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Welding/brazing tips.. Propane vs Acetylene

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Geoff Stevenson11/03/2014 01:57:37
31 forum posts
4 photos

Just a query about oxy/propane vs oxy/acetylene tips. I've recently converted my oxy/propane kit to oxy/acetylene. I have some sections of the VFT boiler I'm building that simply need more heat. Replaced regulators, hoses etc. But I drew the line at the torch and tips. However, I get a ragged noisy flame that does not seem to achieve any more heat than oxy/propane. While I'm burning gas that is so expensive it must have been made personally by the Queen.. haha.. The propane tips have reasonably large recessed orifices that I don't seem to recall from some much earlier experience with acetylene. I think the acetylene tips had small, flush orifices. Would anyone care to comment on my predicament..? Yes, please feel free to tell me I'm an idiot.. If you don't listen, you don't learn. Thank you from downunder.. Geoff.

Simon Collier11/03/2014 05:26:08
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461 forum posts
63 photos

Why not file one of the tips flush to remove the recess and see what difference it makes? I bought an oxy/propane set but found the #8 and 15 tips that came with it were not up to much, so I bought a heating tip for oxy/propane which puts out much more heat. However, it only fits on the cutting attachment, making it awkward. So then I bought a big acetylene tip, #32, and counter-drilled the end to make the recess for propane, but I have not tried it on a job yet. I have no idea why propane requires the recess but would be interested to find out.

mark mc11/03/2014 07:42:32
92 forum posts
16 photos

Yep you need to change to a propane tip, I use these a lot at my work place as they have just changed to propane and the ace tips are useless with propane. You can just change the tip, no need to change torch too.

Geoff Stevenson11/03/2014 09:47:41
31 forum posts
4 photos

Thanks gents.. I'll try a fine popane tip with the recess filed off.. Will let you know how I go.. Cheers, Geoff.

Trevor Drabble11/03/2014 09:49:02
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281 forum posts
5 photos

Geoff,

Have you tried asking an equipment supplier such as BOC Australia ? For my part , I have always found their UK branches to be most helpful in heping with my gas querries.

Trevor.

Ian S C11/03/2014 11:35:22
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7468 forum posts
230 photos

You won't weld with oxy propane, its got more heat than acetylene, but not the temperature, but it's good for brazing, and is good with the cutting torch, it leaves a softer edge on the cut metal. I Use a standard torch, and tips, but use a size bigger. Ian S C

Tim Stevens11/03/2014 18:23:58
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1598 forum posts

Ian says: 'You won't weld with oxy propane, its got more heat than acetylene, but not the temperature...'

Acetylene burns with more energy (heat output) than propane, honest, Ian, so I'm not sure how to interpret your statement. So, you would expect Propane not to produce such a concentrated effect, which explains what you go on to say.

The key thing is to get the gasses mixed properly so that the output is as intense as you can get. Burner nozzle design is complex.

Cheers, Tim

Bazyle11/03/2014 18:48:15
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6324 forum posts
222 photos

Because propane has a larger molecule it takes longer to break down so the flame front moves more slowly than hydrogen (town gas) or aceylene. This means as the volume of gas is turned up for more heat the flame may move away from the orifice because it just isn't burning fast enough and can then blow out. So propane nozzles have a system for slowing the outside edge gas speed so there is an envelope of slower moving flame surrounding the main jet to re-ignite it if necessary. This results in a fatter more diffuse flame.
Methane is similar which is why around 1970 when we switched ot north sea gas in the UK all the appliances had to be modified. I remember at school the chemistry labs got new bunsen burners with the modified top.

In reverse you don't want that slow gas for acetylene as it burnes so quickly the gas at the edge burns explosively back to noxxle edge where it has no air so goes out. Then more gas comes out, mixes with air and is ignited by the central flame. So you can get a succession of minute explosions giving a crackling sound.

Nicholas Farr11/03/2014 19:13:40
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3360 forum posts
1542 photos

Hi Geoff, you only have one option and that is to use a torch/mixer and nozzles that are designed for oxy/acetylene. It is potentionally dangerous to use acetylene gas with equipment that it has not been designed for it. Acetylene is the most explosive gas there is, which will be an explosive mixture from 2% to 82% in air.

Cutting expenditure when dealing with acetylene is not worth the risk.

Regards Nick.

Geoff Stevenson12/03/2014 04:20:11
31 forum posts
4 photos

Thank you again to everyone that responded to this.. A lot of the air out there is profit spin generated by the gas companies aimed at emptying our wallets.. Apart from different regulators and possibly hose considerations (and even that is doubtful) the rest of the equipment, from an oxy propane/acetylene point of view is virtually the same. I must thank a fellow Aussie enthusiast who suggested that the judicious use of a cutting torch instead of a welding tip might achieve the required brazing temperature.. Yes, it did, and the silver flowed beautifully.. The acetylene bottle goes back as soon as the rental is up,, haha.. Best wishes from downunder.. Geoff.

Simon Collier12/03/2014 07:41:43
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461 forum posts
63 photos

The propane heating tip I mentioned above is exactly that: a cutting nozzle except without the central oxygen cutting hole. I had thought about simply using the cutting tips and securing the cutting handle somehow to prevent accidents, but in the end, ordered the special heating tip. As you found, it is a very different beast to the puny brazing tips.

Ian S C12/03/2014 09:19:04
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7468 forum posts
230 photos

Oxy-Acetylene, flame temp 3482*C. BTUs 1475

Oxy-Propane 2699*C. BTUs 2500

Although Oxy-Propane has a lower flame temperature, it has more heat/BTUs. This is not hot enough for fusion welding of steel. Ian S C

 

Info from NZ Industrial Gases Welding Bulletin(now BOC).

Edited By Ian S C on 12/03/2014 09:21:38

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