General

Electric welding processes have been used commercially since about 1880, when Elihu Thomson brought out his low-pressure resistance machine, invented about 1877. In recent years several processes, notably that of Thomson, have become widely known for their successful application to rail welding and to repeat welding of stock pieces in manufactories, such as wheelbarrow spokes, wagon frames, printing chases, etc. Though the several processes in which electric current is used in welding are unlike in apparatus and application, the basic idea of each process is to produce the welding heat by means of resistance to an electric current. The different processes are:

1. La Grange-Hoho process: resistance being set up in an electrolyte.

2. Zerener electric blowpipe: an ordinary electric arc deflected by a magnet.

3. Bernardos arc-welder: the metal to be welded as the positive pole and a carbon negative.

4. Thomson process: in which internal resistance in the metal to be welded generates the heat. This is also called the incandescent process.

The electric welding processes, especially the latter, have followed the adoption of the oxyhydrogen, gas, and oil flames, and slightly antedate the oxy-acetylene and thermit welding methods. The arc-welding systems have followed the commercial introduction of the arc-light in 1881. The internal resistance method was earlier suggested by the experiments of Joule and Moissan. In 1856 Joule welded a bundle of iron wires by burying them in charcoal and heating them with current. While in Moissan's furnace the resistance of a closed metallic circuit (as well as the arc-furnace) generated the heat for melting refractory metals and for making alloys.

The Thomson process, the oldest and most important, will here be last described.