客服QQ:2881952447     

    copyright@ 2020-2024  renrendoc.com 人人文库版权所有   联系电话:400-852-1180

    备案号:蜀ICP备2022000484号-2       经营许可证: 川B2-20220663       公网安备川公网安备: 51019002004831号

    本站为文档C2C交易模式,即用户上传的文档直接被用户下载,本站只是中间服务平台,本站所有文档下载所得的收益归上传人(含作者)所有。人人文库网仅提供信息存储空间,仅对用户上传内容的表现方式做保护处理,对上载内容本身不做任何修改或编辑。若文档所含内容侵犯了您的版权或隐私,请立即通知人人文库网,我们立即给予删除!