Material Drying
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ABS discoloration (yellowing)
Fenómeno do problema
Natural-color ABS products are yellow overall or locally, with large color differences between batches, affecting appearance consistency.
Análise das causas
Too high melt temperature or too long residence time causes thermal degradation; too high screw speed/back pressure generates shear heat, making the actual melt temperature exceed the setting; too high drying temperature or repeated drying can also pre-yellow the ABS.
Solução
①Control the barrel temperature at 200~240℃ and the nozzle at 210~250℃ according to the grade; ②shorten the residence time; ③reduce the screw speed and back pressure to control shear heat; ④the drying temperature does not exceed the upper limit and avoid repeated drying; ⑤purge the machine to remove dead corners.
Conclusão principal
ABS yellowing='a record of thermal history': controlling temperature, limiting time, and reducing shear simultaneously; the actual melt temperature is often higher than the setting, shear heat must be measured, and the drying step cannot be ignored either.
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