Molding Process
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EVOH extruded film thick edges and thin middle
Problem Phenomenon
EVOH extruded film edges are 20-30% thicker than the middle, thickness distributed in a U shape
Cause Analysis
Improper die flow channel design with low edge resistance and large flow; EVOH melt elasticity with greater swell at the edges; air ring cooling with different edge effects
Solution
1) Adopt coat-hanger die design to balance resistance between middle and edges; 2) Fine-tune die gap slightly larger in the middle and slightly smaller at the edges for compensation; 3) Slightly reduce air ring air volume at the edges; 4) Add restrictor bars 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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