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FOCUS ON RAILWAY ENGINEERING
Dish-bolted rail joints have been one of the major locations and causes of maintenance on rail track since the first railway line was built. Discontinuity of the track running surface produces dynamic impact loads, battering the rail joint ends and bending the rail. This causes greater stress on the ballast and subgrade, which in turn increases ballast settlement and produces uneven track. The pumping action at the joints also accelerates rail failure, sleeper wear and fouling of the ballast at the joint.
The introduction of continuous welded rail has vastly improved the geometric stability of the track structure. Nevertheless, the localised change in the metallurgical character of the rail that can occur in the vicinity of welds can ultimately lead to a loss of running smoothness which can initiate corrugations and promote the development of localised track geometry irregularities, pulverisation and movement of the ballast and damage to fastenings and sleepers.
This has improved quite dramatically, however, with the development of the flash butt welding process. This process, with its limited change to the metallurgical character of the rail, reduces the possibility of loss of running smoothness dramatically, thus producing a very high-quality continuous welded rail.
The process charges the two rails to be welded with very high amperage at low voltages. The resistance of the current flow between the two rails causes rapid heating of the two rail ends. Based purely on a time-controlled system, the heated rail ends are forced together at a high pressure during which all impurities are forced out. Flash butt welding does not require any additional welding material as the rail itself is used as a welding compound. The result is a near-flawless weld of which the strength exceeds that of the rail material.
Flash butt welding has been used by railways since around 1930 in stationary welding depots. Initially, a drawback was that flash butt welding was only used in stationary depots, which then required the arduous transportation of the long welded rail, thus setting constructional limits for the production lengths.
If it was possible to perform butt welding on rails in situ, near-perfect continuous welded rails could be possible.
Plasser & Theurer, as the world leader in track maintenance and construction machinery,...