Processing Machinery
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COC Grade Switchover Cross Contamination
Problem Phenomenon
After switching production between COC grades with different Tg, the products show turbidity, streaks and performance fluctuations, and it takes a long time of purging to restore purity.
Cause Analysis
Grades with different Tg have large differences in processing temperature; residual high-temperature grade material does not melt under low-temperature processes, and residual low-temperature grade material degrades under high-temperature processes; incomplete barrel replacement forms cross contamination.
Solution
①When switching grades, fully purge and replace at the new grade temperature; ②pay special attention to residual unmelted particles when switching from high Tg to low Tg; ③disassemble and clean the screw if necessary; ④record and standardize the switchover cleaning duration.
Key Takeaway
The core of COC grade switchover is temperature difference management; the material change direction determines the risk type; standardized cleaning processes avoid human arbitrariness.; After confirming effectiveness, fix the parameters and practices into the work instruction to prevent recurrence
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