EP0604553B1 - Circuit electronique de torche a plasma - Google Patents

Circuit electronique de torche a plasma 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
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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)
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EP0604553A1 (fr
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
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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/fr
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Publication of EP0604553B1 publication Critical patent/EP0604553B1/fr
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    • 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.

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  • 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)

Abstract

On décrit une torche à arc-plasma présentant de nouveaux concepts de circuit électronique (100) dans lequel un bloc d'alimentation stabilisée en courant principal (116) régule le courant pilote avant le transfert de l'arc principal. En outre, le circuit peut contenir deux inducteurs qui sont initialement alimentés par un courant continu, mais ce courant est interrompu lors du transfert de l'arc principal de sorte qu'un inducteur (140) maintienne l'arc pilote tandis que le courant dans le second inducteur (130) provoque l'établissement de l'arc transféré. Il est également avantageux de rendre impulsionnel l'arc de coupe (1e) de même que l'arc pilote en (124).

Claims (16)

  1. Torche à plasma du type comportant un ensemble de torche adapté de manière à pouvoir travailler sur une pièce (128) et comportant une électrode de torche (112), une électrode pilote (114) et un moyen pour fournir un gaz ionisé entre elles, un moyen (116) d'alimentation électrique régulé en courant afin de fournir un courant régulé à la pièce (128) et à l'électrode en pointe (112) de la torche, pendant l'utilisation de cette torche, ce moyen (116) d'alimentation électrique régulé en courant étant connecté électriquement à la pièce (128) par un premier circuit prévu entre le moyen d'alimentation électrique (116) et la pièce (128) et étant connecté électriquement à l'électrode (112) de la torche par un second circuit prévu entre le moyen d'alimentation électrique (116) et l'électrode (112) de la torche, un moyen (118) de commande d'arc pilote pour commander un arc électrique entre l'électrode en pointe (112) de la torche et l'électrode pilote (114), ce moyen (118) de commande de l'arc pilote étant connecté électriquement entre le moyen d'alimentation électrique (116) et l'électrode pilote (114) et étant connecté électriquement à l'électrode pilote (114) par un troisième circuit prévu entre le moyen de commande (118) et l'électrode pilote (114), le moyen (118) de commande de l'arc pilote comportant un moyen de déconnexion (120) entre le moyen d'alimentation électrique (116) et l'électrode pilote (114), un moyen de détection de courant (126) pour détecter le courant dans le premier circuit et pour produire un signal de réaction (138) en réponse à l'utilisation de la torche, et une diode (132) connectée entre les second et troisième circuits afin d'établir un trajet pour le passage du courant vers l'électrode pilote (114), caractérisée en ce qu'elle comprend une première inductance (130) couplée au moyen (118) de commande de l'arc pilote afin de maintenir temporairement le courant pilote lorsque le moyen de déconnexion est ouvert, une seconde inductance (140) prévue dans le moyen d'alimentation électrique (116) afin de forcer l'établissement de l'arc transféré lorsque le moyen de déconnexion a été ouvert, et un moyen d'interconnexion (134) entre le moyen de détection de courant (126) et le moyen de déconnexion (120) de telle façon que le moyen de détection de courant (126) actionne le moyen de déconnexion (120) avec le signal de réaction (138).
  2. Torche à plasma suivant la revendication 1 caractérisée en ce que la diode (132) laisse passer le courant en provenance du moyen (116) d'alimentation électrique régulé en courant uniquement en direction de l'inductance (130), afin de maintenir temporairement le courant pilote lorsque le moyen de déconnexion (120) est ouvert.
  3. Torche à plasma suivant la revendication 2 caractérisée en ce qu'elle comporte en outre une résistance (142) connectée électriquement entre le premier circuit et le moyen de déconnexion (120), cette résistance produisant une chute de tension liée à la demande de courant pilote et entraînant alors un accroissement de la tension entre l'électrode (114) et la pièce (128), afin d'accroître la hauteur du transfert.
  4. Torche à plasma suivant la revendication 1 caractérisée en ce que la seconde inductance (140), prévue dans le moyen d'alimentation électrique (116), répond au courant détecté par le moyen de détection de courant (126), de manière à assurer un filtrage à haute fréquence du moyen d'alimentation électrique (116).
  5. Torche à plasma suivant la revendication 4 caractérisée en ce que le moyen de détection de courant (126) produit un signal appliqué à un comparateur (136) afin de réguler le courant produit par le moyen d'alimentation électrique (116) et de maintenir la pulsation de l'arc entre l'électrode (112) de la torche et la pièce (128).
  6. Torche à plasma suivant la revendication 5 caractérisée en ce que le courant produit par le moyen (116) d'alimentation électrique régulé en courant est également pulsé.
  7. Torche à plasma suivant la revendication 6 caractérisée en ce que le moyen de détection de courant (126) intervient de manière à fournir un arc pilote pulsé.
  8. Torche à plasma suivant la revendication 6 caractérisée en ce que le moyen de détection de courant (126) intervient de manière à fournir un arc principal pulsé.
  9. Torche à plasma suivant la revendication 1 caractérisée en ce que le moyen (116) d'alimentation électrique régulé en courant est connecté électriquement entre les électrodes (112,114) et la pièce (128) de manière à fournir un courant régulé à l'électrode (112) de la torche et à l'électrode pilote (114) pour l'arc pilote et à l'électrode (112) de la torche et à la pièce (128) pour l'arc principal, et le moyen de déconnexion (120) comprend un circuit de déconnexion couplé au circuit (118) de commande de l'arc pilote et intervenant pour ouvrir ce circuit (118) de commande de l'arc pilote afin de produire une tension induite dans une seconde inductance (140) branchée entre le moyen d'alimentation électrique (116) et l'électrode (112) de la torche, pour contribuer à l'amorçage du transfert de l'arc pilote en arc principal.
  10. Torche à plasma suivant la revendication 9 caracterisée en ce que le circuit (118) de commande de l'arc pilote comporte l'inductance (130) pour maintenir temporairement le courant pilote lorsque le circuit de déconnexion est ouvert.
  11. Torche à plasma suivant la revendication 9 caractérisée en ce que le moyen de détection de courant (126) est caractérisé par un capteur de courant couplé à la pièce (128) et au circuit de déconnexion, ce capteur de courant produisant un signal en réponse au courant passant dans la pièce (128) de manière à actionner le circuit de déconnexion.
  12. Torche à plasma suivant la revendication 9 caractérisée en ce que le courant régulé pour l'arc pilote est pulsé.
  13. Torche à plasma suivant la revendication 9 caractérisée en ce qu'un circuit de pulsation est couplé au moyen d'alimentation électrique (116) afin de pulser le courant de l'arc pilote.
  14. Torche à plasma suivant la revendication 13 caractérisée en ce que le circuit de pulsation assure la pulsation du courant de l'arc principal.
  15. Torche à plasma suivant la revendication 1 caractérisée en ce que le moyen (116) d'alimentation électrique régulé en courant, couplé entre les électrodes (112,114) et la pièce (128), fournit un courant régulé à l'électrode (112) de la torche et à l'électrode pilote (114) pour l'arc pilote et à l'électrode (112) de la torche et à la pièce (128) pour l'arc principal et elle est en outre caractérisée par un circuit de pulsation couplé au moyen d'alimentation électrique (116) et intervenant pour pulser le courant pour l'arc pilote.
  16. Torche à plasma suivant la revendication 15 caractérisée en ce que le circuit de pulsation peut intervenir pour pulser le courant pour l'arc principal.
EP92920423A 1991-09-18 1992-09-11 Circuit electronique de torche a plasma Expired - Lifetime EP0604553B1 (fr)

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 (fr) 1991-04-08 1992-09-11 Circuit electronique de torche a plasma

Publications (2)

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

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EP92920423A Expired - Lifetime EP0604553B1 (fr) 1991-09-18 1992-09-11 Circuit electronique de torche a plasma

Country Status (9)

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

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* 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
AU584393B2 (en) * 1985-02-12 1989-05-25 Sermatech International, Inc. A welding apparatus and method for depositing wear surfacing material and a substrate having a weld bead thereon
DE68927261T2 (de) * 1988-03-24 1997-02-06 Komatsu Mfg Co Ltd Plasmabogen-schneidevorrichtung und deren regelung

Also Published As

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

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