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Rust removal by electrolysis

I have found that mechanical methods of rust removal damage the metal and are hard work. I found that using diluted orthophosphoric acid did convert the rust but without other salts didn't offer a long term rust free life. Commercial products based on orthophosphoric acid do work better but are expensive. I have tried one of the expensive organic rust killers and wasn't impressed. On the whole I was not satisfied with these chemical methods despite being trained as a chemical engineer!

Browsing the web I found a number of sites such as;

which described rust removal using electrolysis. The basic idea is to use scrap iron or steel as the anode and the article to be de-rusted as the cathode in an alkaline bath and pass DC through it. The rust is converted into iron which form a loose powder on the surface of the article and any paint will lift off. These residues can be wire brushed off easily leaving a grey, reactive metal surface. The beauty of the method is the article is not damaged by prolonged de-rusting.

I used either a scrap cast iron clutch pressure plate or a length of 25mm steel angle as anodes and the bath was a solution of Mangers Sugar Soap which I guess is trisodium phosphate. The quantity is not critical, all that is needed is a conductive solution. I put a couple of generous tablespoonfuls into about 20 litres of water. I used a home built power supply which gave about 4 to 8 amps at 20volts DC. The current depends mainly on the surface area of the electrodes. The solution gets very dirty with red rust which will stain T shirts etc (How do I know this?). I used a couple of containers; a plastic trug borrowed from my other half and a tall container made from a length of 100mm diameter plastic sewer pipe closed at the bottom with a stopped end fitting.

I have cleaned the suspension tie rods and cups, the front hubs and the steering track rods from my 2CV.

A few caveats;

The two photographs (sorry about the quality) are front and back views of the left and right front hubs, one before and the other after de-rusting. You can see how the paint was removed leaving a shiny surface whereas the rusted areas gave a matte finish.

David Tocher; Chassis #189

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