carbon welding electrode EDR test - uh oh

Jul 03, 2005 5 Replies
G

I posted last week about finding a 3/8x12" carbon rod for arc gouging, unclad, for 35¢. I took a little heat for only buying one. Well, today I tried it, and here's what happened. The wrong electrode bubbled! I have 2 old railroad track tie plates standing in a square 5 gallon detergent bucket, which I've been using as anodes quite successfully, although I have to take them out and wire brush them occasionally. I figured I'd hang the carbon rod in the middle, reverse the connetions, and just derust what had been my sacrificial anodes for awhile. Plugged in the battery charger (red wire to the carbon, black to the steel plates) and the carbon rod bubbled! Thinking the world had somehow stood on end, I swapped the connections. Then the carbon rod REALLY bubbled!



I measured the open circuit voltage of my battery charger to be a little over 18 volts DC, red lead positive (as it always was).



I haven't figured out what the deal is with the positive electrode bubbling, but since it might be nasty gas like chlorine, I stopped. Since the steel cathode didn't bubble, it doesn't appear this will work. Pilot error still seems likely. Any of you smart guys see what's going on? I don't.



Grant Erwin


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G

Still not quite sure, but I swapped in a real (expensive) graphite electrode and it behaved exactly like my carbon rod. In this setup the surface area of the cathode (the rusty steel) completely dwarfs that of the anode (the carbon) so maybe BOTH electrodes normally bubble and I didn't notice it before except at the anode. My electrochemistry training was elementary and long ago, but it seems conceivable that H2 is bubbling off at one electrode and O2 at the other. So maybe the carbon rod will work after all. Waiting for input from others, stay tuned ..

GWE

Grant Erw> I posted last week about finding a 3/8x12" carbon rod for arc gouging,

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H

Isn't that just hydrolysis? One pole liberates hydrogen, the other oxygen?

Harold

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W

Aluminun binder. New stuff. You could test it in air or O2 rich atmosphere.

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M

You want it to bubble! Because there is no iron (or other metal) to dissolve the current causes the separation O- ions from water to turn into O2 molecules instead of the Fe in the electrode turning into Fe+++ ions. There would be twice as much bubbling if the graphite is negative because there are two volumes of hydrogen given off for each volume of oxygen.

If the graphite holds up and doesn't fall apart or get eaten away then we're on to a winner.

Mark Rand RTFM

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