An arc welding process that uses an arc between two metal electrodes in a shielding atmosphere of hydrogen and without the application of pressure. This is an obsolete or seldom used process. See STANDARD WELDING TERMS.
Historical Background
Atomic hydrogen welding was the forerunner of the gas shielded arc welding processes. In the 1930s, it was the best process for welding metals other than carbon and low-alloy steels. With the development and ready availability of inert gases, the gas shielded arc welding processes have largely replaced atomic hydrogen welding.
In the atomic hydrogen process, an arc is maintained between two tungsten electrodes in a shielding atmosphere of hydrogen. Filler metal may or may not be added. The work is part of the electrical circuity only to the extent that a portion of the arc comes in contact with the work, at which time a voltage exists between the work and each electrode.
Both manual and automatic atomic hydrogen welding methods can be used. The simplest equipment is that used for manual welding. It consists of a power control unit, electrode holder, start-stop controls, a source of hydrogen, and the necessary cable and hose for conducting current and hydrogen.
The power control unit is a high reactance, moveable- coil transformer with an open-circuit voltage that permits easy starting and arc maintenance. The arc voltage in this process is higher than in metal arc welding, running as high as 90 or 100 volts. Unlike other methods of arc welding, in atomic hydrogen arc welding the arc does not generate heat in the work.
Heat generated in the arc is transferred to the work by the hydrogen. As hydrogen passes through the arc from the jets or orifices around the tungsten electrodes, the molecules of hydrogen separate into their component parts (atoms). As the gas in the atomic state is being displaced with molecular hydrogen under a slight pressure, it is urged out of the intense heat of the arc and recombines with atomic gases in the outer edge of the arc stream, giving up heat produced by dissociation. This heat produces the welding temperature.
The arc stream, or “fan” as it is commonly known, follows a horseshoe-shaped path from the electrodes, expanding and contracting as the arc is lengthened and shortened. Ordinarily, a 10 to 20 mm (3/8 in. to 3/4 in.) fan or a 50 to 90 volt arc, (which produces a singing noise), is used. A short arc, ranging from 20 to 40 volts (often termed a “silent arc”) is occasionally used to obtain a point source of heat. A long, narrow heat source can be produced by adjusting the arc length. To make a very narrow weld, the fan is carried vertically and approximately parallel to the line of weld; heat is applied over an elongated area, with length approximately four times the width.