Post by JumperI was watching Michael Portillo's Great American Railroad Journeys and
that at a special steel works, they made rail that was a quarter of a
mile long and then it was put onto special trains.
Does National rail, still weld pieces of standard length rail in situ
instead of transporting very long lengths of rail?
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Rail used to be rolled in 60 foot lengths; I think it is somewhat longer these days. These rails are normally welded together in a depot by the flash butt process. I'm not sure what the maximum length is, it's increased over the years, but a quarter of a mile sounds rather too long, at least in this country, maybe they can handle longer lengths over there, or maybe this is the length after the long rails have been welded together on site. These long welded rails are taken to site by special trains; in these lengths rail is quite flexible, so the trains can pass around curves.
Once in place these long rails are then welded into continuous lengths. In America, and various other countries, vehicle mounted flash butt welding machines are sometimes used for this, but a different process is more often used, Thermit welding, where the rails are set up with a gap between them, a mould is assembled around the rail ends, and molten steel run into the gap by igniting a mixture of aluminium and iron oxide, with various additions, in a crucible positioned above the weld.
Flash butt welding produces very high quality welds quickly, while Thermit welding takes much longer, but the equipment is more portable; it will all fit on a P-Way trolley. There is another process, gas pressure welding, where the rail ends are heated by gas flames and then forced together by hydraulic pressure. I think this is mainly used in Japan.
Track is sometimes laid in pre-assembled panels, but after a few days, when the track has settled down, the short rails are taken out and replaced by long welded ones.
Street tram rails are normally welded on site from short lengths due to the difficulty in transporting long rails through the streets.