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Rothenberger Oxy Propane

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Bill Dawes08/05/2021 11:21:32
460 forum posts

Hi all of you silver soldering gurus.

My quest to finish my Emma Victoria boiler seems relentless.

Got to the 'finished it' stage ready for testing. Decided to start off with a soap bubble leak test with a couple of psi.

First test didn't even register on the pressure gauge, leak inside firebox around one of the inner firebox flanges.

Set to with the propane torch re-soldered, and tested again, leak from other side now and a bit from one of the stays on the outside. pickled again and soldered.

Now ready to test again.

Now my question is, silver soldering a 'small' leak inside the firebox with a hefty propane torch seems like using a sledgehammer to crack a nut.

All that heat going in to get one tiny bit up to temperature.

Does anyone use oxy propane for such jobs. A friend of mine has made a few stationary boilers using oxy acetylene and is perplexed at the thought of having to use huge propane burners but then he is a qualified welding engineer and knows what he is doing.

I have seen Helen at Western Steam making silver soldering a boiler look a doddle, she is using what looks like some form of oxy/fuel system.

I was looking at the Rothenberger Roxy 120L kit on sale at various places including Machine Mart but not sure how long the gas lasts, not long I guess but maybe long enough for leak fixes.

Looked on the Rothenberger website but they don't list a 120L,

Any advice would be appreciated, I have gone away several times to count to ten on this boiler and come very close to chucking it in the scrap bin more than once but I am a very patient chap and never give up (coming close to the first time)

If I ever make another steam loco again (unlikely, don't think I will live long enough) it will not include the boiler, I'll find some other mug, sorry expert to make it.

Bill D.

Bill Phinn08/05/2021 11:37:54
512 forum posts
81 photos

I don't think oxy-propane would give you much if any advantage over straight propane for that job, as long as the burner is the right size to get the work up to temperature reasonably quickly.

Personally, I wouldn't buy any of the oxy-propane off-the-peg kits I've seen; the oxygen tends to run out astonishingly quickly, and I don't think the kits are good value.

If you are serious about oxy-propane, consider oxygen cylinder "hire" through Hobbyweld or similar, or, if you aren't planning to use the torch for cutting, maybe choose an oxygen concentrator instead.

Could the two leaks be attributable not so much to the torch but to your soldering preparation and technique?

Keith Hudson 208/05/2021 11:48:16
3 forum posts

My experience with a Oxyturbo set was one of frustration, flame too small, torch not very nice etc. It just about managed to repair a lug on a small aluminium casting using Lumiweld but it was hard work. This was quite a few years ago and things may have improved but the Rothenberger looks very similar to the Oxyturbo that I binned in disgust.

I now want to try again but it will be the lightweight Oxy propane sets that I am looking at, the sort of thing that look and behave like a normal OA torch. The initial cost of kit will be less than the Rothenberger but the deposit on propane and oxygen bottles will take out the saving, however lower re fill cost of gas bottles with make substantial savings if used for more than the occasional bit of silver soldering or brazing.


Edited By Keith Hudson 2 on 08/05/2021 11:50:35

Edited By JasonB on 08/05/2021 16:16:02

John Rutzen08/05/2021 12:35:13
323 forum posts
16 photos

Hi, my biggest improvement in my silver soldering kit has been my Sievert Cyclone burner [ the 10kW] one. This provides terrific heat and will work inside the firebox. I don't think you need anything else if you wrap everything you can with ceramic fibre so as not to lose heat. I got my cyclone burner on ebay for about £15 but they would be worth it if you have to pay full price. You can get the ceramic fibre from pottery suppliers.

SillyOldDuffer08/05/2021 12:58:43
7229 forum posts
1593 photos
Posted by Bill Phinn on 08/05/2021 11:37:54:

I don't think oxy-propane would give you much if any advantage over straight propane for that job, as long as the burner is the right size to get the work up to temperature reasonably quickly.


That's right. Silver-solder melts well below the temperature of Propane burning in Air (650°C vs 1900°C), so temperature isn't the problem.

Burning Propane in Oxygen raises the flame temperature to about 2800°C, but the amount of heat delivered by the torch is about the same. For soldering, heat is wanted, not temperature. The higher temperature risks burning the boiler and the solder close to the flame, whilst still not delivering enough heat to make a satisfactory soldered joint.

What's needed is a large torch delivering more heat from a bigger flame, not a small torch with a high-temperature flame.

I've found Silver-soldering is much easier to do with a big torch. My small set up struggles with more than a cubic inch of metal. Takes so long to bring the job up to solder point that the flux may have boiled off and maybe only one end of the job is hot enough. It's necessary to surround the work with insulating firebrick to stop heat escaping faster than my dinky 900W Sievert can push it in. Watching the same job done with a 14kW torch is an eye-opener - one quick blast and it's done.


Though I'm sure soldering is possible in skilled hands, Oxy flames are really for welding and cutting.

noel shelley08/05/2021 13:29:55
570 forum posts
18 photos

SOD has it ! You CANNOT heat just the bit you want to work on, the whole unit needs to be up to near flow temp for the solder. Keeping the heat in with ceramic fibre is a must - especially if your torch is on the small size.. Oxy fuel gas heating in untrained hands is the quickest way to turn your boiler into scrap, you will burn the metal ! It sounds as though you may not have had enough heat when the boiler was made - hence the leaks. If it takes too long to get to temp the flux may have been exausted and fail. A small kit will run out just as you are ready to feed the solder in - and be costly ! Good Luck Noel.

I have had Oxy A and P for 50 years (BOC)

Bill Dawes08/05/2021 13:42:22
460 forum posts

OK guys thanks, you are really confirming my thoughts because deep down I know it must be me as so many of you guys seem to rattle out boilers using propane like shelling peas.

I've found it frustrating because I thought I have been careful to get everything right. I always do loads of research on most things I do so read all the books, watched videos etc, at the end of the day I appreciate it's practice makes perfect. I find all this embarrassing really as I have spent all my working life in engineering, did engineering apprenticeship including a few years on shop floor but after that all office based on drawing office, tech sales and finally as engineering manager but not spent a lot of years on the workshop side so limited practical skills in model engineering terms, relatively new to ME but I do realise that many people have no engineering background at all and make superb models.

Bill I think you are correct, it's me that's the problem even though I think I have taken great care over everything.

Interesting what you say about the cyclone burner John, tried that at first inside firebox but seemed to take forever to get up to temperature, maybe try it again and make sure it's all well insulated.

So watch this space for the next exciting episode on my saga.

Bill D.

noel shelley08/05/2021 14:01:18
570 forum posts
18 photos

Bill D, Don't feel bad ! Some on here can at the drop of a hat produce wonderful CAD drawings and 3D printed patterns Etc I've only just got the hang of sending Emails Etc, I may know more about how the electronics work that how to use it. We all have our own expertise. Noel

Bill Dawes08/05/2021 15:20:26
460 forum posts

If this lark ended in a school report it would say 'can do better, must do better, see me'

In red pen of course, not permitted these days I understand, too traumatising for the little chaps.

As a matter of interest how long would you normally expect to get up to temperature to melt 455 solder on a 5" boiler, assuming well insulated and using the 2943 (43kw) burner Henry Wood used in his article. I started off making the boiler with a Sievert kit that had a 2941 burner (7.7kw) upgraded to a 3525 cyclone burner (10.3kw) but found both were taking forever to get up to temperature.

I use aerated building blocks and have some ceramic wool but it's gradually becoming just a heap of bits. I do have some spare Rockwool lying around but think that would not stand up to the heat, the binder in it I think rather than the Rockwool itself.

On this subject of insulation one of the things I have found frustrating watching various youtube videos is so often I have seen people getting results apparently not working to 'the rules', an example is a couple of blokes soldering up quite a large boiler, 71/4" possible, just standing on end, no insulation, a couple of burners, these fellas apparently impervious to the the radiated heat, this annoys me as I think well I'm doing it all correctly and it turns out to be a cock up.

Never mind, will press on and see if I get it sorted.

Thanks for advice guys.

Bill D.

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