Material Drying
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Silver Streaks/Material Flowers Appearing on the Surface of Low-Density Polyethylene Injection Molded Products
Problembeschreibung
Silver-white streaks appear on the product surface along the melt flow direction, distributed in a fan shape or radial shape, extending from near the gate to the inside of the product.
Silver streaks not only affect the appearance quality, but may also be accompanied by material degradation, reducing the mechanical strength of the product.
Ursachenanalyse
（1）The moisture content in the raw material exceeds the standard, and the water vaporizes at high temperature to produce silver bubbles, which are carried to the surface by the melt
（2）The barrel temperature is set too high (exceeding the 160-220°C upper limit), and the material thermally degrades in the barrel to produce gas
（3）The screw rotation speed is too fast or the back pressure is insufficient, resulting in poor venting and air mixing into the melt
（4）The nozzle temperature is too low, producing cold material, or the mold venting is poor and the gas in the cavity is involved in the melt
（5）The regrind contains water or many impurities, producing gas at high temperature
Lösung
（1）Fully dry the raw material; the drying temperature of low-density polyethylene is 60-80°C for 2-4h, and the moisture content is controlled below 0.02%
（2）Reduce the barrel temperature to a reasonable value within the 160-220°C range to avoid local overheating
（3）Appropriately increase the back pressure to 5-10MPa and reduce the screw rotation speed to ensure sufficient melt venting
（4）Increase the nozzle temperature to 5-10°C lower than the front barrel temperature to prevent cold material
（5）Check the mold vent grooves; the vent groove depth is 0.01-0.03mm to ensure smooth venting
Wichtigste Erkenntnis
Silver streaks are mainly caused by raw material moisture, thermal degradation, or poor venting, and need to be systematically investigated from three aspects: raw '2079851475616104451, temperature control, and mold venting.
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