Extrusion & Post
4 조회수
Excessive shrinkage of linear low-density polyethylene extruded products (variant: strengthened measures)
문제 현상
Extruded products show obvious dimensional shrinkage after cooling, exceeding the tolerance range.
Excessive shrinkage causes product dimensions to be too small, affecting fitting and use.
Especially, additional attention is needed on top of the original basis; this problem is more prominent and requires focused attention.
원인 분석
(1) Linear low-density polyethylene has high crystallinity; cooling crystallization causes volume shrinkage
(2) Melt temperature is on the high side; large volume expansion leads to large shrinkage after cooling
(3) Slow cooling rate results in high crystallinity and large shrinkage
(4) Haul-off speed is too slow, and the product expands at the die
(5) Improper raw material grade selection results in a large shrinkage rate
(6) On top of the original basis, additional attention is needed as process parameter fluctuations or equipment condition changes aggravate this problem
해결 방법
(1) Appropriately lower barrel temperature to the lower value within the 190-250°C range
(2) Appropriately accelerate the cooling rate to reduce crystallinity and shrinkage
(3) Adjust haul-off speed and appropriately increase the draw ratio
(4) Select grades with a small shrinkage rate, 1.5-2.5
(5) Reserve shrinkage allowance during mold design
(6) And strengthen process monitoring; on top of the original basis, additional attention is needed to pay special attention to parameter stability
핵심 요약
Excessive shrinkage is caused by high crystallinity or high temperature and needs to be solved by controlling temperature and cooling rate.
In different production scenarios, targeted preventive measures need to be taken.
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