Thread: Welding Copper Tube

Hey all,
I'm making a steam engine and instead of sweat soldering the boiler, I'd rather weld it with a TIG machine. I know 'De-oxydised' copper welds best, followed by 'oxygen-free', then 'tough copper'. The copper is AS1432 grade and google searching hasn't helped me. Can someone give advice on weldability of this copper?

Please? Someone with better searching skill than me? I need to know the specification of the copper, otherwise it's just trial and error I guess.

I think you might already know more than the woodies here

Originally Posted by echnidna

I think you might already know more than the woodies here

Ohhh. lol. I'm 14 years old and my dad has taught me everything. He might be able to ask one of the welding teachers at tafe or the people we got the copper from. Thanks anyway

You'll find that copper is a pain to weld properly, especially if you are working on something that needs to be pressure tight and you dont have a lot of experience in welding.

There is no practical difference between deoxidised and oxygen free copper unless you start talking aerospace performance requirements and budgets.

Use a phos-copper brazing rod (in the plumbing aisle at your local Bunnies), they are about a meter long, about 3mm diameter, and they have a yellow splotch of paint on the end. It doesnt need flux, just clean any really bad oxide off the copper.

Good joint fitup is essential so that you dont have to stuff around too much, use a decent bit of overlap on the pieces (the phos-copper alloy will make its way in by capilliary action) and best of all you can do it with a regular propane torch and not crack out the oxy.

Once brazed together the joints wont come apart...even when you heat the bloomin' things to red heat because you did it wrong and want to do it again...not that I'm speaking from experience, cough cough cough.

Have fun.

Thanks for the reply. To do that does it have to be red-heat? If so, I'd just crack out the oxy-lpg, that is, if my dad isn't convinced to weld it

Hi, I do not want to rain on your parade but I hope the following will save you heaps of inconvenience.
As a registered welding inspector I have to tell uou the following:
I assume you are writing about a model railway steam engine boiler.

All of the contacts I have had with the model steamer blokes seem to indicate that the boiler tubes are silver soldered. If you are going to operate your boiler in a public place,you are liable for the safety of the equiptment. I suspect that if it was to be welded you may not get certified or liscenced to operate unless the welding work was carried out by a certified coded welding operator.TIG is not really suitable or applicable for this purpose you have described
There will be an S.A.A. Code that covers this activity somewhere.It may be best that you get one and check it out.
Also the people who have already built and are running engines should be a good source of info for you.

Grahame

I only plan on running it at home, does that mean it is legal to do so just by TIG welding by someone (myself or father) not technically qualified nor approved?

Hi Edd,
Probably ok if it is only at home.It is when there is some sort of public exposure / liability that the authoities get involved. You seem determined to Tig when it is not the best and cost effective way.It sounded like you have the oxy plant already. Go with blue tip silver solder. Look up the specs.on a capillary fit up ( small gap ) I reckon it will come close to 100,000 PSI.
It is used in hydraulics which is much more than steam pressure.If you need more advice send me a PM with all the details and I can work out a procedure for you. I teach this stuff to fellows a bit older than you so its not much trouble.

Cheers
Grahame

Hi Edd
I tried to private email you but the charecter limit was exceded.
Using silver brazing alloy ( silver solder ).
I assume it is a copper to copper joint. If so its dead easy. I suggest a practice run or two with some left over scrap. First of all clean the copper surfaces that will touch each other.A polish with some sandpaper is all that is needed.The SBA flux sometimes dries up .Use water and mix it up to the consistency of toothpaste- say like a thick cream ok!
I use oxy acetylene for SBA but oxy lpg will be ok.
having painted the SBA flux on the mating parts apply the heat. You need to watch for
1. Flux will dry out and turn crusty - keep the heat evenly distributed so that the parts heat up evenly.
2. Copper will come up to red heat pretty quickly so be ready.This flux line at this stage should turn water like - it will be clear like water.
3. Only then should the end of the silver solder stick ( rememmber - blue tip ) be wiped along the joint face- keep the flame off the silver solder stick- if the copper pieces are hot enough
the silver solder will flow.
4.Watch the tiny gap between the two pieces and the silver solder will be sucked into it. Heat above and below the joint line as you wipe the stick along the joint line.
5. When the silver solder runs around the tube joint circumference completely it is done. Don't try for an excess build up - less is best. It should look shiny on the silver solder surface.
5.Clean up when cool with a wire brush and water - the flux residue if not removed will corrode.

6. Give it a go and let me know how you fare. If you still have trouble .If you have a camera send us a pic of your sucess - if you can.

Best of luck with your project
Grahame Collins

You don't really need flux when silver soldering copper to copper, as long as your joint is clean.

Dan

To back up what dan P said about no flux on copper to copper go here

http://www.kembla.com.au/brazingmanl.html

I learn't something new. I had always used flux.If you can't silver solder copper, give welding away.

I ment to ask how you knew about Fronious welders Edd ? They have to be the rolls Royce of welding machines.Trouble is the prices are in the Rolls class as well. My wife works at a place that is the agent for them. they are programmable to an extent. They are really not intended for the Diy er -unless he has had a big win in lotto!

Grahame

Hi Edd,

I’ve just picked up this thread. So I hope that my advice is not too late. First of all the project that you are undertaking is overpowering. As a former metal trades instructor who has worked with your age group I admire you for your enthusiasm.

Before you weld this boiler be really sure that your welding skills are up to the pressures that the boiler is expected to hold. I have had a boiler operator’s ticket for over 25 years and I know how dangerous a boiler can be. Water converted to Steam can expand suddenly more than 1600 times the original volume. Now if that boiler is on a miniature loco that’s a dangerous lot of potential energy between your legs!! (There may be a few fathers :mad: around your place who think that already.)

What I did for my model traction engine (yes I have built a boiler ) boiler tubes were “rolled” in the plate before welding. (Silver soldering). The boiler was then hydrostatically tested; I borrowed the gear for this job.

Edd when you complete this project take it along for every interview you have for that apprenticeship you deserve.

Hey, thanks Fang's Son
I almost completed all the joints with silver soldering on christmas eve. There is a bit left to do, but I've been a bit pre-occupied from christmas day until now. I might try and get it done this weekend, polish it up and show you guys some photos.

Edd,

When you have finished the silver soldering pickle the copper in a weak acid bath for about 48 hours. The boiler will come up clean, the soldering will look “smick” and some mistakes in the welding will show up.

DO NOT be too proud to sweat the soldering off and start again. One model boiler maker of my acutance tried three times to get it right. His little Traction engine is a work of art. He spent an average of 20 hours a week on the project for months.