塑胶成型不良问题及对策处理.docVIP

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. 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 melt-front advancements. (To replay the animation, click Replay) Problems caused by air traps Entrapped 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。 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 race-tracking 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 Place 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,