The process of welding or cutting with the electric arc is possible with nothing more than a source of current at a suitable voltage, some means for regulating the amount of current flowing, and an electrode. Practice has shown, however, that certain other devices are necessary, if satisfactory welding is to be done; and it is the determining of these devices and their proper uses that constitutes the main differences in the various processes used today. In order to do welding or cutting with the arc it is necessary first to connect the work to the positive side of the power-supply circuit and the electrode to the negative side of the circuit, by means of wires or cables, and to insert a regulating resistance in either of these circuits to limit the current flowing to the proper amount. The negative electrode should then be placed in contact with the work and quickly withdrawn, thus establishing the arc, Fig. 52, which provides the temperature required. As the metal soon begins to melt the work may begin at once.
Fig. 53. Are-Welding Lug on Steel Casting Courtesy of Westinghouse Electric and Manufaturing Company.
In general, electric-are welding consists in using the heat of the arc to fuse or melt the filling material into the place to be filled.
Fig. 53, although the article worked upon may be melted down sufficiently to fill the space, if it is large enough at the point to be welded. Two methods or processes of using the arc for welding are in commercial use today, these being the "metallic" and the "graphite" processes. The metallic welding process, Fig. 54, consists in using a piece of wire as the negative electrode of the arc and fusing it into place; the graphite process. Fig. 55, consists in using a piece of carbon or graphite as the negative electrode and fusing a piece of metal into place by the heat of the arc, similar to a gas process. The graphite process is always used for cutting, a slot being melted through the piece to be separated. There is also a third system which will be described later, but it is not used much in the United States.
The Benardos system of electric-are welding is based upon the use of a carbon pencil as the negative electrode and the article worked upon as the positive electrode, using for the purpose a continuous, or direct, current at a moderate voltage (usually from 60 to 70 volts). After the arc is established by touching the electrodes together and withdrawing, a piece of the filling material in the form of a "melt bar" is fused into place by the heat of the are. Any metal, which does not volatilize or bum up too easily at the temperature obtained, may be welded by the Benardos process and this process is the best to use for cast iron, the copper alloys, and aluminum. When using the graphite pencil, it is necessary to give the hand a sort of rotary motion in order to cause the arc to play about over the surface of the job and prevent burning, for the arc never stops melting the metal so long as it exists. This motion also has the effect of causing any slag or impurities on top of the molten mass to flow off to one side, instead of remaining in the veld and spoiling its quality, and of distributing the heat more uniformly over the piece welded. When cutting with the are, the article should be so placed that work can begin at the top and progress downward across the face of the piece.
Fig. 56. siemund Hand Electrode Holder.
Courtesy of Siemund Wenzel Electric Welding Company.
The Slavianoff system of electric-arc welding is based upon the use of a metallic pencil, Fig. 56, as the negative electrode, and the article worked on as the positive electrode, and the use of a continuous current at low voltage. After the arc has been established by touching the electrodes together and separating them, as before, the negative electrode itself begins to melt and thus forms the filling material. This system is more successful for work with iron and steel electrodes than with the other metals, although many of them may be used where high-class work is unnecessary. The main application of this system has been to sheet-steel work, the metal electrode being deposited along the joint to be made and tying the two plates together so that they form practically one piece. This process may also be used for building up worn or missing pieces, filling holes, etc. The current required for the Slavianoff process is much less than that for the Benardos process but it is much slower for operations involving the placing of any very large amounts of metal quickly. The successful development of the Slavianoff system has been the principal cause for the recent rapid spread of electric-are welding in the industries.
The Zerener system consists in having the two electrodes made of carbon and mounted in a frame which holds them at an angle with relation to each other and to the work. Fig. 57. The arc is drawn between them and is then deflected downward by a magnet and used in the same way as a gas flame. The apparatus for holding and feeding the carbon pencils is so bulky and complicated that this system has not been used in America to any reat extent, although it is in use in several plants in Germany. The nature of the apparatus is such that large amounts of current cannot be used; so it is limited to comparatively light work. The weight and size of the holders for even moderate-sized work are such that they must be suspended from above by ropes and moved about over the work, although small holders for use in one hand have been developed for holding the lightest articles. The advantage claimed for this system is that the arc is controlled by a magnet and that finer work can be done.