Extrusion & Post
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Excessive Longitudinal Reversion Rate of High-Density Polyethylene Pipes
Problembeschreibung
After the pipe is heated under specified temperature and time conditions, the longitudinal reversion rate exceeds the standard limit.
Excessive reversion rate reflects large internal stress or incomplete crystallization of the pipe, affecting the reliability of pipe use.
Ursachenanalyse
（1）The residual internal stress of high-density polyethylene after extrusion is large
（2）The cooling rate is too fast, and the molecular chain orientation is not relaxed
（3）The haul-off speed is too large, and the pipe is excessively stretched in the longitudinal direction
（4）The barrel temperature is low, and the melt plasticization is insufficient
（5）The sizing cooling is insufficient
Lösung
（1）Appropriately increase the barrel temperature to a reasonable value within the 180-260°C range to improve plasticization
（2）Appropriately reduce the cooling rate to give the molecular chains time to relax
（3）Adjust the haul-off speed to reduce the draw ratio
（4）Increase the length of the cooling water tank to ensure sufficient cooling
（5）After demolding, perform water bath annealing on the pipe to eliminate internal stress
Wichtigste Erkenntnis
Excessive reversion rate is caused by large internal stress or excessive orientation, and needs to be solved from temperature control, cooling rate, and haul-off speed.
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