Extrusion & Post
5 조회수
Bamboo Stripes/Melt Fracture Appearing on the Surface of High-Density Polyethylene Extruded Products
문제 현상
Periodic coarse ripples or bamboo-like undulations appear on the surface of the extrudate; in severe cases, the shape of the extrudate is distorted.
Melt fracture is a serious defect in the extrusion process and directly leads to product scrapping.
원인 분석
（1）The extrusion speed exceeds the critical shear rate, and the melt flow becomes unstable
（2）The die temperature is too low, and the melt viscosity is high
（3）The die land length is insufficient, and the melt is not fully relaxed
（4）The resin molecular weight is too high or the molecular weight distribution is too wide
（5）The die entrance angle is improper, and the melt entrance flow is unstable
해결 방법
（1）Reduce the extrusion speed to below the critical shear rate
（2）Increase the die temperature to a higher value within the 180-260°C range to reduce the melt viscosity
（3）Increase the die land length, generally 10-20 times the die diameter
（4）Select a grade with a moderate molecular weight distribution
（5）Optimize the die entrance design, with an entrance angle of 30-60°
（6）Add a small amount of processing aid (fluoroelastomer) when necessary to improve flowability
핵심 요약
Melt fracture is flow instability caused by the extrusion speed exceeding the critical value, and it is necessary to reduce the speed, increase the temperature, and optimize the die design.
이 정보가 도움이 되었나요?
0 명이 도움이 되었다고 합니다
의견 주셔서 감사합니다!