Electrolytic Rust Removal
I decided to try electrolytic rust removal after reading about it for several years. I found several sites including Tech Tips -- Electrolytic Rust Removal, Rust removal by electrolysis, Ted Kinsey's recipe for using electrolysis to remove rust from old tools, and some others. I picked up a badly rusted piece of 1/4" steel at my local sharpening service a few weeks ago. It was about 3" x 24". I cut it into two 12 inch pieces. I decided to use it to both experiment and make a couple of anodes I could use for derusting tools.
I don't have a 12 volt battery charger, so I built a 12 volt, 3 amp power supply from parts I picked up at Radio Shack. "Built" is used pretty loosely here, as you can see in the photo below.
The positive lead connects to the anode, which can be iron, steel or stainless steel. It should have at least as much area as the part you are derusting. The negative lead connects to the part you want to remove the rust from. An ideal arrangement is to have the anode completely surround the part, but you can turn the part from time to time if you have it on one side. I use two anodes connected together as a reasonable compromise. The electrolyte is a tablespoon or so of washing soda in a gallon of hot water. Adding more washing soda does not do anything to speed the process up or make it work better. The anodes will eventually be used up if they are not made of stainless steel, but it will take a long time for that to happen. You can find washing soda in most supermarkets near the laundry detergents.
The wood strip is supposed to keep the plates apart in case the cat comes along & gets nosey. Fat chance it will really help. The clamps are holding the bridge rectifier to a scrap of 1/8" aluminum that I'm using as a heat sink. The close-up below shows it a bit better.
I probably don't need the heat sink, but better safe than sorry. The gold-colored object on the left is a 0.1 ohm resistor that I'm using as a shunt to measure current with my digital multimeter, which only reads current up to 2 amps. A reading of 0.1 volt across the resistor equals one amp of current. Although this setup looks scary, it's really pretty safe. The line voltage connections are attached to the transformer with wire nuts and would be difficult to contact, although spilling a lot of electrolyte on the connections would probably not be a good thing. Everything else is low voltage, and the worst case scenario is destruction of the bridge rectifier or the transformer. The transformer will start to smell before it is badly damaged, or at least before it starts smoking and/or bursts into flames if there's a short circuit, and the bridge rectifier is rated for 25 amps - probably 3 or 4 times what the transformer can deliver. I'll be going back to Radio Shack tomorrow to buy a metal case to mount all this stuff in. I'm thinking of adding one or more 1157 automotive bulbs (in parallel) to serve as a current indicator and for short circuit protection. You can see this in the schematic below. I'll use a three wire line cord & ground the case for safety, too. All part numbers are Radio Shack part numbers. Radio Shack won't have the resistor and I'm not sure where you would buy just one of these. Mine came from my junk box. You can eliminate it if you don't want to measure the current draw or if you don't have a good multimeter.
Here's the derusting process part way through
The lower piece was partially derusted and used as the anode for the upper piece. Because there's nothing to protect it, that piece has started to rust again in the few minutes it took to get my camera and take the picture.
With the two plates about 4 inches apart, the power supply was delivering about 12.5 volts at a 1.8 amp draw. That seems to be plenty of current for objects this size. It took less than an hour to derust a half panel.
This is the first tool I am derusting. It was completely covered with a light coating of rust. This picture was taken after about 15 minutes in the bath, at a current of about 2.5 amps.
The tool has been in the bath for about 45 minutes. You can see the electrolyte is getting really ugly. Considering how cheap this stuff is, there's no way I'll be saving it for another session.
Latest update (4-13-04). Seems like it's getting harder and harder to find electronic parts at the retail level. Couldn't find sockets for the 1157 automotive bulbs, so I just left them out. Here's the power supply all packaged up. Looks a lot better than the jury rig I used yesterday.
If you're interested in the electrochemical reactions that are going on, you can find some information here.