Material Analysis
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GPPS Internal Stress Delayed Cracking
Problem Phenomenon
The product cracks by itself about two days after molding and cannot be found during shipment inspection.
Cause Analysis
Molding internal stress is slowly released over time, and cracking occurs when the total stress exceeds the material strength; increased internal stress, increased external stress or decreased material strength are the three elements.
Solution
①Use polarizers to check the stress and orientation state of transparent parts; ②do heat distortion tests to evaluate stress levels; ③optimize molding conditions to reduce internal stress; ④avoid overheating and excessive regrind to protect strength.
Key Takeaway
The troubleshooting framework for delayed cracking is the three elements of internal stress, external stress and strength; polarization and heat distortion tests are two practical stress detection methods.; after confirming effectiveness, fix the parameters and practices into the work instruction to prevent recurrence
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