Molds & Tooling
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PC Weak Weld Line Strength
Problem Phenomenon
Weld lines are visible on transparent PC parts and easy to crack along the weld line, functional tests (drop, pressure resistance) fail, it becomes a structural weak zone.
Cause Analysis
When the two melt fronts meet, the temperature is insufficient and venting is poor, so molecular chain entanglement is poor; PC molecular chains have large rigidity and weak entanglement ability, so weld strength depends more on temperature and venting, and the weld line deteriorates sharply at low temperature and fast cooling.
Solution
①Increase melt temperature and mold temperature to let the fronts meet at high temperature; ②Add vent slots at the meeting point, and set an overflow well if necessary; ③Adjust the gate position to avoid high-stress areas and optical areas; ④Increase injection speed to maintain front temperature; ⑤Reduce the number of gates.
Key Takeaway
PC weld lines rely on 'high-temperature meeting + good venting': PC molecular chains have large rigidity, and the meeting temperature is decisive; plan the gate in advance for structural parts to move the weld line out of the load path, rather than reinforcing afterwards.
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