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Author Topic: Electrolysis - for rust removal  (Read 21144 times)
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« Reply #15 on: July 31, 2012, 09:31:05 AM »

I was using this method back in the early seventies. I used a Black & Decker arc welder with a 30 Amp stud rectifier in series (and no battery). I used a piece of zinc sheet (used for roof flashing) as the anode (?). I used a cupful of salt to form the electrolyte. The polarity has to be correct, otherwise the reaction never really gets going.

It would take 20 - 60 minutes to clean a brake drum. The gas evolved at the boundary between rust and metal would force the rust off, leaving a dull but rust-free metal. It had to be painted or varnished to prevent further rusting. The water became quite hot! It smelt to me of ferric chloride but I'm no expert.
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« Reply #16 on: September 19, 2012, 10:45:30 AM »

It's a great technique! Old arc welder plus the rectifier pack from an old alternator (100A typically) and pair of 30A fuses in parallel, plus a bin with a sheet of steel wrapped inside...

Pressure wash to remove the black scale/sludge, then a quick dip in phosphoric acid to finish it off back to bright metal. (not shown) You can buy bulk (5 litre/25 litre) concentrated phosphoric acid from a farm supply shop, it's labelled up as "milkstone remover" and a quid or two a litre. Dilute 10:1.

Objects will re-rust very quickly, as the surface is chemically clean. Rinse in hot water, then towel dry. Paint with an etching primer and the acid etch will convert/bind the flash rust that you got, and the pitting/porosity of the part means that the paint sticks like the proverbial to a blanket.

When using the welder remember just how much hydrogen you can produce. (we often run at about 40AWe did have a shed explosion incident when a mate of mine started angle grinding in the vicinity of the open shed door. More loud thump than squeaky pop. Cleared most of the dust out though, heh! The hydrogen/oxygen liberated will also corrode any metal tools etc left in the vicinity. Don't use stainless electrodes, as you'll create chromates and they are bad things to put down drains. Steel is fine. The solution lasts forever if topped off with water as it evaporates. Eventually you'll have to shovel the sediment out of the bottom and that's the point I change solution. (about 6 inches in the bottom of the bin)
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