View Full Version : Oxy/Propane brazing - acetylene tip conversion
01-07-2011, 04:32 PM
Hi - wondering if anyone has ever tried to convert an acetylene welding tip to use propane? I use a "standard duty" victor torch with propane cutting tips and the original rosebud, but of course my welding tips (#0, #2, #4) won't light with propane. I see that Smith makes a propane tip - the MW411 which has a coutersunk hole in it - I wonder if this also mixes differently as well? This tip is over $40 however, so I was thinking about putting one of my acetylene welding tips in the drill press to countersink it for oxy/propane brazing. I suppose this will probably ruin the tip, but then again, I never use acetylene anyway...
Any thoughts appreciated...
01-07-2011, 04:59 PM
i have drilled out acetylene welding tips but used them for acetylene. dont think they are countersunk because i didnt countersink it and it works good..sounds like not too much to lose..
why do you want to braze with propane? i know why people cut with it .....i guess you dont need the extra tank around?
01-07-2011, 05:30 PM
I've used standard Victor welding/brazing tips with both propane and MAPP (back when MAPP was available, I haven't tried propylene yet, and don't plan to).
Never had to make any modifications, it worked just fine, BUT
The flame will have different characteristics.
For one, it is much less bright. In fact, the flame wasn't even really visible outdoors, or through a #5 shade. Indoors, I just looked through normal sunglasses. Looked a little like a methanol flame's color
For another, the shape is completely different from oxy-acetylene. Much less pointy tip of the inner cone, longer inner cone, and no visible feather when reducing. It is much more difficult to spot and adjust to a neutral flame.
Yes, there is a gap off of the tip, but a proper oxy-acetylene flame has a gap too (just a little smaller).
One issue, is that propane doesn't burn when too rich.
Acetylene has a LEL of 2.5, and an HEL of 81. That means that it will burn when mixed with air between 2.5% and 81%. Propane has an LEL of 2.1, but an HEL of 10.1.
That means if you have too much propane coming out of the tip when you start, it will blow out (but when mixed with oxygen it's pretty stable), unlike acetylene, which you can open up and light with no problem (sooting up your whole shop).
So, start with just the propane, and VERY low. Like a tealight candle flame low.
Then slowly increase the propane, add some oxygen, and step up and back until you get where you want. It's really not that difficult.
01-08-2011, 11:13 AM
Hi weldbead, really the only reason I want to braze with propane is because I don't have / use anything else. A smaller jug of acetylene around here is upwards of $80, and I already have lots of propane laying around. I often use a little one pounder of propane (I can re-fill them 4 or 5 times from my 20 pounder) with a small 20 cu.ft. oxy tank for my little projects - I have a little tote for them - easy to throw in the truck and drive away...
Hi rlitman - after your post I went out and tried my #2 welding tip again, small flame to start. As usual when I added the oxy it went out. So it occurred to me - maybe turn down the oxy? I reduced it from my normal 10-12 psi down to 5-6. Started with the "tea light" flame and low and behold - it worked!! I can't believe it - the first time I ever got it to stay on! I do some stainless brazing so I can't wait to try this out for real. Thanks much for your post!
01-08-2011, 01:20 PM
No problem. Yeah, your pressures must be way off.
I use 3-5PSI on the acetylene, and 4-5 on the Oxygen (for most of my tip sizes). 10-20 for oxygen with a cutting tip, but you need way less with a welding tip.
You may want to check out Victor's tip charts. The pressures for welding tips will be about the same, regardless of the fuel.
Like I said, its a little hard to spot a neutral flame, and the flame is more elongated, slower moving, and a little softer than o/a. I wish there were nice drawings to compare the two, but the good drawings are all of o/a.
I found oxy-mapp not bad for brazing. Propylene should be the same. I didn't care too much for propane (not as hot, and used more oxygen), but glass blowers use it a lot, as do certain jewelry techniques, because it has almost no soot unlike acetylene.
Oxy-hydrogen is used for platinum work where any carbon or soot would cause a problem as it makes no soot at all. It acts much more like o/a in that the flame is very sharp, but it's so dim, it is almost impossible to see.
Oh, btw, make sure you're using grade "T" hose with propane. R and RM hose will be eaten from the inside out by propane, although it is impervious to acetylene.
01-10-2011, 08:08 AM
Yes most definitely my pressures were not set properly. Got the tip charts now and this is very helpful...
I have to say I've not any real experience with anything except oxy/propane. I always thought the higher BTU output of propane would make it very good for brazing, but I know what you mean about oxygen - it does like the stuff!
I actually bought a 50ft grade T hose, cut 10 feet off for my little portable rig and kept the 40ft piece for the garage...
Thanks for the info - much appreciated!
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