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.
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
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