Material Drying
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ABS discoloration (yellowing)
Problembeschreibung
Natural-color ABS products are yellow overall or locally, with large color differences between batches, affecting appearance consistency.
Ursachenanalyse
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.
Lösung
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.
Wichtigste Erkenntnis
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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