Carbon arc welding

Anybody have experience with single-carbon-arc welding on steel? I gather it was the first arc welding process developed and very
quickly replaced, but would like to know if it has a place in "hobby" welding, where quality of weld matters, as does cost, but speed isn't so important. Seems to me it should resemble O/A welding with a reducing flame. Stick welding never much appealed to me, especially in small work, because the heat and filler can't be controlled separately.
thanks for reading,
bob prohaska
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wrote:

Are you talking about a carbon arc torch - two sticks of carbon and an arc between the two? Used much like a oxy-acet torch for brazing, but difficult to control the heat.
Or some sort of single carbon and strike an arc to the parent metal? Heat control probably similar to stick welding and you need to add filler.
As you say, "developed and very quickly replaced", there was a reason for that.
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No, but rather:

Yes, that's it. Size the electrode and current to the base metal thickness for a stable arc, add filler as needed. Rather like gas welding.

That's the clue I'm looking for. If it was replaced because it's slow that's ok. If it was replaced because it's hard to control, especially for thin (.062 material) the process won't be of much interest. If it makes brittle welds that's another handicap, but a reducing O/A flame isn't a problem if one works briskly with low carbon filler. (And isn't building an airframe!).
Copper clad electrodes seem likely to cause weld contamination but bare electodes appear to be available for fussy gouging jobs.
AWS handbooks would be informative but rather pricey outside a library. I'll check the local libraries.
Thanks for reading,
bob prohaska
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wrote:

In nearly every instance when things are replaced, superceded, by another technique, it happens because the later techniques is better, in some manner. Faster, stronger, easier, cheaper.
You seem to intimate that for some reason oxy-acetylene is not to be used to build an airframe. Strange.
You see, I qualified with oxy-acetylene when it was the designated method of building, or repairing, aircraft airframes and years later welded a bloke's home built airframe which was later subjected to an airworthiness inspection. certainly the CAA/FAA didn't seem to have any objection to using oxy-acetylene :-)

The real question is, "why bother"? One can easily weld with Oxy-Acetylene, Stick, TIG, MIG, or any of the submerged welding techniques. Why would one want to bother with carbon electrodes?

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Agreed. Cheaper is my keyword. Easier is next. Stronger is nice, but this isn't a critical project. Faster does not matter.

O/A with a _neutral_ flame is understood to be acceptable. I did a bit of auto body work with a reducing flame (it was easier to carry a puddle on thin material) and had trouble with weld cracking. Apologies if my meaning was unclear or interpretation mistaken.

Understood, but a carbon electrode seem likely to produce a carburizing atmosphere. Perhaps not to the extent of acetylene, but still reducing. Then again, it might be worse.

For my part, cost, and curiosity 8-) Thanks for reading,
bob prohaska
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wrote:

That is one of the things you learn when becoming a welder :-) Somewhere I have notebooks filled with information about rods, flame, fluxes, parent metals, etc. I've probably forgotten all of it but that is what you had to know.

But why the need for a carbonizing arc? The usual aim is for a neutral flame, if oxy-acetylene welding.

Well, curiosity is a good reason, but cheap is, perhaps a bit far out. After all, you'll need some sort of a power supply to drive that carbon arc; hopefully a variable supply if you want any control of the arc, so you might as well start out with a commercial welding set :-)

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I'd like nothing better than a commercial welder, but I can't justify the cost for what is essentially a hobby. A nice Miller just got away from me and I will keep looking. In the meantime, an improvised scheme that works within limitations is an entertaining project. I played with carbon arcs as a child but never thought to try welding. Then I learned O/A well enough to do useful auto repairs and stick well enough for heavy (1/4") material. That equipment is long out of reach now. TIG is the obvious next step, but that's a serious investment.
A carbon arc might be a useful compromise between the power of stick and the control of O/A, provided the chemistry cooperates, using an improvised power supply. If I can carry a puddle that makes a not-too brittle weld in .050" mild steel it would count as a success, so the goals are fairly modest.
Thanks for reading,
bob prohaska
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wrote:

Err... You talk about an improvised power supply that will hold an arc using a carbon rod, but stick welding, which is holding an arc with a metal rod, is a problem?
As an aside, you can weld considerably thinner metal than 1/4" with an arc welder.
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At low currents it seemed to be. I could carry a steady arc with the output of an old automobile generator (gen, not alt) using heavy pencil leads (graphite) as electrodes. The current was probably in the low tens of amps. Metal electrodes stuck badly.
I'd expect an alternator to work considerably better (more voltage, self-limiting current, which is what I have and plan to try.

For a good operator with modern equipment (and maybe even not-so-modern) that's no doubt true, but at least for me thin electrodes and low current always spelled trouble. Carbon was vastly easier to strike and maintain. Current sufficient to keep a metal arc going always seemed to make for faster work than I found comfortable. That is a fault of the operator, but I'm stuck with him...8-)
In a way, it seems I'm looking for an electrical version of O/A: Heat independent of filler rate, perhaps more power density, no tanks and (above all!) minimum capital cost.
Thanks for reading!
bob prohaska
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wrote:

Well, as for equipment, I used to do it with a simple transformer welding machine :-) But you can easily buy 1.6 mm electrodes which can be used to weld some fairly thin metal, and I knew a bloke that claimed to have some 1 mm rods, although I never actually saw the electrodes.

Which seems to be saying that your weld puddle will have no protective atmosphere and be fully exposed to the air. I have this feeling that your weld beads are going to be somewhat less than an ideal composition.

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This is really the core question that wants an answer. My (possibly mistaken) hope is that the carbon evaporated from the electrode will scavenge oxygen leaving an atmosphere of CO. If this does not happen the whole scheme won't work, which is the knowledge I'm seeking. It may have been the reason for the original abandonment of the process, but nobody has said so yet.
An O/A flame is CO mixed with hydrogen, far as I can tell free hydrogen makes more trouble than it fixes at least with ferrous alloys. On that basis a hydrogen free "flame" ought to be better for welding.
Thanks for reading,
bob prohaska
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wrote:

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.
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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
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wrote:

You can calculate the relative percentages of combined and dissociated H and O from the bond energy and the temperature. http://www.eolss.net/sample-chapters/c08/e3-13-03-01.pdf 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
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wrote:

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.
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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
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wrote:

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.
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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
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On Wed, 12 Mar 2014 08:25:56 -0400, "Jim Wilkins"

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 :-)
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wrote:

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