Extrusion & Post
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Excessive shrinkage of heat-resistant polyethylene extruded products (Variant: mass production scenario)
Fenómeno del problema
The extruded product shrinks significantly in size after cooling, exceeding the tolerance range.
Excessive shrinkage causes the product size to be too small, affecting fitting and use.
Especially in continuous mass production, this problem is more prominent and requires key attention.
Análisis de la causa
(1) Heat-resistant polyethylene has high crystallinity, cooling crystallization causes volume shrinkage
(2) Melt temperature too high, large volume expansion and large shrinkage after cooling
(3) Cooling rate slow, high crystallinity and large shrinkage
(4) Haul-off speed too slow, product expands at the die
(5) Improper raw material grade selection, shrinkage too large
(6) In continuous mass production, process parameter fluctuations or equipment state changes aggravate this problem
Solución
(1) Appropriately reduce barrel temperature to the lower value within 190-230°C
(2) Appropriately speed up cooling rate, reduce crystallinity to reduce shrinkage
(3) Adjust haul-off speed, appropriately increase draw ratio
(4) Select grades with small shrinkage, shrinkage 1.5-2.5
(5) Reserve shrinkage allowance in mold design
(6) And establish standardized work instructions, paying special attention to parameter stability in continuous mass production
Conclusión clave
Excessive shrinkage is caused by high crystallinity or high temperature, and needs to be solved by controlling temperature and cooling rate.
Targeted preventive measures need to be taken in different production scenarios.
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