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Dan Caster
 
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Default brass brazing with a large propane torch

A couple of thoughts. One is that the original designer was likely
using a larger refillable propane tank. There is less restriction
coming out of the tank and at high flows he probably had higher
pressure at the orifice. If you are going to do much of this I would
buy a 20 lb tank. Propane bought by the gallon is much cheaper than
by the small tank. You can also buy an adapter from Harbor Freight to
refill the small bottles from the larger tank.

You could also use a small sqirrel cage blower to blow air in that
hole in the back. You can control the pressure by a rotating bit of
sheet metal added to restrict the input.

I have made several torches similar to that one, but have not tried to
use them for brazing.

You can also buy a brazing rod called Sil-Fos. It is mostly copper
with a little silver and some phosphorous. It works well for copper
and copper alloys. The AWS spec isBCuP-5. Any welding supply shop
should have it and maybe plumbing supply houses. I have used it with a
small propane torch on things that are not too big. And as someone
else said some insulating fire brick around and under your work will
help a lot.

Where are you located?

Dan



(Eric Chang) wrote in message

When it was done, it lit OK, but it did not work. The main problem
was that it did not seem to get hot enough. It produced a huge long
flame, which was yellowish at the extremeties, indicating that the
mixture was too rich.


Contrary to the
original designer's experience, the torch was very sensitive to
plugging the tube in the back. The flame became even richer. From
some more investigations with google, it seemed that this kind of
burner requires a venturi. It is odd that the one on
www.backyardmetalcasting.com did not. A venturi was fabricated with
an inlet taper down to about 3/8" within 1/2" and out to full diameter
within 3 1/2". This venturi did not work well at all. It made the
flame very rich, looking like it had almost no air. Furthermore,
propane leaked out of the
holes which were supplied to draw in air, and was easily ignited.
This created an unpleasant odor, as well as a safety hazard.

Several posts recommended the use of a tweco contact tip as an air
orifice. This was difficult to retrofit, due to the design of the
upwind burner, since the rear of the burner tube is not really
accessible. Being a little wiser from previous experiences, I did not
want to do anything really permanent without more careful
investigation, so the tip was just clamped in the propane hose with
some twisted steel wire, and stuffed in the back of the burner tube.
This worked a little better, but the miserable makeshift venturi was
really interfering with the airflow. The venturi was removed, and the
flame looked more reasonable with a shorter inner blue cone, but it
still had some yellow indicating richness.


Has anyone noted any success with these
large torches for brazing? They certainly do have the potential do
generate a lot of heat, since it only took several minutes to empty a
partially filled disposable cooking propane cylinder, although to no
real use.

Thanks,
Eric