Posted by David Sherman on Saturday, December 30, 2006 at 16:52:29 :
In Reply to: rust posted by bill in pa. on Saturday, December 30, 2006 at 15:04:30 :
It works well. I used it on a lot of rusty old lathe tooling and it produced a nice black oxide finish that, after oiling, was smoother and more rust-resistant than steel that's been pickled in acid. The washing soda doesn't participate in the chemical reaction and the amount of it isn't critical to success. All it does is make the solution conductive enough for the electricity to go through it. Baking soda will also work. The amount needed is very little, perhaps a tablespoon or two in a 5-gallon bucket. The exact amount isn't important.
The main problem with this method is that the scrap iron that "collects" the rust quickly gets covered with so much rust that it stops making good contact with the water and the reaction slows to a crawl. On things that are pretty rusty, I have to take the scrap metal out and clean it off frequently. I use a wire wheel on an angle grinder to do it. It occurs to me that perhaps the scrap iron could be replaced with something that the rust doesn't stick to as well, so it would be easy to knock or scrape it off. Next time I might try some stainless steel, copper, or even aluminum. Gold or platinum would probably be great, but I don't have a lot of gold or platinum scrap laying around.