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1、Airtraps困氣Whatisanairtrap?Anairtrapisairthatiscaughtinsidethemoldcavity.Itbecomestrappedbyconvergingpolymermeltfrontsorbecauseitfailedtoescapefromthemoldvents,ormoldinserts,whichalsoactasvents.Air-traplocationsareusuallyinareasthatfilllast.Lackofventsorundersizedventsintheselast-to
2、-fillareasareacommoncauseofairtrapsandtheresultingdefects.Anothercommoncauseisrace-tracking(thetendencyofpolymermelttoflowpreferentiallyinthickersections),causedbyalargethicknessratio.困氣是氣體存在于模具型腔內無法排出,困氣會形成氣孔是其聚集在熔體前端或未從模具排氣孔以及鑲件排出。困氣通常發生在最終填充位置。在填充末端缺少排氣孔或排氣孔太小都會引起空位造成制品缺陷。另一個較為普
3、遍的原因是跑馬場效應(聚合物熔體有優先向肉厚方向流動的趨勢),是由于壁厚突變引起的。FIGURE1.Airtraplocationsindicatedbythecomputer-predictedmelt-frontadvancements.(Toreplaytheanimation,clickReplay)ProblemscausedbyairtrapsEntrappedairwillresultinvoidsandbubblesinsidethemoldedpart,ashortshot(incompletefill),orsurfacedefectss
4、uchasblemishesorburnmarks.Toeliminateairtraps,youcanmodifythefillingpatternbyreducingtheinjectionspeed,enlargingventing,orplacingproperventinginthecavity.困氣將引起成型制品內部空位和氣泡,短射(澆不足),或表面缺陷如污痕或燒焦。可以利用改善成型條件來解決困氣問題,如減少注射速度,擴大排氣孔,或者適當位置開設排氣孔。Inthefigurebelow,anairtrapresultsfromrace-track
5、inginapartwithalargethicknessratio.Inthiscase,theentrappedaircanbeventedbychangingthethicknessratioorbyplacingavent(e.g.,viaanejectorpin)attheairtraplocation.以下的例子中,困氣是由于壁厚突變產生的跑馬場效應引起的。困氣可以由減小壁厚變化率或者適當位置開設排氣孔消除。Remedies補救措施Alterthepartdesign改變零件的設計Reducethethicknessratio.減少壁厚變化Thi
6、swillminimizetherace-trackingeffectofpolymermelt.可以減少聚合物熔體的跑馬場效應。Alterthemolddesign改變模具的設計Paycloseattentiontotheproperplacementofyourvents.密切關注開設排氣孔位置Placeventsintheareasthatfilllast.在熔體流動末端開設排氣槽Ventsaretypicallypositionedatdiscontinuitiesofmoldmaterial,suchasatpartingsurfaces,betw
7、eentheinsertandmoldwall,atejectorpins,andatmoldslides.排氣孔通常開設在模具中斷處,比如分型面、鑲件與模具間隙、頂針、滑塊等。Re-designthegateanddeliverysystem.重新設計澆口和澆注系統Changingthedeliverysystemcanalterthefillingpatterninsuchawaythatthelast-to-fillareasarelocatedattheproperventinglocations.改變澆筑系統可以改變充填形式使得流動末端布置好排氣。
8、Makesuretheventsizeislarge