7.5" Diameter Copper Boiler

[sunworksco]

What would be the difference in steam-up time between the steel boiler and the all-copper boiler ?
Can I silver-solder the steel boiler together in lieu of welding ?
What should be the wall thickness size ?

 

[Jasonb]

Giovanni, we have told you several times that you need to do the calculations for teh boiler to establish material thicknesses etc.

Also bear in mind thet there is a minimum thickness the tube plates should be when expanding the tubes otherwise you can weaken the tube.

Jason

 

[Jasonb]

One other thing to consider when going for steel instead of copper is that the increased wall thickness will reduce your boiler capacity.

If we assume the volume taken up by your flues is say 30% of the volume then copper will give you a 25% greater water capacity than steel based on 1/8" copper vs. 1/4" steel. The steel boiler having a capacity of approx 100cu ins. and the copper 125cu ins. If you cram in more tubes like the original then the percentage will become greater.

So opting for steel due to its easy availability may result in a less efficient boiler and reduced steam output in the long run. This is why copper is the prefered material for smaller boilers.

Jason

 

[sunworksco]

I was talking to a copper still maker that was telling me that copper is 4 times more conductive than steel. ???

 

[GWRdriver]

The "K" factor, the coefficient of thermal conductivity in Btu/(hr/°F/ft) for copper is around 220. The "K" for wrought steels is around 35. More than four times.

 

[sunworksco]

Very good!

 

[sunworksco]

Looks like the best option is an all copper boiler.
I can have a machine shop roll the copper plates.
I am planning to use 1/4 inch copper plate for the bulkheads.
The bulkheads will be laser cut then the edges will be recessed to flange over the boiler shell ends.
This will give more silver soldered surface area and also look more scale-like to the Stanley boiler.
The full-scale boiler shell was wrapped by piano wire so I will be wrapping the shell in stainless steel fishing leader wire.

 

[Jasonb]

Will you have sufficient solder area using that recessed method?

Your endplates at 1/4" are quite thick, with the amount of tubes you have staying the tubeplate I would think 4mm (5/32) would be nearer the mark. You would then need a surface area of 3 times the plate thickness for soldering, this is why tubeplates are flanged.

Your recessing method would likely only have 1/8" inside the tube and 1/8" end bearing assuming you are using 1/8" plate for the barrel and 1/4" tubeplates

If you want it to look like the original then I would make it with flanged tubeplates and then roll a ring of copper to solder to the outside of teh barrel at each end.

 

[sunworksco]

I could just machine cut an 1/8 inch groove in the 1/4 inch boiler tubeplates so the boiler shell will seat into.
This would also create a dam for the silver solder.

 

[sunworksco]

I have a machine shop advising me to have the 7.5" diameter copper shell seam welded and then silver-solder the tubeplates on.
Any advice is welcomed.

 

[Jasonb]

It is possibel to tig weld boiler barrels, the only thought with your design is that the weld will beed to be ground flush on the outside for the winding wires, make sure they know that as it will affect the strength of the joint.

Have you or they done the calcs to see if a welded joint will be sufficient for the pressure and pass any local boiler regs.

We have very few welded copper boilers here, but some of the ones I have seen have a welded barrel.

Why not have then weld the tube plates as well then if you want to silver solder the tubes into place you don't have to worry about the tubeplate solder melting. Or just weld the lot.

J

 

[JorgensenSteam]

As I recall, there was an example of a TIGG welded copper boiler that Jason pointed out, and it seems like a special rod or something was used to prevent cracking.

Seems like there was more to it than just TIGG welding it (to prevent cracking).

 

[sunworksco]

Thanks, guys.
I do know that the copper plate needs to be oxygen-free to keep from cracking.

 

[Jasonb]

As BOS says I think its a bit more involved than just tig welding, the company say they spent 18months developing the process. Possibly some form of heat treatment after welding. They can now also weld bronze bushes onto copper boilers.

http://www.steam-technology.co.uk/process.htm


They are actually a specialist welders and Steam Tecchnology is just one branch of the company. Probably have a bit more knowledge than your local fab shop.

http://www.weldinginnovations.co.uk/services.html

J

 

[sunworksco]

Beautiful welding work there!
I do have a very professional copper welder prepared to weld the shell seam. I can silver-solder the tubeplates and tubes myself.
I will atempt to post photos when the project begins.