Copper V Steel

[wiltsrob]

Morning all

As some of you will be aware from my other threads i am just starting the scale up of a 3.5" 16DA "Natal" as published in ME in the 80's to 7.25" gauge

As to the boiler ... i know that which ever route i go i will need to jump through hoops so lets not get into those discussion as they have been done to death on this and almost every other forum out there....

the boiler is 12" od and 54" long .. with a 18 x 16" foundation ring

My question is in reallity .. does the extra cost of making a copper one out weight the longevity of steel

my understanding is that on the steel boiler i will need to retube the boiler every 5 years or so depending on how much use i give it and maybee a new inner firebox at the same time.

I was looking at 6.25mm wall thickness for the copper and a WP of 125psi or 9bar(8.92 to be exact ) and gives me a bar/ltr of 465 if my math is correct ( for copper )( to be double checked after as thickness of materials will affect result )
this falls below the 500bar/ltr limit for club inspection..

Robert

[baggo]

Hi Rob,

For that size boiler I personally would go for steel. I shudder to think how much a copper boiler would cost

With rolled in copper tubes and proper water treatment etc. a steel boiler should last at least 20 years before needing attention, probably longer.

You will lose a bit of grate area due to the increased thickness of the steel sheets but that is unlikely to affect the steaming of such a large boiler.

John

[pondok]

Wow Robert, that will be an epic project. It's a great design for a serious passenger hauler in 7.25", they are such handsome engines and not so obviously narrow-gauge outline as equivalent heavyweights like the Rio Grande K-36s, and if you leave the drivers flangeless, minimum radius would not be so restricted as an eight coupled. (Not to detract from Jimmy's jaw-dropping class 25NC 4-8-4 that I'm going to have wet dreams over...)
Having owned the 3.5" version in the past, heard from at least 2 other owners, and part-restored another for a friend, I can say for sure that the valve gear needs redesigning ideally, or take the valve gear from the works drawings. The expansion link top fouls the lifting arm, eccentric rod dimensions and return crank position are wrong as drawn by Martin Evans, and events are uneven.
He made some departures from the original boiler that gave no advantage over the proper design:
-mixed up the 2 versions of 16DA in Natal, using the later wide firebox boiler but dome regulator. In fact the wide firebox boilers all had smokebox regulators, which is no disadvantage to the modeller, as the handy PTFE gas type ball valve is far easier to install and maintain IMHO
-single gauge glass column instead of twin
-Sorry to go on like this, but another thing is he drew the blower pipe as a hollow stay through the boiler, not silver soldered but just tapped and screwed into bushes.
- His steam manifold sits atop the backhead, under the cab roof, GWR style. I guess that's not necessarily a disadvantage if you're not concerned about accuracy to prototype.

Hope that helps you to avoid recreating some of the 3.5" niggles.

Very envious!
cheers
andy

[3405jimmy]

Building in 2" scale i think the boiler decisions is easy i wont live long enough to earn the corn necessary for a copper boiler so steel its going to be. The quote i have had for a steel one is hefty enough anyway.

You probably know this already but original drawing are available from Johns web site

www.sarsteam.co.za/product-info.php?pid92.html

jim

[wiltsrob]

Jim..

I have a set of works already ..

I am a fan of copper boilers ... and would build this one myself rather than spending shed loads of money on a commercial one ..2 reasons

1... i am more than capable ( blowing my own trumpet a bit ) to build it as long as i can get my hands on a big enough brazing hearth and the nessesary heating .... ( although i would tig weld the boiler rather than braze
2.... i object to paying 35% profit to the commercial company to get the materials and the labour to make the flanged plates ... i dont know of any commercial company who would glue together the plates and bits supplied by a customer....

Having only just started looking into it i recon the cost wouldnt be that much different fro steel v copper ... i dont have a budget for the boiler in mind mainly because its going to be a few years before i am ready to make it .... but all costs including red tape shouldnt be much more than 6K for a copper one and maybe 5K for the steel as most suppliers charge per KG for materials

I have heard ( mainly from the traction engine world ) that steel boilers need constant retubing and that in the long run ( say a 20 year period ) it would be cheaper to have copper but the copper one would be 50% more to start with.

Robert

[kwil]

Robert,

If you are going to Tig weld it, why do you need a brazing hearth? I would start buying the materials now, they can only increase in price while you are thinking about it. I saved half of my brazing costs by buying the "silver solder" when I first started on the idea.
K

[wiltsrob]

Hia..

I would tig weld by preferance but most clubs seam to want brazed or silver soldered..

Robert

[davebreeze]

Feb 13, 2012 21:21:59 GMT wiltsrob said:

... i dont know of any commercial company who would glue together the plates and bits supplied by a customer....

One of our club members had that done, I think it was Swindon Boilers. He had started doing the boiler and given up, they finished it for him.

[wiltsrob]

Morning all

I have had a chat with RSA and they have sent me a load of paperwork to read through about getting the boiler certified and CE marked.. the procedure doesnt look too complicated and it isnt as expensive as i had expected.

It looks like steel is the way forward - I had a long chat with Great Northan Steam who make both steel and copper boilers and he was very helpfull.. He has said that at the working pressures and the size of the boiler that steel is really the only choice and other than retubing the boiler should last 25 years.
The thing with once the boiler is retified i can at any time in the future get any boiler maker to make a replacement or if someone else decides they would like to make the same loco then the paperwork is done it is just a case of ordering it..

Robert