Material Drying
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PA6 '2079851475616104452 Yellowing
Problem Phenomenon
Natural-color PA6 turned yellow, and light transmission and appearance deteriorated.
Cause Analysis
Excessively high material temperature or too-long residence causes thermal oxidation; excessively high drying temperature and too-long time also cause pre-yellowing; shear heat makes the actual melt temperature exceed the standard; during on-site troubleshooting, verify item by item according to this mechanism, and avoid blindly adjusting the machine based only on experience.
Solution
①Control material temperature at 240~270℃;②shorten the residence time of the melt in the barrel to reduce heat accumulation degradation;③drying temperature does not exceed 90℃;④thoroughly clean the machine to remove accumulated material in the dead corners of the barrel and hot runner;⑤reduce screw speed and back pressure to reduce shear heat generation.
Key Takeaway
PA6 yellowing = 'management of heat + oxygen': check at three places of material temperature, residence, and drying temperature; nylon is sensitive to thermal oxidation, and heat history must be strictly controlled; after confirming effectiveness, solidify the parameters and practices into the work instruction to prevent recurrence.
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