Extrusion & Post
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POM internal stress cracking and embrittlement
Problem Phenomenon
Cracks appear in products after a period of use, starting first at assembled stressed parts, improving after annealing or reducing injection pressure.
Cause Analysis
Excessive injection pressure and too low mold temperature cause large internal stress in products; POM crystalline material releases internal stress slowly and cracks along stress concentration points when stressed or in contact with media.
Solution
①Reduce injection and holding pressure; ②increase mold temperature; ③extend cooling time for slow shaping; ④perform annealing to release stress if necessary.; after adjustment, continuously sample to verify the effect, and resume mass production only after confirming stability
Key Takeaway
Internal stress cracking has a lag and is difficult to detect at the factory; a mild process with low pressure and high mold temperature is the prevention principle, and critical parts should undergo stress verification.; after confirming effectiveness, fix the parameters and practices into the work instruction to prevent recurrence
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