Extrusion & Post
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CEF extrusion melt fracture
Problem Phenomenon
CEF shows severe melt fracture at too high extrusion rates, the extrudate twisted in a spiral shape
Cause Analysis
CEF melt elasticity too high, elastic recovery at the die exit exceeds the critical value; die L/D ratio too short <10, melt not fully relaxed; extrusion temperature low
Solution
1) Reduce the extrusion rate to 2-3m/min; 2) Increase the die L/D ratio to 15-20; 3) Increase the extrusion temperature to 160-220°C; 4) Add a 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 the critical value, speed reduction and longer die are the core countermeasures
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