Injection Molding
11 조회수
Weld lines appearing on polypropylene injection molded products
문제 현상
Linear marks appear on the product surface where two or more melt fronts meet, usually in the form of V-shaped grooves or color difference lines, with low strength.
Weld lines not only affect the appearance but are also weak links of the product, which easily crack from here when stressed.
원인 분석
（1）Multi-gate design or complex product structure causes the melt to split and then meet, and the melt temperature at the meeting point is low and the fusion is insufficient
（2）The injection speed is too slow, the melt temperature drops too much during mold filling, and it cannot fully fuse when meeting
（3）The barrel temperature is too low, the melt flowability is poor, and the pressure at the meeting point is insufficient
（4）The mold temperature is too low, the melt cools rapidly after contacting the mold wall, and the fusion strength of the meeting interface is low
（5）Poor venting, the gas at the meeting point cannot be discharged, forming a barrier layer
해결 방법
（1）Raise the melt temperature to the higher value within the range of 200-280°C to improve melt flowability
（2）Raise the mold temperature to the higher value within the range of 40-90°C to delay melt cooling
（3）Increase the injection speed, shorten the mold filling time, and reduce the melt temperature loss
（4）Adjust the gate position and quantity to minimize melt splitting; add overflow grooves to eliminate weld lines when necessary
（5）Improve mold venting, setting venting grooves or venting pins at the weld line positions
핵심 요약
Weld lines are a manifestation of poor fusion of melt fronts, and the melt fusion quality is improved by raising the melt temperature, injection speed, and mold temperature.
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