Re: injection unit for EVA
I’m not familiar with EVA, but your screw looks fine to me. Clean it with a brass brush. I don’t think EVA should be corrosive and nylon certainly isn’t (although glass-filled grades are obviously abrasive and will cause screw wear). Your screw appears to have some sort of mixing geometry, which may be adding shear and contributing to the black speck problem. If you have a standard square-pitch screw, use that instead. Otherwise, try lowering your back pressure and/or screw rpm on recovery.
Re: injection unit for EVA
The screw looks pretty good to me as well. It just needs to be properly cleaned. I also see the secondary screw flight so
I suspect it's maybe a barrier screw so it requires a specific barrel heat profile to work its best. You really should purge the barrel down with something more heat stable than EVA. Never ran it though I've used some colors made with it that showed low heat preference and residence time issues.
Rick
Re: injection unit for EVA
Thank you for replies. Yes, it is a barrier screw. What methods do you recommend to clean it. My maintenance department do not do this so I'm asking. Do you use something else after brass brush?
Re: injection unit for EVA
No but the copper gauze is better and faster. Clean the barrel and all parts before reassembly.
Rick.