Wednesday, November 20, 2013

Project "Bantam" - easy rust removal through chemistry and electricity

I was going to media blast the rust off, but I recalled an electrolysis process which might work well.  Since I just lent out my media blaster, I figured this was an easy enough thing to try on a sunny afternoon.  I rigged up a variable power supply with ground fault protection, and overcurrent / short circuit protection.  Its not fancy but it works.  The autotransformer (variac) feeds an isolation transformer which has a huge 24vac secondary.  I put a 5 amp breaker in series with the variac output to protect it.  The limiting factor is the rectifier which is protected by a 10 amp fuse.  I also put a ammeter in series to watch the action and adjust the variac as needed.

I got a plastic tub, which I estimate to hold 12 gallons, and filled it with the appropriate mixture of water and soda ash (sodium carbonate).  The grocery store had a nice box of Arm&Hammer Washing Soda in the detergent isle.  I applied power, and watched for smoke!  It was eventful enough to get some nice bubbles form on the electrodes as the variac was dialed up to 3 amps DC current drain from the tank.  Now I just watch and wait while chemistry takes the labor out of rust removal.

Process Started 
Witches brew of ions and oxides
Unfortunately, its going to be too hard to get the whole tractor frame in a tank big enough.

The results were rather good.  The old paint and rust just came right off after about 24 hours of electrolysis.  The anodes needed scraped clean every so often as the current dropped off due to the increased resistance.  After removing the grill from the tank, the smallest pits of the original casting were free from rust.  I was pleasantly surprised.  The wire brush took care of the rest of the residue with a minimal amount of scrubbing.  The resulting "black rust" magnetite conversion scrubs right off.  I shot the grill with a quick coat of primer to avoid any more red iron oxide rust.  The whole surface will need to be glazed and sanded with a fine grit to eliminate the appearance of any pits once the top coat is applied.

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