soldering copper to steel

[nigel jones 5Participant @nigeljones5]

using regular 55% silver solder and flux, 20g cu tubes into 1/2" holes in 6mm mild steel – anything to look out for?

[nigel jones 5Participant @nigeljones5]

[JasonBModerator @jasonb]

I'd use Tenacity5 or HT5 flux rather than regular easyflo as its going to take you a while to get it upto temp, keep the heat on the steel as thats going to take a lot of heating and you don't want to overheat the tubes.

I'm assuming these are not the tubes you failed to expand sucessfully as if they are then you may not have enough gap for the solder to flow into the joint.

 

J

Edited By JasonB on 13/09/2012 18:29:21

[nigel jones 5Participant @nigeljones5]

no..they were 7/16, now bored out to 1/2", I intend to check the gap when the tubes arrive (just cos they say 1/2" Od doesnt mean they will be! I will leave a few thou clearance.

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

Hi Fizzy ,

(1) Your chances of doing the silver soldering job described above succesfully are in the region of nil .

(2) The only ways left of saving this boiler are to either :

(a) expand another set of copper tubes in and do everything nescessary to ensure success .

or

(b) use steel tubes and weld them in . Stainless preferably but would need very careful research to identify suitable grade . It would be an awkward welding job up inside that very narrow firebox but not impossible .

Personally I'd go for another attempt at the expanded copper tubes .

Regards ,

Michael Williams .

Edited By MICHAEL WILLIAMS on 13/09/2012 19:35:33

[nigel jones 5Participant @nigeljones5]

Thanks michael, might you elude as to why it might be nil?? I cant see soldering steel to copper being that difficult, ive done it on the bench before?

[JasonBModerator @jasonb]

I think like Michael the chances of getting enough heat into the boiler given the restricted space in the firebox will make it almost impossible to get it hot enough to be confident of a good joint. From your other post I hope you are not thinking that a fillet of solder will do rather than full penitration.

I assume you have run these changes to your approved design past your boiler inspector before going ahead?

J

[nigel jones 5Participant @nigeljones5]

My other post is unrelated to this one, and if 200bar of oxy wont get it hot enough I will eat my welding mask! Designs are all approved, indeed soldering in the tubes makes for a far more robust boiler in terms of strength.

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

Hi Fizzy ,

You ask me a question with a hundred answers but here are some of the main points :

(1) As Jason makes clear it will be difficult to get heat into the right places in the firebox . Its not a question of getting overwhelming heat in there – it has to be an even heat and in quite a narrow band of allowable temperature . Too low a temperature and solder won't melt – to high and it will degrade or even vaporise .

(2) All heating will be done from one side of plate ie inside the firebox . With such thick plate and so much heat soak away to adjacent metal the other side of the plate will always be at a lower temperature . To get to soldering temperature right through the heated side will have to be very hot indeed and this may by itself take you outside the acceptance temperature for the solder .

(3) The big mismatch in thicknesses of tube and plate mean that tube will get hot almost instantly whereas plate will take (relatively) a long time . This means that there is the near certainty of burning through some tubes before the plate gets hot enough .

(4) The steel is heavily oxidised from welding . To silver solder properly it has to be absolutely scoured clean and bright – outside , inside and in the hole . It may not be impossible to get clean metal everywhere but it will be very difficult and a few missed bits will spoil the whole job .

(5) Separate from (3) above copper tube in contact with steel at high temperature will be chemically eroded . This is a slow process and normally doesn't matter but with a long heat and uncertain top temperature it will cause problems .

(6) The big variations in temperature in the boiler whilst silver soldering and the different expansion of copper tube to steel boiler shell means that the tubes will try to pull out of the joint as job cools down . This can lead to very weak joints . This effect has been a problem to a some people making all copper boilers but is likely to be worse with a steel / copper one .

Regards ,

Michael Williams .

[nigel jones 5Participant @nigeljones5]

many thanks – this is advice I can work on

[William RobertsParticipant @williamroberts98085]

Fizzy, take note what Jason and Michael are telling you or you could waste a lot of good work you have done and money . It dont make any difference about 200 bar of oxy I doubt if you can keep a flame in such a small space as the firebox , but good luck if you want to try. Regards Bill.

[JasonBModerator @jasonb]

Well with Oxy there should not be a problem of keeping the flame as you are providing oxygen for the combustion process, this is what is driven off when using just propane in a confined space and why the cyclone type burners are good as they draw air from outside the box..

Michael has it pretty well covered, the hardest thing will be getting even heat and on the right side of teh tubeplate as solder likes to flow from cold to hot, that is why on an all copper boiler its preferable to solder in the tubes at an earlier stage

Just out of interest what method were you using to expand the tubes?

J

Edited By JasonB on 14/09/2012 14:24:33

[nigel jones 5Participant @nigeljones5]

I used a tapered mandrel at .5 degree first, then 1.5 degree, drawn from other end of tube. There was only one tube which wouldnt seat, but I did not feel confident about any of them. I should have soldered in the tubes before I even welded up the firebox inner – we all live and learn. This process has been completed with good results in the past, I just need to get it right first time. Bought tenicity5 flux in the hope it will allow more time to heat.

[VersabossParticipant @versaboss]

It is not widely known – it seems – that an oxy-acetylene burner takes a lot of oxygen from the surrounding air. So I would be among these thinking that's a bad idea with the soldering of the tubes.

Our club has a loco with expanded tubes. For this I made already two roller expanders (the first reached the end of its travel), and although the rolling was not too easy in the confined space, all went well and the loco doing fine again.

For this tool I found a sketch in an old M.Eng; if there is interest I can dig out the issue. Maybe it's in Dias Costa's index?. There are no measures; you have to adapt the dimensions for your case. But it's not too difficult; I built it in about 4 hours (thanks to the Stevenson indexing blocks!).

Greeting, Hansrudolf

[nigel jones 5Participant @nigeljones5]

perhaps i should just slit my wrists and do everyone a favour?? hardly a positive response in sight, right in line with my club response…in 10 yrs time there wont be any model eng clubs…buthey, lets keep the old sckool die hards happy eh????? viva wolfe!

[Author]

Posts