Apparatus for inductor current control in electric arc welding

Claim 2

Apparatus for electric arc welding comprising a D.C. source of welding power, a fusible electrode, means for advancing said electrode towards a workpiece at a constant rate, first circuit means connecting a first terminal of said source of welding power to said electrode, second circuit means connecting a second terminal of said source of welding power to the workpiece, said first circuit means having an inductor connected in series between said first terminal and said electrode, a shunt branch connected across spaced-apart points of a winding of said inductor, said shunt branch containing a resistor in series with a half-wave rectifier poled to block a flow of current through said branch caused by the voltage induced in said winding on decrease of the welding current through said inductor, and delayed operation switching means connected in said branch responsive with a delay not less than 0.3 second to a flow of welding current for reducing the conductivity of said branch in respect of currents having the direction admitted by said halfwave rectifier from an initial level to a substantially lower level.

Claim 3

Apparatus for electric arc welding comprising a D.C. source of welding power, a fusible electrode, means for advancing said electrode towards a workpiece at a constant rate, first circuit means connecting a first terminal of said source of welding power to said electrode, second circuit means connecting a second terminal of said source of welding power to the workpiece, said first circuit means having an inductor connected in series between said first terminal and said electrode, a shunt branch connected across spaced-apart points of a winding of said inductor, said shunt branch having a resistor connected in series with a silicon controlled rectifier poled to block a flow of current through said branch caused by the voltage induced in said winding on decrease of the welding current through said inductor, a firing circuit connected between the anode lead and the gate lead of the silicon controlled rectifier for causing a firing current to flow from the anode lead through said firing circuit into said gate as soon as a positive voltage differential appears between the anode lead and the cathode lead of said silicon controlled rectifier, and means for rendering said firing circuit inoperative after a predetermined peRiod.

Claim 4

Apparatus for electric arc welding comprising a D.C. source of welding power, a fusible electrode, means for advancing said electrode towards a workpiece at a constant rate, first circuit means connecting a first terminal of said source of welding power to said electrode, second circuit means connecting a second terminal of said source of welding power to the workpiece, said first circuit means having an inductor connected in series between said first terminal and said electrode, a shunt branch connected across spaced-apart points of a winding of said inductor, said shunt branch having a resistor connected in series with a silicon controlled rectifier poled to block a flow of current through said branch caused by the voltage induced in said winding on decrease of the welding current through said inductor, a firing circuit connected between the anode lead and the gate lead of the silicon controlled rectifier for causing a firing current to flow from the anode lead through said firing circuit into said gate as soon as a positive voltage differential appears between the anode lead and the cathode lead of said silicon controlled rectifier, and means for rendering said firing circuit inoperative after a predetermined peRiod.

Claim 5

Apparatus for electric arc welding comprising a D.C. source of welding power, a fusible electrode, means for advancing said electrode towards a workpiece at a constant rate, first circuit means connecting a first terminal of said source of welding power to said electrode, a second circuit means connecting a second terminal of said source of welding power to the workpiece, said first-circuit means comprising an induction connected in series between said first terminal and said electrode, a shunt branch connected between spaced-apart points of a winding of said inductor, said shunt branch containing a resistor in series with a silicon controlled rectifier poled to block a flow of current through said branch caused by the voltage induced in said winding on decrease of the welding current flowing through said inductor, and a firing circuit for said silicon controlled rectifier comprising a capacitor, a charging resistor and a half-wave rectifier connected in series between the anode lead and the gate lead of the silicon controlled rectifier, said half-wave rectifier being poled so as to allow the flow of a positive current from said anode lead to said gate lead and said capacitor having sufficient capacity to ensure that at least two successive firing pulses are required to charge the capacitor to a voltage at which subsequent charging pulses are too weak to fire the silicon controlled rectifier.

Claim 6

Apparatus for electric arc welding comprising a D.C. source of welding power, a fusible electrode, means for advancing said electrode towards a workpiece at a constant rate, first circuit means connecting a first terminal of said source of welding power to said electrode, a second circuit means connecting a second terminal of said source of welding power to the workpiece, said first-circuit means comprising an induction connected in series between said first terminal and said electrode, a shunt branch connected between spaced-apart points of a winding of said inductor, said shunt branch containing a resistor in series with a silicon controlled rectifier poled to block a flow of current through said branch caused by the voltage induced in said winding on decrease of the welding current flowing through said inductor, and a firing circuit for said silicon controlled rectifier comprising a capacitor, a charging resistor and a half-wave rectifier connected in series between the anode lead and the gate lead of the silicon controlled rectifier, said half-wave rectifier being poled so as to allow the flow of a positive current from said anode lead to said gate lead and said capacitor having sufficient capacity to ensure that at least two successive firing pulses are required to charge the capacitor to a voltage at which subsequent charging pulses are too weak to fire the silicon controlled rectifier.

Claim 7

Apparatus as claimed in claim 3 in which the capacitor is shunted by a bleeder resistor providing discharge of the capacitor on conclusion of a welding operation.

Claim 8

Apparatus as claimed in claim 3 which further comprises a bypass resistor connected between the anode lead and the cathode lead of the silicon controlled rectifier.