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
Thanks for any insights on this,
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.
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.
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.
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.
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.
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, 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,
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
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).
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