Injection Molding
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Cracking caused by internal stress in styrene-acrylonitrile copolymer products
Problem Phenomenon
The product cracks during use or storage; the root cause is internal stress generated during processing.
Cause Analysis
(1) Injection speed is too fast, and molecular chain orientation produces orientation stress
(2) Holding pressure is too high or holding time is too long
(3) Mold temperature is too low, and rapid melt cooling produces thermal stress
(4) Product wall thickness is uneven, and stress concentrates at thick-thin junctions
(5) Mechanical stress during demolding
Solution
(1) Reduce injection speed, using multi-stage injection
(2) Appropriately reduce holding pressure
(3) Increase mold temperature to the higher value within the 50-90°C range
(4) Optimize 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 material strength.
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