Injection Molding
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Cracking of Biaxially Oriented Polypropylene Film Products Caused by Internal Stress
Problem Phenomenon
The product cracks during use or storage; the root cause is the internal stress generated during processing.
Cause Analysis
(1) The injection speed is too fast, and the orientation of molecular chains generates orientation stress
(2) The holding pressure is too high or the holding time is too long
(3) The mold temperature is too low, and the melt cools rapidly, generating thermal stress
(4) The wall thickness of the product is uneven, and stress concentrates at the junction of thick and thin parts
(5) Mechanical stress during demolding
Solution
(1) Reduce the injection speed and adopt multi-stage injection
(2) Appropriately reduce the holding pressure
(3) Increase the mold temperature to the higher value within the range of 20-60°C
(4) Optimize the product design with uniform wall thickness and enlarged fillets at corners
(5) Ensure uniform force during demolding
Key Takeaway
Internal stress cracking is a manifestation of processing stress exceeding the strength of the material.
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