I derusted the inside of a welding water cooler tube last night. I used
an uncoated carbon arc gouging rod, maybe 3/8" diameter, insulated in
two places by multiply wrapped rubber bands, for an anode. Worked just
great, tube came out fine. I ran about 4 amps. The tube is about 8-10"
long, and about 1" ID. That works out to 125-150 milliamperes per
square inch. I figure that's a pretty good place to start when figuring
out how much of a power supply one will need to electrolytically derust
Thanks for the info Grant. I've been saving/archiving all of
these little tidbits of information concerning derusting.
Yours is one of the first to suggest some specific amperage
values based on square inches that I recall.
I too have been archiving electrolytic derusting info and had this link
where he currently recommends 1ma per square centimeter. Interestingly
enough my archived page (Oct-2004) shows his recommendation
as 1-5 mA per square centimeter.
Other electrolytic derusting links FYI:
Here are a couple more that you can add to the list.
I keep the whole page/info locally, so I can't be sure
anymore where some of it came from...
One square inch equals 6.45 square centimeters. My figure was 125-150 mA per
square inch, which would translate about to 20-23 mA per square centimeter.
I guess I like a little brisker bubbling action than those guys, or maybe I
made a mistake in my calculations. Reading the rust.htm link I see that he
recommends leaving the piece in "for a few days" and also he doesn't like
brisk bubbling action. Obviously he likes to use less current than I do.
I looked through the links below (thanks!) and most of them had some minor
point which I would take issue with. For example, Orrin's page describes
cutting out a disc (disk?) from a coffee can lid and using it stuck over a
steel rod as a spacer inside a cylinder. I prefer spacers that allow current
to flow much more freely. Nothing against Orrin or his page, it's where I
What I'm most interested in now is the use of lead sheet for the cathode. I
have tried this (as I've posted) and it works great, no current drop as I always
used to see with steel cathodes. The lead electrode turns red, so I suspect the
formation of red lead (lead tetraoxide) as opposed to lead carbonate as another
person has suggested. My only reason for thinking that is the color - lead
carbonate is white, and of course lead tetraoxide is red, and my electrode
turned red, not white. I don't believe that much lead is going into the bath,
and of course I wash my hands after handling it.
I wish I knew more chemistry sometimes.
Leon Fisk wrote:
'twas me Grant. In my case I was using washing soda solution (sodium
carbonate) as the electrolyte. The growth on the cathodes was white, which is
why I assumed lead carbonate. I assume that you are using a different
I could live with lead tetroxide as a contaminant... Wash it, dry it, grind it
and use it when scraping, It would save me the cost of buying more of the
Yes, I was using washing soda too. On my electrode, just above the
water line, there is some crusty white residue. This could be washing soda, or
it could be lead carbonate. The rest of the electrode is a smooth brown color.
That's what I thought might be red lead.
Hmm, same setups, different results, maybe current density and electrolyte
concentration play a part. I guess it can only be lead oxide or iron oxide. I
don't think I'm going to stop using lead cathodes in either case. Neither the
carbonate or the oxide is soluble and any build up stays in the tank.
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