Posted by Sherman in Idaho [108.162.245.23] on Sunday, May 22, 2016 at 23:17:44 :
In Reply to: Electric Rust Removal Questions posted by Joe Lorenzino [108.162.242.206] on Sunday, May 22, 2016 at 21:58:46 :
I keep an electrolytic de-rusting bucket full and ready to use at all times. I use it for pretty much anything that will fit. The wonderful thing about it is that you can't over-clean parts and it leaves them with a slightly blued finish which resists flash rust. It also doesn't leave a rough surface, other than the pits from where it took the rust out. As a bonus, it removes grease and paint.
Cleaning plated parts can be dicey. Usually well-attached plating stays on. I just cleaned a pair of ornate copper-plated cast-iron book ends that had been through a fire and they cleaned up nicely and none of the copper came off. On other things, I've had the plating lift.
The sacrificial electrode isn't really sacrificial. It doesn't have to dissolve to make the system work. The problem is that oxygen is evolved at the anode and it tends to corrode pretty much everything. Platinum would obviously be ideal, but we can't afford it. Heavy scrap steel will work but you need to take it out frequently and brush the rust off it or it will stop conducting. I use scrap stainless steel, which works fine, although some guys claim I'm poisoning everything downstream due to the chrome dissolving. It does so only very slowly, and mostly only if I let part of it stick up above the solution. But that could be a concern. Graphite is supposed to be excellent, not sure about old battery "carbons". I think they're too soft and would fall apart. I don't have access to titanium. Copper dissolves fairly fast as an anode. Aluminum is also no good. So, for now I'm using stainless steel scrounged from only sinks and restaurant equipment, cut to size with a plasma torch. My usual setup is a SS cylinder in a 5-gallon plastic bucket. When there's too much gunk on the bottom, which might take a few months, I dump it all down the drain and start with fresh solution. Any weak alkali will do for the electrolyte. I use washing soda, but baking soda or lye also work. The stronger the solution, the more conductive it is, which affects the speed, but not the quality, of the operation.
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