JPS6229879B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a plasma burner, and in particular to an electrode holder for supporting a center electrode and an outer electrode, means for supplying a voltage to create an electric arc between these electrodes, and means for supplying gas to the electric arc area of the electrodes. This relates to a type of plasma burner equipped with: Plasma burners are used for a variety of purposes, such as rapid heating of material surfaces, melting of materials, heating of solid and liquid materials, and carrying out chemical reactions at temperatures above those normally obtained by other forms of heating. ing. Heating is primarily caused by hot rays from the extremely hot gaseous components of the plasma flame.
This heat ray is absorbed by the surface of the object to be heated. It is known to utilize different types of plasma burners for different materials for purposes such as combustion and melting. A common property of these different types of plasma burners is that they are virtually free from deformation during operation as a result of melting or evaporation of the parts of which the burner is constructed. One reason this deformation must be avoided is that it changes the electrical characteristics of the burner.
This results in cooling of the parts of the burner that receive heat from the plasma flame. Heat is typically removed from these parts to the outside by a cooling medium (liquid or gas) flowing in conduits formed in the heated portion of the burner. Evaporative cooling is also possible. To achieve cooling, it is necessary to use packing or other materials that can withstand high temperatures in the design of plasma burners. When conductive materials are used in a burner to create an electrical connection (often called a jet) between the inner and outer electrodes, an electrical short can occur and destroy the burner. It has not been possible to use plasma burners of hitherto known types in crowded environmental conditions and at high temperatures or immersed in conductive metals, slags or salt melts. Due to the complex structure of the plasma burners known so far and the different conditions required for the plasma electrodes in these burners, it is necessary to avoid contact between the parts of the plasma burner and metal slags or salt melts exposed to high temperatures. becomes. This meant that the plasma burner could not be brought into contact with the medium to be heated. If the plasma burner is to be located far from the object to be heated, a large amount of energy is lost in the propagation of heat from the plasma burner. If the burner is placed, for example, in a state close to the liquid phase, undesired local overheating can occur, which leads to undesired evaporation of the substance to be heated. The main object of the invention is to provide a new plasma burner that can be used in conditions where, due to its construction and the materials used, it was technically impossible to use hitherto known plasma burners. . It is also an object of the invention to be able to avoid introducing a cooling medium in the plasma burner. The plasma burner of the invention can be fired together with electrodes, and the plasma flame can also be immersed in the melt. If, by mistake or due to interruptions in operation, molten material enters the space between the electrodes and a short circuit occurs, this does not result in a permanent change in the properties of the plasma burner according to the invention. The electrode structure of the present invention consists of an inner pipe-shaped or rod-shaped electrode and an outer pipe-shaped electrode, and is not of the type in which the electrode itself is internally cooled with water or other cooling substance. The invention is distinguished in this respect from the highly complex constructions previously known, which use water-cooled, essentially non-consumable metal electrodes. The radial dimensions of each electrode are such that heating in the electric arc erodes the electrode at the same rate in the axial direction for both electrodes, thereby ensuring that electrical and gas-dynamic operating conditions and This allows the plasma environmental conditions, which are composed of the heating effect of flowing gas and the blowing effect (impact), to remain substantially unchanged even when the electrodes are worn out. In addition,
Even after various experiments, it is not possible to clearly determine mathematically the dimensional relationship between the inner and outer electrodes to keep the rate of wear of both constant. Therefore, it changes. However, it must be noted that if the thickness of the outer electrode is too small compared to the thickness or width of the inner electrode, it will wear out quickly or locally. That is, the outer electrode should have a substantial thickness. Ultimately, in the present invention,
Rather than trying to maintain constant plasma environmental conditions by using non-consumable electrodes and preventing deformation due to plasma generation, we use consumable electrodes and experimentally set their dimensional relationships. The feature is that both poles are consumed equally, and as a result, the plasma environmental conditions are maintained constant. The concentrically arranged electrodes are attached to a suitable electrode holder along with a means for supplying current, a means for supplying gas to the hollow space between the electrodes, a means for supplying cooling water for cooling the electrode support, etc. . Although there is in principle no restriction on the length of the electrodes, it should be taken into account that the applied voltage must be high enough to cover the ohmic voltage effects along the length of the electrodes. It is desirable to use suitably arranged spacing members to accurately position relatively long electrode rods. The spacing member is preferably made of a high melting point, electrically insulating material. One of the features of the plasma burner of the invention is that the free end of the electrode on which the electric arc burns assumes a natural, stable shape with a short adjustment time. Rod-shaped and pipe-shaped electrodes can actually be cut straight at the start of work. In this respect, the present invention clearly differs from the prior art. In the past, the electrical and gas-dynamic conditions depended on how precisely the electrodes and other parts of the plasma burner were designed, and the applications were therefore extremely limited. . The plasma burner of the present invention can be operated with chemically inert gases such as argon helium, nitrogen, etc., as well as gases or gas mixtures that chemically react with the electrode materials at high temperatures. When it is necessary to obtain a special effect by using chemically active gases, for example when using air or hydrogen with graphite electrodes, chemical changes can lead to depletion. It's okay if there is. The erosion inevitably caused by the electric arc, and the chemical depletion that accompanies it, is itself a characteristic feature of the burner, unless significant changes occur in the shape of the electrode tip producing the electric arc and in the electrical properties of the electrode. Since the performance does not deteriorate, the electrode can function stably regardless of the reduction in the length of the electrode. If desired, fine solid powders or liquid substances may be added to the gas for the purpose of effecting chemical changes with substances in the burner atmosphere. This is the case, for example, when impurities are removed from a metal melt for scouring purposes, or when fluxing agents are added to lower the melting point of the molten material. The plasma burner is made of graphite felt.
It can be ignited very easily by creating a short short circuit by inserting steel wool, metal fabric, etc. into the opening of the electrode. In contrast to the metal electrodes used in hitherto known burners, graphite or silicon carbide electrodes are not damaged by partial melting of the surface as a result of short circuits. The plasma burner of the present invention can also be initiated by immersion in an electrically conductive melt, such as a metal. In this way, no special expensive equipment is required to ignite the burner of the invention. In industrial applications, to cope with rough handling and to protect the pipe-shaped electrodes, which are most sensitive to external influences, for greater mechanical strength without increasing the thickness of the material, suitable metallic materials such as heat-resistant steel are used. This is achieved by protecting the tubular electrode with a relatively thin walled jacket (pipe). It melts gradually during operation without disturbing the electrical conditions, so the energy generated by the plasma burner does not change. Such metal pipes around the outer electrode may also reduce erosion of carbon from the outside of the electrode as a result of oxidation or other chemical attack. It is well known that the overall voltage drop of a plasma burner depends on the external physical conditions in which the electrical plasma discharge occurs. Under certain circumstances, the electrode material of the plasma burner of the present invention can react with the liquid in which the electrode is immersed. If such an electrode made of graphite is immersed in molten liquid steel, the carbon will melt into the melt, resulting in an undesirable reaction between the graphite and the steel. Such a melting reaction can be prevented or reduced to a suitable extent by immersing the surface of the outer electrode together with the electrode and coating it with an oxidizing, refractory material. Some of these oxidants include “Gun Clay”, “Gunmix”, “Uniguncast-S”,
There are substances known by trade names such as “Trimrecast,” “Durax1600,” and “H44.” The plasma burner of the present invention can be operated with either direct current or alternating current. As in other gas discharge devices, a power supply with significant voltage drop characteristics is used. Also, the no-load voltage of the power supply must be sufficiently higher than the normal combustion voltage of the burner. In an experiment in which the plasma burner of the present invention was used to heat a metal melt and the electrode part (made of graphite in this case) was immersed in the metal melt, the rod-shaped electrode was slightly retracted from the pipe-shaped electrode, It has been discovered that the voltage and energy increase unexpectedly when the axial distance between the end faces of the electrodes is made substantially larger than the radial distance between the electrodes.
This phenomenon is considered to be due to the following reasons. If both electrodes are of the same length, an electric arc is ignited from the rod-shaped electrode and reaches the bottom of the gas-filled hollow created below the open end of the interior of the electrode structure, after which the current passes through the metal melt to the outer electrode. will return to. Massive evaporation of the metal at the contact surface of the electric arc with the melt causes the electric arc to burn in an atmosphere containing a high density of easily ionizable metal vapor, which can be combined with a feed gas such as nitrogen. , which provides significantly lower voltages than combustion in an atmosphere of vaporizable electrode materials, such as carbon vapor. This is clearly what happens when the rod-shaped electrode is pushed back a considerable length with respect to the pipe-shaped electrode. Plasma of the present invention
One advantage of the burner is that when the electrode is immersed in the melt and ignited, the voltage level at which the burner is operated can be adjusted by adjusting the relative position of the rod electrode to the pipe electrode. Previously known attachment means for opening the melting zone have proven unsatisfactory given the working conditions. There are various types of attached means for this purpose, but the main one is the use of an air drill, which has a limited depth with a spout and is not suitable for use. It could only be used at certain temperatures. In contrast, according to the present invention, the tap can be used even at fairly high temperatures without any restrictions. Electric burner pins basically consist of graphite electrodes connected to the electrical equipment of the furnace. However, it is not possible to have a tap with a limited diameter and sufficient depth in this type of equipment. In addition, the material to be combusted must be sufficiently conductive, which is not always the case in practice. Oxygen blowing usually occurs through a thin iron or steel pipe inserted into the tap. Compared to the plasma burner of the present invention, the co-thermal combustion oxygen pipe makes it difficult to control the size and orientation of the spout. Air blowing with zinc balls is certainly suitable for a clean spout. This effect is due to the instantaneous evaporation of the zinc balls inside the spout. This requires a tap with a certain depth and high temperature. The danger of splashing water is extremely high. The plasma burner of the invention is also suitable for this purpose. The plasma burner of the invention is particularly suitable for transferring heat to melts having relatively high melting or oxidation temperatures. Electric arc heating, resistance heating or induction heating is mainly used for conductive materials. What these devices have in common is that they require separate equipment that is expensive to purchase and operate, take up a lot of space, and are not versatile enough to use varying amounts of melt. That's true. Heating of the melt phase from the furnace, which imparts excessive latent heat, often has an adverse effect on operations. It becomes difficult to carry out the desired chemical reaction under the most favorable temperature conditions. Gas burners are also available, but these become very inefficient thermally in raising the temperature of the melt when normal conventional fuels are used. In addition to the mechanical configuration and energy benefits, the plasma burner of the invention allows a series of metallurgical operations to be carried out with higher yields than is obtainable with other heating devices. In particular, the combination of the plasma burner of the invention with heat retention and blowing of gases and solid particles provides very suitable conditions for chemical reactions between solid and molten phases, gas/molten phases or between molten phases. It is something that can be provided. This condition is due to the control of melt temperature and stirring conditions which allows chemical reactions to occur much more quickly than in conventional methods. Embodiments of the present invention will be described below with reference to the drawings. Referring to FIGS. 1 and 2, the plasma burner of the present invention is made of graphite and has a rod-shaped electrode 1 with a diameter of 30 mm. The rod-shaped electrode 1 has a contact mechanism A consisting of an upper contact member 2 and a lower contact member 3 fixed together by two pairs of screw bolts 4.
is fixed. In a cross section perpendicular to the longitudinal axis of the plasma burner, the lower (or upper) contact member 3 or 2 has a diameter of 30 mm and extends 1 mm below (or above) from the lower (or upper) side of the other contact member. A semicircular groove with a center is formed. This configuration of the contact mechanism allows for a good electrical connection and stable central positioning of the bar electrode without requiring significant precision in electrode manufacturing. The upper contact member 2 is provided with a contact rail 5 for attaching an electric wire. In this example,
For example, the wires are two standard 500A parallel welded cables. Electrical connection of the upper and lower contact members is achieved by bolts 4. Both contact members are provided with four longitudinally connected conduits 6 in series, together with inlet and outlet pipes for cooling water (only one pipe is shown in FIG. 1). The gas required for the operation of the plasma burner (electrically 25-250 N/min) is led through the conduit 8 of the upper contact member 2 into the annular space 9 located around the rod-shaped electrode. This space 9 is the contact member 2
and 3 is formed by enlarging the groove described above at one end. However, the one end portion can also be formed from a plate fixed to the bodies of the contact members 2 and 3. The purpose of the space 9 is to achieve a more uniform diffusion of the gas flow between the rod-shaped electrode and the pipe-shaped electrode. The contact mechanism A of the rod-shaped electrode is electrically insulated from the corresponding contact mechanism B of the pipe-shaped electrode by an insulating plate 10.
The insulating plate 10 is made of a suitable heat-resistant insulating material, such as the material known under the trade names "Syndanyo" or "Marinite." Between the rod electrode and the insulating plate 10 is a relatively narrow annular column through which gas and optionally powder can pass. For example, a plasma burner may be used in conjunction with a tap opening to remove powder material, for example to remove impurities in the metal melt, or to feed alloying components into the metal melt or to lower the melting point of refractory materials. When used for injection, the powder can be fed together with the gas through the conduit 8, passed through the electrode holder, and transferred to the pneumatic device between the two electrodes. The contact mechanism B for the pipe-shaped electrode can be constructed on the same principle as the contact mechanism for the rod-shaped electrode. This contact mechanism consists of an upper contact member 12 and a lower contact member 13, which are joined by two pairs of bolts 14. Furthermore, the contact mechanism includes a contact rail 15 and inlet and outlet pipes 1 for cooling water.
It has a cooling conduit 16 connected to 7 and 18. The grooves of the contact members 12, 13 are sized and shaped to match the outer diameter of the pipe-shaped electrode. Each contact mechanism A and B for the annular electrode 1 and the pipe-shaped electrode 11 as well as the central insulating plate 10 is mechanically connected to a stable substrate 21 made of solid insulating material by means of two pairs of screws 19, 20, respectively. is fixed to. Board 2
The screw holes in 1 are made somewhat larger than the dimensions of the screws 19 so that the contact mechanism A is somewhat adjustable relative to the contact mechanism B, allowing accurate positioning of both electrodes. Open end Preferably, a suitable number of short, relatively thin-walled tubular pieces 22 are placed and positioned between the electrodes about 10-20 cm from the electrodes. For example, 20 to 21 sleeves each having a diameter of 4.5 to 5 mm and a length of about 15 mm are placed between a rod-shaped electrode of 30 mm in diameter and a pipe-shaped electrode of 40 mm in internal diameter. Using a sleeve-like positioning means made of high melting point ceramic materials "Pythagoras" or "Alumina" it was found that when the distance from the sleeve to the forward arc became sufficiently short as a result of erosion of the electrode First, these sleeves evaporate without causing significant operational disturbance. In particular, spacing members of boron nitrate have been found to be particularly suitable. If the burner of the invention is used immersed in a metal melt, the excess pressure applied at the electrode holder must be greater than the pressure in the melt. For example, when immersing 1m in molten iron, at least
0.7 bar is required. In order to prevent large amounts of gas from leaking, a suitable packing agent is applied to the contact members 2 and 2, respectively.
It is placed between 3, 12, and 13. Furthermore, it is also possible to use particularly dense graphite,
Also, if necessary, a particularly thick material can be used in the pipe electrode to prevent diffusion of gas from the pipe wall. In the latter case, it is undesirable for gas to be generated from the electrode surface. The standard dimensions and standard working conditions for AC matching are as follows.

【table】

[Table] Since some portion of the ohmic heat pel. generated in the electrode in a given state of use is not available, the thermal efficiency is indicated by the highest and lowest values.As the length of the electrode increases, the loss of cooling water decreases. At the same time, pel. increases in proportion to the electrode length when other conditions are similar.
The efficiency to obtain any effect increases with increasing voltage. Referring to FIG. 3, the plasma burner includes a stationary or movable ring 3 made by any known method.
1, in which the electrode holder can be moved up and down within the slide 33 by a spindle driven by a motor 34 or the like. By doing this, the electrode structure 35
The amount H of immersion in the metal melt 36 can be adjusted.
The inclination of the electrode structure 35 is caused by sliding 33 around the shaft 37, for example by means of a hydraulic cylinder 38.
It can be adjusted by turning. Electrical current, gas and cooling water are supplied through cables and hoses. By using a water-cooled current cable, the use of separate cooling water hoses can be avoided if desired. In FIG. 4, the plasma burner 41 is mounted on a rig 42 made in a known manner, which is movable along a track and follows the slow rotational or oscillatory movement of the pot 44 of the furnace. I'm starting to do that. The introduction of the burner into the sprue 46 is controlled by a slide and worm mechanism 45 and a hydraulic cylinder 47 for adjusting the inclination angle. The plasma burner's current supply means may be provided in place or mounted on the rig.

[Brief explanation of the drawing]

FIG. 1 is a front vertical cross-sectional view of a plasma burner showing an embodiment of the present invention, FIG. 2 is a vertical cross-sectional view of the electrode holder shown in FIG. 1, and FIG. FIG. 4 is a side view showing the plasma burner of FIG. 1 used in an open sprue in an electric melting furnace. DESCRIPTION OF SYMBOLS 1... Rod-shaped electrode, 2, 3... Holder for rod-shaped electrode 1, 10... Insulating plate, 11... Pipe-shaped electrode, 1
2, 13... Holder for pipe-shaped electrode 11, 21...
...Insulating support substrate, 22... Spacing member.

Claims (1)

[Claims] 1. A tubular or rod-shaped inner electrode 1 made of a material that is consumed by plasma, and a tubular outer part made of the same material as the inner electrode 1 and having a substantial thickness and coaxially arranged with the inner electrode 1. The electrode holder includes an electrode 11 and an electrode holder for holding the electrodes 1 and 11, and the electrode holder includes a contact rail member for supporting electric wires connecting the inner and outer electrodes 1 and 11 to a power source, respectively. 5, 15, and a conduit 8 for supplying gas for generating an electric arc to the electrode region between the tip of the inner electrode 1 and the tip of the outer electrode 11, and the material and diameter of each electrode are selected such that their axial length wear rates are continuously equal and their tip shape and plasma environmental conditions are maintained substantially constant. 2. A pair of rear contact holding members 2, 3 for contacting and holding the part of the inner electrode 1 that the electrode holder protrudes from the outer electrode 11, and a pair of front contact holding members for contacting and holding a part of the outer electrode 11. Member 12,1
3, an insulating plate 10 is disposed between these front and rear contact holding members, and each pair of holding members maintains their integrity and is attached to an insulating substrate 21.
The plasma burner according to claim 1, characterized in that the plasma burner is fixed to. 3 Each pair of electrode holding members 2 and 3, and 12
and 13 consist of contact holding members 2 and 3 having semi-cylindrical grooves facing each other corresponding to the outer diameter of the electrode to be held, and 12 and 13, and are fixed to each other with tightening bolts 4 and 14, respectively. 3. The plasma burner according to claim 2, wherein the integrity of each pair is maintained by this. 4 The holding members 2 and 3 of the inner electrode 1 have an annular space 9 located around the inner electrode, and this annular space is connected to a fluid passage between the electrodes 1 and 11 and an external gas source through the annular space of the insulating plate. A plasma burner according to claim 2 or 3, characterized in that the plasma burner is connected to a plasma burner. 5. Claims 1 to 4 characterized in that the inner electrode 1 is supported so as to be axially displaceable with respect to the outer electrode 11, so that the axial distance between the free ends of the electrodes 1 and 11 can be adjusted. The plasma burner according to any one of the above. 6. Claims 1 to 5, characterized in that the external electrode 11 is surrounded by a jacket made of a thin wall of a metal material, and the metal material melts during operation without disturbing the electrical conditions. The plasma burner according to any one of the above. 7. The electrodes 1, 11 are positioned relative to each other by a plurality of electrically insulating strips 22 distributed around the inner electrode at a distance from the free ends of the electrodes. The plasma burner according to any one of items 1 to 6.