Extrusion & Post
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Random copolymer polypropylene pipe special material (Nordic standard） extruded products surface bamboo marks/melt fracture（Variant: Strengthened Measures）
Fenómeno del problema
Periodic coarse corrugations or bamboo-like undulations appear on the extrudate surface, and in severe cases the extrudate shape is distorted.
Melt fracture is a serious defect in the extrusion process and directly causes product scrapping.In particular, extra attention is needed on top of the original basis, this problem is more prominent and requires key attention.
Análisis de la causa
（1）Extrusion speed exceeds the critical shear rate, melt flow becomes unstable\
（2）Die temperature too low, melt viscosity high\
（3）The die land length is insufficient, the melt is not fully relaxed\
（4）The resin molecular weight is too high or the molecular weight distribution too wide\
（5）The die entrance angle is improper, melt entrance flow unstable\
（6）On top of the original basis, extra attention is needed: process parameter fluctuations or equipment status changes aggravate this problem
Solución
（1）Reduce the extrusion speed below the critical shear rate\
（2）Increase the die temperature to the higher value within the 200-220°C range, reduce melt viscosity\
（3）Increase the die land length, generally 10-20 times the die diameter\
（4）Select grades with moderate molecular weight distribution\
（5）Optimize the die entrance design, entrance angle 30-60°\
（6）If necessary, add a small amount of processing aid (fluoroelastomer) to improve flowability\
（6）And strengthen process monitoring; on top of the original basis, extra attention is needed, paying special attention to parameter stability
Conclusión clave
Melt fracture is flow instability caused by the extrusion speed exceeding the critical value, requiring reduced speed, increased temperature and optimized die design.Targeted preventive measures need to be taken in different production scenarios.
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