Molds & Tooling
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Storage cracking/delayed cracking of styrene-acrylonitrile copolymer PS products
Problem Phenomenon
PS products crack hours or days after processing, namely delayed cracking, caused by the slow release of residual stress.
Cause Analysis
(1) Product residual stress is large, and stress release over time causes cracking
(2) Product wall thickness is uneven, and internal stress is large at thick-wall areas
(3) Mold temperature is too low, and fast cooling speed results in high residual stress
(4) Improper demolding produces mechanical damage that becomes a crack source
(5) Ambient temperature changes accelerate stress release
Solution
(1) Increase mold temperature to reduce residual stress
(2) Optimize 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 products in a constant-temperature environment
Key Takeaway
PS delayed cracking is caused by the slow release of residual stress.
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