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Exothermic welding was developed by Hans Goldschmidt around 1895.[2] The first non-ferrous application for exothermic welding was developed in 1938 by Dr. Charles Cadwell, a professor at the Case School of Applied Science (now Case Western Reserve University), in Cleveland, Ohio. The original use of the process was to weld signal bonds to railroad tracks.
The method was patented by John H. Deppeler in 1928 while working for the Metal and Thermit Corporation. It is United States patent number 1671412.
In the United States, an investigation into exothermic rail welding was conducted by the Committee On Welded Rail Joints, with the goal of improving and standardizing rail welding. Composed of members from the American Bureau of Welding and the American Electric Railway Engineering Association, this committee conducted extensive physical testing of welded rail joints, as well as testing of various parameters of the welding process.[2]

Typically, the ends of the rails are cleaned, aligned flat and true, and spaced apart 25 millimetres (0.98 in).[2] This gap between rail ends for welding is to ensure consistent results in the pouring of the molten steel into the weld mold. In the event of a welding failure, the rail ends can be cropped to a 75 millimetres (3.0 in) gap, removing the melted and damaged rail ends, and a new weld attempted with a special mould and larger thermite charge. A two or three piece hardened sand mould is clamped around the rail ends, and a torch of suitable heat capacity is used to preheat the ends of the rail and the interior of the mould. The proper amount of thermite with alloying metal is placed in a refractory crucible, and when the rails have reached a sufficient temperature, the thermite is ignited and allowed to react to completion (allowing time for any alloying metal to fully melt and mix, yielding the desired molten steel or alloy). The reaction crucible is then tapped at the bottom. Modern crucibles have a self-tapping thimble in the pouring nozzle. The molten steel flows into the mould, fusing with the rail ends and forming the weld. The slag, being lighter than the steel flows last from the crucible and overflows the mould into a steel catch basin, to be disposed of after cooling. The entire setup is allowed to cool. The mould is removed and the weld is cleaned by hot chiselling and grinding to produce a smooth joint. Typical time from start of the work until a train can run over the rail is approximately 45 minutes to more than an hour, depending on the rail size and ambient temperature. In any case, the rail steel must be cooled to less than 370 °C (698 °F) before it can sustain the weight of rail locomotives.