Soldering/brazing a boiler.

[Keith HaleParticipant @keithhale68713]

Lets clear something up from square 1

The 2%, 5% and 15% silver alloys are not "silver solders". They are copper (Cu) phosphorus (P) alloys for the fluxless brazing of copper in air.

The 45% silver alloy is a silver solder that contains copper, zinc and possibly cadmium or tin.

Generally, increasing silver contents lowers the effective liquidus (temperature at which a joint can be made) and improves the ductility of the alloy itself.

It makes very little difference to the solidus (temperature at which the alloy freezes)

Data from the International Standard for Brazing Materials ISO 17672 shows the following melting ranges:

2% 645 – 825 or 643 – 788 dependent on the phosphorus content. Ductility 5%

5% 645 – 815 or 643 – 771 dependent on the phosphorus content Ductility 6%

15% 645 645 – 800 Ductility 25%

The ductility figures are as stated by manufacturers.

The 2%, 5% and 15% alloys can be used to join copper alloys but need an external flux. Use a suitable silver solder flux to suit the heating cycle.

In reality it makes little difference to the joint ductility for the model engineer because the copper is fully annealed at brazing temperature and as usual the parent material will fail first.

A word of caution.

DO NOT USE THESE ALLOYS TO JOIN COPPER OR ITS ALLOYS TO NICKEL OR FERROUS ALLOYS. They form brittle inter-metallic compounds in the parent materials that will lead to catastrophic joint failure.

DO NOT USE THESE ALLOYS IN HOT SULPHUROUS ATMOSPHERES eg COAL FIRED BOILERS. The sulphur will go through the joint like a hot knife through butter!

Keith

[Brian JohnParticipant @brianjohn93961]

I have gathered all the parts together to make a slightly larger version of the Midwest boiler : mine uses 65mm end caps and is 75mm in length/height, excluding the firebox. I had a few problems drilling the large 19mm hole to take the flue/chimney. There is slight gap which I hope you can see in the pictures : the tube does not fit in the hole as well as I would like. How big is too big a gap ? I was thinking of silver soldering that copper washer around the chimney to improve the situation ?

Edited By Brian John on 23/01/2015 17:20:55

Edited By Brian John on 23/01/2015 17:22:22

[Michael GilliganParticipant @michaelgilligan61133]

Brian,

First; let me congratulate you again, on the inspired use of those end-caps !!

Second; life will be much easier when you get a lathe … that hole could have been bored to size.

Third; My rescue plan would be to make a snug-fitting ring of Copper wire and press it into the gap; then solder the lot … Silver Solders really need quite close fits, so that they work by capilliary flow.

MichaelG.

[JasonBModerator @jasonb]

The washer should do the trick or Michael's wire.

Are you going to add a couple of cross tubes to the flue to help get the most from the available heat? Now would be the time to do something about it before you start putting things together.

J

[Brian JohnParticipant @brianjohn93961]

Michael : yes, the lathe would have been very handy for drilling the hole and levelling off the top of the end cap (I had to do it by hand with a file). I could also have thinned the base of the end cap a bit. At 1.58mm thick it may not conduct heat as well as say 1mm thick copper. The sides of the boiler are 1mm thick ; I could not find the thicker copper pipe at the scrap yard.

A ring of copper wire would not work as the hole is not quite round ! It is slightly oval which is why I went for the copper washer idea. When I drilled the hole I had the end cap in a vice which slightly distorted the end cap and hence distorted the hole. Next time I will slacken the vice on the last step of the step drill and hold the end cap by hand to get a neat circular hole.

Jason : what diameter cross tube would you suggest ? I am not really confident enough about the whole project ; it is adding more potential leak points which would be almost impossible to fix. I have no way to pressure test the flue with the cross tubes before fitting it….a nice idea though.

Is this what you had in mind ?

http://modelsteam.myfreeforum.org/archive/new-vertical-boiler-build-.__o_t__t_40231.html

Edited By Brian John on 24/01/2015 04:33:31

Edited By Brian John on 24/01/2015 04:34:12

Edited By Brian John on 24/01/2015 04:36:40

[JasonBModerator @jasonb]

Yes thats the sort of thing, you could probably only get one or two 1/4" tubes in that space. Maybe save that for the next one.

[Brian JohnParticipant @brianjohn93961]

I am thinking about how to pressure test the flue with its cross tubes. Would such a thing make much difference on this small scale ?

I also want to build a spirit burner with two wicks/burners so that they are positioned either side of the flue and not directly underneath it.

[Brian JohnParticipant @brianjohn93961]

I have soldered the larger boiler together and I am ready to solder the firebox to the base of the boiler. I have built two fireboxes : one has three air holes and the other has six air holes. Which one would you use or would it not really matter on this small scale ?

NOTE : I have already soldered a firebox to the smaller Midwest boiler and it makes a huge difference. It raises steam much more quickly now. The firebox on the Midwest boiler has three air holes.

Edited By Brian John on 30/01/2015 12:35:47

Edited By Brian John on 30/01/2015 12:37:32

[JasonBModerator @jasonb]

Possibly fit the 3 hole one and if you find it needs more you can always drill them once it is assembled, you will still be drawing a lot of air in from the large hole where the burner tube fits.

Rest looks a good job

J

[Brian JohnParticipant @brianjohn93961]

Should the sooty deposits be cleaned regularly from the inside of the firebox ? Does it affect the thermal efficiency by letting the soot build up ?

Edited By Brian John on 20/02/2015 17:11:42

[Brian JohnParticipant @brianjohn93961]

The finished products : both the Midwest steam boiler and my own larger copy. I am not sure if the larger boiler needs the two boiler bands. They are tricky things to fit !

I will be replacing those steel brackets with something made of brass soon.

Edited By Brian John on 07/03/2015 05:50:55

[JasonBModerator @jasonb]

Looking good Brian, just need to get hold of a lathe and then you can make a larger version of the wobbler to go with the bigger boiler

[Ian S CParticipant @iansc]

Brian, it would be nice if you could fit the support brackets inside the firebox, with the feet turned inward, that would look a little tidier, to match the nice work you have done on the rest of the boiler.

Ian S C

[Brian JohnParticipant @brianjohn93961]

Jason : I use the big boiler to run the PM research engines. I am still looking for a lathe. I go to China on the 5th April….I wonder if I can bring one back on the plane ?

Ian : that is a good idea

[Ian S CParticipant @iansc]

You could stuff the lathe in your jacket, might be difficult getting through the metal detector though. Maybe you could make enquiries though, it might not cost the earth to ship it home.

Ian S C

[Bruce VoelkerdingParticipant @brucevoelkerding91659]

I have a question, when silver soldering the end caps. does one apply flux to the surfaces and then push them together, or does one just apply flux at the joint after assembling the parts ? What about the washer by the chimney ? Would one apply flux on top of the cap and under the washer, or not ?

I have silver soldered various pipe fittings, but never a boiler.

[Brian JohnParticipant @brianjohn93961]

1. When I silver soldered the end caps to the pipe I put flux on all surfaces and then pushed them together.

2. I applied flux to both sides of the washer, the top of the end cap on which is sits, and the chimney where it makes contact.

[Brian JohnParticipant @brianjohn93961]

Here is the PM Research twin cylinder engine combined with my own boiler all fitted together on a single wooden base. I have made brass struts to hold the boiler with the feet facing inwards as per Jason's suggestion. There is a larger copper plate to take the twin funnel burner and it is separated from the boiler's copper plate by a 1mm gap. This is to stop the burner getting hot when in use although the small pins I have fitted to the bottom of the burners seemed to have solved this problem anyway.

Edited By Brian John on 03/04/2015 06:49:58

Edited By Brian John on 03/04/2015 07:10:23

Edited By Brian John on 03/04/2015 07:13:05

[Brian JohnParticipant @brianjohn93961]

My old solder supplier (Miniature Steam) is no longer selling solder or bar stock. But he has assured me another supplier has the same solder (with cadmium to aid the flow ) so I purchased about $80 worth from him. I tried it for the first time today and it did not go well : I had to heat the copper up much more than usual and even then it did not flow very well. It seems very similar to the plumbers silver solder I tried a few months ago which had no cadmium at all. I did not end up with a nice shiny fillet of solder. It will probably do the job but it looks very unprofessional….''rough as guts'' is how I would describe it.

1. I am using LPG gas and this has worked for me in the past with the old solder. Should I be using a hotter gas ?

2. What colour should the copper be when the flux melts and it is time to apply the solder ?

3. Some people soft solder their boilers. What temperature of soft solder would be safe enough to use in a tiddler boiler ? I do have some 240 degree soft solder but I would think it would have to be higher than that.

[JasonBModerator @jasonb]

Brian can you post the exact details of the solder, eg what is is described as and any make, spec, etc.

J

[Brian JohnParticipant @brianjohn93961]

No, it does not come in any packing : I can give no details or description. I was told over the phone that it was 45% silver.

What should I be asking for ?

Edited By Brian John on 28/07/2017 12:57:13

[JasonBModerator @jasonb]

Well 45% with cadmium should melt OK as that is what the basic proportions of Easiflo solder is/was and should not be any more difficult to use than what you had before.

The metal should just have a dull red glow as the flux turns to liquid when viewed in a dull room, you may not see it in bright sunlight.

J

[Brian JohnParticipant @brianjohn93961]

That was interesting : I just tried the old solder. It was a bit better… but not much better. I wonder if the flux has gone off ? It is EZI WELD 602 and there is 1/4 of a jar left. I would have thought it would be good until the last drop !

[JasonBModerator @jasonb]

I've not used the paste flux b t have a feeling it may have a shelf life once opened. Powdered won't go off.

[Brian JohnParticipant @brianjohn93961]

I bought some new flux today from Bunnings. The EZI-WELD 602 silver brazing flux has been replaced by CA 602. It is the same composition but by a different company according to a few websites. The result is a big improvement over yesterday.

I am surprised the old flux had gone ''off''.

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