Coefficients of thermal expansion over different temp ranges 3

[rotta]

I have found a reference which defines the coefficient of thermal expansion for a gray iron over several different ranges. The puzzler is why they all begin at ambient temp. Ex. 68-212° is 5.6 and 68-392° is 5.9. How can this be? What if the final temp falls in both ranges (195°) then you get two answers for the same equation.

 

[corus]

It's not an equation, as such. Basically the expansion at (212-68) (or 144 degrees temperature change) is 5.6 and at (392-68) is 5.9. Interpolate to get the value at (195-68), as an approximation.

corus

 

[zekeman]

They are giving the AVERAGE thermal expansions per degree for each of these ranges, not very useful if you need another range or at a single temperature
That coefficient is a function of temperature so if you want the expansion over any range you must get a curve of L vs T where L is the length of the specimen; the coefficient at any temperature would be
delta L/(L*delta T)
This would be the average over the range delta T. If delta T were very samll, then in the limit it would be the coefficient at that T.

 

[unclesyd]

The thermal expansion coefficient of gray iron is reported as 6 x 10 ^-6 per ^oF within the materials useful range.
When you run across a set values as you have you should take the range that is the closest to you temperature requirements.