By all means try the one cooled slowly and one cooled quickly if you
like. As long as you held both at the same temperature (at least dull
red) for the same amount of time (at least a few minutes,) they will
behave the same as long as they are copper or brass. Iron-based
(ferrous) alloys behave much differently; quick cooling freezes the
hard components into place, without allowing them time to
differentiate into their constituent elements. Copper and brass can
be heated and then quickly cooled without hardening.
How it works: Copper and brass crystal grains grow in size when the
metal is hot (which is why you need to hold it at temperature for a
while -- to allow time for the crystal structure to grow) and these
large crystals are frozen in place as the material cools. These large
crystals are themselves soft and are easily deformed. Copper and
brass work harden because the individual crystals are broken as the
metal is worked, and the grain boundaries prevent motion of the bits
of crystals past each other.
HTH,
Donald.
> From: LBC286@aol.com
> Date: Fri, 15 Nov 2002 13:00:21 EST
>
> In a message dated 11/14/02 1:29:48 PM Pacific Standard Time, rwil@cts.com
> writes:
>
> >
> > Non ferrous metals anneal by heating and then quick cooling, such as
> > dunking in water. They are the reverse of ferrous metals in this
> > regard. Copper and brass are the two I know best.
> >
>
> - - - - - - - - - -
>
> Thanks for all the replies on the copper gaskets. You all seem to agree on
> the procedure. I received the reply below on the other list. He seems to
> think that copper gets brittle if cooled quickly. Any comments?
>
> "Cool your copper gasket slowly, if you allow it to cool quickly the
> molecules
> in the metal will freeze in the heat-excited location they are in and it can
> be in a brittle state. If you allow to cool slowly (the chap who mentioned
> the heated bricks was going along the right lines) they will tend to align
> and
> become more flexible.
> It does work harden fairly quickly as well but this property isn't being
> used.
> When you are heating it try to keep it on a flat straight surface! If you
> are
> using a metal (iron) block to rest it on and that has got warm after heating
> -
> place a bit of heat insulation around it to slow the heat loss down. If you
> are doing it in an oven just leave it in for half an hour after turning off.
> If you are doing it with flame give it a little keep warming breathing on
> with
> the flame every couple of minutes for 20mins or so.
> Basically you want the molecules within the metal to break their current
> location/bonds, jump around a bit and cool down in a relaxed state. Slow
> cooling achieves this.
> In metal terms it is cold when you can pick it up without your fingers
> cooking
> and you don't have to drop it.
>
> Alan - try it with a couple of bits of scrap copper, one cooled slowly and
> the
> other quenched. Then bend both bits the same amount several times and see
> which one breaks first! The quenched one is partially brittle (or work
> hardened without the work) before bending and should split before the slow
> cooled one. OR, ask a plumber which joint snaps first, a soldered one or a
> compression fitting!"
>
>
> Thanks again,
>
> Allen Hefner
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