Extrusion & Post
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Longitudinal Reversion of Polypropylene Pipe Exceeding the Standard
Fenómeno del problema
After the pipe is heated under the specified temperature and time conditions, the longitudinal reversion exceeds the standard limit.
Excessive reversion reflects large internal stress or imperfect crystallization of the pipe, affecting the use reliability of the pipe.
Análisis de la causa
(1) The residual internal stress of polypropylene 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 over-stretched longitudinally
(4) The barrel temperature is too low, and the melt plasticization is insufficient
(5) The sizing cooling is insufficient
Solución
(1) Appropriately increase the barrel temperature to a reasonable value within the range of 200-280°C to improve plasticization
(2) Appropriately reduce the cooling rate to allow time for molecular chain relaxation
(3) Adjust the haul-off speed and reduce the stretch ratio
(4) Increase the length of the cooling water tank to ensure full cooling
(5) Perform water bath annealing treatment on the pipe after demolding to eliminate internal stress
Conclusión clave
Excessive reversion 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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