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1、Air traps 困气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. Air-trap locations are usually in areas that fill last. Lack o
2、f vents or undersized vents in these last-to-fill areas are a common cause of air traps and the resulting defects. Another common cause is race-tracking (the tendency of polymer melt to flow preferentially in thicker sections), caused by a large thickness ratio. 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
3、模具排气孔以及镶件排出。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。FIGURE 1. Air trap locations indicated by the computer-predicted melt-front advancements. (To replay the animation, click Replay) Problems caused by air traps Entrapped air will result in voids and
4、 bubbles 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. 困气将引起成型制品内部空位和气泡，短射（浇不足），或表面缺陷如
5、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。In the figure below, an air trap results from race-tracking 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
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Alter the part design改变零件的设计Reduce the thickness ratio.减少壁厚变化This will minimize the race-tracking effect of polymer melt.可以减少聚合物熔体的跑马场效应。Alter the mold design改变模具的设计Pay close attention to the proper placement of your vents.密切关注开设排气孔
7、位置Place vents in the areas that fill last.在熔体流动末端开设排气槽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-design the gate and delivery system.重新设计浇
8、口和浇注系统Changing the delivery system can alter the filling pattern in such a way that the last-to-fill areas are located at the proper venting locations.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。Make sure the vent size is large enough so that the air present in the cavity can escape during injection.排气槽尺寸应足够大以使得气体可以在
9、充填过程中排出。Be 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，排气槽不能太大防止制品产生飞边。对于结晶型塑料，排气槽应小于0.025mm，不定形塑料应小于0.038mm。Adjust t
10、he molding conditions改善填充条件Reduce the injection speed.减少注射速度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.速度过高会引起喷射，这会使气体无法逃脱。较低的注射速度可以使气体有充足的时
11、间从排气槽排出。Black 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 seve
12、re.黑斑和黑痕是出现于制品表面或贯穿在整个零件内部的黑点或黑条纹。它们都是同种形式的缺陷，是不太严重的烧焦或色变。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过热或树脂被污染而引起的。Material degradation Overheated materials can degrade and lead t
13、o black streaks. 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. 材料过热会降解导致黑痕，材料在加热过程中停留在粗糙的料筒和螺杆表面的时间过长会烧焦并讲解，导致产品缺陷。Material contamination Contaminants in the air or m
14、aterial, 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.在空气中或被其它材料污染，比如被污染的外来料，不同颜色的材料，低熔点材料，都通常引起黑斑和黑痕的原因。空气中
15、的粉尘也是会引起成型制品表面的黑斑。Other defects resulting from the same causes 相同原因引起的其他缺陷 Brittleness 脆化 Burn marks 烧焦 Discoloration 色变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.确保没有被污染的材料，比如脏的再生料加入到原材料当中。Put the co
16、ver on the hopper and all bins of material. Airborne dirt can contaminate the original material, leading to black spots.将容器盖上盖子，空气中的灰尘会污染原料导致黑斑。Alter the mold design改变模具设计Clean the ejectors and slides. The streaks could be caused by the grease or lubricants on the slides or ejectors.清洁顶针和滑块，条纹可以由滑块或顶针上的油脂或润滑油引起。Improve the venting system. If the black specks are found at the end of flow p
