Injection Molding
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PA12 Discoloration and Thermal Degradation
Problem Phenomenon
【Problem phenomenon】PA12 products turned yellow and dark, with hue drift between batches
Cause Analysis
Excessively high melt temperature, excessively fast injection speed causing shear heat generation, too-small gate, and poor venting are the four major causes of discoloration; discoloration often indicates that the molecular weight has been damaged; during on-site troubleshooting, verify item by item according to this mechanism, and avoid blindly adjusting the machine based only on experience
Solution
Lower barrel temperature, screw speed, and back pressure; lower injection speed and pressure; enlarge the gate size; open or add vent holes and grooves; after adjustment, take consecutive samples to verify the effect, and resume mass production only after confirming stability
Key Takeaway
Discoloration is a thermal degradation alarm; lower temperature, lower speed, enlarge the gate, and vent trapped air together; after confirming effectiveness, solidify the parameters and practices into the work instruction to prevent recurrence; include this case in the defect archive as a reference for troubleshooting similar problems in the future
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