Silver soldering

[Malcolm]

Does anyone know whether silver solder loses strength at elevated temperatures in the same way that copper does? I am thinking of steam fittings made of bronze parts silver soldered together. With substantial superheat, would the solder lose strength more rapidly than the bronze?

[SteveW]

Malcolm,

It's just a guess but I suspect the biggest issue is whether it melts or not. I know folk to use Silver Solder on the superheaters but I think they make sure that the joint isn't out above the fire.

Remember that there are a number of Silver Solder temperature ranges to consider. Maybe pick one and ask your question again. If you are worried better braze them rather than silver solder, it's basically the same technology just 'otter.

Generally a good silver soldered joint is a capilary joint, the solder is only a glue/sealant. The major strength is from the male/female joint members. In this case the joint is going to need to get very hot indeed before it falls apart.

[alanstepney]

The temperatures needed to affect the higher-temperature silver solders (what used to be B4 and C6) are above what one would use copper for. Of the order of, 720c and over.

In any water/steam environment, the pressure that represents is way over anything we will ever see.

I wouldnt worry about the usual run of fittings.

The one area where silver solder is not really suitable is on stainless steel firebox superheaters, where the temperature can get really high.
In that case, welding is the answer.
TIG being best.

[steammadman]

Hi Malcolm.
go to JOHNSON MATHEY metal joining we-site ,there you will get all the techo you will ever need and more.
hpoe you dont get baffled with science ,(i did).
good luck hope you get your answer, if not, e-mail them ,click on their contact tab
for adress
steammadman

[Malcolm]

Thanks Gentlemen. I got in touch with Johnson Matthey, and they say that silver brazing should not be used at any temperature over 200 deg C. I am sure that the steam temperature in many models with superheaters approaches or exceeds this, but I have never seen any warnings against using silver solder.

[gwrfan]

Hi Malcolm,

This is quite interesting reading, as I assume that most of us carry out silver soldering tasks with little thought to temperatures in our model boilers. Looking at a table in K N Harris' book, 'Model Boilers & Boilermaking', I see that as steam pressure increases, so does the temperature, and vice versa (of course!). At Gauge Pressure of 125 psi the temperature is 178 C, and at 150 psi it is 185 C. I wonder what the actual temperature is in a firebox itself, where the stays are silver soldered?

Anyone have further thoughts on this?

Geoff

[alanstepney]

I am surprised that JM would say that. The melting points, and indeed the temperature that it begins to soften, are much higher than that stated.

The firebox temperature can be, and according to Prof. Bill Halls measurements, is way over 200c, but the water in the box would keep the actual stay temperature down below that figure.

The main "concern" is any silver soldering where the joint is NOT in contact with water, which is why superheaters are usually welded (if stainless steel) or placed so that they dont get the full force of the fire.

As it has been used for so many years without any problems, I dont think any of us has any need to worry.

[Tel]

Hear, hear AJ, I've made fabricated fittings for many years now & all I've ever used has been 45% silver solder. Never had a failure (well, I've had a few failures in the manufacture, but not in service)

Personally, I'd be pretty surprised if the temps in our steam circuits its got anywhere near 200°C

[the_viffer]

tel said:

Personally, I'd be pretty surprised if the temps in our steam circuits its got anywhere near 200°C

I don't know Terry. According to my steam tables it is only less than a 50C superheat on 5 atmospheres gauge. I regularly get steamchest pressures of this amount with a wp of 100psi and have radiant superheaters. I like to think that at points in the circuit I am way above that. In passing I really notice the difference in performance once I get the fire really hot and as I hope the superheaters too. According to Ostwald's' law the energy emitted by an approximation to fire is proportional to the fourth power of the temperature so a small increase in fire temperature can result in loads of extra power.

I feel slightly bad about using silver solder on the really hot parts of the circuit. I've never had joints fail from this cause but as someone pointed out earlier in the thread the hot joints are not taking a huge load.

I tend to use high silver content solder too. I'm rather a fan of hallmarking quality as I've a syringe of it mixed up with flux which is really handy for fittings as well as jewellry making.

If JM thought the questioner was talking about joints for strength held at temperature for long periods then I can understand why they might be concerned.

[chameleonrob]

don't forget that superheated steam doesn't conduct heat as well as wet steam and that the surface area is large conpared to the volume, superheated steam would need to quite a bit hotter than 200 ^oC to get the fitting that hot.

[steammadman]

Gentlemen, what are we trying to become? , scaremongers, boffins ,or just plain ,
white coated think i know better model engineers.
i am into my 70's, been model engineering since i was about 12 or 13,and , i have never known , or, heard of silver solder melting in a boiler.
Dont forget the daddies of ALL model engineers, L B S C ,PERCIVAL MARSHAL , E . T . WESTBURY, K. N. HARRIS , HENRY GREENLY ,J. N. MASKELYNE ,and many more, sadly no longer with us,ALL used to SOFT SOLDER firebox stays and they used to stand up to steaming
also remember silver solder is FAR SPERIOR today than it was in the early 1900's.
As L B S C would have said,(i think),"don't be inspector meticulas, get on with the job in
hand, MODEL ENGINEERING."
I hope i have not upset anyone with my preachings but, i believe in getting on with the job in hand, and not pretending to be a scientist, I'm just a plain old model engineer.
and i have enjoyed being so for almost 60 years, with ,(hopefully) many more to come
thank you all.
STEAMMADMAN

[gwrfan]

steammadman said:

i have never known , or, heard of silver solder melting in a boiler.

Hahaha, Steamy! You're almost as bad as my 'better half', who tells me off if the radiators get too hot, in case her airing clothes catch fire, LOL! ;D

[steammadman]

sorry GWR FAN,
I did not mean to sound as though i was telling you off! ! ! .

but being a L N E R fan we don't like you G W R boys to get away
with out a challenge or two.

seriously though my first loco a mighty " TICH" did have soft soldered
stays, (actually they were white metal ,which found it's way into my lunch
box , when i was working at Doncaster Plant, in 1952.
That boiler is still steam tight today, but of course i can't use it.
( i weigh too much for the little loco to pull)

[gwrfan]

Steamy (hope you don't mind me calling you that? LOL),

No, I wasn't even thinking that you were telling me (or anyone else) off, just advising the rest of us that age and time proven practises are still usually the best 'rules' to follow.

Oh, and I should have added in my Member Bio, that I also have a 90 percent completed B1, so it's not all Great Western, haha. Must admit that I bought it 'as is', and it will have to be sold to fund the building of my 'Manor'


Geoff, in frosty Cornwall

[the_viffer]

steammadman said:

Gentlemen, what are we trying to become? , scaremongers, boffins ,or just plain ,
white coated think i know better model engineers.
i am into my 70's, been model engineering since i was about 12 or 13,and , i have never known , or, heard of silver solder melting in a boiler.
Dont forget the daddies of ALL model engineers, L B S C ,PERCIVAL MARSHAL , E . T . WESTBURY, K. N. HARRIS , HENRY GREENLY ,J. N. MASKELYNE ,and many more, sadly no longer with us,ALL used to SOFT SOLDER firebox stays and they used to stand up to steaming
also remember silver solder is FAR SPERIOR today than it was in the early 1900's.
As L B S C would have said,(i think),"don't be inspector meticulas, get on with the job in
hand, MODEL ENGINEERING."
I hope i have not upset anyone with my preachings but, i believe in getting on with the job in hand, and not pretending to be a scientist, I'm just a plain old model engineer.
and i have enjoyed being so for almost 60 years, with ,(hopefully) many more to come
thank you all.
STEAMMADMAN

Preach away. As gwrfan says it reminds us of our wives and girlfriends (may they never meet!)

I don't have a huge problem with the idea of soft solder caulked stays. I know someone who contends they are safer than silver soldered as they leak when they are abused.

T'old men had some great ideas and we'll not see their like again. However not all their ideas were good ones. Anyone here want to stand up and vote for fittings tapped straight into plates, unflanged plates, fire tubes screwed into plates (even Keith Wilson favoured that one long ago!), or cast boiler plates?

Old LBSC never could it seems to me quite make his mind up about superheat. I suspect he liked it but couldn't get his systems to work really hot with poorly lubricated gm cylinders. Even he said that you had to be wary about superheater spear points. He kept them well away from the fire and brazed them with coarse spelter. I do remember reading him write of an exhaust T run with soft solder that came apart on a continuous track suggesting that either someone's sv's needed adjustment or he'd a fair bit of superheat.

These days we can use fair more efficient superheaters and I really do believe that well designed modern steam circuits are hotter than those of 50 years ago, especially as 50 years ago many tracks were short up and down runs instead of the long continuous runs we now often use.

Yes we should concentrate on making stuff but I think that not all the old mens' idea were the ideal solution and as model and experimental engineers we should continue to question, experiment and have away the odd unconsidered (non-custard) trifle in our lunch boxes.

[Malcolm]

Glad to have stirred things up a bit! I feel I should quote the JM reply in full. "Silver brazing filler metals like Easy-flo No.2 are only suitable for service up to temperatures of 200 deg C. Over this temperature their strength drops off dramatically. At 300 deg C they would be quite plastic. We could therefore not recommend any silver brazing filler metal for service above 200 deg C". How about that then? I feel that I should point out that I asked the question in connection with a full-sized steam launch. I do not want a jet of superheated steam in my face!