soldering copper to steel

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

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

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.

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?

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

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.

many thanks - this is advice I can work on

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.

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

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.

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

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!