boiler building

Hi,

I have the bulk of the copper sheet and tubes etc for a small loco boiler and am about to order the brazing rod and silver solder. I wondered if there is a rule of thumb how much is needed, for example per foot of tube, sq ft of sheet or by weight. Also, what sorts of the solder and brazing rod?

Thanks

Dave

Dave,

What are you proposing to "braze" as opposed to silver Solder, which is strictly a brazing filler (See Johnson Matthey)?

What size of boiler? By way of example, my Highlander boiler (7.25" )weighs in at 75kg approx. of which 2kg is silver solder. All solder is 42% silver  (old 842 grade)

Edited By KWIL on 13/06/2012 15:54:04

Hi David,

More practically - what size and design of boiler are you building?

My experience is very limited but for tubes I'd guess about twice the length of the joints in 1mm wire and twice the length of bigger joints (e.g. endplates to barrel, bushes) in rod. Then for me I'd add some extra to allow for always pushing a bit more into the joint to be on the safe side.

Neil

Thanks for the ideas, it's been useful in putting my mind in the right direction. The boiler is only a tiny thing and I will be speaking to one of the various Boiler Examiners of my M.E. society when I can.

Dave

Heronsgate - my problem is that due to severe health and other difficulties in my family, I rarely get to the meetings of the society so being able to access this site and the mostly helpful folk is a useful aid but not a replacement for the real world...

Edited By David Haynes on 13/06/2012 21:38:02

I don't mean to hijack this thread, but the comment on brazing prompts me to ask if it is possble to braze boilers - using brass brazing rod, as opposed to silver solder? I have often seen comments about 'brazing' boilers, using silver solder - this seems to me to be a terminological error. I have used true brazing (with brass rod) to join small metal fabrications (not a boiler), and the mechanical properties of the joints(steel brazed to steel) seem good to me (admittedly no real way to test them), and were easy to make using a small oxy/MAPP torch.

I ask because it seems silver solder of suitable grade for boiler building is gradually being priced out of existance - silver solder of any type is impossibel to obtain where I live, so I wondered if brazing was possible, and what are possible drawbacks.

I would have thought Davids question about quantities of solder is not really easy to answer - When I first learned to silver solder many years ago, my first joins were messy to say the least (and silver solder was cheap then!), now I can make virtually invisible joints if a fillet is not required, and use considerably less solder.

Wotsit, Firstly, as above, reference to the Johnson Matthey site will confirm that silver solder is considered as a "silver brazing alloy"

Secondly, you ask about "true" brazing using a brass rod, fine if you are not in contact with water or combustion products, both of which will, to a greater or lesser extent, dezincify the brass and cause a joint failure. Even with a silver solder, sulphur (from coal) in a fire box will attack the joints, which is why the use of a headed rivet, head inside the firebox, protects the silver soldered joint to an extent and therefore increses the life expectancy of such joints. You could well go down the route of TIG welding the copper, increasingly used by some builders (usually professional), which with care and skillfull work, produce a well constructed and long lived joint. Mind you if you want to change a fire tube, it might be more difficult. I do not TIG weld copper but I have watched it being done.

David;

I'm currently finishing a boiler for a 3-1/2" gauge 2-6-0 (Ivatt from Martin Evans), and will be working on a 7-1/4" one later this summer.

Some in our club use higher point melting point silver solder for bushes, etc. The 2-6-0 boiler will be my 4th boiler; the first one (Tich #1) was a learning experience; Tich #2 was much better.

I'm using "easyflo-45" which I don't think you can get in England any more. I have no idea how much I'm going to use, because it was purchased about 10 years ago. It's all I use for fittings, boilers, and fabrications. If you purchase too little, get more! if you purchase too much, you'll use it on making fittings, etc. I find I'm using more than I thought I would.

I like the Kozo Hiraoka approach of just putting on enough silver solder to do the joint, but I do in fact have to keep a flux jar, a pointed "scraper", and a bit of silver solder for dabbing when required.

I have a Sievert torch, but also now have a "Turbo Torch" with the A-32 tip; different torches; the Sievert one is a soft flame, the TurboTorch is more "put the heat here".

As I use copper rivets for boiler firebox stays where possible, and no soft solder "caulking" like used to be used in LBSC days, the turbo torch is good in that it does not go out as readily sticking it into a boiler firebox. It draws air in around the handle, while the Sievert draws air in around the burner head.

If you can get a copy of Alec Farmers' boiler building book, it is worth it. I borrowed a copy years ago, and I don't know if it is still available.

Boiler building is fun; wish I could do more of it to keep my skills up.

Hope this rambling message helps;

Another JohnS

hi david,

you will have to use silverflo 55 for the boiler as easyflo and easyflo No.2 are no longer available. i used silverflo 55 on my last boiler (a 5"g job). suggest you buy at least £150 worth plus a large tub of flux that is suitable for long heat operations such as thessco F. the amount of silver solder used depends on your skill and the accuracy of the fit of the plates etc, but my view has always been better than too much than not enough.

sifbronzing boiler joints seems to have fallen out of favour these days... this is what LBSC used when he referred to 'brazing rod' as opposed to silver solder. alec farmer recommended sifbronzing certain sub assemblies to aid construction, but if this is your first boiler i would stick to silverflo 55 throughout, and use comsol with its special flux for the stays (threaded and nutted).

good luck!

cheers,

julian

David,

Note that Silverflow 55 is a trade name, CuP alloys also have a 55% silver solder and a lot more practical advice available han the other trade mark owner provides. Talk to Keith at CuP and/or read their Website data.

Why anyone persists in using Comsol and threaded stays I will never know (must be another unfortunate LBSC legacy I guess) Stick with silver solder throughout for a proper job.

As an experiment I tried brazing with some 'common brass wire' and borax as a flux. It needed a helluvalot of heat, but worked OK.

Neil

I often use brass, either wire,swarf, or bits of shim, and borax as a flux. Because of the heat require ment I can only use it on small parts, but its strong, and cheap. If you won't higher temperature, try copper wire, it gives a thin joint, but much more heat required. Ian S C

Have a chat with Kieth at Cup Alloys

Bob

whilst i agree with KWIL that a fully siver soldered boiler (including stays) is superior (and ive done it this way), i wouldnt advise silver soldered stays for a beginner. without oxy-acetylene (and a lot of experience using it) the inner firebox door plate has to be left off if using propane, and this makes things very complicated for a first attempt at boiler construction. unless the boiler is quite a bit above 80psi working pressure, threaded stays caulked with comsol are perfectly ok. let's not put anyone off making their own boiler by making things too complicated!

i would not advise the use of brazing with brass wire on boilers, and i dont know a single boiler inspector who would pass a boiler made with brass wire brazed joints! this is simply due to the decompisition of the brass caused by de-zincification in joints exposed to the water space. ok for steel fabrications such as frame stretchers and drag boxes, but NOT in a boiler please!

I might have been misunderstood - but I was under the impression that Comsol could not be used for new boiler construction? I thought that new boilers had to be fully silver soldered. Is this true?

Phil H

Phil H,

comsol caulked threaded and nutted stays are perfectly acceptable under the current boiler regs.

cheers,

julian

Absolutely right, but, I would expect that a fully silver soldered boiler would handle a "boil the boiler dry" situation better.

It does happen, (have seen it, and seen the boiler survive, even if soft soldered parts close to boiler did not) and the boiler survived just fine.

As we all know, there is not just one way of making copper boilers.

(finishing copper boiler #4, starting copper boiler #5 shortly, if that helps)

Another JohnS.

May I try to address some of the points raised in this thread?

Gentlemen - BRAZING is a generic term for one form of joining two pieces of metal together.

If you are using capillary flow to effect a joint between two closely adjacent surfaces and it is being done above the melting point of aluminium - you are brazing.

If you are doing the same but below the melting point of aluninium - you are soldering

Brazing is carried out using gold, palladium, nickel, copper alloys including brass and silver solder. Silver soldering is a common term for a range of alloys used in the brazing process.

Brazing is still a cost effective way of joining metal including the use of silver solder. Use it as it should be used.. Appreciate the basic principles of the process and stick to them to achieve this. The trade publishes a lot of good stuff to set model engineers right. They have a lot of experience to offer. Read that literature. Our brazing experience goes back to 1969.

Silver solder can be expensive made so by banks, speculators and to some extent demand so be sure you know what you are buying. There are cheap silver solders around that will braze but are no good for boiler work - you won't melt them!. Ask for certificates conformity or labelling that shows clearly what it is. There are 3 or 4 of us that do this. Pick one

This small band carry in stock, a wide range of alloys to suit all needs. There is no problem with availability.

If you want good quality meat you don't go to the fishmonger for help and advice, you go to a butcher and probably not the one in the onestop supermarket.

Keith Hale (CuP Alloys)