Extrusion & Post
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Excessive Shrinkage Rate of High-Density Polyethylene Extruded Products
Problembeschreibung
The extruded product shrinks significantly in size after cooling, exceeding the tolerance range.
Excessive shrinkage rate makes the product size smaller, affecting fitting and use.
Ursachenanalyse
（1）The crystallinity of high-density polyethylene is high, and cooling crystallization causes volume shrinkage
（2）The melt temperature is 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 haul-off speed is too slow, and the product expands at the die
（5）The raw material grade is improperly selected, and the shrinkage rate is large
Lösung
（1）Appropriately reduce the barrel temperature to a lower value within the 180-260°C range
（2）Appropriately accelerate the cooling rate, reduce the crystallinity, and reduce shrinkage
（3）Adjust the haul-off speed and appropriately increase the draw ratio
（4）Select a grade with a small shrinkage rate, shrinkage rate 1.5-3.0
（5）Reserve shrinkage allowance in mold design
Wichtigste Erkenntnis
Excessive shrinkage rate is caused by high crystallinity or high temperature, and needs to be solved by controlling temperature and cooling rate.
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