Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work.

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Old November 4th 03, 01:15 AM
Eric Chang
 
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Default brass brazing with a large propane torch

Hi. I read a post on google that said that it was possible to do
brass brazing with a large propane torch. The typical Home Depot
variety don't have enough heat output to get the metal up to
temperature. So, I bought some Bernzomatic brass brazing rods, and
looked up a simple design (www.backyardmetalcasting.com). There is a
design called "upwind burner" which I thought would be big enough.

The burner is made out of 3/4" steel tubing with a 1:12 flare at the
end. There is a crosswise 1/4" copper tube (the original prototype by
L. Oliver used steel pipe). One end of this tube is sealed, and a
0.04" orifice is drilled in the tubing. This sprays gas down the
tube. Six 3/8" holes are drilled downwind of the orifice, three on
the top and three on the bottom; and two were drilled on the sides,
even though the text said that they are not necessary. The site also
said that there was no need to leave the main burner tube open on the
back end, but it was left open anyway, since that is how the prototype
was made.

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. It was barely able to raise the target (about
3"x1/2" of 18 ga steel tubing) up to red heat, and this was
insufficient to more than soften the brass rod. It was enough to burn
most of the flux off, due to the large flame. 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.

There are alternate burner designs, perhaps more well tried, which use
venturi's made out of pipe reducers. Would these designs be more
recommended? The lionel Oliver design is appealing due to its
simplicity, but if it is difficult to get it to work, perhaps some
investigation should be made into the EZ-burner type of design, which
has the air inlet in the back. The tweco tip can still be used.
Although www.backyardmetalcasting.com has an e-mail button, it is
discouraged to send e-mail to Lionel Oliver, since he is
understandably very busy. 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

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Old November 4th 03, 01:50 AM
jim rozen
 
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Default brass brazing with a large propane torch

In article , Eric Chang says...

There are alternate burner designs, perhaps more well tried, which use
venturi's made out of pipe reducers. Would these designs be more
recommended?


The trouble with any kind of air/gas torch is that 80% of
the air that is flowing through it is nitrogen, which is
purely parasitic from a heat standpoint. It has to be
raised up to the exhaust gas temperature, which robs
the flame of energy, and it does not contribute to combustion
at all.

This is the primary reason why oxy-fuel torches are so much
better suited to brazing or silver soldering. If you try
it once you will *never* ever go back. The only other
suggestions I could possibly give are to a) preheat the
items in a charcoal grill, and b) be sure to surround them
with firebrick when doing the brazing so that some of the
heat of the flame is contained.

But seriously, borrow an oxyacetlyene rig and try it.

Jim

==================================================
please reply to:
JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com
==================================================

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Old November 4th 03, 04:35 AM
Leo Lichtman
 
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Default brass brazing with a large propane torch

Technically, brazing brass is welding, since the parent metal and the filler
rod are the same. If you ever do get it up to temperature, you will be
creating a seam of brass on brass, fuzed, not wetted.

How about using Mapp gas. I have never used it, but I know it produces a
much higher flame temperature than propane. The next step after that is
Prestolite, which is air/acetylene--should be hot enough to melt brass.

But, I agree with the others. If you can get your hands on oxy/acetylene,
your troubles will be over.

Have you considered silver solder? It makes very strong joints on brass if
the fit-up is good.


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Old November 4th 03, 06:08 AM
clare @ snyder.on .ca
 
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Default brass brazing with a large propane torch

On Tue, 04 Nov 2003 03:35:11 GMT, "Leo Lichtman"
wrote:

Technically, brazing brass is welding, since the parent metal and the filler
rod are the same. If you ever do get it up to temperature, you will be
creating a seam of brass on brass, fuzed, not wetted.

How about using Mapp gas. I have never used it, but I know it produces a
much higher flame temperature than propane. The next step after that is
Prestolite, which is air/acetylene--should be hot enough to melt brass.

But, I agree with the others. If you can get your hands on oxy/acetylene,
your troubles will be over.

Have you considered silver solder? It makes very strong joints on brass if
the fit-up is good.

Looking at the "small" propane torches, and even Mapp, the high
turbulence torches make more heat with Propane than a standard torch
does with Mapp . The problem is, it's not the AMOUNT of heat produced
that counts, it's the temperature of the flame.
The high swirl Propane torch may produve 4 times as many BTUs as the
regular Mapp torch, and still be several hundred degrees cooler.
Brazing, and welding, require high temperature in a concentrated area.
High enough to melt the subject metal - whether it be Silver Solder,
Spelter (for brazing) or steel in the case of welding.


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Old November 4th 03, 07:58 AM
Tim Williams
 
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Default brass brazing with a large propane torch

"Eric Chang" wrote in message
om...
Hi. I read a post on google that said that it was possible to do
brass brazing with a large propane torch. The typical Home Depot
variety don't have enough heat output to get the metal up to
temperature. So, I bought some Bernzomatic brass brazing rods, and
looked up a simple design (www.backyardmetalcasting.com). There is a
design called "upwind burner" which I thought would be big enough.


I never really got the idea behind it. Apparently his model worked
quite nicely, but personally I don't see how it could possibly draw
in enough air. Maybe his jet hole drill was much smaller than he
thought.

A bit of EMT tubing is certainly a convienient and tempting burner
tube, and I managed to make one work very nice. My construction
requires brazing using yet another burner, but you could use welding,
rivets or other hardware, etc. instead. Even soft solder will work
if you use enough of it!
Anywho, I took a 6" piece of 3/4" dia. (I think it's listed as 1/2",
go figure) conduit, brazed a flare to one end (a 3x1" sheet of steel
bent in a cylinder and skewed to get the taper) and a bit of steel
rod to the other. This rod is bent, to mount the jet tube to. The
jet tube consists of 1/4" copper tubing with the gas attachment of
your choice at one end (I use 1/4" flare, you might use compression
fittings instead, whatever), and at the other, a .023" tweeco tip.
The thread on the tip is 1/4-20, so if you care you can drill and tap
a bit of steel, such that the 1/4" tubing slides in one end and the
tip screws in the other. Mind that this will not seal well, and all
needs to be soldered/silver soldered/brazed in place (copper will
accept brass filler well, just don't overheat it excessively).
Anyway, once you get the tip attached to the supply tube, braze/silver
solder it onto the offset rod you attached to the EMT earlier.

The end of the tip should be between 1/8 and 1/2" from the rim of the
EMT, and centered in it, shooting straight down its length. No venturi
necessary. Approxamately speaking, farther the tip is from the end of
the tube, the leaner the mixture is. Since that brazed-on rod isn't
very adjustable, I recommend using some thin sheet steel flaps, or just
masking tape so you can fine-tune the mixture.

Or grab some various bits of pipe, venturi-like bits for the pipes, some
sort of crude flares for them, and a jet/gas supply tube with an adequate
diameter hole in it, and have at it!

Oh, and for reference, a #57 drill (.04"-ish I think) is best fitted
to a 1" pipe (that is, with extra lean-ness headroom to choke it down
to neutral).

I gotta go to the bathroom so I can't proofread this big post....

Tim

--
"That's for the courts to decide." - Homer Simpson
Website @ http://webpages.charter.net/dawill/tmoranwms


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Old November 4th 03, 04:51 PM
Stan Schaefer
 
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Default brass brazing with a large propane torch

http://www.riel1.net

This guy has a lot of burner designs, they are meant for forges. For
open-air heating I don't know how they'll do, they're meant for use in
a highly insulated forge box. My opinion is that, if you want to get
the job done, go rent/buy an oxy-acetylene rig. If your aim is to
make burners, go full speed ahead. What's your time worth?

Stan
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Old November 4th 03, 06:14 PM
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

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Old November 5th 03, 06:46 PM
Eric Chang
 
Posts: n/a
Default brass brazing with a large propane torch

"Tim Williams" wrote in message ...
....
I never really got the idea behind it. Apparently his model worked
quite nicely, but personally I don't see how it could possibly draw
in enough air. Maybe his jet hole drill was much smaller than he
thought.


Hi Tim. Thank you for confirming my suspicions. The flame really
does look too rich. This may be the only problem. So, if I go with a
smaller jet hole, things should work better. Or, I can use one of the
more tried and true designs, such as the Ron Reil EZ Burner. He does
not mention it on his web page, but google says that he has brazed
very large items with his burners. My little prototype will not even
melt brass held in the middle of the flame. One of the www pages he
links to says that a good burner flame will melt a cast aluminum
washing machine transmission in open air, and is hard to stand even 6
feet away from.

....
fittings instead, whatever), and at the other, a .023" tweeco tip.


AHA! I am using a .035" tip. Your first hand information is really
valuable.

....


Oh, and for reference, a #57 drill (.04"-ish I think) is best fitted
to a 1" pipe (that is, with extra lean-ness headroom to choke it down
to neutral).


Got it, thanks Tim!!

Eric
....


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