Welding of Rails and Effects on Crack Initiation and Propagation

Overview

Railway rails are made in various lengths from 30 m up to about 120 m. These rails are then flash butt welded into a length of 400 m in a stationary welding unit and transported and laid in the track. The two most common methods for the final welding in track are aluminothermic (thermite) welding and flash butt welding.

Flash butt welding can be done either in stationary plants or in mobile plants at the track. The welding operation comprises three sequences: preheating, burning-off, and upsetting; see Fig 1below. Preheating is performed by alternately moving the two rails together and separating them as an electric current passes across the interface. An electric potential is applied to one of the rails, while the other rail remains at ground potential. In the second stage, the edges are slightly parted creating a small gap, and a constant current is flowing through the surfaces heating the rails. In the third and last step, the upsetting, the current is shut off and a...