Plasma arc torch interlock with disabling control arrangement system

• US 4,929,811 A
• Filed: 12/05/1988
• Issued: 05/29/1990
• Est. Priority Date: 12/05/1988
• Status: Expired due to Term

• Current Assignee: Lincoln Global Incorporated (Lincoln Electric Holdings Incorporated)
• Original Assignee: Lincoln Electric Company (Lincoln Electric Holdings Incorporated)
• Inventors: Blankenship, George D.
• Primary Examiner(s): Paschall, M. H.
• Application Number:
  US07/280,240
• Time in Patent Office: 540 Days
• Field of Search: 219/121.54, 219/121.52, 219/121.57, 219/121.59, 219/124.01, 219/130.32, 219/130.4
• US Class Current: 219/121.54
• CPC Class Codes: H05H 1/34 Details, e.g. electrodes, nozzles
• CPC Class Codes: H05H 1/3436 Hollow cathodes with internal coolant flow
• CPC Class Codes: H05H 1/3473 Safety means
• CPC Class Codes: H05H 1/36 Circuit arrangements H05H1/38, H05H1/40 take precedence

Abstract

A plasma arc torch system includes a fault detect circuit for sensing a short between the electrode and the nozzle and disabling the power supply when the short is sensed. A sensing circuit within the torch cable is provided for actuating the fault detect circuit when the cable is severely punctured. The sensing circuit includes a foil embedded within the cable which circumscribes the main conductor to which a drain lead is connected. The drain lead senses a short between the foil and main conductor from a penetrating foreign object and actuates the fault detect circuit. Additionally, the fault detect circuit is effective in combination with a unique continuity interlock circuit disclosed to insure a safe torch. Further, a rectified control circuit is provided to maintain a stable arc preventing erosion of the nozzle and subsequent exposure of the electrode.

Claims

1. A plasma arc torch system for effecting various metal processes on a workpiece comprising:

an electrical power source;

a gas supply source for generating a plasma;

a torch body including an electrode and an insulated, electrically conductive nozzle assembly circumscribing said electrode at a fixed distance therefrom;

fault detect circuit means including a pilot arc lead connected to the nozzle assembly at one end and at its other end to ground for sensing a short circuit between said nozzle assembly and said electrode and disabling said power source in response thereto;

a cable connected to said torch body, a main electrical conductor within said cable connected at one end to said electrode and at its other end to said power source; and

sensing means within said cable detecting a puncture of the cable sufficient to contact said main conductor and in response to said contact actuating said fault detect circuit means to disable said power source;

said sensing means including a continuous, electrically conductive shield circumscribing the main conductor and a drain lead in electrical contact with said shield and said pilot arc lead so that a short between the drain lead and main conductor will be sensed and conveyed to pilot arc lead to actuate said fault detect circuit means.

2. The plasma arc torch system of claim 1 wherein said torch body includes a pilot arc contact wire in electrical contact with said nozzle assembly and said drain lead, a pilot arc switch, a pilot arc lead connected to said fault detect circuit means and said pilot arc switch and said pilot arc contact wire, a main power switch between said electrode and said power source, said fault detect circuit means actuated when said pilot arc switch and said main power switch are activated to establish a pilot arc between said nozzle assembly and said electrode and a predetermined voltage measured relative to said pilot arc lead is exceeded.

3. The plasma arc torch system of claim 2 wherein said fault detect circuit is effective to disable said power source when said pilot arc switch is open and when said sensing means is activated.

4. The plasma arc torch system of claim 2 wherein said electrode is a cathode, said workpiece represents ground potential, said power source supplies a d.c. voltage of about 250-350 volts to said electrode, said pilot arc switch connected to said ground potential and said predetermined value is the voltage sensed between said pilot arc lead relative to said ground potential.

5. The plasma arc torch system of claim 4 wherein said predetermined value is not less than about 66 volts and not more than about 250 volts.

6. The plasma arc torch system of claim 5 wherein said cable has a generally cylindrical outer jacket of an insulating, pliable plastic material;

said shield comprises a metal foil embedded in said jacket;

said drain lead comprises a bare wire extending the length of said cable and in contact with said foil;

said main conductor contained in an insulated, plastic coating so that said outer jacket must be initially pierced and said coating must be subsequently punctured by an electrically conductive object extending therebetween before said sensing means is actuated.

7. The plasma arc torch system of claim 1 wherein said nozzle assembly includes a generally cylindrical nozzle sleeve member within said torch body and a cup shaped tip member adapted to be threadingly secured to said nozzle body, said drain lead affixed as a pilot arc wire contact to said nozzle sleeve body member;

a continuity lead within said torch body, a continuous circuit source of electrical power connected to said continuity lead, said cup shaped tip member when properly fastened to said body establishing an electrical connection therethrough from said continuity lead to said drain lead and continuity circuit means measuring continuity between said continuity lead and said pilot arc wire contact so that in response to a lack of continuity therebetween said main power source is disabled.

8. The plasma arc torch system of claim 7 wherein said nozzle sleeve member has an annular contact ring portion protruding from the torch body with an internally threaded central opening and a generally flat face surface, and a cylindrical base portion extending from the opposite side of said ring portion and fixedly secured within said torch body, said ring portion having an electrically insulated segment formed therein and a groove within said insulated segment, said continuity lead in the form of a continuity spring wire contact extending within said groove and protruding beyond said face of said base portion when said nozzle assembly is in an unassembled position, and

said nozzle cup shaped tip member having an annular contact base surface and an externally threaded sleeve extending from said contact surface and adapted to be threadingly engaged with said internally threaded central opening of said nozzle sleeve member whereby said contact base surface seats against said flat face surface and moves said continuity spring wire contact within said groove when said cup shaped tip is properly secured to said nozzle body member, thereby establishing continuity for measurement by said continuity circuit means.

9. The plasma arc torch system of claim 8 further including a gas conduit within said torch body, a gas distributor block in fluid communication at one end with the outlet of said gas conduit and positioned within said cylindrical base portion of said nozzle sleeve member, an insulating annular seating ring member between said gas distributor and said ring portion of said nozzle sleeve member electrically isolating said gas distributor from said nozzle sleeve member, said gas distributor having a base with an internally threaded opening adjacent said ring portion;

said electrode having a cylindrical body portion with a rounded end, an annular shoulder at one end of said cylindrical body portion and an externally threaded end extending from said shoulder, said externally threaded end of said electrode threadingly engaged with said internally threaded opening of said gas distributor;

said cup shaped nozzle tip member internally configured to closely match said cylindrical body portion of said electrode to define an electrode spark space therebetween, said space gradually increasing to a maximum spark distance at a point generally adjacent said rounded end of said electrode'"'"'s cylindrical body portion and having a nozzle orifice centrally positioned therein;

said insulating seating ring having gas passages in fluid communication with said electrode spark space;

said gas distributor block having gas passages in communication with said gas conduit and a space between said gas distributor block and said cylindrical base portion of said nozzle sleeve member whereby an ionizable gas is injected through said orifice.

10. The plasma arc torch system of claim 9 further including a gas cooling cup circumscribing a portion of said nozzle cup shaped tip member and sealing means to secure said cup to said torch body;

said ring portion of said nozzle sleeve member having at least one gas passage in fluid communication with a space between said cooling cup and said nozzle cup shaped tip member whereby a portion of the gas leaving said gas conduit is directed against said nozzle cup shaped tip member for focusing gas into the cut zone of the work for removing melted metal while also incidentally cooling said nozzle cup shaped tip member.

11. The plasma arc torch system of claim 1 further including

rectifying means to generate a series of d.c. electrical pulses applied to said electrode;

switch means to initiate a pilot arc between said nozzle and said electrode during start-up of said torch system which is transferred to said workpiece as a plasma arc during normal operation of said plasma arc torch system;

triggering means to vary the phase angle of said pulses from one value when said pilot arc is established to a second value when said plasma arc is established;

means to sense the current in each electrical pulse during the formation of a pilot arc and in response to a pulse exceeding a predetermined current value, at the moment said pilot arc is transferred to said plasma arc, to actuate said triggering means to reduce the phase angle of said pilot arc pulses.

12. The plasma arc torch system of claim 11 further including stabilizing means to sustain said plasma arc when said sensing means actuates said triggering means to reduce the phase angle of said pilot arc pulses.

13. The plasma arc torch system of claim 12 wherein said rectifier means which generate said electrical pulses includes a three-phase a.c. power supply, a transformer associated with each of said phases and a rectifying bridge circuit including controlled rectifiers, the input of said rectifying circuit being connected to the secondary circuit of said transformer and the output of said rectifying circuit providing direct operating voltage between said electrode and said workpiece;

said triggering means including means to control the degree of rectification of said rectifying circuit in response to actuation of said switch means.

14. The plasma arc torch system of claim 13 wherein said stabilizing means includes a capacitor in series with a diode for charging thereof and a resistor in parallel with said diode for discharging said capacitor, said capacitor of sufficient size to provide sufficient current to sustain said pilot arc for about 12 milliseconds.

15. The plasma arc torch system of claim 14 wherein said triggering means to vary the phase angle retards the rectification of said electrical pulses in said plasma arc mode by about 25°

.

16. The plasma arc torch system of claim 12 wherein said rectifier means which generate said electrical pulses includes a three-phase a.c. power supply, a transformer associated with each of said phases and a rectifying bridge circuit including controlled rectifiers, the input of said rectifying circuit being connected to the secondary circuit of said transformer and the output of said rectifying circuit providing direct operating voltage between said electrode and said workpiece;

said triggering means including means to control the degree of rectification of said rectifying circuit in response to actuation of said switch means.

17. The plasma arc torch system of claim 7 further including

rectifying means to generate a series of d.c. electrical pulses applied to said electrode;

switch means to initiate a pilot arc between said nozzle and said electrode during start-up of said torch system which is transferred to said workpiece as a plasma arc during normal operation of said plasma arc torch system;

triggering means to vary the frequency and current of said pulses from one value when said pilot arc is established to a second value when said plasma arc is established;

means to sense the current in each electrical pulse during the formation of a pilot arc and in response to a pulse exceeding a predetermined current value, at the moment said pilot arc is transferred to said plasma arc, to actuate said triggering means to reduce the phase angle of said pilot arc pulses.

18. The plasma arc torch system of claim 17 further including stabilizing means to sustain said plasma arc when said sensing means actuates said triggering means to reduce the phase angle of said pilot arc pulses.

19. The plasma arc torch system of claim 17 wherein said rectifier means which generate said electrical pulses includes a three-phase a.c. power supply, a transformer associated with each of said phases and a rectifying bridge circuit including controlled rectifiers, the input of said rectifying circuit being connected to the secondary circuit of said transformer and the output of said rectifying circuit providing direct operating voltage between said electrode and said workpiece;

said triggering means including means to control the degree of rectification of said rectifying circuit in response to actuation of said switch means.

20. The plasma arc torch system of claim 19 wherein said stabilizing means includes a capacitor in series with a diode for charging thereof and a resistor in parallel with said diode for discharging said capacitor, said capacitor of sufficient size to provide sufficient current to sustain said pilot arc for 12 milliseconds.

21. The plasma arc torch system of claim 20 wherein said triggering means to vary the phase angle retards the rectification of said electrical pulses in said plasma arc mode by about 25°

.

22. The plasma arc torch system of claim 18 wherein said rectifier means which generate said electrical pulses includes a three-phase a.c. power supply, a transformer associated with each of said phases and a rectifying bridge circuit including controlled rectifiers, the input of said rectifying circuit being connected to the secondary circuit of said transformer and the output of said rectifying circuit providing direct operating voltage between said electrode and said workpiece;

said triggering means including means to control the degree of rectification of said rectifying circuit in response to actuation of said switch means.

23. The plasma arc torch system of claim 1, wherein said drain lead comprises a bare wire extending the length of said cable and in contact with said foil.

24. A plasma arc torch system for effecting various metal processes on a workpiece comprising:

an electrical power source;

a gas supply source for generating a plasma;

a torch body including an electrode and an electrically conductive nozzle assembly circumscribing said electrode at a fixed distance therefrom;

fault detect circuit means for sensing a short circuit between said nozzle assembly and said electrode and disabling said power source in response thereto;

a cable connected to said torch body, a main electrical conductor within said cable connected at one end to said electrode and at its other end to said power source;

sensing means within said cable detecting a puncture of the cable sufficient to contact said main conductor and in response to said contact actuating said fault detect circuit means to disable said power source;

said sensing means includes a continuous, electrically conductive shield comprised of a metal foil embedded in said cable and circumscribing said main conductor and extending the length of said cable; and

a drain lead in electrical contact with said shield and said nozzle assembly, said sensing means actuated when any electrically conductive object punctures said shield and contacts said main conductor thus establishing a short circuit between said electrode and said nozzle;

said cable has a generally cylindrical outer jacket of an insulating, pliable plastic material;

said shield comprises a metal foil embedded in said jacket;

said drain lead comprises a bare wire extending the length of said cable and in contact with said foil;

said main conductor contained in an insulated, plastic coating so that said outer jacket must be initially pierced and said coating must be subsequently punctured by an electrically conductive object extending therebetween before said sensing means is actuated.

25. In a plasma arc torch system including an electrical power source, a torch body having an electrode and an insulated, electrically conductive nozzle assembly circumscribing said electrode at a fixed distance therefrom, a fault detect circuit means including a pilot arc lead connected to the nozzle assembly at one end and at its other end to ground for sensing a short circuit between said nozzle assembly and said electrode and disabling said power source in response to a short detected thereby;

and a disabling mechanism comprising;

a cable connected to said torch body, a main electrical conductor within said cable connected at one end to said electrode and at its other end to said power source; and

sensing means within said cable detecting a puncture of the cable sufficient to contact said main conductor and in response to said contact actuating said fault detect circuit means to disable said power source, said sensing including a continuous, electrically conductive shield circumscribing the main conductor and a drain lead in electrical contact with said shield and said pilot arc lead so that a short between the drain lead and main conductor will be sensed and conveyed to said pilot arc lead to actuate said fault detect circuit means.

26. The plasma arc torch system of claim 25 wherein said torch body includes a pilot arc contact wire in electrical contact with said nozzle assembly and said drain lead, a pilot arc switch, a pilot arc lead connected to said fault detect circuit means and said pilot arc switch and said pilot arc contact wire, a main power switch between said electrode and said power source, said fault detect circuit means actuated when said pilot arc switch and said main power switch are activated to establish a pilot arc between said nozzle assembly and said electrode and a predetermined voltage measured relative to said pilot arc lead is exceeded for a given time period, said electrode is a cathode, said workpiece represents ground potential, said power source supplies a d.c. voltage of about 250-350 volts to said electrode, said pilot arc switch connected to said ground potential and said predetermined value is the voltage sensed between said pilot arc lead relative to said ground potential and said predetermined value is not less than about 66 volts and not more than about 250 volts.

27. The plasma arc torch system of claim 25 wherein said nozzle assembly includes a generally cylindrical nozzle sleeve member within said torch body and a cup shaped tip member adapted to be threadingly secured to said nozzle body, said drain lead affixed as a pilot arc wire contact to said nozzle sleeve body member;

said torch further includes a continuity lead within said torch body, a continuous circuit source of electrical power connected to said continuity lead, said cup shaped tip member when properly fastened to said body establishing an electrical connection therethrough from said continuity lead to said drain lead and continuity circuit means measuring continuity between said continuity lead and said pilot arc wire contact so that in response to a lack of continuity therebetween said main power source is disabled.

28. The plasma arc torch system of claim 27 wherein said nozzle sleeve member has an annular contact ring portion protruding from the torch body with an internally threaded central opening and a generally flat face surface, and a cylindrical base portion extending from the opposite side of said ring portion and fixedly secured within said torch body, said ring portion having an electrically insulated segment formed therein and a groove within said insulated segment, said continuity lead in the form of a continuity spring wire contact extending within said groove and protruding beyond said face of said base portion when said nozzle assembly is in an unassembled position, and

said nozzle cup shaped tip member having an annular contact base surface and an externally threaded sleeve extending from said contact surface and adapted to be threadingly engaged with said internally threaded central opening of said nozzle sleeve member whereby said contact base surface seats against said flat face surface and moves said continuity spring wire contact within said groove when said cup shaped tip is properly secured to said nozzle body member, thereby establishing continuity for measurement by said continuity circuit means.

29. The plasma arc torch system of claim 28 further including a gas conduit within said torch body, a gas distributor block in fluid communication at one end with the outlet of said gas conduit and positioned within said cylindrical base portion of said nozzle sleeve member, an insulating annular seating ring member between said gas distributor and said ring portion of said nozzle sleeve member electrically isolating said gas distributor from said nozzle sleeve member, said gas distributor having a base with an internally threaded opening adjacent said ring portion;

said electrode having a cylindrical body portion with a rounded end, an annular shoulder at one end of said cylindrical body portion and an externally threaded end extending from said shoulder, said externally threaded end of said electrode threadingly engaged with said internally threaded opening of said gas distributor;

said cup shaped nozzle tip member internally configured to closely match said cylindrical body portion of said electrode to define an electrode spark space therebetween, said space gradually decreasing to a minimum spark distance at a point generally adjacent said rounded end of said electrode'"'"'s cylindrical body portion and having a nozzle orifice centrally positioned therein;

said insulating seating ring having gas passages in fluid communication with said electrode spark space;

said gas distributor block having gas passages in communication with said gas conduit and a space between said gas distributor block and said cylindrical base portion of said nozzle sleeve member whereby an ionizable gas is injected through said orfice.

30. The plasma arc torch system of claim 29 further including a gas cooling cup circumscribing a portion of said nozzle cup shaped tip member and sealing means to secure said cup to said torch body;

said ring portion of said nozzle sleeve member having at least one gas passage in fluid communication with a space between said cooling cup and said nozzle cup shaped tip member whereby a portion of the gas leaving said gas conduit is directed against said nozzle cup shaped tip member for focusing gas into the cut zone of the work for removing melted metal while also incidentally cooling said nozzle cup shaped tip member.

31. The plasma arc torch system of claim 25 further including

rectifying means to generate a series of d.c. electrical pulses applied to said electrode;

switch means to initiate a pilot arc between said nozzle and said electrode during start-up of said torch system which is transferred to said workpiece as a plasma arc during normal operation of said plasma arc torch system;

triggering means to vary the phase angle and current of said pulses from one value when said pilot arc is established to a second value when said plasma arc is established;

means to sense the current in each electrical pulse during the formation of a pilot arc and in response to a pulse exceeding a predetermined current value, at the moment said pilot arc is transferred to said plasma arc, to actuate said triggering means to reduce the phase angle of said pilot arc pulses.

32. The plasma arc torch system of claim 31 wherein said rectifier means which generate said electrical pulses includes a three-phase a.c. power supply, transformer associated with each of said phases and a rectifying bridge circuit including controlled rectifiers, the input of said rectifying circuit being connected to the secondary circuit of said transformer and the output of said rectifying circuit providing direct operating voltage between said electrode and said workpiece;

said triggering means including means to control the degree of rectification of said rectifying circuit in response to actuation of said switch means; and

further including stabilizing means to sustain said plasma arc when said sensing means actuates said triggering means to reduce the phase angle of said pilot arc pulses.

33. The plasma arc torch system of claim 32 wherein said stabilizing means includes a capacitor in series with a diode for charging thereof and a resistor in parallel with said diode for discharging said capacitor, said capacitor of sufficient size to provide sufficient current to sustain said pilot arc for about 12 milliseconds, and said triggering means to vary the phase angle retards the rectification of said electrical pulses in said plasma arc mode by about 25°

.

34. The plasma arc torch system of claim 27 further including

rectifying means to generate a series of d.c. electrical pulses applied to said electrode;

switch means to initiate a pilot arc between said nozzle and said electrode during start-up of said torch system which is transferred to said workpiece as a plasma arc during normal operation of said plasma arc torch system;

triggering means to vary the phase angle and current of said pulses from one value when said pilot arc is established to a second value when said plasma arc is established;

means to sense the current in each electrical pulse during the formation of a pilot arc and in response to a pulse exceeding a predetermined current value, at the moment said pilot arc is transferred to said plasma arc, to actuate said triggering means to reduce the phase angle of said pilot arc pulses.

35. The plasma arc torch system of claim 34 wherein said rectifier means which generate said electrical pulses includes a three-phase a.c. power supply, a transformer associated with each of said phases and a rectifying bridge circuit including controlled rectifiers, the input of said rectifying circuit being connected to the secondary circuit of said transformer and the output of said rectifying circuit providing direct operating voltage between said electrode and said workpiece;

said triggering means including means to control the degree of rectification of said rectifying circuit in response to actuation of said switch means; and

further including stabilizing means to sustain said plasma arc when said sensing means actuates said triggering means to reduce the phase angle of said pilot arc pulses.

36. The plasma arc torch system of claim 35 wherein said stabilizing means includes a capacitor in series with a diode for charging thereof and a resistor in parallel with said diode for discharging said capacitor, said capacitor of sufficient size to provide sufficient current to sustain said pilot arc for about 12 milliseconds, and said triggering means to vary the phase angle retards the rectification of said electrical pulses in the phase angle plasma arc mode by about 25°

.

37. The plasma arc torch system of claim 25, wherein said drain lead comprises a bare wire extending the length of said cable and in contact with said foil.

38. A plasma arc torch system including an electrical power source, a torch body having an electrode and an electrically conductive nozzle assembly circumscribing said electrode at a fixed distance therefrom, a fault detect circuit means for sensing a short circuit between said nozzle assembly and said electrode and disabling said power source in response to a short detected thereby;

and a disabling mechanism comprising;

a cable connected to said torch body, a main electrical conductor within said cable connected at one end to said electrode and at its other end to said power source;

sensing means within said cable detecting a puncture of the cable sufficient to contact said main conductor and in response to said contact actuating said fault detect circuit means to disable said power source;

said sensing means includes a continuous, electrically conductive shield embedded in said cable and circumscribing said main conductor and extending the length of said cable;

a drain lead in electrical contact with said shield and said nozzle assembly, said sensing means actuated when any electrically conductive object punctures said shield and contacts said main conductor to establish a short circuit between said electrode and said nozzle to actuate said fault detect circuit means;

said cable has a generally cylindrical outer jacket of an insulating, pliable plastic material;

said shield comprises a metal foil embedded in said jacket;

said drain lead comprises a bare wire extending the length of said cable and in contact with said foil;

said main conductor contained in an insulated, plastic coating so that said outer jacket must be initially pierced and said coating must be subsequently punctured by an electrically conductive object extending therebetween before said sensing means is actuated.

39. A plasma arc torch system for effecting various processes on a metal workpiece comprising

an electrical power source;

a gas supply source for generating a plasma;

a torch body including an electrode connected to said main power source and an insulated, electrically conductive nozzle assembly circumscribing said electrode;

fault detect circuit means for sensing a short circuit between said nozzle assembly and said electrode and disabling said power source in response thereto;

a pilot arc contact wire in electrical contact with said nozzle assembly, a pilot arc switch, a pilot arc lead connected to said fault detect circuit means and said pilot arc switch, a pilot arc lead connected to said fault detect circuit means and said pilot arc switch, a main power switch between said electrode and said power source, said fault detect circuit means actuated when said pilot arc switch and said main power switch are actuated to establish a pilot arc between said nozzle assembly and said electrode a predetermined voltage measure relative to said pilot arc lead is exceeded;

said nozzle assembly includes a generally cylindrical nozzle sleeve member within said torch body and a cup shaped tip member adapted to be threadingly secured to said nozzle body, as a pilot arc wire contact;

a continuity lead within said torch body, a continuous circuit source of electrical power connected to said continuity lead, said cup shaped tip member when properly fastened to said body establishing an electrical connection therethrough from said continuity lead to said drain lead and continuity circuit means measuring continuity between said continuity lead and said pilot arc wire contact so that in response to a lack of continuity therebetween said main power source is disabled whereby said torch is rendered safe at all times.

40. The plasma arc torch system of claim 39 wherein said nozzle sleeve member has an annular contact ring portion protruding from the torch body with an internally threaded central opening and a generally flat face surface, and a cylindrical base portion extending from the opposite side of said ring portion and fixedly secured within said torch body, said ring portion having an electrically insulated segment formed therein and a groove within said insulated segment, said continuity lead in the form of a continuity spring wire contact extending within said groove and protruding beyond said face of said base portion when said nozzle assembly is in an unassembled position, and

said nozzle cup shaped tip member having an annular contact base surface and an externally threaded sleeve extending from said contact surface and adapted to be threadingly engaged with said internally threaded central opening of said nozzle sleeve member whereby said contact base surface seats against said flat face surface and moves said continuity spring wire contact within said groove when said cup shaped tip is properly secured to said nozzle body member, thereby establishing continuity for measurement by said continuity circuit means.

41. The plasma arc torch system of claim 40 further including

rectifying means to generate a series of d.c. electrical pulses applied to said electrode;

switch means to initiate a pilot arc between said nozzle and said electrode during start-up of said torch system which is transferred to said workpiece as a plasma arc during normal operation of said plasma arc torch system;

triggering means to vary the frequency and current of said pulses from one value when said pilot arc is established to a second value when said plasma arc is established;

means to sense the current in each electrical pulse during the formation of a pilot arc and in response to a pulse exceeding a predetermined current value, at the moment said pilot arc is transferred to said plasma arc, to actuate said triggering means to reduce the phase angle of said pilot arc pulses; and

stabilizing means to sustain said plasma arc when said sensing means actuates said triggering means to reduce the phase angle of said pilot arc pulses.

42. The plasma arc torch system of claim 41 wherein said rectifier means which generate said electrical pulses includes a three-phase a.c. power supply, a transformer associated with each of said phases and a rectifying bridge circuit including controlled rectifiers, the input of said rectifying circuit being connected to the secondary circuit of said transformer and the output of said rectifying circuit providing direct operating voltage between said electrode and said workpiece;

said triggering means including means to control the degree of rectification of said rectifying circuit in response to actuation of said switch means; and

stabilizing means includes a capacitor in series with a diode for charging thereof and a resistor in parallel with said diode for discharging said capacitor, said capacitor of sufficient size to provide sufficient current to sustain said pilot arc for about 12 milliseconds.

43. A plasma arc torch system for effecting various processes on a metal workpiece comprising

an electrical power source;

a gas supply source for generating a plasma;

a torch body including an electrode connected to said main power source and an insulated, electrically conductive nozzle assembly circumscribing said electrode;

fault detect circuit means for sensing a short circuit between said nozzle assembly and said electrode and disabling said power source in response thereto;

rectifying means to generate a series of d.c. electrical pulses applied to said electrode;

switch means to initiate a pilot arc between said nozzle and said electrode during start-up of said torch system which is transferred to said workpiece as a plasma arc during normal operation of said plasma arc torch system;

triggering means to vary the phase angle and current of said pulses from one value when said pilot arc is established to a second value when said plasma arc is established;

means to sense the current in each electrical pulse during the formation of a pilot arc and in response to a pulse exceeding a predetermined current value, at the moment said pilot arc is transferred to said plasma arc, to actuate said triggering means to reduce the phase angle of said pilot arc pulses.

44. The plasma arc torch system of claim 43 further including stabilizing means to sustain said plasma arc when said sensing means actuates said triggering means to reduce the phase angle of said pilot arc pulses.

45. The plasma arc torch system of claim 44 wherein said rectifier means which generate said electrical pulses includes a three-phase a.c. power supply, a transformer associated with each of said phases and a rectifying bridge circuit including controlled rectifiers, the input of said rectifying circuit being connected to the secondary circuit of said transformer and the output of said rectifying circuit providing direct operating voltage between said electrode and said workpiece;

said triggering means including means to control the degree of rectification of said rectifying circuit in response to actuation of said switch means.

46. The plasma arc torch system of claim 45 wherein said stabilizing means includes a capacitor in series with a diode for charging thereof and a resistor in parallel with said diode for discharging said capacitor, said capacitor of sufficient size to provide sufficient current to sustain said pilot arc for about 12 milliseconds.

47. The plasma arc torch system of claim 46 wherein said triggering means to vary the phase angle retards the rectification of said electrical pulses in the phase angle plasma arc mode by about 25°

.

48. The plasma arc torch system of claim 44 wherein said rectifier means which generate said electrical pulses includes a three-phase a.c. power supply, a transformer associated with each of said phases and a rectifying bridge circuit including controlled rectifiers, the input of said rectifying circuit being connected to the secondary circuit of said transformer and the output of said rectifying circuit providing direct operating voltage between said electrode and said workpiece;

said triggering means including means to control the degree of rectification of said rectifying circuit in response to actuation of said switch means.