Extrusion & Post
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Longitudinal reversion of linear low density polyethylene pipes exceeding standard (Variant: strengthened measures)
Problem Phenomenon
After the pipe is heated under specified temperature and time conditions, the longitudinal reversion exceeds the standard limit.
Excessive reversion reflects large internal stress or incomplete crystallization of the pipe, affecting pipe use reliability.
In particular, additional attention is needed on the original basis; this problem is more prominent and requires key attention.
Cause Analysis
(1) Large residual internal stress in linear low density polyethylene after extrusion
(2) Cooling rate too fast; molecular chain orientation not relaxed
(3) Haul-off speed too high; excessive longitudinal stretching of the pipe
(4) Barrel temperature too low, insufficient melt plasticization
(5) Insufficient sizing cooling
(6) On the original basis, additional attention is needed as process parameter fluctuations or equipment status changes have aggravated this problem
Solution
(1) Appropriately increase barrel temperature to a reasonable value within the 190-250°C range, improve plasticization
(2) Appropriately reduce cooling rate, allow molecular chains relaxation time
(3) Adjust haul-off speed, reduce draw ratio
(4) Increase cooling water tank length, ensure full cooling
(5) Perform water bath annealing after pipe demolding to eliminate internal stress
(6) And strengthen process monitoring; on the original basis, additional attention is needed, with special attention to parameter stability
Key Takeaway
Excessive reversion is caused by large internal stress or excessive orientation; it needs to be solved from temperature control, cooling rate, and haul-off speed.
Targeted preventive measures need to be taken in different production scenarios.
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