Electric welding - Hamilton

Electric welding has become so important an art in the mechanical industries that a comprehensive treatise on this subject covering both the resistance and the arc welding processes is needed in the trade. A special study of the subject has, therefore, been made by the authors of this work, who have been assisted in their work by the experts in resistance and arc welding of some of the most prominent concerns in the United States engaged in this line of work. Credit is especially due the C. & C. Electric & Mfg. Co., the General Electric Co., the Lincoln Electric Co., the Thomson Electric Welding Co., the Westinghouse Electric & Manufacturing Co., and the Wilson Welder & Metals Co. for the cooperation and assistance which they have rendered in supplying information in connection with this undertaking. Consultations with the experts of these companies have made it possible to obtain thoroughly up-to-date information embodying the latest developments and discoveries in the art, and it is believed that, for this reason, the book will prove especially useful to those who are already employing electric welding equipment or who are contemplating its use, as well as to the students of the subject who desire to obtain authoritative information on the electric welding processes. Credit is also due Mr. Alan M. Bennett, whose treatise on Arc Welding, Titten for Machinery, has been freely consulted and employed in the writing of the chapter on Arc Welding.

The application of electrical energy has occupied the minds of some of the foremost inventors during the past forty years, and the development that has taken place in this branch of engineering has been remarkably rapid. Some of the greatest manufacturing industries in the world have been built up on the basis of the inventions made in the electrical field; and, furthermore, the practical applications and uses of the electric current are by no means limited to the fields it has already invaded. It is not only likely, but quite certain, that in the future the service rendered by the electric current will be still more extensively employed. One of the many uses of electric energy in the metal working trades is found in its application to electric welding. Although the electric welding process passed out of the experimental and into the practical stage many years ago, the subject is one that is still rather vague in the minds of most mechanics. Electric welding, however, plays an important part in the industries at the present time, and several large companies have been formed that devote their entire attention to the manufacture of articles in the making of which electric welding forms one of the principal processes. Without the methods 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. In these introductory paragraphs, the different processes of electric welding will be briefly reviewed, so as to provide a comprehensive review of the whole subject; in subsequent chapters, each of the more important welding systems will be taken up in detail, and the apparatus and the methods of doing the work will be shown and described.

Different Systems of Electric Welding - The principle of electric welding is simple; the parts that are to be welded together are heated to a welding temperature by means of an electric current. There are two ways in which the electric current can be utilized for heating to a welding temperature, and, according to the methods used, two main processes or systems of electric welding may be distinguished - the electric resistance-welding process, and the electric arc-welding process. In the former - the resistance-welding process - the parts to be welded are brought to a welding heat by the passage through them of an electric current of such voltage and amperage that the resistance to the flow of the current is great enough to produce sufficient heat at the points or surfaces to be welded, so that, when the parts are brought together by a slight pressure, they will be joined by the fusing of the metal - that is, by welding. In the latter system - the arc-welding method - an electric arc is drawn between two electrodes, or between the work and one electrode. This arc is brought into such a position relative to the work that the heat from the arc melts the metal to be welded, and enables the parts to be united. There are various modifications of this latter process, but, in principle, the above description is correct.

The resistance process of electric welding, in turn, may be divided into two specific processes, differing from each other in some important details. The process generally known as the resistance or incandescent welding process was developed by Elihu Thomson, in 1886, and is, therefore, also generally known by the name of the inventor as the Thomson process. The percussion electric welding process, which was developed by L. W. Chubb at the Westinghouse Electric & Manufacturing Co., is also in principle a resistance-welding process.

There are at least four distinct methods under the head of electric arc-welding processes. These methods are named after the men who are generally credited with their development, and are known, respectively, as the Zerener process, the Bernardos process, the Slavianoff process, and the Strohmenger Slaughler process. Another method known as the "voltex" process may- be considered as a development and improvement on the Zerener process. The Slavianoff process is sometimes not considered as a distinct method, but merely as a development of the Bernardos process.

There is still another process which is frequently classified as an electric welding process - the LaGrange-Hoho method - also known as the "water-pail forge." This method differs from the regular resistance or arc-welding processes in that it is simply a heating process replacing the blacksmith's forge, the welding itself being accomplished by hammering on an anvil, as in ordinary forge welding.

Resistance Welding - In the resistance, incandescent or Thomson electric welding process, the metals to be welded are brought into intimate contact by being held closely together by metal clamps actuated by springs or levers, so as to permit a constant pressure on the parts to be welded, even after the metal at the welding surfaces becomes plastic. The parts to be welded form an electric circuit, and the resistance at the point of contact between the two surfaces to be welded produces a welding temperature in a very short time; the metal parts are then forced together and thus welded. A distinct feature of the resistance welding process is that the interior of the metal is raised to a welding temperature before the surface reaches that heat, so that, if the exterior surface is welded, it is certain that the interior is also properly welded, since it is at a somewhat higher heat. When work is heated for welding in a forge, the opposite conditions take place. A perfect weld may be indicated on the surface, but this weld may cover an imperfect joint inside.

Welding machines built in many different designs for handling various classes of work are used for electric resistance welding. These machines consist principally of a transformer for changing the current to a low voltage and a high amperage, which is required in order to produce the necessary resistance; clamps for holding the work, which also transmit the current to the work and which arc generally known as "electrodes;" means for forcing these clamps or electrodes together; and electrical control for regulating the flow of the current in accordance with the area of the section to be welded. Single-phase alternating current is used, and the voltage of the generated current is generally 220 or 440, with a frequency of 60 cycles. When multi-phase current is employed, the welding machine can be connected with one phase of the system. Higher voltages and lower frequency than mentioned above may also be employed.

The resistance welding process is employed for regular butt and lap-welding, as well as for a number of special welding methods that have been developed in connection with electric welding, known as ''spot" welding, "point" or "projection" welding, and "ridge" welding. Work may also be heated in electric welding machines for upsetting to form collars on the ends of pieces of metal, heating blanks for forging or bending, as well as for heating work for hardening or annealing. The resistance process is especially adapted for duplicate work and is extensively used in such industries as automobile and bicycle manufacture, small-tool manufacture, where the cutting parts of tools are welded to the shanks, and in many other instances. Generally speaking, the resistance process is more applicable to manufacturing work than to repair work, and the process is not applicable to the repair of broken or defective castings, unless these are of extremely simple forms. In cases of this kind, the arc- welding processes are employed.

The advantages claimed for the resistance welding process are briefly: A homogeneous weld is obtained; finished or nearly finished work may be welded without damage to the finish; the process is rapid; impurities are forced out of the joint; the cost of labor is reduced; and the welding operation is in plain view as it proceeds, so that defective welds may be easily prevented.

Percussion Electric Welding - In the percussion electric welding process, the parts to be welded are heated instantly by the sudden discharge of a heavy electric current from a con- denser; at the very moment when the current is discharged from the condenser, the two parts to be welded are forced together with a rapid blow. The sudden rush of current momentarily melts the portions of the work that are to be joiner], and by forcing them together at that moment, a good weld is secured. The process is of recent development and has so far been applied mainly to the welding of wires of the same or dissimilar metals, and to the welding of the end of a wire to another object of larger dimensions. The process will probably find many other applications in the future.

Zerener Arc-welding Process. - In the Zerener process, two carbon electrodes, so arranged in a holder that they form a V, are employed. An arc is drawn between the carbon electrodes and this arc is caused to impinge upon the metal surfaces to be welded by being so located in relation to a powerful electro- magnet that the arc is forced toward the work. This causes the arc to act in a manner similar to the flame of an oxy-acetylene torch. This welding system, also commonly known as the electric blow-pipe method, on account of the peculiarity of the impinging arc, was invented by Dr. Zerener, of Berlin, Germany, some twenty years ago. In this case, no current passes through the work. The Zerener system, as well as all the arc- welding systems, is based upon the fact that when two rods of carbon or other electrodes connected to the poles of a generator, so that current flows through them, are brought into contact, a flame will play between them, this flame being known as an electric arc. The size of this flame or arc may be varied by increasing the gap or distance between the ends of the carbon electrodes, by increasing or decreasing the amount of current passing through the electrodes, or by placing varying resistance in the circuit. The Zerener method is used, to a limited extent, for comparatively small work on steel and brass, and for welding small corners in tubes and tanks. The process, however, is inefficient and complicated, and requires great skill to properly apply. Hence, it is not used as extensively as the Bernardos and the Slavianoff arc-welding methods.

In a development of the Zerener arc-welding process known as the voltex process, the carbon electrodes contain a small percentage of metallic oxide which is converted into a metallic form and then vaporized. The metallic oxide used is frequently oxide of iron. The metallic vapor created by this arrangement increases the size of the arc and minimizes or prevents the carburization of the work by the carbon of the electrodes at the welding point, which is one of the difficulties met with in the regular Zerencr arc-welding process.

Bemardos Arc-welding Process - The Bernardos electric arc-welding process is, perhaps, the best known of the arc-welding methods and, until recently, was the most extensively used. It is specially adapted to large and heavy work. In this process, the arc is drawn between the metal of the work to be welded and a single carbon or graphite electrode. The process is, therefore, commonly known as the carbon electrode welding process. It is evident that the metal to be welded forms one electrode and the carbon the other electrode for the circuit. The arc is drawn by touching the electrode to the work andwithdrawing it to the proper distance in a manner similar to that in which an arc lamp is lighted. The temperature of the arc is approximately 3500 degrees C. (6300 degrees F.), and the heat is confined to a comparatively small space directly in contact with the arc. The use of a small electrode with low amperage permits comparatively light material to be welded, but the process is generally used with large electrodes and heavy currents for heavy work.

In the early development of this process, it was first attempted to use the carbon electrode as the positive terminal and the work as the negative terminal. These attempts, however, were unsuccessful, because part of the carbon from the electrode was carried into the work, making it very hard and, therefore, difficult to subsequently machine. It is, therefore, considered advisable always to connect the work to the positive side of the circuit and the carbon electrode to the negative. By this method, also, the greater portion of the heat of the arc is concentrated at the work, which is the positive terminal. The rod of carbon which forms the negative electrode varies generally in size from 3/16 to 1½  inch in diameter, according to the size of the work to be welded. It is held in an insulated holder, which the workman holds in his hand, striking the arc by placing the carbon in contact with the work and quickly withdrawing it a distance from the metal. The operator then manipulates the arc so as to spread it, and heats the work at or near the point to be welded with what is called a "soaking" heat. The pieces of metal to be welded are melted on their faces together with a small iron rod which acts as a solder and flows in between the two surfaces to be joined. The work is often hammered after the weld has been made by the arc. Screens with colored glass windows and heavy gloves must be used to protect the eyes and skin of the workmen from the effects of the violet rays of the arc.

The Bernardos system when properly adapted to the work to be done is practical, simple, and efficient. Direct current is used. The quantity of current, depending upon the thickness to be welded, generally ranges from 200 to 500 amperes.

Slavianoff Arc-welding Process - The Slavianoff electric arc- welding process is also commonly known as the metallic arc-welding process, because, in this case, a metal electrode is used instead of the carbon electrode. The objects of using a metal electrode are to prevent the introduction of carbon in the weld, to obtain a stronger weld, and to make vertical and overhead welding possible. The arc is drawn by touching the work with the metal electrode and drawing it away in the same manner as in the Bernardos process. No metal rod to act as a solder is required, however, as the metal electrode itself accomplishes this purpose by gradually melting away and entering the weld. The Siavdanoff process produces a softer weld than the Bernardos process, because of the freedom from extraneous carbon in the weld. The arc is smaller than in the Bernardos process and, for that reason, the process is slower, but this is of less importance on small work. As the arc itself will carry the metal from the electrode to the work, it is possible to use this method for welding on a vertical wall or overhead, and hence the process is largely used in overhead repair work, in lirebo.xes, for welding flues in locomotive boilers, and, in general, when repairs must be made in place. It is also largely used for welding steel plate in the manufacture of tanks, etc.

Strohmenger-Slaughter Arc-welding Process. - In the Strohmenger-Slaughter electric arc-welding process, the parts to be welded together are placed in the required position and an electrode, consisting of a soft iron rod covered all over, except at the extreme ends, with a flux suitable for the metal to be welded, and which also serves as an insulator, is laid upon and along the welding line. The work acts as one electrode, the same as in the Bernardos process. The work and one end of the electrode are brought into contact and an arc is thereby struck. This causes the electrode to melt, the weld being coated with the flux at the same time, thus preventing oxidation. The process is claimed to be successful in the welding of rails and for filling up worn places, but it is not so generally used as the other systems. In this process, either direct or alternating current may be used, but alternating current is preferred. Successful welding has been carried out with 85 volts direct current and 220 volts alternating current.

LaGrange-Hoho Electric Heating Process - The LaGrange-Hoho electric welding process is, strictly speaking, not an electric welding process at all, but merely an electric method of heating the metal to a welding temperature. The method, sometimes referred to as the "water-pail forge," makes use of a wooden tank filled with a suitable fluid in which the positive electrode of the electric circuit is placed. A negative electrode is connected to the metal to be heated and this metal is then immersed in the fluid until it reaches a welding temperature. It is then removed and the actual forging or welding is carried out under a hammer or at the anvil in the usual manner.

Earliest Use of Arc Welding - Arc welding appears to have been first used in 1881 by de Meritens for welding together parts of storage-battery plates. In this case, the work was connected to the positive pole of the current supply and a carbon electrode was used. The heat generated by the arc fused the lead of the storage-battery plate, the various parts of which were thus united or welded.


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