Processing Machinery
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PBT Shutdown Cleaning
Problem Phenomenon
After shutdown, PBT carbonizes in the barrel, and when restarting, black specks appear in batches, difficult to clean
Cause Analysis
Retained PBT material at shutdown carbonizes and decomposes at residual temperature; on restart, the carbonized material contaminates the product; promptly cleaning the barrel with PE or PP material at shutdown is the standard procedure; during on-site troubleshooting, verify item by item according to this mechanism, and avoid blindly adjusting the machine based only on experience
Solution
①Clean the barrel with PE or PP at shutdown; ②Lower the temperature for long shutdowns; ③Purge the first few shots when restarting; after adjustment, take samples continuously to verify the effect, and resume mass production only after confirming stability
Key Takeaway
Replacing PBT with PE/PP for shutdown cleaning is an iron rule; the lessons of carbonization black speck accidents all without exception point to omitting this step; after confirming effectiveness, solidify the parameters and practices into the work instruction to prevent recurrence
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