Molding Process
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MP extruded film thick edges thin middle
Problem Phenomenon
MP extruded film edges 20-30% thicker than the middle, thickness U-shaped distribution
Cause Analysis
die flow channel design improper, edge resistance low, flow large; MP melt elasticity swells more at the edges; air ring cooling edge effect different
Solution
1) adopt a coat-hanger die design to balance resistance between middle and edges; 2) fine-adjust die gap slightly larger in the middle, slightly smaller at the edges for compensation; 3) slightly reduce air ring air volume at the edges; 4) add a restrictor bar to adjust edge flow
Key Takeaway
U-shaped thickness is caused by die flow channel and swell difference; coat-hanger die and gap fine-adjustment are key
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