Extrusion & Post
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Longitudinal reversion rate of general-purpose polyethylene pipes exceeding the standard
Fenómeno do problema
After the pipe is heated under the specified temperature and time conditions, the longitudinal reversion rate exceeds the standard limit.
Reversion rate exceeding the standard reflects large internal stress or imperfect crystallization of the pipe, affecting the use reliability of the pipe.
Análise das causas
（1）The residual internal stress of general-purpose 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
Solução
（1）Appropriately raise the barrel temperature to a reasonable value within the range of 160-260°C to improve plasticization
（2）Appropriately reduce the cooling rate to allow time for the molecular chains to relax
（3）Adjust the haul-off speed and reduce the draw ratio
（4）Increase the length of the cooling water tank to ensure sufficient cooling
（5）After the pipe is demolded, perform water bath annealing to eliminate internal stress
Conclusão principal
Reversion rate exceeding the standard 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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