Due to the effects of repeated thermal degradation, recycled material differs significantly from virgin material in terms of flowability, strength, and moisture content; simply applying processing parameters intended for virgin material easily leads to defects such as silver streaks, bubbles, sink marks, brittleness, and dimensional instability. Properly adjusting molding parameters helps stabilize product quality and reduce defect rates.
Intensify drying: Recycled materials contain more impurities and have higher moisture content; therefore, extend the drying time and appropriately raise the drying temperature to prevent moisture from causing bubbles or silver streaks.
Consistent Mixing Ratio: Maintain a fixed ratio of virgin material to recycled material and avoid arbitrary changes; thorough mixing using a blender is recommended.
Screening and Control: Remove metal impurities and burnt material from regrind to prevent mold scratches and nozzle clogs.
Temperature settings: Since regrind is prone to thermal decomposition, lower the overall barrel temperature by 5–15°C; reduce the temperatures of the nozzle and the front section to minimize carbonization and carbon buildup.
Melt control: Appropriately reduce screw speed and back pressure to prevent material degradation caused by shear-induced overheating.
Pressure and Speed: Due to significant fluctuations in the flowability of recycled material, slightly increase the injection pressure; use medium-to-low injection speeds to prevent excessive internal stress.
Cooling time: The shrinkage characteristics of recycled material differ; fine-tuning the cooling duration helps mitigate issues such as sink marks and deformation.
Improve the mold venting grade to prevent scorching and short shots caused by gases generated during the decomposition of regrind material.
Control the cycle time, avoid prolonged heat soaking, and promptly empty the barrel during shutdowns.
Stabilize mold temperature and reduce product dimensional fluctuations.
The higher the proportion of recycled material, the greater the extent of process adjustments required; product toughness and appearance should be tested via periodic sampling. For long-term production, it is recommended to establish dedicated process profiles for recycled materials to facilitate quick machine setup.
Stable pretreatment combined with standardized process parameters is the key to the mass production of blends containing recycled materials, effectively controlling defects and raw material waste.
