Control for reverse-polarity welding

Claim 2

In combination: an alternating current power supply supplying welding current having a waveform with alternating straight polarity loops and reverse-polarity loops, and means for reducing the welding current during at least a portion of each of the reverse-polarity loops, said means comprising a load resistor; means for connecting said load resistor in parallel with a welding arc during said portion of each of said reversepolarity loops; said connecting means comprising means comprising switching means connected in series with said load resistor, and means including a unijunction transistOr for closing said switching means only during said reverse-polarity loop, for diverting a portion of the welding current from said welding arc to said load resistor.

Claim 3

The combination of claim 1, including means for opening said switching means during said straight-polarity loops, for reestablishing the full welding arc during said straight-polarity loop.

Claim 4

The combination of claim 1 including a timing circuit having: a timing-capacitor timing element; at least one variable timing-resistor timing element; means for serially connecting said timing capacitor and said timing resistor, said connection having a takeoff point; means for directing electric current to flow through said serially connected timing elements, for causing the potential at said takeoff point to change in a manner controlled by the values of said timing elements; a unijunction transistor; a connection from said takeoff point to the base electrode of said unijunction transistor-whereby said changing potential at said takeoff point may activate said transistor; and connecting means connected between said transistor and said switching means for causing said transistor, when activated, to produce a trigger signal for closing said switching means.

Claim 5

In combination: an alternating current power supply supplying welding current having a waveform with alternate straight-polarity loops and reverse-polarity loops applied across a gap formed between an electrode and workpiece to produce a welding arc; first means for producing an initiating signal at each change of polarity loops of said waveform; second means for producing the welding current during at least a portion of each of the reverse-polarity loops, said second means comprising a load resistor; and connecting means for temporarily connecting said load resistor in parallel with said welding arc during said portion of each said reverse-polarity loops; said connecting means comprising switching means connected in series with said load resistor, and closing means-activated by said initiating signal-for closing said switching means only during said reverse-polarity loops, for diverting a portion of the welding current from said welding arc to said load resistor; said closing means comprising a timing circuit; means for causing said initiating signals to produce a control signal; and means for applying said control signal to said timing circuit, causing said timing circuit to produce a delayed trigger signal for closing said switching means; and means-activated by said initiating signal-for opening said switching means during each of said straight-polarity loops, for reestablishing the full welding arc during each of said straight-polarity loops.

Claim 6

In combination: an alternating current power supply supplying welding current having a waveform with alternate straight-polarity loops and reverse-polarity loops applied across a gap formed between an electrode and workpiece to produce a welding arc; first means for producing an initiating signal at each change of polarity loops of said waveform; second means for producing the welding current during at least a portion of each of the reverse-polarity loops, said second means comprising a load resistor; and connecting means for temporarily connecting said load resistor in parallel with said welding arc during said portion of each said reverse-polarity loops; said connecting means comprising switching means connected in series with said load resistor, and closing means-activated by said initiating signal-for closing said switching means only during said reverse-polarity loops, for diverting a portion of the welding current from said welding arc to said load resistor; said closing means comprising a timing circuit; means for causing said initiating signals to produce a control signal; and means for applying said control signal to said timing circuit, causing said timing circuit to produce a delayed trigger signal for closing said switching means; and means-activated by said initiating signal-for opening said switching means during each of said straight-polarity loops, for reestablishing the full welding arc during each of said straight-polarity loops.

Claim 7

The combination comprising: first means for producing alternating current whose current waveform has alternate straight-polarity loops and reverse-polarity loops; second means for producing an initiating signal at each change of polarity of said waveform; third means for applying the alternating current across an electrode/workpiece gap to produce a welding arc; fourth means for reducing the current during at least a portion of each of the reverse-polarity loops; said fourth means comprising a load resistor; and connecting means for temporarily connecting said load resistor in parallel with said welding arc during said portion of each of said reverse-polarity loops; said connecting means comprising switching means connected in series with said load resistor; and closing means-activated by said initiating signal-for closing said switching means only during each of said reverse-polarity loops, for diverting a portion of the current from said welding arc to said load resistor; said closing means comprising a flip-flop circuit; means for causing said initiating signals to control the state of said flip-flop circuits; means for causing a given state of said flip-fLop circuit to produce a control signal; and a timing circuit; said timing circuit having: a timing-capacitor timing element; at least one variable timing-resistor timing element; means for serially connecting said timing capacitor and said timing resistor, said connection having a takeoff point; means for directing said control signal from said flip-flop to flow through said serially connected timing elements, for causing the potential at said takeoff point to change in a manner controlled by the values of said timing elements; a unijunction transistor; a connection from said takeoff point to the base electrode of said unijunction transistor-whereby said changing potential at said takeoff point may activate said transistor; and connecting means connected between said transistor and said switching means for causing said unijunction transistor, when activated, to produce a trigger signal for closing said switching means at a given instant in correspondence with the start of each of said reverse-polarity loops; and fifth means-activated by said initiating signal-for opening said switching means at a given instant in correspondence with the start of each of said straight-polarity loops.

Claim 8

The combination comprising: first means for producing alternating current whose current waveform has alternate straight-polarity loops and reverse-polarity loops; second means for producing an initiating signal at each change of polarity of said waveform; third means for applying the alternating current across an electrode/workpiece gap to produce a welding arc; fourth means for reducing the current during at least a portion of each of the reverse-polarity loops; said fourth means comprising a load resistor; and connecting means for temporarily connecting said load resistor in parallel with said welding arc during said portion of each of said reverse-polarity loops; said connecting means comprising switching means connected in series with said load resistor; and closing means-activated by said initiating signal-for closing said switching means only during each of said reverse-polarity loops, for diverting a portion of the current from said welding arc to said load resistor; said closing means comprising a flip-flop circuit; means for causing said initiating signals to control the state of said flip-flop circuits; means for causing a given state of said flip-fLop circuit to produce a control signal; and a timing circuit; said timing circuit having: a timing-capacitor timing element; at least one variable timing-resistor timing element; means for serially connecting said timing capacitor and said timing resistor, said connection having a takeoff point; means for directing said control signal from said flip-flop to flow through said serially connected timing elements, for causing the potential at said takeoff point to change in a manner controlled by the values of said timing elements; a unijunction transistor; a connection from said takeoff point to the base electrode of said unijunction transistor-whereby said changing potential at said takeoff point may activate said transistor; and connecting means connected between said transistor and said switching means for causing said unijunction transistor, when activated, to produce a trigger signal for closing said switching means at a given instant in correspondence with the start of each of said reverse-polarity loops; and fifth means-activated by said initiating signal-for opening said switching means at a given instant in correspondence with the start of each of said straight-polarity loops.

Claim 9

Welding apparatus comprising: electrode means for establishing a weld arc with a workpiece; a power supply for applying current across the arc alternately in forward- and reverse-polarity increments; delay means; means, responsive to start of the reverse-polarity increment, for actuating the delay means; means, responsive to termination of the period established by the delay means, for attenuating the reverse-polarity current increment, so that the period of said delay means is considerably less than one-half duration of the reverse-polarity current increment.

Claim 10

Welding apparatus comprising: electrode means for establishing a weld arc with a workpiece; a power supply for applying current across the arc alternately in forward- and reverse-polarity increments; delay means; means, responsive to start of the reverse-polarity increment, for actuating the delay means; means, responsive to termination of the period established by the delay means, for attenuating the reverse-polarity current increment, so that the period of said delay means is considerably less than one-half duration of the reverse-polarity current increment.