Help: Acrylic Black Specks and Pitting

[Joel JS]

Hello everyone, and Help!

We have a couple of jobs that run in different machines, that run same material. These parts are opaque and called 'Windows". I am not able to get rid of black specks and pitting (small imperfection, kind of looks like surface struck by a needle) We scrap 20 to 25% of product for mostly these 2 issues. The black specks and pitting are not in the same spot every time.

Picture of the smaller part attached, (did not try to get picture of defects, as they are small and likely too small to capture well in picture.) Other part is similar, just larger, and has similar defects.)

- Pictured job runs in a 40 ton, and shot size is at 100% of screw capacity (not ideal, I know), Other job in a 88 ton and at 30% shot capacity.

- edge gated,
- Hot Sprue/Inlet
- Material, Acrylic (Acrylite H15, compounded dark grey) dried at 180F for 4 plus hours, and I believe that material is properly dried.

I have tried many variations of process parameters, so here are the most typical settings....

Barrel Temps 470 front - 460 Rear, 2 zones dme at 410F
H20 180
Back Pressure, 25%, (sorry, working on getting an exact number for this)
Fill Time - 1.5 seconds.
Overall Cycle time 35 seconds.

Running Virgin, have filtered the pellets for fines coming in with raw material. Have pulled and cleaned screws too! Nothing has worked.

Thx!, Joel