Method for treatment of solidifying liquid metal, plasma generator, electrode for plasma generator

Description

Field of application of the invention The subject of the invention is a method for the heat treatment of solidified molten metal, a plasma generator for implementing the method, and an electrode for such a plasma generator. Plasma generators are used in many technological processes for the heat treatment of various objects, for example in metallurgy the so-called plasma arc reflow, plasma casting, plasma cleaning, etc. In one aspect, the method of the invention is to heat a liquid metal seated and crystallizing in a mold with a circulating plasma arc, which aims to eliminate typical casting defects such as voids, pores, encrustation, absorption voids, inhomogeneity in chemical composition and crystal structure within the casting, etc. avoidance. Technical background of the invention Plasma generators containing plasma torches have been known for a long time, and general descriptions of their design and various metallurgical applications can be found in many technical monographs or handbooks, such as the Metals Handbook (9th edition, volume 15, Metals Park, Ohio, US): Plasma Melting and Casting casting) and 314-315 of Dembovsky's monograph published in 1985 entitled Elsevier: Plasma Metallurgy, The Principles. pages. Plasma generators are divided into two basic groups, namely those where both the cathode and the anode of the plasma generator form part of the equipment, and which are otherwise called internal arc or internal plasma arc (non-transferable arc, non-transferable plasma arc) plasma generators, and those which only they contain one electrode and the other electrode is formed by an electrically conductive body, which are otherwise called transferred arc plasma generators or transferable arc plasma generators (in English: transferable arc or transferable plasma arc generator). Document number GB 1268843 describes an internal arc plasma generator with a water-cooled cathode and two ring-shaped anodes - one for ignition and the other for normal operation - which are connected to a power supply. The tip of the cathode is protected by injecting an inert gas such as argon, helium or nitrogen. US 5,958,057 describes a typical transferred arc plasma generator used for heating metal in a continuous casting operation. This transferred arc plasma generator contains a cylindrical cathode holding element and an associated cooling arrangement, an ignition anode and an annular cathode formed with an internal channel for the introduction of an inert shielding gas. An electric discharge is created between the object to be treated and the cathode, connected as a cathode. The fundamental shortcoming of traditional plasma generators, both in the case of the internal arc and the transferred arc types, is that for their proper operation either the injection of shielding gas or water cooling is necessary. When gas cooling is used, so-called plasma torches are used, which contain nozzles that emit plasma. The injection of pressurized gas into the plasma torch results in the formation of an elongated plasma jet that exits the plasma emitting nozzle at high speed, and this high-speed plasma jet exerts local pressure on the surface of the still-solidifying material in the case of solidified cast metal treatment. and this leads to the formation of large voids in the surface during cooling. The presence of cooling water creates a danger because, in case of the smallest leakage, the water coming into contact with the liquid metal can cause an explosion. Plasma generators are also known in which the plasma arc is moved in a controlled manner along an open, for example, straight line, or a closed, for example, outline, along a correspondingly designed electrode. This displacement avoids overheating, promotes more uniform handling of the object, reduces electrode erosion, and thus extends the life of the equipment. Accordingly, document numbered US 5132511 describes an internal arc plasma torch, which contains two uniaxially arranged tubular electrodes, which are axially spaced apart, and an electromagnetic coil is associated with them for the purpose of rotating the arc. The coil is mounted in a closed cylindrical chamber located between the two electrodes. Document numbered US 5393954 describes an internal arc plasma torch that contains two uniaxially arranged tubular electrodes, at least one of which is surrounded by a magnetic field associated with an electronic control device, and with the help of which the base point of the arc is rotated in a controlled manner. When the gas that produces the plasma is injected into the chamber that separates the electrodes, the arc is ignited. It is known that the arc formed in the plasma generator can be moved by exerting a ponderomotive or otherwise Lorentz force. Lorentz force is formed when an electric charge moves in a magnetic field, and the magnitude of the force is proportional to the magnetic induction of the magnetic field, the electric charge, the speed of movement of the charge, and also depends on the angle formed by the vector of the magnetic induction and the speed vector of the moving charge close with each other. It is known that the Lorentz force created in the plasma generator is the result of the interaction between the arc (which is a strong electric discharge), its magnetic field and the magnetic field created in the generator by the electric current flowing through the electrodes. When the electrodes form a so-called two-rail structure, the Lorentz force accelerates and moves the electric arc. In this description, the definition of "two-rail structure" refers to electrodes in which the electrodes of the plasma generator are formed by two parallel current-carrying objects (so-called rails), which are located at a distance from each other, and each of them is connected to one of the terminals of an electrical power supply. When between the two electrodes elect2 HU 226 678 Β1 destructive arc is created, then this arc moves along the rails away from the place where the rail is electrically connected to the power supply. In accordance with the usual names in technical practice, in the case of plasma generators where the arc discharge is accelerated by ponderomotive force in the space between the parallel electrodes, they are sometimes called electromagnetic rail accelerators or rail-arranged plasma accelerators. The phenomenon according to which the Lorentz force accelerates and displaces the plasma arc in the two-rail plasma generator is also known as the electromagnetic acceleration principle. The professional literature sometimes also calls them plasma accelerators or magnetohydrodynamic generators, for example the article by Aleksandrov et al entitled Impulsus plasma accelerators (Kharkov 1983, pp. 192-194) and the article by J. Kompan and E. Seribinyin entitled Electric slag welding and electroslag melting (Masinostrojenyi 1989, pp. 191-192). A typical application of the Lorentz force is described in Sizing Relationships for Plasma Armatures and Rail Guns by Lindsay D. Tomhill et al (Transactions of Plasma Science Vol. 21, No. 3, June 1993, pp. 289-290). An internal arc plasma generator with magnetic rail acceleration is described, for example, in document SU 890567. In this generator, the electrodes are formed in the form of two uniaxial elliptical tubes, and there is an insulating material in the space between the electrodes. One wall of each tube is axially split in such a way that the part of the wall of the other tube that does not have a slot is located opposite the slot formed in one tube. An electrical connection is made next to each slit, and in this way a two-rail structure is achieved. In order for the plasma arc to circulate without interruption, the arc must be able to pass through the slits, and to do so, the width of each slit must be less than the thickness of the arc. However, when passing through the gaps, when the arc reaches exactly the place that is in the range of the adjacent electrical connection, that is, the place where further movement is indefinite, as a result of which the speed of the movement of the arc decreases near the gaps, and the discharge sometimes even breaks, which is an obvious disadvantage. Document number SU 847533 describes a transferred arc plasma generator, which is used to treat an electrically conductive object. This plasma generator has a main electrode as part of it, and the electrically conductive object is switched on as the other electrode. The shape of the main electrode is a hollow elongated body wound in a spiral line, which has a coil whose partially overlapping ends are placed at an angular distance from each other and have an air gap between them. The edge of one end of the spiral body is placed near the body to be treated (proximal edge) and is connected to one of the poles of the electric power supply with connectors that are located near this air gap. The spiral shape of the electrode can be characterized by the following relationship: Y=K(X)3 / 2in which context Y is the pitch of the spiral K proportionality factor and X is the linear distance between the electrical connector and the end of the spiral, measured along the sheath of the spiral. Acceleration of the arc along the spiral electrode is said to be possible in accordance with this relationship. However, the use of an electrode with such a design and satisfying the conditions imposed by the above relationship is accompanied by a number of shortcomings: (a) the production of the spiral-shaped electrode from graphite, tungsten or other materials commonly used for the production of electrodes for plasma generators is complicated and expensive; (b) according to the above relationship and due to the exponentially increasing dependence of the value of Y on the value of X, the plasma current fluctuates, as a result of which the plasma generator designed according to document SU 847533 works reliably in practice only up to a spiral diameter of 6 cm without the use of additional devices, but in the case of larger diameters the plasma arc may be interrupted. To prevent such interruptions, the plasma arc discharge must be re-ignited at each cycle using a high-voltage oscillator; (c) since the acceleration of the plasma along the edge of the spiral-shaped proximal electrode is not uniform, the electrode heats unevenly, and this requires an efficient and reliable water cooling system, which also requires the use of suitable devices for controlling the temperature and pressure of the water. All these circumstances make the plasma generator more expensive and make it impossible to use it for purposes where the use of cooling water is undesirable or unavoidable due to the dangerous consequences of leakage. Objective to be achieved with the invention One of the goals to be achieved by the invention is the development of a process that can be heat treated with a circulating plasma arc of solidifying liquid metal in molds. Our further aim with the invention is to create a transferred arc plasma generator with which the procedure can be implemented and which contains a new type of electrode. The plasma generator is designed in such a way that solidifying molten metal in molds can be heat treated with it. Our further goal with the invention is to create a simple and cheap electrode for a plasma generator, which is suitable for generating a continuously circulating self-stabilizing plasma arc, without the need for any water cooling or shielding gas injection, and which is approx. It is functional up to an output power of 50 kW within a considerable lifetime. Discovery of the invention In the present description and claims, the designations "longitudinal" and "longitudinal" are defined by the two closing flanges containing the tubular body producing the plasma arc3 HU 226 678 Β1 is used in connection with the seen electrode in a context that denotes any path or direction along the wall of the tubular body leading from one edge to the other; furthermore, the names "lateral" and "lateral" mean a direction that intersects a longitudinal line. From one point of view, the invention is a method created for the heat treatment of molten metal, during which a plasma arc is generated between the lower edge of the plasma generator electrode and the molten metal forming its counter electrode, and the molten metal is heated with this plasma arc. The procedure is characterized by a) the distance between the lower edge of the electrode and the surface of the molten metal forming the counter electrode is set, b) the electrode is connected to one corner of an electrical power supply and c) by connecting the counter electrode to the other corner of the electric power supply, igniting the plasma arc, we move it in the first direction in a closed path along the lower edge of the electrode while the molten metal solidifies. In another aspect, the invention is a plasma generator for the heat treatment of molten metal, which includes an electrode and a counter electrode, which form a two-rail structure trained to create a plasma arc, and moves the plasma arc in a closed path in the first direction without interruption during the solidification of the molten metal forming the counter electrode along the working edge of the electrode, which electrode has a body equipped with an upper flange and a working lower flange, and is equipped with a set of connectors connected to an electrical power supply. The connector set includes at least one connection location located on the electrode of the two-rail structure, and the electrode is connected to a terminal of the electric power supply at the connection location, and the electrode body has at least one longitudinal air gap, and the air gap has an upper air gap section at the upper edge of the electrode body , there is a lower air gap section at the lower edge of the body, and a main air gap section is located between them, and each air gap divides the wall of the electrode body into two sectors, and each sector has a lower edge and an upper edge, and the connection point of the connector set is located at the air gap of one sector, and the zone receiving the plasma arc is located on its lower edge, and the zone transmitting the plasma arc is located on the lower edge of another sector, where the zone transmitting the plasma arc and the receiving zone are separated from each other by the lower air section of an air gap and are located on both sides of it, and the body of the electrode connector on the bottom edge the projection of the connection point of the old set is located at a distance from the zone receiving the plasma arc in the second direction opposite to the first direction. From a further point of view, the electrode created for heat treatment of molten metal of the invention for such a plasma generator, for submitting a plasma arc and for moving the plasma arc in a closed path, in the first direction, along the working edge of the electrode without interruption during solidification, which electrode has a body formed with an upper edge and a lower edge, and has a body designed for connection to an electrical power supply and equipped with a set of connectors designed for connection to an electrical power supply. The plasma generator electrode connector set includes at least one connection location located on the electrode body, and the electrode body has at least one longitudinal air gap, and the air gap has an upper air gap section at the upper edge of the electrode body, a lower air gap section at the lower edge of the body, and these a main air gap section is located between, and each air gap divides the wall of the electrode body into two sectors, and each sector has a lower edge and an upper edge, and the connection point of the connector set is located at the air gap of one sector, and the zone receiving the plasma arc is located on its lower edge, and a on the lower edge of another sector there is a plasma arc transmitting zone, where the plasma arc transmitting zone and the receiving zone are separated from each other by the lower air section of an air gap, and they are located on both sides of it, and also the projection of the connection point of the connection set on the lower edge of the electrode body from the plasma arc receiving zone to the first one is located at a distance in the second direction opposite to nn, due to which a Lorentz-like force is generated in the two-rail structure during operation, which moves the plasma arc formed between the electrode generating the plasma arc and the counter electrode along the second peripheral region along a path closed in the first direction without interruption, and moves it through each in the air section in the second peripheral region. The solution according to the invention is an electrode producing a plasma arc, which together with a counter electrode forms a two-rail structure, which is suitable for creating a plasma arc discharge that can be moved in the first direction along a closed path, and which electrode is provided with an electrical connection structure for connection to a direct current source, and is essentially a tubular is formed by a body, which has a first edge forming part of the first edge region, and a second working edge forming part of the second edge region, which serves for electric arc discharge. The essentially tubular body of the plasma generator electrode according to the invention can be cylindrical, column-shaped, a column formed with a star-shaped profile or the like. In one possible embodiment of the invention, the tubular body has a single air gap and the two sectors are combined into a single body that extends from one side of the air gap to the other. Thus, in the case of this embodiment of the electrode, the tubular body is formed with a single slit. In the case of another possible embodiment of the invention, the tubular body has several air gaps and several sectors, and each sector is located between two air gaps. The part of the plasma arc that is in contact with the second peripheral part of the plasma generator electrode is the section 4 HU 226 678 Β1 is known in the literature as the "foot point" of the arch. During operation, in the case of the electrode according to the invention that produces the plasma arc, the bottom of the arc moves in a closed path in the second peripheral region. In the case of a preferred embodiment of the plasma arc generating electrode according to the invention, each air gap section in the second edge region is sized so that it is essentially no wider than the smallest effective diameter of the column of the plasma arc: and the projection of the contact point on the second edge portion associated with the air gap, and the electrical the distance between the arc-receiving zone is essentially not smaller than the largest effective diameter characteristic of the base of the plasma arc column. We would like to note that the diameter of the column of the plasma arc and the diameter of the base of the arc are values ​​that can be determined by inspection and can be measured visually. However, the smallest and largest values ​​characterizing the diameter of the column of the plasma arc can be calculated from the largest and smallest values ​​of the plasma current, and the relationships necessary for this are known to the expert. For example, in the case of a current of 300 A in a gaseous medium at atmospheric pressure, the diameter of the column on a solid electrode is approx. It reaches a value of 5 cm, and the diameter of the sole is usually between 3 and 5 mm. The importance of the conditions given above is that even the narrowest arc column produced in the structure is able to pass through an air gap, but at the same time the largest base point of the arch does not cover the zone below the connection point while it passes through the air gap section in the second peripheral region, but rather passes through the on an electric arc-receiving zone, which is laterally removed from the connection location as specified, which enables the uninterrupted movement of the electric arc. The connection points are preferably located near the first peripheral region. If desired, the second peripheral area of ​​the electrode can be beveled, which increases the surface for the electric discharge and deviates from the direction perpendicular to the axis of the tubular body, and thus allows the direction of the arc to be adjusted. In the case of the plasma generator electrode according to the invention, the main air space section of at least one longitudinal air gap is designed in such a way that the connection point associated with the air gap and projected onto the second peripheral part is located in the sector that contains the zone emitting the electric arc. In the case of one embodiment of the invention, the sectors of the tubular body are designed in such a way that the connection point associated with each air gap projected onto the second peripheral part is located outside the closed path, namely inside or outside the perimeter of this closed path. If desired, the electrode sectors of the plasma generator according to the invention are designed in such a way that the air gap section of each air gap in the second edge region is formed by the overlap between the sector parts adjacent to each other and containing the plasma arc emitting and receiving zones. In the case of such a design, the cross-sectional area of ​​the electrode is larger than that of the cylindrical tubular body, the circumference of which is determined by the connection points of the first edge. The shape of the tubular body of the electrode can be, for example, a polygonal shape similar to a star, and it can be composed of several modular body segments that partially overlap each other along their edges. In the case of power supply, the plasma generator electrode according to the invention - which is made, for example, of graphite or heat-resistant metal - is suitable for creating a plasma arc discharge up to a power of 50 kW without the need for water cooling. However, if the cross-sectional size of the electrodes according to the invention does not exceed 7 cm, the operation may have to be carried out intermittently. In a second aspect, the solution according to the invention is a plasma generator which includes the given type of electrode. The plasma generator equipment can be either internal arc or transferred arc type. The internal arc plasma generator device according to the invention can be used to treat non-conductive objects with plasma, such as construction raw materials, waste or any other electrically insulating material. In the case of one embodiment, the transferred arc plasma generator according to the invention contains an electrode that produces a plasma arc in cooperation with an electrically conductive object that functions as an electrode, which plasma generator electrode and the counter electrode together form a two-rail structure that is suitable for creating a plasma arc discharge that can be moved along a closed path in the first direction , and which plasma generator electrode is equipped with an electrical connection structure to be connected to a direct current source, and is essentially designed as a tubular body, which has a first edge forming a first edge region and a second working edge forming part of a second edge region for electric arc discharge, in which electrode: (i) the connection structure of the electrode includes at least one connection location on the electrode; (ii) the tubular body has at least one longitudinal air gap, which includes a first peripheral region air gap section, a main peripheral region air gap section, and a second peripheral region air gap section, each of which air gaps is laterally divided into two sectors, each of which has a first and a second peripheral portion, and one of the sectors is a connection point associated with the air gap carries; (iii) the second peripheral part of one of the sectors has a plasma arc emitting zone, and the second peripheral part of the wall part carrying the connection point has a plasma arc receiving zone, where the plasma arc emitting and receiving zones are separated and bounded by the second peripheral air gap section of the longitudinal air gap, and thereby forming two sides of the air gap section; (iv) and which connection point associated with the air gap is located in such a way that, projected onto the second peripheral part, laterally in the opposite direction to the first HU 226 678 Β1 is moved away from the zone receiving the plasma arc in the second direction, due to which a Lorentz force is generated in the two-rail structure during operation, which creates a plasma arc between the electrode generating the plasma arc and the counter electrode along the second peripheral region along a path closed in the first direction without interruption moves it and moves it through the air gap section in each of the second peripheral regions. In the remainder of the description, the plasma generator electrode according to the invention - which forms part of the plasma generator - will be referred to as "main electrode" in some cases. In the case of a possible embodiment, the plasma generator according to the invention contains a cylindrical housing that surrounds the main electrode and is placed at a distance from it and together with it forms an annular chamber. If desired, a cover can be formed, which separates the housing from the end farthest from the inner edge of the electrode. If desired, an ignition device can also be designed to ignite the plasma arc discharge, which can be installed in the annular space between the housing and the main electrode near the first edge, which creates an additional arc after ignition, which initiates the main arc. Typically, the actuation device may include a first filament-like electrode spaced inside a second uniaxially arranged tubular electrode, and the first and second electrodes may be connected to two poles of the DC electrical power supply, and a third rod-shaped electrode is installed in a substantially perpendicular position to the second tubular electrode compared to and in the part towards its end, and which third electrode can be electrically connected to a high-voltage oscillator. Preferably, the end portion of the tube is formed with an inner flange defining a tapered air gap between the fiber-shaped and tubular electrodes in the region where the voltage of the high-voltage oscillator is applied through the third rod-shaped electrode. In a typical design, the igniter is attached to the housing cover and extends axially to the region of the second edge of the main electrode. In the preferred embodiment of the transferred plasma generator according to the invention, the main electrode is associated with a structure that moves it axially, with the help of which the distance between the second edge and the object can be regulated and optimized during operation. The typical field of application of the transferred plasma generator according to the invention is the heat treatment of molten metals during solidification, which molten metal is placed in a suitable mold, for example a mold. Accordingly, the solution according to the invention, examined from the first point of view, constitutes a process for the heat treatment of solidifying liquid metal in a mold, during which a transferred arc plasma generator device containing a main electrode is brought into cooperation with an electrically conductive object serving as a counter electrode, and during which the main electrode is connected to the electrically conductive object cooperates to form a two-rail structure, which creates a plasma arc discharge that can be moved in the first direction along a closed path, and whose main electrode has an electrical connection structure for connecting to a direct current electric current source, and also essentially contains a tubular body, the first edge of which is part of the first edge region, and the second edge region is part of and electric it has a second working edge for arc discharge, which at the electrode: i) the connection structure of the electrode includes at least one connection point on the electrode; ii) the tubular body has at least one longitudinal air gap, which includes a first peripheral area air gap section, a main air gap section and a second peripheral area air gap section, each of which air gaps is laterally divided between two sectors, and each of them has a first and a second peripheral part, and one of the sectors is the connection point associated with the air gap carries; iii) the second peripheral part of one of the sectors has a plasma arc emitting zone, and the second peripheral part of the wall part carrying the connection point has a plasma arc receiving zone, where the plasma arc emitting and receiving zones are separated and bounded by the second peripheral air gap section of the longitudinal air gap, and thereby forming two sides of the air gap section; iv) the connection point associated with the air gap is located in such a way that, projected onto the second edge part, it is laterally moved in the second direction opposite to the first direction from the zone receiving the plasma arc, and the plasma generator is placed in such a way that the second edge is located closer to the liquid metal forming the counter electrode surface and at a suitably selected distance from it, then the main electrode is connected to one corner of the electric power supply unit and the liquid metal forming the counter electrode to the other corner, then an electric arc is ignited, which creates a Lorentz force in the two-rail structure during operation, which is the plasma moves the plasma arc formed between the arc-generating electrode and the counter-electrode in the first direction without interruption along the closed path in the second edge region and crossing the air gap section in each second edge region; the treatment is continued until the liquid metal reaches its solid state. Controlling the cooling and solidification process of the liquid metal with the plasma arc according to the invention improves the quality of the solidified metal. During the development of the invention, we found that this improvement is due to the displacement of the plasma arc in a closed orbit under the influence of the Lorentz force and the force produced inside the novel plasma generator. We have also found that, according to the invention, due to such treatment, previous casting defects such as the formation of voids and pores, enrichment, formation of absorption cavities or casting of chemical composition and crystal structure6 HU 226 678 Inhomogeneity within Β1 can be avoided. We have also found that the amount of metal waste generation is reduced due to the application of the invention. We also found that the structure of the solidified crystal improves as a result of the heat treatment according to the invention, possibly due to the electromagnetic fields that create the Lorentz force. Brief description of the drawings For the sake of better comprehensibility, some typical embodiments of the invention will be described hereafter, solely for the sake of example, with reference to the attached drawing. In the drawing: Fig. 1 is a schematic view of one embodiment of the plasma generator electrode according to the invention, Fig. 2a. Fig. 2b is a side view of another embodiment of the electrode according to the invention with a schematically indicated counter electrode. Figure 2a. top view of the embodiment according to figure 3, figure 3 is a schematic view of a further embodiment of the plasma generator electrode according to the invention together with a counter electrode, figure 4 is a view of another embodiment of the plasma generator electrode according to the invention! Fig. 5 is a schematic cross-sectional view of an embodiment of the internal plasma generator device according to the invention, Fig. 6 is a schematic cross-sectional view of an embodiment of the transferred plasma generator according to the invention, Fig. 7a. Fig. 7b is a schematic cross-sectional view of a further embodiment of the transferred plasma generator according to the invention. Figure 7a. bottom view of the embodiment according to Figure 8, Figure 8 is an enlarged cross-sectional view of the ignition structure of the plasma generator according to the invention, Figure 9 is an overview of the arrangement for controlling the cooling and solidification of the liquid metal in the mold and containing a plasma generator, and Figure 10 is the plasma generator treated with a circulating plasma arc according to the invention and pictures of untreated bugs. Detailed description of the individual designs Figure 1 shows the appearance of the plasma generator electrode according to the invention! shows his picture. As can be seen from the figure, the electrode 2 has a tubular cylindrical body characterized by a longitudinal center line, and its first edge has a second working edge 4 for electric arc discharge, and forms a component of a two-rail structure, which during operation forms a closed path of the Lorentz produced in the device for an electric arc moving due to force. The side wall 5 of the body of the cylindrical electrode 2 is split open with a single through air gap 6, which is essentially in the axial direction and has an air gap section in the region of the first edge 3, a main air gap section 8 and an air gap section 9 in the region of the second edge. As shown in the figure, the main air gap section 8 consists of two parts with an obtuse angle between them. Air gap 6 divides the wall into two sectors 10 and 11. The 2 electrodes have 12 connection points connected to an air gap on their first 3 edges, which are equipped with 13 connectors for connecting to one terminal of a direct current (not shown) power source. It should be noted that the connection point 12 is not necessarily on the first 3 edges, but can be placed at any level of the tubular body, but preferably at such a reasonable distance from the working edge 4 that it is not affected by the plasma arc and the smoke released from the object. The arrow marked with a dashed line in Figure 1 indicates the direction of movement of the produced electric arc during operation, i.e. the so-called first direction, which is formed under the influence of the Lorentz force. As mentioned earlier, for this movement, the electrode 2 together with the second rim 4 forms one component of the required two-rail structure, while the other component is formed by the opposite electrode 15. The air gap section 9 in the second peripheral region separates zones 16 that emit or transmit electric Ivet and zones 17 that receive electric arcs. In the case of this embodiment, it can be seen that the air gap 6 is designed in such a way that the projection 19 of the connection point 12 projected onto the second edge 4 of the electrode 2 is located near the zone 16 emitting the electric arc and is separated by a distance L from the zone 17 receiving the arc, namely in the opposite direction to the first direction (so-called second direction). In essence, this distance L is not smaller than the largest diameter characteristic of the type point of the produced plasma arc column. When the arc forms between the 2 electrodes and the opposite 15 electrodes, it forms a current-carrying plasma body that connects the two electrodes 2 and 15 to each other. Since the two, 2 electrodes and electrodes together form a two-rail structure, the electric current flowing through it creates a magnetic field that interacts with the current of the arc and its magnetic field, and this interaction creates a Lorentz force that drives the column of the arc it is folded along the second edge 4, namely in the direction 14 away from the projection 19 of the connection place 12, which is indicated by the arrow indicated by a dashed line. According to the solution according to the invention, the uninterrupted movement of the plasma arc is achieved by the fact that every time the plasma arc crosses the air gap section 9 on the second edge 4, the base point of the plasma arc (in terms of the direction 14 indicated by the arrow) is located before the range of the electrical effect exerted by the connection point 12, i.e. before the projection 19. The 2a. and 2b. figure shows another embodiment of the electrode according to the invention, which comprises a rectangular tubular body assembled from segments forming the sectors 21 of the electrode 20 and which HU 226 678 Β1 are separated from each other by obliquely formed air gaps 22. The upper edges of the segments forming the sectors 21 form the first edge 24 of the electrode 20, while their lower edges form the second edge 27, and thus each sector 21 has a first and a second edge part. Each sector 21 of the electrode 20 is provided with electrical connection points, which are provided with laterally projecting connectors 23 located within the upper part of the sectors 21 near the first edge 24. Each connector 23 is connected to each other by 25 sheets carrying a common current, which can be connected to a direct current source (not shown) by means of an electrically conducting rail 26. In essence, the position of the connectors 23 associated with each air gap with the relevant 22 air gaps, and with respect to the regions that emit and receive the electric arc on both sides of the air gap section in the second peripheral region, and the position of each connection location on the second peripheral part is similar to the arrangement according to Figure 1, although the shape and number of sectors and air gaps differ from it. As can be seen, the projection of each connector 23 associated with the respective air gap 22 relative to the plane supporting the second rim 27 falls on the adjacent electrode segment close to the plasma arc transfer zone. The 2a. and 2b. Fig. 28 schematically shows a counter electrode, which is located below the second edge 27 of the electrode 20. The counter electrode 28 is designed with a terminal 29 for connection to the opposite terminal of the direct current source (not shown). When an electric arc discharge is created between the electrode 20 and the counter electrode 28, a Lorentz force is also generated, as a result of which the plasma arc moves without interruption along the second working edge 27 of the tubular body, 2b. in the direction of the arrow shown with a dashed line in the figure (that is, in the first direction). Figure 3 shows a further embodiment of the electrode 30 according to the invention, which is star-shaped in nature and comprises a substantially tubular body composed of several truncated triangular segments, which form sectors 31 separated from each other by air gaps 32 in the axial direction. In the direction of the center line of the tubular body of the electrode 30, it is located between the first (upper) edge 33 and the second (lower, working) edge 34. Each of the truncated triangular sectors 31 has a first wall part 35 which holds the plasma arc receiving zone as well as the electrical connector 37 and a second wall part 36 which holds the plasma arc emitting zone. The edge 38 of the first wall part 35 of the sectors 31 is located adjacent to the relevant air gap 32 and is considered the proximal edge, and the edge 39 on the opposite side of the second wall part 36 of the adjacent sector 31 is considered the distal edge 39. The electrical connection structure 37 of each sector 31 of the electrode 30 is connected to a sheet 40 carrying a common current, which is provided with a rail 41 for connection to one pole of a direct current source (not shown). A counter electrode 42 is schematically indicated below the electrode 30, which is provided with a terminal 43 for connection to the opposite pole of the direct current source (not shown). It can be seen that the sectors 31 are arranged in such a way that the projections of the connectors 37 on the second edge 34 are located within the circumference of the closed path of movement of the arc moving in the first direction, which is indicated by a dashed arrow in the figure. In addition, the first wall part 35 of each sector 31 partially overlaps the second wall part of the adjacent sector 31, which together form the air gaps 32. thus, each proximal edge 38 with its associated connector 37 is separated from the adjacent distal edge 39 in the second direction, namely by a distance L taken in the opposite direction to the first direction. In the case of this typical embodiment, this distance forms the distance between the zone receiving the electric arc and the projection of the electric connector on the second edge 34. (As defined, the arc emitting zone and the arc receiving zone form one side of the air gaps 32 in the region of the second edge 34.) As a result of this arrangement, each electric arc emitting zone (not shown in the figure) emits or transfers the moving arc column to the one adjacent to it. arc receiving zone, i.e. passes it on the air gap section in the second peripheral area, namely in a place which is located after the location of the connector 37 in terms of the arc's direction of travel, and thereby ensures that the arc can continue without interruption in the first direction indicated by the dashed arrow. Figure 4 schematically shows a further embodiment of the electrode 44 according to the invention. As in the case of the embodiment according to Figure 3, they form axial air gaps in line with their first region air gap section, main air gap section and second edge region air gap section, and the projections of the relevant connectors on the second, working edge P plane of the electrode 44 are located outside the same P plane of the plasma arc compared to its considered closed 47 movement paths. Compared to Figure 3, however, the difference is that the projections of the connectors 45 fall outside the circumference of the movement path 47, and the sectors of the electrodes 44 do not overlap each other near the air gaps 49. Similar to the embodiment according to Figure 3, the projection of each connector 45 on the plane P containing the second edge 46 is removed from the relevant plasma arc emitting zone, namely in a direction that is opposite to the direction of movement of the plasma arc, and this removal is characterized by a distance L, and as a result, it is possible for the plasma arc to move along the closed motion path without interruption during operation. 1-4. all the embodiments shown in the figures produce a plasma arc that circulates without interruption in a plasma generator. As already mentioned, the width of the second air gap section in the peripheral region is preferably not larger than the smallest designed diameter of the arc column of the plasma arc to be created on the electrode, and the distance L is preferably not smaller than the largest size of the base of the arc created on the electrode. The design of the electrode according to the invention enables relatively HU 226 678 Β1 use of large-sized electrodes, without the need for RF cooling or the injection of the shielding gas that stabilizes the plasma discharge, and this at least approx. output power up to kW can be implemented. Figures 5 and 6 show, as an example and schematically, the embodiments of the plasma generator device according to the invention, specifically for both internal arc and transmitted arc types. Figure 5 shows a simplified cross-sectional view of one embodiment of the plasma generator 50 according to the invention, taken along the axis line, and according to the figure, it contains a main tube electrode 51, which according to the invention is equipped with a through air gap 52 made of copper and is equipped with an electrical connector 53. The main electrode 51 is surrounded by a uniaxially arranged cylindrical housing 54 made of conductive material, which is provided with a cover 55. Please note that cover 55 should only be used if necessary and desired. Electrode 51 and housing 54 are connected to opposite poles of a high current DC source 56, and as is known per se, housing 54 forms the counter electrode of the apparatus. The plasma generator 50 is also equipped with an ignition device 57, which ignites an auxiliary arc discharge. The ignition device 57 contains an ignition electrode 58, which is fed by a high-voltage oscillator 59 in a manner known per se, and a projection 60 is formed on the inner surface of the housing 54, which is located near the main electrode 51 and serves to facilitate the ignition of an auxiliary arc 61 during ignition. moves towards the lower edge of the main electrode 51. The vertical displacement of the auxiliary arc 61 is also created by the Lorentz force, which in this case is formed due to the fact that current flows through a rail-like arrangement including the main electrode 51 and the housing 54. The main plasma arc 62 is formed between the lower edge region of the main electrode 51 and the housing 54 forming the counter electrode, and begins to circulate around the lower edge 63 of the tubular electrode 51, thereby realizing the heat treatment of the object 64 (for example, a concrete slab). Figure 6 shows a schematic cross-sectional view of 70 plasma generators working with a transferred plasma arc. The main tubular electrode 71 of the plasma generator 70 is formed in the shape described above and is connected to the positive corner of the direct current source 72, while the negative corner is connected to an electrically conductive object to be treated, and this forms the counter electrode 73 at the same time. The negative corner of the current source 72 is also connected to the cylindrical housing 74 surrounding the main electrode 71 and arranged on the same axis as it. The lower part of the inner casing surface of the housing 74 is covered with an electrically insulating layer capable of withstanding high temperatures, and it is provided with a coating (not shown) formed with, for example, suitable paint. An ignition electrode 75 is installed in the space between the main electrode 71 and the housing 74. The ignition electrode 75 is powered by a high-voltage oscillator 76, and with the help of this, an auxiliary arc 77 can be created between the main electrode 71 and the ignition electrode 75, which then migrates to the region of the lower edge 78 of the main electrode 71. The region of the lower edge 78 is beveled as shown in the figure and this gives the desired shape and direction of the main plasma arc 79. The region of the chamfered rim 78 and the painted cladding surface of the housing 74 cause the plasma arc 79 to form between the rim 78 and the surface of the counter electrode 73 and not in the direction of the wall of the housing 74 . The 7a. and 7b. Fig. 8 shows a further embodiment of the plasma generator 80 according to the invention in a schematic axial cross-sectional view and in a bottom view. The plasma generators 80 have a main tubular electrode 81, which is installed in a cylindrical housing 82 and is covered from above by a cover, but its use is not necessary. The plasma generator 80 is connected to a DC power supply, which includes a high-current power source and a high-voltage oscillator (not shown), which are used to power the main and counter electrodes of the device and the ignition device 85 of the device. The main electrode 81 is located with a center line perpendicular to the surface to be treated, for example a metal object connected as a counter electrode 86. The housing 82, which accommodates the main electrode 81, is located at a distance W from the surface of the metal object in order to form a working distance for the plasma arc discharge. The main electrode 81 according to the invention can be formed from graphite or from an electrically conductive, heat-resistant material resistant to erosion. The ignition device 85 extends from the cover 83 and is located in the annular space formed between the main electrode 81 and the housing 82. A detachable electrically conductive connector 93 is installed in the lid 83 and is electrically connected to one end of the power supply 84, the opposite end of which is connected to the main electrode 81 to provide electrical power. The 7a. air gap 88 shown in Fig. starts from the upper and first edge 89 of the cylindrical tubular main electrode 81 downwards to the lower second and working edge 90, and has the air gap section 91 in the first edge region, the main air gap section, and the air gap section 92 in the second edge region. As stated in 7a. shows, the air gap 88 has two parts, one of them is vertical and parallel to the cylindrical wall of the electrode 81, and also has a sloped part, and these parts form an obtuse angle with each other. In the case of the formation of the air gap 88 in this way, the air gap sections 91 and the air gap sections 92 in the first and second peripheral regions are not in a line and are in different angular positions, which is the result of Fig. 7b. can be seen from fig. The main electrode 81 has a single sector provided with a single electrical connector 93, which is installed in the cover 83 by means of an insulating sleeve, and the position of the first edge 89 of the electrode 81 is close to the air gap section 91 of the first region. The projection of the connector 93 onto the second edge 90 is located between the air gap section 92 in the second region and the projection of the air gap section 91 in the first edge region onto the second edge 90, and is located at a distance L from the air gap section 92 in the direction that HU 226 678 Β1 is opposite to the direction 94 indicated by the dashed outline arrow. Fig. 8 shows a possible embodiment of the ignition structure of the plasma generator according to the invention, for example Fig. 7a. 85 showed its ignition mechanism in the embodiment according to fig. The ignition device 85 can be detachably attached to it 7a. and 7b. 80 for the plasma generator cover 83 shown in Fig., in order to be located between the main electrode 81 and the inner surface of the housing 82. Of course, the ignition device can also be placed in other positions. In the case of the embodiment according to Figure 8, the ignition device 85 has a first electrode 95, a second electrode 96, and a third electrode 97, which are electrically connected to the power supply 84 and are attached inside an insulating cap 98 suitable for high voltage insulation. The electrode 95 is an elongated stem, which is partially and uniaxially located inside the second tubular electrode 96, and which is located at a distance from it and together forms an annular space 99. The third electrode 97 is formed by a horizontal tray located near the upper edge of the tubular electrode 96 with its inner end near the electrode 95. Electrode 97 is substantially perpendicular to electrode 95 and electrode 96 and is electrically coupled to the high voltage oscillator (not shown). It is advantageous if the upper region of the tubular electrode 96 is formed with an internal protrusion 100, which serves the purpose of forming a narrower air gap between the electrode 95 and the electrodes 96 in the region to which the voltage of the high-frequency oscillator is applied. Preferably, the ignition device 85 is located away from the working space defined by the distance W, and in this way its operation is not significantly affected by the hot and highly erosive atmosphere in the working space. In practice, it is recommended to design the ignition device as a separate module, so that it can be quickly and conveniently maintained or replaced. 7a, 7b. and the plasma generator shown in Figure 8 can be used in the following way. After switching on the power supply, approx. A working voltage of 170 V is simultaneously connected inside the working space between the main electrode 81 and the metal surface forming the counter electrode 86, the main electrode 81 and the housing 82, and the electrode 95 and the electrode 96 of the ignition device 85 within the ring-shaped space 99. The high voltage oscillator is then turned on to supply a high alternating voltage between the electrode 97 and the protrusion 100 and between the protrusion 100 and the electrode 95, a voltage sufficient to produce an electrical discharge. This arc discharge is followed by the formation of an additional plasma arc in the air gap between the uniaxially located electrode 95 and 96 electrode structure. This plasma arc slides down along the wall of the main electrode 81 as a result of the accelerating effect of the current-carrying rail that forms between the surfaces of the cylindrical housing 82 and the main electrode 81, and this force pushes the arc down approx. at a speed of 40 m / s in the direction of the second edge 90 of the main electrode 81. The ignition! the total time required for each step is no more than 0.002 s. After the auxiliary plasma arc produced by the discharge caused during ignition reaches the second edge 90, it takes the form of the plasma arc 101 caused by the main discharge between the second edge 90 of the main electrode 81 and the surface of the metal object to be treated, such as the counter electrode 86, and this plasma arc is formed by the distance W rotates in the specified workspace. Figure 9 schematically shows the use of the plasma generator device according to the invention for the heat treatment of liquid and solidified metal in a mold. The arrangement according to Figure 9 contains a mold 120, the bottom of which has a molding channel 121. Liquid metal is poured from a mold or crucible, not shown, into the funnel 124 of the casting channel 121, which enters the mold 120 from below and fills it up to a height controlled by a sensor 125. Adjacent to the upper part of the mold 120 is a plasma generator 126 containing the main electrode 127 according to the invention, which is suspended from a carriage 128 equipped with a wheeled structure 135 on rails 129 and which allows it to be moved from a rest position when removed from the line of the mold 120 to a position where it is in line with the mold. In addition, the plasma generator 126 is provided with a structure (not shown) suitable for raising and lowering it. The plasma generator 126 contains a main power supply unit 130, a high-voltage oscillator 131, and a control panel 132 for moving the plasma generator 126 out of the working position and for controlling its operation during the work session. In order to implement the tasks, the control panel 132 is provided with appropriate electronic control elements (these are not shown), which enable it to be operated either manually or according to a predetermined program. The power supply unit 130, the high-voltage oscillator 131 is connected to the plasma generator 126 via the control panel 132 via the bus 133 containing appropriate electrical cables, and via the connector 134 to the liquid metal forming the counter electrode 122, as well as to the structure 135 and the sensor 125. In practice, the plasma generator 126 is brought into the working position above the mold 120, the liquid metal is poured in up to a certain level controlled by the sensor 125, and this level is determined by the surface of the liquid metal in the mold forming the counter electrode 122 and the second (lower) main electrode 127 a distance W specifying the width of the working space between its edges. The width W is usually kept in the range of 8-10 mm, if the operating voltage is between 60-80 V. For operating voltages greater than 80 V, this width can be increased, and for example, at 170 V, this width can be 25 mm. After setting the required width of the working space, we turn on the power supply 130 and the high-voltage oscillator 131, thereby igniting an auxiliary arc and maintaining it until the main plasma arc discharge HU 226 678 Β1 does not start and the heat treatment of the metal surface does not start. The high-voltage oscillator is normally kept on until the main arc is produced, which is indicated by the flow of electric current corresponding to the power required for the relevant application. In the case of a voltage of 170 V, a main arc discharge with a strength of 300 A is achieved, which gives an electric power of 50 kW. The height of the main 127 electrode is approx. For a 20 kg casting, approx. 40-60 mm. The duration of the main arc discharge, i.e. the length of time required for heat treatment, can be regulated using a suitable timer device (not shown). In practice, such a timer structure must be flexible in order to be able to activate the power supply continuously or intermittently during the solidification process of the casting in the mold. After finishing the heat treatment, the plasma generator is switched off and removed from the working position, and after further cooling, the cooled casting can be removed from the mold. We would like to note that due to the constant circulation of the main arc discharge, the solution according to the invention enables the required heat treatment to be performed while changing the width of the working space. If desired, the plasma generator can therefore be equipped with a structure (not shown) with which the main electrode 127 can be moved vertically in alternating directions within the housing of the plasma generator 126, thereby controlling the width of the working space determined by the distance W (see Figure 7a). This vertical displacement can be continuously controlled by the sensor 125, which monitors the height of the liquid metal level in the mold, and thereby it is possible to lower the electrode 127 according to the shrinkage of the metal, thereby improving the quality of treatment, as a result of which defects in the casting can be eliminated. , and the amount of metal waste can be reduced. Figure 10 illustrates the result achieved by the heat treatment according to the invention, namely, it shows a photograph of two castings (a) and (b) made of aluminum alloy type A332.0, and the casting (a) without treatment, while the casting (b) is the invention made by heat treatment with a circulating plasma arc according to The weight of the castings is 7.2 kg. There are gas inclusions in the upper part of the casting (a) made in the traditional way, and consequently a considerable layer of thickness must be cut from the casting when it is used. On the other hand, the upper surface of casting (b) made by using the solution according to the invention and treated with a plasma arc during cooling for 50 minutes is smooth and does not require any additional treatment, as it has the required exact size.

Claims

PATENT CLAIMS 1. Method for heat treatment of molten metal, during which a plasma arc is generated between the molten metal forming the lower edge (4, 27, 34,46,63,78, 90) and the counter electrode (15, 28, 42, 54, 73, 86, 122) of the electrode (2, 20, 30, 44) of a plasma generator (50, 70, 80, 126), and the molten metal is heated with this plasma arc, characterized in that a) the lower edge (4, 27, 34, 46, 63, 78, 90) of the electrode (2, 20, 30, 44, 51, 71, 81, 127) contacts the counter electrode (15, 28, 42, 54, 64, 73, 86, 122) is adjusted with respect to the surface of the molten metal forming the electrode (W), b) the electrode (2, 20, 30, 44, 51, 71, 81, 127) is connected to one corner of the electrical power supply (56, 72, 84, 130), and c) the counter electrode (15, 28, 42, 73, 86, 122) is connected to the other corner of the electrical power supply (56, 72, 84, 130) to ignite the plasma arc (62, 79) while the molten metal solidifies, the lower edge (4, 27, 34,46, 63, 78, 90) on a closed path in the first direction (14).

2. The method according to claim 1, characterized in that the distance (W) between the lower edge (4, 27, 34, 46, 63, 78, 90) of the electrode (2, 20, 30, 44, 51, 71, 81, 127) and the surface of the metal forming the counter electrode (15, 28, 42, 73, 86, 122) is kept constant by controlled lowering or raising of the electrode (2, 20, 30, 44, 51, 71, 81, 127).

3. A plasma generator comprising an electrode and a counter electrode forming a two-rail structure adapted to generate a plasma arc and moving the plasma arc in a closed path in a first direction without interruption during solidification of the molten metal forming the counter electrode along the working edge of the electrode, the electrode having a body formed with an upper edge and a working lower edge and provided with a set of connectors for connection to an electrical power supply, characterized in that the connector (13, 23, 37, 45, 53, 93) comprises at least one connection point (12) located on the electrode (2, 20, 30, 44, 51, 71, 81, 127) of the two-rail structure, and the electrode (2, 20, 30, 44, 51, 71, 81, 127) is connected to the electrical power supply (56, 72, 84, 130) is connected to one of the terminals at the connection point (12), and the body of the electrode (2, 20, 30, 44, 51, 71, 81, 127) has at least one longitudinal air gap (6, 22, 32, 49, 52, 88), and the air gap (6, 22, 32, 49, 52, 88) is connected to the electrode (2, 20, 30, 44, 51, 71,81, 127) has an upper air gap section (7, 91) at the upper edge (3, 24, 33, 39) of the body, a lower air gap section (9, 92) at the lower edge (4, 27, 34, 46, 63, 78, 90) of the body, and a main air gap section (8) is located between them, and each air gap (6, 22, 32, 49, 52, 88) divides the wall (5) of the body of the electrode (2, 20, 30,44, 51, 71, 81,127) into two sectors (10,11; 21, 21; 31,31; 48, 48), and each sector (10, 11; 21,21; 31,31; 48,48) has a lower edge and has an upper edge, and the connection point (12) of the connector (13, 23, 37,45, 53, 93) is located at the air gap (6, 22, 32, 49, 52, 88) of one sector (11; 21; 31; 48), and the zone (17) receiving the plasma arc (62, 79) is located on its lower edge, and furthermore, the zone (16) transmitting the plasma arc (62, 79, 101) is located on the lower edge of another sector (10; 21; 31; 48), where the zone (16) transmitting the plasma arc (62, 79, 101) and the receiving zone (17) are separated by the lower air gap section (9, 92) of an air gap (6, 22, 32, 49, 52, 88) HU 226 678 Β1 apart,and are located on both sides thereof, and furthermore, the projection of the connection point (12) of the connector (13, 23, 37, 45, 53, 93) on the lower edge (4, 27, 34, 46, 78, 90) of the body of the electrode (2, 20, 30, 44, 51, 71, 81, 127) is located at a distance from the plasma arc (62, 79, 101) receiving zone (17) in a second direction opposite to the first direction (14)., 4. Plasma generator according to claim 3, characterized in that the two-rail structure comprises a counter electrode (73, 86, 122) made of an electrically conductive material.

5. A plasma generator according to claim 3, characterized in that the electrode (2, 20, 30, 44, 51, 71, 81, 127) is surrounded by a cylindrical housing (54, 74, 82) spaced apart therefrom, forming an annular chamber therewith.

6. Plasma generator according to claim 5, characterized in that the annular chamber at the upper end of the cylindrical housing (54, 74, 82) is closed by a sealing cover (55, 83).

7. Plasma generator according to claim 5 or 6, characterized in that an ignition device (57, 75, 85) for igniting a plasma arc (62, 79, 101) is located in the annular chamber.

8. Plasma generator according to claim 7, characterized in that the ignition device (57, 75, 85) is mounted near the upper edge (3, 24, 33, 39) of the body of the electrode (2, 20, 30, 44, 51, 71, 81, 127).

9. Plasma generator according to claim 3, characterized in that the electrode (2, 20, 30, 44, 51, 71, 81, 127) is connected to an axially moving structure.

10. Electrode 3-9. A plasma generator (50, 70, 80, 126) according to any one of claims 1 to 5 for initiating a plasma arc and continuously moving the plasma arc in a closed path in a first direction along the working edge of the electrode while solidifying the molten metal, the electrode having a body with an upper edge and a lower edge, and having a body adapted for connection to an electrical power supply, and being provided with a set of connectors adapted for connection to an electrical power supply, characterised in that the connector (13, 23, 37, 45, 53, 93) comprises at least one connection point (12) located on the body of the electrode (2, 20, 30, 44, 51, 71, 81, 127), and further comprising at least one longitudinal air gap on the body of the electrode (2, 20, 30, 44, 51, 71, 81, 127) (6, 22, 32, 49, 52, 88) and the air gap (6, 22, 32, 49, 52, 88) has an upper air gap section (7, 91) at the upper edge (3, 24, 33, 39) of the body of the electrode (2, 20, 30, 44, 51, 71, 81, 127), and a lower air gap section (4, 27, 34,46, 63, 78, 90) has a lower air gap section (9, 92), and a main air gap section is located between them, and each air gap (6, 22, 32, 49, 52, 88) divides the wall (5) of the body of the electrode (2, 20, 30, 44, 51,71, 81, 127) into two sectors (10, 11; 21, 21; 31,31; 48, 48), and each sector (10,11; 21, 21; 31, 31; 48, 48) has a lower edge and an upper edge, and the connector (13, 23, 37, 45, 53, 93) connection point (12), and on its lower edge is located the zone (17) receiving the plasma arc (62, 79, 101), furthermore, on the lower edge of another sector (10; 21; 31; 48) is located the zone (16) transferring the plasma arc (62, 79, 101), where the zone (16) transferring the plasma arc (62, 79, 101) and the receiving zone (17) are separated from each other by the lower air gap section (9, 92) of an air gap (6, 22, 32, 49, 52, 88) and are located on both sides thereof, furthermore, on the lower edge (4, 27, 34, 46, 63, 78,The projection of the connection point (12) of the connector (13, 23, 37, 45, 53, 93) in the 90) is spaced apart from the plasma arc (62, 79, 101) receiving zone (17) in a second direction opposite to the first direction (14).

11. The electrode according to claim 10, characterized in that the width of each lower air gap section (9, 92) of the body is not greater than the actual smallest designed diameter of the plasma arc column (62, 79, 101), and the distance (L) between the projection of the connection point of the connector (13, 23, 37, 45, 53, 93) on the lower edge (4, 27, 34, 46, 63, 78, 90) and the zone (17) receiving the plasma arc (62, 79, 101) is not less than the largest actual diameter of the characteristic base point of the plasma arc column (62, 79, 101).

12. An electrode according to claim 10 or 11, characterized in that the body has a single air gap (6, 52, 88) and the two sectors (10, 11) of the wall (5) combine to form a single section extending from one side of the air gap (6, 52, 88) to the other side.

13. Electrode according to claim 10 or 11, characterized in that the body has a plurality of air gaps (22, 32, 49) and the wall (5) consists of a plurality of sectors (21, 31, 48), each of which is located between two adjacent air gaps (22, 32, 49).

14. The electrode of claim 10, wherein at least one longitudinal air gap (6, 22, 32, 49, 52, 88) has an upper air gap section (7, 91) and a lower air gap section (9, 92) that are not aligned with each other.

15. An electrode according to claim 14, characterized in that the at least one longitudinal air gap (6, 22, 32, 49, 52, 88) has a main air gap section consisting of two parts, which form an obtuse angle.

16. Electrode according to claim 14, characterized in that the at least one longitudinal air gap (6, 22, 32, 49, 52, 88) is formed obliquely.

17. Electrode according to claim 10, characterized in that the connection point (12) is located near the upper edge (3, 24, 33, 39) of the body.

18. Electrode according to claim 10, characterized in that the lower edge (4, 27, 34, 46, 63, 78, 90) is angled.

19. The electrode according to claim 10, characterized in that the main air gap section of the at least one air gap (6, 22, 32, 49, 52, 88) comprises two parts forming an obtuse angle with each other, and the projection of the connection point (12) of the connector (13, 23, 37, 45, 53, 93) onto the lower edge (4, 27, 34, 46, 63, 78, 90) of the body is located in the sector (10; 21; 31; 48) of the body wall (5) on which the plasma arc (62, 79, 101) transmitting zone (16) is located.

20. The electrode according to claim 10, characterized in that the projection of each connection point (12) of the connector (13, 23, 37, 45, 53, 93) onto the lower edge of the body (4, 27, 34, 46, 63, 78, 90) is located outside the closed path of the plasma arc (62, 79, 101).

21. The electrode according to claim 10, characterized in that the projection of each connection point (12) of the connector (13, 23, 37, 45, 53, 93) onto the lower edge (4, 27, 34, 46, 63, 78, 90) of the body is located within the enclosing line of the closed path of the plasma arc (62, 79, 101).

22. The electrode according to claim 10, characterized in that the projection of each connection point (12) of the connector (13, 23, 37, 45, 53, 93) onto the lower edge (4, 27, 34, 46, 63, 78, 90) of the body is located outside the enclosing line of the closed path of the plasma arc (62, 79, 101).

23. Electrode according to claim 10, characterized in that in the region of the lower edge (4, 27, 34, 46, 63, 78, 90) of the body, each air gap (6, 22, 32, 49, 52, 88) has at least one lower air gap section (9, 5 92) formed by the overlap between adjacent sectors (10, 11; 21, 21; 31, 31; 48, 48) comprising the plasma arc transmitting and receiving sectors (62, 79, 101).

24. Electrode according to claim 10, characterized in that the body has a star-like polyhedron shape and is composed of a plurality of truncated triangular modular segments, each of these segments forming a sector (31) of the body wall (5), and adjacent sectors (31) overlap each other near the respective air gap (6, 22, 32, 49, 52, 88).