Injection Molding
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Black specks (carbonized spots) in PP '2079851475616104452
Problem Phenomenon
Small black specks and black streaks randomly appear on the surface/inside of light-colored or natural-color PP parts, especially glaring on white parts, and often appear intermittently.
Cause Analysis
There are dead spots in the barrel, nozzle, or hot runner; melt stagnates, carbonizes, then falls off and mixes into the new material; the raw material or regrind is contaminated, mixed with other materials or carbonized particles; staying at high temperature for a long time also causes local degradation and discoloration of PP.
Solution
①Thoroughly purge the machine, and disassemble and clean the nozzle, hot runner, and screw head when necessary; ②check and standardize the storage of raw material and regrind to avoid contamination; ③avoid long-time high-temperature idling and heat preservation of the barrel; ④thoroughly displace with purging compound when changing materials; ⑤for intermittent black specks, focus on investigating dead spots rather than repeatedly adjusting the process.
Key Takeaway
PP black specks come from carbon deposits in equipment dead spots or material source contamination nine times out of ten; 'purging the machine + checking the material source' is far more effective than adjusting parameters; treating black specks as a process problem and testing repeatedly will only expand scrap and cover up real equipment hazards.
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