There are four methods employed for the welding of rails.
1. Electric Arc welding (Metal Arc welding)
2.Oxy – acetylene welding (gas pressure welding)
3.Flash Butt welding.
4.Chemical or Thermit welding.
Chemical or Thermit welding is widely used in renewal of rails. Generally the plant is mobile in nature and can be used at the site as well. This method involves the use of chemicals such as Aluminium and Iron Oxide. Heating of the two ends is done by the use of a furnace placed at the bottom of the rail joint. A mould is used to retain the liquid mixture and after the mixture solidifies, it is removed and the surface grinding is done.
In this method Aluminium and iron oxide are mixed in powder form and ignited.On ignition a chemical reaction takes place and produces intense heat .This reaction is exothermic in nature .
The reaction is as follows.
Fe2O3 + 2 Al = Al2 O3 +2 Fe + Heat
After the reaction Fe gets deposited in the gap of the rail ends which are preheated.