Injection Molding
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TPU scorch marks and burnt
Problem Phenomenon
Local blackening and carbonization of the product, mostly near the gate or at the end of the melt flow.
Cause Analysis
TPU is sensitive to shear; excessive injection speed causes shear heat decomposition near the gate; excessive melt temperature, too long residence time, or poor mold venting also cause scorch marks.
Solution
①reduce injection speed; ②reduce barrel temperature to prevent overheating; ③shorten barrel residence time; ④add vents to the mold and clean blockages; after adjustment, continuously sample to verify the effect, and resume mass production only after confirming stability
Key Takeaway
For TPU scorch marks, suspect shear overheating first; compared with SEBS-based TPE, TPU is more sensitive to shear, and speed control is the first means of preventing scorching; after confirming effectiveness, fix the parameters and practices into the work instruction to prevent recurrence
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