The operation of electric riveting is a form of upsetting, and is accomplished by making the rivet blank the path for the heavy secondary current. For this purpose. it is only nec essary to include the blank, with or without head, between the heading tools of heavy bronze or copper, kept cool by water circulation through them, and when the blank has reached a plastic state by the current heating it, to force the tools one toward the other until the heads are sufficiently formed (Fig. 11). With sufficient energy of current the rivet body actually welds into the plates, and the plates themselves may, in part, be welded together. The heating of pieces for hot spinning or rolling may be accomplished, and the rotation of the pieces, even during the passage of current, presents no considerable dif ficulty. The apparatus in this case resembles a lathe, the heads of which are insulated, and then connected to the terminals of a secondary circuit of a transformer of the same construction as for welding. The tool post, or the part corresponding thereto, carries rolls or formers for manipulating the revolving hot metal, through which the current is passed for heating, and the work ing may proceed while the heating is in progress. The heat may also be maintained at the proper degree for giving the requisite plasticity or continuous annealing. In this way iron tubing rotated may be reduced or expanded, its ends closed, beads rolled in its sides, etc.
Adapting the strength of the current, or rather the heating effect of the current, to the size of the pieces in electric welding, brazing, forging, shaping, etc., is a matter easily provided for by suitable regulators. Where
the pieces included in the circuit are of different sections or resistances, they will not heat equally, unless special precautions are taken. such as proportioning the currents traversing each piece, or arranging the conduction, or cooling of the pieces during work so as to affect in greater degree the piece of higher resistance, which would, otherwise, tend to overheat. In welding, this is frequently done by giving but a relatively smaller projection from the clamps to the piece of smaller section or higher resistance, In some instances in practical work it has been found that some saving of energy in electrical welding can be obtained by heating the pieces to a red heat before insertion into the clamps of the welding machine, which then raises the temperature to the welding heat. and only at the joint. This, for special kinds of work. may be made to save the energy required for the incipient heating during welding. Frequently, also, fuel products which are wastes of other parts of the manufacture can be employed to generate steam for electric welding. and, of coarse, where water-power is abundant the energy of the water may be turned into heat for the same uses.
Welding Tubes : see Pipe and Tube-making Machines.