Extrusion & Post
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Longitudinal reversion of homopolymer polypropylene pipes exceeding standard
Fenómeno do problema
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.
Análise das causas
(1) Large residual internal stress in homopolymer polypropylene 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
Solução
(1) Appropriately increase barrel temperature to a reasonable value within the 200-280°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
Conclusão principal
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.
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