>a response on this subject by another lister erroneously implied thermal
expansion rates are tied to metal thickness>
Thickness of metal has nothing to do with rate of expansion. Rate of
expansion is a material property expressed in (distance per unit of
distance) per degree of temperature. For example, stainless steel (Type 304)
has an "alpha" (alpha is the Greek letter usually assigned for rate of
thermal expansion in the engineering community) of about 9.9x 10^ -6
inch/inch per degree F. Carbon steel (i.e., similar to cast iron) has an
alpha of 8.4 x 10^ -6 (and thus changes dimension less than stainless). As
for temperature, 2 metals with different thermal conductivities (a material
property that tells rate that heat flows through the material) could result
in the same temperature if the thicknesses of the metals were adjusted such
that you had more of the faster conducting metal, and less of the slower
conducting metal. Usually, you would pick a better conducting metal because
you could then use less of it and have lower temperatures than if you had a
poorer conducting metal or material. The better the material conducts heat,
the better it is for some applications (assuming it also has a relatively
low thermal expansion coefficient). This is why carbon brakes are better
than metal brakes -- carbon has better thermal properties and can withstand
much higher temperatures with little expansion compared to metal.
That means stainless (there are many varieties of "stainless" each with a
somewhat different value of alpha) would expan (or contract) 0.000010 of an
inch per inch of thickness, per degree F of temperature change. If you had a
1 inch thick piece and changed its temperature by 100 degrees F, then its
thickness would be 1 inch plus (100 x 10 x 10^-6) = 1.001 inches (it would
have grown by 0.001 inch). Cast iron would have only grown by about 0.00084
inch -- or less than the stainless).
Generally, stainless steel is a poor conductor of heat compared to "regular
steel". In fact, Type 304 stainless conducts heat only about 1/3 a well as
"regular" steel.
Roy
'60 TR3 TS63103LO (in restoration)
techman@metrolink.net
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