Silver Streak / Material Flower

Silver-white streaks appear on the surface of the part along the flow direction. Silver streaks appear as silver-white radial or comet-tail-shaped streaks along the melt flow direction, most obvious on transparent or dark-colored parts. The essence of silver streak formation is that volatile components (moisture or decomposition gas) in the melt are stretched into bubble filaments during filling, which then rupture or collapse during cooling, leaving fine silver-white grooves. Silver streaks not only affect appearance; more importantly, they indicate that the part material has undergone a certain degree of hydrolytic degradation, and its mechanical properties have substantially declined.

1. Equipment factors: moisture in the material, excessive barrel temperature causing decomposition, air entrainment by the screw, excessive nozzle temperature. 2. Mold comprehensive factors: in addition to venting, mold design parameters such as cooling water channel layout, gate position and size, and demolding draft angle all have a systematic impact on part quality, and optimization is required from the source of mold design.

1. Process parameter optimization and adjustment: fully dry the material, lower barrel and nozzle temperature, increase back pressure, reduce screw speed. 2. Systematic troubleshooting method: troubleshoot item by item in the order of "parameters -> material -> mold -> equipment". First adjust the parameters that are easiest to change, such as injection pressure and temperature, and observe the effect; if there is no improvement, check the drying and fluidity of the raw material; further check mold venting and gate design; finally check the mechanical condition of the equipment (check ring, screw). Change only one variable at a time to determine the root cause. 3. Preventive management: establish standardized process parameter cards and quality control limits for each mold/product, and regularly conduct process capability index (CPK) evaluation. For recurring problems, use fishbone diagram or 5Why analysis to trace the root cause, and fix the countermeasures as PFMEA control points.

The essence of silver streaks is that gas/volatile components expand in the melt to form surface defects. The first priority of the solution is always to fully dry the raw material, followed by controlling the barrel temperature to avoid material degradation and gas generation, supplemented by optimization of back pressure and screw speed.