My handbook (Mark's Mechanical Engineer's Handbook) states that brass with
less than 15% zinc are not subject to what they call "Season Cracking" which I
think is what we are concerned with. There are several long lists of "brass"
and/or "bronze" alloys all with different properties and characteristics. All
in small print that challenges my old eye balls. Since most of my brass is
"junk yard source" I have no idea of the actual composition so I just don't
braze brass fittings into copper boilers. Metals under heat and stress show
wide differences in application (Even cast iron can not be used over 600
degrees
(F) as the carbon will migrate over years to form graphite inclusions
weakening the material (Major explosion at West Point years ago with cast iron
valves in their power plant)
If you buy your brass from a reputable dealer you can specify which alloy
you want, but, like myself you pick up some nice looking hex stock to make
bushings, valves etc at a scrap yard I would never braze that unknown material
into a copper boiler.
Maybe Koso buys only brass from a source that the actual zinc content is
known and specifies what the alloy consists of. A small amount of lead is added
to many brass alloys to make a free machining material used on CAM and
Automatic Screw Machine work. Which is what I usually find in the scrap bin.
John Meacham
LBSC Tich, Virginia
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