Extrusion & Post
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Random copolymer polypropylene pipe special material (Nordic standard） extruded products surface bamboo marks/melt fracture
Fenómeno do 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.
Análise das causas
（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
Solução
（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
Conclusão principal
Melt fracture is flow instability caused by the extrusion speed exceeding the critical value, requiring reduced speed, increased temperature and optimized die design.
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