Copper Boiler Design

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keyrouteken
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Re: Copper Boiler Design

Post by keyrouteken » Sun Dec 23, 2012 1:39 am

Many years ago, National 'Live Steam' legend "Victor Shattock" made close to thirty locomotives all with copper boilers in 1/2-inch, 3/4-inch and 1-inch scales over a sixty year building period. Several were equipped with Superheaters. Most of the boilers were either brazed or silver soldered, but two or three in the early years were only soft-soldered.
All were hydrostatically tested up to 150 lbs psi.
He never once had any trouble with his boilers. Ken Shattock
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Harold_V
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Re: Copper Boiler Design

Post by Harold_V » Sun Dec 23, 2012 2:26 am

It's a bit reckless to suggest boilers that operate at and above 100 psi can be soft soldered. I fully expect that's a recipe for misery, or even death. Readers should exercise caution before making that decision.

Harold
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Bill Shields
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Re: Copper Boiler Design

Post by Bill Shields » Sun Dec 23, 2012 3:08 am

not just soft soldering - recommending brazing is also a path to eventual destruction. Reckless is a rather mild description of my thoughts on such a comment.

Soft soldered / brazed boilers, even if they will pass a hydrotest when new, will eventually fail as a result of deterioration of the joining media.

I have one such boiler here in my shop that I am replacing for a friend.

It was silver soldered, then soft soldered over top of it to fix the leaks.

Granted, it lasted 40 years and outlived it's maker, but still was not the way a boiler should be built.

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LVRR2095
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Re: Copper Boiler Design

Post by LVRR2095 » Sun Dec 23, 2012 7:25 am

I think a distniction needs to be made. Back in the 1920's and 1930's many copper boilers were built that were in effect rivitted boilers with screwed stays. The soft solder was there merely as caulking. I know of several locomotives with boilers built that way that are still giving good service with a maximum allowable working pressure of 80psi or less.
Is it a method that I would recommend? No as there are far superior ways to build a boiler. But if you find a classic live steam locomotive from the 1920's or 1930's I would not necessarily condemn the boiler out of hand just because it was caulked with soft solder.

Keith

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gwrdriver
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Re: Copper Boiler Design

Post by gwrdriver » Sun Dec 23, 2012 9:24 am

Well said Keith. Having advised or mentored a few hundred aspiring copper boiler builders in the last couple of decades, mostly newcomers to live steam, I have come to see there are two aspects of this question. The first of course is the current era "Party Line" - which is All Silver-Solder All the Time. Not phos-copper (Sil-Phos), not brazing (bronze), but high silver content silver solder. That's our Law of the Land and that is as it should be.

But then I'm a reasonable, honest, and practical guy and when I'm asked the question "Can I use soft solder?" I'm presented with a dilemma. Do I lie to them and say no absolutely not, there is no such thing any more? What I do is answer them honestly, and the answer is always "Yes, BUT (and this is a big but) you will be going against many decades of live steam grain and such a boiler has to be made to be completely structurally self-sufficient by mechanical means (plates, stays, rivets, screws, etc) because you may not assume or rely upon the solder for any, meaning zero, structural strength and are you prepared to engineer this design. In addition, in certain circumstances there may be penalties for going against the Law of the Land, events where you may not be allowed to steam, and in certain circumstances you may not be allowed to participate in any insurance scheme there might be. I then leave the decision to them, and in almost every case they make the right one.
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gwerhart0800
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Re: Copper Boiler Design

Post by gwerhart0800 » Sun Dec 23, 2012 9:30 am

gwrdriver wrote:All Silver-Solder All the Time. Not phos-copper (Sil-Phos), not brazing (bronze), but high silver content silver solder. That's our Law of the Land and that is as it should be.
What is your opinion on TIG welding of copper? Maxitrak has shifted to using all TIG welded copper boilers in their products.

http://www.maxitrak.co.uk/boilers.asp
George Erhart
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gwrdriver
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Re: Copper Boiler Design

Post by gwrdriver » Sun Dec 23, 2012 9:44 am

George,
It looks interesting and appears to have promise, but otherwise I can't form or render an opinion because I don't own or know the equipment, haven't observed it being done, and I don't know the long-term performance of welding. Bill Shields (IIRC) is a TIG advocate and has done it so he may be the one to describe the results.
GWRdriver
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Bill Shields
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Re: Copper Boiler Design

Post by Bill Shields » Sun Dec 23, 2012 8:35 pm

I have an almost finished boiler that Marty put together the firebox, throat and backhead for me.

You cannot do the entire boiler with TIG (cannot do tubes) and I wouldn't want to think about stays.

and it takes quite a bit of experience and a good TIG machine to do properly...

there are also concerns regarding the proper grade of copper that should be followed.

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Marty_Knox
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Re: Copper Boiler Design

Post by Marty_Knox » Sun Dec 23, 2012 9:01 pm

Bill Shields wrote:I have an almost finished boiler that Marty put together the firebox, throat and backhead for me.

You cannot do the entire boiler with TIG (cannot do tubes) and I wouldn't want to think about stays.

and it takes quite a bit of experience and a good TIG machine to do properly...

there are also concerns regarding the proper grade of copper that should be followed.
The right grade of copper is alloy 101. Most copper commonly found is alloy 110 (de-oxidized). The phosphorus causes cracking.
I have a 300 amp machine - running at max amps I could only weld about 1 inch at a time. I needed the high amps to start the arc, but couldn't back off enough to keep from melting the copper once it heated up.

redneckalbertan
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Re: Copper Boiler Design

Post by redneckalbertan » Sun Dec 23, 2012 11:47 pm

Marty_Knox wrote:I needed the high amps to start the arc, but couldn't back off enough to keep from melting the copper once it heated up.
What do you have for a TIG machine?

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jschoenly
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Re: Copper Boiler Design

Post by jschoenly » Tue Jan 23, 2018 9:17 am

This is an old thread, but since the discussion went from design (flow and areas) to construction (Fastening and silver soldering), I'd like to revive it for a discussion on sheet design. I'm currently in ownership of a 1" engine with a copper boiler which has some parts made for it but far from complete or ready to assemble.

My question is about material thickness on the tube sheets, backhead, etc. This boiler has some of the sheet work done and has 3/8" thick copper sheets. There are some drawings/sketches from the process that seem to indicate the intent for the tube nest to stay the full thickness and other areas to be thinned down with a milled pocket.

Now I'm used to seeing all the sheets formed from essentially the same material thickness (give or take) as the boiler shell and all parts. I also know that some old designs used thicker cast tube and throat sheets, etc.

In my brief searching, I didn't see much about any disadvantage to having thick sheets. It adds weight and structure (obviously doesn't replace the need for stays) but aside from the cost if you had to buy the material, is there a downside to the design and/or joint strength?

I have all this material now so if no downsides, it makes for a more rigid structure to build, but if there is a detriment to the thickness I would likely form the sheets from more reasonable thickness material. I appreciate any input. Thanks!
Jared Schoenly

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Bill Shields
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Re: Copper Boiler Design

Post by Bill Shields » Tue Jan 23, 2018 12:31 pm

only downsides are that 3/8 is tough to form (for a flange) and you may be reducing the water space between tubesheet(s) and
outer shells...and in a 1" scale boiler, losing 1/4" of water space can be significant.

I do NOT recommend that you consider ROLLING copper tubes into copper sheet....even though 3/8" thick, it will deform.

were you planning on drilling directly into the side of the front / backhead and attaching the firebox wrapper without making a flange??

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