Extrusion & Post
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Longitudinal retraction rate of polyolefin plastomer pipes exceeding the standard (Variant: Enhanced Measures)
Problem Phenomenon
After the pipe is heated under the specified temperature and time conditions, the longitudinal retraction rate exceeds the standard limit.
Excessive retraction rate reflects large internal stress or incomplete crystallization of the pipe, affecting the reliability of the pipe in use.
In particular, additional attention is needed on the original basis; this problem is more prominent and requires focused attention.
Cause Analysis
（1）The residual internal stress of the polyolefin plastomer after extrusion is large
（2）The cooling rate is too fast and the molecular chain orientation has not relaxed
（3）The hauling speed is too large and the pipe is overstretched longitudinally
（4）The barrel temperature is too low and the melt plasticization is insufficient
（5）The sizing cooling is insufficient
（6）On the original basis, additional attention is needed: fluctuations in process parameters or changes in equipment status have aggravated this problem
Solution
（1）Appropriately raise the barrel temperature to a reasonable value within the range of 180-230°C to improve plasticization
（2）Appropriately reduce the cooling rate to allow the molecular chains time to relax
（3）Adjust the hauling speed and reduce the stretching ratio
（4）Increase the length of the cooling water tank to ensure sufficient cooling
（5）Perform water bath annealing treatment on the pipe after demolding to eliminate internal stress
（6）And strengthen process monitoring; on the original basis, additional attention is needed to pay special attention to parameter stability
Key Takeaway
Excessive retraction rate is caused by large internal stress or excessive orientation, and needs to be solved from temperature control, cooling rate, and hauling speed.
Targeted preventive measures need to be taken in different production scenarios.
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