Patent GB-518182-A (GB)
Title: Improvements in method and apparatus for welding sheet metal, in particular can bodies
IPC: B23K11/06
Filed: 1938-08-17
Abstract: 518,182. Making can bodies &c. AMERICAN CAN CO. Aug. 17, 1938, No. 24216. Convention date, Sept. 25, 1937. [Classes 83 (ii) and 83 (iv)] Angular bending; welding.-In a method of progressively effecting overlapping spot welds on the longitudinal seams of thin sheet metal parts such as the side seam of a can body, the beginning andending of the flow of current is controlled so that the outermost welds a, z have their centres spaced inwardly from the end ,edges of the blanks so that the welds terminate at the end edges without extrusion of metal therefrom.. The area e, Fig. 10, contained between the boundary line c of the first spot a and the boundary line d of the second spot b is twice reduced to molten condition so as to obtain a continuous hermetic joint. A flat blank 21 to form a can body is placed in a pocket on a table 42 under a horn 24 and is held in position on the horn by a block 84 operated by a wedge-shaped pin 77 which is forced forward against the action of a spring 81 by a lever 74 operated by the surface 72 of a cross-head 55 raised by a treadle 61 through a rod 66. When the treadle is released the cross-head rests on adjustable stops 53 on fixed studs 52. Pressure on the treadle at the same time, through a pair of spring-controlled rods 126 connected to the cross-head 55, operates bell crank levers on a shaft 109 which engage through ball joints 104 and pivoted rods 102, a pair of jaws 91, 92 so as to bend the blank into tubular form. The jaws are pivoted at 94 and the connection between the rod 126 and lever 116 of bell crank 108 has lost motion so that the jaw 91 is first actuated to bend the edge 22 on to the horn, whereupon the jaw 92 superposes the offset edge 23 thereon. The horn is provided with a U- shaped hand-operated stripper 257 engaging grooves in the horn and having stripping projections 258. Welding is effected between a fixed electrode 25 mounted in the horn and a roller electrode 26 in a cage 137 pivoted at 139 on an arm 141 projecting from a slide 142 and pressed down by spring-urged pins 155 to give the welding pressure. The roller in its lowest position is prevented from engaging the horn by engaging the heads of bolts 153 carried by the slide. Welding is effected by alternating or pulsating current, the spacing of the centres of successive spot welds being a function of the speed of traverse of the roller electrode and the frequency of the current. The slide 142 is connected by links 161, 163 to' a slide 164 traversed by a reversible electric motor through a, worm 167. The slide 164 operates a welding switch 211, 213 through a rack bar 233 carried thereby engaging a pinion 242 loosely mounted on a shaft 195 and formed on its hub with ratchet teeth 251. During the forward or operative stroke of the slide 164 the wheel 242 rotates the shaft 195 by engagement of a ratchet tooth with a spring-pressed pawl 245 on a block 243 keyed to the shaft 195. On the head 221 of the shaft is adjustably mounted a cam 222 which engages a projecting ridge 226 on the spring- closed movable arm 212 of the switch so as to separate it from the fixed contact 211. The head 221 may have a cam surface 224 to co-operate with the cam 222 to alter the length of the cam surface. The switch parts are carried by a box 191 which is angularly adjustable about the shaft 195 and secured in position by bolts 203 and arcuate slots 202. The electrodes 26, 25 are connected to the ends of the secondary of a transformer, the primary of which, containing the switch 211, 213, being connected to the source through a panel containing a contact of the kind known under the Registered Trade Mark "Thyratron." The traversing motor is put into action by a pin 284 and lever 285, which operates a further switch when the treadle is pressed. The circuit thereof contains a reversing switch.