An arc welding process that uses an arc between a carbon electrode and the weld pool. The process is used with or without shielding and without the application Of pressure. See STANDARD WELDING TERMS. See also BENARDOS PROCESS, GAS CARBON ARC WELDING, SHIELDED CARBON ARC WELDING, and TWIN CARBON ARC WELDING.

Carbon arc welding is, for all practical purposes, an obsolete process. Like the gas-tungsten arc process (GTAW), it uses non-consumable electrodes, either carbon or graphite. Unlike GTAW, however, the electrodes erode rapidly. And unlike GTAW, which has the

great advantage of inert gas shielding, fluxes were often used to protect the weld metal and some of the filler wires used were coated with suitable fluxes. Carbon contamination is a potential problem and must be carefully avoided when igniting the arc with a scratch start, or by accidental contact while using very short arcs. Because of the poor shielding and potential for carbon contamination, the process was used most frequently for welding copper and its alloys, and cast

irons.

Historical Background

Carbon arc welding is presently used only to a very limited extent, but much was learned about shielding during the early development of arc welding (circa 1925) when CAW was popular.

Welders using the carbon arc to fusion-weld iron and steel learned to control the nature of the welding atmosphere by resorting to simple methods. As an example, the oxidizing effect of air aspirated into the arc was reduced by inserting a string of combustible material into the arc alongside the electrode to combine with at least some of the oxygen in the arc area. If the string consisted of tightly rolled-up paper, it burned to form water vapor and carbon dioxide, both

of which are more protective of the molten steel than oxygen. The string was fed into the upper part of the arc, the narrowest part which contained the largest amount of air. By removing a large portion of the uncombined oxygen from the arc, the combustible material sometimes permitted welding to be performed without a flux. When more effective protection was needed in carbon arc welding, the string of combustible material was impregnated with slag-forming ingredients. As the string burned, these ingredients melted and performed their functions right at the point

where they were most needed. The nature of the slag and flux varied with the metal being welded.

For steels, minerals such as clay and asbestos were used for forming the slag, and fluorspar was favored as the flux. From this simple beginning, shielding the arc with gases and protecting the molten metal with slag and flux developed into a highly refined and complex technology. Reference: George E. Linnert, Welding Metallurgy, Vol. 1, 4th Edition, 722-23. Miami, Florida: American Welding Society, 1994.

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