EP1139701A1 - Plasma torch with electrode/nozzle contact starting - Google Patents

Abstract

The plasma torch has the nozzle carrier (11) axially mobile in a guide that forms a sliding bearing. The guide has first (18) and second (19) pressure chambers with variable internal volume, separated by an intermediate wall (5). Both the first chamber and second chamber are fed (10,9) with a fluid under pressure to ensure sealed axial sliding of the nozzle carrier.

Description

The present invention relates to an electric arc work torch, in particular a plasma torch with a removable head.

In the field of automatic plasma cutting, when the torch plasma is arranged on a cutting machine, two types of torches are conventionally used, namely so-called "monoblock" torches and torches in two parts, say "removable head".

The architecture and operation of these different types of torches are described in particular in the following documents which can be see for more details: EP-A-144267, EP-A-410875, EP-A-772957, EP-A-902606, EP-A-810052, EP-A-845929, EP-A-790756, EP-A-196612, WO-A-89/11941, US-A-4,521,666, US-A-4,059,743, US-A-4,163,891, US-A-5,591,357, EP-A-599709, EP-A-872300, EP-A-801882 and EP-A-941018.

In addition, these different torch systems can be classified in two sub-categories according to the mode of striking the pilot arc in the torch.

Indeed, the initiation of the pilot arc can be done either by creation and high frequency (HF) spark between the electrode and the torch nozzle, either by temporarily short-circuiting the electrode and the nozzle by means of their mechanical contact.

The ignition of the pilot arc by the blasting of an HF spark between the electrode and the nozzle is very widespread because it is simple to design and set up work (see Figure 1 below).

• émission d'importantes radio nuisances, lors du jaillissement des étincelles HF, pouvant perturber et endommager les systèmes électroniques et informatiques insuffisamment protégés se trouvant dans l'environnement de la source HF,
• propagation par induction ou conduction de perturbations sur le réseau électrique du site industriel pouvant nuire gravement au bon fonctionnement des systèmes électroniques et informatiques insuffisamment protégés qui sont alimentés par le même réseau que la source HF,
• du fait des caractéristiques de tension et de fréquence des systèmes à HF, introduction de contraintes importantes d'isolement dans la conception des torches, des circuits électriques d'alimentation et de commande et des appareils constitutifs des installations de coupage ou de soudage.

However, the HF boot mode has the disadvantages and poses the following problems:

• emission of major radio nuisances, when HF sparks fly, which can disturb and damage the inadequately protected electronic and computer systems located in the environment of the HF source,
• propagation by induction or conduction of disturbances on the electrical network of the industrial site which can seriously impair the proper functioning of insufficiently protected electronic and computer systems which are supplied by the same network as the HF source,
• due to the voltage and frequency characteristics of HF systems, introduction of significant insulation constraints in the design of torches, electrical supply and control circuits and the devices constituting cutting or welding installations.

In order to try to solve these problems, torches have been proposed plasma whose operation is based on short-circuiting temporary electrode and nozzle through contacting mechanics of these, so as to create the pilot arc, as illustrated by the Figure 2 attached. A very effective arc ignition system of this type is given, for example, in document EP-A-599709, which teaches a system ignition device comprising a movable electrode in the torch body according to the axis of the torch and a nozzle kept fixed; the electrode being successively brought into contact with the nozzle and then separated from the latter so as to create the arc.

• d'une part, la continuité électrique du circuit alimentant l'électrode de la torche étant assurée par une douille élastique de contact dans laquelle doit pouvoir coulisser à débattement le porte-électrode sous l'action de forces pneumatiques s'exerçant sur la tête de piston dont est doté ledit porte-électrode, le dimensionnement de la douille élastique est fonction du courant maximal auquel elle sera soumise en tenant compte de la résistance de contact inhérent au système et des échauffements locaux qui peuvent en découler. Ce qui revient à dire que, s'il faut 1 unité de douille de contact pour un courant de 150 A, il faudrait l'équivalent de 2 unités de douille pour un courant de 300 A et de 4 unités de douille pour un courant de 600 A, ce qui se répercute alors négativement sur les dimensions de la torche devant contenir de tels agencements ;
• d'autre part, la force nécessaire pour faire coulisser le porte-électrode dans la douille de contact est sensiblement proportionnelle au nombre d'unités de douille requis par le courant maximal, soit à titre d'exemple pour établir une relation : 10 daN pour 150 A, 20 daN pour 300 A et 40 daN pour 600 A. On comprend alors immédiatement que si la pression en air comprimé alimentant le piston de manoeuvre de l'électrode est une constante, par exemple 5 bars, il faut alors dimensionner le piston de telle façon à avoir une section active en proportion avec la force à vaincre, soit pour illustrer la relation : 2 cm² pour 150 A, 4 cm² pour 300 A et 8 cm² pour 600 A, ce qui se répercute aussi négativement sur les dimensions de la torche.

In practice, it has been observed that this priming system, although very effective, has, in certain cases, the following limits:

• on the one hand, the electrical continuity of the circuit supplying the electrode of the torch being ensured by an elastic contact sleeve in which the electrode holder must be able to slide under the action under the action of pneumatic forces exerted on the head of piston with which said electrode holder is fitted, the dimensioning of the elastic sleeve is a function of the maximum current to which it will be subjected, taking into account the contact resistance inherent in the system and the local heating which may result therefrom. This amounts to saying that, if 1 contact socket unit is required for a current of 150 A, the equivalent of 2 socket units would be required for a current of 300 A and 4 socket units for a current of 600 A, which then has a negative impact on the dimensions of the torch which must contain such arrangements;
• on the other hand, the force necessary to slide the electrode holder in the contact socket is substantially proportional to the number of socket units required by the maximum current, that is to say as an example to establish a relationship: 10 daN for 150 A, 20 daN for 300 A and 40 daN for 600 A. It is then immediately understood that if the compressed air pressure supplying the electrode operating piston is a constant, for example 5 bar, then the piston must be dimensioned so as to have an active section in proportion to the force to be overcome, either to illustrate the relationship: 2 cm ² for 150 A, 4 cm ² for 300 A and 8 cm ² for 600 A, which also has a negative impact on the dimensions of the torch.

From this, we understand that, if the short-circuit starting system by movement of the electrode is very interesting for weak torches and medium powers, i.e. for current intensities of at most 150 A, it quickly becomes unacceptable for high powers, that is to say when the intensities which reach or exceed the value of 300 A.

In an attempt to resolve these problems, torches have been proposed to initiation by reverse operating circuit opposite to that described above, i.e. with fixed electrode and movable nozzle which can move in and out in contact with said electrode so as to create the pilot arc, the return of the nozzle in its working position usually done via a return spring, as illustrated in Figure 3 attached.

• le ressort de rappel de la tuyère doit être d'une force suffisamment grande pour obtenir un bon contact de court-circuit entre électrode et tuyère mais suffisamment faible pour que la pression dynamique exercée par le gaz puisse repousser la tuyère jusqu'à sa butée inférieure. Cela peut conduire soit à un contact aléatoire entre électrode et tuyère, soit à interdire les réglages de pression de gaz plasmagène dont la valeur serait égale ou inférieure à celle exercée par le ressort. Ce système conduit donc à limiter l'usage de la torche aux procédés qui développent des pressions dynamiques internes à la tuyère notablement supérieures à la force du ressort.
• le ressort est utilisé comme conducteur électrique pour transmettre le courant d'arc pilote à la tuyère. Selon la valeur de l'intensité du courant d'arc pilote et le temps d'application dudit courant, il peut s'ensuivre un vieillissement prématuré du ressort, par échauffement et perte de caractéristiques élastiques, pouvant nuire à l'efficacité du système.
• le retour de la tuyère, depuis la butée inférieure vers la butée supérieure constituée par l'électrode, s'effectuant sous le seul effet de la force du ressort, le temps nécessaire à effectuer la course de retour est fonction du temps de purge des circuits de gaz disposés entre l'électrovanne de sectionnement du gaz et l'orifice de sortie de la tuyère, le temps de purge desdits circuits étant lui-même fonction de la capacité volumique de ces circuits, de la pression de gaz y régnant et du calibre de l'orifice de sortie de la tuyère. Dès lors, d'une part, le temps de retour de la tuyère vers l'électrode pour y établir un nouveau court-circuit est une variable tributaire d'un certain nombre de paramètres opératoires et, d'autre part, lorsqu'il y a enchaínement de plusieurs séquences de travail nécessitant des extinctions d'arc et des réallumages successifs, le temps d'attente nécessaire pour obtenir de bonnes conditions de ré-allumage d'arc est difficilement prédictible et se prête, par conséquent, mal à une automatisation fiable.

However, this method of striking the pilot arc also has drawbacks, namely:

• the nozzle return spring must be of sufficient force to obtain a good short-circuit contact between the electrode and the nozzle but sufficiently weak so that the dynamic pressure exerted by the gas can push the nozzle to its bottom stop . This can lead either to random contact between the electrode and the nozzle, or to prohibit the plasma gas pressure adjustments whose value would be equal to or less than that exerted by the spring. This system therefore leads to limiting the use of the torch to processes which develop internal dynamic pressures in the nozzle which are significantly greater than the force of the spring.
• the spring is used as an electrical conductor to transmit the pilot arc current to the nozzle. Depending on the value of the intensity of the pilot arc current and the time of application of said current, it can result in premature aging of the spring, by heating and loss of elastic characteristics, which can adversely affect the efficiency of the system.
• the return of the nozzle, from the lower stop towards the upper stop constituted by the electrode, being effected only by the force of the spring, the time necessary to carry out the return stroke is a function of the purge time of the circuits of gases disposed between the gas sectioning solenoid valve and the nozzle outlet, the purge time of said circuits being itself a function of the volume capacity of these circuits, the prevailing gas pressure and the caliber from the nozzle outlet. Consequently, on the one hand, the return time from the nozzle to the electrode to establish a new short-circuit therein is a variable dependent on a certain number of operating parameters and, on the other hand, when there is a sequence of several work sequences requiring arc extinctions and successive re-ignitions, the waiting time necessary to obtain good conditions for re-igniting the arc is difficult to predict and therefore lends itself poorly to automation reliable.

• le ressort est utilisé comme conducteur électrique pour transmettre le courant d'arc pilote à la tuyère et donc le problème du vieillissement prématuré du ressort n'est pas résolu.
• le retour de la tuyère s'effectuant, là encore, sous le seul effet de la force du ressort, le temps nécessaire à effectuer cette course de retour est, dans ce cas aussi, fonction du temps de purge des circuits disposés entre l'électrovanne de sectionnement du gaz et l'orifice de sortie de la tuyère, ce qui engendre les mêmes problèmes de fiabilité que dans le cas précédent.

In order to solve these problems, an improvement to the priming system has been proposed in document EP-A-326445. However, the pilot arc ignition mode given in this document, the torch of which also uses a return spring, although more effective than in the previous solution and not dependent on the gas pressure, still presents disadvantages, namely:

• the spring is used as an electrical conductor to transmit the pilot arc current to the nozzle and therefore the problem of premature aging of the spring is not resolved.
• the return of the nozzle being carried out, there again, under the sole effect of the force of the spring, the time necessary to carry out this return stroke is, in this case also, a function of the purge time of the circuits arranged between the solenoid valve sectioning the gas and the nozzle outlet, which creates the same reliability problems as in the previous case.

The aim of the present invention is therefore to solve the problems aforementioned landing with art arc work torches and propose a torch system capable of priming effective pilot arc between the electrode and the torch nozzle, without generating electromagnetic disturbances by radiation or by conduction and which or, in particular, adaptable to plasma torches with removable head.

• pas d'émission de radio nuisances, pas de propagation par induction ou conduction de perturbations sur le réseau électrique, pas de contraintes importantes d'isolement électrique dans la conception des matériels de mise en oeuvre des procédés à arc plasma,
• pas de limitation technique ou dimensionnelle pouvant avoir un caractère rédhibitoire pour la transposition du système d'amorçage à des matériels de forte puissance,
• pas d'influence de la variation de la pression du gaz plasmagène sur l'efficacité du système,
• pas d'échauffement lié à la durée d'application de l'arc pilote risquant de nuire à l'efficacité et à la fiabilité du système d'amorçage,
• pas d'influence significative des paramètres opératoires sur le système d'amorçage pouvant conduire à des délais d'attente variables ou aléatoires entre une commande d'extinction d'arc et un ré-allumage d'arc,
• système d'amorçage de l'arc pilote efficace et fiable, exempt de nuisances pour l'environnement et se prêtant particulièrement bien à une automatisation optimisée du procédé de fabrication,
• système convenant aussi pour les fortes puissances, c'est-à-dire lorsque les intensités de courant atteignant ou dépassant la valeur de 300 A.

In other words, the object of the invention is to propose a plasma torch having the following advantages:

• no radio nuisance emissions, no propagation by induction or conduction of disturbances on the electrical network, no significant constraints of electrical isolation in the design of equipment for implementing plasma arc processes,
• no technical or dimensional limitation which may be prohibitive for the transposition of the priming system to high power equipment,
• no influence of the variation of the plasma gas pressure on the efficiency of the system,
• no overheating linked to the duration of application of the pilot arc, which could harm the efficiency and reliability of the ignition system,
• no significant influence of the operating parameters on the ignition system which can lead to variable or random waiting times between an arc extinction command and an arc re-ignition,
• efficient and reliable pilot arc ignition system, free from environmental pollution and particularly suitable for optimized automation of the manufacturing process,
• system also suitable for high powers, that is to say when the current intensities reaching or exceeding the value of 300 A.

• au moins une première position dans laquelle la tuyère portée par ledit bloc porte-tuyère est mise en contact mécanique avec ladite électrode portée par ledit porte-électrode, et
• au moins une deuxième position dans laquelle la tuyère portée par ledit bloc porte-tuyère est située à une distance non nulle de ladite électrode,

   caractérisée en ce que ledit bloc porte-tuyère est mobile axialement par l'intermédiaire d'au moins un carter de guidage formant palier de coulissement pour ledit bloc porte-tuyère,

• le carter de guidage comprenant une première chambre de pression et une deuxième chambre de pression, lesdites première et deuxième chambres de pression étant à volumes internes variables et étant séparées l'une de l'autre par au moins une cloison intermédiaire,
• le carter de guidage, le bloc porte-tuyère et ladite cloison intermédiaire étant agencés de manière à maintenir les deux chambres de pression sans communication fluidique l'une avec l'autre et à assurer un coulissement axial étanche du bloc porte-tuyère par l'intermédiaire du carter de guidage pour faire varier les volumes internes desdites première et deuxième chambres de pression,
• au moins un premier passage d'alimentation en fluide débouche dans la première chambre de pression pour permettre une alimentation en fluide sous pression de ladite première chambre de pression, et
• au moins un deuxième passage d'alimentation en fluide débouche dans la deuxième chambre de pression pour permettre une alimentation en fluide sous pression de ladite deuxième chambre de pression.

The solution of the present invention is then an electric arc work torch, in particular a plasma torch, comprising a torch body and a torch head, said torch comprising at least one electrode holder for receiving an electrode. and a nozzle holder block allowing to receive at least one nozzle, said electrode holder being fixed in said torch and said nozzle holder block being axially movable between:

• at least a first position in which the nozzle carried by said nozzle holder block is brought into mechanical contact with said electrode carried by said electrode holder, and
• at least a second position in which the nozzle carried by said nozzle holder block is located at a non-zero distance from said electrode,

characterized in that said nozzle holder block is axially movable by means of at least one guide housing forming a sliding bearing for said nozzle holder block,

• the guide housing comprising a first pressure chamber and a second pressure chamber, said first and second pressure chambers being of variable internal volumes and being separated from each other by at least one intermediate partition,
• the guide housing, the nozzle holder block and said intermediate partition being arranged so as to maintain the two pressure chambers without fluid communication with each other and to ensure a sealed axial sliding of the nozzle holder block by the intermediate of the guide housing for varying the internal volumes of said first and second pressure chambers,
• at least a first fluid supply passage opens into the first pressure chamber to allow a supply of pressurized fluid to said first pressure chamber, and
• at least one second fluid supply passage opens into the second pressure chamber to allow supply of pressurized fluid to said second pressure chamber.

• les première et deuxième chambres de pression sont séparées l'une de l'autre par au moins une cloison intermédiaire mobile axialement et portée solidairement par le bloc porte-tuyère, ladite cloison formant tête de piston à actionnement fluidique, de préférence ladite cloison mobile constitue un épaulement ou un renflement radial venant du bloc porte-tuyère.
• les première et deuxième chambres de pression sont séparées l'une de l'autre par au moins une cloison intermédiaire fixe et solidaire de la partie fixe du carter de guidage formée par au moins une partie du porte-électrode, et le bloc porte-tuyère comprenant une première expansion radiale formant paroi supérieure de la deuxième chambre de pression et une deuxième expansion radiale inférieure formant paroi de la première chambre de pression, ledit bloc porte-tuyère et lesdites première et deuxième expansions radiales internes étant mobiles solidairement et axialement.
• la deuxième chambre de pression est délimitée par la surface interne de la paroi latérale du carter, la surface interne de la paroi supérieure du carter, la surface externe de la paroi latérale du porte-électrode et la surface supérieure de la cloison fixe formant tête de piston solidaire du porte-électrode, et la première chambre de pression est délimitée par la surface interne de la paroi latérale du carter, la surface interne de la paroi inférieure du carter, la surface externe de la paroi latérale du porte-électrode et la surface inférieure de la cloison fixe formant tête de piston solidaire du porte-électrode.
• la deuxième chambre de pression est délimitée par la surface interne de la paroi latérale du carter, la surface interne de la paroi supérieure du carter, la surface externe de la paroi latérale du bloc porte-tuyère et la surface supérieure de la cloison mobile formant tête de piston solidaire du bloc porte-tuyère, et
• la première chambre de pression est délimité par la surface interne de la paroi latérale du carter, la surface interne de la paroi inférieure du carter, la surface externe de la paroi latérale du bloc porte-tuyère et la surface inférieure de la cloison mobile formant tête de piston solidaire du bloc porte-tuyère.
• des moyens d'étanchéité sont agencés entre le carter de guidage, le bloc porte-tuyère et/ou le porte-électrode et ladite cloison intermédiaire de manière à permettre un coulissement axial étanche du bloc porte-tuyère dans le carter de guidage et/ou sur au moins une partie du porte-électrode pour maintenir les première et deuxième chambres de pression sans communication fluidique l'une avec l'autre, de préférence les moyens d'étanchéité comprennent des joints d'étanchéités.
• le premier passage d'alimentation en fluide sous pression permet d'acheminer un fluide sous pression, de préférence un gaz, jusque dans ladite première chambre de pression par l'intermédiaire d'un premier orifice pratiqué dans une paroi du carter de guidage, et le deuxième passage d'alimentation en fluide sous pression permet d'acheminer un fluide sous pression, de préférence un gaz, jusque dans ladite deuxième chambre de pression par l'intermédiaire d'un deuxième orifice pratiqué dans la paroi du carter de guidage.
• le premier passage d'alimentation en fluide sous pression traverse au moins une partie de ladite deuxième chambre de pression, ladite cloison intermédiaire et débouche dans ladite première chambre de pression.
• elle comporte, en outre, au moins une chambre de décompression communiquant avec l'atmosphère ambiant par l'intermédiaire d'au moins un passage de sortie de gaz.
• elle comporte, en outre, une électrode munie d'un insert émissif en zirconium, hafnium ou tungstène, pur ou allié.
• elle comporte des moyens d'assemblage/désassemblage permettent d'associer et/ou de dissocier la tête de torche du corps de torche, lesdits tête de torche et corps de torche étant séparables l'un de l'autre.
• elle est de type mono flux ou double flux et/ou en ce qu'elle comporte des moyens de distribution de flux sur le mode axial ou sur le mode tourbillonnaire.

Depending on the case, the torch of the invention may include one or more of the following characteristics:

• the first and second pressure chambers are separated from each other by at least one axially movable intermediate partition and carried integrally by the nozzle holder block, said partition forming the piston head with fluid actuation, preferably said movable partition constitutes a shoulder or a radial bulge coming from the nozzle holder block.
• the first and second pressure chambers are separated from each other by at least one fixed intermediate partition integral with the fixed part of the guide housing formed by at least part of the electrode holder, and the nozzle holder block comprising a first radial expansion forming the upper wall of the second pressure chamber and a second lower radial expansion forming the wall of the first pressure chamber, said nozzle holder block and said first and second internal radial expansions being movable integrally and axially.
• the second pressure chamber is delimited by the internal surface of the side wall of the casing, the internal surface of the upper wall of the casing, the external surface of the side wall of the electrode holder and the upper surface of the fixed partition forming the head of piston secured to the electrode holder, and the first pressure chamber is delimited by the internal surface of the side wall of the housing, the internal surface of the lower wall of the housing, the external surface of the side wall of the electrode holder and the surface bottom of the fixed partition forming the piston head secured to the electrode holder.
• the second pressure chamber is delimited by the internal surface of the lateral wall of the casing, the internal surface of the upper wall of the casing, the external surface of the lateral wall of the nozzle holder block and the upper surface of the movable partition forming the head piston secured to the nozzle holder block, and
• the first pressure chamber is delimited by the internal surface of the side wall of the casing, the internal surface of the bottom wall of the casing, the external surface of the side wall of the nozzle holder block and the bottom surface of the movable partition forming a head piston integral with the nozzle holder block.
• sealing means are arranged between the guide casing, the nozzle holder block and / or the electrode holder and said intermediate partition so as to allow a sealed axial sliding of the nozzle holder block in the guide case and / or on at least part of the electrode holder to maintain the first and second pressure chambers without fluid communication with each other, preferably the sealing means include seals.
• the first pressurized fluid supply passage makes it possible to convey a pressurized fluid, preferably a gas, into said first pressure chamber via a first orifice made in a wall of the guide casing, and the second pressurized fluid supply passage makes it possible to convey a pressurized fluid, preferably a gas, as far as said second pressure chamber via a second orifice made in the wall of the guide casing.
• the first pressurized fluid supply passage passes through at least part of said second pressure chamber, said intermediate partition and opens into said first pressure chamber.
• it further comprises at least one decompression chamber communicating with the ambient atmosphere via at least one gas outlet passage.
• it further comprises an electrode provided with an emissive insert of zirconium, hafnium or tungsten, pure or alloyed.
• it comprises assembly / disassembly means used to associate and / or dissociate the torch head from the torch body, said torch head and torch body being separable from one another.
• it is of the mono-flow or double-flow type and / or in that it comprises means for distributing flow in the axial mode or in the vortex mode.

The invention also relates to an automatic arc working installation plasma comprising a plasma torch according to the invention, preferably a plasma cutting torch, mounted on a support frame comprising at least one motorized axis of movement, control means making it possible to command at least the ignition sequence of said torch by allowing and / or prohibiting the introduction of a pressurized fluid, preferably air, in the first pressure chamber or in the second pressure chamber pressure so as to vary the internal pressure and / or volume of said chambers and thus cause movement on approach or, conversely, away from at least the nozzle holder block and the nozzle relative to the electrode holder and to the electrode by axial sliding of at least the nozzle holder block through the guide housing, means for managing work sequences and means of programming and management of work trajectories like a numerical control.

By the invention also relates to a method of striking a pilot arc in a plasma torch comprising a fixed electrode and a movable nozzle jointly supported by an axially movable nozzle holder block in the torch, in which a pilot arc is struck between the nozzle and the electrode by introducing a pressurized fluid, preferably a gas, into at least a first pressure chamber cooperating with at least the nozzle holder block so as to vary the pressure and / or the internal volume of said pressure chamber and thus cause an approaching movement at least the nozzle holder block and the nozzle relative to the electrode holder and to the electrode by axial sliding of at least the nozzle holder block by through a guide housing until contact is obtained between the nozzle and the electrode with the formation of an electric arc between them, and at least one second pressure chamber cooperating with at least the nozzle holder block so as to obtain a movement away from at least the nozzle holder block and the nozzle with respect to the electrode holder and the electrode, when varies the pressure and / or the internal volume of said second chamber pressure, by axial sliding of at least the nozzle holder block in said guide housing.

Alternatively, the invention also relates to a priming process of a pilot arc in a plasma torch comprising a fixed electrode and a movable nozzle supported integrally by an axially movable nozzle holder block in the torch, in which a pilot arc is struck between the nozzle and the electrode by introducing a pressurized fluid, preferably a gas, in at least a second pressure chamber cooperating with at minus the nozzle holder block so as to vary the pressure and / or the volume internal of said second pressure chamber and thereby causing a movement in approach of at least the nozzle holder block and the nozzle relative to the electrode holder and to the electrode by axial sliding of at least minus the nozzle holder block via a guide housing up to get contact between the nozzle and the electrode with an arc electric between them, and at least a first pressure chamber cooperating with at least the nozzle holder block so as to obtain a movement away from at least the nozzle holder block and the nozzle by relative to the electrode holder and to the electrode, when the pressure is varied and / or the internal volume of said first pressure chamber, by sliding axial of at least the nozzle holder block in said guide housing.

Furthermore, the invention also relates to a plasma cutting process. a piece, preferably metallic, such as sheet steel, stainless steel or aluminum alloy, implementing a method of striking an arc driver as described above.

• les figures 1 à 4 représentent des torches selon l'art antérieur représentées en coupe longitudinale,
• la figure 5 est un schéma de principe, en coupe longitudinale, d'une torche à amorçage par contact selon la présente invention, et
• les figures 6 à 8 représentent plusieurs vues différentes, en coupe longitudinale, d'une version industrielle d'une torche à amorçage par contact selon la présente invention.

The invention will now be better understood thanks to the detailed description below and with reference to the appended figures, given by way of illustration but not limitation, among which:

• FIGS. 1 to 4 represent torches according to the prior art represented in longitudinal section,
• FIG. 5 is a block diagram, in longitudinal section, of a contact ignition torch according to the present invention, and
• Figures 6 to 8 show several different views, in longitudinal section, of an industrial version of a contact ignition torch according to the present invention.

Figure 1 is a block diagram of an HF ignition torch according to the prior art, which comprises a nozzle 102 pierced with an axial orifice 103 for ejecting the plasma jet 104. An electrode 105 with an emissive insert 106 is fixed coaxially and away from the nozzle 102. A main source of electric current 107 is connected by one of its poles 108 to the part of work 109, via a connecting cable 181, and by the other pole 110 to the electrode 105, via a connecting cable 101. A link is also established between the pole 108 and the nozzle 102, via a cable 182 and a sectioning contact 183. A first auxiliary HF source 111 and a second auxiliary source 112 of low intensity current, called the pilot arc current source, are each connected to terminals 108 and 110 of source 107. To obtain ignition of the pilot arc, sources 107 and 112 are energized, a flow of plasma gas 113, here swirling, is injected into the space between the nozzle 102 and the electrode 105, the isolating contact 183 is closed, the source of HF 111 is excited causing a spark to flash between the end of the electrode 105 and the inside bottom of the nozzle 102. The path electric created by the HF spark then allows the low intensity current delivered by the source 112 to flow between the electrode 105 and the nozzle 102 and thus creating the pilot arc, which under the effect of the gas flow 113 stretches through the orifice 103 in the direction of the part 109. When the pilot arc is stabilized, the torch 100 is moved closer to part 109 until an area sufficiently ionized from jet 104 comes into contact with the surface of the part 109 thus allowing the establishment of an electrical circuit between the electrode 105 and part 109. A current relay, not shown, placed in circuit 181 then detects the presence of a current, commands the opening of the contact sectioning 183 and raising the intensity of the current to the level required to perform the cutting or welding operation. A movement of adapted speed is communicated to the torch 100 or to the piece 109 in order to form the cutting, welding or marking trajectory.

Figure 2 shows a block diagram of a priming torch by short circuit with mobile electrode according to the prior art. This 200 torch partially arranged similarly to the torch of Figure 1 and essentially differentiating by the electrode 205 which is here fixed on an electrode holder 221 mounted axially sliding in a casing 222 forming a pressure chamber 223 delimited by a bulge in the electrode holder 221 forming piston head 224 and by reducing the diameter 225 of the casing 222 forming upper landing. Seals are embedded in the head piston and the upper bearing so as to prevent any communication of the pressure chamber 223 with the ambient medium and with a compartment 226 delimited by the piston head 224 and a second reduction in diameter 227 casing 222 forming lower bearing, said lower bearing being provided with a seal sealing. At its upper part, the electrode holder is extended by a end 228 in the form of an axially sliding rod in a socket elastic of electrical contact 220 itself encased in a sleeve 230 forming mechanical support and electrical connector for a 211 cable connection with pole 210 of the main current source 207. A distributor pneumatic 232 electrically powered by air source 231 under pressure. A first air distribution line 233 is connected to the pressure chamber 223 by a tap 235 and a second line of air distribution 234 is connected to the pressure chamber 226 by a stitching 261. A downward movement is given to the assembly 228, 221, 224, 205 by pressurizing the chamber 223, the descent stroke being fixed by the abutment of the end of the electrode 205 in the bottom of the nozzle 202. Conversely, an upward movement is given to this together by pressurizing chamber 226, the rise stroke being fixed by the abutment of a bulge 229 of the electrode holder 221 on the underside of the housing 222. The residual difference Δe corresponds to the distance normal to separate the electrode 205 from the nozzle 202 when the plasma arc is on. To obtain the pilot arc ignition, sources 207 and 212 are energized, a stream of plasma gas 213 is injected into the space separating the nozzle 202 and the electrode 205, and the contact of section 283 is closed. The electrode 205 descends on mechanical contact and electric from the nozzle 202, a current delivered by the auxiliary source 212 can then circulate in the circuit formed. An intensity relay, not shown, placed on circuit 282 then detects the presence of an electric current and subsequently controls the ascent of the electrode 205 by reversing the distributor control 232. It follows, when the short circuit breaks between electrode and nozzle, the formation of a spark which, as described previously created an electric path conducive to the establishment of the arc pilot. In other words, it is the electrode 205 which is movable along the axis of the torch, while the nozzle 202 is still kept fixed. An example of realization of this arc ignition system is given in document EP-A-599709.

Figure 3 shows a block diagram of a priming torch by short circuit with movable nozzle according to the prior art. Torch 300 partially, arranged similarly to the torch of Figure 1 and essentially differentiating by the nozzle 331 which is axially sliding in a housing 333. An elastic member 332, such as a spring is trapped between a first stop 302 coming from the nozzle 331 and a second stop 304 coming from the housing 333. The spring 332 exerts an axial force tending to bring the inner bottom of the nozzle 331 into contact with the electrode 305. A seal seal 334 is encased at the top of the nozzle 331. A solenoid valve 335, supplied with plasma gas 336 under pressure, is connected to a fluid inlet 338 by means of a pipe 337. When the solenoid valve 335 is controlled upon opening, gas 313 is distributed between the electrode 305 and the nozzle 331, and exerts pressure on the internal walls of the nozzle, to create a repulsive force greater than the force of the spring 332 and thus drag the nozzle downward until that the stop 302 of the nozzle 331 comes into contact with the counter-stop 303. To obtain the ignition of a pilot arc, sources 307 and 312 are put under voltage and solenoid valve 335 is closed. Thus, the nozzle 331 is pushed back by the spring 332 in contact with the electrode 305. The isolating contact 383 is closed and a current from the auxiliary source 312 can flow in the circuit formed. A current relay, not shown, placed on circuit 382 then detects the presence of a current and controls the opening of the solenoid valve 335, the gas flow 313 thus delivered exerts pressure on the wall of the nozzle 331 causing it to descend by compression of the spring 332. When the short circuit breaks, a spark occurs which as described above allows the establishment of the pilot arc.

Figure 4 shows a block diagram of another torch to priming by short circuit with movable nozzle according to the prior art. The torch 400 similar to that of FIG. 3 comprises, to reinforce the force exerted by the action of the gas on the nozzle, an additional arrangement. The nozzle 441 is mounted with axial movement in a casing 443. A spring 442 is trapped between a circular stop 431 and a bulge 412. The spring 442 exerts an axial force tending to bring the nozzle 441 into contact with the electrode 405. A narrowing 432 of the upper part of the casing 443 delimits a pressure chamber 445. A circular section 444 allows the passage of a gas distributed by a nozzle 433 passing through the narrowing 432 to supply the pressure chamber 445, while maintaining a significant pressure in pressure chamber 445, while the gas flows in the open air in a peripheral flow 452, via an annular slot 434 and the spaces between turns of spring 442. A seal 447 in the shrinkage 432 isolates the distribution circuit 438 in plasma gas from the distribution circuit 451. A solenoid valve 448 supplied with gas 449 under pressure, such as compressed air, is connected to the fluid inlet 451 via the line 450. This additional fluid flow allows cooling of nozzle 441 and the development of sufficient pressure on the section of the bulge 412 forming the piston head to exert a force specific to compress the spring 442 and cause the descent of the nozzle 441. The nozzle 441 lowering stroke is limited by the abutment of a bulge 412 on the narrowing 432 of the casing 443. To obtain ignition of a pilot arc, sources 407 and 406 are energized and the solenoid valves 435 and 448 controlled in the closed position. So in the absence of gas flows in the torch, the nozzle 441 pushed back by the spring 442 is in contact with electrode 405. The isolating contact 483 is then commanded to close and a current delivered by the source auxiliary can circulate in the formed circuit. An intensity relay, no shown, on circuit 482 detects the current and controls the opening simultaneous solenoid valves 435 and 448. The flow of cooling gas external to the nozzle 441 coming from 451 combined with the flow rate of plasma gas 413, internal to said nozzle and coming from 438, develop forces causing its compression spring 442. The formation of a spark and the pilot arc occurs as described above. Such a priming system a first arc is given in document EP-A-326445.

Figure 5 shows a block diagram of the operation of a torch with short-circuit ignition according to the present invention. Torch 500 according to the invention comprises an electrode 506 secured to an electrode holder 561 fixed to the torch body, a nozzle 507 disposed with the axis coincident with that of electrode 506, secured to a nozzle holder 508, axially movable relative to a guide housing 509 forming a sliding bearing for said nozzle holder 508. At the upper internal part of the casing 509 is fitted a first pressure chamber 511 delimited by the surface internal lateral of the casing 509, a narrowing 595 coming from the casing 509, the external lateral surface of the nozzle holder 508 and a bulge 581, forming a head piston, coming from the nozzle holder 508. At the inner bottom of the housing 509 is fitted a second pressure chamber 512 delimited by the internal lateral surface of the casing 509, a narrowing 596 coming from the casing 509, the external lateral surface of the nozzle holder 508 and the bulge 581. In order ensure leaktight sliding of the nozzle holder 508 in the casing 509 and thus maintain the two pressure chambers without communication mutual fluidics and without communication with the surrounding elements, seals 591, 582, 592 are arranged respectively in the 595 upper shrinkage, 581 bulge and lower shrinkage 596. A first connection 597 for the connection of a supply means in pressurized gas from the first pressure chamber 511 is practiced in the wall of the casing 509, a second tap 598 for the connection a means for supplying pressurized gas to the second chamber pressure 512 is practiced in the wall of the casing 509.

A main source of electric current 520 is connected conventionally to the workpiece 524 and to the electrode holder 561 and a connection is also established between the source 520 and the nozzle 507. A source auxiliary 523 of low intensity electric current, called source of pilot arc current, is also connected to terminals 521 and 522 of the main source 520.

A pneumatic distributor 551 is supplied by an air source 550 under pressure. A first air distribution channel 552 is connected to the pressure chamber 511 by connection 597, a second air distribution 553 is connected to the pressure chamber 512 by the tapping 598. By acting on the distributor 551, a downward movement is given to the assembly 508, 507 by pressurizing the chamber 511, the downhill race being fixed by the abutment of the arrangement 583 of the bulge 581 of the nozzle holder 508, forming a bearing face, on the internal face 593 of the narrowing 596 of the casing 509, forming against the bearing face. AT conversely, an upward movement is given to this same set by placing in pressure of the chamber 512, the rise stroke being fixed by setting abutment of an area of the internal surface of the nozzle 507 on the end of the electrode 506. The residual difference Δe corresponds to the normal distance in front separate the electrode 506 from the nozzle 507 when the plasma arc is on. To to facilitate the movements of descent and ascent of the assembly 508, 507, the distributor 551 has two vents 514 and 515 for venting the respective supply channels 552 and 553.

To obtain the ignition of a pilot arc, sources 520 and 523 are energized, a stream of plasma gas 513 is injected into the space separating the nozzle 507 and the electrode 506 and the contact of section 517 is closed. The distributor 551 is then activated so that the nozzle 507 rises until it contacts electrode 506 and a current delivered by the auxiliary source 523 can then circulate in the circuit as well form. A current relay, not shown, placed on circuit 516 detects then the presence of an electric current and subsequently controls the lowering of the nozzle 507 by reversing the control of the distributor 551. It follows, when the short circuit between the electrode and the nozzle breaks, the formation of a spark which, as already described previously allows ignition of the pilot arc. The following operations to generate the cutting process for work piece 524 will not be detailed because similar to that described above.

FIG. 6 represents a diagram of an industrial embodiment a short-circuit ignition torch according to the present invention and, more specifically, a plasma cutting torch consisting of a torch body main monoblock. However, it should be emphasized that the invention can be applied also to a torch with removable body, that is to say separable from the base of torch permanently attached to an automatic machine frame for example, such the torch described in EP-A-599709, or generally to any type of torch comprising an electrode and a nozzle requiring the ignition of an arc pilot between these parts, regardless of the transformation process thermal implemented subsequently by said torch, namely a plasma cutting, plasma welding or plasma marking process by examples.

The torch of Figure 6 has an extended metal rear block 2 forward by a metal electrode holder 3 of tubular structure of revolution endowed with a thread at its lower end for sealing an electrode 4 comprising an emissive insert 41 by effect thermionic and two O-rings 43 and 42, one 43 on the outer body of said electrode 4, the other 42 under the screwed assembly of said electrode. The electrode holder 3 consists of an assembly of elements, such as a tube interior 31, an outer jacket 32 and a dip tube 33, all three metallic, forming a cooling circuit for all of the above by forced convection of a fluid, for example water, in a passage central fluid inlet 34 and annular fluid return 35. Part upper of block 2 is located the connection means 21 of a pipe combining the electrical supply of electrode 4, via the electrode holder 3 and block 2, and the supply of coolant to the aforementioned items. Another connection means, not shown, is implanted in said block 2 for a fluid evacuation pipe from cooling of the aforementioned elements. A first tubular sheath of revolution 36 made of an electrically insulating material, such as plastic, and fixed to the electrode holder 3 by a screwed / locked assembly 37, covers the latter. A second tubular sheath of revolution 38 made of a material mechanically resistant, like a metal, fixed to the insulating sheath 36 by a screwed / locked assembly 39, covers the insulating sheath 36. A head of piston 5 disc-shaped and provided with seals 51, 52 is maintained locked against a stop 384, coming from the metal sleeve 38, by a nut 6 secured by a screwed assembly 61 to said metal sheath 38. A sheath exterior 7, made of an electrically insulating material and secured to the block 2, partially covers said block 2 and forms a tubular support extending backwards to fix torch 1 to an element of machine. The lower part of block 2 is extended by a reduction of receiving diameter, by an assembly 22 screwed / locked on a flat surface 23 coming from block 2, an outer sheath 8 of generally tubular shape of downward stretching revolution made of electrically insulating material internally and locally lined with tubular elements of revolution 81, 82 made of a mechanically resistant material, such as a metal, sealed in the constituent material of said insulating sheath 8. In the upper part of said sleeve 8 is drilled a hole 83 through the insulating tube 8 and the gasket metallic 82 thus connecting the interior atmosphere of the sheath 8 and the external atmosphere of said sheath 8. In the lower part said sheath 8 is mounted in the groove an O-ring seal 84. A first tube 9 for supplying a pressurized fluid, such as compressed air, sealed in block 2, stretches down to the vicinity of the upper surface of the piston head 5. In its central portion is disposed in the groove a seal external sealing ring 91. A second tube 10 for supplying a fluid under pressure, like compressed air, sealed in block 2, stretches downward passing through its thickness the piston head 5. In its upper portion an outer O-ring seal 116 is arranged and in its part lower another outer O-ring 115 in connection with the piston head 5. At the top of block 2 are located the means of connection 24 and 25 of the pipes respectively supplying the tubes 9 and 10 in pressurized fluid. All the elements described above constitutes the fixed crew of torch 1. When the torch is in order of service this set is a unit, that is to say that no element composing it is not animated in particular during arc ignition sequences pilot.

The following describes all the elements making up the crew torch movable 1. During the pilot arc ignition sequences in particular, this assembly forms an integral block and is set in axial translational movement. A front block 11, of generally tubular shape of revolution and made of metal, has a first O-ring 118, mounted in an internal groove machined to the upper part of the bore of said block 11 and of a second O-ring 114, mounted in an internal groove machined at the bottom of the bore of said block 11. A sheath 14, of generally tubular shape and made of a material insulating like a plastic, is secured to the axis coinciding by a screwed assembly / blocked 117 in block 11. A first lining 141, of general shape tubular of revolution and made of metal, is sealed with the same axis on the outer periphery of the lower part of said sheath 14. A second gasket 142, of tubular shape of revolution and made of metal, is sealed to joint axis and tightness in the bore of the upper part of said sheath 14. The sub-assembly 11, 14 is mounted with the same axis and so sliding on the sheath 38 of the electrode holder 3 and on the piston head 5. The seals 118, 51 and 84 ensure a tight sliding of the block 11, of the gasket 142 and gasket 141 respectively on the sleeve 38 of the electrode holder 3, the piston head 5 and the sheath 8. A rear block 16, of form general tubular of revolution and made of metal, is fitted between the lining 142 of the sleeve 14 and the sleeve 38 of the electrode holder 3, forming thus cover of the sub-assembly 11, 14. The block 16 is fixed in position by screws, not shown, radially passing through the sheath 14 and its lining 142. The tubes 9 and 10 coming from block 2 pass through block 16 in all its thickness thanks to holes, machined with coincident axes, in said block 16, the seals 91 and 116 mounted in the groove on the respective tubes 9 and 10 allow a sealed sliding of the block 16 on said tubes 9 and 10. A first seal O-ring 161 mounted in a groove on the outer periphery of said block 16 ensures the tightness of the assembly 16, 142. A second O-ring 162 mounted in groove in the bore of said block 16 ensures sealed sliding of block 16 on the sleeve 38 of the electrode holder 3. In suitable housings fitted in the lower bore of block 11 are placed a gas diffuser plasmagen 12, slidably mounted on the jacket 32 of the electrode holder 3, and a nozzle 13. A cap 17, cup-shaped made of metal, covers the nozzle 13 and the block 11 delimiting an annular space 171 forming cooling fluid circulation chamber for the nozzle 13. The peripheral tightness of said chamber 171 is ensured by the seals O-rings 172 and 173, mounted in the groove in the internal wall of the cap 17 and the O-ring 114 mounted in a groove in the lower bore of block 11. A nut 15, by a screw 151 on the lining 141 drives, via a stop 152 obtained by reciprocal arrangement of the cap 17 and the nut 15, the cap 17 until the lips bordering the groove of the joint 172 plate the nozzle 13 in its housing, trapping the seal on relative diffuser 12 between a high stop 121 and a low stop 122. The seal 43 of the electrode 4 then allows a tight sliding of the diffuser 12 on said electrode 4. The mobile assembly thus mounted on the fixed assembly of torch 1, then forms three variable volume chambers, namely a lower pressure 18 supplied by the tube 10, a pressure chamber median 19 supplied by the tube 9, and a decompression chamber upper 20 with its vent hole 83.

• le tube 9 alimente la chambre médiane 19 en air comprimé, sous l'effet de la pression délivrée le bloc 16 est repoussé vers le haut et entraíne dans le même mouvement l'ensemble de l'équipage mobile donc la tuyère 13 qui vient alors en contact de court-circuit avec l'électrode 4. Pendant le mouvement de remonté de l'équipage mobile, d'une part l'air contenu dans la chambre inférieure 18 et soumis à compression s'échappe par l'évent correspondant du distributeur pneumatique, via le tube 10 et la canalisation raccordée au piquage 25 et d'autre part l'air contenu dans la chambre supérieure 20, soumis également à compression, s'échappe par l'orifice 83 de mise à l'air libre. La figure 6 montre la torche lorsque la tuyère est au court-circuit avec l'électrode.
• le courant circulant dans le circuit électrique fermé par le court-circuit étant détecté, l'alimentation en air comprimé du tube 9 est coupée et remplacée simultanément par l'alimentation en air comprimé du tube 10 établissant ainsi une pression dans la chambre inférieure 18. Dans le même temps est ouvert l'évent du distributeur pneumatique permettant la mise à l'air libre de la chambre médiane 19 via le tube 9 et la canalisation reliée au piquage 24. Sous l'effet de la pression régnant dans la chambre inférieure 18 et exerçant une force de répulsion sur la face inférieure interne de ladite chambre inférieure 18, que forment le bloc 11 et le fourreau 14, l'ensemble de l'équipage mobile descend quasi instantanément jusqu'à ce qu'un aménagement 143 de la garniture 141, formant butée, vienne en contact avec un aménagement 85 de la garniture 81, formant contre-butée. L'écart résiduel séparant l'électrode 4 de la tuyère 13 correspond à la distance normale pour l'arc plasma soit établi correctement. Au moment de la rupture du court-circuit entre électrode et tuyère, Il s'ensuit la formation d'une étincelle qui comme déjà décrit précédemment crée un chemin électrique propice à l'établissement d'un premier arc ou arc pilote. La suite des opérations permettant d'engendrer le processus de découpe de la pièce de travail ne sera pas détaillée car similaire à celle décrite ci-dessus.

By comparison with the block diagram of FIG. 5 and the corresponding explanations, it is easy to understand the operation of the torch of FIG. 6. When an order to strike the pilot arc is given, all other things being in operating order, i.e. the main and auxiliary current sources under voltage, the flow of plasma gas injected between electrode and nozzle, the isolating contact of the electric circuit of the nozzle closed, the coolant circulating in the circuits provided for this purpose and the distributor excited in correspondence with the following sequences:

• the tube 9 feeds the middle chamber 19 with compressed air, under the effect of the pressure delivered the block 16 is pushed upwards and causes in the same movement the whole of the movable assembly therefore the nozzle 13 which then comes in short-circuit contact with the electrode 4. During the movement of the mobile assembly, on the one hand the air contained in the lower chamber 18 and subjected to compression escapes through the corresponding vent of the pneumatic distributor , via the tube 10 and the pipe connected to the nozzle 25 and on the other hand the air contained in the upper chamber 20, also subjected to compression, escapes through the orifice 83 for venting. Figure 6 shows the torch when the nozzle is short-circuited with the electrode.
• the current flowing in the electric circuit closed by the short circuit being detected, the supply of compressed air to the tube 9 is cut off and replaced simultaneously by the supply of compressed air to the tube 10 thus establishing a pressure in the lower chamber 18. At the same time, the vent of the pneumatic distributor is opened, allowing the middle chamber 19 to be vented to the open air via the tube 9 and the pipe connected to the nozzle 24. Under the effect of the pressure prevailing in the lower chamber 18 and exerting a repulsive force on the inner underside of said lower chamber 18, which form the block 11 and the sheath 14, the whole of the movable assembly descends almost instantaneously until an arrangement 143 of the lining 141, forming a stop, comes into contact with an arrangement 85 of the lining 81, forming a counter-stop. The residual distance separating the electrode 4 from the nozzle 13 corresponds to the normal distance for the plasma arc to be established correctly. When the short circuit between the electrode and nozzle breaks, a spark ensues which, as already described above, creates an electrical path conducive to the establishment of a first arc or pilot arc. The following operations to generate the cutting process of the workpiece will not be detailed as similar to that described above.

Figure 7 gives another sectional view of the torch 1, crew mobile in the low position. The internal plasma gas distribution circuit composed of a metallic tube 26, sealed at its bottom in block 11, successively passes through the sheath 14, the piston head 5 and block 16. O-rings 260, 262 and 263 are arranged in grooves in said tube 26 so as to obtain respectively a static seal in the sleeve 14, a sliding seal in the piston head 5 and a static seal in the block 16. At the top of the tube 26 is assembled by a screw 264, sealing on a joint 265, a nozzle 27 slidably engaged in a housing 271 machined with the same axis in the block 2. An O-ring 266 seals the plasma gas circuit between the nozzle 27 and the block 2. The tube 26 is supplied with gas under pressure by the nozzle 30, intended for the connection of the supply pipe corresponding, and distributes said gas under pressure in space 125 separating the electrode 4 from the nozzle 13 via a plurality of injection orifices 126, a distribution chamber 127 and the holes 123 and 124 made in the block 11. The sub-assembly 26, 27, 265, 266, 263, 262, 260 is integral with the mobile equipment of torch 1 and therefore accompanies said mobile equipment in all its movements. The connection of the electrical supply circuit of pilot arc current at the nozzle comprises a metal rod 28 of section circular, sealed in block 11 by means ensuring continuity electric, successively passes through the sheath 14, the piston head 5 and the block 16. O-rings 287, 286 and 285 are arranged in grooves in said rod 28 so as to obtain respectively a static seal in the sleeve 14, a sliding seal in the piston head 5 and a static seal in the block 16. At the upper part of the rod 28, a extension 284, of reduced diameter, is engaged by sliding in a socket 29, of electrical contact, encased in a support 291, shaped in a cup, having a threaded extension 292 protruding from the rear of the block 2, intended to receive the connection of an electric current supply cable to the nozzle circuit. A shirt 293, of tubular shape of revolution produced made of an electrically insulating material such as plastic, is interposed between the sub-assembly 291, 29 and block 2. A nut 294 resting on a washer 295, made of an electrically insulating material such as plastic, blocks the sub-assembly 291, 29, 293 in a housing provided in block 2. The sub-assembly 28, 287, 286, 285 is integral with the mobile assembly of the torch and accompanies it in all its movements.

Figure 8 gives another sectional view of torch 1. The circuit go cooling by forced convection of the nozzle with a circuit supply of cooling fluid, such as distilled water, comprising a metal tube 31, sealed at its lower part in the block 11, successively passes through the sheath 14, the piston head 5 and the block 16. Des O-rings 311, 317 and 318 are arranged in a groove in said tube 31 of so as to obtain respectively a static seal in the sleeve 14, a sliding seal in the piston head 5 and a seal static in block 16. At the top of tube 31 is assembled by a screwing 314, sealing on a seal 315, a nozzle 32 engaged at sliding in a housing 321 machined with the same axis in block 2. A 316 O-ring seals the coolant circuit between the end piece 32 and the block 2. The tube 31 is supplied with pressurized fluid by the tap 33, intended for the connection of the supply pipe corresponding, and distributes said fluid under pressure in the annular space 171 separating the nozzle 13 from the cap 17 via the hole 174 made in the block 11. The sub-assembly 31, 32, 315, 316, 318, 317, 311 is integral with the mobile equipment of torch 1 and therefore accompanies said mobile equipment in all its movements. The coolant return circuit further comprises the metal tube 34, sealed at its part lower in the block 11, successively crosses the sheath 14, the head of piston 5 and block 16. O-rings 341, 342 and 343 are arranged in groove in said tube 34 so as to obtain respectively a static seal in the sleeve 14, a sliding seal in the piston head 5 and a static seal in the block 16. At the part upper part of the tube 34 is assembled by a screwing 344, sealed on a seal 345, a nozzle 35 slidably engaged in a housing 351 machined to axis merged in block 2. An O-ring 346 seals the circuit coolant between the nozzle 35 and the block 2. The fluid under pressure is collected in the annular space 171 separating the nozzle 13 from the cap 17 by the hole 175 made in the block 11 and is evacuated by the nozzle 36, intended for connection of the evacuation pipe corresponding, via the tube 34, the end piece 35 and the housing 351. The sub-assembly 34, 35, 345, 346, 343, 342, 341 is integral with the moving assembly of torch 1 and therefore accompanies said mobile assembly in all of its movements.

Claims (16)

Electric arc work torch (1) comprising a torch body and a torch head, said torch comprising at least one electrode holder (3) for receiving an electrode (4) and a holder block (11) nozzle for receiving at least one nozzle (13), said electrode holder (3) being fixed in said torch and said nozzle holder block (11) being axially movable between: at least a first position in which the nozzle (13) carried by said block (11) nozzle holder is brought into mechanical contact with said electrode (4) carried by said electrode holder (3), and at least a second position in which the nozzle (13) carried by said block (11) nozzle holder is located at a non-zero distance from said electrode (4), characterized in that said nozzle holder block (11) is axially movable by means of at least one guide housing (5, 8, 14, 16, 38, 81, 141, 142) forming a sliding bearing for said nozzle holder block (11), the guide housing (5, 8, 14, 16, 38, 81, 141, 142) comprising a first pressure chamber (18) and a second pressure chamber (19), said first and second chambers (18, 19) pressure with variable internal volumes and being separated from each other by at least one intermediate partition (5), the guide housing (5, 8, 14, 16, 38, 81, 141, 142), the nozzle holder block (11) and said intermediate partition (5) being arranged so as to maintain the two pressure chambers (18 , 19) without fluid communication with each other and to ensure leaktight axial sliding of the nozzle holder block (11) by means of the guide housing (5, 8, 14, 16, 38, 81, 141 , 142) to vary the internal volumes of said first and second pressure chambers (18, 19), at least a first fluid supply passage (10) opens into the first pressure chamber (18) to allow a supply of pressurized fluid to said first pressure chamber (18), and at least one second fluid supply passage (9) opens into the second pressure chamber (19) to allow supply of pressurized fluid to said second pressure chamber (19). Torch according to claim 1, characterized in that the first and second pressure chambers (18, 19) are separated from each other by at least one intermediate partition (5) axially movable and carried integrally by the block (11 ) nozzle holder, said partition (5) forming a piston head with fluid actuation, preferably said movable partition (5) constitutes a shoulder or a radial bulge coming from the nozzle holder block (11). Torch according to claim 1, characterized in that : the first and second pressure chambers (18, 19) are separated from each other by at least one intermediate partition (5) fixed and integral with the fixed part (5, 8, 38, 81) of the guide housing (5, 8, 14, 16, 38, 81, 141, 142) formed by at least part of the electrode holder (3), and the nozzle holder block (11) comprising a first radial expansion (16) forming the upper wall of the second pressure chamber (19) and a second lower radial expansion (14) forming the wall of the first pressure chamber (18), said block (11) nozzle holder and said first and second internal radial expansions (16, 14) being movable integrally and axially. Torch according to claim 3, characterized in that : the second pressure chamber (19) is delimited by the internal surface of the side wall of the housing, the internal surface of the upper wall of the housing, the external surface of the side wall of the electrode holder (3) and the upper surface of the fixed partition (5) forming the piston head secured to the electrode holder (3), and the first pressure chamber (18) is delimited by the internal surface of the side wall of the casing, the internal surface of the bottom wall of the casing, the external surface of the side wall of the electrode holder (3) and the bottom surface of the fixed partition (5) forming the piston head secured to the electrode holder (3). Torch according to claim 2, characterized in that : the second pressure chamber (19) is delimited by the internal surface of the side wall of the casing, the internal surface of the upper wall of the casing, the external surface of the side wall of the nozzle holder block (11) and the upper surface the movable partition (5) forming the piston head secured to the nozzle holder block (11), and the first pressure chamber (18) is delimited by the internal surface of the side wall of the casing, the internal surface of the bottom wall of the casing, the external surface of the side wall of the nozzle holder block (11) and the bottom surface of the movable partition (5) forming a piston head integral with the nozzle holder block (11). Torch according to one of Claims 1 to 5, characterized in that sealing means (51, 52, 118, 161, 162) are arranged between the guide casing, the nozzle holder block (11) and / or the electrode holder (3) and said intermediate partition (5) so as to allow sealed axial sliding of the nozzle holder block (11) in the guide housing and / or on at least part of the electrode holder (3) to maintain the first and second pressure chambers (18, 19) without fluid communication with each other, preferably the sealing means comprise seals. Torch according to one of Claims 1 to 6, characterized in that the first passage (10) for supplying pressurized fluid makes it possible to convey a pressurized fluid, preferably a gas, to said first pressure chamber (18) via a first orifice made in a wall the guide housing, and the second passage (9) for supplying pressurized fluid makes it possible to convey a pressurized fluid, preferably a gas, to said second pressure chamber (19) via a second orifice made in the wall of the guide housing. Torch according to one of claims 1 to 7, characterized in that the first passage (10) for supplying pressurized fluid passes through at least part of said second pressure chamber (19), said intermediate partition (5) and opens into said first pressure chamber (18). Torch according to one of Claims 1 to 8, characterized in that it further comprises at least one decompression chamber (20) communicating with the ambient atmosphere via at least one passage (83) gas outlet. Torch according to one of claims 1 to 9, characterized in that it further comprises an electrode (4) provided with an emissive insert (41) made of zirconium, hafnium or tungsten, pure or alloyed. Torch according to one of Claims 1 to 10, characterized in that assembly / disassembly means make it possible to associate and / or dissociate the torch head from the torch body. Torch according to one of Claims 1 to 11, characterized in that it is of the single-flow or double-flow type and / or in that it comprises means for distributing flow in the axial mode or in the vortex mode. Automatic plasma arc installation comprising a plasma torch according to one of claims 1 to 12, preferably a plasma cutting torch (1), mounted on a support frame comprising at minus a motorized movement axis, control means making it possible to command at least the ignition sequence of said torch by allowing and / or prohibiting the introduction of a pressurized fluid, preferably air, in the first pressure chamber (18) or in the second chamber (19) pressure so as to vary the internal pressure and / or volume of said chambers (18, 19) and thereby causing movement in approach or, conversely, away from at least the nozzle holder block (11) and the nozzle (13) relative to the electrode holder (3) and to the electrode (4) by axial sliding of at least the nozzle holder block (11) via guide housing (5, 8, 14, 16, 38, 81, 141, 142), management means work sequences and means for programming and managing work trajectories like a numerical control. Method of striking a pilot arc in a plasma torch comprising a fixed electrode (4) and a movable nozzle (13) carried integrally by a nozzle holder block (11) movable axially in the torch (1), in particular a torch (1) according to one of claims 1, 3, 4 or 6 to 12, in which a pilot arc is struck between the nozzle (13) and the electrode (4) by introducing a pressurized fluid, preferably a gas, in at least a first pressure chamber (18) cooperating with at minus the nozzle holder block (11) so as to vary the pressure and / or the internal volume of said pressure chamber (18) and thereby causing a movement in approach of at least the nozzle holder block (11) and the nozzle (13) relative to the electrode holder (3) and to the electrode (4) by axial sliding of at least the nozzle holder block (11) by means of a guide housing (5, 8, 14, 16, 38, 81, 141, 142) until contact is obtained between the nozzle (13) and the electrode (4) with the formation of an electric arc between them, and at least one second pressure chamber (19) cooperating with at minus the nozzle holder block (11) so as to obtain a movement in distance of at least the nozzle holder block (11) and the nozzle (13) by compared to the electrode holder (3) and the electrode (4), when the pressure and / or the internal volume of said second pressure chamber (19), by axial sliding of at least the nozzle holder block (11) in said housing guide (5, 8, 14, 16, 38, 81, 141, 142). Method of striking a pilot arc in a plasma torch comprising a fixed electrode (4) and a movable nozzle (13) carried integrally by a nozzle holder block (11) movable axially in the torch (1), in particular a torch (1) according to one of claims 1, 2 or 5 to 12, in which a pilot arc is struck between the nozzle (13) and the electrode (4) by introducing a pressurized fluid, preferably a gas, in at least one second pressure chamber (19) cooperating with at minus the nozzle holder block (11) so as to vary the pressure and / or the internal volume of said second pressure chamber (19) and to cause thus a movement in approach of at least the block (11) nozzle holder and of the nozzle (13) relative to the electrode holder (3) and to the electrode (4) by axial sliding of at least the nozzle holder block (11) by means of a guide housing (5, 8, 14, 16, 38, 81, 141, 142) until contact is obtained between the nozzle (13) and the electrode (4) with the formation of an electric arc between them, and at least a first pressure chamber (18) cooperating with at minus the nozzle holder block (11) so as to obtain a movement in distance of at least the nozzle holder block (11) and the nozzle (13) by compared to the electrode holder (3) and the electrode (4), when the pressure and / or the internal volume of said first pressure chamber (18), by axial sliding of at least the nozzle holder block (11) in said housing guide (5, 8, 14, 16, 38, 81, 141, 142). Plasma cutting process for a part, preferably metallic, such as sheet steel, stainless steel or aluminum alloy, operates a method of striking a pilot arc according to claim 14 or 15.

Images