Silver Streaks/Material Flow Marks on the Surface of High-Density Polyethylene Injection-Molded Products (Variant: Strengthened Measures)

Silver-white streaks appear on the product surface along the melt flow direction, distributed in a fan shape or radial pattern, extending from near the gate to the inside of the product. Silver streaks not only affect appearance quality but may also be accompanied by material degradation, reducing the mechanical strength of the product. In particular, additional attention is needed on the original basis; this problem is more prominent and requires focused attention.

(1) The moisture content in the raw material exceeds the standard; at high temperature the moisture vaporizes to produce silvery bubbles that are carried to the surface by the melt (2) The barrel temperature is set too high (exceeding the upper limit of 200-270°C), 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 material, or the mold venting is poor and gas in the cavity is involved into the melt (5) The regrind contains moisture or many impurities, producing gas at high temperature (6) On the original basis, additional attention is needed: fluctuations in process parameters or changes in equipment status have aggravated this problem

(1) Fully dry the raw material; dry block copolymer polypropylene at a drying temperature of 60-80°C for 2-4h, and control the moisture content below 0.02% (2) Reduce the barrel temperature to a reasonable value within the range of 200-270°C to avoid local overheating (3) Appropriately increase the back pressure to 5-10MPa and reduce the screw speed to ensure full venting of the melt (4) Increase the nozzle temperature to 5-10°C lower than the front-section barrel temperature to prevent cold material (5) Check the mold vent grooves; the vent groove depth is 0.01-0.03mm, ensuring smooth venting (6) Also strengthen process monitoring; on the original basis, additional attention is needed to pay special attention to parameter stability

Silver streaks are mainly caused by moisture in the raw material, thermal degradation, or poor venting, and need to be systematically investigated from three aspects: raw '2079851475616104451, temperature control, and mold venting. Targeted preventive measures need to be taken in different production scenarios.