Extrusion & Post
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Excessive shrinkage of random copolymer polypropylene extruded products
Fenómeno do problema
Extruded products show obvious dimensional shrinkage after cooling, exceeding the tolerance range.
Excessive shrinkage causes product dimensions to be too small, affecting fitting and use.
Análise das causas
(1) Random copolymer polypropylene has high crystallinity; cooling crystallization causes volume shrinkage
(2) Melt temperature is on the high side; large volume expansion leads to large shrinkage after cooling
(3) Slow cooling rate results in high crystallinity and large shrinkage
(4) Haul-off speed is too slow, and the product expands at the die
(5) Improper raw material grade selection results in a large shrinkage rate
Solução
(1) Appropriately lower barrel temperature to the lower value within the 190-260°C range
(2) Appropriately accelerate the cooling rate to reduce crystallinity and shrinkage
(3) Adjust haul-off speed and appropriately increase the draw ratio
(4) Select grades with a small shrinkage rate, 1.0-2.0
(5) Reserve shrinkage allowance during mold design
Conclusão principal
Excessive shrinkage is caused by high crystallinity or high temperature and needs to be solved by controlling temperature and cooling rate.
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