In the on-going search to easily remove one and achieve the other, the last several weeks of experimenting has yielded some results.
Soda ash (sodium hydroxide) didn’t work, it will strip paint and powder coating, though it doesn’t touch mill scale, but is just too nasty of a chemical to deal with safely IMO. It does however make an outstanding pre-wash type detergent and mixed 20-50:1 with water and just a dash of denatured alcohol thrown in it’s incredibly cheap, or you could just by it at the auto parts store, it’s called Castrol Superclean, not so cheap.
Oxi-solve works well, but better as a rinse if all scale and rust has been removed, it’s just too slow to effectively work as a production type use if mill scale and rust removal is the goal.
Other manufacturers including DuPont, PPG, POR, have phosphating chemical systems that will double as rust and mill scale removers , but you pay for them, alot. If time and scrubbing aren’t a factor they will work but will really lighten your wallet.
The best mill scale remover? Muratic acid, good ‘ol hydrochloric.
This is not a phosphating chemical but mixed 1:1 with de-mineralized water, mill scale will literally come off before your eyes, for $3.99 a gallon at your local hardware store. Once this has done the work in a fraction of the time required by the others, rinse, then spray with the phosphating chemical of your choice rinse again and viola’, no more endless, destructive messy sandblasting. Plus you have a surface for powdercoating that doesn’t get any better.