bronze for small scale boiler heads and bushings

[mike44]

I am attempting to build a small scale boiler . The boiler is 1-1/2" ID buy 8" long.
It will run at 30 PSI and test at 60 PSI. I am wondering if bronze can be substituted for copper. Only for the front and back heads and several bushings. The boiler itself is copper.
I would like to make the heads 3/8" thick so I eliminate bushings. The thick heads will allow me to fasten the heads with brass screws or copper rivets I will turn 1/16"x 1/16" recess on the perimeter to hold the hard solder.
This is my second attempt. First attempt leaked from the front head. 3 tries did not fix it.
I could not take the head off to flux it properly as the stay was in and hard soldered to both the front and and back heads. I am starting over again.
I was told to try a liquid flux for high temperature solder. Even if works I am still going to build another boiler. Hopefully I'll get it right this time
mike

 

[Rudd]

Why not ask in a place where people deal with small hobby boilers?
Live Steam - The Home Machinist!

 

[rke[pler]

You might have ductile and expansion problems with the bronze where it bears on the copper, but for something with very little use and at such a low pressure you're probably alright.

You might try to caulk the leaks with soft solder, assuming that you used a silver braze in the initial effort. There are also "high flow" silver brazes if you didn't reach far enough and "high fill" crack-filling brazes to try before going to soft solder.

Do your high pressure test hydrostatically, or fill the boiler all the way with boiled and cooled water (leaving no air in the boiler), seal and put in the sun. You can easily get 60psi with the thermal expansion of the water filled boiler with pretty mild heating.

 

[mike44]

Why not ask in a place where people deal with small hobby boilers?
Live Steam - The Home Machinist!

Thanks, I did just that a few minutes ago. I asked here because I asked the same question on another forum , Home shop Machinist. I got about 75 reviews but no replies so I figured this forum could help. I am a retired carpenter and farmer that got interested in maching 15+ years ago. I know the rules and respect the fact this forum is for machinists, not home shop types like myself.
I have learned a lot from the posts though.
mike

 

[mike44]

I like your idea of the pressure test. I'll try it whenb I complete the new boiler. I used Harris hard solder and black fluz which worked except for one area on the back head. I won't use soft solder , I would rather start over again.
mike

 

[rke[pler]

I like your idea of the pressure test. I'll try it whenb I complete the new boiler. I used Harris hard solder and black fluz which worked except for one area on the back head. I won't use soft solder , I would rather start over again.
mike

It's completely acceptable to caulk with a soft solder on a boiler in your pressure range. If you want a little more strength you could use a silver bearing solder, I recall 4% will give quite a bit more strength to a lead/tin solder.

You might want to look for a book "Model Boilers and Boilermaking" by K N Harris, he covers all this.