> where is info about which to use on my small boiler(s)?
> In other words, what is the "right" composition?
I think all those books we've been discussing off and on have this information
(Tim Coles, Martin Evans, KN Harris). In any case, for boilers you MUST
have silver solder (which has at least 40-45% silver) and NOT silver-bearing
solder (which is lead/tin solder with 4-5% silver). The silver-bearing is really
good stuff to get extra strength when putting together parts which are not
exposed to the high heat of a boiler, but your boiler will literally fall apart under
steam if made with silver-bearing.
Silver-soldering boilers in our scales can be done with MAPP torches (with
difficulty) or propane weed-burner type torches, but even for a 2x12 inch
copper tube you need a LOT of heat -- you can hardly have enough. Note
that "heat" is not the same as "temperature". You must have at least 1100
degrees F to melt silver solder, but a tiny acetylene head will produce this
temp and not melt the solder because it's being sucked away by the copper
so fast.
So, you have to have a lot of heat volume in addition to sufficient temp. You
may be able to get it with two or three MAPP canisters simultaneously. The
"pros" often use several different torches to keep the boiler body saturated
with heat and apply the working heat where the solder is being applied.
I could go on and on about things I have mostly second-hand knowledge of --
but won't. In short, if you want to build a boiler, start reading all the books you
can find (Sulphur Springs carries Tim Coles' and Martin Evans' books) and
start asking people who are farther along the road than you. And practice.
You'll doubtless ruin a couple before you get it right, but once you do you're
golden!
Since there is a fairly small range of commercially made products available, I
do think that knowing about silver soldering is an integral part of this niche of
the hobby. You may never do it, but you don't build your own electric engines
either and still need to understand how electric motors work to maintain your
equipment. And someday, you may decide to take the plunge....
regards,
-vance-
Vance Bass
Albuquerque, New Mexico, USA
Small-scale live steam resources: http://www.nmia.com/~vrbass
