Extrusion & Post
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Random copolymer polypropylene pipe special material (Nordic standard） extruded products excessive shrinkage rate
Problembeschreibung
The extruded product shrinks significantly in size after cooling, exceeding the tolerance range.
Excessive shrinkage makes the product undersized, affecting fit and use.
Ursachenanalyse
（1）The random copolymer polypropylene pipe special material (Nordic standard） 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, crystallinity high and shrinkage large\
（4）Haul-off speed too slow, the product expands at the die\
（5）Improper raw material grade selection, shrinkage rate too large
Lösung
（1）Appropriately lower the barrel temperature to the lower value within the 200-220°C range\
（2）Appropriately speed up the cooling rate, reduce crystallinity to reduce shrinkage\
（3）Adjust the haul-off speed, appropriately increase the draw ratio\
（4）Select grades with small shrinkage rate, shrinkage rate 1.0-1.5\
（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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