EP0604553B1 - Plasma torch electronic circuit - Google Patents

Plasma torch electronic circuit Download PDF

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Publication number
EP0604553B1
EP0604553B1 EP92920423A EP92920423A EP0604553B1 EP 0604553 B1 EP0604553 B1 EP 0604553B1 EP 92920423 A EP92920423 A EP 92920423A EP 92920423 A EP92920423 A EP 92920423A EP 0604553 B1 EP0604553 B1 EP 0604553B1
Authority
EP
European Patent Office
Prior art keywords
current
pilot
electrode
torch
arc
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
EP92920423A
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German (de)
English (en)
French (fr)
Other versions
EP0604553A1 (en
Inventor
Dennis J. Solley
David A. Tatham
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Victor Equipment Co
Original Assignee
Thermal Dynamics Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from US07/762,852 external-priority patent/US5170030A/en
Application filed by Thermal Dynamics Corp filed Critical Thermal Dynamics Corp
Publication of EP0604553A1 publication Critical patent/EP0604553A1/en
Application granted granted Critical
Publication of EP0604553B1 publication Critical patent/EP0604553B1/en
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Classifications

    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
    • H05H1/00—Generating plasma; Handling plasma
    • H05H1/24—Generating plasma
    • H05H1/26—Plasma torches
    • H05H1/32—Plasma torches using an arc
    • H05H1/34—Details, e.g. electrodes, nozzles
    • H05H1/36—Circuit arrangements

Definitions

  • the present invention is in the field of plasma torches and in particular is directed to a plasma torch having an improved pilot and main arc generating circuit.
  • Plasma torches otherwise known as electric arc torches, are known in the art for performing operations, such as cutting, welding, etc., on workpieces, and operate by directing a plasma consisting of ionized gas particles towards a workpiece.
  • An example of the conventional single gas plasma torch is illustrated in Hatch, U.S. Pat. No. 3,813,510, assigned to the assignee herein.
  • Other patents disclosing such torches are U.S. Pat: Nos. 4,225,769; 4,663,512; and 4,663,515.
  • a gas to be ionized such as nitrogen, is fed through channels in the torch mechanism in such a manner as to swirl in front of the end of a negatively charged electrode.
  • the tip which is adjacent the end of the electrode has a sufficiently high voltage applied thereto to cause a spark to jump the gap between the electrode and the tip, thereby heating the gas and causing it to ionize.
  • a pilot DC voltage between the electrode and the tip maintains the pilot arc.
  • the ionized gas in the gap appears as a flame and extends externally of the tip where it can be seen by the operator.
  • the extension of the pilot arc and the flame which for practical purposes, may be considered as being co-extensive depends upon the power in the gap -- i.e., the arc current -- as well as the pressure of the gas forced into the gap and out of the torch. In actual practice, when the pilot arc is on, a loop-shaped arc extending out of the torch can be seen. As the torch head is brought down towards the workpiece, the pilot arc jumps from the electrode to the workpiece due to the fact that the impedance of the workpiece current path is lower than the impedance of the tip current path.
  • pilot arc circuits which provide a 5-100 amp. pilot arc current at 100-200 volts across the electrode-tip gap, resulting in an extension of the arc about 1/8-1 ⁇ 2 inch (3mm to 13mm) past the tip.
  • the torch must be brought in proximity to the workpiece at a maximum distance governed by this and other factors in order to transfer the pilot arc to the workpiece so that the cutting or welding operation can begin.
  • the maximum distance required is typically in the range of the extent of the pilot arc. Small transfer distances create difficulties in the starting of cutting or welding operations.
  • European Patent Application 0 436 021 Al discloses a plasma-arc cutting machine and a method of controlling the same.
  • the plasma-arc cutting machine includes a rise compensation circuit inserted in parallel between an electrode and a nozzle and a transfer compensation circuit inserted in parallel between the electrode and a workpiece, each circuit consisting of a charge/discharge capacitor and a resistor. Further, a diode is inserted between the nozzle and the transfer compensation circuit.
  • a detector for current control is provided between the electrode and the rise compensation circuit and another detector for detecting the arc transfer is provided between the transfer compensation circuit and the workpiece.
  • a voltage between the electrode or the nozzle and the workpiece is detected, and the power source is stopped when the voltage exceeds a preset value.
  • WO 90/11865 shows a power transfer circuit for a plasma torch for transferring the plasma arc from the nozzle of the torch to a workpiece as cutting commences and vice versa as cutting is completed.
  • the circuit includes a switching transistor for alternately providing power to the nozzle or the workpiece.
  • the transistor is responsive to the voltage differential between the workpiece and the nozzle for transferring the plasma arc. Below a specified lower voltage differential, the transistor is turned off and all power is delivered to the workpiece. Above a specified upper voltage differential, the transistor is turned cn and all power is delivered to the nozzle. Between the specified upper and lower voltage differentials, the transistor switches at a specified frequency.
  • the present invention comprises new elctronic circuit concepts for a plasma arc torch wherein main current regulated power means regulates the pilot current prior to main arch transfer.
  • the circuit may contain two inductors to which DC current initially flows but is interrupted upon main arc transfer such that one inductor maintains the pilot arc while the current in the second inductor forces the establishment of the transferred arc. Also, advantages are presented in pulsing the cutting arc as well as pulsing the pilot arc.
  • Torch 10 includes torch tip electrode 12 and annular torch pilot electrode 14 spaced from tip electrode 12.
  • An electronic pilot circuit P connected between tip electrode 12 and pilot electrode 14 provides an electric potential between electrodes 12 and 14 to create a pilot arc which heats a supplied gas such as nitrogen causing it to ionize as is well known in the art.
  • Fig. 1 shows prior art circuit C which uses a resistively regulated pilot arc having a current regulated power means 16 and a pilot regulator means 18 including a disconnect means 20 in series with a resistor 22.
  • a high frequency pilot initiation means 24 is positioned in series with pilot regulator means 18 and may be inserted in the circuit adjacent either electrode 12 or electrode 14 as shown in Fig. 1 to initiate generation of plasma gas to commence pilot operations.
  • a current sensing means 26 is connected in parallel with pilot regulator means 18 and connects with the metal to be worked at 28 in main circuit M. When tip electrode 12 is placed sufficiently close to the metal work 28 the arc will transfer to the work 28 causing current to flow through main circuit M and current sensing means 26 will sense the current differential and act to disconnect pilot regulator means 18 by opening pilot regulator means 18 by opening its disconnect means 20.
  • circuit voltage of current regulated power means 16 must be large compared with the torch piloting voltage between tip electrode 12 and pilot electrode 14 to allow the pilot regulator means 18 to perform the function of a current source during pilot operation. This causes circuit 10 to be inefficient, power being dissipated as heat in pilot regulator means 18.
  • Fig. 2 shows another prior art circuit 10' similar to that of Fig. 1 in that it also contains electronically controlled pilot regulator means 18' in pilot circuit P' and a parallel main circuit M'.
  • the circuit 10' of Fig. 2 also includes similar current operated power means 16', tip electrode 12', pilot electrode 14', current sensing means 26', pilot initiation means 24' (alternatively positioned as shown) and work piece or member 28'.
  • the difference between circuit 10' of Fig. 2 and circuit 10 of Fig. 1 is the provision of circuit connection on the opposite side of power means 16' from current means 26' connected to pilot regulator means 18' in order to provide a second current regulated control loop, one for pilot arc operation and one for transferred main arc cutting.
  • Fig. 2A shows one prior art pilot regulating circuit 18'a wherein the pilot is linearly regulated; that is, the pilot current is regulated against a set demand means 3d by varying the conductance of a linear element 3a.
  • Fig. 2B shows another prior art pilot regulating 18'b wherein the pilot is switch regulated. That is, the pilot is regulated against a set demand 3d' to vary the duty cycle of a switching element 3g within a feedback loop.
  • Either scheme can tightly regulate the pilot arc against Ac line variations and against plasma gas in use, however, both add parts count and cost to the torch and are relatively inefficient.
  • Fig. 3 shows the preferred plasma torch circuit 100 in accordance with the principles of the present invention.
  • circuit 100 includes torch tip electrode 112, pilot electrode 114, current regulated power means 116, pilot regulator means 118, alternatively positionable pilot initiation means 124, current sensing means 126, and metal work 128.
  • Pilot regulator means 118 comprises an electronic disconnect 120 in series with a current smoothing and energy storage inductor 130, and a free-wheeling diode 132 connected in parallel with disconnect 120 and in series with inductor 130.
  • current sensing means 126 not only controls disconnect 120 through line 134, but also sends a current signal to comparator 136 through line 138 which controls the output of power means 116.
  • disconnect means 120 is "on” and is in its saturated state.
  • the voltage seen between the metal work piece 128 and torch tip electrode 112 is essentially the voltage at which the torch maintains the pilot arc determined by torch geometry and the plasma gas used. This voltage is considerably lower than the open circuit voltage used in prior art torch circuits.
  • sensing means 126 acts through line 134 to force disconnect means 120 to its "off” or high impedance state.
  • the pilot arc is maintained by current flowing through energy storage inductor means 130 and the free-wheeling diode means 132.
  • the current flowing in through the smoothing inductor means 140 of power regulator 116 is forced to flow between the workpiece 128 and torch tip electrode 112, thereby maintaining the transferred plasma arc.
  • the pilot arc between torch tip electrode 112 and pilot electrode 114 self extinguishes.
  • transfer is detected in current sensing means 126 the pilot demand means le is changed and the power means 116 changes the power to that demanded for the torch operation on work piece 128.
  • a further embodiment of the present invention resides in additionally pulsing the pilot current.
  • the demand may be pulsed between two (or more levels) at various frequencies and duty cycles. During this pulsing the pilot arc is maintained throughout and no high frequency arc initiation means 124 is required, as would be the case for a 'blown-out' pilot.
  • This pulsing feature offers several advantages. First, higher standoff distances between the work metal 128 and torch tip electrode 112 at the moment of transfer. Second, a tip cleaning action is observed, i.e., during plasma cutting molten metal is blown onto the tip face where it adheres in particulate form. At the same time, electrode material is removed from the torch electrode and adheres to the inside tip. Both forms of contamination can cause the tip orifice to become distorted. When the pilot arc is pulsed following each cut significantly more power is dissipated in the tip electrode 112 for the pulse duration. This thermal modulation is believed to be responsible for dislodging metal particles from the inner and outer tip surfaces.
  • FIG. 4 there is shown an alternative circuit wherein a small resistor 142 is added in series with the pilot means 118.
  • This modification can further improve the obtainable standoff on some plasma torch designs.
  • the pilot current (Ip) flows through resistor 142 to generate a voltage drop (Ip x R) which is in series with the pilot voltage measured between torch tip 112 and pilot electrode 114.
  • Ip x R voltage drop
  • the power dissipated in this resistor is then a function of the pilot demand and pulse duration.
  • a further alternative circuit provides a pulsing cutting or main arc. From the invention pulsing the pilot arc before transfer it is clear that it is possible to pulse the current demand means le, after the arc has transferred and while the transferred plasma arc is cutting the work metal means 128.
  • This provision of pulsing the main arc offers several potential advantages. First, by selecting the appropriate pulse rate and duty cycle in relation to the cutting variables, it will offer a proportionally greater arc cutting capacity /penetration for a small increase in power consumption. Second, it allows the tip orifice size to be reduced in comparison to a conventional plasma cutting system operating in response to a DC demand level. This will allow a smaller focussed plasma column and result in smaller kerf widths. Plasma arc stability may also improve as a result of pulsing.
  • Figs. 5A and B are a more specific electronic circuit schematic diagram embodying some of the concepts of the invention as enumerated above.
  • Like reference numerals appearing in Fig. 5 refer to like circuit components or group of components as appear in Figs. 3 and 4.
  • Reference numeral 120c depicts the control circuity for disconnecting means 120.
  • the power supply means is not shown in Fig. 5.

Landscapes

  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Plasma & Fusion (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Arc Welding Control (AREA)
  • Plasma Technology (AREA)
  • Absorbent Articles And Supports Therefor (AREA)
EP92920423A 1991-09-18 1992-09-11 Plasma torch electronic circuit Expired - Lifetime EP0604553B1 (en)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
US07/762,852 US5170030A (en) 1991-04-08 1991-09-18 Plasma torch electronic pulsing circuit
US762852 1991-09-18
PCT/US1992/007518 WO1993006702A1 (en) 1991-04-08 1992-09-11 Plasma torch electronic circuit

Publications (2)

Publication Number Publication Date
EP0604553A1 EP0604553A1 (en) 1994-07-06
EP0604553B1 true EP0604553B1 (en) 1997-07-09

Family

ID=25066193

Family Applications (1)

Application Number Title Priority Date Filing Date
EP92920423A Expired - Lifetime EP0604553B1 (en) 1991-09-18 1992-09-11 Plasma torch electronic circuit

Country Status (9)

Country Link
EP (1) EP0604553B1 (es)
JP (1) JP3188702B2 (es)
KR (1) KR100257863B1 (es)
AT (1) ATE155309T1 (es)
AU (1) AU660491B2 (es)
DE (1) DE69220805T2 (es)
MX (1) MX9205284A (es)
NZ (1) NZ244352A (es)
ZA (1) ZA927166B (es)

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE10210914C5 (de) * 2002-03-04 2009-02-12 GTV-Gesellschaft für thermischen Verschleiss-Schutz mbH Plasmabrenner und Verfahren zur Erzeugung eines Plasmastrahls

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3577030A (en) * 1967-10-30 1971-05-04 Us Navy Inductive energizing circuit for arc plasma generator
EP0194050B1 (en) * 1985-02-12 1989-08-16 Metallurgical Industries, Inc. A welding apparatus and method for depositing wear surfacing material on a substrate
WO1989009110A1 (en) * 1988-03-24 1989-10-05 Kabushiki Kaisha Komatsu Seisakusho Plasma-arc cutting machine and a method of controlling the same

Also Published As

Publication number Publication date
DE69220805D1 (de) 1997-08-14
JPH06510708A (ja) 1994-12-01
KR100257863B1 (ko) 2000-06-01
AU660491B2 (en) 1995-06-29
DE69220805T2 (de) 1997-11-27
MX9205284A (es) 1993-05-01
NZ244352A (en) 1995-04-27
AU2661892A (en) 1993-04-27
JP3188702B2 (ja) 2001-07-16
KR940702678A (ko) 1994-08-20
ZA927166B (en) 1993-03-23
ATE155309T1 (de) 1997-07-15
EP0604553A1 (en) 1994-07-06

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