Material Drying
2 views
General-purpose polyethylene injection molded products surface silver streaks/material streaks
Problem Phenomenon
Silvery-white stripes appear on the product surface along the melt flow direction, distributed in a fan-shaped or radial pattern, extending from near the gate toward the interior of the product.
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 the raw material exceeds the standard; at high temperature the moisture vaporizes producing silvery bubbles carried to the surface by the melt\
（2） Barrel temperature set too high （exceeding the 160-260°C upper limit）, material undergoes thermal degradation in the barrel producing gas\
（3） Screw speed too fast or back pressure insufficient, causing poor venting and air mixing into the melt\
（4） Nozzle temperature too low producing cold slug, or poor mold venting causing gas in the cavity to be drawn into the melt\
（5） Regrind contains moisture or many impurities, producing gas at high temperature
Solution
（1） Fully dry the raw material, general-purpose polyethylene drying temperature 60-80°C for 2-4h, moisture content controlled below 0.02%\
（2） Lower the barrel temperature to a reasonable value within the 160-260°C range to avoid local overheating\
（3） Appropriately increase back pressure to 5-10MPa, reduce screw speed, ensure adequate melt venting\
（4） Increase nozzle temperature to 5-10°C lower than the front barrel section temperature to prevent cold slug\
（5） Check mold vent grooves, vent groove depth 0.01-0.03mm, ensure smooth venting
Key Takeaway
Silver streaks are mainly caused by moisture in the raw material, thermal degradation or poor venting, requiring systematic investigation from three aspects: raw '2079851475616104451, temperature control and mold venting.
Was this helpful?
0 people found this helpful
Thank you for your feedback!