Aluminothermic Welding

Thermit (GB), via its parent company the Goldschmidt Group, has championed the Thermit welding process for over 100 years.

The generic alumino-thermic reaction is based primarily around the principle of the reduction of heavy metal oxides by aluminium. Once started, the reaction is highly exothermic generating temperatures in excess of 2500°C with no additional external heat source being required. In the case of the Thermit welding process, the heavy metal oxides are those of iron producing end products of aluminium oxide, Al2O3, and iron, both in liquid form. The heavier metal separates from the less dense Al2O3 which floats to the top of the reaction vessel as slag. The generation of a liquid metal and a large quantity of heat in this way lends itself to the site welding of rails producing cost effective welds of high integrity and uniformity.

The reduction of iron oxides occurs as per the reactions given below:


The Thermit process was first used in the UK in 1904 for the purpose of welding tram rails in Leeds. Since this time, the process has been refined and selective alloying additions made to the Thermit ingredients to produce welds having matching hardness and metallurgical properties to those of the rails being welded together. The generic welding process involves the placement of pre-formed refractory moulds around the gap between the rails to be welded and the siting of a refractory crucible containing the Thermit portion onto the moulds. Following ignition of the portion, and ultimately completion of the reaction in the crucible, the crucible is tapped and liquid steel runs into the moulds to form the weld.

For more information on the Thermit process, watch our step by step video here

This development approach has led to the Thermit process being altered in order to function on a wide variety of rail profiles including, but not limited to:

  • Conventional “Flat bottom” or “Vignole” Rails
  • Special Section Railway rails
  • Grooved Tram Rails
  • Heavy Section Crane Rails
  • Electrical Conductor Rails

Rare and bespoke products can also be provided, due to our extensive reach from our position within the Goldschmidt-Thermit Group.

Through Thermit Welding (GB) Ltd it is possible to acquire all resources and training required for an Aluminothermic welding, this includes: