EP0204052A2 - Method and system for controlling the electrode erosion of a plasma torch - Google Patents

Method and system for controlling the electrode erosion of a plasma torch Download PDF

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Publication number
EP0204052A2
EP0204052A2 EP85420199A EP85420199A EP0204052A2 EP 0204052 A2 EP0204052 A2 EP 0204052A2 EP 85420199 A EP85420199 A EP 85420199A EP 85420199 A EP85420199 A EP 85420199A EP 0204052 A2 EP0204052 A2 EP 0204052A2
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EP
European Patent Office
Prior art keywords
arc
electrodes
value
plasma torch
field coil
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EP85420199A
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German (de)
French (fr)
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EP0204052B1 (en
EP0204052A3 (en
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Michel G. Drouet
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Hydro Quebec
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Hydro Quebec
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Priority to AT85420199T priority Critical patent/ATE66562T1/en
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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
    • H05H1/40—Details, e.g. electrodes, nozzles using applied magnetic fields, e.g. for focusing or rotating the arc
    • 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
    • H05H1/3431—Coaxial cylindrical electrodes

Definitions

  • the present invention relates to a method and a system for controlling the erosion of the electrodes of a plasma torch. More specifically, the invention relates to the use of the plasma torch under conditions where the electrodes of the latter have a substantially prolonged life by increasing the surface swept by the arc foot.
  • coal is also used as an energy source to make steel by directly transforming the metal in a hearth furnace or in oxygen and coke ovens, as well as in the other treatment stages (coke oven and high - gas stove).
  • fusion and heating must use other forms of energy.
  • This gas varies with the electric power delivered in the electric arc and the gas flow. This temperature being able to reach from .3000 ° to 10000 °, the hot gas produced is strongly ionized, it is therefore a plasma hence the name of plasma torch given to this device.
  • the electrical power of commercially available torches varies between a few kW and ten MW.
  • the service life of the electrodes is an essential element.
  • the torch manufacturers indicate durations varying between 100 and 1000 hours for cooled electrodes.
  • the rate of erosion of the electrodes depends on the operating conditions: value of the arc current, materials and temperature of the electrode, nature and pressure of the ambient gas, movement of the arc foot.
  • the wear phenomenon is very poorly understood.
  • the tangential injection of cold gases and the presence of an axial magnetic field each have the effect of creating a rotation of the arc foot on the surface of the tubular electrodes.
  • the arc is driven by the rotating gas or pushed by the force 1 x B resulting from the interaction between the magnetic field B and the arc current I.
  • the speed of the arc increases with the value of the field magnetic applied transversely to the arc.
  • the arc is usually moved rapidly over a circle on the surface of the electrode by a constant magnetic field, thus distributing over the internal surface of the electrode.
  • cylindrical where the arc attaches to the inevitable erosion which occurs in contact with the arc with the surface of the elec trode.
  • An object of the present invention relates to an o roceded by e. which causes an axial displacement of the trajectory of the arch foot.
  • the invention relates to a method for controlling the erosion of the electrodes of a plasma torch, in which an electric arc is established, when the electrodes are connected to a power supply and an axial magnetic field generated by a coil system. field, causes the arc feet to rotate in a circular path inside the electrodes.
  • the value of the current in the field coil system used to rotate the arc is varied periodically, thus causing an axial displacement of the circular path of the arc foot.
  • the current value is continuously modulated in the coil system, so as to cause each of the arc feet to move on a cylindrical surface, for example along a helical path.
  • the field coil system comprises one, two or more field coils for each electrode.
  • the value of the current (s) in one or more of the coils can be continuously modulated, so as to modify axially the position of the minimum of the resultant of the fields thus causing an axial displacement of the radial trajectory of the arch foot.
  • the modulation of the value of the currents is adjusted, in order to synchronize the axial displacements of the arc feet at the two electrodes to keep a constant arc length and thus keep the arc voltage at the same value.
  • the invention also relates to a plasma torch comprising two cylindrical electrodes making it possible to obtain an electric arc when the electrodes are connected to a power supply, and a field coil system for each electrode to cause the rotation of the arc feet according to a circular path inside the cylindrical electrodes.
  • means are provided for periodically varying the value of the currents in the field coil system used to rotate the arc, thus causing an axial displacement of the circular path of the arc foot.
  • said means are arranged to continuously modulate the value of the currents in the coil system, so as to cause each of the arc feet to move on a cylindrical surface.
  • means are provided for continuously modulating the value of the current in one of the two coils, so as to modify the position of the minimum of the sum of two fields axially, thus causing an axial displacement of the radial trajectory. of the arc foot.
  • means are provided for adjusting the modulation of the value of the current, in order to synchronize the axial displacements of the arc feet at the two electrodes in order to maintain a constant arc length and thus maintain the arc voltage at the same value.
  • the torch 29 has at least two field coils 31 and 33 for each electrode unlike commercial torches which have only one.
  • the value of current in one of the coils (or both) is modulated by any known means 35 continuously, so as to modify axially the position of the minimum of the sum of the two fields thus causing an axial displacement d of the radial trajectory a or b of the foot d arc 37.
  • the arc foot no longer describes a circle, it moves on a cylindrical surface.
  • the axial movements of the arc feet at the two electrodes can be synchronized by any known means to maintain a constant arc length and thus keep the arc voltage at the same value.
  • each electrode of the plasma torch comprises only a single coil and a vortex injection of the gas; this displacement can, in fact, be obtained by continuously modulating the current in the coil. This control is nevertheless less effective than by the use of two or more coils.
  • the erosion rate of a commercial torch has been measured by several manufacturers; . it is approximately 1.5 x 10 -9 kg per coulomb of electricity.
  • the amount of material eroded after 400 hours of operation at 1000A of a torch is therefore:
  • the length X eroded in the axial direction is of (density for copper 8.95):

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Plasma & Fusion (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Plasma Technology (AREA)
  • Discharge Heating (AREA)

Abstract

Method and device for controlling the erosion of the electrodes of a plasma torch, in which an electrical arc is produced when the electrodes are connected to an electrical supply. An axial magnetic field generated by a system of field coil causes the rotation of the extremities of the arc according to a circular trajectory inside the electrodes. The relative position of the field coils is such that there exists a position on the electrode surface where the value of the total magnetic field is a minimum where the arc runs thereby controlling the erosion of the electrodes. According to the invention, the value of current is periodically varied in the system of field coil used to cause the rotation of the arc, thereby producing a controlled axial displacement of the circular trajectory of the extremity of the arc. The plasma torch according to the invention is characterized by structure to periodically vary the value of the current in the field coil system used to cause the rotation of the arc thereby producing a controlled axial displacement of the circular trajectory of the extremity of the arc. Under these conditions, the life of the electrodes is substantially increased.

Description

La présente invention concerne un procédé et un système de contrôle de l'érosion des électrodes d'une torche à plasma. Plus précisément, l'invention se rapporte à l'utilisation de la torche à plasma dans des conditions où les électrodes de cette dernière ont une vie sensiblement prolongée en augmentant la surface balayée par le pied d'arc.The present invention relates to a method and a system for controlling the erosion of the electrodes of a plasma torch. More specifically, the invention relates to the use of the plasma torch under conditions where the electrodes of the latter have a substantially prolonged life by increasing the surface swept by the arc foot.

On sait que l'industrie du fer et de l'acier demande beaucoup d'énergie, cette dernière étant surtout produite par des combustibles, et fait assez peu usage d'électricité. C'est ainsi que dans les usines soit disant intégrées, on préfère utiliser du charbon pour fournir la plus grande partie de l'énergie (chimique et thermique) pour la réduction du minerai de fer à l'état métallique. On utilise aussi le charbon comme source d'énergie pour fabriquer de l'acier en transformant directement le métal dans un four à sole ou dans les fours à oxygène et à coke, ainsi que dans les autres étapes de traitement (four à coke et haut-fourneau à gaz). D'autre part, on sait que dans les usines non intégrées, la fusion et le chauffage doivent utiliser d'autres formes d'énergie.We know that the iron and steel industry requires a lot of energy, the latter being produced mainly by fuels, and makes little use of electricity. This is how in so-called integrated factories, it is preferable to use coal to provide most of the energy (chemical and thermal) for the reduction of iron ore to the metallic state. Coal is also used as an energy source to make steel by directly transforming the metal in a hearth furnace or in oxygen and coke ovens, as well as in the other treatment stages (coke oven and high - gas stove). On the other hand, we know that in non-integrated factories, fusion and heating must use other forms of energy.

Pour toutes sortes de raisons, il y aurait intérêt à convertir le plus possible de ces usines à l'électricité, si seulement cela s'avérait rentable. Cependant, aux taux présents de l'électricité, surtout si l'on utilise de l'équipement conventionnel, il n'est pas apparu pratique d'effectuer la conversion. Il reste la torche à plasma qui pourrait se montrer d'utilisation intéressante et pratique surtout dans la production de courant d'air chaud ou de gaz réducteur pour les hauts- fourneaux, le reforming de carburant fossile pour réduction directe, le remplacement des électrodes dans les fours à arc, le préchauffage de la ferraille, la fusion aux gaz inertes, la mise à feu des boulettes, le chauffage des lingots et le préchauffage des poches.For all kinds of reasons, it would be beneficial to convert as many of these factories as possible to electricity, if only it proved to be profitable. However, at present rates of electricity, especially if using conventional equipment, it did not appear practical to carry out the conversion. There remains the plasma torch which could prove to be of interesting and practical use especially in the production of hot air stream or reducing gas for blast furnaces, the reforming of fossil fuel for direct reduction, the replacement of the electrodes in arc furnaces, preheating of scrap, fusion with inert gases, ignition of pellets, heating of ingots and preheating of pockets.

L'utilisation d'arcs électriques pour obtenir des gaz à très haute température date du début du -jècle et l'appareil dont on se sert pour produire ces températures est communément nommé torche à plasma. Ces dispositifs sont rapidement passés de simples curiosités de laboratoires à des équipements spécialisés pour la fabrication d'objets uniques. Récemment, les prix croissants et des incertitudes quant à la disponibilité des combustibles à base d'hydrocarbures légers ont mené les experts à considérer l'application des torches à plasma à un plus grand nombre de procédés industriels opérant à hautes températures. Deux raisons principales sont à la base de cette proposition. En premier lieu, ce dispositif permet d'atteindre des températures beaucoup plus élevées, résultant en des taux d'efficacité de chauffage beaucoup plus élevés que ce que l'on peut obtenir par simple combustion. En second lieu, on a découvert que dans plusieurs cas, les rendements obtenus sont plus élevés qu'en opérant de façon conventionnelle.The use of electric arcs to obtain gases at very high temperatures dates from the beginning of the century and the apparatus used to produce these temperatures is commonly called a plasma torch. These devices quickly went from simple laboratory curiosities to specialized equipment for the manufacture of unique objects. Recently, rising prices and uncertainties about the availability of light hydrocarbon fuels have led experts to consider the application of plasma torches to more industrial processes operating at high temperatures. There are two main reasons for this proposal. First, this device achieves much higher temperatures, resulting in much higher heating efficiency rates than can be achieved by simple combustion. Secondly, it has been discovered that in several cases, the yields obtained are higher than operating in a conventional manner.

On sait, d'autre part, que les torches à plasma comportent des électrodes que l'on doit éventuellement remplacer à cause de l'érosion produite au pied de l'arc. Or, si ce remplacement intervient à des fréquences trop rapprochées,l'utilisation de la torche à plasma ne devient plus rentable comme c'est la plupart du temps le cas.We know, on the other hand, that plasma torches have electrodes that must eventually be replaced because of the erosion produced at the foot of the arc. However, if this replacement occurs at too close frequencies, the use of the plasma torch no longer becomes profitable as it is most of the time.

L'invention va être décrite ci-après à l'aide des dessins annexés, lesquels sont donnés à titre illustratif et sans caractère limitatif. Dans les dessins :

  • la figure 1 illustre le schéma de principe d'une torche à plasma connue ;
  • la figure 2 est une courbe de la tension de l'arc en fonction de la vitesse à courant constant ;
  • la figure 3a est un schéma illustrant la trace du pied d'arc à la surface de l'électrode dans une configuration électrodes-bobine de champ ;
  • la figure 3b est une courbe illustrant la position de la trace du pied d'arc à la surface de l'électrode en fonction du champ appliqué ;
  • la figure 3c est une courbe représentant le tracé des valeurs des forces d'entraînement en fonction de la position de la trace du pied d'arc le long de l'axe de l'électrode ;
  • la figure 4 est un schéma d'un montage de torche à plasma selon l'invention, et
  • la figure 5 est un graphique illustrant la distribution axiale du champ produit et la position des minima pour deux valeurs du champ produit par une des bobines de la torche illustrée en figure 1.
  • Plus précisément, la torche à plasma est utilisée pour convertir l'énergie électrique en énergie thermique d'un gaz, en faisant passer le gaz en contact avec un arc électrique maintenu entre deux électrodes. Une torche typique est illustrée sur la figure 1 et comporte
  • (a) deux électrodes cylindriques 1,3 reliées à une alimentation électrique 5,7 et entre lesquelles existe un arc électrique 9 ;
  • (b) une injection tangentielle 11 des gaz froids créant un vortex 13 et assurant un transfert maximum d'énergie entre l'arc 9 et le gaz 11 ;
  • (c) des bobines 17,19 créant un champ magnétique axial pour faire tourner les pieds d'arc 21,23 répartissant ainsi l'érosion inévitable des électrodes et,
  • (d) un orifice de sortie 25 du gaz chauffé à très haute température et appelé plasma 27.
The invention will be described below using the accompanying drawings, which are given by way of illustration and without limitation. In the drawings:
  • Figure 1 illustrates the block diagram of a known plasma torch;
  • FIG. 2 is a curve of the voltage of the arc as a function of the speed at constant current;
  • FIG. 3a is a diagram illustrating the trace of the arc foot on the surface of the electrode in an electrode-field coil configuration;
  • FIG. 3b is a curve illustrating the position of the trace of the arc foot on the surface of the electrode as a function of the field applied;
  • FIG. 3c is a curve representing the plot of the values of the driving forces as a function of the position of the trace of the arch foot along the axis of the electrode;
  • FIG. 4 is a diagram of an assembly of a plasma torch according to the invention, and
  • FIG. 5 is a graph illustrating the axial distribution of the field produced and the position of the minima for two values of the field produced by one of the coils of the torch illustrated in FIG. 1.
  • More specifically, the plasma torch is used to convert electrical energy into thermal energy of a gas, by passing the gas in contact with an electric arc maintained between two electrodes. A typical torch is shown in Figure 1 and has
  • (a) two cylindrical electrodes 1,3 connected to a power supply 5,7 and between which there is an electric arc 9;
  • (b) a tangential injection 11 of the cold gases creating a vortex 13 and ensuring maximum energy transfer between the arc 9 and the gas 11;
  • (c) coils 17,19 creating an axial magnetic field to rotate the arc feet 21,23 thus distributing the inevitable erosion of the electrodes and,
  • (d) an outlet orifice 25 for the gas heated to a very high temperature and called plasma 27.

La température de ce gaz varie avec la puissance électrique débitée dans l'arc électrique et le débit gazeux. cette température pouvant atteindre de .3000° à 10000°, le gaz chaud produit est fortement ionisé, c'est donc un plasma d'où le nom de torche à plasma donné à cet appareil.The temperature of this gas varies with the electric power delivered in the electric arc and the gas flow. this temperature being able to reach from .3000 ° to 10000 °, the hot gas produced is strongly ionized, it is therefore a plasma hence the name of plasma torch given to this device.

La puissance électrique des torches disponibles commercialement varie entre quelques kW et une dizaine de MW.The electrical power of commercially available torches varies between a few kW and ten MW.

Pour les opérations industrielles, la durée de vie des électrodes est un élément primordial. Les fabricants de torche Lndiquent' des durées variant entre 100 et 1000 heures pour des électrodes refroidies.For industrial operations, the service life of the electrodes is an essential element. The torch manufacturers indicate durations varying between 100 and 1000 hours for cooled electrodes.

Le taux d'érosion des électrodes dépend des conditions d'opération : valeur du courant d'arc, matériaux et température de l'électrode, nature et pression du gaz ambiant, mouvement du pied d'arc. Cependant, le phénomène d'usure est très mal compris.The rate of erosion of the electrodes depends on the operating conditions: value of the arc current, materials and temperature of the electrode, nature and pressure of the ambient gas, movement of the arc foot. However, the wear phenomenon is very poorly understood.

L'injection tangentielle des gaz froids et la présence d'un champ magnétique axial ont chacure pour effet de créer une rotation du pied d'arc à la surface des électrodes tubulaires. L'arc est entraîné par le gaz en rotation ou poussé par la force 1 x B résultant de l'interaction entre le champ magnétique B et le courant d'arc I. Ainsi, la vitesse de l'arc augmente avec la valeur du champ magnétique appliqué transversalement à l'arc.The tangential injection of cold gases and the presence of an axial magnetic field each have the effect of creating a rotation of the arc foot on the surface of the tubular electrodes. The arc is driven by the rotating gas or pushed by the force 1 x B resulting from the interaction between the magnetic field B and the arc current I. Thus, the speed of the arc increases with the value of the field magnetic applied transversely to the arc.

Par contre, la tension d'arc augmentant avec sa vitesse de déplacement, l'arc cherchera toujours à brûler dans la région où sa vitesse sera minimum, ainsi qu'on le voit sur la figure 2 où B est la valeur du champ magnétique de soufflage, d est la longueur de l'arc, V la tension de l'arc produit et I l'intensité de courant, c'est-à-dire qu'il se placera dans la région où la somme des sollicitations hydrodynamiques et magnétiques est minimale. Ce phénomène est très bien illustré par des résultats obtenus dans une torche à plasma (puissance ≃ 1 MW) comme l'indiquent les figures 3a, 3b et 3c, où A et B sont tels que définis ci-dessus et x représente la position de la trace du pied d'arc : la trace A laissée par le pied d'arc sur la surface interne de l'électrode est circulaire et sa distance par rapport à l'espace interélectrode où le gaz 11 est injecté augmente quand le champ magnétique B est réduit.On the other hand, the arc voltage increasing with its speed of displacement, the arc will always seek to burn in the region where its speed will be minimum, as can be seen in Figure 2 where B is the value of the magnetic field of blowing, d is the length of the arc, V the voltage of the arc produced and I the current intensity, that is to say that it will be placed in the region where the sum of the hydrodynamic and magnetic stresses is minimal. This phenomenon is very well illustrated by results obtained in a plasma torch (power ≃ 1 MW) as indicated in Figures 3a, 3b and 3c, where A and B are as defined above and x represents the position of the arc foot trace: the trace A left by the arc foot on the internal surface of the electrode is circular and its distance from the interelectrode space where the gas 11 is injected increases when the magnetic field B is reduced.

En somme, selon la technique présentement utilisée pour augmenter la durée de vie des électrodes, l'arc est habituellement déplacé rapidement sur un cercle à la surface de l'électrode par un champ magnétique constant, répartissant ainsi sur la surface interne de l'électrode cylindrique où l'arc s'attache l'inévitable érosion qui se produit au contact de l'arc avec la surface de l'électrode. Cette amélioration augmente sensiblement la vie de l'électrode qui subit l'érosion, étant donné que le pied d'arc ne reste pas attaché en un seul point mais qu'au contraire le pied d'arc balaie une surface circulaire. Il reste néanmoins que l'électrode est endommagée à ce point, qu'après un certain temps, il faut la changer. Il existe donc un net besoin de pouvoir recourir à une technologie qui augmente encore la vie des torches à plasma, du moins si l'on désire étendre le champ d'application de ces dispositifs.In short, according to the technique currently used to increase the service life of the electrodes, the arc is usually moved rapidly over a circle on the surface of the electrode by a constant magnetic field, thus distributing over the internal surface of the electrode. cylindrical where the arc attaches to the inevitable erosion which occurs in contact with the arc with the surface of the elec trode. This improvement appreciably increases the life of the electrode which undergoes erosion, since the arch foot does not remain attached at a single point but, on the contrary, the arch foot sweeps a circular surface. The fact remains, however, that the electrode is damaged to such an extent that after a certain time it must be changed. There is therefore a clear need to be able to use a technology which further increases the life of plasma torches, at least if one wishes to extend the field of application of these devices.

Selon la présente invention, il est possible de prolonger la vie des électrodes des torches à plasma en augmentant la surface balayée par le pied d'arc.According to the present invention, it is possible to extend the life of the electrodes of plasma torches by increasing the surface swept by the arc foot.

Un objet de la présente invention concerne un orocédé par le.quel on provoque un déplacement axial de la trajectoire du pied d'arc.An object of the present invention relates to an o roceded by e. which causes an axial displacement of the trajectory of the arch foot.

L'invention concerne un procédé de contrôle de l'érosion des électrodes d'une torche à plasma, dans laquelle s'établit un arc électrique, lorsque les électrodes sont reliées à une alimentation électrique et un champ magnétique axial engendré par un système à bobine de champ, provoque la rotation des pieds d'arc selon une trajectoire circulaire à l'intérieur des électrodes. Selon l'invention, l'on fait varier périodiquement la valeur du courant dans le système à bobine de champ utilisé pour faire tourner l'arc, entraînant ainsi un déplacement axial de la trajectoire circulaire du pied d'arc.The invention relates to a method for controlling the erosion of the electrodes of a plasma torch, in which an electric arc is established, when the electrodes are connected to a power supply and an axial magnetic field generated by a coil system. field, causes the arc feet to rotate in a circular path inside the electrodes. According to the invention, the value of the current in the field coil system used to rotate the arc is varied periodically, thus causing an axial displacement of the circular path of the arc foot.

De préférence, l'on fait moduler continuellement la valeur du courant dans le système de bobine, de façon à faire déplacer chacun des pieds d'arc sur une surface cylindrique, par exemple selon une trajectoire hélicoïdale.Preferably, the current value is continuously modulated in the coil system, so as to cause each of the arc feet to move on a cylindrical surface, for example along a helical path.

Selon une réalisation préférée de l'invention, le système à bobine de champ comporte une, deux ou plusieurs bobines de champ pour chaque électrode.According to a preferred embodiment of the invention, the field coil system comprises one, two or more field coils for each electrode.

La valeur du ou des courants dans une ou plusieurs des bobines peut être modulée continuellement, de façon à modifier axialement la position du minimum de la résultante des champs entraînant ainsi un déplacement axial de la trajectoire radiale du pied d'arc. De préférence, l'on ajuste la modulation de la valeur des courants, afin de synchroniser les déplacements axiaux des pieds d'arc aux deux électrodes pour conserver une longueur d'arc constante et ainsi conserver la tension d'arc à la même valeur.The value of the current (s) in one or more of the coils can be continuously modulated, so as to modify axially the position of the minimum of the resultant of the fields thus causing an axial displacement of the radial trajectory of the arch foot. Preferably, the modulation of the value of the currents is adjusted, in order to synchronize the axial displacements of the arc feet at the two electrodes to keep a constant arc length and thus keep the arc voltage at the same value.

L'invention concerne aussi une torche à plasma comportant deux électrodes cylindriques permettant d'obtenir un arc électrique lorsque les électrodes sont reliées à une alimentation électrique, et un système à bobine de champ pour chaque électrode pour provoquer la rotation des pieds d'arc selon une trajectoire circulaire à l'intérieur des électrodes cylindriques. Selon l'invention, on prévoit des moyens pour faire varier périodiquement la valeur des courants dans le système à bobine de champ utilisé pour faire tourner l'arc entraînant ainsi un déplacement axial de la trajectoire circulaire du pied d'arc. Par exemple, lesdits moyens sont agencés pour moduler continuellement la valeur des courants dans le système à bobine, de façon à faire déplacer chacun des pieds d'arc sur une surface cylindrique.The invention also relates to a plasma torch comprising two cylindrical electrodes making it possible to obtain an electric arc when the electrodes are connected to a power supply, and a field coil system for each electrode to cause the rotation of the arc feet according to a circular path inside the cylindrical electrodes. According to the invention, means are provided for periodically varying the value of the currents in the field coil system used to rotate the arc, thus causing an axial displacement of the circular path of the arc foot. For example, said means are arranged to continuously modulate the value of the currents in the coil system, so as to cause each of the arc feet to move on a cylindrical surface.

Selon une réalisation préférée de l'invention, des moyens sont prévus pour moduler continuellement la valeur du courant dans une des deux bobines, de façon à modifier axialement la position du minimum de la somme de deux champs entraînant ainsi un déplacement axial de la trajectoire radiale du pied d'arc.According to a preferred embodiment of the invention, means are provided for continuously modulating the value of the current in one of the two coils, so as to modify the position of the minimum of the sum of two fields axially, thus causing an axial displacement of the radial trajectory. of the arc foot.

Selon une autre réalisation préférée de l'invention, des moyens sont prévus pour ajuster la modulation de la valeur du courant, afin de synchroniser les déplacements axiaux des pieds d'arc aux deux électrodes pour conserver une longueur d'arc constante et ainsi conserver la tension d'arc à la même valeur.According to another preferred embodiment of the invention, means are provided for adjusting the modulation of the value of the current, in order to synchronize the axial displacements of the arc feet at the two electrodes in order to maintain a constant arc length and thus maintain the arc voltage at the same value.

En se référant à la figure 4, on verra que la torche 29 comporte au moins deux bobines de champs 31 et 33 pour chaque électrode contrairement aux torches commerciales qui n'en comportent qu'une seule. La valeur du courant dans une des bobines (ou les deux) est modulée par tout moyen connu 35 continuellement, de façon à modifier axialement la position du minimum de la somme des deux champs entraînant ainsi un déplacement axial d de la trajectoire radiale a ou b du pied d'arc 37. Le pied d'arc ne décrit plus un cercle, il se déplace sur une surface cylindrique.Les déplacements axiaux des pieds d'arc aux deux électrodes peuvent être synchronisés par tous moyens connus pour conserver une longueur d'arc constante et ainsi conserver la tension d'arc à la même valeur.Referring to Figure 4, we will see that the torch 29 has at least two field coils 31 and 33 for each electrode unlike commercial torches which have only one. The value of current in one of the coils (or both) is modulated by any known means 35 continuously, so as to modify axially the position of the minimum of the sum of the two fields thus causing an axial displacement d of the radial trajectory a or b of the foot d arc 37. The arc foot no longer describes a circle, it moves on a cylindrical surface. The axial movements of the arc feet at the two electrodes can be synchronized by any known means to maintain a constant arc length and thus keep the arc voltage at the same value.

Un déplacement axial de la trajectoire du pied d'arc peut également être obtenu dans le cas où chaque électrode de la torche à plasma ne comporte qu'une seule bobine et une injection tourbillonnaire du gaz ; ce déplacement peut, en effet, être obtenu en modulant continuellement le courant dans la bobine. Ce contrôle est néanmoins moins efficace que par l'emploi de deux ou plusieurs bobines.An axial displacement of the arc foot path can also be obtained in the case where each electrode of the plasma torch comprises only a single coil and a vortex injection of the gas; this displacement can, in fact, be obtained by continuously modulating the current in the coil. This control is nevertheless less effective than by the use of two or more coils.

Le taux d'érosion d'une torche commerciale a été mesuré par plusieurs fabricants ; . il est approximativement de 1,5 x 10-9 kg par coulomb d'électricité. La quantité de matière érodée après 400 heures de fonctionnement à 1000A d'une torche est donc de :

Figure imgb0001
The erosion rate of a commercial torch has been measured by several manufacturers; . it is approximately 1.5 x 10 -9 kg per coulomb of electricity. The amount of material eroded after 400 hours of operation at 1000A of a torch is therefore:
Figure imgb0001

Pour une torche de 7 cm de diamètre intérieur d'électrode et de 1 cm d'épaisseur utile au point de vue érosion, la longueur X érodée selon la direction axiale est de (densité pour le cuivre 8,95) :

Figure imgb0002
For a torch of 7 cm inside diameter of electrode and 1 cm of useful thickness from the point of view of erosion, the length X eroded in the axial direction is of (density for copper 8.95):
Figure imgb0002

Si toute la surface de l'électrode d'une longueur supérieure à 50 cm est utilisée, il y a une augmentation de la durée de vie d'un facteur de 4,5 (soit 2000 heures).If the entire surface of the electrode longer than 50 cm is used, there is an increase in the service life by a factor of 4.5 (i.e. 2000 hours).

Claims (14)

1- Procédé de contrôle de l'érosion des électrodes (1,3) d'une torche à plasma, dans laquelle s'établit un arc électrique, lorsque les électrodes (1,3) sont reliées à une alimentation électrique (5,7), un champ magnétique axial engendré par un système à bobine de champ (17,19) provoquant la rotation des pieds d'arc (21,23) selon une trajectoire circulaire à l'intérieur des électrodes (1,3)., caractérisé en ce que l'on fait varier périodiquement la valeur du courant dans le système à bobine de champ (17,19) utilisé pour faire tourner l'arc, entraînant ainsi un déplacement axial de la trajectoire circulaire du pied d'arc (21,23). 1 - Method for controlling the erosion of the electrodes (1,3) of a plasma torch, in which an electric arc is established, when the electrodes (1,3) are connected to a power supply (5,7 ), an axial magnetic field generated by a field coil system (17,19) causing the arc feet (21,23) to rotate along a circular path inside the electrodes (1,3)., characterized in that the value of the current is periodically varied in the field coil system (17,19) used to rotate the arc, thus causing an axial displacement of the circular path of the arc foot (21, 23). 2- Procédé selon la revendication 1, caractérisé en ce que l'on fait moduler continuellement la valeur du courant dans le système de bobine (17,19), de façon à faire déplacer chacun des pieds d'arc (21,23) sur une surface cylindrique.2- A method according to claim 1, characterized in that the current value is continuously modulated in the coil system (17,19), so as to move each of the arc feet (21,23) on a cylindrical surface. 3- Procédé selon la revendication 2, caractérisé. en ce que les pieds d'arc (21,23) se déplacent selon une trajectoire hélicoïdale.3- A method according to claim 2, characterized. in that the arc feet (21,23) move in a helical path. 4- Procédé selon la revendication 1, caractérisé en ce que le système à bobine de champ comporte une bobine de champ (17,19) pour chaque électrode respectivement (1,3).4- A method according to claim 1, characterized in that the field coil system comprises a field coil (17,19) for each electrode respectively (1,3). 5- Procédé selon la revendication 1, caractérisé en ce que le système à bobine de champ comporte au moins deux bobines de champ (31,33) pour chaque électrode.5- Method according to claim 1, characterized in that the field coil system comprises at least two field coils (31,33) for each electrode. 6- Procédé selon la revendication 5, caractérisé en ce que la valeur du courant dans au moins une des bobines est modulée continuellement, de façon à modifier axialement la position du minimum de la somme des champs entraînant ainsi un déplacement axial de la trajectoire radiale du pied d'arc.6- A method according to claim 5, characterized in that the value of the current in at least one of the coils is continuously modulated, so as to modify axially the position of the minimum of the sum of the fields thus causing an axial displacement of the radial trajectory of the arc foot. 7- Procédé selon la revendication 6, caractérisé en ce que l'on ajuste la modulation de la valeur des courants, afin de synchroniser les déplacements axiaux des pieds d'arc aux deux électrodes pour conserver une longueur d'arc constante et ainsi conserver la tension d'arc à la même valeur.7- A method according to claim 6, characterized in that one adjusts the modulation of the value of the currents, in order to synchronize the axial displacements of the arc feet at the two electrodes to maintain a length constant arc and thus keep the arc voltage at the same value. 8- Torche à plasma comportant deux électrodes cylindriques (1,3) permettant d'obtenir un arc électrique lorsque lesdites électrodes sont reliées à une alimentation électrique (5,7), un système à bobine de champ (17,19) pour chaque électrode pour provoquer la rotation des pieds d'arc selon une trajectoire circulaire à l'intérieur des électrodes cylindriques, caractérisée en ce que des moyens (35) sont prévus pour faire varier périodiquement la valeur du courant dans le système à bobine de champ utilisé pour faire tourner l'arc entraînant ainsi un déplacement axial de la trajectoire circulaire du pied d'arc.8- Plasma torch comprising two cylindrical electrodes (1,3) making it possible to obtain an electric arc when said electrodes are connected to a power supply (5,7), a field coil system (17,19) for each electrode for causing the arc feet to rotate along a circular path inside the cylindrical electrodes, characterized in that means (35) are provided for periodically varying the value of the current in the field coil system used to make rotate the arch thus causing an axial displacement of the circular path of the arch foot. 9- Torche à plasma selon la revendication 8, caractérisée en ce que lesdits moyens sont agencés pour moduler continuellement la valeur du courant dans le système à bobine, de façon à faire déplacer chacun des pieds d'arc sur la surface interne des électrodes.9- plasma torch according to claim 8, characterized in that said means are arranged to continuously modulate the value of the current in the coil system, so as to move each of the arc feet on the internal surface of the electrodes. 10- Torche à plasma selon la revendication 9, caractérisée en ce que le déplacement sur la surface cylindrique s'effectue selon une trajectoire hélicoïdale.10- plasma torch according to claim 9, characterized in that the displacement on the cylindrical surface is carried out along a helical path. 11- Torche à plasma selon la revendication 8, caractérisée en ce que le système à bobine de champ comporte une bobine de champ (17,19) pour chaque électrode, respectivement (1,3).11- plasma torch according to claim 8, characterized in that the field coil system comprises a field coil (17,19) for each electrode, respectively (1,3). 12- Torche à plasma selon la revendication 11, caractérisée en ce que le système à bobine de champ comporte au moins deux bobines de champ (31,33) pour chaque électrode.12- plasma torch according to claim 11, characterized in that the field coil system comprises at least two field coils (31,33) for each electrode. 13- Torche à plasma selon la revendication 12, caractérisée en ce que des moyens (35) sont prévus pour moduler continuellement la valeur du courant dans une des bobines, de façon à modifier axialement la position du minimum de la somme des deux champs entraînant ainsi un déplacement axial de la trajectoire radiale du pied d'arc.13- Plasma torch according to claim 12, characterized in that means (35) are provided for continuously modulating the value of the current in one of the coils, so as to modify axially the position of the minimum of the sum of the two fields thus causing an axial displacement of the radial trajectory of the arch foot. 14- Torche à plasma selon la revendication 13, caractérisée en ce que des moyens sont prévus pour ajuster la modulation de la valeur du courant, afin de synchroniser les déplacements axiaux des pieds d'arc aux deux électrodes pour conserver une longueur d'arc constante et ainsi conserver la tension d'arc à la même valeur.14- plasma torch according to claim 13, characterized in that means are provided for adjusting the modulation of the current value, in order to synchronize ser the axial displacements of the arc feet at the two electrodes to maintain a constant arc length and thus keep the arc voltage at the same value.
EP85420199A 1985-06-07 1985-11-08 Method and system for controlling the electrode erosion of a plasma torch Expired - Lifetime EP0204052B1 (en)

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AT85420199T ATE66562T1 (en) 1985-06-07 1985-11-08 METHOD AND SYSTEM FOR CONTROLLING ELECTRODE EROSION OF A PLASMA TORCH.

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CA483451 1985-06-07
CA000483451A CA1248185A (en) 1985-06-07 1985-06-07 Method and system for erosion control of plasma torch electrodes

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FR2685850A1 (en) * 1991-12-31 1993-07-02 Electricite De France METHOD AND ELECTRICAL POWER SUPPLY FOR PLASMA TORCH.
WO2010070051A1 (en) * 2008-12-19 2010-06-24 Europlasma Method of monitoring the wear of at least one of the electrodes of a plasma torch

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EP0277845A1 (en) * 1987-01-07 1988-08-10 Electricite De France Plasma torch with a longitudinally moving up-stream arc root,and method for controlling its displacement
FR2685850A1 (en) * 1991-12-31 1993-07-02 Electricite De France METHOD AND ELECTRICAL POWER SUPPLY FOR PLASMA TORCH.
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US8502109B2 (en) 2008-12-19 2013-08-06 Europlasma Method of monitoring the wear of at least one of the electrodes of a plasma torch

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EP0204052B1 (en) 1991-08-21
CA1248185A (en) 1989-01-03
US4683367A (en) 1987-07-28
ATE66562T1 (en) 1991-09-15
DE3583864D1 (en) 1991-09-26
EP0204052A3 (en) 1987-11-04

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