Material Drying
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Silver streaks/material flowers appearing on the surface of random copolymer polypropylene injection molded products
Fenómeno do problema
Silver-white streaks appear on the product surface along the melt flow direction, distributed in a fan or radial pattern, extending from near the gate into the product interior.
Silver streaks not only affect appearance quality but may also be accompanied by material degradation, reducing product mechanical strength.
Análise das causas
(1) Moisture content in the raw material exceeds the standard; moisture vaporizes at high temperature to produce silvery bubbles carried to the surface by the melt
(2) Barrel temperature is set too high (exceeding the 190-260°C upper limit); the material thermally degrades in the barrel and produces gas
(3) Screw speed is too fast or back pressure is insufficient, resulting in poor venting and air mixing into the melt
(4) Nozzle temperature is too low producing cold material, or poor mold venting causes gas in the cavity to be drawn into the melt
(5) Regrind contains moisture or many impurities, producing gas at high temperature
Solução
(1) Fully dry the raw material; random copolymer polypropylene is dried at 60-80°C for 2-4h, with moisture content controlled below 0.02%
(2) Lower barrel temperature to a reasonable value within the 190-260°C range to avoid local overheating
(3) Appropriately increase back pressure to 5-10MPa and reduce screw speed to ensure full melt venting
(4) Increase nozzle temperature to 5-10°C lower than the front barrel temperature to prevent cold material
(5) Check mold vent grooves; vent groove depth is 0.01-0.03mm to ensure smooth venting
Conclusão principal
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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