Extrusion & Post
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Excessive shrinkage of cross-linked polyethylene extruded products (Variant: strengthened measures)
Problembeschreibung
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 on the original basis, additional attention is needed, and this problem is more prominent and requires key attention.
Ursachenanalyse
(1) Cross-linked 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) On the original basis, additional attention is needed: process parameter fluctuations or equipment state changes aggravate this problem
Lösung
(1) Appropriately reduce barrel temperature to the lower value within 170-220°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 1.0-2.0
(5) Reserve shrinkage allowance in mold design
(6) And strengthen process monitoring; on the original basis, additional attention is needed, paying special attention to parameter stability
Wichtigste Erkenntnis
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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