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 of 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 trapsEntrapped air will result in voids and 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.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...
