Extrusion & Post
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Excessive shrinkage rate of random copolymer polypropylene pipe special material extruded products (Variant: mass production scenario)
Problem Phenomenon
The extruded product shrinks significantly in size after cooling, exceeding the tolerance range.
Excessive shrinkage rate causes the product size to be small, affecting fitting and use.
In particular, in continuous mass production, this problem is more prominent and needs key attention.
Cause Analysis
（1）Random copolymer polypropylene pipe special material has high crystallinity, and cooling crystallization causes volume shrinkage
（2）The melt temperature is high, the volume expansion is large, and the shrinkage after cooling is large
（3）The cooling rate is slow, the crystallinity is high, and the shrinkage is large
（4）The haul-off speed is too slow, and the product expands at the die
（5）The raw material grade is improperly selected, and the shrinkage rate is large
（6）In continuous mass production, process parameter fluctuations or equipment status changes have aggravated this problem
Solution
（1）Appropriately lower the barrel temperature to the lower value within the range of 200-220°C
（2）Appropriately increase the cooling rate to reduce the crystallinity and reduce shrinkage
（3）Adjust the haul-off speed and appropriately increase the draw ratio
（4）Select a grade with a small shrinkage rate, shrinkage rate 1.0-1.5
（5）Reserve shrinkage margin in mold design
（6）And establish standardized work instructions, with special attention to parameter stability in continuous mass production
Key Takeaway
Excessive shrinkage rate is caused by high crystallinity or high temperature, and needs to be solved by controlling the temperature and cooling rate.
In different production scenarios, targeted preventive measures need to be taken.
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