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1、Airtraps困气Whatisanairtrap?Anairtrapisairthatiscaughtinsidethemoldcavity.Itbecomestrappedbyconvergingpolymermeltfrontsorbecauseitfailedtoescapefromthemoldvents,ormoldinserts,whichalsoactasvents.Air-traplocationsareusuallyinareasthatfilllast.Lackofventsorunde
2、rsizedventsintheselast-to-fillareasareacommoncauseofairtrapsandtheresultingdefects.Anothercommoncauseisrace-tracking(thetendencyofpolymermelttoflowpreferentiallyinthickersections),causedbyalargethicknessratio.困气是气体存在于模具型腔内无法排出，困气会形成气孔是其聚集在熔体前端或未从模具排气孔以及镶件排出
3、。困气通常发生在最终填充位置。在填充末端缺少排气孔或排气孔太小都会引起空位造成制品缺陷。另一个较为普遍的原因是跑马场效应（聚合物熔体有优先向肉厚方向流动的趋势），是由于壁厚突变引起的。FIGURE1.Airtraplocationsindicatedbythecomputer-predictedmelt-frontadvancements.(Toreplaytheanimation,clickReplay)ProblemscausedbyairtrapsEntrappedairwillresultinvoid
4、sandbubblesinsidethemoldedpart,ashortshot(incompletefill),orsurfacedefectssuchasblemishesorburnmarks.Toeliminateairtraps,youcanmodifythefillingpatternbyreducingtheinjectionspeed,enlargingventing,orplacingproperventinginthecavity.困气将引起成型制品内部空位和气泡，短射（浇不足），或表面
5、缺陷如污痕或烧焦。可以利用改善成型条件来解决困气问题，如减少注射速度，扩大排气孔，或者适当位置开设排气孔。Inthefigurebelow,anairtrapresultsfromrace-trackinginapartwithalargethicknessratio.Inthiscase,theentrappedaircanbeventedbychangingthethicknessratioorbyplacingavent(e.g.,viaanejectorpin)attheairtraplocation
6、.以下的例子中，困气是由于壁厚突变产生的跑马场效应引起的。困气可以由减小壁厚变化率或者适当位置开设排气孔消除。Remedies补救措施Alterthepartdesign改变零件的设计Reducethethicknessratio.减少壁厚变化Thiswillminimizetherace-trackingeffectofpolymermelt.可以减少聚合物熔体的跑马场效应。Alterthemolddesign改变模具的设计Paycloseattentiontotheproperplacementofyou
7、rvents.密切关注开设排气孔位置Placeventsintheareasthatfilllast.在熔体流动末端开设排气槽Ventsaretypicallypositionedatdiscontinuitiesofmoldmaterial,suchasatpartingsurfaces,betweentheinsertandmoldwall,atejectorpins,andatmoldslides.排气孔通常开设在模具中断处，比如分型面、镶件与模具间隙、顶针、滑块等。Re-designthegatean
8、ddeliverysystem.重新设计浇口和浇注系统Changingthedeliverysystemcanalterthefillingpatterninsuchawaythatthelast-to-fillareasarelocatedattheproperventinglocations.改变浇筑系统可以改变充填形式使得流动末端布置好排气。Makesuretheventsizeislarge
