[TowerTalk] Silver Solder

[Jim Lux]

On 8/7/15 9:24 AM, mike stokes wrote:
> Hello
>
> I need to improve my radials and lightning protection.  What Silver Solder
> is best for the job and where is a good place to purchase it ?
>

I'm not sure silver solder (called silver brazing these days) would be 
appropriate for lightning protection.  It's certainly not what the code 
requires for grounding (approved clamps or exothermic welds), although I 
think it's a reasonably workable solution.

For RF purposes (e.g. your ground radials), though, silver brazing isn't 
a bad idea. It's rugged, it's easy (assuming you have the right equipment).

I doubt that the specific alloy makes a lot of difference. What you're 
really looking for is that the melting point is higher than that of 
tin/lead, and that it's mechanically more rugged. I've used a variety of 
"hard solders" from the local hardware store. Typically, they are around 
half silver (price varies with silver content). Pretty much anything 
will work with copper/brass (if you're brazing steel, you need to be a 
bit more careful in material selection).  A typical alloy is something 
like Silvaloy 355 which is about half silver, 1/5th copper, and the rest 
zinc and tin.  No cadmium. At least that's what I found out in the 
garage that still has a label on it.. I'm not a pro welder, with ovens 
to keep my rods dry, records of material certs, etc.. Others on this 
list ARE much more knowledgeable and may have some recommendations on 
the best alloys.

As with all "melt metal to stick metal together" things, the right flux 
and the right heat source is probably more important than the actual 
metal you're melting.

I use the solid white paste flux, and I've used both a oxy-mapp rig (one 
of the ones with the two "propane torch" sized bottles) and a 
oxy-acetylene rig (with a fine tip on the torch).  Either works. The 
bigger rig (with big bottles, either oxy mapp or oxy acetylene) is nicer 
because you don't worry about running out of gas. If you could borrow or 
rent the rig, life is easy.

Silver solder alloys melt around 1000F (compare tin-lead at <400F), but 
lower than bronze brazing rod (typically >1500F).  Note that 1000F is 
"red heat"

I'd say that in a few hours, if you've got experience soldering 
(especially if you've done plumbing) you can crank out perfectly 
serviceable electrically and mechanically brazed joints.  They may not 
be pretty, they may not be something you'd trust your life to for 
mechanical reasons, but they'll work fine.

I find brazing, in general, MUCH easier than doing good plumbing 
fittings with soft solder and a propane torch, and MUCH easier than real 
fusion welding.

With real welding, you have to worry a lot about the metal you're 
welding, and getting the temperature right, and getting just the right 
penetration (whether gas or arc), and it's a lot hotter.   With soft 
solder and plumbing, there's a real art to getting the right flux, and 
the right temperature on the whole joint (not too cold, not too hot) so 
that you get a nice even solder layer with no pinholes and no globs. And 
with plumbing there's always the whole "wet pipe" and "don't light the 
wall on fire" thing.

A small oxy-gas torch has a nice small hot flame that's easily 
adjustable and not too bright, and there's a big temperature range over 
which a good joint can be made  (iron and steel melt at >2500F, copper 
melts at 2000F, the brazing filler melts 1000F less, so lots of room 
between), and the overall lower temperature means you don't need as much 
eye protection, so you can *see* what's going on.