Extrusion & Post
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Cross-linked polyethylene pipe longitudinal reversion rate exceeding standard
Problem Phenomenon
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 imperfect crystallization of the pipe, affecting the reliability of pipe use.
Cause Analysis
(1) Large residual internal stress after cross-linked polyethylene extrusion
(2) Cooling rate too fast, molecular chain orientation not relaxed
(3) Haul-off speed too large, pipe excessively stretched longitudinally
(4) Barrel temperature too low, melt plasticization insufficient
(5) Sizing cooling insufficient
Solution
(1) Appropriately increase barrel temperature to a reasonable value within 170-220°C to improve plasticization
(2) Appropriately reduce cooling rate to give molecular chains relaxation time
(3) Adjust haul-off speed, reduce draw ratio
(4) Increase cooling water tank length to ensure sufficient cooling
(5) After pipe demolding, perform water bath annealing to eliminate internal stress
Key Takeaway
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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