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《模具专业英语 第2版 教学课件 作者 王浩钢 曹艳清 18192模具专业英语电子教案.ppt》由会员上传分享，免费在线阅读，更多相关内容在应用文档-天天文库。
1、Lesson1TheInjectionMoldingandMachin1.TheinjectionmoldingInjectionmoldingisprincipallyusedfortheproductionofthethermoplasticparts,althoughsomeprogresshasbeenmadeindevelopingamethodforinjectionmoldingsomethermosettingmaterials.Theproblemofinjectingameltedplasti
2、cintoamoldcavityfromareservoirofmeltedmaterialhasbeenextremelydifficulttosolveforthermosettingplasticswhichcureandhardenundersuchconditionswithinafewminutes①.Theprincipleofinjectionmoldingisquitesimilartothatofdie-casting.Theprocessconsistsoffeedingaplasticco
3、mpoundinpowderedorgranularformfromahopperthroughmeteringandmeltingstagesandtheninjectingitintoamold②.Afterabriefcoolingperiod,themoldisopenedandthesolidifiedpartejected.Injection-moldingmachinescanbearrangedformanualoperation,automaticsingle-cycleoperation,an
4、dfullautomaticoperation.Theadvantageofinjectionmoldingare:(i)ahighmoldingspeedadaptedformassproductionispossible;(ii)thereisawidechoiceofthermoplasticmaterialsprovidingavarietyofusefulproperties;(iii)itispossibletomoldthreads,undercuts,sideholes,andlargethins
5、ections.2.Theinjection-moldingmachineSeveralmethodsareusedtoforceorinjectthemeltedplasticintothemold.Themostcommonlyusedsysteminthelargermachinesisthein-linereciprocatingscrew,asshowninFigure1-1.Thescrewactsasacombinationinjectionandplasticizingunit.Astheplas
6、ticisfedtotherotatingscrew,itpassesthroughthreezonesasshown:feed,compression,andmetering.Afterthefeedzone,thescrew-flightdepthisgraduallyreduced,forcingtheplastictocompress.Theworkisconvertedtoheatbyshearingtheplastic,makingitasemifluidmass.Inthemeteringzone,
7、additionalheatisappliedbyconductionfromthebarrelsurface.Asthechamberinfrontofthescrewbecomesfilled,itforcesthescrewback,trippingalimitswitchthatactivatesahydrauliccylinderthatforcesthescrewforwardandinjectsthefluidplasticintotheclosedmold③.Anantiflowbackvalve
8、preventsplasticunderpressurefromescapingbackintothescrewflights.Theclampingforcethatamachineiscapableofexertingispartofthesizedesignationandismeasuredintons.Arule-of-thumbcanbeusedtodeter
