Thermit Welding
This process utilises the intense heat developed during the reaction between iron oxide and aluminium. When a mixture of three parts of iron oxide and one part of aluminium by weight is locally burnt with a special ignition powder a vigorous reaction takes place which proceeds rapidly through the mass, resulting in the formation of aluminium oxide and iron and a considerable amount of heat. The heat is sufficient to melt iron and oxide slag. In carrying out thermit welding the thermit mixture is placed in a refractory crucible above the pieces to be welded. The molten metal from reaction is guided to the joint to be welded by a sand mould, which is fastened around the work. By virtue of its superheat, the thermit metal melts a portion of base metal with which it comes in contact. This process is ideal for welding rails of railway tracks.