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Brazing copper

oxy acetylene

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Andrew Schofield 302/12/2020 17:37:30
2 forum posts

In the past I silver solder copper edge to edge with a propane torch to give a stronger joint than solder but it was slow I now hope to use oxy acetylene torch and was wondering what was the best filler rods to use and flux?

Bill Dawes02/12/2020 18:58:19
386 forum posts

Hi Andrew, you mentioned solder which I took to mean soft solder, suggesting you don't need the strength of brazing, is that correct?

I understand some people use oxy acetylene but believe you need to be well experienced to do this, not tried it myself, have enough problems with silver soldering with propane!

Bill D.

Bill Dawes02/12/2020 18:58:31
386 forum posts

Hi Andrew, you mentioned solder which I took to mean soft solder, suggesting you don't need the strength of brazing, is that correct?

I understand some people use oxy acetylene but believe you need to be well experienced to do this, not tried it myself, have enough problems with silver soldering with propane!

Bill D.

Bill Dawes02/12/2020 19:02:06
386 forum posts

PS I do have a friend who is a retired welding engineer, he has silver soldered a boiler with oxy acetylene and obviously doesn't have the problem of the interminable wait for heating up as with propane.

Bill D.

Andy Stopford02/12/2020 19:47:17
59 forum posts
1 photos

I've brazed copper using the standard brass rods (I don't know the precise formulation - it was a long time ago), and borax as flux.

It was easy, no problem getting enough heat.

One job involved fixing a wood-fired water heater that someone had tried to repair with a stick welder and steel filler rods(?!). I had no problem building up a nice thick fillet to bury the resulting lacework.

You'd have to check with those who know about suitability for any sort of pressure vessel, though the flanged joints on the boiler of my espresso machine (a La Pavoni P67, for those who are interested) appear to be brazed. That only runs at about 1 bar though.

Martin Dowing02/12/2020 19:53:57
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292 forum posts
4 photos

For brazing copper there are special rods made out of copper with few % of phosphorus.

They are cheap and work well, used extensively in plumbing.

Oxyacetylene torch is not necessary for brazing copper - done a lot with propane-propylene torch.

SillyOldDuffer02/12/2020 21:06:55
Moderator
6682 forum posts
1501 photos

No direct experience myself but theory suggests oxy-acetylene is a poor choice for brazing. Problem is it burns at about 3500°C and copper melts at 1070°C. And too hot causes more damage than not hot enough. Oxy-acetylene's extra temperature is good for welding and cutting steel (melting point about 1500°C), but it's overkill for most metals. Propane burns at a temperature better suited to brazing and is cheaper to boot.

Dave

Keith Hale02/12/2020 21:12:59
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282 forum posts

Hi Andrew

Be wary, very wary.

Obviously Martin believes that you are going to run your engine on gas. A coal fired boiler produces a hot sulphur bearing atmosphere that destroys joints made with copper phosphorus alloys. Depending on the quality of joint, your engine might run for a couple of occasions. Not a problem if you enyoy building the boiler and subsequent ones. Can't believe that suggestion!

As regards using oxy-acetylene, be equally careful. Such torches in the hands of an amateur creates more problems than it solves. Unless you make sure that you know what you want to achieve and how to do it, a whole catalogue of disasters awaits. Melted copper and brass, weak joints caused by the filler metal not penetrating the joint, excessive use of silver solder.

Make sure you use the experience and knowledge of someone who knows. Check the members profile.

Brazing is a very simple process as long as you understand it. If you don't then expect problems . Talk to your material suppliers and people who understand the process.

Why do you think that professional boiler makers charge what they do?

Mind how you go.

Get professional advice.

Keith

James Alford02/12/2020 21:40:42
412 forum posts
74 photos

I did a lot of bazing of copper for copper art work and sculptures. I used fluxless rods such as the S2 Type Copper Brazing Rods from CupAlloys. I used propane or MAPP gas torches and stood the work on thermalite style blocks. The joint needs to be fairly clean to work. It is quite easy and the rods melt in way which is quite plastic and allows you to "work" the joint if you need to.

Regards,

James.

Andrew Schofield 302/12/2020 21:54:56
2 forum posts

Thanks everyone for the prompt replies.

The joints I will be doing is to make-up an all copper mainfold with plumbing pipe, the main pipe is 28mm dia with a series of intersecting 15mm copper pipes inserted at 90 degrees to it and was told that only silver solder should be used as there will be no overlap to the joints for brazing.

Bill Dawes02/12/2020 22:46:10
386 forum posts

i wouldn't have thought that plumbers solder was much good for butt joints such as you describe.

Bill D

Keith Hale02/12/2020 22:47:47
avatar
282 forum posts

Hi Andrew,

There you go, all brazed joints are designed in shear for maximum strength.

That means there is an overlap between the two components.

All the text books and British standards say so.

Regards

Keith

Bill Dawes02/12/2020 22:50:45
386 forum posts

PS If it is a low pressure job is this not the ideal case for using standard plumbing fittings ie Tee pieces, with or without solder rings. 28 and 15mm are standard pipe sizes I believe.

Bill D.

Keith Hale02/12/2020 23:30:48
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282 forum posts

And plumbing fittings ensure that there is an overlap between the components.

And the reason......?

Keith

Stueeee03/12/2020 15:24:03
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67 forum posts

I have brazed copper joints with O/A kit on a number of occasions. Butted joints aren't ideal, but with good fit up and by using a Silicon Bronze rod such as Sifbronze No. 1 with O/A it's easy to form a nice fillet around the joint which will still provide mechanical strength; the fillet is easy to produce with as it O/A gives a much more focussed heat than possible with a conventional brazing hearth setup. I would use brazing for this in an environment where the joints would not be likely to be exposed to significant vibration.

I must say though, that unless the 15mm "tee offs" are too close together axially, my first choice would be to use a series of 28-15mm reducing end feed or Yorkshire style tees for this job.

Speedy Builder503/12/2020 16:02:19
2186 forum posts
152 photos

If we are talking plumbing (and not a car inlet / exhaust manifold) the French plumbers braze tees off of pipes all the time, no flange, no fittings, just drill a hole in the parent pipe, file a saddle onto the branch pipe forming a simple butt joint. I believe (CuP will correct me ) that they use a Copper Phosphorous 5% silver rod and no flux BUT you will need more heat than when using a silver solder and flux. In my opinion, the silver soldered joint flows better and looks neater than the CuPh joints that look quite knobbly by comparison.

These CuPh joints are used for water and gas systems and expressly not for water/steam coal vessels.

Keith Hale04/12/2020 12:53:53
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282 forum posts

No need to correct you.

But why the French would want to use a 5% silver alloy and not a simple 7% phosphorus copper baffles me

The joint strength is the same ie that of annealed copper.

The brazing temperature with silver is about 20° lower. (Read the small print relating to the brazing temperature of these alloys!)

The corrosion resistance of the filler metal is better than the parent material. Really?

For which, the Frenchman pays an extra £35 or €40 per kg for his filler.

Feel free to follow if you are so inclined but even their gas fired water heaters don't have a silver bearing alloy for their copper to copper joints and experience no problems. Been there!

Keith

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