Molding Process
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Excessive shrinkage rate of cross-linked 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）The cross-linked polyethylene has high crystallinity, and cooling crystallization causes volume shrinkage
（2）The melt temperature is too high, the volume expansion is large, and the shrinkage after cooling is large
（3）The cooling rate is slow, the crystallinity is high, and the shrinkage is large
（4）The hauling speed is too slow and the product expands at the die
（5）The raw material grade is improperly selected and the shrinkage rate is too large
Solution
（1）Appropriately lower the barrel temperature to the lower value within the range of 170-220°C
（2）Appropriately speed up the cooling rate to reduce crystallinity and shrinkage
（3）Adjust the hauling speed and appropriately increase the stretching ratio
（4）Select grades with small shrinkage, shrinkage rate 1.0-2.0
（5）Reserve shrinkage allowance during mold design
Key Takeaway
Excessive shrinkage is caused by high crystallinity or high temperature, and needs to be solved by controlling the temperature and cooling rate.
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