On the occasion of the open company day, we visited Infrabel at South Station. One of the guides was asked how one can now use rails in much longer sections without them being pushed up by heat. He replied that the expansion of a 20 m rail is the same as a 500 m rail. That seems illogical to me. Is it right?
Answer
Dear Willy,
Metals expand when they heat and contract when they cool. They always do this the same amount, namely about 0.001% per degree difference. This indeed means that a long piece of track will expand more than a shorter piece, so more space must be left between two tracks.
At least, that’s how it used to be. The typical ‘kedeng-kedeng’ sound of a train ride was caused by the fact that a space of just over a centimeter was left between two tracks to accommodate expansion. Much more slack could not be allowed for the sake of safety, so the maximum length of each piece of track was limited.
Nowadays, tracks are welded together in kilometers long, so that the journey goes more smoothly, the train runs more efficiently and wears less. These tracks can no longer expand and therefore experience very strong compression forces. As a result, they tend to buckle, but this is prevented by attachment to the track beams. The tracks are also ‘pre-stretched’ before they are placed. Thanks to these measures and thanks to solid welds, the length of a track is no longer an obstacle today.
Answered by
dr. ir. Jan Ronge
Bio-engineer. Electrocatalysis and renewable hydrogen production
Old Market 13 3000 Leuven
https://www.kuleuven.be/
.