Extrusion & Post
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Excessive shrinkage rate of random copolymer polypropylene pipe special material extruded products (Variant: strengthened measures)
Problembeschreibung
The extruded product shrinks significantly in size after cooling, exceeding the tolerance range.
Excessive shrinkage rate causes the product size to be small, affecting fitting and use.
In particular, extra attention is needed on the original basis, this problem is more prominent and needs key attention.
Ursachenanalyse
（1）Random copolymer polypropylene pipe special material has high crystallinity, 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
（6）On the original basis, extra attention is needed: process parameter fluctuations or equipment status changes have aggravated this problem
Lösung
（1）Appropriately lower the barrel temperature to the lower value within the range of 200-220°C
（2）Appropriately increase the cooling rate to 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 1.0-1.5
（5）Reserve shrinkage margin in mold design
（6）And strengthen process monitoring; on the original basis, extra attention is needed, with special attention to parameter stability
Wichtigste Erkenntnis
Excessive shrinkage rate is caused by high crystallinity or high temperature, and needs to be solved by controlling the temperature and cooling rate.
In different production scenarios, targeted preventive measures need to be taken.
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