Molding Process
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PU Extruded Film Thick Edges and Thin Middle
Problem Phenomenon
PU extruded film edges 20-30% thicker than the middle, thickness in U-shaped distribution
Cause Analysis
Die flow channel design improper, edge resistance low and flow large; PU melt elasticity, swell larger at edges; air ring cooling edge effect different
Solution
1) Die with coat-hanger design to balance middle and edge resistance; 2) Fine-tune die gap slightly larger in the middle and slightly smaller at the edges for compensation; 3) Slightly reduce air volume at the air ring edges; 4) Add restrictor bar to adjust edge flow
Key Takeaway
U-shaped thickness is caused by die flow channel and swell differences; coat-hanger die and gap fine-tuning are key
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