Injection Molding
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ABS trapped air burning
Problem Phenomenon
Black/brown burn marks appear at the end of the cavity, rib ends, or weld lines, possibly accompanied by odor, appearing repeatedly at fixed positions.
Cause Analysis
During filling, the air in the cavity is compressed and cannot be discharged, producing the diesel effect that burns the plastic at high temperature; blocked vent grooves, too fast injection at the end, and too large clamping closing the vents all can induce it, and ABS's high processing temperature makes it easier to burn.
Solution
①Open/deepen vent grooves at the burnt position (ABS about 0.02~0.04mm); ②clean the vents blocked by oil; ③reduce the end injection speed; ④moderate clamping force; ⑤reduce the amount of mold release agent.
Key Takeaway
Repeated burning at a fixed position in ABS = venting problem: first clean/open the vent grooves, then adjust the end speed; the burning point is often the last filling point, and the short shot method can locate it precisely.
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