Electric flash butt welding of railways rails

After manufacture, the rails, ranging in length from 25 to 100-110 m, are shipped by train or ship to electric welding shops, usually belonging to the user rail networks.

Welded joints have long since replaced fishplates: the latter consisted of two fittings rolled so that they rested on both sides of the rail on the surface of the web, the lower surface of the head and the upper surface of the base; the assembly was secured by 4 bolts (two per rail).The major disadvantage of this arrangement was that the head ends were caulked, creating a local subsidence which in turn caused dynamic overloads when the wheels passed over them; this overload could cause the rails to break from the bolt holes in the web, resulting in damage to the wheels (not to mention the discomfort caused to passengers by noise).

So, by the 1930s, welding was seen as a profitable alternative. Electric welding began in 1935 with alternating current, and resumed more vigorously after the war.

Electric welding makes it possible to produce long welded bars (known as "LRS") which, transported by special vehicles (usually trains), are laid on tracks, either for new construction or for long sections under repair. The interest in this type of work has grown steadily with the increase in rail length (from 12 m in 1935 to 108 to 110 m today). The productivity of electric welders has risen considerably, as has that of track laying.

Nevertheless, in certain specific cases, welding has not always replaced splicing, as in the case of switch points.

The stresses on the edges of the web holes are such that crack initiation is frequent, with propagation leading to fracture of the jointed area of the rail. While the heavy rails have remained jointed, SNCF has replaced the joint bars with aluminothermic welds.

LRS (Long Welded Rails) are relatively long elementary units that are subsequently welded together in situ by aluminothermic welding.

This article describes the principle of the electrical process, its practical implementation and the few imperfections inherent in the welding process.

Electric welding, first introduced in 1935 and constantly improved, has the major advantage of being forged at high temperature and high pressure (i.e. with complete recrystallization), giving it exceptional track resistance.

Its future is assured by IT improvements at all stages of the welding lines and by the arrival of 100 m long laminated units, ensuring high productivity.