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1、Air traps 困氣What is an air trap？ An air trap is air that is caught inside the mold cavity。 It becomes trapped by converging polymer melt fronts or because it failed to escape from the mold vents, or mold inserts， which also act as vents。 Airtrap locations are usually in areas that fill last. Lack of
2、 vents or undersized vents in these lastto-fill areas are a common cause of air traps and the resulting defects。 Another common cause is racetracking (the tendency of polymer melt to flow preferentially in thicker sections）, caused by a large thickness ratio。 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
3、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。FIGURE 1. Air trap locations indicated by the computer-predicted meltfront advancements。 （To replay the animation， click Replay) Problems caused by air traps Entrapped air will result in voids and bub
4、bles inside the molded part, a short shot (incomplete fill）, or surface defects such as blemishes or burn marks。 To eliminate air traps， you can modify the filling pattern by reducing the injection speed， enlarging venting, or placing proper venting in the cavity. 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
5、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.In the figure below， an air trap results from racetracking in a part with a large thickness ratio。 In this case, the entrapped air can be vented by changing the thickness ratio or by placing a vent (e.g.， via an ejector pin） at the air trap location。以下的例
6、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Alter the part design改變零件的設計Reduce the thickness ratio。減少壁厚變化This will minimize the racetracking effect of polymer melt。可以減少聚合物熔體的跑馬場效應。Alter the mold design改變模具的設計Pay close attention to the proper placement of your vents。密切關注開設排氣孔位置Plac
7、e vents in the areas that fill last。在熔體流動末端開設排氣槽Vents are typically positioned at discontinuities of mold material， such as at parting surfaces, between the insert and mold wall, at ejector pins， and at mold slides。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。Redesign the gate and delivery system.重新設計澆口和澆注系統C
8、hanging the delivery system can alter the filling pattern in such a way that the lasttofill areas are located at the proper venting locations.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。Make sure the vent size is large enough so that the air present in the cavity can escape during injection.排氣槽尺寸應足夠大以使得氣體可以在充填過程中排出.B
9、e careful, however， that the vent is not so large that it causes flash at the edge of the molding. The recommended vent size is 0。025 mm （0.001 inch） for crystalline polymers, and 0。038 mm (0。0015 inch） for amorphous polymers。但是，排氣槽不能太大防止制品產生飛邊.對于結晶型塑料,排氣槽應小于0。025mm，不定形塑料應小于0。038mm.Adjust the moldin
10、g conditions改善填充條件Reduce the injection speed。減少注射速度High injection speeds can lead to jetting， which causes air to become entrapped in the part。 Lowering the injection speed will give the air displaced by the melt sufficient time to escape from the vents.速度過高會引起噴射，這會使氣體無法逃脫。較低的注射速度可以使氣體有充足的時間從排氣槽排出。B
11、lack specks/black streaks黑斑和黑痕What are black specks and black streaks？ Black specks and black streaks are dark spots or dark streaks found on the surface or throughout a molded part。 Brown specks or streaks refer to the same type of defect， except the burning or discoloration is not as severe。黑斑和黑痕是
12、出現于制品表面或貫穿在整個零件內部的黑點或黑條紋。它們都是同種形式的缺陷，是不太嚴重的燒焦或色變。Causes of black specks/black streaks Black specks and black streaks are caused by overheated （degraded， burned） material or by contamination of the resin. 黑斑和黑痕是由于材料過熱或樹脂被污染而引起的。Material degradation Overheated materials can degrade and lead to black s
13、treaks。 Material that stays in the nicked rough surfaces of the barrel wall and screw surfaces for a prolonged period of time after heating will char and degrade， resulting in the defect. 材料過熱會降解導致黑痕,材料在加熱過程中停留在粗糙的料筒和螺桿表面的時間過長會燒焦并講解,導致產品缺陷。Material contamination Contaminants in the air or material，
14、such as dirty regrind, foreign material, different color material, or a lower melt-temperature material， are what most often lead to black specks and black streaks。 Airborne dirt can also cause dark spots on the surface of a molded part.在空氣中或被其它材料污染，比如被污染的外來料，不同顏色的材料,低熔點材料，都通常引起黑斑和黑痕的原因。空氣中的粉塵也是會引起成
15、型制品表面的黑斑.Other defects resulting from the same causes 相同原因引起的其他缺陷 Brittleness 脆化 Burn marks 燒焦 Discoloration 色變Remedies Handle the material carefully小心使用材料Make sure no contaminated materials， such as dirty regrind, are blended into the original material.確保沒有被污染的材料,比如臟的再生料加入到原材料當中。Put the cover on th
16、e hopper and all bins of material. Airborne dirt can contaminate the original material, leading to black spots。將容器蓋上蓋子，空氣中的灰塵會污染原料導致黑斑.Alter the mold design改變模具設計Clean the ejectors and slides。 The streaks could be caused by the grease or lubricants on the slides or ejectors。清潔頂針和滑塊，條紋可以由滑塊或頂針上的油脂或潤滑油引起.Improve the venting system. If the black specks are found at the end of flow p
