The advantage of silver soldering is that it happens at around red heat, and
you're less likely to get burning of the copper or steel. The last issue of NCJ
had a good article on silver soldering, although there were a few points not
covered. The flux used can be something as simple as household borax made into
a thick paste with water, although I use a commercial flux called 'Easyflow',
which you mix with water to a thick paste. Silver solder, depending on which
one you get, flows at between 600C and 700C.. the NCJ article said you mustn't
have a gap: in fact, you need a gap between the materials being joined of
between 2 and 8 thousandths of an inch, depending which silver solder you are
using. The UK 'Easyflo #1' melts atbout 610C and needs a gap of about 1 to 2
thousandths of an inch.
As others have said, for silver soldering, make sure everything is as clean as
for soft soldering - no grease from fingers! - and use lots of flux. You
usually find that the excess flux comes off easily by pouring some cold water
over the joint - for small copper locomotive boilers, it's not unusual to
pickle in dilute sulphuric acid, but that's a bit OTT for this application!
Incidentally, mixing the flux is like mixing epoxy - you can only get two
quantities - too much or too little! Too much is preferred....
73
Peter G3RZP
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