Werdermann, in 1874, proposed to deflect an electric arc formed between the usual carbons by a jet of air, forming thereby an electric blow pipe. More recently Zerener has in a similar way employed an arc deflected by a magnet as a sort of blowpipe for welding iron. In addition, the curious electric heating action first published by Hoho and Lagrange has been proposed for welding metals. If a negative electrode of a direct current circuit having a potential of 100 to 150 volts is of small surface relatively to that of the positive electrode when both are im mersed in a liquid bath, such as a solution of potassium or sodium carbonate, the surface of such negative electrode, where immersed, glows with light, gas bubbles arise from it, and the electrode itself heats rapidly in spite of its im mersion in cold liquid. A bar of iron used as the negative electrode may thus be brought to incandescence and removed for welding, or it may even be melted under the liquid of the bath. The loss of heat in such a liquid heating process is necessarily somewhat great.
The Thomson process of electric welding, which differs radically from the arc heating operations above descnbed, was first announced in 1886. It has since gone into extensive com mercial use. No electric arc is employed, but the heat which effects the welding is solely due to the resistance of those parts of the metal pieces at the contact where they are to be welded together. This resistance is, of course, extremely low, and the delivery of sufficient energy for heating and welding is the result of the passage of relatively enormous currents. Their potential is only two or three volts, more or less. The metal pieces to be welded together are held respectively in massive clamps or vises of highly conducting metal such as copper, with a slight portion only of each piece projecting to form the joint. These projections of the pieces are brought together in firm contact, for which purpose at least one of the clamps is made mov able toward and from the other, both of them being mounted on a firm support. The pieces having been adjusted to meet in correct relation for the subsequent formation of the weld uniting them, an electric current sufficient in amount to heat the meeting portions of the pieces to the temperature at which they soften and unite, is passed from clamp to clamp, thus traversing the joint and the short projecting portions of the pieces between the damps. So heavy is the current at command that a solid bar without break spanning the space between the clamps could be heated and melted. The completion of the weld after heating is effected by pressure exerted to force one clamp toward the other, which results in a slight upsetting or extrusion of metal at the weld called a burr. For copper a pressure of about 600 pounds per square inch of section is usual, while with iron it is 1,200 and with tool steel 1,800 pounds or more. Nearly all of the metals, even those like antimony and bismuth which are brittle and crystalline, may be united by this process, and many different metals and alloys joined one to another. In some cases as with high carbon steels, a flux such as glass of borax, is employed to facilitate union at tem peratures not high enough to burn or destroy the texture of the metal. Mild steel and iron welds are usually made, as in ordinary forges, at weld ing heat, or that which melts or fluxes the or dinary black oxide scale upon the metal. The heavy welding currents cannot be conveyed without great loss to distances of even a few feet unless conductors of prohibitive section and cost be used. The welding clamps are in practice carried directly upon the secondary terminals of a special welding transformer. The Thomson welding transformer is a construc tion like a lighting transformer in which the usual secondary circuit of numerous turns is replaced by a very massive conductor constitut ing ordinarily only a single turn around the iron magnetic core. The primary or inducing cir cuit is similar to that of the ordinary trans former for alternating current and it is sup plied from alternating current dynamos or lines as usual in such work. It will be seen that the secondary conductor is unique in character, be ing often a bar or casting of many square inches of section of copper of short length. The circuit of this single turn secondary is completed only by the meeting ends of the work pieces in the clamps. It will thus be evident that the chief resistance or opposition to the flow of the low voltage current in the single secondary turn will be at the proposed joint or weld between the clamps. Here it is then that the trans formed energy is for the most part given out as heat, the section of metal which can be welded depending upon the scale of the appara tus used and the energy of the primary source which is available. The welding transformer has found convenient application in the heating of metal pieces for forging, bending, shaping, brazing or the like, in addition to welding. It has also in the Lemp process been divested of its welding clamps and applied to the local annealing of the hardened face of armor plates, so as to facilitate drilling and tapping, or cut ting into desired shapes. The welds made by the Thomson process are usually butt welds, though lap welds are also made with almost equal facility. In butt welding there is of course an upset, burr, or extrusion of metal at the joint. In many cases this is not removed, and it renders the joint stronger than other adjacent sections. Oftentimes the joint is pressed or forged while still hot so as to remove the burr at the joint. In other cases the joint is fin ished by filing or grinding. The welding clamps are modified in form and disposition to suit the shape and size of the pieces to be held, and the pressure used to effect the weld is either manually applied by levers or is obtained from a strained spring, or again, in large work, by hydraulic means under control by suitable valves. The heating effects of the electric cur rent are so perfectly adjusted by regulating ap pliances that most of the metals formerly re garded as unweldable, yield good results with the process. Even leaden pieces, such for ex ample, as sections of lead pipe, may be joined together with great ease. The operation of the electric welder is characterized by uni formity, rapidity, flexibility, cleanliness, neat ness, and economy. It has found
extensive application to repetition work; single machines making sometimes as many as 2,000 welds per day of 10 hours. It is used widely in the wagon and carriage industry for tires, axles, bands fifth wheels, etc., and for wire bands for affixing rubber tires to wheels. Many parts of bicycles and automobiles are built up by electric welding. In the construction of tools and parts of machinery and particularly in the wire industry it plays an important part. An other important field is in the welding of wire or strip into hoops or bands for barrels, tubs, pails, etc. Machines are in operation producing electrically welded wire fencing, in which the wires which in the fence are horizontal are welded to verticals at intervals, the action some what resembling that of a loom. In joining pipe into continuous lengths or coils, and also in welding in situ street railway rails into a con tinuous track the electric weld possesses a spe cial adaptability. An interesting application of the electric welder is found in the production of steel tubing by the progressive welding of a longitudinal seam. A long strip of flat sheet or skelp is rolled up so as to cause the lateral edges to meet. It then passes between welding rolls whereby the heating current locally traverses the meeting edges and welds them. The operation is progressive from one end of the pipe to the other as it is fed through the machine. The result is a pipe of uniform diameter with walls of even thickness, having a delicate bead along one side where the weld has been made. This bead is removed if the pipe be subsequently mandrel drawn with a re duction of its diameter. In the earlier electric welders the operations of clamping the pieces in place, applying and cutting off the electric cur rent and exerting mechanical pressure, were usually manually controlled. Machines more or less automatic are now frequently employed. In recent types adapted for rapid repetition of work upon identical pieces, the action is en tirely automatic; the machine runs continuously and its sequence of actions is definitely deter mined by its construction. These machines are power driven, movements being imparted for clamping the pieces as they are fed to the ma chine, for closing the current switch, for exert ing pressure to complete the weld, for cutting off the current and for releasing the pieces from the clamps after the operation. In wire fence and chain machines the stock is itself fed auto matically and the welding amtinued until the machine is stopled or the material exhausted. The energy required to effect electric welds naturally varies with the size of the pieces and with the material. It also depends upon the time consumed in the work, which time may be made shorter or longer even with exactly simi lar pieces. The following table gives the results of some tests made upon different sections of iron, mild steel, brass and copper in the form of bars. The figures are only approximate and would vary considerably if the welds had been made in times different from those given. In general, working at a greater rapidity would lessen the total power used but require larger apparatus for the increased output required dur ing the welding: One of the recent and most important devel opments of electric welding by the Thomson process is known as ((Spot') welding, and is particularly applicable to the union of sheet metal overlapped. The process is known as the Harmatta method, and is an effective sub stitute for riveting with the advantage of leav ing the metal sheets united in spots but without rivet heads or other deformation projecting. The surfaces of the sheets may, in fact, be left smooth or with only slight indentations. To accomplish this result the two sheets to be "spot-welded" are placed one against the other and, as it were, pinched together between two heavy points or electrodes from a welding trans former secondary circuit. These electrodes be ing placed opposite each other press the sheets together at any desired spot, the current is then sent through them, when the sheets, where they are in contact, instantly attain the welding heat and the joint is effected in a spot with unwelded metal around it, as in riveting. The electrodes used usually have at their ends the form of truncated cones; that is, they narrow toward the work, in this way concentrating the current flow at the limited spot to be welded. On cut ting off the current after a weld is made and releasing the pressure of the electrodes on the sheets, they may be moved to a new position, another spot weld effected, and so on until as many are made as desired.
Projection welding is a modification of spot welding in which the sheet metal pieces are first given small projections by stamping or otherwise. In other cases small pieces of metal are placed between the sheets at spots where the weld is to occur. Then the whole is pressed between the current carrying electrodes which may now be of such spread as to cover a num ber of such projections or spots at once, all being welded simultaneously. Spot welding in its various forms finds a large and rapidly extending application, particularly to sheet steel structures, such as steel car bodies, automobile bodies, metal containers, etc. It has become the general method of uniting stamped metal pieces which subsequently are to be enameled. For merly, for example, handles were riveted to sauce pans before enameling and the rivets were plainly to be seen under the enamel. By spot electric welding the union is effected without visible change in the metal surfaces and the covering of enamel is in consequence uninter rupted and without projections.
The process is capable of further great ex tensions in its application to the union of over lapped sheets or plates. Riveted joints, always more or less unsightly and often disadvan tageous to construction by talcing up room and giving an irregular surface, can often be abol ished and the spot weld substituted therefor with benefit Besides its advantage of leaving a smooth surface, it effects a great saving of time and economizes material. As in the case of electric welding generally, the spot weld gives rise to new modes of construction of metal objects and greatly assists the substitu tion of pressed steel for castings or forgings.