brazing or silver soldering

[firebird]

hi

Next year I am going to start on my first steam engine (stationary) which I intend to run on steam. (that sounds a bit like stating the obvious doesn't it) I am going to make a small boiler to provide said steam. The final details have not been decided on yet, I am at the moment acquiring the necessary kit and materials before I start. There has been much discussion in the magazines that I read about whether it is acceptable to use brazed joints on the boiler. What do you guys think about this. I ask because I have done a fair bit of brazing in the past and have oxy acet. kit. but have as yet no experience at silver soldering. Brazing is cheaper which is another advantage that I can see. The boiler Will be made of copper and approx 7inch long X 21/2 inch diameter. Thanks for any advice you can give me.

Cheers

 

[greenie]

The way that I see it, is that Brazing and Silver Soldering are done in EXACTLY the same way.
The only difference is that silver soldering is done at a slightly higher temperature.
I have done both types of this at work and can tell you from experience, that silver is the way to go.
The joins are similar, but silver solder runs into ALL the small cavities and really does seal/grip well.
Brazing has a slightly lower gripping force than silver solder as well, been proven many times with inserts soldered onto the tooling, the brazing will give way before the silver soldered bits do.
For what your doing, just play it on the safe side and go with silver solder, be a real nice site if the brazing gave way, while there was a full head of steam up, eh.

regards greenie

This is the way that I see it only, others might/will disagree, please take ALL suggestions on board and play it on the safe side.

 

[Mcgyver]

technically silver soldering is brazing, but it is a lower temperature than say bronze filler rod. in either case, both have a high tensile strength than the copper. were you to use bronze filler rod on a copper boiler, there may not much melting point differential between parent and filler and the whole boiler might turn into a puddle

good for you for wanting to run on steam, there is a difference. for advice, make sure you either know the engineering or build to a published design and be aware oxy acetylene can be tricky with SS - to high a temp for direct heating

 

[John]

Hi Firebird

I am thinking along the same lines as you regarding building a boiler.

From what I can find, toy steam engines run on boiler pressures under 20 psi - probably more like 5 to 10 psi. Anyone actually measured operating pressures?

The toy Fleishmann engine I have has a soft soldered boiler. I know - I melted a seam once when I let it run out of water!

From this I would expect that a good silver solder joint would be more than adequate from a strength point of view.

John

 

[gilessim]

Hi there, somewhere on the forum someone put a link for a firm (UK I think) that specializes in silver solder, with a list of melting temps. etc. I couldn't find it just now, but I'm sure you would find it useful!...Giles

 

[firebird]

Hi

I think I'll go for the silver solder option but purely out of interest what are the problems associated with brazing? Is there some technical reason why it shouldn't be used. I know brass boilers should be avoided because they can crack with age but Mamod have used brass boilers for years. Just curious.

Cheers

 

[Powder keg]

Brass and brazing rod melt at nearly the same temp. Makes a mess of things. I won't tell you how I know:O)

Wes

 

[Mcgyver]

Is there some technical reason why it shouldn't be used. I know brass boilers should be avoided because they can crack with age but Mamod have used brass boilers for years.

the Mamond boilers are low pressure, but that's not really an excuse....maybe they figure after the initial exultation they'll spend most of eternity on a shelf....anything to do with a boiler should NOT be made of brass. the problem is leaching - the zinc in the brass is actually removed over time leaving the brass brittle. it is also a no-no to use brass for any fittings, bronze must be used, i'd have to look up which bronze.

 

[BobWarfield]

Brownell's for silver solder in the US, although they're never the cheapest source for anything.

BW

 

[Rog02]

Silver soldering is a rather in depth topic. I do a lot of it on some of my sheetmetal art pieces and have found the following links quite helpful in selecting the proper alloy for each piece. I purchase ALL my Brazing and welding supplies from a local, reputable supplier, that can give me tech support when needed.

ESAB
http://www.esabna.com/EUWeb/AS_handbook/596as8_1.htm

Harris
http://www.harrisproductsgroup.com/consumables/brazingSoldering.asp

CuP Alloys, a UK supplier with a lot of valuable information on their website. Worth the time to read especially the Model Engineering and Live Steam pages.
http://www.cupalloys.com/content.php

Belman-Melcor, another site worth spending some time reading. Many good tips and spec charts.
http://bellmanmelcor.com/homepage.htm

And we can' forget about our fearless leader MarvK. He has some good tips on his webpage especially if you are soldering small stuff.

 

[Rog02]

There seems to always be some confusion about silver soldering and brazing. While it is true that some silver bearing solders may fal withing the prescribed classification of "brazing" there are many "low temp alloys" that clearly are considered soldering.

Definitions

What is the difference between soldering, brazing and welding?

Soldering - The AWS defines soldering as a group of joining processes that produce coalescence of materials by heating them to the soldering temperature and by using a filler metal (solder) having a liquidus not exceeding 840ºF (450ºC), and below the solidus of the base metals.

Brazing - Brazing joins materials by heating them in the presence of a filler metal having a liquidus above 840ºF (450ºC) but below the solidus of the base metal.

Welding - In welding, fusion takes place with melting of both the base metal and usually a filler metal.

The above information was provided by Harris Products.
http://www.harrisproductsgroup.com/faq.asp

 

[firebird]

Hi

Thanks to all who have replied. I will use silver solder on the boiler and all fittings and just use brazing on stuff thats not under pressure or has steam in it.

Thanks

 

[Mcgyver]

There seems to always be some confusion about silver soldering and brazing. While it is true that some silver bearing solders may fal withing the prescribed classification of "brazing" there are many "low temp alloys" that clearly are considered soldering.

Silver brazing = silver soldering, although personally i tend to call silver brazing silver soldering, saving brazing for the bronze filler alloys. the difference between brazing and soldering based on temp - 800F iirc. silver bearing solders are solf solders and are not silver solders. silver solder has say 30-60% silver and silver bearing solders 4 or 5%, . the later melt at around 400F vs 1100-1200 for silver solders.. I can't think of any silver solders that are under 840F ??

 

[Loose nut]

While brazing and silver soldering are technically brazing they don't work in the same manner. Brass brazing ( it is not actually brass there are several types of alloys that have different properties) can be used for build-up on parts, filling v-grooves (butt welds) etc. silver solder can't, it is strictly used for capillary joints. Brazing can be used on cast iron were regular silver solder can't. In the old days brazing rod or spelter was used for brazing model boilers but today silver solder is preferred. The gap on a silver solder joint should be .003" any less than .0015" and capillary action won't take place, any more than .005 and the strength of the joint falls off rapidly. An easy way too set the gap is to use an automatic center punch, it will form a small upset of about .003", just space the center punches out equally around the joint and you have a equally spaced gap. It's important to point the flame in the direction that you want the solder to run, the solder follows the heat. When heat is applied to the flux it turns into a sticky clear paste (don't apply solder yet) then turns into a clear liquid and the base metal becomes "clean", this is the flux cleaning the oxides off the metal. If you apply the solder now it should flow into the joint, if applied to soon it will just ball up and oxidize and if to late the metal will be "burned" and the solder will not stick. This is why it is important to use the manufactures matching solder and flux, the flux shows you when the proper temperature for melting the solder is achieved. Silver soldering is an art form and if possible it's best to get someone to help you get started, a good book on soldering is "Soldering and brazing" by Tubal Cain, who wrote for model Engineer magazine. Hope this helped.