Any molder that shoots parts in natural colors or clear knows the havoc black specs and streaks can have on your quality metrics. Some molders have dedicated presses to running only light colored or clear parts trying to avoid contamination. Others have very elaborate analysis systems to determine a barrel/screw/non-return valve system requirements and customization. In a low to mid-volume non-captive environment, the volumes and return on investment assessments point to a system of monitoring and preventative maintenance. The best way to deal with black specs is to have systems in place to attack them at their root, degraded material collecting in the injection system.
Part of preventative maintenance involves monitoring and documenting the life and status of the injection system. The screw, barrel, and non-return valve (check ring) are a system that needs to work in harmony to deliver plastic from the hopper into the mold, achieving efficient melt and accurate volumes.
Preventing pockets and areas in the injection system that allow plastic to accumulate and degrade will go a long way to reducing scrap due to black specs and black streaks.
Other articles you might enjoy:
Material selection – past experience, spin the wheel, throw a dart or ask the expert?
Taking up residence – is the resin overstaying its welcome?
Resin selection – The past vs the future?