automatic welding[¦ȯd·ə¦mad·ik ′weld·iŋ]
electric arc welding in which the basic operations of feeding the electrode into the arc and moving the arc along the line of the weld are mechanized. If only the wire feed is mechanized while the arc is moved by hand, the welding is termed semiautomatic. The most frequently used automatic welding device has a fusible wire electrode wound in a coil weighing between 20 and 60 kg which is continuously fed into the arc as it melts. To protect the welding bath from the air and also to deoxidize the metal and its alloyage, the joint is first filled with a thick layer of flux into which the arc is sunk. The flux ensures high quality of the weld metal, eliminates metal spray, and permits a severalfold increase in the welding current and welding speed compared to open arc welding.
An arc is moved along the line of a weld (for instance, on circular seams) by the motion of an automatic welding machine or of the object itself. If the machine is structurally joined with the traveling mechanism, it is called self-propelled, but if it moves directly on the surface of the object or along a light removable track laid on the object, it is then called a welding tractor. Flexible-hose semiautomatic types of machines are very popular. In these the electrode wire is fed from the mechanism along a flexible hose to a holder in the welder’s hand. Instead of a flux, protective gases such as argon or carbon dioxide, and also gaseous mixtures, are used. However, because of metal spraying in this case, the current and the welding speed are lower than when welding under a flux. Automatic welding using a non-fusible tungsten electrode in a protective gas, usually argon, is also known. In addition to a wire with a solid cross section, a so-called power electrode is also filled with iron powder alloyed with flux-forming components.
K. K. KHRENOV