Abstract: Method of butt-welding metal parts by induction, in particular parts of irregular cross-section such as rails, consisting in pressing the parts against one another with an initial pressure for the entire period of heating, in heating them by induction by means of an inductor which encloses the parts parallel to their contours about the plane of their interface, firstly for a first period at a lower frequency and then, for a second period following the first, at a frequency two to four times higher than the first frequency, and, at the end of the second period, in applying the parts against one another at a forging pressure which is from two to more than six times higher than the initial pressure. The quality of the welded joint is greatly improved and the dimensions of the bulge or upset are limited by restricting the depth of the penetration of the induced current to both sides of the interface by means of two short-circuited turns disposed symmetrically relatively to the inductor to either side thereof.

Abstract: A brazing press for securing exterior claddings to bottoms of metallic receptacles, which includes a support structure and a reciprocable mandrel for exerting pressure against the former. The support structure holds a massive inductor block having a flat bottom and containing an inductor coil for respectively pressing and heating the flat portions of the workpieces, and an encompassing sleeve which is associated with an auxiliary inductor and exerts pressure on the peripheral curved portions of the cladding. Either the sleeve with its auxuliary inductor of the inductor block can be supported by said structure through resilient means which are calibrated, whereby auxiliary pressure is exerted on the peripheral curved portions independently from the one exerted on the flat central portion, when said mandrel is pushed against the inductor block.

Abstract: An induction heating apparatus comprising a static converter including a bidirectional controlled switch having a main thyristor and a diode connected in parallel to conduct in opposite directions. The converter comprises a first circuit for protection against the spurious turning on of the thyristor caused by overshoot voltages due to the sudden interruption of the current flowing through the charging inductor when the switch is turned off. This protection circuit comprises, connected in series across the charging inductor, a diode and a capacitor which is charged through the diode when the voltage across the inductor terminals becomes positive, and discharged through a current-limiting resistor and an auxiliary thyristor into the gate of the main thyristor for triggering it periodically.