Carbon arc welding

According to the "oxy_handbook" the oxy-acet flame produces CO2 and Water, the hydrogen combines with oxygen. Of course if hydrogen combines with iron it weakens it. On the other hand the treatment to eliminate hydrogen embitterment is baking.

I don't think the carbon is consumed nearly fast enough to expect any shielding - the arc is mostly a nitrogen-oxygen plasma (ie, it's air, at

9000 degrees or so.) Any CO/CO2 that _is_ formed will be going _up_ with the force of considerable heating, preventing it from having much of a shielding effect unless you do all your welds overhead. What's getting sucked into the plume across your active weld zone is air.

Any knowledge I have of welding with carbons is is purely historical, not experiential, though I have experience using a _good_ twin carbon torch (with a trigger to adjust the spacing - no 30 second limit - be sure to bring a shade 13 or so filter and full leathers, they throw some MEAN light (UV and visible) - we learned to braze with them using flux coated rods and extra flux.

I believe that the early "electric arc separate filler rod" process used a flux-coated filler rod - the classic tale of someone welding things in an emergency is coathanger and wet newspaper. So you could probably use a normal (cellulosic, anyway) stick rod as filler rod and benefit from its coating/flux. Might want to use a normal electrode holder to hang onto it. I suppose you could also rig up shielding gas for carbon arc welding, but then you're spending money you should probably just spend on a used TIG rig.

Honestly, if you are on a low capital budget and want a process like gas welding, gas welding is it. If you happened to be working in non-ferrous metals there are nice tiny "water torches" that save on buying gas, but of course those are burning hydrogen/oxygen electrically generated at the torch base, so not good for steel. Jewelers use them.

If that's true then we have the answer I didn't want to hear 8-)

Did you observe oxidation of the base metal?

That might be worth a try, if I get that far.

That may be where I end up. The one thing I didn't like about O/A was the large heat affected zone.

I'm looking for general repair, mostly ferrous. Aluminum would be fun, but not really necessary. No refractories or noble metals. Usually small but bigger than jewelry. Bike frame size would be close, but less critical. k Thanks for reading,

bob prohaska

Those are the end products. Inside the flame it is said that "The flame at the apex of the small central white cone has a temperature of about 3000 (C). At that point the flame is almost entirely carbon monoxide surrounded by a jacket of hydrogen. The temperature of the apex of the flame is too high to allow the hydrogen to combine with the oxygen."

That quote is taken of Mellor's Modern Inorganic Chemistry, copyright

1967 but first published in 1912. How it was figured out escapes me. Perhaps spectroscopy. It does seem to suggest that hydrogen embrittlement should be common to O/A welding. Far as I know it's not a big problem....

Thanks for reading,

bob prohaska

That is perhaps the most encouraging lesson to come out of this discussion.

Thank you!

bob prohaska

Your mention of bike frames brings another factor into the discussion. The "fastening together"of the steel bike frame is primarily a matter of "gluing" together some extremely thin steel tubes so the choice of "welding gear" is primarily based on that factor. Aluminum frame bikes of course require specialized aluminum welding gear and the titanium bikes even more esoteric equipment. The selection of the welding equipment is primarily based on what parent metals are going to be joined.

My first welder was a beat-up Sears AC arc machine I bought from a band roadie for $30. He had broken the electrode jack plate and replaced it with sheet metal, which shorted the secondary. The low-range windings were darkened but still functional, and the frozen fan turned again after I disassembled it and flushed out the congealed salad oil. The friction adjustment on the Amps control was useless and not repairable because I didn't trust the strength of my epoxy repair to its broken cam handle, so I tied the handle in place with para cord.

And then it worked fine for years. jsw

You can calculate the relative percentages of combined and dissociated H and O from the bond energy and the temperature.

See Figure 3.

Also you can look at practical experience that says OA welding works fine, whether or not you understand why, and test samples of your own practice welds to destruction with a hydraulic press or BFH.

jsw, BS in Chemistry

No. You cut out the part where I stated that we used them for brazing, with flux. So the flux was doing that job...

I was recently in a Singapore yard that built "dumb barges" up to 200+ foot. Scattered all over the yard were transformer welders, some of which looked to have been bought when the yard was opened :-)

I seem to recall that even when brazing with flux, an O/A torch adjusting to give an ozidizing flame left white zinc oxide near the joint. If you didn't see that it's a good sign.

Thanks for writing,

bob prohaska