As you already know by some of my projects, that I needed away to remove rust from some of the old engines and metal parts that I was restoring. Two of my friends one a machinist and the other a part time farmer liked to repair farm equipment and tools that they found. They both gave me some information on electrolytic rust removal.
The method is a technique for returning surface rust to iron. It uses the effect of a small low voltage electric current and suitable electrolyte (solution). I read an article on this by Ted Kinsey here is the url: http://www.bhi.co.uk/hints/rust.htm/ I have quoted him quite a few times in this article and a lot of this is a reprint.
The advantages this method has over the old standbys, like vinegar, Coke, muriatic acid, Naval Jelly, wire brushing, sand blasting etc. is that these methods all remove material to remove the rust, including un-rusted surfaces. With many, the metal is left with a "pickled" look or a characteristic color and texture. The electrolytic method removes nothing: by returning surface rust to metallic iron, rust scale is loosened and can be easily removed. Un-rusted metal is not affected in any way. If screws, pivots, etc. are "rusted tight" this method will frequently solve these problems, without the need for force, which can break things.
The solutions used are not hazardous; the voltages and currents are low, so there is no electrical hazard. No noxious fumes are produced. The method is self limiting: it is impossible to over clean an object.
Electrolysis is a standard technique in the artifact restoration business. A plastic tub; a stainless steel or iron electrode, water and washing soda (Some people have had success with baking soda) and a battery charger. About a tablespoon of soda to a gallon of water. If you have trouble locating the washing soda, household lye will work just fine. It's a tad more nasty, always wear eye protection and be sure to add the lye to the water (NOT water to lye!!!) The solution is weak, and is not harmful, though you might want to wear gloves. The solution will last forever, though the loosened rust will make it pretty disgusting after a while. Evaporation and electrolysis will deplete the water from the solution. Add water ONLY to bring the level back.
The iron electrode works best if it surrounds the object to be cleaned, since the cleaning is "line of sight" to a certain extent. The iron electrode will be eaten away with time. Stainless steel has the advantage (some alloys, but not all) that it is not eaten away.
THE POLARITY IS CRUCIAL!! The iron or stainless electrode is connected to the positive (red) terminal. The object being cleaned, to the negative(black). Submerge the object, making sure you have good contact, which can be difficult with heavily rusted objects.
To start, turn on the power. If your charger has a meter, be sure some current is flowing. Again, good electrical contact may be hard to make-it is essential. Fine bubbles will rise from the object.
The amount of time that an object stays in the solution depends on the size of the object and of the iron electrode, and on the amount of rust. You will have to test the object by trying to wipe off the rust. If it is not completely clean, try again. Typical cleaning time for moderately rusted objects is a few hours. With heavily rusted objects can be left over night. I have actually left items in the solution for a week. That might be too long but I have had some pretty bad items.
To get the rust off, rub the object under running water. A paper towel will help. For heavily rusted objects, a plastic pot scrubber can be used, carefully. Depending on the amount of original rust, you may have to retreat. I have also used a wire brush and a wire wheel to get the item clean.
If an item is too big you can clean one end and then the other. Lap marks should be minimal if the cleaning was thorough.
The clean object will acquire surface rust very quickly, so wipe it dry and dry farther in a warm oven or with a hair dryer. You may want to apply a light oil, repaint or a coat of wax to prevent further rusting.
This method will not remove pitting. It only operates on the rust in immediate contact with unrusted metal. What's gone is gone. The surface of rusted metal is left black. Rusted pits are still pits. Shiny unrusted metal is untouched. Sound plating will not be affected. Plating under which rust has penetrated will usually be lifted. The solution may soften some paints. Test with a drop of solution in an inconspicuous place. Remove wood handles if possible before treating.
To dispose of the solution? The bath will last until it gets so disgusting that you decide it is time for a fresh one. There is nothing especially nasty about it, it is mildly basic, so disposal is not a concern, except you may not want all the crud in your drains.
Do not use metal containers. Galvanized metal can introduce zinc into the solution. If you have used lye, it will attack aluminum. You may have problems with electrical shorts, etc. Stick to plastic.
To clean odd shaped objects be ingenious. Plastic PVC pipe and gutters, wooden boxes with poly vapor barrier can be used.
My machinist friend uses a 5 gal bucket, a piece of stainless steel and a battery charger. The farmer friend uses a 55 gal drum that is cut in half length ways. He made a frame for his that has straps that holds the drum in place. He also uses a piece of stainless steel and a battery charger. One use baking soda and the other washing soda.
When I built mine I used the farmers design and use a 55 gal drum and built a frame for it. Here is a picture of mine Electrolytic Machine:
I had something interesting that happen to me. My farmer friend gave me some stainless sheeting. I cut pieces off of it and used washing soda for my solution. The stainless steel would disintegrate after a month of use. I finely decide it had some steel in it and that is why it would go bad. My brother in-law gave be a bar of stainless steel and I just got it out of the tank and it had pits all over it. None of the other people I know is having this problem. Their stainless steal sheeting is just like it was when they put it in the tank. I believe there is something in the water at my home. There could be a high content of metal that is interacting with the solution. I am going to try and investigate this further. This project has been a great help with rebuilding some of my projects and I have more to do. Hope this helps you too.