Thermit Welding

a method of welding in which thermite, a mixture of powdered aluminum or magnesium and iron scale, is used to heat the metal.

If aluminum-based thermite is used, the parts being joined are placed in a refractory mold and heated, and a thermite melt, which is ignited by an electric arc or a primer, is poured over the area to be welded. As the molten iron becomes alloyed with the base metal, it forms a durable joint. Welding with aluminum-based thermite is used to join steel and cast iron parts—for example, for welding rails or pipes, filling weld cracks, or fusing surfaces during repair work. Magnesium-based thermite is used primarily to join telephone and telegraph lines and the strands of cables. A cylindrical thermite charge is prepared, with an axial channel for the wire and a recess in the end plate for the primer. The ends of the wire to be welded are inserted in the charge, after which the charge is ignited and the wire is clinched. Magnesium-based thermite can also be used to weld small-diameter pipes.