Material Drying
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PET moisture deep inside the pellets
Problem Phenomenon
PET pellets that are dry on the surface still show bubbles after processing, and only extending the drying time can solve it
Cause Analysis
PET moisture not only adheres to the surface but also penetrates into the pellets to form molecularly bonded water; ordinary hot air can only remove surface water, and deep-layer water must be driven out by low-dew-point long-time dehumidifying drying
Solution
①A dehumidifying dryer must be used rather than ordinary hot air; ②dew point below -40℃ in a closed-loop circuit; ③ensure sufficient residence time for the internal moisture to diffuse out; after adjustment, take consecutive samples to verify the effect, and resume mass production only after confirming stability
Key Takeaway
PET's deep-layer moisture determines the high threshold of the drying process; dew point and time are two hard indicators that cannot be compressed; after confirming effectiveness, solidify the parameters and practices into the work instruction to prevent recurrence
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