Material Drying
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PET moisture content and bubbles
Problem Phenomenon
Tiny bubbles in the PET sheet appear intermittently and disappear after the drying time is extended
Cause Analysis
The solubility of trace moisture in the melt is limited, moisture exceeding the standard vaporizes into bubbles, and bubbles flicker in and out near the critical moisture content; during on-site troubleshooting, verify item by item according to this mechanism, and avoid blindly adjusting the machine based only on experience
Solution
Control the moisture content with sufficient margin and do not produce at the critical value; when bubbles appear, first measure the moisture content and then adjust the process; after adjustment, take consecutive samples to verify the effect, and resume mass production only after confirming stability
Key Takeaway
Intermittent bubbles mostly mean the moisture content is right at the line, and adding margin solves it; after confirming effectiveness, solidify the parameters and practices into the work instruction to prevent recurrence; include this case in the defect archive as a troubleshooting reference for subsequent similar problems
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