When stainless is welded, it often discolours at the weld. Not only is it good to remove this 'scale', or discolouration, for cosmetic reasons; it also may help to prevent corrosion.
For years the only ways I knew of to clean the welds was with abrasives, or by applying a strong pickling acid.... normally in the form of a paste. This paste would typically sit on the weld for half an hour, then you'd use water and a scouring pad or stainless wire brush to remove it.
The traditional pickling paste is a relatively dangerous substance, and the disposal of the rinse water and waste acid is a problem.
Chemicals used as the electrolyte for electro-cleaning can be relatively benign. The liquid featured in this video is a commercial product designed to inhibit rust. I understand that it contains phosphoric acid and another organic chemical which is not essential to the cleaning process (and may even hinder it). So while the results I'm currently getting are good enough for now, I intend experimenting with other chemicals. There are commercially produced weld-cleaning electrolytes that appear to work very well.
I have seen references to citric acid and phosphoric acid as major ingredients for this process. Pure forms of both these substances are sometimes used in food products.
In this video I'm using a 12 volt battery charger as a DC power source. I've also used my TIG welder set on low amps to do the job, and I think it works faster...although sometimes small arcs from the brush will mark the stainless. I've made an adapter for the brush which clamps on to the TIG electrode. I tried using some old, small DC chargers that I had laying around but I burned them out. The battery charger shown in the video 'grunts' a bit when the brush is applied to the metal, but it is still working after quite a few test runs.
With what I know of electroplating and electrolysis, I have assumed that this electro-cleaning will only work with a DC current. However I have read that a low voltage AC source will also work. I am yet to try this. As far as I know, it appears that the voltage to use for the job can typically be anywhere between five and thirty volts. If I were to choose an ideal power source, I'd like one that could happily provide 20 amps, although less will still give results. It may be a good idea to include some sort of resistance like a light bulb wired in series to the circuit to help restrict the current in some circumstances.
The brush is made from carbon fibre. I purchased a small amount of carbon fibre cloth for just a few dollars through AliExpress. The fibres are bound to a bit of 4mm stainless steel rod... the same way that old brooms were made. I used thin polyester thread for the binding on this particular brush, but I've also had success with monofilament fishing nylon.
I've also made a 'brush' by binding strips of scouring pad to the end of a metal bar. This certainly works, but I found that it is easy to get an arc travelling through the pad, and the pad melts or falls to bits easily.
Sturdy rubber gloves and safety glasses should be worn when doing this kind of work.
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