Processing Machinery
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PA66 yellowing
Fenómeno do problema
Natural-color PA66 products turn yellow, appearance and light transmission deteriorate.
Análise das causas
Melt temperature exceeds the upper limit or residence time is long causing thermal degradation; shear heat makes actual melt temperature exceed the standard; PA66 is processed at high temperature, so thermal degradation risk is inherently high; during on-site troubleshooting, verify item by item according to this mechanism, and avoid blindly adjusting the machine based solely on experience.
Solução
①Lower melt temperature into the window; ②shorten melt residence time in the barrel to reduce heat accumulation degradation; ③reduce screw speed and back pressure to reduce shear heat generation; ④thoroughly clean the machine, removing accumulated material in dead corners of the barrel and hot runner; ⑤measure the actual melt temperature with temperature measurement means and calibrate the process settings.
Conclusão principal
PA66 yellowing='temperature or residence time out of bounds': narrow-window materials have zero tolerance for over-temperature; shear heat must be measured, residence time must be managed at the minute level; after confirming effectiveness, fix the parameters and practices into the work instruction to prevent recurrence.
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