GB708747A - Improvements in or relating to welding control arrangements - Google Patents

Abstract

708,747. Control systems for resistance welding. STANDARD TELEPHONES & CABLES, Ltd. Aug. 8, 1952 [Aug. 10, 1951], No. 18859/51. Class 38(4) A control system for a plurality of welding machines comprises a control relay CR for each machine and one or more insulating rotors 1 which are driven at uniform speed (preferably synchronously with the A.C. supplying the machines) and are provided on their surface with conducting areas 2-13 co-operating with a number of sets of brushes equal to the number of machines to be controlled by each rotor. Each set of brushes comprises brushes 14-16, Fig. 2, which co-operate with conducting areas 4-6, respectively, to control the relay CR, and brushes 17, 18 which co-operate with conductive areas 2, 9 (or 12) to control the primary circuit of the welding transformer WT. To reduce sparking at the power supply circuit brush 18 as it engages and leaves the conductive areas 9, 12, these are connected to the auxiliary areas 8, 10 and 11, 13 (each of half a cycle length) by resistors, so that the main current is established and interrupted in two steps. To effect a weld, the operator changes over switch FS so that the relay-picks up by the charging current of condenser C1 when conductive area 4 engages brush 14 and is subsequently held in by current through resistor R1, conductive area 5 and brush 16, the relay falling out when area 5 leaves brush 16. The welding transformer is energized over relay contacts CR<SP>1</SP> and brushes 17, 18 during the period that the relay is energized. To allow adjustment of the welding period, the main conductive areas 9, 12 may comprise a number of smaller sections, any number of which may be connected in series. Resistor R<SP>2</SP> ensures discharge of condenser C<SP>1</SP> when switch FS is released.