Abstract: An apparatus for seam welding is disclosed, in which a metal plate or a surface-clad metal plate in a cylindrical form with a strip-like overlap section S constituted by two overlapping edge portions is passed as process material 4 between pair roller electrodes 1 and 2 via upper and lower wire electrodes 3 for seam welding of the overlap section between the roller electrodes and also between the upper and lower wire electrodes 3 under pressure applied to the section, and also which is provided with a welding current source 8 for supplying a welding current between the roller electrodes 1 and 2.

Abstract: A seam welder with wire electrodes inserted between upper and lower roller electrodes to weld an overlap section of a cylinderical body formed of metal plate between the electrodes. The power supply for the welder includes a rectifying circuit for obtaining a dc voltage from an ac current source, a smoothing circuit for smoothing the dc voltage, a single converting circuit to convert the smoothed dc voltage into an alternating polarity pulse voltage, a transformer for applying this pulse voltage to the upper and lower electrodes and a capacitor connected between the primary side of the transformer and the output side of the converting circuit with a capacitance that produces resonance with the inductance of the transformer primary at the pulse voltage frequency.

Abstract: A method of lap welding an eventual can blank of a metal sheet or the like by passing a lap joint between the upper and lower roller electrodes via upper and lower wire electrodes to be heated and simultaneously applied pressure, thereby forming continuous thermal press bond sections, wherein the width of the contact surface of the upper and lower wire electrodes is set to three times the width of the lap joint, and the thermal press bond sections are formed by thermal press bonding without fusion, the center-to-center distance between adjacent thermal press bond sections being set to be in a range of 0.8.+-.0.2 mm.