Tracey,
As altitude increases I would expect that there would be less
convection taking place, due to the lower air density. Convection is
when a molecule of fluid or fluid like material, in this case air,
is heated, becomes less dense and rises. This means that the material
being heated would loose less heat than at sea level, given the same
surrounding air temperature, and the annealing would take less time.
Scott Steward
Hiya Tracey, Actually, I don’t believe the altitude will do much to
your annealing process. The reason that it takes things longer to
boil and bake is that the decreased air pressure at altitude is
affecting the evaporation process of liquids. Decreased air pressure
actually allows the water to evaporate more quickly so that it takes
less heat to get things boiling. Remember that evaporation is a
cooling process. So, the water boils faster but that means that it
is also cooling faster, and then, since it takes less heat to get it
boiling, you wind up with boiling water that is much cooler than the
old standard of 212 degrees at sea level. Your foods, both baked and
boiled, may dry out more quickly but it takes them much longer to
reach the temperatures required to actually cook the ingredients.
All the increased evaporation equates to increased cooling effects
which in turn results in longer times to attain the temps required
for cooking effectively. You know how easily your skin dries out at
higher altitudes? That’s the increased evaporation at work. You
should actually consume a lot more water to stay hydrated at higher
altitudes.
In the annealing process you are dealing with the thermodynamics of
the conduction of heat through the metal to rearrange the
crystalline structure of the metal. There is no water to evaporate
other than that used in quenching, again a cooling process. The
altitude should have little to do with the conduction of heat
through the metal. Now, if the air around you and the metal is cold,
the metal will radiate it’s heat faster to the atmosphere which will
cause it to cool faster. That would affect crystal formation and
growth in the metal as it cools, but it generally isn’t a factor of
altitude per se. True, higher altitudes tend to run cooler but the
ambient temperature of the atmosphere around the metal as it cools
it what will affect annealing. Hope that isn’t too confusing and I
hope it helps.
Mike
Are you using an acetylene-air torch such as a presto-lite? If so,
then the rarified air may have an impact on the heat of the torch,
and hence the speed at which the sheet comes up to annealing
temperature.
Lee Einer
Dos Manos Jewelry
http://www.dosmanosjewelry.com