> > Wrong. 
> > 
> > Think about it this way.  Start with a sheet of metal.  Cut 
> a disk out 
> > of it.  The disk and the plate are the same material and the same 
> > coefficient of expansion.  If you heat both pieces, the 
> disk obviously 
> > gets larger.....but it's still got to fit in the hole...so the hole 
> > must get bigger!
> 
> This all assumes that both pieces of material are in their 
> entirety at the same temperature so that no elastic 
> deformation occurs. 
> 
> The question is what happens if the material that contains 
> the hole is elastic -- which means that it can deform -- and 
> the material that's farther away from the hole is at the 
> original temperature (i.e. at the original size). 
> 
> I'm pretty sure that there will occur some elastic 
> deformation, and so far nobody seems to have been able to 
> really explain the nature of the elastic deformations and 
> their effect on the hole size. 
> 
> Imagine a steel or iron cylinder (not cast iron, use more 
> elastic iron), 20 cm diameter and 20 cm long (increase as 
> necessary to avoid breaking), and a hole of 1 cm diameter all 
> the way through it along its axis. Now imagine you heat up 
> the inside of the hole. I don't think this is as trivial as 
> "all holes in materials with positive expansion coefficients 
> expand when the material is heated up". I'm pretty sure there 
> happens some elastic deformation of the material around the 
> hole, and I don't think it's completely unreasonable for the 
> hole to become smaller under certain conditions.
> 
> The expanding material has basically three ways of expanding: 
> radially towards the outside (that would be the "hole gets 
> bigger" way), axially (which may or may not increase the 
> diameter of the hole, but probably not) and radially towards 
> the inside. The latter two, and especially the latter, 
> require some elastic deformation, whereas the first option 
> requires that the material compresses (or breaks). Elastic 
> deformation is not unheard of with steel or iron (again, I'm 
> not talking about cast iron), and IMO more probable than 
> compression. The outcome probably depends on the strength of 
> the material around the hole (against breaking), the forces 
> required for elastic deformation in the different directions 
> and the force required for compression.
> 
> Gerhard


That's a fairly contrived case, and is quite possible if you were aggressive
enough in heating the hole.  Don't forget, steel conducts heat very well and
is quite elastic, two factors woking against the shrinking hole.  Cast iron
would be the better choice.

I'm sure people making the main guns on battleships would have noticed
this... or even the people firing them...

I couldn't say with 100% certainty (I no longer work with a metallurgist),
but if it did happen, it wouldn't remain that way for long.

You might as well clamp it in a vice, then heat it.  That would work too  :)

You only work that way once, it's bad for what you are heating up.  Slow
learners do it twice, of course.

Tony

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