Thermit® Welding

Thermit® Welding is a specialist welding process for the joining of rail steels. The Thermit® compound is a mixture of metal oxides, alloying elements and a reducing agent. These react to form the metal, simultaneously liberating intense heat to produce superheated molten steel which forms the weld.

The rails to be joined together are aligned leaving a prescribed gap between their ends. Preformed refactory moulds are fitted around the gap formed at the junction of the two rails.

Photograph: Thermit® Welding pre-heating

Preheat

Using a specially designed burner, the moulds and the enclosed rail ends are pre-heated for a time, dependent upon the rail section, to achieve the correct welding temperature of 900 - 1000¼°C.

Photograph: Thermit® Welding ignition

Ignition

When the correct degree of preheat has been achieved reaction is initiated in the crucible using a special igniter. Superheated molten steel is produced by an Alumino Thermit reaction (the Thermit® reaction).

Photograph: Thermit® Welding weld forming

Weld forming

At the correct time the tapping system at the base of the crucible discharges the superheated molten Thermit® steel followed by the slag into moulds via the pouring cup.

After solidification, surplus Thermit® steel is removed from the rail head using a pneumatic chisel. Following an appropriate cooling period, the railhead is ground to profile and the rail aligned and fastened.