Shop Welding to Produce Long Rails
The process of Flash Butt Welding is used in the shops to join rails which are later to be incorporated into ContinuousWelded Rail sites. This process involves clamping the rails at a predetermined gap distance and passing a high current across the gap at a low voltage, during which the work pieces are brought together.
Electrical resistance heating first causes contacting surface irregularities to melt and subsequently raises the temperature of the whole interface to near melting point. Once the components are sufficiently heated they are forged together, and excess molten steel at the interface is forced out of the weld area.
The stages of FBW in the shops include burn off, preheating, flashing, forging and post weld treatment.
Once the weld has solidified, integral shears at the welding plant remove the excess upset from the periphery of the weld, leaving about 1mm proud all round the weld section. The welds are then straightened and the railhead ground to give a smooth profile for the weld along the length on the rail.
Fig. 5.7. Continuous welded track.
Unlike with metal arc welding, no electrodes or added metal is used, only the parent metal is fused. Because some of the metal at the rail ends is forced out of the section profile, the overall effective length of the rail reduces by about 20mm for each weld.