Molds & Tooling
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Yellow-brown or black specks appear locally on the product
Problem Phenomenon
Yellow-brown or black specks appear locally on the product, accompanied by burnt odor, burnt areas rough and carbonized on the surface
Cause Analysis
Barrel temperature too high (far exceeding the 170-230°C upper limit), severe material degradation
Screw speed too fast, excessive shear, thermal degradation
Poor mold venting, gas compressed and heated
Residence time too long, material repeatedly heated in the barrel
Regrind ratio too high, degradation accumulation
Solution
Lower barrel temperature to the reasonable 170-230°C range
Reduce screw speed to reduce shear heat
Improve mold venting to prevent gas compression heating
Reduce residence time, shorten cycle time
Reduce regrind ratio ≤15%
Key Takeaway
Burnt is caused by overheating degradation or poor venting
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