Material Drying
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TPU silver streaks
Problem Phenomenon
Silvery-white streaks or spots appear on the product surface, distributed in a fan shape near the gate.
Cause Analysis
Raw material moisture or volatiles exceed the standard (the same source as bubbles but to a lesser degree); uneven melt mixing with unmelted particles; poor fit between the nozzle and the gate allows cold material to enter the cavity.
Solution
①strengthen drying and add a hot air hood on the hopper to prevent moisture absorption; ②appropriately increase screw speed to enhance shear mixing (not exceeding 60r/min); ③clean the nozzle and check gate blockage; ④add cold slug wells at the end of the runner.
Key Takeaway
TPU silver streaks have the same source as bubbles but to a lesser degree; troubleshoot the three aspects of drying, mixing, and cold material; cold slug wells are a simple and effective measure to intercept cold material; after confirming effectiveness, fix the parameters and practices into the work instruction to prevent recurrence
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