Processing Machinery
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Black spots and color patches on products
Problem Phenomenon
Black spots or brown patches appear inside or on the surface of the product, with uneven color
Cause Analysis
Material stays locally in the barrel for too long, causing thermal degradation and carbonization; the screw or barrel has dead zones with accumulated material; purging is not thorough during color change
Solution
Shorten material residence time to <5 minutes; regularly disassemble the screw to clean accumulated material in dead zones; use special purging material (such as AS-based purging material) for thorough purging during color change
Key Takeaway
Black spots are a sign of material degradation and carbonization, reflecting residence time and dead zone problems
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