Molding Process
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EVA extruded film thick at edges and thin in middle
Fenómeno del problema
EVA extruded film edges 20-30% thicker than middle with U-shaped thickness distribution
Análisis de la causa
Improper die flow channel design with low edge resistance and large flow; EVA melt elasticity with greater swell at edges; air ring cooling with different edge effect
Solución
1) Adopt coat-hanger design for die to balance resistance between middle and edges; 2) Fine-tune die gap slightly larger in middle and slightly smaller at edges for compensation; 3) Slightly reduce air ring edge air volume; 4) Add restrictor bar to adjust edge flow
Conclusión clave
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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