Material Drying
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TPU bubbles (air trap and degradation type)
Problem Phenomenon
Bubbles still appear after sufficient drying, concentrated at the end of the melt flow or in thick-walled areas.
Cause Analysis
Excessive injection speed causes the cavity to not vent in time and wraps air; excessive melt temperature causes TPU degradation and gas generation; insufficient feeding compensation in thick-walled areas forms vacuum bubbles that also manifest as bubbles.
Solution
①reduce injection speed by 10~20% and optimize venting; ②reduce melt temperature by 5~10℃, not exceeding 230℃; ③strengthen holding pressure feeding compensation; ④optimize the structural design of thick-walled areas.
Key Takeaway
Bubble identification must be divided into four categories: moisture, air trap, degradation, and vacuum bubbles; after drying is ineffective, troubleshoot the remaining sources one by one according to position characteristics; after confirming effectiveness, fix the parameters and practices into the work instruction to prevent recurrence
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