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 CHAPTER I ELECTRIC WELDING PROCESSES Although the electric welding process passed out of the experi- mental into the practical stage some years ago, electric welding is still a rather vague subject to most mechanics. Electric welding, however, plays an important part nowadays in the manufacture of a great many articles, and several companies have been formed which devote their entire attention to the manufacture of articles in which electric welding is an integral part of the manufacturing process. Without the process of electric welding, many of these products would have to be manufactured in an entirely different way, and in many cases at a greatly increased cost. There are at least five diistinct processes of electric welding in use at the present time. These processes are common-ly known as the Zerener, the. Benardos, the Strohmenger-Slaughter, the La Grange- Hoho, and the Thomson processes. The Zerener Process In the first process mentioned above, the Zerener process, perhaps more commonly known as the electric blow-pipe method, an electric arc is drawn between two carbon electrodes. This arc is then caused to impinge upon the metal surfaces to be welded by means of an electro-magnet. This welding system was introduced by Dr. Zerener of Berlin, Germany, some twenty years ago. No current passes through .the work in this case. The Zerener system, as well as all arc-welding systems, is based upon the fact that when two rods of carbon, connected by suitable means to the poles of a dynamo or to the terminals of current supply cables, are brought into contact, a flame is caused to play between them, this flame being known as an arc. Variations in the gap or distance between the carbon electrodes, or the interposition of resist- ances of varying intensity, increase or decrease, as the case may be, the amount of current passing through the electrodes, and thuj alter the size of tire flame or arc. In an improvement on this method, known as the Voltex process, the carbons contain a small percentage of metallic oxides oxide of iron, for instance which is converted by the heat generated into its metallic form and then vaporized. The vapor tends to increase the size of the arc and minimizes or prevents the carbonization of the work by the carbon of the electrodes at the welding point. The various systems of electric arc welding are especially valuable when the parts to be welded must, a-fter welding, retain their original positions or relationship with reference to each other. A crack in a machine part illustrates such a case. These methods are also ap- 747591