488,414. Electric welding. DAIMLERBENZ AKT.-GES. March 15, 1938, No. 8055. Convention date, March 15, 1937. [Class 83 (iv)] A portable electric spot-welding machine, particularly for welding motor vehicle bodies, comprises an electrode roller and a bearing roller which grip between them the work and also a work support serving as the counter electrode. In Fig. 1, the electrode roller 21 and a bearing roller 22, which project from the side of a housing 15, grip between them the work parts 13, 14 and a pair of conductor bars 10, 11, which are separated by insulation 12 and are connected to the opposite terminals of a transformer secondary. The bar 10 forms the counter electrode and the current from the bar 11 passes to the electrode 21 by way of roller 22 and flexible cable 20, which may be water cooled. The rollers are geared together at 18, 19 and are driven by worm gear 23, 24 from an electric motor 25, the casing of which serves as the handle of the apparatus. The motor shaft drives through gearing a commutator roller which closes the welding circuit at intervals so as to obtain spot-welds. The apparatus is canted by raising or lowering the handle so as to obtain the welding pressure. In a modification, the roller 21 only is driven and current is conducted from the roller 22 to the roller 21 by discs on their shafts against which are spring- pressed stationary conductor rings connected together by a flexible cable. In another form, Fig. 5, the conductor bars 10, 11 are arranged side-by-side, the current being conducted directly from the bar 11 to the electrode roller which is formed in two replaceable parts 55, 56 connected with its shaft 57 by a Cardan joint so as to compensate for differences in level between the upper edges of the bars 10, 11. The housing 15 is bevelled at 59, 60 so as to set the roller in the direction in which the apparatus advances. The bearing roller 51 in this case is made of insulating material and is carried by a slide 52 pressed by a spring 54 on a square pin 53 connected to the housing. In a modification of this form, Fig. 6, the bars 10, 11 are arranged at right-angles to each other and the bearing roller 51 is profiled as shown to engage them. The electrode roller 50 is screwed on its shaft 62 so as to be axially adjustable thereon. This roller is cooled by water circulating through the hollow shaft 62 from a supply 67 to exit 66. In a further form, Fig. 7, the bar 79 conducting current to the roller 21 is rounded to engage a grooved bearing roller 22 which is carried by a yoke 76 secured to a resilient yoke 77 to provide the welding pressure. The current is conducted from the bar 79 via roller 22 and contacts 81, 80 pressed apart by a yoke conductor 82. A plug 84 of insulating material is used to prevent short circuits. In a further form, a single conductor bar 10, Fig. 8, is used which is connected to one terminal of the transformer, the other terminal being connected by a flexible cable 89 to a spring-pressed slip ring 90 which engages a contact disc 92 on the shaft of the roller 21. In this case an insulating spring-pressed bearing roller 51 is used. In a modification of this form, Fig. 9, the electrode roller 21 is mounted on a flexible shaft 96, which is carried by one terminal of a rotating transformer secondary 93, so as to supply current thereto also. The other terminal carries a slip ring 97 engaging a sliding contact 98 connected by a flexible cable 99 to the electrode bar 10. The transformer secondary is rotated by gearing 95 from the motor 25 which is carried by the housing 94 of the transformer. The housing is suspended by rollers 105 so as to travel along a rail 106.