Brazing/fuel question

deereman75 · May 10, 2012

Well we will be changing to propane soon, and trying to decide if we should keep the acet tank or not. I know we will have to give up gas welding if we sell the acet tank, but I can live without that. The main issue is I will still need some way to work with sheet metal. What I am getting at is can I braze with propane or not. The other issue is can I use my smith gas welding tips with propane. I know acet cutting tips cant be used with propane, but I have no idea about welding tips. If my wood bowls sell well, I will get a mig in a while, so even though it isnt perfect, brazing will work for my thin metal for now.

IslandTractor · May 10, 2012

I haven't done it but you can certainly braze with propane or MAPP. Just need to reach the temperature that the brazing rod will melt and as it is brass that means just 1000-1100 degrees F. Propane and air get up to 3800 degrees (add oxygen and you get 5300 degrees) so there is plenty of heat in propane to braze.

deereman75 · May 10, 2012

IslandTractor said:
I haven't done it but you can certainly braze with propane or MAPP. Just need to reach the temperature that the brazing rod will melt and as it is brass that means just 1000-1100 degrees F. Propane and air get up to 3800 degrees (add oxygen and you get 5300 degrees) so there is plenty of heat in propane to braze.

I knew the heat wouldnt be an issue, I was going to hook it up to the airco or smith O/A torch to use for cutting mainly. I just wasnt sure if it was like gas welding, where only acet will work for it. Something about the combustion gasses needed to shield the weld. I guess the real issue for me is will my favourite smith aircraft torch and welding tips work with propane.

crash325 · May 10, 2012

#1 best solution - Try brazing with your propane before getting rid of your Acetylene tank.

I recently changed to propane for cutting. There is a learning curve there as it works a little differently. Lift the bright blue flame back 1/2" to 1" from the cut. Propane heats a little slower, so give it a little more time. In my case, once I got the technique correct, cuts were cleaner, with a lot less slag.

I've done a fair amount of heating using my old rosebud. It is pretty temperamental, very fussy to adjust and blows out pretty easy. Heating is much slower and again hold the tip back about an inch. When the first heating a lot of moisture forms right around the area where the flame is at.

In 1962 I was working in a small plant and doing a lot of high temp silver brazing / soldering. Tried propane, it seemed to form a film that no amount of flux or scratching would help. Silver just wanted to ball up, nothing would get it to flow out.

IslandTractor · May 10, 2012

deereman75 said:
I knew the heat wouldnt be an issue, I was going to hook it up to the airco or smith O/A torch to use for cutting mainly. I just wasnt sure if it was like gas welding, where only acet will work for it. Something about the combustion gasses needed to shield the weld. I guess the real issue for me is will my favourite smith aircraft torch and welding tips work with propane.

No concerns about type of gas. The flux generates whatever chemical conditions are needed. Brazing is really a very neat process with many advantages over welding so long as the joint design is appropriate.

As you don't need oxygen there is no mixing issue I can recall so I would guess ( note guess) that the standard tips can be used. Frankly you could use a BBQ as you just need to get the metal to the right temperature so the brazing rod melts.

deereman75 · May 10, 2012

IslandTractor said:
No concerns about type of gas. The flux generates whatever chemical conditions are needed. Brazing is really a very neat process with many advantages over welding so long as the joint design is appropriate.

As you don't need oxygen there is no mixing issue I can recall so I would guess ( note guess) that the standard tips can be used. Frankly you could use a BBQ as you just need to get the metal to the right temperature so the brazing rod melts.

I have one of those little cheep disposible oxy map torches from a hardware store (pissed us off so much we bought a nice relabled cocona airco style torch kit) I tried lighting it with just propane, no oxy, and it just had a huge clear blue flame starting about 3 inches off the tip. It seems the welding tip style needs o2 to work, and for propane only you need a tip like a turbo torch. I hope monkywrench (forgot exact spelling) or yomax4 adds to this, those two seem to know everything imagenable about torches.

IslandTractor · May 10, 2012

You can use the plumber's style simple propane torch to braze but as you point out it would work better on a large area than on a couple of small pieces. Industrial brazing is actually done in ovens where the pieces to be brazed and a specially molded piece of brazing material and flux are preassembled and clamped together. They then just heat the whole shebang up to the desired brazing temp and when it cools it is finished. Point being that unlike welding where intense heat is a single spot is needed, with brazing you are operating well below the melting point of the pieces to be joined so precise control of the flame is not necessary. Check a welding book but I believe for mild steel the rule of thumb is to get it dark cherry red which is about 1100 degrees. As it is so far below the melting point of steel (2700), it doesn't matter if a larger area than you are interested in gets hot or not. Certainly a precise flame would be nice but the point is that even the plumber's torch can be used to braze.

deereman75 · May 10, 2012

IslandTractor said:
You can use the plumber's style simple propane torch to braze but as you point out it would work better on a large area than on a couple of small pieces. Industrial brazing is actually done in ovens where the pieces to be brazed and a specially molded piece of brazing material and flux are preassembled and clamped together. They then just heat the whole shebang up to the desired brazing temp and when it cools it is finished. Point being that unlike welding where intense heat is a single spot is needed, with brazing you are operating well below the melting point of the pieces to be joined so precise control of the flame is not necessary. Check a welding book but I believe for mild steel the rule of thumb is to get it dark cherry red which is about 1100 degrees. As it is so far below the melting point of steel (2700), it doesn't matter if a larger area than you are interested in gets hot or not. Certainly a precise flame would be nice but the point is that even the plumber's torch can be used to braze.

I will have to try it with the plumbers torch, what I mentioned was more of a cheep immitation of a welding torch. What I was really asking, was if an oxy acet welding tip would work with oxy propane. If not, I will have no use for my beloved smith aw1.

IslandTractor · May 11, 2012

deereman75 said:
I will have to try it with the plumbers torch, what I mentioned was more of a cheep immitation of a welding torch. What I was really asking, was if an oxy acet welding tip would work with oxy propane. If not, I will have no use for my beloved smith aw1.

Don't quote me but I recall the regulator works, you need new hoses, and I just don't recall whether the tips work.

Gary Fowler · May 11, 2012

You will have a hard time using the acetylene tip even to braze with as they wont put out much heat and tend to pop and go out really bad. I would keep my acetylene tank if you plan to use the welding tips for anything at all. For cutting, you have to have all new tips to use propane or MAPP or any other gas other than acetylene. You have to have a lot more gas with them than acetylene so the tips have to be a different design. Initial cash layout to switch over is going to offset the cost of cheaper propane, but for just cutting and heating (you need a different head on you rosebud also) propane is going to do you a good job.
Maybe you could buy a small acetylene tank just for your welding. AS for hoses, I have seen people use the same one on both gases for years with no problem with deterioation. The worst that could happen is you have to buy new hoses after several years, so use what you have till they go bad (if ever)then buy the ones rated for acetylene and propane as replacements. Just make sure you check them for blisters etc before you use them and never leave the bottles on when not in use. I shut mine off after each use anyway and back out the regulator screws.

I think you would have to use a heck of a lot of gas to justify the change over if you have to buy new rosebud, all new cutting tips of varing size and new hose and still want to do gas welding which means you still need the bottle. I own my bottles so there is no demerge cost or minimum monthly fill etc. I might use one bottle per year of gas