Extrusion & Post
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EVA extrusion melt fracture
Problem Phenomenon
Severe melt fracture occurs when EVA extrusion rate is too high, with extrudate twisted in spiral shape
Cause Analysis
EVA melt elasticity too high with elastic recovery at die exit exceeding critical value; die L/D ratio too short <10 with melt not fully relaxed; extrusion temperature too low
Solution
1) Reduce extrusion rate to 2-3m/min; 2) Increase die L/D ratio to 15-20; 3) Increase extrusion temperature to 140-200°C; 4) Add small amount of low-elasticity resin to reduce system elasticity; 5) Progressive converging die entrance design
Key Takeaway
Melt fracture is caused by elastic recovery exceeding critical value; reducing speed and lengthening die are the core countermeasures
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