Copper boiler plate flanging, or not?

Bob,

I am not convinced you need to worry about silfos - you are not going to use it if you build a new boiler?

Regarding the gaps. You form the outer wrappers carefully using a former and various metal bars etc and keep offering it up to the flanged plates. You check the gap with something like a set of feeler gauges and your eyes. You gently tap the wrapper with a soft mallet until you have it right.

Thousands of boilers have been built using the 'normal' methods on youtube etc. 'What one idiot can do - another can follow' (that is not an insult - it is actually from a quote inside a book on Calculus).

Phil H

Bob,

If you have a bucket load of silfos I think you should use it to make more buckets or use it on other less critical projects than a boiler. Following is taken from Silfos 5 product data sheet but the other grades have similar comments.

"Normally the corrosion resistance of Sil-Fos 5 is of the same order as copper, but under certain conditions it may corrode more rapidly. Sil-Fos 5 should not be used where the joints are exposed to sulfur compounds, especially in gasses or oils at temperatures above normal room temperature. As the corrosion by sulfur is cumulative, even very small percentages will eventually cause failure of the joint by disintegration. Exposure to pressured steam can also result in accelerated corrosion. "

Even if you use a sulfur free heat source to fire the thing it will still be exposed to pressurised steam. A decent solder will be fine with a conventionally designed joint, there have been thousands made that have performed perfectly well, this that I have seen that have leaked or had failed joints were down to the gaps being too small for the solder to properly penetrate forming a nice looking fillet on the outside but with nothing actually in the joint.

Paul.

Edited By Paul Kemp on 09/07/2020 21:29:30

You're getting too hung up on this 5 thou number, As long as there is a small gap to allow the capillary action, and it isn't too big so you can't fill it, then silver soldering works. Obviously a big gap uses a lot of solder, but a few strategically sited bronze screws or copper rivets (not closed firmly up) will keep it all in place and any gaps which are too big you just tap round the outside with a soft faced hammer (as others have said). Soft copper is very pliable, you don't have to beat the *** out of it

If you use oxy only then you can run into all sorts of local expansion issues. Heat up the bulk with propane and use oxy to get the final temp locally if you must

Oxy/Propane is great alternative to Oxy/Acetylene providing you do not want to weld with it. It will happily silicone bronze braze, but you will not be doing that. I do 95% of my silver solder joints using it. From the data I have the gap should be closer to 2 thou, which as Duncan says is easily controlled using bronze screws, a mallet and feeler gauges. You do not flux the joint until you are ready solder so visibility should not be an issue.

Dave

Back, just replied to another post about a Minnie boiler, the throat plate to boiler joint doesn't have a flange, just a simple 1.5mm thick solder joint. In MY, emphasise MY, book that is simply unacceptable.

Duncan's comment about getting hung up on the 5 thou gap is simply wrong. I am an electronics engineer, and have had to cope with surface mount components, and a 5 thou gap simply means the item fails later on. Tin solder is awful stuff, I have to hand solder, fine if you have got the gear to flow solder the 98% tin 2% silver solder. But even that fails after a few years. I have been seriously burnt by lead free solder, I won't use it.

There is lots of comment about expansion, yes, but why is a solid tube plate different to a flanged one? The solder is easily able to cope with the stresses created, as is the copper sheet, not a problem. It all comes back to not really knowing just how much solder is in the joint. There will also be a slight reduction in water space, but just shift the plate to keep the 1/4" or whatever gap between plates, firebox isn't going to notice.

I will buy a little boiler and make it.

As said there have been thousands of boilers made, but where are they? Going back to the 40's and models were made everywhere, but do you see them? The exhibitions all seem to have new models. Beginnings to wonder if all the thousands have actually been turned into static models, or simply scrapped. Seems like making boilers from steel, up to 2" scale, just having to scrap the thing after 100 steamings because you have no idea of its condition.

Boiler bangs are not a problem, keep it that way!

Bob,

You don't seem to want to accept any of the answers given here but before you waste money on materials for the very thick plates (because I think they will be quite expensive) why not have a word with whoever is going to inspect and test your boiler.

Phil H

Many differences between soldering boilers and electronics. Applying boiler methods to electronics would be a disaster, and soldering a boiler electronic style is an expensive way of failing.

Electronics are soft-soldered with a mild built-in flux, the joints have to be clean, and components shouldn't be overheated. Provided electric joints are secure, they don't need to be mechanically strong.

Boilers are made by hard-soldering. Older low-pressure boilers were soft-soldered, but the practice hasn't been accepted for decades. Hard-soldering's done at high temperature with an aggressive flux. Joint strength is important and it depends on the solder flowing by capillary action between the metals being joined. A gap is needed to ensure full penetration, but I'm sure Duncan is right - don't get hung up on 5 thou.

Beware of cross-over engineering. Tales of woe involving high-Tin solder and SMD are irrelevant to boiler construction - they're different problems requiring different techniques.

Dave

I have many volumes of ME going back in a few cases more than 100 years, BUT..........

What was then was then, and with any magazine article you don't always get to read the correction a month or so later. IIRC Keith Wilson replied in a letter to one instance where he had recommended the use of Silfos agreeing it was not suitable. Another example was J. Austen-Walton's boiler design for 'Twin Sisters' which had no flanged or extra thick plates and was described as dangerous about 10 years later in the same magazine as published the original design. Simplex's boiler was not accepted as safe under the Australian Boiler code due to being designed with too small a factor of safety, and Highlander's boiler went through a redesign a couple of issues after the original was published.

Basically, just because an editor in the past accepted the article for publication does not mean that following that path today is right. Our boilers today are safer than they have ever been, but that is only because we make them according to what is felt to be safe today by today's experts, ie experienced boilermakers and silversolderer's today and of course your boiler inspector first and foremost.

Whilst agreeing that many boilers have been built to Simplex's design (and indeed to many others that are now not considered safe) in a letter in Model Engineer vol 143, edition 3558 Reg. V.Wood commented on behalf of the AMBSC that they had never considered the Simplex boiler design unsafe because of the crown stay design, but rather because of the inadequate factor of safety.

My point about the 5 thou is that it is important. Bend a leg on a chip with lots of legs and it will work on the conductive flux, for a while. Crossover engineering could be really good, can't think of an example at the moment of course!

My point about Simplex was simply that it used a thick throat plate, not flanged, which I found interesting. What is the too small factor of safety?

I do have a bucket load of Silfos, was used to solder coax cables, but I won't be using it.

For 30 years I have sold items all around the world, and they were required to be good, however defined, even though the buyer had not a clue about what was inside. I take the same attitude with model engineering, it has to be good. This discussion is much better than none.

I can't find the magazine with Keith Wilson Silfossing a huge boiler to check later issues.

Cost is obviously of importance, but I am currently selling off stuff I am no longer interested in, Meccano, valves, test equipment etc so I do have money to spend, more so no doubt than most people.

Bob,

I am not sure the size of your bank balance is of great interest to many and I am positive a large bank balance does not always equall sound reasoning or a sound appreciation of engineering principles. I suggest you spend some of it and add a copy of the Australian Boiler Construction Code to you library, it's not a document I fully agree with but it is well written and sets some common national standard. I was involved very much on the periphery when a British version was being considered but that seemed to quickly lose momentum, particularly with extending it to steel boilers.

The non issue with the Minnie boiler in another post I tried to reply to but due to the vagaries of this forum it logged me out instead of posting it and I can't be bothered to type it out again!

As an aside I have heard more than once the simplex boiler was not compliant with the Australian code but do not recollect a definitive reason why not. Does anyone have a definitive explanation as to why it does not comply? Too low FOS may be due to many reasons, plate thickness, joint design, stay size and spacing or type etc. Where exactly does it fall down?

Paul.

As a non boiler maker, but with some very small experience of oxy acetylene welding, I would have thought that you would only have problems of burning the metal if the flame is not kept moving.

I have repaired an exhaust pipe, where even a brazing flame caused the thin corroded metal to melt, but succeeded in brazing and welding new steel to make a lobster back on the the corroded pipe, which was gas tight. It was not pretty but no one was going to crawl under an old bus to examine!

I would have thought that the original reason for flanging was to provide metal for the plates to be rivetted to the boiler shell.

In our smaller sizes, with lower pressures, the flange allows braze or silver solder to fill the joint and small gaps by capilliary action, to provide a seal, and by virtue of the length of joint, provide the necessary shear strength.

I saw a steel tube plate being flanged in Meiningen, the oxy acetylene several torches were ENORMOUS, and boots of the chap standing on the plate, directing operations were smoking! But they produced a flange some 150 mm wide.

Howard

I design PCBs in my day job. Even on a fine pitch device, 5 thou is nothing. I don’t have any datasheets to hand but off the top of my head but I think that is normally less than the manufacturer’s tolerance for leg position. If it isn’t, a properly designed footprint will allow for it. Even if you’re talking about 5 thou off the surface of the PCB, a correctly applied solder joint will cope with it.

Brian

It’s the crown stays; the Australians don’t allow girder stays. Despite their use in full size boilers, particularly road steam and portable engines, they insist on rod stays between firebox crown and outer wrapper.

I've just re-read that letter and find it rather confused. Although the points above are present, there is no justification whatsoever for the claim about the factor of safety of the Simplex boiler design.. The letter then goes on to critisize the use of girder crown stays, with broad comparisons to other boilers, and recommends crown stays attached to the outer wrapper, as used by a commercial boiler maker down under.

The implication is that girder stays are unsafe, although this rather contradicts his earlier assertion. This was the reason for my earlier post.

I've read the AMBSC code, can't find anything banning girder stays.

Nigel,

Thanks for that. As I said in my post I do think the Australian Code is a good document that gives some harmony to the nation's small boilers but I do think parts of it are well OTT. Like yourself it would seem, I don't see anything wrong with girder stays, anything but uncommon in full size. With a round top boiler the curved surface needs no additional support and the flat surface of the crown is ably supported by the girders. When you consider full sized unstayed crowns like the Marshall pressed Maltese cross and Fowlers "corregations" girders are eminently safe. Even rod stays will not prevent quilting of the crown but decent girders offer far more support.

Paul.

Duncan,

Its a long time since I read it and in truth it has probably been updated since. Did you note anything re FOS and how they specify it is calculated? Nigel's comment re girder stays rang a bell, is it anything to do with the "girder" if permitted must be attached to the wrapper and the crown? I have heard several comments that the design is not accepted in Australia over the years but do not recollect a specific reason, hence my question!

Paul.

Hello Bob,

It seems you are convinced that thick copper plate is better than flanging thinner plate. Well go ahead and do it, I would like to see and hear how you get on. There are quite a few people on the forum that stick to the tried and tested ways of boiler making, me included.

I am all for someone else experimenting and showing how wrong we have been.

Andrew.