Material Drying
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PA6 Silver Streaks from Insufficient Drying
Problem Phenomenon
Fan-shaped silver-white streaks appeared on the surface of PA6 products, spreading outward from the gate; appearance parts were directly scrapped, often accompanied by tiny bubbles.
Cause Analysis
PA6 contains polar amide groups and has strong hygroscopicity; moisture-containing particles are heated in the barrel, moisture vaporizes and fills with the melt, leaving silver streaks on the cavity surface; insufficient drying, dryer dew point not meeting the standard, or secondary moisture absorption after drying are the main causes, and the moisture content allowed for PA6 is extremely low.
Solution
①Dehumidification drying at 80℃ for 4~6 hours, reducing moisture content to below 0.2%;②dryer dew point monitoring (recommended below -20℃);③seal after drying to prevent secondary moisture absorption and use up within a time limit;④verify moisture content by the Karl Fischer method when necessary;⑤appropriately reduce speed and increase back pressure for venting.
Key Takeaway
PA6 silver streaks = 'drying is the first suspect': verify moisture before adjusting the machine; PA6 absorbs moisture quickly and has a strict window, drying is both an appearance gate and a performance gate, and moisture content verification must be included in the startup SOP and cannot rely on feeling.
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