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.
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