Thermal expansion and combining materials in an assembly

I tried to title this thread as generically as possible should this happen to be a common topic in the forums…

I’m trying to work on an impact resistant plastic shell design for a metal cooking pot (PTFE-coated Aluminium or Stainless I assume). The shell and pot will not be permanently joined together i.e. two detachable parts of the final assembly.
The obvious crux here is thermal expansion as the assembly will have to work at a temp range from -30°C of the shell to approx. 100°C of the pot, so there are many tolerance issues to consider.
I found that Aluminium and fibre reinforced Polycarbonate have similar thermal expansion coefficients (10-6 m/m K) of 22.2 for Al and 21.5 for Poly.
So to figure out the tolerances I assume I have to determine the extremes for both parts (-30°C shell and 100°C pot) and go from there? The tolerances will then increase, thusly loosening the assembly as the temperature for both parts equalizes, yes? Are the coefficients close enough? Should I consider other material combinations? Am I trying to solve the unsolvable?

I’m no engineer so please spare me the scientific jargon and explain like I’m five.

Many thanks in advance!

I would say they are close enough. To check you can run the numbers with your pot’s dimensions and the formula for linear expansion:

dL/L = a*dT

a = your coefficient
dT = your change in temp.
L = your nominal dimension
dL = change in dimension

Just using a basic dimension of 1 m it comes out to:

Aluminum - 22.210^-61301 = 0.002886 m
Poly - 21.5
10^-6*130 = 0.002795 m

So its a pretty small amount of expansion difference.

Also, depending on what your design is, for a cooking pot, I would think you would want a temp range of more than -30C to 100C.

^ What they said! :wink: