Material Drying
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Silver streaks/material bloom on the surface of homopolymer polypropylene injection products
Problem Phenomenon
Silvery white stripes appear on the product surface along the melt flow direction, distributed in fan or radial shapes, extending from near the gate toward the product interior.
Silver streaks not only affect appearance quality, but may also be accompanied by material degradation, reducing product mechanical strength.
Cause Analysis
(1) Moisture content in raw material exceeds standard; at high temperature moisture vaporizes producing silvery bubbles carried to the surface by the melt
(2) Barrel temperature set too high (exceeding the 200-280°C upper limit); material thermally degrades in the barrel producing gas
(3) Screw rotation speed too fast or back pressure insufficient, causing poor venting, air mixed into the melt
(4) Nozzle temperature too low producing cold material, or poor mold venting with cavity gas drawn into the melt
(5) Regrind contains moisture or many impurities, producing gas at high temperature
Solution
(1) Fully dry raw material; homopolymer polypropylene drying temperature 60-80°C for 2-4h, moisture content controlled below 0.02%
(2) Reduce barrel temperature to a reasonable value within the 200-280°C range, avoid local overheating
(3) Appropriately increase back pressure to 5-10MPa, reduce screw rotation speed, ensure sufficient melt venting
(4) Increase nozzle temperature to 5-10°C lower than the front barrel temperature, prevent cold material formation
(5) Check mold vent grooves; vent groove depth 0.01-0.03mm, ensure smooth venting
Key Takeaway
Silver streaks are mainly caused by raw material moisture, thermal degradation, or poor venting; systematic investigation is needed from three aspects: raw '2079851475616104451, temperature control, and mold venting.
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