ION - Waterloo Region's Light Rail Transit

[ijmorlan]

Question about welding where there was a gap: for welding, wouldn’t the two pieces of rail need to touch each other? So how does the gap get filled? Does the welding actually fill the gap, or do they pull the rails together, or something else entirely?

I'm under the impression, from my admittedly amateur understanding of how welding works, and from videos I've seen, that the weld will bridge some gap, possibly a gap is even necessary.  The process of welding actually adds material.  In more traditional welding there is a steel rod as the added material, but in thermite welding, I believe the added iron material is a product of the thermite reaction which also produces the heat.

https://www.youtube.com/watch?v=KNBDWuWz9ZE

https://en.wikipedia.org/wiki/Exothermic_welding

Thanks for the info, especially the video, which seems to make it clear that they do indeed fill a gap. They even had a calibration tool to ensure they left exactly the right gap. I had been under the impression that welding primarily meant heating up the two parts until they softened enough to merge upon being pressed together but that is apparently not the case.