Rotor - you would really need to find out the specific formulation of poly that was used for the top to be able to say for sure. (GE alone has over 170 different blends, lol, with CTEs of in the teens up to the 60 range) If the poly had a CTE in the teens, it would match up well with brass fittings.
Some CTE values:
Free cutting brass - 11.4 uin-in/F
Polycarbs - I've seen from 16 up to 70 uin-in/F
What the numbers mean - multiply the dimension of interest by the CTE and delta temp to find out how much it will grow or shrink.
Example: A 2" thick piece of brass that was going to see a -40F temperature change.
2 * 11.4x10E-6 * 40 = 912x10E-6 or .000912"
Of course the other issue is what cold temps do to a particular kind of polycarbonate (how brittle does it get).
|