Brazing, how difficult is it?

[C-Bag]

I have heard about oxygen concentrators.
Any experience here with that kind of propane/oxy brazing?

Thanks,
Brian

One of my favorite solderers of mechanical is Wes Lee who is a brass and wind instrument repair man. This is just one of his many vids but compares silver solder to soft solder. His repairs of seemingly trashed horns are amazing. Lots of metal work and de soldering and re soldering back together. If you listen closely he uses an oxygen concentrator. And the reason is he uses one of those mini torches. Anything bigger than that and I don’t think it would work. I’ve been on the lookout for one for a while as I have one of those mini torches and it’s become my fav instead of the full sized I’ve been using my whole life. Wonderful for soldering and aluminum brazing and welding.

 

[bulgie]

[snip] he uses an oxygen concentrator. And the reason is he uses one of those mini torches. Anything bigger than that and I don’t think it would work.

I use an O2 concentrator for brazing, with either propane or acetylene. I've brazed some heavy-ish stuff, say up to ~1/4" thick.

When using acetylene, fuel is the bottleneck, not O2, due to the max withdrawal rate with acetylene, which depends on your bottle size. Most smaller bottles, like what a home user would have, don't let you use a very big tip, lest you exceed the max withdrawal. When that happens, the acetylene can't buble out of solution fast enough (it's dissolved in acetone in the bottle), so you get liquid acetone coming through the reg and the hose. Acetone attacks a lot of the materials that regulator diaphragms and hoses are made of, weakening them, possibly leading to a leak, fire or explosion.

I don't know how dangerous this is really. I have experienced acetone coming out the torch a time or two, and nothing bad happened. But that was in a busy production shop where we rebuilt our regs with new diaphragms and other parts now and then, and replaced hoses as soon as they looked worn or iffy. On the assumption that they wouldn't have this "rule" for no reason, let's assume you don't want acetone coming through the torch. If nothing else, because it screws up the flame.

But I digress! The point is, the O2 concentrator is not the bottleneck to how big a flame I can get, for the things I make anyway (mostly bicycle frames and forks).

My acetylene torch is a Smith AW1A, a small aircraft-style welding torch, not a jewelery size. If you know Smith tip sizes - I can use up to a 207 with my 5 liter per minute concentrator (5 l/m), which is my biggest tip short of a rosebud. That tip will exceed the max withdrawal rate of my #3 acetylene bottle.

With propane, which has no practical withdrawal rate limit, I can run a 'small' rosebud on the 5 l/m concentrator, and I just bought a 10 l/m concentrator that I haven't used yet. I'm almost positive I will be able to run my biggest rosebud off that.

5 l/m concentrators are far more common than 10 l/m, and the typical craigslist cost of the 10 l/m units is much higher. Roughly speaking, in Seattle anyway, you can usually find a 5 for under $200, with 10's going more like $500-800, when you can find one. It'd be cheaper to buy two 5s and daisy-chain 'em. On any given day there are several 5s for sale on Seattle CL, and zero 10s. I lucked out, bought my 10 for $75 from a guy who didn't know what he had. That's not uncommon, since they usually go up for sale because the patient died, and the heirs just want it gone. (You know these are medical devices, right? Technically you can't buy one without a prescription from your doctor, tho that is moot for buying used on CL.)

I could go on... Let me know if there's interest in more info.

 

[C-Bag]

Concentrators are all over the map here with the majority being in LA or SF. And most being $300-$500+.What makers would you suggest? I’ve seen several Devilbis and it’s a name I know from compressors but don’t know if that carries any weight here.
I did see a very interesting one that I think was 10L and could bottle the gas in small bottles. It came with two. They wanted $650.

 

[Ulma Doctor]

Ulma, there are SO MANY products out there. I have about the same need for another project. Can you suggest exactly what to purchase?

Thank you

I usually have the Harris brand on hand
I use the Stay-Silv 15% silver for most of the brazing on lighter material

 

[bulgie]

[snip] What makers would you suggest? I’ve seen several Devilbis and it’s a name I know from compressors but don’t know if that carries any weight here.
I did see a very interesting one that I think was 10L and could bottle the gas in small bottles. It came with two. They wanted $650.

I don't know of any bad ones. I've had 3 brands, have two currently, they all worked. I actually forget the brands, can go look tomorrow if interested.

Doug Fattic is a bike frame builder who has been teaching it since the mid-'70s. He's quite the guru on using propane and O2 concentrators instead of traditional bottled oxy/acetylene. He has mentioned that he likes DeVilbiss but I don't think it was all that strong a recommendation. I think he would agree all or most all of them are fine. They all have to meet the stringent requirements for medical devices. Maybe some are more durable, I can't speak to that from first-hand.

Doug has mentioned there's a company that sells refurbished units with a warranty, and the price seemed reasonable, if a bit high, but having it freshly serviced and certified is worth a bit. I imagine shipping is pretty expensive, I think mine are around 30 lb or more, and fragile. I can ask Doug for that company name if you're interested. If they're still around; last I heard of it was a few years ago.

To the extent that my experience with cheap used ones off CL means anything, from a sample size of 3, all I can say is all 3 of them worked reliably with no repairs needed beyond replacing the air filters. I'm a cheap bastard though, bit of a bottom feeder. People who value their own time more than I do might want to pay more for a bit of peace of mind.

About those detachable refillable bottles, I see how they'd give some mobility to medical patients, so they don't have to stay within a few feet of that noisy machine all the time. But I can't see how they'd be of any use to us, for running a torch. Maybe for oxygenating your wort when making beer, to kick-start the yeast? Do people do that anymore? (My homebrewing was 30+ years ago). Ooh I know, one of those bottles would be great for getting the charcoal going faster, or bring it camping to help start the campfire.

Not for brazing though, eh?

 

[C-Bag]

Not for brazing though, eh?

Dunno, but wouldn’t it follow that it could supply Ox at the same rate as the machine for a limited time? And you have two bottles. The whole thing is an unknown so just asking. I’m also cheap but with the price of welding gas these days it might pay for itself and mean one less logistics pull. But I don’t OA weld like I used to and haven’t refilled my bottles in years.

 

[rwm]

Silver solder. I would use 56% Harris cause it's the lowest melting point. For 3/16" rod I think a regular plumber torch would get hot enough.
I happen to have a 5l/min O2 concentrator that I run with propane. That is even hotter but probably not necessary.

 

[Ulma Doctor]

Silver solder. I would use 56% Harris cause it's the lowest melting point. For 3/16" rod I think a regular plumber torch would get hot enough.
I happen to have a 5l/min O2 concentrator that I run with propane. That is even hotter but probably not necessary.
View attachment 510461

Awesome setup you got there Robert!!!

 

[rwm]

I got the O2 concentrator for $150. It's a little tricky to get the O2 feed right but not as tricky as dealing with Airgas.

 

[bulgie]

Dunno, but wouldn’t it follow that it could supply Ox at the same rate as the machine for a limited time? And you have two bottles. The whole thing is an unknown so just asking. I’m also cheap but with the price of welding gas these days it might pay for itself and mean one less logistics pull. But I don’t OA weld like I used to and haven’t refilled my bottles in years.

Yeah I am probably being too negative on the usefulness of the O2 bottles filled from a concentrator.
I just thought of another use for them: doing a small braze right away. When you first turn the concentrator on, it doesn't make high-purity O2 at first, you have to run it a little while, maybe a minute. But once it's "up to speed", you could fill a couple bottles; then the next time you have a small braze to do, you can spark up right away, not have to wait for the warmup time on the concentrator.

I don't know how much pressure (and thus how many O2 molecules) that concentrator can put in a bottle, so you'd have to figure out your burn time by trying it. The bottles are smaller than most compressed O2 bottles from the welding gas store, and I doubt they are very high pressure. So I'm guessing burn time will be low unless you're talking jewelry-sized flames.

BTW propane uses about 4x as much O2 as acetylene for the same BTUs. I don't remember why, probably stoichiometry. So the little low-pressure bottles might be more useful with acetylene.