Old train rails had gaps between beams due to thermal dilatation, but modern rails don’t have gaps. Is dilatation not a factor anymore?

Question

Old train rails had gaps between beams due to thermal dilatation, but modern rails don’t have gaps. Is dilatation not a factor anymore?

In: Engineering

Answer 1

It is. The rails are mechanically stretched before being welded, so in their normal state the are trying to pull themselves shorter. When they are heated, the expansion relieves the pulling before it starts actually pushing (trying to buckle). Basically the temperature where the expansion is large enough to cause issues can be shifted upwards and out of normal summer temperatures.