The joining is frequently effected without the use of a flux, though in sonic cases a flux. such as glass of borax, is found to assist the operation. The energy required to effect a weld is of course different with the different metals, according to conductivity for heat and elec tricity, fusibility. section, shape of pieces, and other factors.
The following table shows seine of the results obtained in welding iron, etc., and with the time occupied in the work.
It will be seen that the foot pounds of energy for a given section of copper are about half as much again as with the same section of iron, and that the figures for iron and brass are n•)t very different. The high heat conductivity of copper, in consequence of which more of the length of bar is heated, or more heat conducted away from the joint., doubtless accounts for the difference noted. It may also be remarked that the energy required increases more rapidly than the section, and in a certain proportion, which is doubtless due to the fact that in the larger pieces, though less subject to radiation of heat during the welding than smaller pieces, there is required a longer time for the welding, and consequently an increased conduction of heat from the joint results. If the time of welding were made the same for varying sections, it would appear that the energy used would be more nearly in propor tion to the section. The end pressure in forcing the pieces together should, for the best work, be carefully kept, as, if a proper amount be applied, the welding will be at once effected on the metal pieces arriving at a certain degree of plasticity, the quickness or slowness of the heating simply governing the time which will be consumed in heating to that plas ticity. The pressure to be applied in effectingbutt welds electrically varies with the material and section of the pieces at the weld. It is with steel abort 1,800 lbs. per sq. in.; with wrought-iron, about 1,200 lbs.; and for copper, about 600 lbs. per sq. iu.
In the industrial application of the process the source of current has usually been a special dynamo, con structed to deliver alternating currents at about 800 volts, and of a periodicity of about 50, or 100 alternations per sec ond. Where but a single welder h as been employed it has been customary to regulate the weld ing currents by va rying the field-ex citing current by a resistance or other device. Fig. 3 shows a plan of the con nections use d in such a case. Fig. 4 also shows the ar rangement of a com posite-field self-ex citing dynamo, which is controlled by a variable reactive coil alongside the welder, altering the self-induction in an arma ture branch or circuit, which in turn causes a variation in the field current of the dynamo.
In other cases in which quick work is to be done, the condi tions at the dynamo are set once for all, and the mere clos ing of a switch effects the weld, and the current is self-regu lating. In this case the namo is greatly over-com pounded, ,..r increases its elec
tromotive force rapidly with an increase of resistance, or counter force, in its circuit, due to heating of the pieces during welding. In the case of several welders fed from the same dynamo as a source of pri mary currents, such methods are inadvisable, and are re placed by constructions which yield constant potentials, or the dynamos are self-regulating in the same sense as dynamos used in electric lighting are The actual construction used in the welders themselves undergoes great variation, according to the size and character of the work for which they are designed. The direction and nature of movement to be given to the clamps in effecting the weld will of course govern the construction of the welder itself to a large extent. As the electric welding machine may be regarded as a special induction coil or transformer, combined with holding and moving clamps and pressure apparatus simply, it will also be understood that a change in the latter does not necessarily involve a change in the former. lucked, in the type of welder called Universal," the strong iron frame containing and supporting the transformer portion of the apparatus simply has an upper double platform, the portions of which are the terminals of the heavy secondary conductor, insulated from each other and provided with grooves and holes for bolts similar to an iron planer bed. These permit the attachment of varying forms or arrangements of clamping devices to suit a variety of forms and sizes of welding work or metal shaping, for which the machine is adapted. Such a machine is shown in Fig. G. bearing clamps for axle-welding bolted to its platen. hydraulic cyl inders are arranged to move back and forth one terminal of the secondary, arranged in guides, and whereby the welding pressure and movement is obtained. In these and other machines for electric welding. the primary coil of many turns, and the very heavy sec ondary conductor of only one turn, arc con structed so as to be closely associated around a laminated iron core. Arrangements such as in Figs. 6 and 7, where P and $ represent relatively the sections of primary and sec ondary, and I the iron magnetic circuit, are used. The secondary is cut, as in Fig. 7, at K, leaving its terminals free for conveyine- cur rent to clamps which may be attached thereto. Fig. 8 shows a welder adapted for welding sec tions of pipe by band-pressure. and gives a fair idea of the substantial character of work demanded in these later electrical productions. A pipe-welding machine of more elaborate type is provided with hydraulic-pressure cylinders, for forcing the pieces together. Both these pipe machines are provided with water circulation through the clamps, for keep ing them cool and in working condition. A top view of a tire-welding machine is given in Fig U. the pipe for water circulation being clearly seem the special clamps, the pressure lever, and the tire in place as welded in the machine.