Bill

I think the "avoid direct heat" is probably more to do with oxy-acetylene or oxy-propane, where the flame is particularly hot and fierce. It can easily over-cook the flux or melt the metal locally! With a straight propane torch, you can't really avoid "direct heat"! I've built a few copper boilers in my time using only propane, and the sensible advice is to use the correct flux for the grade of solder you're using, heat things up quickly (so the flux doesn't go off), and make sure the surfaces are clean and well-fitting (with 0,1mm/0.004" clearances or so) before you start.

It would probably be a good idea to get somebody experienced to be with you when you start cooking up the boiler seriously – even if he (or she!) merely nods their head quietly in the background. If you're in a club, a likely choice is one of the boiler inspectors.

Indeed, beware a very hot flame – and in particular the blast pressure of the oxy flame. I avoid direct heat wherever possible but its not normally a problem with propane. Flux choice also becomes critical with heat type and boiler size.

Hi BIll,

you are correct the price of silver has dropped recently and this is reflected in our prices on the web.

http://www.cupalloys.co.uk

Hi Bill ,

Thre is no specific rule about rod size to use . As you say yourself it depends on size of job or I suppose more accurately the size of the actual joint being made . One thing to consider though is the rate at which rods get shorter as you have to feed them in – too small a rod and they just disappear in seconds on boiler work .

A few general notes :

You might like to consider using pre-placed silver solder for some jobs . When doing doing steel assemblies I often jig the parts together , pre flux and pre apply solder and then just heat as rapidly as possible . A developed version of this procedure is used extensively in the aerospace industry using closed kilns / furnaces . Sometimes air atmosphere but more commonly vacuum or inert gas atmosphere . Special brazing materials are made for this work – sometimes supplied in fine granular form rather than rod .

Anyone getting propane heating equipment anew might like to get forced air supply type torches rather than self blowing type . They are a bit expensive but not too difficult to make yourself .

Gas torches usually have two flame zones – an inner hot cone and a more diffuse and larger outer cone . A less well defined zone in the flame has a reducing characteristic – it will remove oxides off (especially) copper work pieces . You can use this property deliberately during long heats to avoid too much oxidation and sometimes to clean up an area of work which is a bit dirty . There is a theoretical region where the flame should be reducing but better to find it yourself experimentally – hot copper shows as bright clean metal in the flame when you've got it right .

There's lots more .

Regards ,

MikeW

I don't know if others find this, but with my propane torch I find that, even if the tip of the cone is the hottest bit, the most heat goes into big jobs if the tip of the cone is 1/2" – 1" away from the job. I wonder if too close interferes with full combustion of the gas.

Neil