EP0277845A1 - Plasma torch with a longitudinally moving up-stream arc root,and method for controlling its displacement - Google Patents

Plasma torch with a longitudinally moving up-stream arc root,and method for controlling its displacement Download PDF

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Publication number
EP0277845A1
EP0277845A1 EP88400007A EP88400007A EP0277845A1 EP 0277845 A1 EP0277845 A1 EP 0277845A1 EP 88400007 A EP88400007 A EP 88400007A EP 88400007 A EP88400007 A EP 88400007A EP 0277845 A1 EP0277845 A1 EP 0277845A1
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EP
European Patent Office
Prior art keywords
electrode
upstream
torch
gas
upstream electrode
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.)
Granted
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EP88400007A
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German (de)
French (fr)
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EP0277845B1 (en
Inventor
Pierre Pasquini
Jean-Pierre Serrano
Maxime Labrot
Didier Pineau
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Electricite de France SA
Airbus Group SAS
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Electricite de France SA
Airbus Group SAS
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Priority to AT88400007T priority Critical patent/ATE69684T1/en
Publication of EP0277845A1 publication Critical patent/EP0277845A1/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
    • 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
    • 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
    • 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
    • H05H1/3468—Vortex generators
    • 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
    • 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
    • H05H1/3494—Means for controlling discharge parameters

Definitions

  • the present invention relates to plasma torches and, more particularly, high power plasma torches whose longevity of the electrodes is increased.
  • Plasma torches or arc plasma torches are known in the art.
  • This type of torch consists of two electrodes, an anode and a tubular and coaxial cathode. An arc is established between the electrodes, and simultaneously, a plasma gas is injected. The arc which bursts between the electrodes is maintained and carries the gas at very high temperature and ionizes it. At the outlet of one of the electrodes, this gas is driven at a high speed and the plasma which it constitutes forms the heat-transfer agent.
  • the arc which gushes between the two electrodes is for example struck by contact using an auxiliary starting electrode and is then transferred between the two tubular electrodes under the action of the vortex injection of a gas into a chamber located between the electrodes. This also ensures the rotation of the foot of the downstream arc on itself to avoid the fusion of the corresponding electrode.
  • the displacement of the upstream arc foot on itself is obtained by an auxiliary magnetic field generated by a coil which surrounds the upstream electrode which is in the manner of a thermowell with a bottom.
  • upstream and downstream are identified with respect to the direction of flow of the plasma.
  • Certain types of plasma torches deliver powers between 10 and 50 kW and those to which the invention applies more particularly can produce several megawatts.
  • Such a plasma torch includes consumable elements: the electrodes.
  • the longevity of electrodes is a function of many parameters, for example the power of the torch and more particularly the value of the arc current, the nature of the plasma gas injected due to its decomposition and the reactions it can have on the constituent materials of the electrodes .
  • the longevity of the electrodes is also a function of the service of the torch depending on whether it is continuous or discontinuous. It is conventional that the longevity of the electrodes varies from a few tens of hours for the torches of relatively small power to several hundred hours for those of high power which the invention relates to.
  • the object of the invention is essentially to regulate the wear of the upstream electrode and for this to control the place of attachment of the arc foot to the upstream electrode.
  • the subject of the invention is a method for regulating the wear, in order to increase its longevity, of an electrode of a plasma torch made up, inter alia, of two coaxial tubular electrodes between which an arc is established and which are separated by a chamber into which a plasma gas is injected, according to which the movement of the foot of the arc on the upstream electrode is controlled to make it describe it by scanning according to a longitudinal translation alternative to the oscillatory requirement at a frequency of 1 Hz approximately or less.
  • this scanning is discrete and staggered or continuous and progressive and is done in a single or multiple stroke accompanied, if necessary, by an oscillation or vibration of the upstream arc foot on itself around each of the various positions it occupies during its electrode sweep.
  • the subject of the invention is also a plasma torch consisting of an upstream electrode and a downstream tubular and coaxial electrode separated by a vortex plasma gas injection chamber into which opens a priming electrode and which is equipped with: '' there is a coil coaxial with the upstream electrode which when it is traversed by a current contributes to determining the position of attachment of the upstream arc foot on the upstream electrode and which is equipped with means for control the position of the attachment of the arc to the upstream electrode and to increase the usable range in order to regulate wear and increase the longevity of the electrode.
  • These means cause the upstream foot of the arc in the upstream electrode to move by alternating longitudinal scanning, possibly with oscillation.
  • These means include an electrical supply where a generator is placed which delivers a direct current of constant or non-optionally pulsating wavy average value whose frequency is of the order of 1 Hz or less.
  • These means include a hole in the bottom of the upstream electrode and a diffuser arranged transversely to the axis of the latter near its bottom to deliver a preferably vortex gas and a secondary gas supply with a modulated flow which is on the order of three to thirteen times less than the flow rate of the plasma gas injected into the chamber located between the electrodes by a main supply.
  • a conventional torch 10 is made up of different assembled elements. Only those that relate directly or indirectly to the invention will be referenced and described. All the other constitutive elements are conventional for the specialist in the technique considered and we will therefore not extend them further.
  • This torch 10 comprises a downstream electrode 11, an upstream electrode 12, a priming electrode 13 and a coil 14 intended to generate a field magnetic axial.
  • a chamber 15 is formed, the role of which will be explained later.
  • Such a plasma torch is supplied by means of an electric circuit 200 shown in more detail schematically in FIG. 2.
  • the supply of plasma gas for example air, is via an orifice 30 of a pipe associated with an injector 31 disposed in the vicinity of the chamber 15.
  • the plasma gas supply is capable of delivering volumes of 500 to 1000 m3 / h, brought back to normal pressure, under pressures of 8 to 10 bars (0.8 to 1 MPa), it comprises a compressor and remote-controlled distribution valves.
  • the torch is also associated with servitudes such as a cooling water supply connected to a pipe 40 and a control and regulation system not shown.
  • the cooling water supply is capable of delivering 50 m3 / h under 30 bars (3 MPa) approximately. It includes a medium pressure pump, remote controlled distribution valves and a secondary circuit to recover or evacuate the calories acquired from the torch.
  • Plasma gas supplies, cooling water and the control and regulation system are very conventional and will not be described in more detail. It will simply be indicated that the command and regulation system comprises sensors, computers, automata, a control console which act on the electrical supply 200 as will be specified below and the gas and cooling water supplies. , respectively, so as to ensure the proper functioning of the plasma torch according to the conditions which have been assigned to it.
  • FIG. 2 where the electrical supply 200 of a plasma torch is schematically represented.
  • this supply 200 comprises two separate circuits: a circuit 210 intended to supply the coil and a circuit 250 more specifically intended to supply the arc.
  • the circuit 210 comprises a transformer 211, for example of 100 kVA installed, which supplies rectifiers 212 with thyristors and diodes; as indicated below, these rectifiers deliver the current to the setpoint value of the current which supplies the coil according to the invention.
  • This circuit also includes disconnectors and circuit breakers whose role is conventional and on which we will not expand.
  • the circuit 250 comprises a transformer 251, for example of 2.5 MVA, a series of rectifiers 252 with thyristors and diodes and an inductance 253 for adaptation or coupling. Here also classic disconnectors and circuit breakers are shown.
  • circuit breakers as is conventional.
  • Such a plasma torch supplied with a continuous intensity of 900 A is capable of delivering a power greater than approximately 2 MW.
  • such a plasma torch requires, in addition to its power supply for the arc, a direct current electric source of 100 kVA installed for the sole supply of the field coil.
  • This field coil is used to generate an induction which has a double function: that of ensuring the rotation of the flow of ionized particles and, also, that of determining the position of the upstream arc foot on the upstream electrode.
  • the supply current of the field coil for example between 600 and 900 A, the duration of each level being a few hundred hours as illustrated in Fig.3C where the instantaneous value fluctuates in a pulsating manner at very low frequency, of the order of 1 Hz, with a constant amplitude which can be between 0 and about 150 A.
  • the magnetic field is insufficient to stabilize the arc and it crosses the median plane of the coil and clings to the bottom of the rapidly deteriorating electrode.
  • the technique according to the invention is used which standardizes and extends over practically its entire length the wear of the upstream electrode, and therefore contributes to increasing its service life, by controlling displacement of the arc on the upstream electrode.
  • the upstream electrode is scanned axially in particular alternatively at the arc foot.
  • the rectifiers 212 are piloted in voltage, for example a Graetz bridge, so that the reference value of the current flowing through the coil has a pulsating wavy continuous intensity of constant average value as shown in Fig.3A.
  • the duration at half height of the pulse is about a quarter of that of the period.
  • This control is ensured, for example, by a 0-10 V voltage generator commercially available with linear operation which operates so that at the voltage 0 V corresponds a current in the coil of approximately 200 A and that at the voltage 10 V corresponds to an intensity of 1000 A.
  • This voltage generator is controlled by a programmable microcomputer according to a law established experimentally as indicated below.
  • a frequency of 1 Hz or less is chosen and a ratio of maximum and minimum intensities of the order of about 2.5.
  • this curve is approximately parabolic, the intensity of the current in the coil varies according to FIG. 3A.
  • a gas is injected through the bottom of the upstream electrode with a modulated flow rate and preferably by making it swirl.
  • a diffuser is placed in the vicinity of the bottom of the upstream electrode so as to supply it with air or gas, the nature of which is for example the same or different from that of the plasma gas, using a vortex to rotate the upstream arc foot in the electrode, before the chamber, and establish a barrier which prevents the arching of the arc at the bottom of the electrode.
  • the flow determines the position of the arc foot and the modulation regulates the oscillation of the latter.
  • the upstream electrode 120 and the diffuser 131 which is associated therewith, according to the invention, are shown in detail in FIGS. 5 and 6.
  • the upstream electrode comprises a hollow cylindrical body, for example made of copper, at the bottom of which is placed for example by screwing the diffuser according to the invention.
  • the tubular cylindrical part has an internal diameter of 70 mm over a length of approximately 380 mm. While the bottom of the upstream electrodes for high power torches according to the prior art can be considered to be closed because only crossed by a very small hole intended to allow passage to a pressure sensor, the electrode according to the invention has a bottom that can be described as open because it is pierced by a hole 126 for fixing a pipe to inject gas delivered by a secondary supply.
  • the diffuser 131 shown schematically in perspective in Fig.6 is made for example of an alloyed copper. It is in the form of a disc 132 of approximately 65 mm in diameter and a thickness of the order of 10 mm; it is extended on one side by a cone 133 projecting about 15 mm. This cone has a base 134 of approximately 50 mm which delimits a flange 135 on one face of the disc. As can be seen, the flange 135 is pierced with oblique channels 136, inclined by 30 ° for example on the face, and distributed uniformly around the periphery of the crown, at an angular pitch of 30 ° in this embodiment. These inclined channels, with a diameter of approximately 2 mm, have axes which project a year 30 ° between two successive oblique channels.
  • the diffuser has only one crown of channels.
  • the dimension of the collar can be chosen so that it is possible to arrange therein several concentric crowns of channels and that the channels of the same crown or of different crowns may not be identical. They can vary by their angular pitch, their inclination on the face, the angle they make between them, their directions and also by their respective size.
  • cylindrical channels with a circular cross section there is nothing to prevent these channels from having a different configuration and profile, for example they can be conical or biconic to form venturi.
  • the choices of these parameters are classic in aerodynamics; they are a function, for example, of the flow rate, pressure, speed, rotation of the gas to be chosen.
  • the bottom of the upstream electrode according to the invention is extended towards the outside by a tail at the end of which an end piece has been provided so as to be able to fix the supply pipe therein for the gas to be injected.
  • the pressure and the flow rate of the injected vortex gas determine the place of attachment of the foot of the arc.
  • a minimum flow rate is required which depends on the geometry of the torch; for the embodiment described and shown, this minimum flow rate is approximately 33 g / s.
  • the secondary gas supply which allows insufflation from the bottom of the upstream electrode is composed of conventional equipment chosen according to the flow rates, pressures and modulation rate and the nature of the gas.
  • the power of the torch could be increased by increasing the voltage, but then the length of the arc also increased.
  • the gas injected by the bottom is swirled.
  • FIG. 4 regular wear of the upstream electrode is obtained over a large area.
  • This figure is the superficial cartography, on a large scale, of a meridian section, according to an anamorphosis where the ordinates are multiplied by a factor of fifty relative to the abscices.
  • the outer surface is given the reference 122, the inner surface the reference 123a, before operation, and 123p after operation.
  • the zone of influence of the coil bears the reference 121 and the arrow fixes the upstream / downstream orientation. It is observed that the wear is uniform over the appropriate range.
  • the life of the upstream electrode has more than quadrupled.
  • the invention resides in the fact of the longitudinal displacement, along the axis of the torch, if there is an alternative and if necessary oscillatory, of the upstream foot of the arch in the upstream electrode and that this technique can be implemented electromagnetically by supplying the coil with variable direct current and / or pulsating ripple and / or aerodynamically by injecting through the bottom of the upstream electrode a gas modulated preferably in flow rate and in particular vortex.
  • the means set out for implementing the invention can operate independently or act together to combine their effects.
  • the ratio of maximum and minimum intensities of the pulsating direct current flowing through the coil can be of the order of a thousand.
  • the invention finds application, for example, in the iron and steel industry for reheating or overheating wind in blast furnace nozzles, for assisted combustion of coal in blast furnaces, and in cement works for decarbonising clay raw materials.

Abstract

The invention concerns plasma torches comprising an upstream electrode (12), a downstream electrode (11), a chamber (15) for the injection of plasma producing gas, a priming electrode (13) and optionally a magnetic field coil (14), in which the upstream root of the arc is displaced on the upstream electrode. According to the invention, in order to control a continuous or reciprocating and/or an oscillatory translation, the field coil is supplied with a variable direct current, if need be a pulsatory undulatory current, and/or a diffuser is placed at the inner end of the upstream electrode which is supplied with a modulated flow of gas which it causes to whirl. Application in high power plasma torches for regularizing and rendering uniform the wear of the electrodes so as to prolong the life thereof.

Description

La présente invention concerne les torches à plasma et, plus particulièrement, les torches à plasma de grande puissance dont la longévité des électrodes est augmentée.The present invention relates to plasma torches and, more particularly, high power plasma torches whose longevity of the electrodes is increased.

Les torches à plasma ou chalumeaux à plasma d'arc sont connus dans la technique. Ce type de torche est constitué de deux électrodes, une anode et une ca­thode tubulaires et coaxiales. On établit un arc entre les électrodes, et simultanément, on injecte un gaz plasmagène. L'arc qui éclate entre les électrodes est entretenu et porte le gaz à très haute température et l'ionise. A la sortie de l'une des électrodes ce gaz est animé d'une grande vitesse et le plasma qu'il constitue forme l'agent caloporteur.Plasma torches or arc plasma torches are known in the art. This type of torch consists of two electrodes, an anode and a tubular and coaxial cathode. An arc is established between the electrodes, and simultaneously, a plasma gas is injected. The arc which bursts between the electrodes is maintained and carries the gas at very high temperature and ionizes it. At the outlet of one of the electrodes, this gas is driven at a high speed and the plasma which it constitutes forms the heat-transfer agent.

L'arc qui jaillit entre les deux électrodes est par exemple amorcé par contact à l'aide d'une électrode auxiliaire de démarrage puis est ensuite transféré entre les deux électrodes tubulaires sous l'action de l'injection tourbillonnaire d'un gaz dans une chambre située entre les électrodes. Ceci assure aussi la rotation sur lui même du pied de l'arc aval pour éviter la fusion de l'électrode correspondante. Le déplacement sur lui même du pied d'arc amont est obtenu par un champ magnétique auxiliaire engendré par une bobine qui entoure l'électrode amont qui se pré­sente à la manière d'un doigt de gant avec un fond. Les termes amont et aval sont repérés par rapport au sens d'écoulement du plasma.The arc which gushes between the two electrodes is for example struck by contact using an auxiliary starting electrode and is then transferred between the two tubular electrodes under the action of the vortex injection of a gas into a chamber located between the electrodes. This also ensures the rotation of the foot of the downstream arc on itself to avoid the fusion of the corresponding electrode. The displacement of the upstream arc foot on itself is obtained by an auxiliary magnetic field generated by a coil which surrounds the upstream electrode which is in the manner of a thermowell with a bottom. The terms upstream and downstream are identified with respect to the direction of flow of the plasma.

Certains types de torches à plasma délivrent des puissances comprises entre 10 et 50 kW et celles auquel l'invention s'applique plus particulièrement peuvent produire plusieurs mégawatts.Certain types of plasma torches deliver powers between 10 and 50 kW and those to which the invention applies more particularly can produce several megawatts.

Une telle torche à plasma comprend des élé­ments consommables: les électrodes. La longévité des électrodes est fonction de nombreux paramètres, par exemple la puissance de la torche et plus particuliè­rement la valeur du courant d'arc, la nature du gaz plasmagène injecté du fait de sa décomposition et des réactions qu'il peut avoir sur les matériaux cons­titutifs des électrodes. La longévité des électodes est fonction, aussi, du service de la torche suivant que celui-ci est continu ou discontinu. Il est clas­sique que la longévité des électrodes varie de quel­ques dizaines d'heures pour les torches de relati­vement petite puissance à plusieurs centaines d'heures pour celles de grande puissance que concerne l'inven­tion.Such a plasma torch includes consumable elements: the electrodes. The longevity of electrodes is a function of many parameters, for example the power of the torch and more particularly the value of the arc current, the nature of the plasma gas injected due to its decomposition and the reactions it can have on the constituent materials of the electrodes . The longevity of the electrodes is also a function of the service of the torch depending on whether it is continuous or discontinuous. It is conventional that the longevity of the electrodes varies from a few tens of hours for the torches of relatively small power to several hundred hours for those of high power which the invention relates to.

La longévité relativement réduite des élec­trodes est un inconvénient notable.The relatively short life of the electrodes is a notable drawback.

Pour tenter d'augmenter la durée de vie des électrodes, et en particulier celle de l'électrode amont, on a proposé une solution pour une torche à plasma dont l'électrode amont se présente sous la for­me d'un doigt de gant à fond plein. Selon cette solu­tion, pour agir sur l'usure par érosion des électrodes on a déjà utilisé une source de courant alternatif ou encore injecté le gaz plasmagène dans la chambre in­terélectrode en faisant varier sa pression.In an attempt to increase the lifetime of the electrodes, and in particular that of the upstream electrode, a solution has been proposed for a plasma torch whose upstream electrode is in the form of a thermowell full. According to this solution, to act on the wear by erosion of the electrodes, an alternating current source has already been used or else the plasma gas has been injected into the interelectrode chamber by varying its pressure.

Cette technique, qui paraît séduisante, est toutefois loin de remédier totalement à l'inconvénient signalé.This technique, which seems attractive, is far from completely remedying the drawback reported.

En effet, si on constate que la longévité de l'électrode croît quelque peu, celle-ci s'use trop localement. Il serait possible d'augmenter la plage d'usure par augmentation des variations de débit du gaz plasmagène mais alors lesdites variations de débit seraient préjudiciables à la constance de puissance délivrée par la torche.In fact, if it is found that the longevity of the electrode increases somewhat, the latter wears out too locally. It would be possible to increase the wear range by increasing the variations in the plasma gas flow rate, but then said flow variations would be detrimental to the constancy of power delivered by the torch.

On a constaté que pour une torche de puis­sance donnée, la consommation en masse de l'électrode était une fonction croîssante de l'intensité et que la longueur de l'arc était aussi une fonction croîssante de la tension. On compend donc que si l'on veut, à consommation d'électrode constante, augmenter la puis­sance de la torche il faille augmenter la tension d'où un accroîssement concomitant de la longueur de l'arc c'est-à-dire de l'encombrement physique de l'instal­lation. Pour des raisons pratiques on ne peut pas dépasser certaines limites. Il faut donc imaginer des solutions qui permettent d'augmenter la longueur de l'arc tout en conservant, dans toute la mesure du possible, constante la longueur de la torche.It was found that for a given power torch, the mass consumption of the electrode was a growing function of the intensity and that the length of the arc was also a growing function of the voltage. We therefore understand that if we want, at constant electrode consumption, to increase the power of the torch, it is necessary to increase the voltage, hence a concomitant increase in the length of the arc, i.e. physical size of the installation. For practical reasons one cannot exceed certain limits. It is therefore necessary to imagine solutions which make it possible to increase the length of the arc while keeping, as far as possible, constant the length of the torch.

L'invention a essentiellement pour but de régulariser l'usure de l'électrode amont et pour cela de maîtriser le lieu de l'accrochage du pied d'arc sur l'électrode amont.The object of the invention is essentially to regulate the wear of the upstream electrode and for this to control the place of attachment of the arc foot to the upstream electrode.

L'invention a pour objet un procédé pour régulariser l'usure, afin d'en augmenter la longévité, d'une électrode d'une torche à plasma constituées, entre autres, de deux électrodes tubulaires coaxiales entre lesquelles s'établit un arc et qui sont séparées par une chambre où est injecté un gaz plasmagène, selon lequel on maîtrise le déplacement du pied de l'arc sur l'électrode amont pour la lui faire décrire par ba­layage selon une translation longitudinale alternative au besoin oscillatoire à une fréquence de 1 Hz environ ou moindre.The subject of the invention is a method for regulating the wear, in order to increase its longevity, of an electrode of a plasma torch made up, inter alia, of two coaxial tubular electrodes between which an arc is established and which are separated by a chamber into which a plasma gas is injected, according to which the movement of the foot of the arc on the upstream electrode is controlled to make it describe it by scanning according to a longitudinal translation alternative to the oscillatory requirement at a frequency of 1 Hz approximately or less.

Selon l'invention, ce balayage est discret et échelonné ou continu et progressif et se fait en une course unique ou multiple accompagnée, s'il y a lieu, d'une oscillation ou vibration du pied d'arc amont sur lui même autour de chacune des diverses positions qu'il occupe au cours de son balayage de l'électrode.According to the invention, this scanning is discrete and staggered or continuous and progressive and is done in a single or multiple stroke accompanied, if necessary, by an oscillation or vibration of the upstream arc foot on itself around each of the various positions it occupies during its electrode sweep.

L'invention a aussi pour objet une torche à plasma constituée d'une électrode amont et d'une électrode aval tubulaires et coaxiales séparées par une chambre d'injection de gaz plasmagène tourbillon­naire dans laquelle débouche une électrode d'amorçage et qui est équipée s'il y a lieu d'une bobine coaxiale à l'électrode amont qui lorsqu'elle est parcourue par un courant contribue à déterminer la position d'ac­crochage du pied d'arc amont sur l'électrode amont et qui est équipée de moyens pour maîtriser la position de l'accrochage de l'arc sur l'électrode amont et pour augmenter la plage utilisable afin de régulariser l'usure et d'accroître la longévité de l'électrode. Ces moyens font déplacer par balayage longitudinal alternatif éventuellement avec oscillation le pied amont de l'arc dans l'électrode amont. Ces moyens comprennent une alimentation électrique où est placé un générateur qui délivre un courant continu de valeur moyenne constante ou non éventuellement ondulé pulsatoire dont la fréquence est de l'ordre de 1Hz ou moindre. Ces moyens comprennent un perçage dans le fond de l'électode amont et un diffuseur disposé transversalement à l'axe de cette dernière à proximité de son fond pour délivrer un gaz de préférence tour­billonnair et une alimentation secondaire en gaz avec un débit modulé qui est de l'ordre de trois à treize fois moindre que le débit du gaz plasmagène injecté dans la chambre située entre les électrodes par une alimentation principale.The subject of the invention is also a plasma torch consisting of an upstream electrode and a downstream tubular and coaxial electrode separated by a vortex plasma gas injection chamber into which opens a priming electrode and which is equipped with: '' there is a coil coaxial with the upstream electrode which when it is traversed by a current contributes to determining the position of attachment of the upstream arc foot on the upstream electrode and which is equipped with means for control the position of the attachment of the arc to the upstream electrode and to increase the usable range in order to regulate wear and increase the longevity of the electrode. These means cause the upstream foot of the arc in the upstream electrode to move by alternating longitudinal scanning, possibly with oscillation. These means include an electrical supply where a generator is placed which delivers a direct current of constant or non-optionally pulsating wavy average value whose frequency is of the order of 1 Hz or less. These means include a hole in the bottom of the upstream electrode and a diffuser arranged transversely to the axis of the latter near its bottom to deliver a preferably vortex gas and a secondary gas supply with a modulated flow which is on the order of three to thirteen times less than the flow rate of the plasma gas injected into the chamber located between the electrodes by a main supply.

La description qui va suivre est une forme particulière mais non limitative de l'invention pou­ vant s'appliquer à toute puissance de torche.The description which follows is a particular but non-limiting form of the invention for Before applying to any torch power.

D'autres caractéristiques de l'invention ap­paraîtront à la lecture de la description qui suit et à l'examen des dessins annexés donnés seulement à titre d'exemple où :

  • - la Fig.1 est une demi-coupe demi-éléva­trice longitudinale d'un mode de réalisation d'une torche à plasma selon la technique classique ;
  • - la Fig.2 est un schéma d'une alimentation électrique d'une telle torche, perfectionnée selon l'invention;
  • - les Fig.3A, 3B et 3C sont des courbes illustrant la variation du courant continu alimentant la bobine selon l'invention ;
  • - la Fig.4 est un graphique illustrant à très grande échelle la manière dont l'électrode amont s'use ;
  • - la Fig.5 est une coupe partielle de l'ex­trémité amont d'une électrode amont selon l'invention; et
  • - la Fig.6 est une vue perspective schéma­tique illustrant la configuration d'un mode de réa­lisation du diffuseur associé à l'électrode de la Fig.5 selon l'invention.
Other characteristics of the invention will appear on reading the following description and on examining the appended drawings given only by way of example where:
  • - Fig.1 is a longitudinal half-elevating half-section of an embodiment of a plasma torch according to the conventional technique;
  • - Fig.2 is a diagram of an electrical supply of such a torch, improved according to the invention;
  • - Fig.3A, 3B and 3C are curves illustrating the variation of the direct current supplying the coil according to the invention;
  • - Fig.4 is a graph illustrating on a very large scale how the upstream electrode wears out;
  • - Fig.5 is a partial section of the upstream end of an upstream electrode according to the invention; and
  • - Fig.6 is a schematic perspective view illustrating the configuration of an embodiment of the diffuser associated with the electrode of Fig.5 according to the invention.

Comme on le voit plus particulièrement en se reportant à la Fig.1 du dessin, une torche classique 10 est constituée de différents éléments assemblés. Seuls seront référencés et décrits ceux que concernent directement ou indirectement l'invention. Tous les autres éléments constitutifs sont classiques pour le spécialiste de la technique considérée et on ne s'y étendra donc pas plus amplement.As seen more particularly with reference to Fig.1 of the drawing, a conventional torch 10 is made up of different assembled elements. Only those that relate directly or indirectly to the invention will be referenced and described. All the other constitutive elements are conventional for the specialist in the technique considered and we will therefore not extend them further.

Cette torche 10 comprend une électrode aval 11, une électrode amont 12, une électrode d'amorçage 13 et une bobine 14 destinée à engendrer un champ magnétique axial. Dans l'intervalle inter-électrodes, à proximité de l'électrode d'amorçage 13, est ménagée une chambre 15 dont le rôle sera explicité par la suite. Une telle torche à plasma est alimentée à l'ai­de d'un circuit électrique 200 représenté plus en détail schématiquement sur la Fig. 2.This torch 10 comprises a downstream electrode 11, an upstream electrode 12, a priming electrode 13 and a coil 14 intended to generate a field magnetic axial. In the inter-electrode interval, near the initiation electrode 13, a chamber 15 is formed, the role of which will be explained later. Such a plasma torch is supplied by means of an electric circuit 200 shown in more detail schematically in FIG. 2.

L'alimentation en gaz plasmagène, par exem­ple de l'air, se fait par un orifice 30 d'une cana­lisation associée à un injecteur 31 disposé dans le voisinage de la chambre 15.The supply of plasma gas, for example air, is via an orifice 30 of a pipe associated with an injector 31 disposed in the vicinity of the chamber 15.

L'alimentation en gaz plasmagène, non repré­sentée, est capable de débiter des volumes de 500 à 1000 m³/h, ramenés à la pression normale, sous des pressions de 8 à 10 bars (0,8 à 1 MPa), elle comprend un compresseur et des vannes de distribution télécom­mandées.The plasma gas supply, not shown, is capable of delivering volumes of 500 to 1000 m³ / h, brought back to normal pressure, under pressures of 8 to 10 bars (0.8 to 1 MPa), it comprises a compressor and remote-controlled distribution valves.

A la torche sont encore associées des ser­vitudes telles qu'une alimentation en eau de refroi­dissement raccordée à une tubulure 40 et un système de commande et de régulation non représenté.The torch is also associated with servitudes such as a cooling water supply connected to a pipe 40 and a control and regulation system not shown.

L'alimentation en eau de refroidissement est elle capable de débiter 50 m³/h sous 30 bars (3 MPa) environ. Elle comprend une pompe moyenne pression, des vannes de distribution télécommandées et un circuit secondaire pour récupérer ou évacuer les calories acquises auprès de la torche.The cooling water supply is capable of delivering 50 m³ / h under 30 bars (3 MPa) approximately. It includes a medium pressure pump, remote controlled distribution valves and a secondary circuit to recover or evacuate the calories acquired from the torch.

Les alimentations en gaz plasmagène, en eau de refroidissement et le système de commande et de régulation sont des plus classiques et on ne les décrira pas plus en détail. On indiquera simplement que le système de commande et de régulation comprend des capteurs, des calculateurs, des automates, un pupitre de commande qui agissent sur l'alimentation électrique 200 comme on le précisera par la suite et les alimentations en gaz et en eau de refroidissement, respectivement, de manière à assurer le bon fonction­nement de la torche à plasma selon les modalités qui lui ont été assignées.Plasma gas supplies, cooling water and the control and regulation system are very conventional and will not be described in more detail. It will simply be indicated that the command and regulation system comprises sensors, computers, automata, a control console which act on the electrical supply 200 as will be specified below and the gas and cooling water supplies. , respectively, so as to ensure the proper functioning of the plasma torch according to the conditions which have been assigned to it.

On se reportera maintenant plus particuliè­rement à la Fig.2 où est représentée schématiquement l'alimentation électrique 200 d'une torche à plasma.Reference will now be made more particularly to FIG. 2 where the electrical supply 200 of a plasma torch is schematically represented.

Comme on le voit, cette alimentation 200 comprend deux circuits distincts: un circuit 210 destiné à alimenter la bobine et un circuit 250 plus spécialement destiné à alimenter l'arc.As can be seen, this supply 200 comprises two separate circuits: a circuit 210 intended to supply the coil and a circuit 250 more specifically intended to supply the arc.

Comme dessiné, le circuit 210 comprend un transformateur 211, par exemple de 100 kVA installés, qui alimente des redresseurs 212 à thyristors et diodes; comme on l'indique par la suite, ces redres­seurs délivrent l'intensité à la valeur de consigne du courant qui alimente la bobine selon l'invention. Ce circuit comprend aussi des sectionneurs et disjonc­teurs dont le rôle est classique et sur lequel on ne s'étendra pas.As shown, the circuit 210 comprises a transformer 211, for example of 100 kVA installed, which supplies rectifiers 212 with thyristors and diodes; as indicated below, these rectifiers deliver the current to the setpoint value of the current which supplies the coil according to the invention. This circuit also includes disconnectors and circuit breakers whose role is conventional and on which we will not expand.

Le circuit 250 comprend un transformateur 251, par exemple de 2,5 MVA, une série de redresseurs 252 à thyristors et diodes et une inductance 253 d'adaptation ou couplage. Ici aussi des sectionneurs et disjoncteurs classiques sont figurés.The circuit 250 comprises a transformer 251, for example of 2.5 MVA, a series of rectifiers 252 with thyristors and diodes and an inductance 253 for adaptation or coupling. Here also classic disconnectors and circuit breakers are shown.

Ces deux circuits 210 et 250 sont alimentés en haute tension au travers de disjoncteurs, comme il est classique.These two circuits 210 and 250 are supplied with high voltage through circuit breakers, as is conventional.

Une telle torche à plasma alimentée avec une intensité continue de 900 A est capable de délivrer une puissance supérieure à 2 MW environ.Such a plasma torch supplied with a continuous intensity of 900 A is capable of delivering a power greater than approximately 2 MW.

Pour son fonctionnement, une telle torche à plasma nécessite, en plus de son alimentation de puis­sance pour l'arc, une source électrique en courant continu de 100 kVA intallés pour la seule alimentation de la bobine de champ. Cette bobine de champ est uti­lisée pour engendrer une induction qui a une double fonction: celle d'assurer la mise en rotation du flux de particules ionisées et, aussi, celle de déterminer la position du pied d'arc amont sur l'électrode amont.For its operation, such a plasma torch requires, in addition to its power supply for the arc, a direct current electric source of 100 kVA installed for the sole supply of the field coil. This field coil is used to generate an induction which has a double function: that of ensuring the rotation of the flow of ionized particles and, also, that of determining the position of the upstream arc foot on the upstream electrode.

Lorsqu'une telle torche fonctionne, on par­vient à augmenter la durée de vie de l'électrode amont en faisant varier, par paliers par exemple d'une cin­quantaine d'ampères, l'intensité d'alimentation de la bobine de champ, par exemple entre 600 et 900 A, la durée de chaque palier étant de quelques centaines d'heures comme illustré sur la Fig.3C ou la valeur instantanée fluctue d'une manière pulsatoire à très basse fréquence, de l'ordre de 1 Hz, avec une am­plitude constante pouvant être comprise entre 0 et environ 150 A. En dessous de la valeur minimale donnée à titre d'exemple et fonction de la torche particu­lière, le champ magnétique est insuffisant pour sta­biliser l'arc et celui-ci franchit le plan médian de la bobine et s'accroche au fond de l'électrode qui se détériore rapidement. Ce type de fonctionnement aboutit à une usure de l'électrode par "tranches" qui correspondent aux différents paliers de l'alimentation de la bobine de champ qui fixent chacun une position paraticulière d'accrochage du pied amont sur l'électro­de, position qui balaye par plages successives, d'une de ses extrémités à l'autre, l'électrode en une trans­lation longitudinale unique ; l'usure se tradit par des gorges annulaires successives, que l'on s'efforce de rendre contigües, qui occupent, chacune, axialement quelques dizaines de millimètres soit en tout, addi­tionnées, une zone relativement restreinte d'une centaine de millimètre s'étendant entre l'extrémité aval et le plan médian de la bobine, alors que la plage théoriquement utilisable de l'électrode est égale à trois ou quatre fois par exemple, cette valeur, c'est-à-dire égale à pratiquement la longueur intérieure de l'électrode amont. On voit donc, qu'en théorie on a intérêt à placer la bobine de manière que son plan médian soit voisin du fond de l'extrémité amont de l'électrode pour bénéficier de toute la lon­gueur de cette dernière. Des contrainte pratiques font que cela est presque impossible.When such a torch operates, it is possible to increase the service life of the upstream electrode by varying, by stages for example of fifty amps, the supply current of the field coil, for example between 600 and 900 A, the duration of each level being a few hundred hours as illustrated in Fig.3C where the instantaneous value fluctuates in a pulsating manner at very low frequency, of the order of 1 Hz, with a constant amplitude which can be between 0 and about 150 A. Below the minimum value given by way of example and depending on the particular torch, the magnetic field is insufficient to stabilize the arc and it crosses the median plane of the coil and clings to the bottom of the rapidly deteriorating electrode. This type of operation results in wear of the electrode by "slices" which correspond to the different stages of supply of the field coil which each fix a paraticular position for hooking the upstream foot on the electrode, which position sweeps in successive ranges, from one of its ends to the other, the electrode in a single longitudinal translation; wear results in successive annular grooves, which one strives to make contiguous, which occupy, each, axially a few tens of millimeters or in all, added up, a relatively restricted area of a hundred millimeters s' extending between the downstream end and the median plane of the coil, while the theoretically usable range of the electrode is equal to three or four times for example, this value, that is to say equal to practically the internal length of the upstream electrode. It can therefore be seen that, in theory, it is advantageous to place the coil so that its median plane is close to the bottom of the upstream end of the electrode in order to benefit from the entire length of the latter. Practical constraints make this almost impossible.

On peut aussi utliser des paliers dont les écarts sont plus restreints, les "sauts" étant de l'ordre de quelques ampères. La valeur moyenne de l'intensité du courant continu dans la bobine tend alors à varier d'une manière très progressive et l'on peut au besoin lui donner la configuration d'une ligne "continue" (Fig.3B) et non plus échelonnée (Fig.3C), dans un sens croissant ou décroissant avec également une valeur instantanée fluctuant de manière pulsatoire à très basse fréquence, de l'ordre de 1 Hz, avec une amplitude constante pouvant être comprise entre 0 et environ 150 A. Une telle variation du courant continu s'obtient de manière classique et le spécialiste dis­pose de nombreuses techniques pour y parvenir.You can also use bearings whose deviations are more limited, the "jumps" being of the order of a few amps. The average value of the intensity of the direct current in the coil then tends to vary in a very progressive way and one can if necessary give it the configuration of a "continuous" line (Fig.3B) and no longer staggered (Fig.3C), in an increasing or decreasing direction with also an instantaneous value fluctuating in pulsation at very low frequency, of the order of 1 Hz, with a constant amplitude which can be between 0 and approximately 150 A. Such a variation of the direct current is obtained in a conventional way and the specialist has many techniques to achieve this.

Pour remédier à l'usure trop localisée de l'électrode on utilise la technique selon l'invention qui uniformise et étend sur pratiquement toute sa longueur l'usure de l'électrode amont, et donc con­tribue à augmenter sa durée de vie, en maîtrisant le déplacement de l'arc sur l'électrode amont.To remedy the too localized wear of the electrode, the technique according to the invention is used which standardizes and extends over practically its entire length the wear of the upstream electrode, and therefore contributes to increasing its service life, by controlling displacement of the arc on the upstream electrode.

Selon l'invention on fait balayer axialement notamment de manière alternative au pied d'arc l'élec­trode amont. Pour ce faire, selon l'invention on pi­lote en tension les redresseurs 212, par exemple un pont de Graetz, pour que la valeur de consigne du courant qui parcourt la bobine présente une intensité continue ondulée pulsatoire de valeur moyenne cons­tante comme dessiné sur la Fig.3A. Comme on l'y voit, la durée à mi-hauteur de l'impulsion est d'environ le quart de celle de la période.According to the invention, the upstream electrode is scanned axially in particular alternatively at the arc foot. To do this, according to the invention, the rectifiers 212 are piloted in voltage, for example a Graetz bridge, so that the reference value of the current flowing through the coil has a pulsating wavy continuous intensity of constant average value as shown in Fig.3A. As can be seen, the duration at half height of the pulse is about a quarter of that of the period.

Ce pilotage est assuré, par exemple, par un générateur de tension 0-10 V. du commerce à fonction­nement linéaire qui opère de manière qu'à la tension 0 V corresponde une intensité dans la bobine d'environ 200 A et qu'à la tension 10 V corresponde une inten­sité de 1000 A. Ce générateur de tension est commandé par un microcalculateur programmable selon une loi établie expérimentalement comme il est indiqué par la suite.This control is ensured, for example, by a 0-10 V voltage generator commercially available with linear operation which operates so that at the voltage 0 V corresponds a current in the coil of approximately 200 A and that at the voltage 10 V corresponds to an intensity of 1000 A. This voltage generator is controlled by a programmable microcomputer according to a law established experimentally as indicated below.

On a exposé qu'à chaque valeur de consigne de l'intensité du courant dans la bobine correspond une position bien définie du pied d'arc sur l'élec­trode amont. On a observé que l'orsqu'on fait décroî­tre cette valeur de consigne par palier régulier d'écart ou pas constant, l'intervalle qui sépare deux positions successives correspondantes du pied d'arc va croîssant. La fonction mathématique représentative de cette loi dépend de la géométrie de l'électrode et des caractéristiques électromagnétiques de la bobine. Pour toute torche de configuration donnée on peut dresser expérimentalement par des méthodes classiques la cour­be représentative de la position du pied d'arc en fonction de l'intensité du courant dans la bobine et écrire comme il est bien connu l'équation d'une telle courbe. Connaissant cette équation et sachant qu'on fait, selon l'invention, par exemple balayer alter­nativement régulièrement axialement le pied d'arc amont avec une amplitude fixée et à un rythme choisi, on écrit le programme du calculateur qui commande le courant dans la bobine en intensité et fréquence pour que le pied d'arc suive cette loi. Les techniques de programmation des calculateurs sont classiques et on ne s'y étendra pas plus amplement.It has been explained that for each setpoint of the current intensity in the coil there corresponds a well-defined position of the arc foot on the upstream electrode. It has been observed that when this setpoint is decreased by regular steps of deviation or not constant, the interval which separates two corresponding successive positions of the arc foot will increase. The mathematical function representative of this law depends on the geometry of the electrode and the electromagnetic characteristics of the coil. For any torch of given configuration, it is possible to draw up experimentally by conventional methods the curve representative of the position of the arc foot as a function of the intensity of the current in the coil and write as it is well known the equation of such a curve. Knowing this equation and knowing that, according to the invention, for example, alternately regularly sweeping the upstream arc foot axially with a fixed amplitude and at a chosen rhythm, we write the program of the computer which controls the current in the coil in intensity and frequency so that the arc foot follows this law. The programming techniques of the computers are conventional and we will not extend them further.

Pour un mode de réalisation de l'invention on choisit une fréquence de 1 Hz ou moindre et un rap­port des intensités maximale et minimale de l'ordre de 2,5 environ. Lorsque cette courbe est approximative­ment parabolique, l'intensité du courant dans la bo­bine varie selon la Fig. 3A.For an embodiment of the invention, a frequency of 1 Hz or less is chosen and a ratio of maximum and minimum intensities of the order of about 2.5. When this curve is approximately parabolic, the intensity of the current in the coil varies according to FIG. 3A.

Il est classique de mettre en rotation le pied d'arc sur l'électrode en injectant de l'air ou tout autre gaz plasmagène dans la chambre 15 à l'aide d'un vortex. On fait tourbillonner le gaz selon l'axe longitudinal et à contre-courant du sens d'éjection du plasma, mais ceci s'est avéré totalement insuffisant.It is conventional to rotate the arc foot on the electrode by injecting air or any other plasma gas into the chamber 15 using a vortex. The gas is swirled along the longitudinal axis and against the current of the plasma ejection direction, but this has proved to be completely insufficient.

Pour éviter l'usure et la dégradation du fond de l'électrode amont résultant de l'accrochage du pied d'arc, selon l'invention on fait parcourir axia­lement par balayage éventuellement de manière alterna­tive et s'il y a lieu oscillatoire au pied d'arc l'é­lectrode amont. Pour ce faire on injecte un gaz par le fond de l'électrode amont avec un débit modulé et de préférence en le faisant tourbillonner. Pour cela on dispose au voisinage du fond de l'électrode amont un diffuseur de manière à l'alimenter en air ou en gaz dont la nature est par exemple la même ou différente de celle du gaz plasmagène, suivant un vortex pour mettre en rotation le pied d'arc amont dans l'élec­trode, avant la chambre, et établir une barrière qui interdit l'accrochage de l'arc en fond d'électrode. Le débit détermine la position du pied d'arc et la mo­dulation règle l'oscillation de ce dernier.To avoid wear and degradation of the bottom of the upstream electrode resulting from the attachment of the arch foot, according to the invention, it is scanned axially, optionally alternately, and if necessary oscillating at the foot the upstream electrode. To do this, a gas is injected through the bottom of the upstream electrode with a modulated flow rate and preferably by making it swirl. For this, a diffuser is placed in the vicinity of the bottom of the upstream electrode so as to supply it with air or gas, the nature of which is for example the same or different from that of the plasma gas, using a vortex to rotate the upstream arc foot in the electrode, before the chamber, and establish a barrier which prevents the arching of the arc at the bottom of the electrode. The flow determines the position of the arc foot and the modulation regulates the oscillation of the latter.

L'électrode amont 120 et le diffuseur 131 qui lui est associé, selon l'invention, sont repré­sentés en détail sur les Fig.5 et 6.The upstream electrode 120 and the diffuser 131 which is associated therewith, according to the invention, are shown in detail in FIGS. 5 and 6.

L'électrode amont comporte un corps cylin­drique creux, par exemple en cuivre, au fond de la­quelle se trouve placé par exemple par vissage le dif­fuseur selon l'invention. La partie cylindrique tubu­laire présente un diamètre intérieur de 70 mm sur une longueur de 380 mm, environ. Alors que le fond des électrodes amont pour torche de grande puissance selon la technique antérieure peut être considéré comme étant fermé car seulement traversé par un tout petit trou destiné à livrer passage à un capteur de pres­sion, l'électrode selon l'invention présente un fond que l'on peut qualifier d'ouvert car il est transpercé par un perçage 126 permettant d'y fixer une canalisa­tion pour y injecter du gaz délivré par une alimenta­tion secondaire.The upstream electrode comprises a hollow cylindrical body, for example made of copper, at the bottom of which is placed for example by screwing the diffuser according to the invention. The tubular cylindrical part has an internal diameter of 70 mm over a length of approximately 380 mm. While the bottom of the upstream electrodes for high power torches according to the prior art can be considered to be closed because only crossed by a very small hole intended to allow passage to a pressure sensor, the electrode according to the invention has a bottom that can be described as open because it is pierced by a hole 126 for fixing a pipe to inject gas delivered by a secondary supply.

Le diffuseur 131 représenté schématiquement en perspective sur la Fig.6 est réalisé par exemple en un cuivre allié. Il se présente sous la forme d'un disque 132 de 65 mm environ de diamètre et d'une épaisseur de l'ordre de 10 mm ; il est prolongé d'un côté par un cône 133 en saillie de 15 mm environ. Ce cône présente une base 134 de 50 mm environ qui déli­mite une collerette 135 sur une face du disque. Comme on le voit, la collerette 135 est percée de canaux 136 obliques, inclinés de 30° par exemple sur la face, et répartis uniformément à la périphérie de la couronne, selon un pas angulaire de 30° dans ce mode de réalisa­tion. Ces canaux inclinés, d'un diamétre de 2 mm envi­ron, présentent des axes qui font en projection un an gle de 30° entre deux canaux obliques successifs.The diffuser 131 shown schematically in perspective in Fig.6 is made for example of an alloyed copper. It is in the form of a disc 132 of approximately 65 mm in diameter and a thickness of the order of 10 mm; it is extended on one side by a cone 133 projecting about 15 mm. This cone has a base 134 of approximately 50 mm which delimits a flange 135 on one face of the disc. As can be seen, the flange 135 is pierced with oblique channels 136, inclined by 30 ° for example on the face, and distributed uniformly around the periphery of the crown, at an angular pitch of 30 ° in this embodiment. These inclined channels, with a diameter of approximately 2 mm, have axes which project a year 30 ° between two successive oblique channels.

Dans le mode de réalisation décrit et repré­senté sur la Fig. 6, le diffuseur présente une seule couronne de canaux. Il est clair que la dimension de la collerette peut être choisie de manière à ce que l'on puisse y ménager plusieurs couronnes concentri­ques de canaux et que les canaux d'une même couronne ou de couronnes différentes peuvent ne pas être iden­tiques. Ils peuvent varier par leur pas angulaire, leur inclinaison sur la face, l'angle qu'ils font entre eux, leurs sens et aussi par leur taille res­pective. On a représenté des canaux cylindriques à section droite circulaire; rien ne s'oppose à ce que ces canaux aient une configuration et un profil autres, par exemple ils peuvent être côniques ou bicôniques pour former des venturi. Les choix de ces paramètres sont classiques en aérodynamique; ils sont fonction par exemple du débit, de la pression, de la vitesse, de la rotation du gaz à choisir.In the embodiment described and shown in FIG. 6, the diffuser has only one crown of channels. It is clear that the dimension of the collar can be chosen so that it is possible to arrange therein several concentric crowns of channels and that the channels of the same crown or of different crowns may not be identical. They can vary by their angular pitch, their inclination on the face, the angle they make between them, their directions and also by their respective size. There are shown cylindrical channels with a circular cross section; there is nothing to prevent these channels from having a different configuration and profile, for example they can be conical or biconic to form venturi. The choices of these parameters are classic in aerodynamics; they are a function, for example, of the flow rate, pressure, speed, rotation of the gas to be chosen.

Dans le mode de réalisation dessiné sur la Fig. 5, le fond de l'électrode amont selon l'invention se prolonge vers l'extérieur par une queue à l'extré­mité de laquelle on a ménagé un embout pour pouvoir y fixer la canalisation d'amenée du gaz à injecter. On peut retenir d'autres solutions; selon l'invention le fond ou à défaut la paroi d'électrode voisine est transpercé par un perçage 125 pour le passage du gaz.In the embodiment drawn in FIG. 5, the bottom of the upstream electrode according to the invention is extended towards the outside by a tail at the end of which an end piece has been provided so as to be able to fix the supply pipe therein for the gas to be injected. We can retain other solutions; according to the invention the bottom or failing this the neighboring electrode wall is pierced by a bore 125 for the passage of gas.

La pression et le débit du gaz tourbillon­naire injecté déterminent le lieu de l'accrochage du pied de l'arc. Pour empêcher le pied de l'arc de s'accrocher sur le fond de l'électrode amont, il faut un débit minimal qui est fonction de la géométrie de la torche; pour le mode de réalisation décrit et re­présenté ce débit minimal est d'environ 33g/s. En modulant l'injection, de préférence le débit, on fait osciller longitudinalement le pied d'arc; le taux de modulation détermine l'amplitude de l'oscillation alors que le choix de la valeur moyenne détermine la position autour de laquelle se produit l'oscillation ou vibration. On comprend donc qu'en insufflant du gaz par le fond de l'électrode amont on puisse faire dé­crire au besoin alternativement et s'il y a lieu de manière oscillatoire au pied de l'arc toute, ou pra­tiquement toute la longueur de l'électrode amont, de son extrémité aval au diffuseur.The pressure and the flow rate of the injected vortex gas determine the place of attachment of the foot of the arc. To prevent the foot of the arc from catching on the bottom of the upstream electrode, a minimum flow rate is required which depends on the geometry of the torch; for the embodiment described and shown, this minimum flow rate is approximately 33 g / s. By modulating the injection, preferably the flow, the arc end is oscillated longitudinally; the modulation rate determines the amplitude of the oscillation while the choice of the average value determines the position around which the oscillation or vibration occurs. It is therefore understandable that by blowing gas through the bottom of the upstream electrode, it is possible to have an alternate description, if necessary, and if necessary, oscillating at the foot of the arc, all, or practically the entire length of the upstream electrode, from its downstream end to the diffuser.

L'alimentation secondaire en gaz qui permet l'insufflation par le fond de l'électrode amont est composée d'équipements classiques choisis en fonction des débits, des pressions et du taux de modulation et de la nature du gaz.The secondary gas supply which allows insufflation from the bottom of the upstream electrode is composed of conventional equipment chosen according to the flow rates, pressures and modulation rate and the nature of the gas.

On a indiqué précédemment qu'à consommation d'électrode constante on pouvait augmenter la puis­sance de la torche en accroissant la tension mais qu'alors la longueur de l'arc croissait aussi. Pour permettre un tel allongement de l'arc tout en le con­finant dans une torche d'encombrement inchangé on fait tourbillonner le gaz injecté par le fond.It was previously indicated that at constant electrode consumption, the power of the torch could be increased by increasing the voltage, but then the length of the arc also increased. To allow such an extension of the arc while confining it in a torch of unchanged size, the gas injected by the bottom is swirled.

Comme on peut le voir sur la Fig.4, on ob­tient une usure régulière de l'électrode amont sur une grande étendue. Cette figure est la cartographie su­perficielle, à grande échelle, d'une section méridien­ne, selon une anamorphose où les ordonnées sont multi­pliées par un facteur cinquante relativement aux abs­cices. La surface extérieure porte la référence 122, la surface intérieure la référence 123a, avant fonc­tionnement, et 123p après fonctionnement. La zone d'influence de la bobine porte la référence 121 et la flèche fixe l'orientation amont/ aval. On observe que l'usure est uniforme sur la plage appropriée.As can be seen in Fig. 4, regular wear of the upstream electrode is obtained over a large area. This figure is the superficial cartography, on a large scale, of a meridian section, according to an anamorphosis where the ordinates are multiplied by a factor of fifty relative to the abscices. The outer surface is given the reference 122, the inner surface the reference 123a, before operation, and 123p after operation. The zone of influence of the coil bears the reference 121 and the arrow fixes the upstream / downstream orientation. It is observed that the wear is uniform over the appropriate range.

Grâce à l'invention on a plus que quadruplé la longévité de l'électrode amont.Thanks to the invention, the life of the upstream electrode has more than quadrupled.

Il va de soi que les indications qui ont été données à propos de l'alimentation de la bobine ou du diffuseur et de l'injection de gaz par le fond ne sont que des valeurs indicatives et qu'il est possible d'y apporter des modifications, changements, variations pour tenir compte de l'incidence des autres paramètres qui concourent au bon fonctionnement de la torche à plasma de manière à optimiser les résultats en fonc­tion de l'usage qui est fait de la torche et des buts visés.It goes without saying that the indications which have been given concerning the supply of the coil or the diffuser and the gas injection from the bottom are only indicative values and that it is possible to provide modifications, changes, variations to take into account the impact of the other parameters which contribute to the proper functioning of the plasma torch so as to optimize the results according to the use which is made of the torch and the intended purposes.

De ce qui a été exposé on comprend que l'in­vention réside dans le fait du déplacement longitudi­nal, selon l'axe de la torche, s'il y a lieu alter­natif et au besoin oscillatoire, du pied amont de l'arc dans l'électrode amont et que cette technique peut être mise en oeuvre électromagnétiquement en ali­mentant la bobine en courant continu variable et/ou ondulé pulsatoire et/ou aérodynamiquement en injectant par le fond de l'électrode amont un gaz modulé de préférence en débit et notamment tourbillonnaire. Les moyens exposés pour la mise en oeuvre de l'invention peuvent fonctionner indépendamment ou agir ensemble pour conjuguer leurs effets. C'est ainsi que si l'action du diffuseur est prépondérante, le rapport des intensités maximale et minimale du courant continu pulsatoire parcourant la bobine peut être de l'ordre de mille.From what has been explained, it is understood that the invention resides in the fact of the longitudinal displacement, along the axis of the torch, if there is an alternative and if necessary oscillatory, of the upstream foot of the arch in the upstream electrode and that this technique can be implemented electromagnetically by supplying the coil with variable direct current and / or pulsating ripple and / or aerodynamically by injecting through the bottom of the upstream electrode a gas modulated preferably in flow rate and in particular vortex. The means set out for implementing the invention can operate independently or act together to combine their effects. Thus, if the action of the diffuser is predominant, the ratio of maximum and minimum intensities of the pulsating direct current flowing through the coil can be of the order of a thousand.

L'invention trouve application par exemple en sidérurgie pour le réchauffage ou la surchauffe de vent aux tuyères de hauts fourneaux, pour la combus­tion assistée du charbon dans les hauts fourneaux, et en cimenterie pour la décarbonation des crus d'argile.The invention finds application, for example, in the iron and steel industry for reheating or overheating wind in blast furnace nozzles, for assisted combustion of coal in blast furnaces, and in cement works for decarbonising clay raw materials.

On voit donc le grand intérêt pratique de l'invention qui, en améliorant la longévité de l'élec­trode amont consommable, réduit les interventions de remplacement et d'échange et diminue les coûts des achats de fournitures.We therefore see the great practical interest of the invention which, by improving the longevity of the consumable upstream electrode, reduces the interventions of replacement and exchange and lowers the costs of purchasing supplies.

Claims (15)

1. Procédé pour régulariser l'usure afin d'en augmenter la longévité d'une électrode d'une torche à plasma constituée de deux électrodes tu­bulaires coaxiales entre lesquelles s'établit un arc et qui sont séparées par une chambre où est injecté du gaz plasmagène, selon lequel on maîtrise le déplace­ment du pied de l'arc sur l'électrode amont, repérée par rapport au sens d'écoulement du plasma, pour lui faire balayer longitudinalement et alternativement une partie de la surface interne de l'électrode amont caractérisé en ce que le parcours alternatif s'effec­tue à la fréquence de 1Hz environ ou moins.1. Method for regulating wear in order to increase the longevity of an electrode of a plasma torch consisting of two coaxial tubular electrodes between which an arc is established and which are separated by a chamber into which gas is injected plasmagen, according to which one controls the movement of the foot of the arc on the upstream electrode, identified with respect to the direction of flow of the plasma, to make it sweep longitudinally and alternately a part of the internal surface of the upstream electrode characterized in that the alternative route is carried out at the frequency of approximately 1 Hz or less. 2. Procédé conforme à la revendication 1, caractérisé en ce qu'on fait osciller sur lui même le pied d'arc amont pendant le balayage.2. Method according to claim 1, characterized in that the upstream arc foot oscillates on itself during the sweep. 3. Procédé conforme à l'une quelconque des revendications 1 et 2, selon lequel on injecte par le fond de l'électrode amont un gaz qu'on fait tourbil­lonner suivant l'axe longitudinal et dont on module le débit pour faire se mouvoir longitudinalement le pied de l'arc dans l'électrode amont caractérisé en ce qu'on injecte le gaz avec un débit de trois à quinze fois plus petit que le débit du gaz plasmagène qu'on introduit dans la chambre.3. Method according to any one of claims 1 and 2, according to which is injected through the bottom of the upstream electrode a gas which is swirled along the longitudinal axis and whose flow is modulated to move longitudinally the base of the arc in the upstream electrode, characterized in that the gas is injected with a flow rate of three to fifteen times less than the flow rate of the plasma gas which is introduced into the chamber. 4. Procédé selon l'une quelconque des reven­dications 1 à 3 où la torche est équipée d'une bobine qui entoure localement l'électrode amont et qu'on ali­mente en courant continu variable, caractérisé en ce qu'on alimente la bobine avec un courant continu va­riable dont l'intensité change par paliers.4. Method according to any one of claims 1 to 3 wherein the torch is equipped with a coil which locally surrounds the upstream electrode and which is supplied with variable direct current, characterized in that the coil is supplied with a variable direct current whose intensity changes in stages. 5. Procédé selon la revendication 4, carac­térisé en ce qu'on alimente la bobine avec un courant continu variable dont l'intensité change progressiv­ ment.5. Method according to claim 4, characterized in that the coil is supplied with a variable direct current whose intensity changes progressively is lying. 6. Procédé selon l'une quelconque des re­vendications 4 et 5, caractérisé en ce qu'on alimente la bobine avec un courant continu dont l'intensité change d'une manière ondulée pulsatoire.6. Method according to any one of claims 4 and 5, characterized in that the coil is supplied with a direct current whose intensity changes in a pulsating wavy manner. 7. Procédé selon la revendication 6, ca­ractérisé en ce qu'on utilise un courant continu on­dulé pulsatoire à la fréquence de 1 Hz ou moins.7. Method according to claim 6, characterized in that a pulsating ripple direct current is used at the frequency of 1 Hz or less. 8. Torche à plasma notamment pour la mise en oeuvre d'un procédé conforme à l'une quelconque des revendications 1 à 7, constituée de deux électrodes (11, 12) tubulaires coaxiales entre lesquelles s'éta­blit un arc, d'une chambre (15) séparant les élec­trodes et où est injecté du gaz plasmagène, qui com­prend des moyens (14, 212 ; 125, 131) pour maîtriser le déplacement du pied amont sur l'électrode amont (12), repérée par rapport au sens d'écoulement du plasma, de manière à lui faire décrire une course longitudinale alternative afin d'en régulariser l'usure et en augmenter la longévité et qui est équi­pée d'une bobine de champ magnétique (14) qui entoure localement l'électrode amont et qui est alimentée par un circuit électrique, caractérisée en ce que ces moyens comprennent insèrés dans ce circuit, des re­dresseurs (212) délivrant un courant continu ondulé pulsatoire à partir d'une valeur de consigne de cou­rant bobine ondulée pulsatoire.8. Plasma torch in particular for implementing a method according to any one of claims 1 to 7, consisting of two coaxial tubular electrodes (11, 12) between which an arc is established, a chamber (15) separating the electrodes and into which plasma gas is injected, which comprises means (14, 212; 125, 131) for controlling the movement of the upstream foot on the upstream electrode (12), marked with respect to the direction of flow of the plasma, so as to make it describe an alternative longitudinal course in order to regularize the wear and increase its longevity and which is equipped with a magnetic field coil (14) which locally surrounds the upstream electrode and which is supplied by an electrical circuit, characterized in that these means include, inserted in this circuit, rectifiers (212) delivering a pulsating rippled direct current from a pulsating corrugated coil current set value. 9. Torche conforme à la revendication 8, ca­ractérisée en ce que ces redresseurs produisent un courant ondulé pulsatoire à la fréquence de 1 Hz envi­ron ou moindre.9. Torch according to claim 8, characterized in that these rectifiers produce a pulsating ripple current at the frequency of about 1 Hz or less. 10. Torche conforme à la revendication 8 ou 9, caractérisée en ce que la durée à mi-hauteur de l'impulsion est d'environ le quart de la période.10. Torch according to claim 8 or 9, characterized in that the duration at mid-height of the pulse is about a quarter of the period. 11. Torche conforme à la revendication 8, 9 ou 10, caractérisée en ce que ces redresseurs produi­sent un courant ondulé pulsatoire dont le rapport des amplitudes maximale et minimale varie de 1 à 1000 et est de préférence de l'ordre de 2,5.11. Torch according to claim 8, 9 or 10, characterized in that these rectifiers produce a pulsating ripple current whose ratio of maximum and minimum amplitudes varies from 1 to 1000 and is preferably of the order of 2.5. 12. Torche conforme à l'une quelconque des revendications 8 à 11, caractérisée en ce que ces mo­yens comprennent dans le fond de l'électrode amont (12) un perçage (125) pour injecter du gaz et, placé transversalement à l'axe de l'électrode amont à proxi­mité de son fond, un diffuseur (131) que traverse le gaz injecté.12. Torch according to any one of claims 8 to 11, characterized in that these means comprise in the bottom of the upstream electrode (12) a bore (125) for injecting gas and, placed transversely to the axis of the upstream electrode near its bottom, a diffuser (131) through which the injected gas passes. 13. Torche conforme à la revendication 12, caractérisée en ce que ce diffuseur (131) communique au gaz qui le traverse un mouvement tourbillonnaire.13. Torch according to claim 12, characterized in that this diffuser (131) communicates to the gas passing through it a vortex movement. 14. Torche conforme à l'une quelconque des revendications 11 à 13, caractérisée en ce que ce diffuseur (131) est constitué d'un disque (132) transpercé de canaux (136) obliques orientés prati­quement tangentiellement et équidistants.14. Torch according to any one of claims 11 to 13, characterized in that this diffuser (131) consists of a disc (132) pierced by oblique channels (136) oriented substantially tangentially and equidistant. 15. Torche conforme à l'une quelconque des revendications 13 et 14, caractérisée en ce que les débits des gaz injectés dans la chambre et par le fond de l'électrode amont sont dans un rapport compris entre trois et treize.15. Torch according to any one of claims 13 and 14, characterized in that the flow rates of the gases injected into the chamber and through the bottom of the upstream electrode are in a ratio of between three and thirteen.
EP88400007A 1987-01-07 1988-01-04 Plasma torch with a longitudinally moving up-stream arc root,and method for controlling its displacement Expired - Lifetime EP0277845B1 (en)

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AT88400007T ATE69684T1 (en) 1987-01-07 1988-01-04 PLASMA TORCH WITH LONGITUDINAL MOVABLE UPPER ARC END AND METHOD OF CONTROLLING THE SHIFT.

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FR8700078 1987-01-07
FR8700078A FR2609358B1 (en) 1987-01-07 1987-01-07 PLASMA TORCH LONGITUDINALLY MOBILE UPSTREAM ARC AND METHOD FOR CONTROLLING ITS MOVEMENT

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DE3866250D1 (en) 1992-01-02
BR8800022A (en) 1988-08-02
US4847466A (en) 1989-07-11
EP0277845B1 (en) 1991-11-21
AU610109B2 (en) 1991-05-16
JPH0719672B2 (en) 1995-03-06
KR880009540A (en) 1988-09-15
FR2609358A1 (en) 1988-07-08
ZA8866B (en) 1988-06-27
ES2027388T3 (en) 1992-06-01
CA1301259C (en) 1992-05-19
JPS63252398A (en) 1988-10-19
KR950003971B1 (en) 1995-04-21
ATE69684T1 (en) 1991-12-15
FR2609358B1 (en) 1991-11-29
AU1004488A (en) 1988-07-14

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