Processing Machinery
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PPS Black Specks from Residual Material
Problem Phenomenon
Black specks and discolored streaks appear on the parts; the situation improves briefly after barrel cleaning but recurs
Cause Analysis
After PPS shutdown, material remaining in the barrel above 280°C for a long time degrades and carbonizes; upon restart, carbonized material is released periodically; during shutdown, the barrel temperature should be lowered below 280°C for heat preservation
Solution
①During shutdown, lower the barrel temperature below 280°C for heat preservation; ②For long shutdowns, purge by replacement with HDPE; ③Upon restart, purge the first few shots; after adjustment, take continuous samples to verify the effect, and resume mass production only after confirming stability
Key Takeaway
Ninety percent of PPS black specks trace back to shutdown retention; the 280°C heat-preservation line and HDPE replacement are standard procedures; after confirming effectiveness, fix the parameters and practices into the work instruction to prevent recurrence
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