At 12:23 AM 11/28/06 EST, you wrote:
>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. - John Meacham
Years ago I began making larger bushings (over 1/2"diam) from SAE660
(now C93200) continuous-cast "bearing" bronze stock because it was easier
and cheaper to get than the preferred material, phosphor bronze (C510).
I was challenged early-on (1970's) by a couple of old-timers who said
"it tweren't no good" for bushings because it was actually a brass (which
it is not) and lead-bearing so it won't silver solder (which it will.)
To be safe rather than sorry I consulted one of the major manufacturers
of continuous-cast bronze (Ampco) and I was told that levels of up to 8%
zinc are below the threshold of problem dezincification and that 660 was
used universally for high pressure silver soldered fittings which operated
up to 500degF. The 15% John quotes may be the upper threshold beyond which
drezincification is a problem, I haven't ever checked that out.
A typical analysis of SAE660 is:
Lead (Pb), 6.00 % - 8.00 %
Tin (Sn), 6.30 %- 7.50 %
Zinc (Zn), 2.00 % - 4.00 %
Copper (Cu), Remainder
Regards,
Harry
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