Processing Machinery
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PVC Black Specks and Burnt Particles
Problem Phenomenon
Black spots and burnt streaks appear on the surface/inside of products; profiles and pipes are directly scrapped, often appearing intermittently at unfixed positions.
Cause Analysis
Degraded PVC carbonizes and stays at screw, die head dead corners or screen pack, forming black spots and black streaks after falling off; long-time heat soaking, incomplete purging, and exhausted stabilizer are the main causes; material accumulated in dead corners continuously contaminates new material, hence intermittent and stubborn.
Solution
①Clean the barrel, screw, die head dead corners, dismantle and wash if necessary; ②Replace the screen pack and monitor pressure differential; ③Standardize shutdown (emptying or cooling), avoid heat soaking; ④Check whether the stabilizer has been consumed; ⑤For intermittent black specks, focus on equipment dead corners rather than adjusting the process.
Key Takeaway
PVC black specks = 'carbonized retained material falling off': dead corner treatment is the core, purging is more effective than parameter adjustment; intermittent, stubborn black specks are the typical fingerprint of equipment dead corners — without finding the root cause on the equipment, black specks can never be fully cleared.
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