Tuesday, June 26, 2007

Electrolytic rust removal

Recently I have been experiencing problems with rust on my cars. I looked around on the internet and found an easy, but very effective method for rust removal. The method utilizes electrolysis and compared to other methods it's superb as it doesn't remove any base material. The only limitations for the method is that the part could be disassembled and that you have a tub with sufficient volume where you could submerge it.

You need a couple of ingredients for the method:
1. Caustic soda or crystal soda - 10g per liter, for the electrolytic bath
2. An iron or steel with low alloy content, as electrode
3. A plastic or plastic covered tub
4. Water
5. A variable current source. You could use a battery or an old car charger, but it's necessary to alter the current by adding extra resistors like a car bulb
6. Wires
7. A part that is rusted (duh)

I got asked by a colleague if I could try the method on a part for a cam shaft that he accidently had left on the floor of his leaking car. This is how the part looked before the rust removal:

The process creates hydrogen. As hydrogen is explosive with oxygen I found it safest to work outdoors.

I used caustic soda as it was impossible to obtain crystal soda. I read that others were using crystal soda, but that it should be safe to use caustic soda for the bath. Water was first filled, caustic soda was later weighed and added 10g per liter.

I used an old model train current source, but needed to rectify the voltage as it was AC, not DC as needed. The positive wire was connected to the sacrificial iron electrode and the negative wire was connected to the part that I wanted to remove rust from. The process starts faster if the wire has contact with base metal. The wire(s) to the sacrificial electrode(s) should not be submerged as it would destroy it/them. If the object is large you should surround it with several electrodes. This is my setup:

The current was adjusted to the lowest possible value as a medium sized object (dependent on the surface) needs approximately 200mA. I had ~170mA for what I consider a small object. It's not crucial that the current is low, but a fast process is supposed to make a non optimal result. You notice the start of the transformation by small hydrogen bubbles appearing on the surface of the part. I left the part for approximately one day in the tub, but you could keep it there forever if you wanted. After removal I rinse the part in water with a tooth brush, scrape off excess rust with a knife, remove water by rubbing it with paint thinner and cover it in oil. This is the result of the process (some rust are still seen on the picture, but this was easily removed with a small knife). I would highly recommend the method to others.