I have an interesting dilemma to propose to the group. Normally, we
cast precious metals, etc. for making jewelry. However, I have been
challenged with trying to duplicate a key for an antique lock, which
needs or probably should be made out of brass. So I took about 10
brass keys that I had laying around, and melted them down and added
some borax as we normally would do during the casting process. The
casted key came out perfect. But the problem is that the key bends
too easy. Anyone know what I can do to harden up the brass metal?
It appears that when I melted the keys, they lost their hardness.
Is there a brass casting alloy that I can use instead of melting
keys or is there something I can add to the melted keys while it is
molten to harden it back up? I am not experienced with much other
than the precious metals. Since I have the mold, it would be easy
to re-cast the key. Thanks for your help.
Annealing Non-Ferrous Material: Almost all non-ferrous metals are
annealed by heating to somewhere just below the melting point and
then cooling in air or by quenching in water. Quenching in water is a
convenience.
Alpha brasses (64-99% copper) are annealed by heating to 700 to 1400
F (the hotter the softer) and can then be be quenched.
Alpha-beta brasses (55 to 64% copper) are annealed at the same
temperature and can hardened slightly by quenching from the
annealing temperature.
The key word above is slightly. Cold working produces a much greater
degree of hardness. The amount of hardening is so low my copper
alloys book does not give specific data. If quenched from the low end
of the annealing temperature there would be no discernable
difference.
Common brazing alloy is:
Cu 56 - 60%
Sn 0.8 - 1.0
Fe .25 - 1.20
Al, Si, Mg, Pb trace (no greater than 0.1% each)
Zn balance
Most all brass alloys do not harden via heat treatment and only get
harder with cold working so there is no practical way to harden the
already cast key. Re-cast the key in silicon bronze (one trade name
for it is Everdur) it will have the right color and be much harder
than the brass that you used.
Jim Binnion
James Binnion Metal Arts
Phone (360) 756-6550
Toll Free (877) 408 7287
Fax (360) 756-2160
@James_Binnion
Member of the Better Business Bureau
Actually the only way to harden most all non ferris metal is through
work hardening. Quenching will not do anything towards hardening
them. Hammer, draw, roll in a mill, bend, and to an extent, even
bead blasting will harden non ferris metal to one degree or another.
Out of curiosity, wouldn't extended tumbling with steel shot
harden the brass key?
tumbling can harden the SURFACE layer of the metal being hardened,
but only to the degree that the metal is deformed. It’s still work
hardening, and that needs deformation, not just force applied.
Normally, tumbling soft metal hammers the surface down, moving metal.
In smooth nice shapes, you don’t notice the surface deformation,
since it’s just pressing the metal down upon itself slightly. but
with a key, or other precision shaped part, you’d find that if you
tumble it long enough to get significant surface hardening, then the
key wouldn’t fit the lock so well any more.
And more important, while the surface would harden and be more
resistant to scratches and the like, the depth of this type of
hardening is very shallow. maybe a half millimeter or so. So the
bulk of the key will still be soft, leaving the key still almost as
prone to things like bending in use…