Extrusion & Post
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Excessive shrinkage of heat-resistant polyethylene extruded products
Problem Phenomenon
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.
Cause Analysis
(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
Solution
(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
Key Takeaway
Excessive shrinkage is caused by high crystallinity or high temperature, and needs to be solved by controlling temperature and cooling rate.
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