I need to remove what I think is called black oxide from some steel plates. These range from 2' square to 20" round x 3/8 thick.

We use them at the plant for moving large valves on stainless steel ball tables. The ball tables get covered in black crap coming off these plates and it is causing a contamination problem.

I wore out a new 4 1/2" Dewalt flap disc on one plate today (60 grit) and had to finish with something else. That disc cost 8 bucks. There will be 30+ of these plates and both sides need to be clean.

Maybe a grinding disc followed by sanding? Rust shouldn't be a problem, the plates stay covered in hydraulic fluid 24 /7. This first one is a trial to make sure they don't rust.

I want to stay away from chemicals. What do you suggest? or any ideas to prevent this contamination would also help. These ball tables are very hard to clean.