Crazy boiler idea?

[paul]

It seems that leaky boilers due to difficulty in soldering are a fairly common problem. It just occured to me that it might be possible to use completely flat end plates (rather than flanged) if these were soldered AND bolted together;on a horizontal boiler maybe having square end plates with threaded rod running parallel to the boiler tube connecting the corners of each end plate. since the end plates would be flat maybe that would be easier to fabricate and solder than flanged end plates? On a small boiler the solder would be acting more as caulking than bonding.

Obviously appearance would be an issue but it might be easy to conceal the whole thing witihin a larger diameter tube...

I'm a total novice to this stuff so it maybe it's a a nutty idea!

[gwrfan]

Hi Paul,

I don't think I've ever seen a square boiler, certainly not in a steam locomotive! In our higher pressure boilers (up to 100 PSI and above), a flat plate wouldnot suffice, flanges are required to allow for a sufficient surface for silver solder to run and bond. Also, a flat-sided boiler would need a great deal of stays in order to prevent distortion, as the steam pressure inside would be trying to make the whole thing round!

Or have I completely misunderstood your suggested plan?

Geoff

[paul]

Sorry Geoff I meant a normal tubular boiler with flat end plates - imagine a double acting cylinder with the ends of that bolted to each other, the bolts running parallel to the cylinder (boiler).

[gwrfan]

Aha! The word 'square' confused me, hahaha.

Geoff

[havoc]

While everyone seems to like flanged endplates, there is no real need for them concerning strenght. Just a flat plate soldered to the tube will stand a lot of pressure.

Some nice reading about gauge 1 boilers tested to destruction: www.ritginc.org/ follow'RITG Incorporated" followed by the "paper" at the entry "Proposed AMBSC Boiler Code"

You will have to use stays to keep your flat plate flat, but that is another issue.

[greasemonkey]

I guess flat plate may work in the smaller pot boilers but I dont know how you use it in the larger gauges!! The more tubes you put in the harder it is going to be.

Andy

[GWRdriver]

Paul et al,
Disc heads vs flanged heads depends upon a number of factors, staying patterns being one, but it's generally ruled by barrel diameter. There are potential problems from joint fatigue when using flat plates above about 3"OD. These aren't imminent dangers but the potential for fatigue cracking at joints does exist thus most Ga0 and Ga1 boilers use flat heads and boilers from say 2.5"ga up go to flanged heads and plates.. There is a bit of flexure in a flange head at its perimeter that does not occur in the same way in a flat plate.

A substantial case for plain joints anywhere in a boiler can be made by saying that a properly made joint (silver soldered copper) is stronger than the parent metal, which is true, but the question isn't solely about joint strength. The potential for problems with cold joints, inclusions, or cracks is higher in a butted joint than in a flanged one, and assembly is also a part of the equation. In most designs the best way, if not the only way, to hold certain assemblies together while soldering, when friction can't be used, is by riveting or screwing in the flanges.

Also, since construction details and the techniques vary with the size, scale, material of the boiler it would be very helpful when trying to answer boiler questions to know the size and material of the boiler being cussed or discussed.

[modeng2000]

I would like to say that as I am in the process of making a boiler for a 45mm loco, this discussion has been most helpful.
Thanks to all.

[paul]

That paper linked by Havoc was very interesting. Having quickly read through it (I'm at work!) I am quite encouraged - what I originally envisaged at the top of the thread was a 50mm tube with, using terminology from that paper, flat butt-jointed end plates soldered in position without any internal flue but with external stays connecting those plates.

Here, I've made a crude 3D model to illustrate...
www.squealingpiglet.plus.com/10.jpg

As I'd probably be running it at only maybe 30-40psi I'd imagine it would be pretty safe. Whether or not it is appealing to the eye is another matter! now I've made that computer model it looks somehow familiar - maybe this type of boiler already exists?

[the_viffer]

Martin Evans drew the throatplate of his 3.5" "Jubilee" 2-6-4T made out of flat plate instead of flanged. It was thicker than the other boiler plates. Around 10 years ago a Southern Fed official (I don't recall who) told me that this was then not acceptable. I don't recall the reason for this either (cracking on cooling springs to mind) but I'd suggest caution. I think the drawings may have been revised since original publication to show a conventional flanged plate.

I was reading at the weekend an old ME article by A Howarth on an electrically fired boiler. I have to say I found it generally hair raising (pun intended with exposed 240V terminals involved) with a number of features which would not be common these days. One boiler end was a piece of stainless steel of unspecified grade (see) bolted up against a built up and welded flange on the end of the ss main tube. The advantage of this was that the boiler was easily taken apart for heater element replacment and boiler descaling.

That idea is not new and some portable engine boilers had endplates bolted in position for "easy" boiler cleaning.

[havoc]

now I've made that computer model it looks somehow familiar - maybe this type of boiler already exists?

Looks a lot like some pneumatic/hydraulic cylinders.

[jackrae]

Hi paul

Your concept is indeed very like pneumatic cylinders as used on large control valves

A couple of points to bear in mind ;
If the end plates are relatively thin they will tend to bulge in the centre which will produce a turning moment at the joint where they contact the cylinder walls. The joint is then in both tension and twist or wrap (like the proverbial key on a tin of sardines). To overcome such effect the end plates need to be quite a bit thicker than the skin of the cylinder, probably as much as 3 or 4 times.

On the basis that the 4 (or more) tie bolts are to actually perform a useful function, your calculations for bolt strength should be based upon the soldered joint as having catastrophically failed - or not being there at all. If you consider this a bit OTT (over the top) then ask yourself this question, why bother having them in the first place.

It is my understanding that all boiler silver soldered joints should be stressed in shear rather than tension and hence the use of overlapping faces as per flanged ends.

In the final analysis if your happy with your design then go ahead and have fun. But if you are involving friends then bear in mind your obligations to ensure their well being by ensuring your construction is both sound and fit for purpose.

regards
jack

[Malcolm]

Its not relevant to loco boilers. but I have seen an approved design for a water tube (Yarrow) boiler for a steam launch which had a main drum eight inches diameter with flat plate ends stayed with four three quarter inch screwed rods. It was rated for 250 psi,so the idea does work. The plates were not welded or soldered, but butt jointed into an annular recess, probably with a copper joint.

[alanstepney]

Although there may be exceptions, present day boiler design is the work of over 200 years experience, of models, in excess of 100 years experience, coupled with a lot of knowledge and expertise.

Throughout that time, changes have been made in the light of that experience or technical advances, and particularly in an effort to make them as safe as possible.

I would be very reluctant to try to "re-invent the wheel" without there being very good reason for so doing.

[paul]

Malcolm: That's interesting thanks.
Alan: I realise that and the fact that I know diddly-squat about any of this really - it was just an idea (and we'll get nowhere if no-one has any of those!).

[havoc]

Although there may be exceptions, present day boiler design is the work of over 200 years experience, of models, in excess of 100 years experience, coupled with a lot of knowledge and expertise.

Yes, but a lot has changed since then.

When I see a test to destruction of a gauge 1 boiler (and that is the size Paul is talking about here) that is nothing more than a piece of copper pipe with plain copper endplates in a butt joint. And then the result is that this boiler fails an hydraulic test at 1500psi at the bushing. And if then further inspection shows that one of the butt joints wasn't even properly flowed through.

So if Paul proposes just an identical boiler for 30-40psi I guess he should not worry about strenght. It will require proper soldering etc followed by hydraulic test etc.

I do have my questions with the external "stays". In the configuration proposed they won't take much of the pressure unless the end plates are very thick. And that will then be harder to solder. Or you will have to put on external braces over the end plates.

[Chris Kelland]

Hi All,

Why not read the new version of the Southern Fed 'Red Book' and perhaps K N Harris's Model boilers and boiler making, between them, I think it says it all!


Regards,

Chris K.

[spurley]

Hi Chris

Is there an online version of the 'Red book' available? I have done a little bit of research but haven't found it yet! Got the HSE guidline etc though. Alternatively, where does one get hold of a copy? Any advice gratefully received.

Cheers

Brian

[Chris Kelland]

Hi Brian,

Sorry, as far as I am aware there is no on line version.
The new code of practice is jointly published by the Southern Federation, Midlands Federation, Northern Association and the 7 1/4 gauge Society. Any club that is amalgamated to any of these should have copies. As I am going to the S Fed AGM on the 11th. I'll try and find out about supplying by post.

Regards,


Chris K.

[spurley]

Hi Chris

Thanks for your reply I would be very grateful for any leads on this, cheers. I am sure that my club's boiler inspector's have a copy of the book however I would like to see if I can get my own copy for reference etc.

Cheers

Brian