The General Electric Co. Ltd., Magnet House, Kingsway, London, W.C.2, have designed in their research laboratories a 4kVA electronically controlled spot welder for welding very thin wires and sheets. In the application illustrated (FIG. 1) it is used to weld the scam between two disks which make up a diaphragm; the material is monel 0.008 in, thick. Normal methods of resistance welding had not proved practicable in production owing to the electrodes picking up monel metal. This machine has, however, overcome the difficulty. A jig forms the lower electrode, and the upper is in the form of a chromium copper disk, free to rotate. Both electrodes are water cooled. In this case the jig is rotated by an electric motor at such speed that the spot welds overlap, giving a continuous seal. The spot welder supplies current in the form of heavy pulses of from one to six cycles’ duration, timed by the electronic control circuit. A synchronizing circuit ensures that the weld always starts at the same point in a supply cycle. The top electrode is carried in a low inertia holder to give the quick follow‐up necessitated by the rapid collapse of the metal being welded.
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