SE357148

1,234,930. Flame cutting. TANAKA SEISAKUSHO K.K. 12 Dec., 1969 [13 Dec., 1968], No. 60768/69. Heading B3V. A non-cutting condition during a flame cutting operation is detected by detecting a change in voltage between a torch 2 and the metal 4 being cut. A relay 8 is connected across the workpiece and torch mounted on a movable trolley 12, and is arranged to close when the voltage exceeds 0À8-0À9 volts. During a normal cutting operation the voltage across the workpiece and torch is 1À2-1À8 V. so that the relay 8 is closed and power is supplied through a cable 7 to the motor or clutch of the trolley 12. If a non-cutting condition arises, the volta ge across the workpiece and torch falls to 0-0À5 V. to cause the relay 8 to open and the trolley 12 to stop. The cutting oxygen supply is switched off preferably for a predetermined period to allow the workpiece 4 to be heated further so that when the cutting oxygen supply is resumed, the cut is restarted and the voltage is raised causing the trolley 12 to be moved again. If the voltage falls to zero indicating that the flame is no longer contacting the workpiece, both the oxygen and fuel gas supplies are automatically cut off. When the torch moves off the workpiece at the end of the cut, the voltage falls to cause the relay 8 to open and the trolley 12 to stop.