Patent GB-682191-A (GB)
Title: Improvements in and relating to the electric welding of sheet-metal articles
IPC: B23K11/00
Filed: 1949-11-16
Abstract: 682,191. Welding by pressure. KREFT, H. Nov. 16, 1949, No. 29373/49. Class 83 (iv). Bending.-In welding the seams of containers or other sheet-metal articles by electric resistance welding the articles are placed between one or more pairs of electrodes extending the entire length of the seam and upon application of a predetermined pressure by the electrodes to the seam a single welding current impulse of high value and short duration is passed therebetween; the electrodes not being separated till after the current flow has ceased in order to prevent sparking. Tinned or plain metal sheets 2 fed to a die 5, where their ends are bent over in a known manner, are passed to a welding position 8 where they are bent round a mandrel 11 into an overlapping circular body form 12 by jaws 9, 10. The overlapping portion of the body 12 is compressed between an electrode 14, eccentrically mounted in the mandrel 11, and a counter-electrode 15, mounted in the end of a push-rod 16, whereupon the pushrod 16 is moved upwards by an eccentric 19. The pressure between the electrodes 14, 15 may be varied by mounting the electrode 15 in a sleeve with an adjustable spring at the end of the push-rod 16, Fig. 3 (not shown). Welding is effected by passing a current impulse between the electrodes 14, 15 when a predetermined pressure therebetween has been reached. The current impulse may be obtained from a condenser 32, Fig. 2, or from a half-wave current pulse through a gaseous discharge path 34, Fig. 4, in which current is supplied from a source 33 when electrodes 14, 15 are pressed together. A positive terminal of a condenser 36 is connected through an auxiliary gaseous discharge path 37 so that the opposed potential opposes current flow through the discharge path 34 and forces extinction of such current. A device 38 recharges the condenser 36 during the pause in current flow through the discharge path 34. In an alternative arrangement current is forced through a discharge path 40, Figs. 5 and 6, and load 45 at the instant 39. An auxiliary path 48 is activated at instant 47, when the terminal 42 of a condenser is positive, and the cathode potential 49 of the discharge path 40 is then raised from a value 51 to 50 to quench the path 40. When the electrodes 14, 15 are pressed together a strong inductive load 45 is created and the potential at terminal 49 sinks from value 50 to 56. If one weld is required for each half-wave cycle period the half wave swing 50-56 should be shorter than or equal to the time between points 47, 53. The discharge path 48 goes out after the half-wave oscillation 50-56 and the condenser 41 retains a negative potential 56 at which it has the necessary charge to effect a further welding impulse. The welding impulse in the negative half-wave cycle is initiated by the ignition of the discharge path 55 and its extinction at point 58 and this is achieved by an auxiliary discharge path 59 being ignited and its potential is brought down from the potential 57 to the value 60 so that it thus becomes more negative than the cathode of the discharge path 55 and hence the potential of the left-hand terminal of condenser 41 climbs from the value 60 in a half-wave oscillation to a point equivalent to the point 50. A direct current source may be inserted so that terminal 42 is at middle potential and the anode of valve 48 at positive potential and the cathode of 59 at negative potential. The electrodes 14, 15 are rotated a predetermined angle after each welding operation by gears 24, 25 in order to prevent localized overheating or burning. They may also be cooled by an airblast or by water supplied through tubes 26, 27 and discharged through tubes 28, 29. To prevent inductive effects, due to the looping of the lead, solid conductors 63, 64, Fig. 7, are connected to jaws 68, 69. The conductors 63, 64 are separated by a thin strip of insulation 65 and the jaws are held in contact with electrodes 66, 67 by a compression spring 70, the lower jaw 69 being pulled downwards by a tension-spring 71 attached to the machine frame.