GB1310157A - Method and apparatus for welding - Google Patents

Abstract

1310157 Control systems for resistance welding POWER CONTROL CORP 8 April 1970 16755/70 Heading H2H [Also in Division B3] In resistance seam welding, particularly of the overlapped edges 12 of can bodies 10 traversed relative to a pair of electrodes 14, 16, a steady state direct current is passed between the electrodes 14, 16 the magnitude of the current being sufficient to raise the temperature of the edges to a point slightly below the melting point, and current pulses are superimposed on the steady state current, of sufficient magnitude to raise the temperature of the metal to its melting point thus producing along the seam a line of contiguous spot welds. The welding electrode may comprise a pair of wheels, one of which, 16 is mounted on a mandrel around which the can bodies are formed. In a suitable electric circuit a threephase source 24 is connected through a variable controller 26 and threephase transformer 28 to a rectifier 20 the output of which is smoothed by a capacitor 22 and applied as a steady D.C. voltage to the electrodes 14, 16. The circuit also includes an inverter 30 of the semi-conductive-controlled rectifier type controlled by a firing circuit 32, the inverter converting the D.C. output from a rectifier 34 into a square wave output. This output is applied through transformer 36 to a circuit 38 comprising a pair of silicon controlled rectifiers 40, 42 having their anodes connected to the ends of the secondary winding of transformer 36 and their cathodes connected to the upper electrode 14. The lower electrode 16 is connected to a centre tapping on the secondary winding. A firing circuit 44 controls the point at which the rectifiers 40, 42 fire thereby controlling the power applied to the electrodes. The frequency of the output of the circuit 38 is double that of the inventor 30. An inductive choke 18 isolates the rectifier 20 from the high frequency pulse output and diodes 46, 47 serve to prevent arcing between the electrodes 14, 16 when the latter leave the end of a can body. In an alternative method an alternating current is superimposed on the steady-state direct current.