Injection Molding
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COC Internal Stress Causing Stress Cracking
Problem Phenomenon
COC products crack after contacting chemical media or long-term use, cracks originate from gates, sharp corners or assembly stress points, transparent parts have high crack visibility.
Cause Analysis
COC has high stress cracking sensitivity, crack resistance largely depends on the internal stress state of the product; high injection pressure, low holding pressure and mold temperature and fast filling all freeze large orientation stress.
Solution
①Adopt segmented injection speed, lower holding pressure and higher mold temperature to obtain low-stress products; ②holding pressure time limited to just eliminating sink marks; ③structure eliminates sharp corners; ④do stress cracking verification test according to end-use conditions.
Key Takeaway
The concept of COC stress management is prevention first; low-stress process combination needs to be verified and fixed at the mold trial stage; end-use medium contact test cannot be omitted.; after confirming effectiveness, fix the parameters and practices into the work instruction to prevent recurrence
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