Molds & Tooling
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Storage Cracking/Delayed Cracking of Biaxially Oriented Polypropylene Film PS Products
Problem Phenomenon
PS products crack several hours or days after processing, namely delayed cracking, which is caused by the slow release of residual stress.
Cause Analysis
(1) The residual stress of the product is large, and the stress is released over time, causing cracking
(2) The wall thickness of the product is uneven, and the internal stress at the thick wall is large
(3) The mold temperature is too low, the cooling speed is fast, and the residual stress is high
(4) Improper demolding produces mechanical damage that becomes a crack source
(5) Environmental temperature changes accelerate stress release
Solution
(1) Increase the mold temperature to reduce residual stress
(2) Optimize the product design with uniform wall thickness
(3) Annealing treatment (60-80°C, 1-4h) to release stress
(4) Ensure uniform force during demolding
(5) Store the products in a constant-temperature environment
Key Takeaway
PS delayed cracking is caused by the slow release of residual stress.
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