Extrusion & Post
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Melt fracture in PVA extrusion
Problembeschreibung
When extrusion rate is too high, PVA shows severe melt fracture, extrudate twisted in spiral shape
Ursachenanalyse
PVA melt elasticity too high, elastic recovery at die exit exceeds critical value; die L/D ratio too short <10, melt not fully relaxed; extrusion temperature too low
Lösung
1) Reduce extrusion rate to 2-3m/min; 2) Increase die length-to-diameter ratio to 15-20; 3) Increase extrusion temperature to 140-200°C; 4) Add a small amount of low-elasticity resin to reduce system elasticity; 5) Gradually converging die entrance design
Wichtigste Erkenntnis
Melt fracture is caused by elastic recovery exceeding the critical value; reducing speed and lengthening the die are the core countermeasures
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