electrolytic derusting - a figure for current density

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 an item.
Grant Erwin Kirkland, Washington
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On Tue, 07 Aug 2007 16:33:07 -0700, Grant Erwin

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.
--
Leon Fisk
Grand Rapids MI/Zone 5b
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I too have been archiving electrolytic derusting info and had this link http://myweb.tiscali.co.uk/andyspatch/rust.htm#considerations 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: http://users.moscow.com/oiseming/rustdemo/rustdemo.htm http://www.davidbradley.net/ERR.html http://www.bhi.co.uk/hints/rust.htm http://www.nothingtodo.org/projects/norust.htm
Art
wrote:

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On Wed, 8 Aug 2007 13:40:43 -0700, "WoodButcher"

Here are a couple more that you can add to the list.
http://www.650rider.com/Content/pid=6.html
http://engines.rustyiron.com/electrolysis/index.html
I keep the whole page/info locally, so I can't be sure anymore where some of it came from...
--
Leon Fisk
Grand Rapids MI/Zone 5b
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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 learned.
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.
Grant Erwin Kirkland, Washington
Leon Fisk wrote:

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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 electrolyte... What?
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 stuff :-)
Regards Mark Rand RTFM
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Mark Rand wrote:

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.
Grant
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wrote:

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.
Mark Rand RTFM
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