Injection Molding
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PMMA Trapped Air Burning
Problem Phenomenon
Black burn marks and bubbles appear at the end of the melt flow, and burn marks are eliminated after venting improvement.
Cause Analysis
Poor venting at the end of the cavity causes adiabatic compression of air to heat up and burn PMMA; too-fast injection speed leaves no time for gas to escape, aggravating burning.; During on-site troubleshooting, verify item by item according to this mechanism to avoid blindly adjusting the machine based on experience alone.
Solution
①Set 0.02~0.04mm vent grooves on the parting line; ②add venting at the end and at weld lines; ③reduce injection speed; ④clear contaminated vent grooves.
Key Takeaway
PMMA is sensitive to trapped-air defects and burn marks are irreparable; venting design is a mandatory mold requirement, and depth must be controlled per specification to prevent flash.; After confirming effectiveness, fix the parameters and practices into the work instruction to prevent recurrence.
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