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Post by eightpot on May 24, 2019 21:45:41 GMT
Making the superheater for Martin Evans' 5" gauge 'Enterprise', an LNER 2-6-2 tank loco. It has two 1" o/d x 16 gauge flues into which the out and back 3/8" x 20 gauge stainless steel tubes go. These are silver-soldered into the 1 - 1/4" diameter bronze lump of the superheater header. I have used CuP alloys 55%Silver Brazing alloy with both their HT5 and red Sifbronze fluxes on test pieces but the silver solder doesn't appear to adhere to the stainless tube very well. This tube is marked ASTM A273 & A269, also TP304/TP304L. As a possible replacement would copper tube, say of 18 gauge be suitable as an alternative on this type of superheater? Suggestions welcomed.
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don9f
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Les Warnett 9F, Martin Evans “Jinty”, a part built “Austin 7” and now a part built Springbok B1.
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Post by don9f on May 24, 2019 22:01:42 GMT
Hi, I’m afraid copper superheater elements probably wouldn’t last very long....stainless is the way to go. I hope others may be able to help you with advice re the silver soldering and grade of stainless etc. Tenacity No 5 is the flux I would use myself but I have no experience with the 55% CuP stuff, as I’m still using up old stocks of Easyflo.
Cheers Don
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Post by builder01 on May 25, 2019 1:23:05 GMT
Typically, return bends on superheaters are stainless tubes that are TIG welded. This is the only part of my boiler that I did not make myself, as I don't the equipment for this.
With the right type of flux, it is not hard to silver solder stainless to copper. I use high temp black flux. I don't know how well the return bend will hold up if silver soldered versus TIG.
David
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smallbrother
Elder Statesman
Errors aplenty, progress slow, but progress nonetheless!
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Post by smallbrother on May 25, 2019 8:25:49 GMT
The copper radiant elements burnt out on my Holmside. I don't know how old they were but seems pointless to me when for maybe a bit more cost a much better result is obtained with SS.
At the moment the superheaters are shortened but I will get proper radiant ones (in SS) before too long.
Pete.
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Post by eightpot on May 26, 2019 12:02:29 GMT
Typically, return bends on superheaters are stainless tubes that are TIG welded. This is the only part of my boiler that I did not make myself, as I don't the equipment for this. With the right type of flux, it is not hard to silver solder stainless to copper. I use high temp black flux. I don't know how well the return bend will hold up if silver soldered versus TIG. David Any suggestion of a name and source for this 'black flux', please? |
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Post by builder01 on May 27, 2019 1:44:27 GMT
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Tony K
Elder Statesman
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Post by Tony K on May 27, 2019 9:30:22 GMT
I have always used Cup alloys HT5 on stainless with success (cue Keith?) hereWith stainless steel spears I have always bought TIG welded ones (Polly Models) and done the transition to copper where most convenient - it matters little where it is, but away from the firebox as the temperature decreases. Other suppliers are available  |
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Tony K
Elder Statesman
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Post by Tony K on May 27, 2019 9:32:47 GMT
The copper radiant elements burnt out on my Holmside. I don't know how old they were but seems pointless to me when for maybe a bit more cost a much better result is obtained with SS. At the moment the superheaters are shortened but I will get proper radiant ones (in SS) before too long. Pete. Pete, was there noticeable difference in performance after shortening? |
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smallbrother
Elder Statesman
Errors aplenty, progress slow, but progress nonetheless!
Posts: 2,269
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Post by smallbrother on May 27, 2019 20:02:48 GMT
The copper radiant elements burnt out on my Holmside. I don't know how old they were but seems pointless to me when for maybe a bit more cost a much better result is obtained with SS. At the moment the superheaters are shortened but I will get proper radiant ones (in SS) before too long. Pete. Pete, was there noticeable difference in performance after shortening? Million dollar question there Tony. Really not sure. Some days she makes loads of steam, others not so much. Is it the coal, atmosphere/temp, my firing? I think I would have to conclude it didn't make a huge difference. I had someone do a quick TIG weld repair at the start of the 2018 season when the problem occurred. We also altered the smokebox pipework so it is easy to get the assembly in and out. Because of this, I am going to get the superheater extended to make it properly radiant again, probably later this year. I think I will have a better idea then, as it could be the original had a problem from when I bought it in October 2016, although not enough to be obvious. Pete. |
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smallbrother
Elder Statesman
Errors aplenty, progress slow, but progress nonetheless!
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Post by smallbrother on Jun 1, 2019 20:56:06 GMT
Well today she didn't steam very well. Took her off after 2 hours and cleaned the tubes and smokebox, seemed ok but after 45 minutes struggling again.
Dropped the fire and saw the grate was 1/3 covered with clinker. The same bag of coal gave me 3 hours very good steaming a month ago.
Next time this happens the fire will be dropped asap. It takes just a few minutes.
Pete.
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Post by Oily Rag on Jun 1, 2019 21:51:55 GMT
A common mistake when silver brazing stainless steel is that many think the stainless material is clean because it looks clean after using solvents and or acid pickle etc. But the oxide remains and that is why they have trouble with it wetting out and even if does appear to wet out the bond is flawed. Mechanically clean stainless steel, you must chew out these hard oxides that coat stainless, use new and clean grit cloths, sharp clean files and flux and braze within the hours. Do not use the cheap fluxes, Harris Stay Silv or the best brew I have ever known is the "Cycle Designs Stainless Light" . I hear all sorts of stories of stainless being hard , near impossible to braze, nah, just need to the right stuff and the right approach.
And I have heard of many stories of silver brazed return bends popping off radiant super heaters. TIg seems the way to go.
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Post by shauncup on Jun 6, 2019 12:21:11 GMT
Hi Eightpot. First thing I would ask does your stainless contain nickel? For example is it one of the 300 range eg 316L? One way to check is to use a magnet, nickel bearing stainlesses are non magnetic. The reason I ask this is because non nickel stainless steels when in contact with water can suffer from crevice corrosion. When Oilyrag says he's seen return bends 'pop off' this could be the reason. If your stainless is non magnetic then you are certainly using the right materials, ie 455 and HT5. Sif flux will not work with 455. As stated, the key to joining stainless steel is the flux. Chromium oxides are very stubborn and need an aggressive flux to remove them, our HT5. A word of caution their residues are equally aggressive so please clean well post brazing. DON'T pre-clean with a grit based product, grit can be left behind which the flux won't shift. As long as the joint is reasonably clean and free from oil and dirt then you should have no problems if following the basic principles. Mix the flux into a paste with water and a drop of washing up liquid. Apply all around joint and heat. Use the flux as a temperature guide, it will go like milk and then clear like water. You are now near brazing temperature. A bit more heat and away you go. Any problems give me a call.
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timb
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Post by timb on Jun 6, 2019 18:27:47 GMT
All the above is excellent advice, I would add to NOT use any wirebrushing, either hand or powered. The wire for the brushes, even if stainless, will contain iron which will get into the surface of you piece and cause rust over time.
Tim
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