Topband: Silver solder

[Mike Waters]

Paul,

If you had trouble with an oxyacetylene torch, then I'll bet you used
"silver-bearing" (tin-copper-silver) solder, which melts at well under 700
degrees. (In that kind of solder, the small amount of silver is added
mainly to lower the melting point a little). That's commonly referred to as
"lead-free solder". I use it all the time here. That is NOT what is
commonly called "silver solder" in the trades.

With hard silver solder --the kind that melts at a red heat-- an
oxyacetylene torch with a #4 or smaller tip works just fine. Just keep the
flame size down, and/or turn down the oxygen a little for a carburizing
flame*.

 * A carburizing flame has a third cone that's not as bright as the flame
right next to the tip, but is brighter than the rest of the flame.

And don't touch the bright blue part of the flame (>6000 degrees F) to the
work, and especially to the solder! That portion of the flame can melt and
weld steel, it's so hot.

Use that opaque white borax-type silver solder flux, which is applied to
the silver solder by heating the solder a little bit below its melting
point, and then dipping the hot solder into the flux to coat it. Or, you
can buy silver solder already coated; but IMO, it's not as good.

This is similar to brazing, but brazing is much hotter and uses a
silver-free brass alloy as a filler material.

I use MAPP gas and oxygen to silver solder nowadays, because it's all I
have here right now.

73, Mike
www.w0btu.com

On Wed, Dec 31, 2014 at 8:03 AM, Paul Christensen <w9ac at arrl.net> wrote:

> "The only issue is that solder requires a bit more heat then the leaded
>> solder."
>
>
> I once tried oxyacetylene (a pure oxygen + acetylene mixture) and had a
> disastrous result.  The torch temperature rises rapidly with even a small
> volume of mixed oxygen.  Good for some welding applications, but not
> silver-soldering.