To the average individual, perhaps, electric welding appears to be an outcome of the War; an expedient rendered necessary by the insistent demand for the speeding up of production by all available means. As a matter of fact various processes of welding by the aid of the electric current, notably carbon arc welding, have been in commercial operation for a quarter of a century or more, this country having been among the first to adopt and develop some of them. Some of them, too, had, long before the War, been much in vogue both on the Continent and in the United States of America. In the case of the latter country electric welding had, for years before the outbreak of hostilities, been most successfully resorted to for many purposes to a considerable extent, especially for repair work on railway rolling stock. Sweden, among countries on this side of the Atlantic, may be cited as being in the forefront in the employment of electric welding for ship repairing.

Nevertheless it is quite true that the War gave such an impetus to the use of the newer method of welding as many years of endeavour during times of peace would have failed to impart to it. Moreover, the War greatly enlarged the sphere of its application, and was instrumental in bringing home to our manufacturers what a powerful agent was the electric current for the carrying out of certain types of work. As a consequence it has, nowadays, become the rule, rather than the exception, to find electric welding plants in our factories, and there appears to be every probability of such plants being even more extensively employed than they are at present. Furthermore, the War has undoubtedly had the effect of developing and improving the machines and appliances which both arc and resistance welding call for.

The central idea around which the articles were written for The Engineer was to impart to the readers of that Journal a good general knowledge of the different systems of electric welding which have been evolved and of the various machines and pieces of apparatus which are required or are desirable for their efficient operation. No attempt was made to go, in detail, into the history of the subject, though certain historical matters are referred to. Nor was it sought to provide a handbook to the subject by giving minute" instructions as to the correct manner in which to work the various systems. To have done either, or both, would have entailed the introduction of a vast amount of matter which would have resulted in the enlargement of the volume to unwieldy dimensions, as well as in the production of a sense of weariness in the mind of the reader, who, if he intends to adopt electric welding, in one or other of its various forms, will naturally seek for practical instruction in the manner of working it, which it is, of course, impossible adequately to convey in a book. Again, it was considered undesirable to endeavour to enumerate, at length, the possible applications of electric welding. Such an effort would have proved to be a futile task since the number of such applications multiplies from day to day. Yet it will be found that mention has been made of such a varied selection of applications as will enable the reader to form a very fairly accurate conception of the wide area which has already been covered.

Electric welding, which is far from being a novelty, has recently come prominently into public notice. It has not only been employed by the Admiralty for the construction of vessels, but Lloyd's Register has issued regulations under which it is prepared to sanction its use in shipbuilding operations generally. Moreover, the astonishing rapidity with which the damaged interned German liners were repaired by this process, thus enabling many thousands of American soldiers to be brought to Europe long before such transportation was deemed to be possible, is still fresh in the public memory. We feel sure, therefore, that a discussion of the subject will be of interest to our readers, and we propose in the present and succeeding chapters to deal with the question at some length. No attempt will be made to go in detail into the evolution of the various processes involved, our purpose being, rather, to show what has been and is being done, than to relate exactly who was the inventor of this and who was the discoverer of that. It will suffice to say that, quite early in the use of electric energy, experiments with a view to using the current for welding purposes were instituted, and that thirty years and more ago electric welding was practised notably by that prolific inventor and distinguished investigator, Elihu Thomson, and by the Russian Benardos. Of the work of these two men we shall have much to say, but we shall not attempt to deal with it exhaustively, so that what follows in no way claims to be a complete history of their discoveries, nor, indeed, of electric welding as a whole. It is noteworthy that though introduced at no widely differing periods of time the methods of Thomson and Benardos were entirely dissimilar, the one employing what is termed the resistance process and the other the arc process. All the electric welding systems in use at the present day may be classed under one or other of these two heads, though there are numerous variations in the application of the two principles.

Resistance welding resembles much more closely the original welding of the blacksmith than does arc welding ; indeed, saving that the manner of arriving at welding heat is different in the two cases, the welding of the smithy is identical with the welding by the resistance method. In both the portions of the parts to be joined together are raised to a proper heat in the immediate neighbourhood of the proposed weld, and then welding is effected either by means of pressure or by percussion. The same precautions regarding the cleanness of the surfaces to be joined together have to be exercised in each case. Arc welding is essentially different in that the metal is in the majority of cases actually melted at the weld, and that neither pressure nor hammering is absolutely necessary, though in some cases, they may be beneficially applied. As we shall show, however, there are cases in which the arc is used simply to obtain welding heat. In such instances, of course, percussion or pressure is required to consolidate the welds. Both arc and resistance welding are being more and more extensively employed and, from present indications, it would appear highly probable that both will continue in vogue, since each has its own sphere of usefulness, in which it performs with better effect than does the other. Nor does it seem likely that either will oust the acetylene method, which likewise pre-eminent in certain directions; so that the engineer of the present day is fortunate in having three more methods by which welding can be effected than had his predecessor of the last generation. It may be even said that he has more than that if the oxy-hydrogen or oxy-coal.gas methods be taken into account.

In both resistance and arc welding a certain amount of special machinery or apparatus is required, though with the latter it is generally less elaborate than with the former. For resistance welding alternating current is almost universally employed in practice, though there is no reason why direct current should not be used, saving the difficulty of dealing with the heavy currents. In arc welding, on the other hand, either direct or alternating current can, under certain circumstances, be employed, though direct current is most generally used. Resistance welding may be effected by three methods: - (a) Butt welding; (6) spot welding; and (c) line or seam welding, together with several modifications. Arc welding may be performed either with bare metal electrodes, with flux-covered metal electrodes, or with carbon electrodes.

The quality of the current - if such an expression be permitted - employed in the two processes differs very widely. In resistance welding there must always be a very heavy current - in some cases it amounts to thousands of amperes - and a very low pressure, say, from J to 6 volts. Some largo machines have recently been built in America in which voltages considerably in excess of the higher of these figures have been employed. We shall refer to them later. In arc welding, on the other hand, the voltage must always be high enough to maintain an arc - say, from 20 to 56 volts - and the current is relatively small. As a matter of fact, it is found in practice that the electromotive force available should, at any rate with metal electrodes, be at least from 60 to 75 volts, while some processes require an available pressure of from 100 to 110 volts. With carbon electrodes a pressure of 90 volts is commonly employed. The current in arc welding is adapted to the nature of the work being carried out. It may be quite small, say, from 15 to 20 amperes, and it is very rarely, we believe, that it exceeds 800 amperes with carbon electrodes, and less than half that with metal electrodes, the average in actual practice being considerably less than the smaller figure. In the arc process, as originally introduced by Benardos, the work which was to be welded was connected to the negative terminal of a source of electrical energy - in the first instance storage batteries were employed - while the positive terminal was connected to the carbon electrode. An arc was formed by touching the work with the electrode and quickly withdrawing the latter, the result being that the metal immediately adjacent to the point of impingement of the arc was quickly raised to a very high temperature, and a stick of similar metal could also be melted just over the spot much in the same manner as solder is melted with a soldering iron. Later, this arrangement was found to possess the disadvantage that, as the direction of the current was from the electrode to the work, there was a tendency for the carbon, either in the form of vapour or in minute highly heated particles, to be carried over to the latter, so that it entered into combination with the molten metal, and sometimes, undesirably altered its composition. Hence the polarity of the work and electrode were interchanged, the former becoming the positive and the latter the negative. A further reason is put forward by the advocates of the carbon arc process as to why the work, and not the metal electrode, should be made the positive terminal, and that is that the positive terminal of an electric arc is hotter than the negative terminal. We believe we are right in stating that carbon arc welding was first employed commercially in this country by the firm of Uoyd and Uoyd, of Birmingham, which is now merged in the firm of Stewarts and Lloyd. It has also been used with success, for twenty years or more, by the Steel Barrel Co., Limited, of Uxbridge.

For arc welding the special appliances actually necessary are but few. In addition to the source of electric current and the electrode with its holder, all that is essential is a steadying resistance, connected in series with the arc, and possibly an ammeter as well. As will be seen later, however, Special machines have been introduced with the purpose of preventing rushes of current. It will be readily understood that, unless means for controlling the current are employed, a resistance, or some such device, in series with the arc is an absolute necessity, for without it when the electrode touches the work there is a complete short circuit until the arc is struck. Although, however, but few special appliances are required, it is generally found that the supply of current available is not suitable for welding. For instance, it is very rare nowadays to find a public supply with as low a voltage as even 1 10. Hence it is necessary,, if the current be not specially generated, to reduce the pressure so that there may not be an excessive waste of energy in the resistance. If the current be alternating the reduction in pressure is readily effected by means of a static transformer, which may have different tappings in the primary, so that different voltages and currents to suit different kinds of work may be obtained. This arrangement, of course, applies only if alternating current is to be employed in the arc. As a matter of fact, direct current is, as we have said, almost universally used, at any rate in this country, and to produce the low voltage direct current a motor generator may be employed. The direct current half of motor generators designed for arc welding are ordinarily compound wound, and are preferably provided with commutating poles, so that sparking may be minimised. The size of machine required depends, naturally, upon the nature and amount of the Work being carried out. The variation in the. current when using metallic electrodes may be between, gay, 15 and 250. These may be regarded as extremes, only met with in special cases, the more usual range experienced in actual practice being between, say, 20 and 200 amperes. With carbon electrodes, on the other hand, much heavier currents are experienced. We understand that satisfactory results cannot be looked for with currents under 300 amperes, and that not infrequently 500 and in special cases as many as 800 amperes may be required. With these figures an estimate may be arrived at regarding the capacity of the machine necessary for any given number of welders.