I had a 5" King boiler made 2 years ago by this lot. Fusion welded copper boiler with silver soldered bushes.

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fusion welded boilers

regards Martin

I've had a TIG setup for about a year now, mostly used for stainless and for aluminium. I have tried a little copper just for the fun of it, but just test pieces. From what I have found, I think the design of a boiler would need to be changed if it was to be TIG welded. I've found with making stainless steel fuel and water tanks for my steam launch that you don't actually want flanges on the joints. Or if you do, you want them coming outwards, like the seams we sometimes used to see on motorcycle tanks. Two edges are much easier to weld successfully than one edge and a rounded corner.

If I was going to TIG weld a copper boiler, I would want to make sure that both sides of the joint were protected by the gas shield, for instance by arranging to feed argon inside. This is quite a common thing to do with critical welds, it prevents contamination getting into the molten metal. In the case of copper , we want to avoid getting any oxygen into the metal. Provided we do prevent that, a copper weld is ideal, since copper is normally used pure, so the weld is the same as the parent metal and we don't get a heat affected zone where the proportions of any alloying elements may be different, and the heat treating history is certainly different to the parent metal. The copper that has been hot will of course be annealed, but a few stress cycles will take it back to the work hardened state. This is in contrast to alloys like stainless and aluminium, where even with an excellent weld, the heat affected zone may not be as sound as the parent metal. The design needs to take this into account, particularly with aluminium.

But I'm not an expert, and I'm certainly not going to weld a boiler.

John

For too many years, the longitudinal seam on domestic copper hot water cylinders has been welded using the MIG welding process. Initially the wire was 0.2% Si, 0.2%Mn, bal Cu. The shielding gas was argon.

Argon is expensive.

Replacing the Si and Mn with Ti and Al allowed the use of nitrogen as the shield gas – much cheaper. When we became the second UK supplier, the wire became more readily available to the industry, it was no longer rationed and we picked up a substantial volume of brazing alloy business.

However all the other joints tops, bottoms, and bosses are, I believe, still brazed. This is due, in part, that in order to cope with the increasing gap on a circular weld, the volume of filler that needed to be put down increased. This is at odds with a wire feed mechanism delivering wire at a constant rate.

Whilst at Johnson Matthey, we spent many hours trying to automate the brazing of copper cylinders using a wire feeder but all to no avail.

You can TIG a boiler, but MIG ……….?

Keith