Extrusion & Post
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Excessive shrinkage rate of homopolymer polypropylene extruded products
Problembeschreibung
Extruded products shrink significantly after cooling, exceeding the tolerance range.
Excessive shrinkage rate causes undersized product dimensions, affecting fit and use.
Ursachenanalyse
(1) High crystallinity of homopolymer polypropylene; cooling crystallization causes volume shrinkage
(2) Melt temperature too high; large volume expansion, large shrinkage after cooling
(3) Slow cooling rate; high crystallinity, large shrinkage
(4) Haul-off speed too slow; product swells at the die
(5) Improper raw material grade selection, excessive shrinkage rate
Lösung
(1) Appropriately reduce barrel temperature to the lower value within the 200-280°C range
(2) Appropriately speed up cooling rate, reduce crystallinity to reduce shrinkage
(3) Adjust haul-off speed, appropriately increase draw ratio
(4) Select grades with small shrinkage rate, shrinkage rate 1.5-2.5
(5) Reserve shrinkage allowance in mold design
Wichtigste Erkenntnis
Excessive shrinkage rate is caused by high crystallinity or high temperature; it needs to be solved by controlling temperature and cooling rate.
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