Material Drying
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PC Silver Streaks from Insufficient Raw '2079851475616104451
Problem Phenomenon
Fan-shaped silver-white streaks appear on the PC product surface, mostly radiating outward from the gate, transparent parts and appearance parts are directly scrapped, often accompanied by tiny bubbles.
Cause Analysis
PC is a strongly hygroscopic engineering plastic; trace moisture rapidly vaporizes in the 280~320°C barrel, enters the cavity with the melt, and leaves silver streaks on the surface; insufficient drying time, the dryer's dew point not meeting the standard, or secondary moisture absorption after drying are the main causes, and PC allows an extremely low moisture content.
Solution
①Use a dehumidifying dryer with dew point ≤-40°C; ②Fully dry according to grade requirements (generally around 120°C, more than 4 hours); ③Use the Karl Fischer method to verify moisture content ≤0.02% before starting the machine; ④Store sealed after drying and use up within a limited time; ⑤Appropriately reduce injection speed and increase back pressure for venting.
Key Takeaway
PC silver streaks are almost always a drying problem: PC is extremely sensitive to moisture, and moisture content must be managed at the 0.02% level; verify moisture before adjusting the machine, speak with data, instead of repeatedly trying process parameters, which only wastes time and material.
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