Thermal Expansion question

1. Sep 26, 2010

Nai

1. The problem statement, all variables and given/known data

The question is : Wheels for railway cars are made of a disk shaped cast iron body of outer diameter 930.0 mm and a steel rim of inner diameter 927.0 mm at 20 degrees Celsius. To what temperature must the steel rim be heated so that it will just slip over the cast iron body?

2. Relevant equations

I know we use the linear expansion formula which is :
The change of length=alpha(initial length)( change of temperature)
The alpha would be the coefficient of linear expansion in this case would be the steel's coefficient which is 1.3e-5 K^-1.
I dont think it's possible to get 268.9 degrees for the steel to expand o-o

3. The attempt at a solution

My work:
(930-927)=(1.3e-5)(927)(T-20)
T=268.9 degrees Celsius

I think I'm doing something wrong >___<
If anyone could help me, it would be awesome.

2. Sep 27, 2010

hikaru1221

I don't think it's wrong. An expansion of 3mm is quite big. The answer is still far away from the melting point of iron (~ 1500 Celsius degrees)