In a message dated 11/15/02 9:02:04 AM Pacific Standard Time,
grday@btinternet.com writes:
> 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.
>
- - - - - - - - - - -
I posted to the shoptalk list again, after I received the above message.
Those guys didn't think the speed of cooling mattered, so I wanted to get
more info. The reply below makes sense, but I am not a metallurgist, so "Ya
pays yer money and ya takes yer chances."
Allen Hefner
- - - - - - - - - - - - - - -
"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."
/// unsubscribe/change address requests to majordomo@autox.team.net or try
/// http://www.team.net/mailman/listinfo
/// Archives at http://www.team.net/archive/spridgets
|