(a) The history of electric welding extends over a much longer period of time than is generally supposed. Some years ago, Prof. Elihu Thomson, among experiments by which he intended to prove the substantially identical nature of electrical energy under any and all circumstances, reversed an ordinary Ruhmkorf induction coil, showing thereby the difference of potential between the current in the primary and that in the secondary of the coil. In performing this experiment he brought the terminals of the coarse-secondary winding of the coil into contact, and was surprised to notice that a high degree of temperature was reached instantaneously at the point of contact - in fact, such a high degree of heat that the ends were stuck quite firmly together, the copper wire being actually melted, so that it required considerable force to separate them. Later, in the course of manufacturing electric-lighting apparatus, it became an imperative necessity to discover some means of having more perfect joints in copper wire than could then be obtained. Then his mind reverted to the old experiment, and electric welding became an assured art. This discovery was made several years prior to the building of a welding machine.
Subsequently Prof. Thomson designed and built a small machine with which to weld fine wires. The experiments with this apparatus were so successful that the inventor decided to build larger and better apparatus, and experiment further with a view to welding, if possible, much larger pieces of metal. These experiments were also successful, and the invention has been much further developed in the past year or two.
The principle involved in the Thomson process of electric welding is very simple, as indeed is most of the apparatus also. The Thomson process of electric welding consists simply in forcing through the pieces of metal to be welded currents of such large volume that these pieces can carry them without heating. Now, when the pieces are placed in abutment, the point of greatest resistance is where they contact with each other, and it is of course at this point that the heat is first generated. The instant heat is generated at the point of contact, the resistance at that place enormously increases, and a consequent mope rapid development of heat is the immediate result. The metals are consequently raised to a high welding temperature in a very remarkably short space of time, and upon a slight pressure being applied to force the pieces together, a perfect welding is effected.
The field that is open for the process of electric welding is surprisingly vast. One of the most important reasons why electric welding is making way so rapidly is that the heat generated by the current is the only pure heat known. The blacksmith, when welding with either a gas furnace or a coal fire, is constantly running the risk not only of burning his metal, but of introducing into it foreign matter in the form of gases which are very deleterious to the substances of either iron or steel, which are the principal metals worked by blacksmiths. The heat generated by the electric current is absolutely free from all foreign and harmful substances. Again, the heat effected by the current is under perfect control, and can be made entirely automatic. The heat can be begun, and a stop put on the apparatus which will control the heat perfectly.
Then, welding by the Thomson process is a much neater and quicker operation; also, no skilled labour is necessary to operate an electric welding apparatus. A young man not knowing anything of the conditions under which different metals should be welded, in a very short time became so expert in handling these machines that he can now, on the first trial, make perfect welds in any of the ordinary metals and in almost all varieties of steel, including even Mushet and manganese steels.
There are hundreds of applications of the process. As an example of small work, the welding of gold rings is an assured success, making a better joint than is now made, doing away entirely with soldering, and in its place making a continuous gold ring; the work is accomplished in about 1/5 of the time; and soldering material is saved, an enormous wasting of heat is done away with, and the dangers of burning gas are entirely obviated.
As an example of somewhat larger work, there is the welding of axes. The axe is made of a body of ordinary wrought iron, to which is welded an edge or face of fine tool steel, tempered and toughened. The pieces of metal, before welding, have to be prepared somewhat in this manner. That is, a groove is cut in the body of the axe while a taper is cut on tjie face or blade, the latter being set into the former and the pieces welded in this position. Now, in electric welding this preparation is done away with.
As an example of much larger work, take the welding of pedestals and locomotive frames. This is an entirely different class of work. The pieces have to be carefully prepared, a raised portion being left on the base or edge of the frame, and a taper groove being cut in the pedestal, so that it may fit down over the raised portion referred to. In the first place, on locomotives are 5 or 6 copper rings, the wire composing which is of small diameter. The joints in these rings are at present made with a blowpipe flame, and it takes an expert some 4 or 5 minutes to make a single one. Electricity can make them in as many seconds. There are also on each one of these locomotives at least 150 joints in iron, from 1/2 in. area of section to several in. area. Now, it takes 4-15 minutes to make these joints by the ordinary process; electricity can do the work in at least £ of the time. There are on each locomotive 4 frames, each frame having on it at least 2 - sometimes 3, 4, and 5 pedestals. Suppose that the average is 3 pedestals per frame. That makes 12 pedestals to the locomotive. To prepare the ends of the pedestals and the taper on the base of the frame takes some 40 minutes. They have to be heated and hammered into shape while hot.