Carbon Arc Torch question

Howdy,
I have the need to braze a fitting (carbide) on the end of a brass rod (1/2" diameter). While an Oxy/Acetylene setup would be the "best" way to
accomplish this, I am nontheless wondering if a carbon arc torch would also work. Since I already have an AC arc welder, picking up an arc torch would be a lot cheaper than an O/A setup, and I wouldn't need to hassle with tanks. .
Thanks for any insights on this,
Jon
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wrote:

I would try using a propane torch and silver solder. You will need to use some insulating firebrick to contain the heat and might need to use a second propane torch to keep the heat from being conducted away by the brass rod. Depends on how long the rod is. A carbon arc torch will provide a lot more heat than you need, but will work.
Dan
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Thanks Dan, and also Roy.
I did try propane, both a Bernzomatic torch and a homemade forge job. The Bernzomatic didn't heat it sufficiently, and the homemade job, while putting out sufficient heat, was rather unweildy and hard to work around.
My main concern with the carbon arc torch was lack of heat, but if it puts out enough heat I'll give it a try.
Thanks again,
Jon
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Heat is not an issue. Control is an issue. But give MAPP gas a try.
Jon Danniken wrote:

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wrote:

The amount of heat from a carbon arc torch depends on the welder. But I expect you will find you will have more than enough heat. If the piece you are brazing the carbide on does not have to look good, you might just get some carbon rods and put one in your electrode holder and use the arc between that rod and the work.
Dan
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Ah, good idea, thanks for the tip. It certainly doesn't have to win any beauty contests, just be secure.
I'll pick up a carbon rod and play around with it that way.
Thanks again,
Jon
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wrote:

Jon, it sounds like you really want to try out a carbon arc torch. I encourage all such experimentation and use a carbon torch myself for occasional highly specialized tasks like welding wire screen tubes for epoxy bolt installation in brick walls. In that case I use it in a contact heating mode, not in an arc mode. Plenty of heat at the contact point, but somewhat hard to control. I use a high current, low voltage transformer for that task. It is about a 1 KW transformer, I think. A very few volts at a few hundred amps. Sold under the GE trade name "Pyrotip," and probably about 60 or 80 years old, judging from the style. If you do try the carbon approach I recommend starting with very low current with a single carbon in hard contact with the carbide. Work up gradually with the current until you get sufficient heating. Almost all heat generation will be at the contact point. If you let it arc you will erode the workpiece.
However, I do not think the carbon torch will be your best selection for soldering the carbide tip. A MAPP gas torch, only slightly more expensive than a home style propane torch, should do the job fine and with much more controllability. Set up a propane torch to preheat the rod just back from the tip. When the rod is as hot as it's going to get with the propane torch, apply the MAPP flame to the pre-fluxed tip. You will probably find it easiest to use spelter, a mixture of silver solder filings and flux, pre-applied in the joint, rather than only a wire of silver solder applied to the hot joint. The latter will work fine, but the spelter assures that silver solder is present throughout the joint. An alternative is thin sheet silver solder put into the joint with flux before heating. You can buy sheet silver solder at jewellers suppliers or for a small job, you can pound your own out of wire with a CLEAN hammer and anvil.
Have fun.
awright
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awright wrote:

I never used a carbon arc torch but a long time welder friend of mine swears by them for doing a lot of jobs including brazing.
John
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wrote:

I havent done any welding in about 20 years but when I was learning my instuctor would use one much like a TIG welder. I specifically remember him brazing the house of a cast iron water pump that cracked due to freezing.. I recently bought a Hobart AC/DC stick welder and have done enough projects around the house that I feel confident to build the trailer I wanted. I too would like to learn more about using a carbon arc to weld/braze with but the information seems scarce. I was thinking of getting some old welding books. I think AUDEN used to have one.
Jimmie
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Jimmie, I think you are thinking of AUDEL books, and I too remember seeing such a book once.
The Welding Handbook, Vol 3, 7th ed., Welding Processes...," published by the American Welding Society has about four pages of useful information on carbon arc welding. Try finding it in a book search like abebooks. Just now three come up for $12, $20, and $24. Google, "book search."
They make it sound like a useful technology used somewhat in the fashion of TIG, but with less effective shielding. Most of the shielding is from CO produced in the cabon arc (which also suggests that good ventilation would be important). Temperature is 7000 to 9000 degrees F, depending upon current, which reinforces (to me) my earlier suggestion to use contact heating of the carbide with a carbon pressed hard against the carbide insert, rather than using a carbon arc.
For welding, they suggest a long tapered tip to 1/2 the carbon rod diameter. The illustration shows a taper length of about 5 rod diameters, but it's not clear that that is intended to be accurate because it also shows the taper going to a point. They give a table of current ranges for "baked carbon" rod diameters:
1/8" 15-30 amps. 3/16" 25-55 amps. 1/4" 50-85 amps. 5/16" 75-115 amps. 3/8" 100-150 amps. 7/16" 125-185 amps. 1/2" 150-225 amps. ------------------------------ 7/8" 300-500 amps.
Higher currents can be used but carbons will be consumed more rapidly. Recommended current ranges are about 10 - 15% higher for Graphite electrodes, but graphite rods are consumed more rapidly than baked carbon rods.
Electrode negative. 4 or 5 inches rod stickout from holder for steel. Clamp joint tightly together with no root opening (for steel plate). Initiate arc by contact and pulling away, but if reigniting an arc on a hot bead, strike away from the bead to prevent a carbon inclusion that can harden the deposit at the point of restriking. Use technique like TIG with or without filler rod as required for the joint. (Sounds like a poor man's TIG welder.) Vertical or overhead welding difficult because you are puddling the molten metal. Use backing for welding thin sheet. They comment that carbon arc welding on outside corners on 14 - 18 ga. sheet steel with no filler produces neater joints more cheaply than SMAW.
They point out that the carbon arc can be used to braze galvanized sheet without burning the galvanizing by directing the heat on the brazing rod, rather than on the work (but I have my doubts).
Have fun.
awright
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Awright your alright. I belive you can control whether the heat is on the rod or the work with polarity selection. Also I have only seen this done at low current, Basically an AC/DC welder cranked as low as it will go.
Yeah I realised AUDEN should Have been AUDEL right after I hit the send button.
Jimmie
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A carbon arc torch provides lots of heat but not much precision. I've used one for brazing up castings where you need to heat the whole thing red hot, much cheaper than O/A gas. Not sure I'd tackle a small object with one. Someone else mentioned silver solder and a MAPP gas torch, much better idea than the Carbon Arc. I think you can get the brazing rod to flow on that small a project using MAPP.
Jon Danniken wrote:

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