GB947814A - Electric arc welding plant - Google Patents

Abstract

947,814. Automatic control systems for arc welding. F. HIRSCHMANN. April 13, 1962 [April 15, 1961], No. 13656/61. Heading G3R. Welding apparatus is provided with means for adjusting the voltage/current characteristic of the supply to a welding arc. As shown, a rectifier 4 is connected to the mains supply 1 over a switch 2, a transformer 3 and a transductor 5, and supplies the current to produce a welding arc between an earth 6 and a consumable electrode 7. A potentiometer 11 is connected to the mains 1 over a transformer 8, a transductor 10 and a rectifier 9, and the voltage across the potentiometer is applied, in series opposition with the output voltage of the rectifier 4, to the control winding 22 of a further transductor 20, which is connected to the mains over a transformer 26. The output from transductor 20 is applied over a rectifier 24 to the control winding 19 of transductor 5, the arrangement being such that if the voltage set on potentiometer 11 is above the output voltage of the rectifier 4, then the output from transductor 20 and current through control winding 19 are increased till the balance between the voltages is restored. Biasing windings 18, 13 and 21 for the transductors 5, 10 and 20 are supplied from the mains over a transformer 7 and rectifier 28. Transductor 10 has further control windings 14, 15, 16 which can be energized in dependence upon the load current and which can influence the voltage across potentiometer 11, thereby determining the voltage/current characteristic. The secondaries of load current transformers 31, 32, 33 are connected respectively over rectifiers 34, 35, 36 and potentiometers 37, 38, 39 to the windings 14, 15, 16, the connection to winding 14 including a Zener diode 41 and the connection to winding 15 including a capacitor 40. In operation, the output voltage of the rectifier 4 is maintained constant from low load to full load by the setting of potentiometer 11, subject to the effect of the control windings 14, 15, or 16, which effect can be zero. Potentiometer 39 can be set so that the effect of control winding 16 produces a linear falling load characteristic. Control winding 14 will be inoperative as long as the voltage taken from potentiometer 37 does not exceed the breakdown voltage of Zener diode 41; at this point, further increase in load current will cause current to flow in winding 14 whereby the output voltage from rectifier 4 will be reduced. Control winding 16 comes into operation if the arc is shortcircuited, e.g. by molten metal; the sudden increase in current will cause capacitor 40 to charge and a current flows in winding 16 again reducing the output voltage from rectifier 4.