Tig Welder and Silver Soldering

[davidimurray]

Hello

During the recent discussions with Brozier I've been thinking about how to work on boilers easily. Most people use propane to heat parts but this requires heating the whole assembly (and the world around) to high temps.

The next option is Oxy-acetylene. Here we get exremely high temps, but it's not the safest kit to have around the house and the emergency services won't be happy if anything happens. Of course the half way house is oxy-propane but there are still dangers associated with oxygen bottles - ever seen one get dropped - they go very far!

So, I was thinking, could you not use a tig welder as a heat source and then use silver solder as the filler rod. I would have thought this would be even easier if you used fluxed rods. Has anyone tried this? You can pick up a 200amp Tig welder nowadays for just over £200

[jasonb]

You could possibly use a cheap arc welder with the carbon arc rods used for brazing, give a similar heat to Oxy-acetylene but not sure how clean you could keep the work. I've only ever used them with sif-bronze brazing rods.

Jason

[havoc]

If you have a tig at hand, then why not just weld the boiler instead of brazing it? It seems like an unnecessary complication to me.

You'll have to learn to weld copper with it and likely need a bottle of argon. But otherwise what is stopping you.

[davidimurray]

If you have a tig at hand, then why not just weld the boiler instead of brazing it? It seems like an unnecessary complication to me.

Would a boiler inspector accept an amateur welded copper boiler? The beauty of silver soldering is that it is a commonly accepted practice, the only difference is the source of heat.

[havoc]

The previous boiler inspector at the club didn't want to hear about welded boilers -whatever material or wo made it- because that isn't the way it is done according to tradotion since 1900 or so. I haven't checked with the new one.

The code (ours here) itself doesn't say anything about it. It only considers welded steel boilers and there it doesn't say anything about "amateur" or "professional" welders. So I do not see why an amateur couldn't weld a copper boiler.

On the other hand, I had a long talk with a chap selling that stuff (tig) as I had interest to weld copper boilers. From him I got the strong impression that welding copper with tig isn't the easiest job. He insisted several times to go on a course and only to an instructor that would teach me that. Not taking "just follow the course, it is all the same" as an answer.

[baggo]

There's an interesting account on J-E Nystrom's site about a TIG welded copper boiler but I doubt you would find a boiler inspector in this country who would give you a certificate for one

John

[simonwass]

Someone at my work has just bought a 5" Brit, has a Swindon boiler and is supposedly MIG welded?

[GWRdriver]

About 1975, when I was away fom my own soldering kit for an extended period of time, I had a commercial welding shop electrically weld a few plates together on a copper boiler. I don't know what system they used, whether it was conventional arc, or gas shielded in some form, but they let me know they had fits with the job because among other reasons the entire assembly had to be pre-heated to near red heat to get the metal to weld. They did a fine job though. I know welding kit has improved dramatically since then, but I don't know if pre-heating is still necessary.

[Chris Kelland]

Hi All,

The main problem is getting enough heat into the job. I've looked at a few figures and find small propane torch, about 6 - 7 Kw, Big torch - approx 20 Kw, large torch, 50 Kw up.

I have tried carbon arc but limited to about 3 Kw by mains power. Very high temperature but so concentrated I burnt through the copper. I have decided to stay with propane and pack the job tightly with broken fire brick or my favorite Thermalite.

Regards,


Chris.

[havoc]

The heat needed for copper is indeed an issue. IIRC the guy I talked to quoted 60A/mm thickness for tig welding copper. Or about 3x as much as for steel.

So sad that model engineering doesn't want to progress with its time.

[weldsol]

I have used TIG as a heat souce for silver soldering and for certain jobs it does work.
But you will never use it for a copper boiler.
You will not get the amount of capillary action required.
If you want to TIG weld copper then you will need a high preheat
and you would be better to go for an Argon / Helium gas mix this will raise the arc energy that you could get from a small TIG set.

Paul

[jackrae]

Acceptance of technology or "modern" techniques is not the issue in our hobby.

We all love to try things out and experiment with materials and methods of sticking bits together.

However, this is a hobby enjoyed and practiced by participants of a wide degree of expertice, working within a framework (rules) that are clearly capable of being understood by all members

It therefore follows that the tools we use and the techniques we use them for must be capable of use by a reasonably competent but not necessarily highly skilled body of persons. Silver soldering is a subject widely understood which produces excellent, and relaible, joints in the materials we know are safe to use for the applications and pressures we require.

Similarly our boiler inpsectors are, in all probability, not necessarily "qualified" to the level of certification required by industry, but, by virtue of their experience and skills, are,or should be, capable of using their individual expertice and judgement in assessing fabrication quality to a degree of competence satisfactory for our hobby needs.

Boilers could be manufactured from all sorts of exotic metals using all sorts of exotic techniques but these , in order to prove them fit for purpose, would have to be certified by suitably qualified inspectors. In all probability well outwith the norm for most clubs.

It's up to each and every club to act reasonably within the limitations of their own rules and their terms of insurance. If they permit exotic materials and techniques, and can prove a suitable regime of inspection and testing, all well and good. Most of us are however happy to make do with silver solder which we know will produce reliable joints with minimal requirements.

Jack

[stantheman]

Every so often a subject similar to this comes up for discussion, and often you get some interesting debates. However on this one I must say that in practically every word Jack has written there is a very large element of truth and sensibility. Many years ago I was asked to produce a small cylindrical test piece, like an unstayed boiler. It only measured three inches diameter and was about two inches long, it was to be TIG welded. An inlet boss was placed and the vessel pressurised. Immediately all around were aware they were getting damp if not wet. On very close (magnifying glass) inspection it was found both the entire welded joints were full of very tiny perforations. This was finally traced back to the fact we should have used de-oxidised copper sheet and rods and not just straight commercial grade.
The fact is there are very feww boiler testers that are qualified to inspect and test any boiler made in such a way and more to the point there are even fewer model engineers qualified to perform the welding of such vessels.

As Jack has said already silver solder has been used very succesfully for a number of years and there really is no reason to change, it brings forward the old saying, 'if it ain't broke why try to mend it'.

I also agree that you would not succesfully replace the flame with a TIG arc to satifactorially complete a silver soldered joint, especially those of the complex nature used for our boilers.

One very fact worth perhaps considering is, 'if alternative ways, rather than those tried and tested over many years, of completing a copper boiler were available why do the commercial makers not use them?'

Stan.

[Laurie_B]

Having done some TIG welding in the past,it is a very good way of joining metals.But it is a welding process.I agree that there wouldn't be sufficient heat for silver solder to fully penetrate a joint.
Most model boiler designs incorporate lapped joints that rely on the full penetration of the silver solder for their strength.The design of the boiler joints would have to be completely reappraised if TIG welded,rather than silver soldered joints were going to be used.

[davidimurray]

Hello

Well this started quite a discussion It's great to get this sort of chat going.

I've been doing a bit of further reserach and it becomes obvious that due to the thermal conductivity of copper you actually need quite a big tig welder to succesfully weld copper -http://www.millerwelds.com/education/calculators/tig_amperage_calculator.php

A 1/8" lap joint requires 200-250A. You also need to use deoxidized copped and the back of the joint being made should be shielded with Argon gas.

Even if you can get around this one of the biggest issues I can see is having too much heat and 'rushing' the joint.

One very fact worth perhaps considering is, 'if alternative ways, rather than those tried and tested over many years, of completing a copper boiler were available why do the commercial makers not use them?'

I strongly disagree with this. Having been involved with a couple of industries where 'we've always done it like that' prevails, just because it ain't being used don't mean that it ain't viable. Why would a small commerical copper boiler maker spend the time, energy and money perfecting a new technique when at the moment they can virtually charge what they want and take as long as they want to make them. Companies don't want to take the time and associated risk to develop things unless they have to to keep up with the market. Perhaps if a boiler maker was producing 10,000 boilers a year it would be a different matter.

[stantheman]

Agreed, TIG is probably one of the nicest ways of welding a lot of materials (metal or alloys), one of the beautys of it is in the way the heat is localised so preventing many problems including distortion. On the issue about boiler joints, then of course you would have to re-appraise the whole ethos of boilers being of 'proven design' to enable our present system of boiler testing to remain as it is. No, in all honesty stick to well tried and proven practices, life is too short for major re-design and change.

[GWRdriver]

Aug 19, 2008 7:55:43 GMT jackrae said:

Acceptance of technology or "modern" techniques is not the issue in our hobby. . . . It therefore follows that the tools we use and the techniques we use them for must be capable of use by a reasonably competent but not necessarily highly skilled body of persons. - Jack

I am by no means a Luddite, but I am increasingly amazed (amused) at how folks in the US live steam community, or at least a vocal group, continually try to complicate formerly relatively simple things . . ."industrialize" it perhaps. Nowadays what we formerly made perfectly well by riveting together couple of pieces of black iron sheet can now seemingly only be achieved by using Unobtanium-X2 (centrifugally cast in a weightless environment ), pared down from the solid in a Bridgeport CNC machine, and joined by the latest plasma-laser, followed by X-ray testing. I suppose they think it makes them sound more capable or informed.

Personally one of the things about model engineering that I take greatest enjoyment from is the opportunity, more so than in any other area of my life, to be self-sufficient and to be able to say "I learned these ancient skills and made every bit of this thing from a pile of metal lumps and some bought-out screws, in my own little workshop." I acquired this queer notion from years of reading the Model Engineer. Naturally I will look for better ways to do things, but in the end I will tend to use what will allow me to be most self-sufficient.

[stantheman]

Well said GWR Driver.

Could not have put it better if I had tried.

[havoc]

Personally one of the things about model engineering that I take greatest enjoyment from is the opportunity, more so than in any other area of my life, to be self-sufficient and to be able to say "I learned these ancient skills and made every bit of this thing from a pile of metal lumps and some bought-out screws, in my own little workshop." I acquired this queer notion from years of reading the Model Engineer. Naturally I will look for better ways to do things, but in the end I will tend to use what will allow me to be most self-sufficient.

That's part of the issue. Those welders have become "affordable" (I'm not prepared to go into the reason why) these days. So adding one to the workshop and using it for as much jobs as possible is a possibility. I see some applications but not enough to justify buying one. However if I could include boilermaking then it would be settled and I go out and buy one and follow a course on using it. Maybe then I would even start on larger models than gauge 1. But as long as this reactionary vision reigns iot is an opportunity missed for me.

[alanstepney]

It may well be differetn for you, in Belgium, or for Harry, in the USA, but for those of us in the UK, one factor is that, any change from a published design, or method of construction, would require all the engineering calculations to be submitted, whereas, build it as, for example ME published it x years ago, and all will be well.

Whilst not an impossible task, it does limit change, for existing designs.

Perhaps a more important consideration is, what are the benefits?
I am all in favour of change, if there is a good reason, but change for the sake of it, is pointless.
The "traditional" silver solder methods work well, and are very forgiving of, perhaps, not-so-good workmanship from novices.