Silver solder and Flux

I have read somewhere that it is sensible to use two different silver solders if on need t add items. a normal one, and a higher melting one. For example in making a boiler. Is this correct and if so which Johnson Mathey rods and flux is recommended.

In anticipation thanks.

Malcolm,

Hi Malcolm,

You can start with a higher melting point silver solder for the first parts and then use a lower melting point solder for the rest. Another option is to reflux the already soldered joints before soldering the next.

CupAlloys has a good "Best Practice" guide. Silver-flo 55 or 56 seems to be the silver solders with the lowest melting range, Silver-flo 40 has a slighly higher melting point, for flux you could use Tenacity 5.

Thor

If you can find the first editing (rather than 'first edition' of 'The Complete Car Modeller' by Gerald Wingrove there is an excellent section on using a range of silver solders to build up the fantastic brass engine detail in his models...this remains, for me, the best silver solder guide that exists. The points made include using the temp range of solders well and also the fact that when you re-heat silver solder to melting point a slightly higher temp is required.    All of this, of course, applies to the old solder ranges containing cadmium.

.....I think (if I recall) that the later versions of the book do not have the excellent silver solder treatise of the first version, sadly.   I have never been a car modeller but the Wingrove books are a treasure trove for all artisans including model makers, jewellers, silver smiths, and even clock makers....

Edited By Bob Stevenson on 07/09/2017 17:56:09

Edited By Bob Stevenson on 07/09/2017 18:04:52

I only use one heat range if I can get away with it as it is so much easier to get a good joint without putting excess heat in. I make steam boilers boilers for a living and try to use one temp (630 deg). Beware that if you attempt to solder bronze bushes and the like to a copper boiler using higher temp solders you will most likely end up melting the bush before making the joint. Always use the high grade T5 flux unless you are making a one off small joint otherwise the efficacy of the solder quickly diminishes to the point that it ceases to function = bad joint. You can get away with using just one temp on anything but a small boiler because the heat is leeched away so quickly that the only place where solder will melt is directly where the torch is pointing. It takes a lot of heat to solder a boiler, heaven only knows how they did it with a parafin lamp. It helps that I dont use any form of heat insulation (other than the heat proof hearth bed) for boiler soldering thus allowing other areas to cool quickly, but you need an oxy set to achieve this reliably. Hope this helps.

Hi Malcolm,

If it is your first attempt at a major silver soldering job then I'd suggest using a couple of differing grade filler rods as has been suggested, Having built a good number of boilers over the years I now only use one grade of silver solder for every operation, what I will do though is to lightly flux every previously made joints and always use a flux capable of withstanding prolonged heating, I only use propane for heating, a couple of lamps for the larger 5" gauge boilers with plenty of heat retention, uses less gas and to let the job cool slowly, reducing the risk of any stress cracking etc.

It may be worth you tracking down a copy of Alec farmer's boiler making book, interesting.

Regards,

Bob Youldon

Thank you all for your responses.

The last time I did any "Boiler workm is 60plus years ago. and yes then it was using a blowlamp. Obviously things have moved on !!

Good morning Malcolm,

like yourself all those years ago I started with a blowlamp, in fact my first boiler for a Juliet was completed with the aid of an evil 5 pint ex army blowlamp, that was an experience particularly when it decided to shoot a jet of flaming paraffin about 10 feet forward, just like a flame thrower! mind you as an apprentice, one old fitter used a petrol blowlamp! I always thought that was a bit dangerous especially in confined spaces.

Regards,

Bob

What is the purpose of fluxing previously soldered joints ? Does this stop them remelting ?

Your oxy set has a high temperature but a small heat capacity enabling a local area to get very hot indeed. This is why you can silver solder one part but the rest of the job cools off quickly. A large paraffin lamp is quite the opposite having a heat capacity far larger than oxy enabling a large amount of metal to be brought up to an adequate temperature for silver soldering, but not as high as the local temperature with oxy. Propane is similar.

I have only used a 5 pint paraffin (but even better with 10% petrol added) lamp twice and both times it did its best to kill me, so no way should anybody take this as any kind of recommendation to use one!