Extrusion & Post
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Dimensions of Block Copolymer Polypropylene Injection Molded Products Too Large Exceeding the Upper Limit (Variant: Strengthened Measures)
Fenómeno do problema
The actual dimensions of the product exceed the upper tolerance limit of the drawing, and the gap during assembly is too large or tight fitting is impossible.
Oversized dimensions are usually related to insufficient shrinkage, and are prone to occur after changing the material batch number or adjusting the process.
In particular, extra attention is needed on the original basis; this problem is more prominent and requires key attention.
Análise das causas
（1）The holding pressure is too high or the holding pressure time is too long, and the product is over-compensated
（2）The mold temperature is low, and the fast cooling rate and low crystallinity lead to reduced shrinkage rate
（3）The barrel temperature is low, the melt density is large, and the shrinkage rate is small
（4）The cooling time is too long; the product fully shrinks in the mold and its size becomes smaller, and the shrinkage allowance after demolding is small
（5）The shrinkage rate value taken in mold dimension design is too large
（6）On the original basis, extra attention is needed: process parameter fluctuations or equipment status changes have aggravated this problem
Solução
（1）Appropriately reduce the holding pressure or shorten the holding pressure time
（2）Appropriately increase the mold temperature to a higher value within the 40-90°C range to increase shrinkage
（3）Appropriately increase the barrel temperature to a higher value within the 200-270°C range
（4）Verify the mold dimensions according to the actual shrinkage rate of 1.2-2.0, and repair the mold when necessary
（5）Establish a process parameter recording system, and test the first-piece dimensions at each shift change
（6）And strengthen process monitoring; on the original basis, extra attention is needed, with special attention to parameter stability
Conclusão principal
Oversized dimensions are mainly caused by insufficient shrinkage, and the actual shrinkage rate is controlled within the tolerance range by adjusting the holding pressure and temperature parameters.
Targeted preventive measures need to be taken in different production scenarios.
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