Extrusion & Post
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Dimensions of random copolymer polypropylene injection molded products too small, below the lower limit (variant: strengthened measures)
Fenómeno do problema
Actual product dimensions are smaller than the drawing tolerance lower limit, making assembly difficult or impossible.
Undersized dimensions are usually related to excessive shrinkage and are especially common in thick-walled products or highly crystalline materials.
Especially, additional attention is needed on top of the original basis; this problem is more prominent and requires focused attention.
Análise das causas
(1) Holding pressure is insufficient or holding time is too short; insufficient shrinkage compensation leads to large shrinkage
(2) Mold temperature is on the high side; high crystallinity of random copolymer polypropylene leads to large post-shrinkage
(3) Barrel temperature is on the high side; melt density is small and volume shrinkage is large
(4) Cooling time is insufficient; the product continues to shrink after demolding (post-shrinkage)
(5) The gate solidifies prematurely, and holding pressure cannot be transmitted to the cavity
(6) On top of the original basis, additional attention is needed as process parameter fluctuations or equipment condition changes aggravate this problem
Solução
(1) Increase holding pressure to 80-120MPa and extend holding time to 15-25s
(2) Appropriately lower mold temperature to the lower value within the 40-80°C range
(3) Appropriately lower barrel temperature to the lower value within the 190-260°C range
(4) Extend cooling time to ensure the product is fully cooled and set
(5) Increase gate size to extend gate freezing time
(6) And strengthen process monitoring; on top of the original basis, additional attention is needed to pay special attention to parameter stability
Conclusão principal
Undersized dimensions are caused by excessive shrinkage and need to be controlled by strengthening holding pressure, lowering temperature and extending cooling time.
In different production scenarios, targeted preventive measures need to be taken.
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