Brazing copper

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Brazing copper

This topic has 17 replies, 11 voices, and was last updated 15 February 2012 at 10:06 by Ian S C.

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12 February 2012 at 22:09 #84572
DAVID POWELL 4
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@davidpowell4
I am making the boiler for the Juliet loco. It requires some of the copper pipes to be brazed.

How do you braze copper pipes?
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12 February 2012 at 22:09 #5947
DAVID POWELL 4
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@davidpowell4
12 February 2012 at 23:08 #84580
mgj
Participant
@mgj
With silver solder these days.

If you are just starting out like that, I fear there isn’t enough space on this forum to give you a good compete answer, but everyone has to start somewhere. .

Strongly recommend Tubal Cains Soldering and Brazing, and Alec Farmers Book – Model Loco Boilers.(or similar, but Alec Farmer is the author.) Might also be a good idea to go down to the local club and ask those who have doen it before.

It isn’t difficult, but you do just need to have it properly worked out, with access to the right kit, to avoid disappointment and/or very expensive mistakes.
13 February 2012 at 15:55 #84643
Dusty
Participant
@dusty
I agree 100% with mgj, join your local Club, the members will welcome you and provide advice and encouragement, they sometimes have the kit available for members use. Hopefully you will find someone who will stand on your shoulder while you make your first few joints and offer advice.

Making a mistake with kit if you are buying can be expensive, neither copper or silver solder are cheap these days and a few pounds spent on the books recommended will be an investment, or better still see if your local library can get them, you will probably be the only person wanting them and as such you will have almost sole access to them.

Don’t expect perfect joints first time, only practice makes perfect.
13 February 2012 at 19:49 #84666
DAVID POWELL 4
Participant
@davidpowell4
Thanks for the advice on the books…….Will be collecting Tubal Cains’ book from the library tomorrow.

The boiler is 80% complete all silver soldered as per instructions. However there are 2 copper pipes that need connecting to a ‘made bend’ which is quite acute, hence the need to make it I guess.

Here the instructions and the plans show them as being brazed together not silver soldered. As this design is about 60 years old perhaps using today’s silver solder may be OK (has it changed in 60 years).

So I was just wondering how brazing copper is achieved. Clean the parts OK, apply flux….what flux? then heat up and use a rod of some description to bond the 2 parts together.

So what flux and what rod?

Would silver soldering would be a more than acceptable solution?
13 February 2012 at 20:12 #84673
Dusty
Participant
@dusty
If we start using the correct term of ‘silver brazing’ then things might start to become clearer. I suspect that you may well have realized that there are several grades of ‘silver brazing’ rod available. Silver solder has not changed much in the last 60yrs save that cadmium bearing rods are now banned exept for certain processes. I would use easyflow, or rather its modern equivilent which I think is silverflow 55. I have not indulged in any ‘silver brazing’ since the change but I am sure someone out there has, and can help.
13 February 2012 at 20:40 #84681
John Baguley
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@johnbaguley78655
Hi David,

Is it for the superheater by any chance? i.e. the joints between the superheater tubes and the ‘spearhead’ inside the boiler flue. In the ‘old days’ such connections would have been brazed using brass spelter as that would withstand the very high temperatures in that region.

I would use a modern silver solder such as Silverflo 24 or Cup Alloys 824 along with a high temperature flux such as Tenacity 4A or the Cup Alloys equivalent. I use this combination for stainless steel superheaters that extend into the firebox and and they often glow red hot!

Any connections inside the smokebox can be done with Easyflo (if you’ve still got some) or Silverflo55 as the temperatures are much lower.

John
13 February 2012 at 21:31 #84687
nigel jones 5
Participant
@nigeljones5
I built one of these last year but I made a simple T joint as the one on drawings seems way too tricky! Mine ran fine.
13 February 2012 at 22:54 #84695
mgj
Participant
@mgj
Well one thing is for sure, is that you don’t want to go using brass spelter inside a boiler.I think the risks of dezincification have been very much overstated, but even so, in a joint subjected to HP steam for some time, it would be unwise.

Which leaves you with what we all know as silver solder. – whether its brazing or soldering is a matter of semantics (other than brazing tends to use brass and the rest of the world talks about silver soldering?) – its the temperature range and suitablitiy of the alloys which matters.Any of the silver based eutectics recommended above will be fine. If this component actually sees the firebox temperatures, then you’ll need the high temp alloys.(though I’d prefer to weld) Otherwise the 620C stuff will be fine.

I have used 55. i’ve heard people say it doesn’t flow so well. Can’t say I have noticed much difference personally. More expensive though. Might buy some CD bearing stuff claiming its for electrical connections if it comes to it. Its still legit for that I understand.
14 February 2012 at 08:19 #84707
DAVID POWELL 4
Participant
@davidpowell4
Thanks John Baguley, answer is spot on and I shall follow your recommendation. Nigel Jones 2 too (sounds wrong but is grammatically correct?) has a very useful idea so thanks for that.

MGJ makes the point about dezincification. I was aware of this which was another reason why I posed the original question as this loco is an LBSC, a guru amongst model makers. Did he get it wrong? Was dezincifiction known in his time?

As for the semantics, I think Dusty has a point. The trouble is whose definition do we follow. Brazing is defined as ‘solder with an alloy of brass or zinc’ so if I use a ‘silver solder rod’ is that brazing? But there again isn’t brazing a French word and translated means soldering. So silver soldering and silver brazing means the same thing?

Anyway I need to Hoover the shed, no, I’m going to Electrolux it, on second thoughts I’ll just vacuum it.
14 February 2012 at 09:39 #84715
Terry Lane
Participant
@terrylane
Might be safer just to run a broom over it!
14 February 2012 at 10:13 #84720
MICHAEL WILLIAMS
Participant
@michaelwilliams41215
If you haven’t already made the thing you might like to consider changing the design slightly from spearhead to block type hot end – much easier to make , self jigging for brazing and longer before it burns out .

MGJ makes the point about dezincification. I was aware of this which was another reason why I posed the original question as this loco is an LBSC, a guru amongst model makers. Did he get it wrong? Was dezincifiction known in his time?

Dezincification was known about over a hundred years ago but I doubt whether LBSC had heard of it . He specified spelter brazed joints probably because that’s the way copper pipe joints on steam engines were normally made in his day .

On old steam engines and things like old brewery and distillery equipment there are wonderful examples of hand worked and spelter brazed pipe work . Not just simple pipe joints but S bends with side darts , flaired trumpets – sometimes curved , two into one joining pieces and vessels of complex shape with multiple connections . Many of these pieces would have been charcoal brazed .

MW

Edited By MICHAEL WILLIAMS on 14/02/2012 10:38:35
14 February 2012 at 20:06 #84780
V8Eng
Participant
@v8eng
Hi.

One of the last jobs I worked on while in full time employment involved installing refrigeration pipework, the joints were made using what was described as copper brazing rod, that was (I think) a copper phosporous material and did not need a seperate flux.

This was excellent for running into capillary joints, but I found it slightly less easy to use on flat or curved surfaces (might just have been me of course).

The finished product had all the appearance of copper, but I know nothing about its properties or suitability for any other application, it was also a long time ago!

Regards.

Edited By V8Eng on 14/02/2012 20:08:43
14 February 2012 at 20:23 #84782
mgj
Participant
@mgj
V8 – that is a very dangerous route where boilers are concerned. Its a well known technique, and very good in its place, but somehere in the presence of sulphur is not one of them.

It becomes very brittle, and is useless for our purposes, in our environment. Avoid like the plague in boilers using coal as a fuel.

Dezincification – thats why I feel it has been somewhat overstated as a risk, but its best avoided, at least in the structure of a boiler where an item can’t be replaced easily. Fittings, I think brass is fine. For my money, if after many years something goes brittle, you just take it out and change it.
14 February 2012 at 20:50 #84788
Russell Eberhardt
Participant
@russelleberhardt48058
Posted by DAVID POWELL 4 on 14/02/2012 08:19:13: But there again isn’t brazing a French word and translated means soldering. So silver soldering and silver brazing means the same thing?

Not quite:

French “Brasage” = Brazing.

What is confusing over here in France is that “Soudage” can mean either soldering or welding. Best not to confuse those.

Russell.
14 February 2012 at 21:27 #84792
Sub Mandrel
Participant
@submandrel
I understand that if you have some brass rod and enough heat, you should be able to use this to braze a superheater spearhead using borax (I got mine from a pound shop) as a flux.

I also note that many people including (later) LBSC suggest using a copper block drilled at an angle for the two pipes as easier to braze and more reliable than simply trying to join the free ends of two pipes.

Update: I’v just cut a short ring of 15mm copper pipe, split it and overlapped the ends. I used borax mixed with a bit a bit of spit as flux and 1/16″ brass rod of unknown provenance.

It took a lot of heat – bright red – and I half expected the copper to collapse but eventually the brass flowed and made a very sound joint.

I would practice a few times first if you choose to go this way.

Neil

Edited By Stub Mandrel on 14/02/2012 21:42:22
14 February 2012 at 21:42 #84794
V8Eng
Participant
@v8eng
mgj.

Thanks for the information, I’ve not built a boiler yet, but will certainly bear it all in mind for future reference.

Edited By V8Eng on 14/02/2012 21:58:10
15 February 2012 at 10:06 #84818
Ian S C
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@iansc
I use brass and borax for brazing on my hot air engines, mainly joining steel. Ian S C
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