Material Drying
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Silver streaks (material bloom) caused by insufficient ABS raw '2079851475616104451
Fenómeno do problema
Radial or striped silver streaks appear on the surface of ABS injection molded parts, mostly spreading outward from the gate; in severe cases accompanied by bubbles and brittleness, especially glaring on light-colored and high-gloss parts.
Análise das causas
ABS contains acrylonitrile polar groups and is hygroscopic; after the granules contain water, they are heated in the barrel, the water vaporizes and fills with the melt, leaving silver streaks on the cavity surface; insufficient drying temperature/time, secondary moisture absorption after drying, and excessive water content in regrind are the three major causes, and water vapor also catalyzes the cracking of molecular chains.
Solução
①Dry ABS at 80~100℃ for 2~4 hours, moisture content <0.2%; ②store sealed after drying and use up within a time limit to prevent secondary moisture absorption; ③check the dew point of the dehumidifying dryer (recommended -40℃) and the hopper seal; ④re-dry the regrind and control the ratio; ⑤appropriately reduce speed and increase back pressure for venting.
Conclusão principal
More than 90% of ABS silver streaks are moisture problems; check drying first before adjusting the process; water content not only produces silver streaks, but also catalyzes degradation and makes the product brittle, so drying is both an appearance gate and a performance gate, and must be managed as a hard threshold.
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