acetylene vs propane

[smontanaro]

Thanks all for the comments and kudos. Doug responded about my brake posts much more robustly than I would have. I did, indeed, build the frame up and ride it a couple times before sending it off for paint. According to Strava, I've ridden it 67 miles at this point. I was quite happy with everything, especially the brakes. Now to bring the thread back on-topic...

The day I picked up the frame was a looong day. I drove from Maumee, OH (where I'd dropped my wife to meet a friend for a road trip not involving bikes–what were they thinking?) to Jack Trumbull's place to pick up the frame, then headed back toward Chicago. The last absolutely required piece of my brazing setup was an oxygen concentrator. I had been disappointed with the prices I'd been seeing in the Chicago listings, typically $350-$500 or so for a used DeVilbiss 525, so I just kept watching. I found one or two in the Columbus and Indianapolis areas which had much more reasonable prices, so figured I'd stop and grab one on the way home. Lo and behold, as I'm continuing to scan Chicago area CL listings, I see a DeVilbiss 515 for $50! I got in touch with the seller and gave him my phone number, saying I was on my way back from Ohio, but that I'd pick it up before heading home. I swung by his place, but only had twenties. "Do you have a ten?" I asked. "Nah, $40 is good enough." Shazam! And it has less than 11,000 hours on the clock. The last inspection sticker was dated 2008, so it's probably been tucked away awaiting its second act for a long time.

A few days ago I hooked everything up, but without any firsthand knowledge of regulator setup and operation (and no instructions), I was hesitant to mess around too long trying to get it started. With the help of a YouTube video and a bit of virtual office hours help from Doug, I was confident to make a second try. I believe I invented fire today (any chance I could patent it?). I did this outside where the bbq was sitting, so the flame is a bit hard to see. Still, I was happy with the result.



I went no further than that. The next steps are to get some scraps to practice on and some brazing rod and flux. (I might start with brass just because it will be a cheaper waste of metal.) As Doug has stated repeatedly, results for beginners like myself will be much better with those skinny black hoses. I'll put those on my shopping list as well. Having no brazing experience without them, it was pretty obvious when I held the torch how much more effort was required to position and move the torch with the usual red/green hoses.

[TonyP]

Thanks all for the comments and kudos. Doug responded about my brake posts much more robustly than I would have. I did, indeed, build the frame up and ride it a couple times before sending it off for paint. According to Strava, I've ridden it 67 miles at this point. I was quite happy with everything, especially the brakes. Now to bring the thread back on-topic...

The day I picked up the frame was a looong day. I drove from Maumee, OH (where I'd dropped my wife to meet a friend for a road trip not involving bikes–what were they thinking?) to Jack Trumbull's place to pick up the frame, then headed back toward Chicago. The last absolutely required piece of my brazing setup was an oxygen concentrator. I had been disappointed with the prices I'd been seeing in the Chicago listings, typically $350-$500 or so for a used DeVilbiss 525, so I just kept watching. I found one or two in the Columbus and Indianapolis areas which had much more reasonable prices, so figured I'd stop and grab one on the way home. Lo and behold, as I'm continuing to scan Chicago area CL listings, I see a DeVilbiss 515 for $50! I got in touch with the seller and gave him my phone number, saying I was on my way back from Ohio, but that I'd pick it up before heading home. I swung by his place, but only had twenties. "Do you have a ten?" I asked. "Nah, $40 is good enough." Shazam! And it has less than 11,000 hours on the clock. The last inspection sticker was dated 2008, so it's probably been tucked away awaiting its second act for a long time.

A few days ago I hooked everything up, but without any firsthand knowledge of regulator setup and operation (and no instructions), I was hesitant to mess around too long trying to get it started. With the help of a YouTube video and a bit of virtual office hours help from Doug, I was confident to make a second try. I believe I invented fire today (any chance I could patent it?). I did this outside where the bbq was sitting, so the flame is a bit hard to see. Still, I was happy with the result.



I went no further than that. The next steps are to get some scraps to practice on and some brazing rod and flux. (I might start with brass just because it will be a cheaper waste of metal.) As Doug has stated repeatedly, results for beginners like myself will be much better with those skinny black hoses. I'll put those on my shopping list as well. Having no brazing experience without them, it was pretty obvious when I held the torch how much more effort was required to position and move the torch with the usual red/green hoses.

Here's where I found mine.

https://www.tinmantech.com/products/...welding-hoses/

[Matthias]

Hello,
I'm Matthias, I'm a new member and this is my first post. I hope it's okay to write my introduction here. A little background about me: I am a bikenut, proficient with the TIG (sanitary pipe for the food industry mostly) and while I have once learned to use the oxy-fuel torch for cutting, welding and brazing those things have slowly eroded over time. The torches have slowly been relegated to cutting the really thick stuff in my place as the TIG took on more and more of the welding and the introduction of a plasma cutter took care of cutting all the thinner stuff. Also the little brazing I did was all 'flow it into the joint' type of work, like in tubing or tungsten carbide cutting faces. Never done any fillet brazing and never had any artistic ambition with my brazing.

I have never built a bike frame and I am looking to change that and while I expect to have an easy time using TIG I don't want to go the easy route, also fillet brazing feels more traditional and will teach me a few new skills along the way. I have read through this entire thread with excitement. I have large acetylene tanks. But the expense is unjustified if propane works. Also propane is by far more environmentally friendly, considering how it is produced. I switched from being the absolute car-nut to a radical bicycle-nut for reasons. Seems like you can't have non-polar non-extreme attitudes when you're me

In this post I want to touch on a few things. I hope it's acceptable if I end up splitting up the post in two. Please mind I may word things matter of factly but I want to insist in doubt I know nothing and am always wrong. Topics I plan to touch on:

• A specific torch and it's specific propane accessories.
• Why, when researching startup and shut-off procedures online, you will find instructions that are the polar opposite to each other?
• The flames oxy-propane gives you and how to tell them apart.

I hope my posts, coming from someone just dipping their toes in propane for the first time, helps to get others started using propane as their fuel successfully too. I hope it can be of any use for anyone who just happens to have a maybe handed down torch that is just the one I will be using here. It is a quite common torch in places.

A specific torch and it's specific propane accessories.
When I was pondering the issue of having a torch that I could realistically try this with I was lucky enough to remember this tiny weeny mini torch I have and as an added bonus due to it's small size it was hardly ever used and the entire outfit remained pristine. Both statements, about size and condition, are relative to other torches in my shop.
1.jpg
The small torch is a ZIS MWW 520. The manufacturer survived socialism and is not only still active to this day but also still producing the very same torch and leads by example when it comes to product support. They provide all replacement parts, add-ons and - I have been told - appear very helpful regarding all sorts of requests. So I got my hands on two sizes of propane specific nozzles (the recess type) and a peculiar product they advertise as 'heat dam for use with propane nozzles'. The mixers I am using might be acetylene specific and I also have no certain way to judge which propane nozzle would be appropriate on which size mixer.
heatdamnozzle.jpg
One can tell from those shots that the recessed propane nozzle can get smoking hot during operation, much more so as an acetylene nozzle would, especially when adjusted to an oxidizing flame. The 'heat dam', when installed, provides an insulating gap between the nozzle and the elbow. I suspect the manufacturers intention is to keep the nozzle hot, not so much the elbow cool.

Why, when researching startup and shut-off procedures online, you will find instructions that are the polar opposite to each other? But when you ask around locally everyone will tell you the same, which is also what they once taught you.
Just do a web search. Someone will suggest the manual of operations was to light the fuel first and alone and to cut the oxygen first. Others will suggest you do the opposite. Meanwhile, if you ask around your neighbourhood, I bet everyone is on the same side. Why is that ? My suspicion is that it has to do with something no one talks about: Equal pressure type torches and injector type torches and their regional prevalence. And the fact that the internet is largely agnostic to regions of the world. In my area almost every torch you come across is an injector style torch. I want to show how to identify an injector type torch and run through the manual of operation as close to what I was once taught as possible. All my torches are.
Let's have a look at a few markings commonly found on injector torches and other tell tale features:
injectortype.jpg
Note how the mixer and the tip will both call for an oxygen pressure of 2,5 bar. The equipment is designed to work at this particular oxygen pressure. Not at the source but at the torch of course. The injector principle is rather picky about this and the operator has no margin of discretion here. Also note how the tip features a mark that resembles an 'I' as in Injector, the same mark is often found again on the mixer. Note how the mixer is effectively a jet pump. Oxygen at the pressure of 2,5 bar is forced through the microscopic nozzle, generating a high velocity jet. The two flats on the nozzle are not so much for convenient disassembly but to allow fuel past the nozzle. The oxygen jet will then transfer part of its momentum to the fuel while also mixing with it. The effect is a mix of flammable gas emanating from the business end and negative pressure seen at the fuel inlet. I will clarify this.
With such injector style torch the manual of operation is as follows:
Setting up the torch:

• Inspect your hoses. Inspect your torch. Especially all seals. Do not try to clean anything on the oxygen side unless you know what you're doing. Do not attempt repairs. Take faulty equipment to the welding store. I found a faulty O-ring the last time I used the torch and replaced it. Cheaper than replacing a hand.
• Crack the valve on each bottle open once, to blow out any dirt that may be present. Attach regulators and hoses.
• Connect the oxygen hose to the torch, open the oxygen valve on your torch fully. Open the oxygen bottles valve a hair until the pressure gage stops creeping up. Then open it fully until it seats.
• Adjust the oxygen pressure until it reads the required pressure at the torch. I have simply assumed 0.1 bar of pressure drop along the hose and set it to 2.6 bar to meet the 2.5 bar the stamps call for.
• Open the fuel valve on your torch fully and feel, with your finger, for suction at the fuel connection. Assume the torch is faulty if there is no suction. Never touch your greasy sausage fingers to the oxygen inlet.
• Close the fuel valve followed by the oxygen valve. Make the fuel connection to the torch.
• Crack the fuel bottles valve open a hair. Watch the pressure creep up. Open it a bit more but not all the way. It should be possible to shut it with one motion of the hand.
• Set the fuel pressure. It may be as low as 0. Confused ? I will clarify this.

Starting the torch:

• Open the oxygen valve fully.
• Open the fuel valve a little.
• Use a striker to ignite the flame.
• Judge the flame and adjust according to your needs.

Stopping the torch:

• Cut the fuel.
• Cut the oxygen.

Starting your torch like this will mean you will get any largest flame out of the range of possible flames and no soot. If there is no ignition at all you need to add fuel, if the flame blows away you need to reduce fuel.
Shutting off your injector type torch as described will result in a clean and uneventful stop.
setup.jpg
Now why can you set the fuel pressure to 0, what changes if you give it more than that and why start the torch this way ? The answer lies in the suction on the fuel side explained above. This is also why the manual of operations includes testing for suction. Injector type torches can, as opposed to equal pressure type torches, be fuelled by acetylene generators. Pretty old school. But it works. The torch can also suck the diaphragm open. The regulator, when set to 0 bar, tries to maintain 0 bars at the outlet. When the torch sucks on it the regulator will register negative pressure at the outlet and start supplying fuel to try and make it 0. Notice how, in the picture above, the flame burns happily next to a fuel reg reading 0.
This also means every adjustment on the oxygen side will carry over to the fuel side to some extent. This means theoretically one can make larger steps when adjusting the flames size without leaving the range of possible flame chemistries. But one still must make adjustments to both sides to change a flames size while maintaining its chemistry.
The torch is started in this fashion as the suction of the injector enables gas flow, regardless of its source and its pressure.
If one now gives the fuel positive pressure, say 0.5 bar in my case, it will add a constant offset to the pressure (not flow) response of the injector. This will skew the range of flame chemistry the adjustments offer accordingly. I hope this explanation of injector style torches is easy to digest.
I suspect the reason why one regularly encounters disputes online about what to introduce or cut first when starting or shutting down a torch is due to the equal pressure type torch just being ubiquitous in some areas of the world and the injector type in others. Most peoples experiences are centred around only one of the two types, depending on location.

I want to split this post in two exactly here. It's long already. I will go into the oxy-propane flames and my suspicions about them and their effect on the work in the next post. This is partly due to me not yet being happy with the quality of the pictures I took but also because I will be switching from sharing information in the hopes of getting people started to a more vague and speculative style and also I will be seeking knowledge from experienced oxy-propane brazers.

Thank you all for your patience. I hope I didn't commit any no-no's when cramming my personal introduction in here, leaving out my surname and being a bit verbose.

Matthias

[Matthias]

This is the second instalment of "I teach myself, others get to learn from mistakes I make and hopefully someone points me in the right direction".

• Oxy-propane flames
• A wee bit on flux
• Bonus content

Oxy-propane flames, telling them apart and which to use
There's a lot of speculation out there regarding what the oxy-propane flame can and what it can't do. There's also some good and reliable research out there regarding the chemistry of each part of the flame, the heat produced in each part of the flame and the temperature of each part of the flame.
flames1.jpg
Here is a whole range of flames, from way over fuelled going towards way oxidizing. This was using a tip labelled 2-4 mm and 2.5 bar oxygen with 0.5 bar propane.
It appears that the presumably carburizing flames have no properly formed inner cone but some undefined cone. Up to the middle there is a clear feather visible indicating excess carbon, giving a warm, reddish orange glow. This seems to merge with the cone in the 4th or 5th flame from right. Right after this happens the cone will suddenly turn in a well defined sharp cone.
Experiments that I will touch on lead me to believe this, coincidentally, is a presumably neutral flame. This would finding the neutral flame easy, walk the oxygen up or fuel down until the feather merges with the cone and then a bit further until the cone looses its fringed edge and also suddenly shifts in colour from azure blue to a darker, more saturated blue. Stop there.
Experimentation led me to my current belief, that you want to use something similar to the third flame from right. You can go one more to the left but should strongly avoid anything more oxidizing.
moreoomph.jpg
Shown here is what the same would look like when giving it the beans. I've banished the 4 flames at either extreme to the right. Note the rich flame almost separating from the tip. Looking at the 6 flames in the main sequence I'd choose to braze with the rightmost one but haven't found a flame like the fifth from left to be an issue either. I do think it would be time to go one tip size up here, if a flame this big was really needed.

A wee bit on flux and how to burn it real quick.
I'm currently using a standard flux, the standard is FH 21 and that is really just borax with boric acid. The boric acid announces its presence by making the flame come off your work with a greenish tint. It seems to have done its job and be completely lost by the time brazing temperature is reached any ways. I have also used pure borax which works. I am speculating that if you neglect your material prep the boric acid helps a bit otherwise you don't need it. But I would definitely test a joints strength just to be sure.
20240730_203440.jpg
The sheet fluxed up here was equally rusty as the one next to it and saw no prep.
20240730_204045.jpg
Once the flux has done it's job one can certainly braze on this. But the discolouration of the flux, marking where there was oxides present, implies the flux has already sacrificed some of it's capacity to dissolve oxides before any brazing even started.
20240730_211034.jpg
In contrast the other sheet, shined up real quick and given a wipe with IPA only looks funny where the brush lost some bristles.
burn.jpg
Let's make matters way worse for the first one. Using the flame shown, which must be oxidizing, the sheet is heated to just barely brazing temperature. Where 60 40 brass barely turns mushy.The flux will turn yellow and brown really fast. Go just a bit further and once the flame is flicked off it will immediately oxidize. This flux was burnt in less than 10 seconds. And it is the flame chemistry, not the temperature that is to blame.
neutral.jpg
Shown here is a flame set as outlined above. The slight addition of fuel remedies the issue and the material and flux can be safely taken to temperatures where brass is at or beyond its liquidus temperature.

Bonus content, as promised.
copperbraze.jpg
Copper wire. Copper braze. Just in case this isn't common knowledge. I believe one can get real artsy with it and as long as it's nothing structural it should be fine. Also might be a place to start for someone who just wants to try and can't get their hands on brass right now. Be aware, copper being elemental will behave like an eutectic alloy, solidus and liquidus temperatures will be equal, it will go from solid to liquid and back. No mushy phase to play with.
Also have fun roasting me. One might think someone who uses the TIG alot should have the heat control down. It's the first time I tried to do anything. Mitered and brazed three joints and also tried to lay down some beads. Right now there's way too much going on for me at once. Also I believe 1.5 mm brass was a mistake and I should try bigger if I want to try stacking fat dimes.
Take those results as your reasons for why you shouldn't listen to any of my speculations above. I still hope either this or some corrections people will be able to provide helps me and another guy trying to get a hang of it.

[Scheisserad61]

I think your post shows a lot of thought and a methodical and careful method of trying to figure out some of the questions / mysteries of Propane brazing.

With the small torch / small tips and low pressures used in bike building (and similiar jewelry and aircraft work) I don't think it makes any difference at all how you turn the torch off. None.
Maybe with an injector torch you use it does ? I doubt it, but perhaps it would be worth checking with a couple of equipment manufacturers that produce that sort of equipment.
In the U.S., injector style torches started to fall out of fashion in the 1960's, along with the use of acetylene generators. Everything turned to bottled gas. The only manufacturer I've found that has ANY reference to injector equipment is Harris. It seems they sell equipment worldwide, and in many countries I believe that injector equipment is still common.

Screenshot (2666).jpgScreenshot (18989).jpgHere are some images I saved from Harris catalogs I found online. I think most of them came from Harris.EU sources. There didn't seem to be the same info on the U.S. market web pages.

Keep up your experiences and questions !Screenshot (2665).jpg

[Doug Fattic]

Matthias, I've read that one is supposed to turn off the oxygen first before the fuel. However that can sometimes leave a bit of flame still burning on the tip - which I find unsettling. So i've always turned off the fuel first and that allows the oxygen to completely blow out the flame. I've been doing it that way for 49 years and haven't died yet so I'm unlikely to change now.

[Matthias]

Doug,
exactly. It's what I have learnt, always done and I am neither interesting to change this. Around my circles everyone knows a saying that goes 'oxygen first and oxygen last'. Theres one exception where I violate this rule. I have some tips like the one shown below and the design produces a great internal volume in the tip. Unless one shuts off the fuel really really slow towards the end this tip will report very loudly, unlike all other designs I have ever used. It's my suspicion that it is the increased internal 'dead' volume in the tip that is to blame.
This is the only tip where I like to shut the oxygen first and have the draft of my extractor snuff out the flame.
20240807_202507.jpg
Matthias