We have a new tool that was transfered into us. It's 48 cavity hot runner in acetal (Celcon M90) using a liquid color. We have the process dialed in to make parts at the center of the tolerance range for size (+/- .002).

We are having a lot of issue getting good mixing with the liquid color. Shinning a light through the parts shows swirls of light and dark areas, and on several cavities the knit line has clear variation of light on one side, darker on the other. There seems to be a slight correlation between which cavities show this more than others, but it isn't consistent.

We were feeding the color into the middle of the feed throat just below the loader and changed to using a copper tube to dispense it just above the screw. We moved from a larger diameter tube on the peristaltic pump to a smaller diameter. We tried with and without a .020" mesh filter nozzle body.

Shot size: 230 g
Color ratio: 1%
Cycle time: 20 seconds
Mold temp: 180 C
GP screw, using about 30% of the barrel.

Any advice for getting better mixing? We seemed to get slightly better results from high back pressures and low screw speeds but couldn't get the size in tolerance.