Silver solder or braze?

[firebird]

Hi

A question my learned friends

On the plans for Chub the re the super heater it clearly says that the firebox end should be brazed and the wet head end to be silver soldered?

I have tried to add a snip shot of the plans but it won't let me

Should I braze the firebox end. Brazing has a higher melting point than silver solder.

Cheers

Rich

[uuu]

If the superheater projects into the firebox, it will get hot enough to melt silver solder - particularly when the engine is not in use, so no steam flow inside. So yes, you need to braze it.

Or... the spear-point type are often welded at that end.

Wilf

[JonL]

Not everyones cup of tea but I bought my superheater darts on ebay; stainless and tig welded. They were not expensive and saved me a lot of work and worry. That being said I know most people like to make everything themselves and I respect that!

[JonL]

www.ebay.co.uk/itm/255131974328

[firebird]

Hi

Thanks for the replies, I figured it was brazing but just wanted to make sure. I guess brazing is ok as it is not part of the boiler.

Chub needs 4 return super heaters so would cost £68.00 to buy them. Worth having a go myself

Cheers

Rich

[robmort]

Even brazed joints might not be strong enough at extreme firebox temperatures, depending how far the ends project into it. Welded stainless steel is then the safest solution, or a mechanical alternative.

[Gary L]

Nov 29, 2021 10:45:49 GMT robmort said:

Even brazed joints might not be strong enough at extreme firebox temperatures, depending how far the ends project into it. Welded stainless steel is then the safest solution, or a mechanical alternative.

If you use an ordinary propane torch, you will probably find it won't burn with a hot enough flame to melt the very highest melting-point brazes. But then again, I know at least one other person who has brazed superheater elements with slightly lower MP spelter that will melt under a propane torch, and he hasn't had any trouble. I agree that firebox temperatures can get very hot (hotter than propane), so the reason is a bit obscure (to me). I suspect it might be that the extreme temperatures in a firebox occur in the firebed itself, whereas the superheaters are heated by gas flow and radiation, and don't reach the same elevated temperatures.

If you think about silver-soldering at lower temperatures well within the range of a propane torch, you can still only achieve a melt using the direct flame (or conduction from a direct flame). You can't do it with the convected hot gases from the flame. I think something similar might be going on at the top of the firebox.

I'm ready to be corrected though

Gary

[firebird]

Hi

On Chub the super heaters stop just short of entering the firebox.
I have oxy/propane gear so brazing is not a problem.

Cheers

Rich

P.S. I have tried to upload a clip from the plans but get this error message?

UNABLE TO UPLOAD FILE SCREENSHOT
ERROR: THIS FORUM HAS EXCEEDED ITS ATTACHMENT SPACE LIMIT. YOUR FILE CANNOT BE UPLOADED

[John Baguley]

As I've mentioned before, I've always used Silverflo24 for the return bends on my radiant superheater elements and not had any problems with the solder melting so far. However, I do put the return bends right at the back of the firebox just above the firehole so the temperatures are probably less extreme there than at the front of the firebox.

The melting temperature for Silverflo24 is given as 760 to 800°C so pretty high. I have now got some Silverflo20 and I'll probably use that in future. I've also got a load of Sifbronze rods but never tried those. I'd perhaps need oxy-fuel though to reach the necessary temperature for that?

I think if you get firebox temperatures hot enough to melt a high melting point silver solder or braze then the design of the boiler/loco needs looking into. You shouldn't need to thrash the fire within an inch of it's life to be able to maintain steam pressure

John

[Gary L]

Nov 29, 2021 18:16:44 GMT John Baguley said:

As I've mentioned before, I've always used Silverflo24 for the return bends on my radiant superheater elements and not had any problems with the solder melting so far. However, I do put the return bends right at the back of the firebox just above the firehole so the temperatures are probably less extreme there than at the front of the firebox.

The melting temperature for Silverflo24 is given as 760 to 800°C so pretty high. I have now got some Silverflo20 and I'll probably use that in future. I've also got a load of Sifbronze rods but never tried those. I'd perhaps need oxy-fuel though to reach the necessary temperature for that?

I think if you get firebox temperatures hot enough to melt a high melting point silver solder or braze then the design of the boiler/loco needs looking into. You shouldn't need to thrash the fire within an inch of it's life to be able to maintain steam pressure

John

John

Thanks, that's a valuable insight for me, no doubt for Firebird as well.

Firebird

The reason your files won't upload, is that the Forum ran out of webspace aeons ago. The way we do it now is to publish an uploaded photo or scan on a photo-sharing site (like Flickr) and then link to it in your post. There is a very full description of how to do this by Roger in the General Chat section, thread titled Posting Photos. It is easier than it sounds, once you have opened a free account with Flickr (or whoever you choose)

HTH

Gary

[firebird]

Excuse me I should know how to upload images. Blame it on old age



Cheers

Rich

[Gary L]

Nov 30, 2021 17:08:45 GMT firebird said:

Excuse me I should know how to upload images. Blame it on old age



Cheers

Rich

I can blame a lot more than that on old age! Well done!

Nothing to do with your brazing query, but I’m not an enthusiast for that sort of s/h return bend. They constrict the gas flow and are prone to cause blockages with char. Try to poke through the blockage with a flue brush, and they block the passage of that as well! YMMV.

Gary

[johnhale]

Also a quick note if joining stainless steel to copper Johnson Matthey used to recommend Argo-Braze 56 and gave e 2 rods as a sample, easyflo No2 used to work but eventually it gave up the ghost on my Lilla after very little steaming!

[firebird]

Hi

I completed the super heater and after a couple of minor re solders it seems to be holding pressure ok


youtu.be/yk3CUbPcyZU

Cheers

Rich

[delaplume]

Have only just seen this thread---- A point to bear in mind re}--- superheaters and their failure..Possibly the worst case scenario is actually when a loco with radiant superheaters is stationary, regulator shut and then the blower is turned on hard !!....There is no gas passing within the tubes to carry the heat away and the tubes/return bend will quickly start to overheat....I usually have the loco in mid-gear, drain cocks open and regulator just cracked open also....As well as protecting the superheater it helps keep the cylinders hot,important if you have a queue of trains waiting for despatch in front of you...

[GWR 101]

Rich apologies for using your thread, I am using stainless steel for my superheaters (3 1/2" Jubilee) which are being welded where they enter the firebox. I notice John has commented that he tried easyflow No2 and was not too successful, as I was intending to use PB and copper in the smokebox is there a recommended Silver Solder for joining Stainless and copper/PB. Regards Paul

[firebird]

Hi Paul

I am new to this so am not an expert but I can show you some of my trials (and failures)

The following is the first super heater I made using stainless steel tube and copper ends.

The copper return ends I made from copper tube cut at an angle



Then brazed together. Brazed not silver soldered. Brazing has a higher melting point than silver solder. I used my oxy/propane gear to do the brazing. Once brazed they can be trimmed



They are then silver soldered onto the stainless steel tubes. I used high temp flux from Cup alloys for the stainless steel to copper joints. All the other joints are silver soldered using standard flux.



Unfortunately this super heater ended up in the scrap bin. I had made it too long so cut an inch or so out of the stainless steel tubes and made some short lengths of copper tube to re-join them. I have a good stock of brazing rods so decided to braze them back together. Disaster!!!!! NO NO NO NO Richard. You cannot braze stainless steel to copper, don't know why but you can't. You can silver solder copper to stainless steel but not braze.

My MK2 super heater can be seen in the video I posted above. All copper tubes and return ends. The return ends are still brazed but all other joints are silver soldered.

Let me know if need any more info

Cheers

Rich

[GWR 101]

Rich, thanks for your informative reply, I am having the stainless tubes welded at the firebox end by a professional welder. They are preping the ends similar to yours and then bending them parallel to each other, it's the smoke box end that I need to solder to copper. I am visiting them next week so I will see what they recommend and if you agree I will post it here. Regards Paul

[firebird]

Hi

No problem at all Paul. Please post any info you get

Cheers

Rich

[GWR 101]

Hi Rich, just collected superheater elements from welders I have put pictures on my Jubilee thread. They recommend that I use Tenacity paste for joining to the headers, I only have easyflow so I have ordered some together with a length of Silver-flo 55 Rod. The elements are well over length so I will have some bits to practice with. Hope this is of some help, regards Paul