Material Drying
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Silver streaks/material bloom appearing on the surface of polypropylene injection molded products
Problem Phenomenon
Silver-white stripes 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 interior 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.
Cause Analysis
（1）The moisture content of the raw material exceeds the standard, and the moisture vaporizes at high temperature to produce silver bubbles that are carried to the surface by the melt
（2）The barrel temperature is set too high (exceeding the 200-280°C upper limit), and the material thermally degrades in the barrel to produce gas
（3）The screw 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 slugs, or the mold venting is poor and the gas in the cavity is drawn into the melt
（5）The regrind contains moisture or many impurities, producing gas at high temperature
Solution
（1）Fully dry the raw material; the polypropylene drying temperature is 60-80°C for 2-4h, and the moisture content is controlled below 0.02%
（2）Lower the barrel temperature to a reasonable value within the range of 200-280°C to avoid local overheating
（3）Appropriately raise the back pressure to 5-10MPa and reduce the screw speed to ensure sufficient melt venting
（4）Raise the nozzle temperature to 5-10°C lower than the front barrel temperature to prevent cold slugs
（5）Check the mold venting grooves, with a venting groove depth of 0.01-0.03mm, to ensure smooth venting
Key Takeaway
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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