WO2000027168A1 - Electrode used in electro-metallurgical processes - Google Patents

Abstract

The present invention relates to an electrode used in electro-metallurgical processes, wherein said electrode comprises an outer-envelope component (2) consisting of a first carbon material, a central component (3) consisting of a second carbon material, and a linking member (9). The second carbon material of the central component (3) has a lower specific electric resistance and a higher volumetric mass than the first carbon material of the outer-envelope component (2).

Description

Electrode for electrometallurgical processes

The invention relates to an electrode for electrometallurgical processes with a jacket component made from a first graphite, a core component made from a second graphite and at least one connecting element for connection to a further electrode.

In electrometallurgical processes, in particular in the production of electrical steel in electric arc furnaces, the electrical current is supplied through electrodes which are made of a carbon material. These electrodes are also used in electrical reduction furnaces for electrical energy transfer to the reaction material.

Graphite has established itself as the carbon material for electrodes for electrometallurgical processes. Although graphite is used up in these processes, it has prevailed for electrometallurgical processes because advances in electrode technology and application have made it economically viable. There are several reasons why graphite electrodes are used up. One cause is the electrode erosion, which can be geometrically divided into the tip erosion and the side erosion. The ratio of the erosion values from peak erosion to side erosion is between 1: 1 and 1: 2. The peak erosion and the side erosion together make up about 85% of the total electrode consumption. The remaining 15% of the total electrode consumption is due to the falling off of electrode pieces and broken electrodes.

Graphite is a relatively expensive material. As a result, the consumption of graphite plays an essential role for an economical driving arc furnace and accounts for approximately 4% to 8% of the total operating costs of an arc furnace. There have therefore already been various measures for reducing the electrode consumption, which are primarily intended to reduce side burn-off by oxidation. This involves, in particular, a coating of the electrodes on their outer circumferential surface and water cooling of the electrodes.

In order to reduce electrode consumption due to electrode breakage, EP 0 142476 A discloses an electrode of the generic type, which consists of a jacket component made of a first graphite and a core component made of a second carbon material, which has different mechanical, thermal and electrical properties compared to the first Graphite has to reduce the internal mechanical stress in the electrode. The graphite of the cladding component is said to have a higher electrical and thermal conductivity than the carbon material of the core. For example, the jacket component should consist of electrographite and the core component of anthracite material.

In modern electrical steel production, it is an essential goal to increase productivity by increasing the power density in the melting chamber. For this purpose, in addition to the electrical energy, additive energies are usually supplied to the arc furnace by means of a fuel-oxygen burner or by means of oxygen supply in connection with the blowing in of coal. A higher power supply only from electrical energy would require larger electrode cross-sections and thus a larger electrode weight, which in turn would result in a correspondingly increased outlay in the support arms serving to hold electrode strands and in the electrode control. The object of the invention is to design an electrode of the generic type in such a way that it has a low consumption of graphite and allows an increased power supply of electrical energy in an arc furnace.

This object is achieved in that the second graphite of the core component has a lower specific electrical resistance and a higher bulk density than the first carbon material of the cladding component.

Because the core component consists of a graphite, which has a lower specific electrical resistance than the graphite of the cladding component, the tip erosion of the electrode is particularly uniform on the one hand and particularly low on the other hand. In addition, there is less erosion at the electrode tip due to the higher bulk density of the graphite of the core component. There is less thermal and electrical overload at the electrode tip. This is noticeable by an additional reduction in electrode consumption by minimizing the tip breaks. An electrode string constructed from electrodes according to the invention can absorb particularly high twists and bending forces. It is therefore particularly elastic and therefore not very susceptible to electrode breakage after a scrap collapse. The invention makes it possible to circumvent the restrictions which are imposed by the manufacturing process for graphite electrodes and which make the manufacture of large-format electrodes with low specific electrical resistance difficult. Problems due to eddy current losses and interference from neighboring electrodes (proximity effect), which occur with large Trode cross-sections occur are reduced. The weight of the graphite electrode component divided by the volume is defined as the bulk density. Pores are also included in the bulk density.

With the same electrode diameter, the electrodes according to the invention enable a higher furnace output without the use of additive energies and without increased effort for the construction of the support arms and the electrode control. The energy loss at the electrodes is reduced.

The total current is divided into several parallel currents in the electrode. As a result, the total current is transported with lower voltage losses since the core component has a lower resistivity than the sheath component.

Within the preferred ranges of the specific electrical resistances and the bulk density of the cladding component and the core component, the tuning is chosen so that the specific electrical resistance of the cladding component is 20% to 25% higher than that of the core component. Conversely, the bulk densities are matched to one another in such a way that the core component has a bulk density that is 9% to 10% higher than the shell component.

Further advantageous developments of the invention result from the subclaims.

Further features, advantages and details of the invention result from the following description of exemplary embodiments with reference to the drawing. Show it 1 shows a longitudinal section through an electrode string composed of several electrodes according to the invention in a first embodiment of an electrode according to the invention,

2 shows a cross section through the electrode according to section line II-II in FIG. 1 on an enlarged scale compared to FIG. 1,

Fig. 3 shows a longitudinal section through a composed of electrodes according to a second embodiment of the invention

Electrode string,

Fig. 4 shows a cross section through the electrode according to the section line

IV-IV in Fig. 3,

Fig. 5 shows a longitudinal section through a third embodiment of a

Electrode and

6 shows a cross section through a fourth embodiment of an electrode according to the invention.

1 shows an electrode string which is formed from several electrodes 1 which are identical to one another. Each electrode 1 has a jacket component 2 and a core component 3. The jacket component 2 is designed as a hollow cylinder with a circular cross-section, in which the solid circular cylindrical core component 3 is arranged, leaving an annular gap 4 free. The jacket component 2 and the core component 3 and thus also the annular gap 4 are concentric a common central longitudinal axis 5 arranged. The annular gap 4 can be filled with a coating component 6 attached to the core component 3.

As can be seen from the cross-sectional illustration according to FIG. 2, enlarged compared to FIG. 1, the core component 3 has a radius R _k . The jacket component 2 has an inner radius R; and an outer radius R _a . The ratio of the radii to one another is 0.3 <Rk / (R _a + Ri) <3.0 and preferably 0.3 <R (R _a + Ri) <0.8. The relationship R _a Ri defines the wall thickness of the casing component 2.

The electrodes 1 each have a so-called box 7 at their ends, which is a frustoconical recess 7 which is formed only at both ends of the casing component 2 and tapers towards the core component 3, on the inside of which a correspondingly tapering internal thread 8 is formed. So-called nipples 9 are used to connect two electrodes 1, which are double-conical, ie double-truncated cone-shaped bodies with two corresponding conical external threads 10. Because of the frustoconical configuration of the nipple 9 and the box 7, the respective nipple 9 can be inserted relatively deep into a box 7 before the external thread 10 of the nipple 9 overlaps the internal thread 8. The threaded connection can then be produced with a few turns, in such a way that the adjacent annular end faces 11, 12 of two adjacent jacket components 2 come into contact with one another. Another tight, two-dimensional connection exists via the external thread 10 and internal thread 8. The end faces 13 of the nipple 9 and the facing end faces 14 of the adjacent core components 3 have a small distance from one another.

The jacket component 2 consists of a first graphite, which is solid and compact. This is preferably an electrographite with a specific electrical resistance of 6.5 to 9.0 Ωμm and a bulk density of 1.5 to 1.64 g / cm ³ . The core component 3 consists of a compact second graphite. The second graphite is an electrographite with a specific electrical resistance of 4.5 to 6.4 Ωμm and a bulk density of 1.65 to 1.75 g / cm ³ . This second graphite for the core component 3 is the same graphite as is used for the nipple 9. Due to selected raw materials, small grain size and multiple impregnations, it has a high bulk density and a low specific electrical resistance. The relatively high bulk density is achieved by multiple impregnation with liquid pitch and annealing at 800 ° C to 900 ° C. The core component 3 can contain an application, ie a thin layer of metal or metal alloy (not shown in the drawing), as a result of which the overall electrical resistance of the core component 3 can be suppressed below the limit values that are possible for graphite. The metals that can be used are aluminum, titanium and nickel.

Aluminum is preferably used as the material for the coating component 6, which fills the annular gap between the core component 3 and the jacket component 2. Since aluminum is an electrical conductor, this improves the transport of electricity inside large-sized electrodes because it counteracts the current displacement on the outside of the electrode. Aluminum also acts on the during operation the temperatures occurring as a thermoplastic coating, which compensates for different thermal expansions of core component 3 and jacket component 2.

The coating component 6 can, however, also be constructed from several layers of metallic aluminum, nickel, aluminum alloys and one or more layers of refractory oxides, such as Si0 ₂ or A1 ₂ C » ₃ . Alternatively, the annular gap can also be filled with a coating component 6 made of a carbonized mass. For this purpose, it is possible, after the so-called green production of sheath component 2 and core component 3, to insert the core component 3 into the sheath component 2 and then to impregnate both together with impregnating pitch or impregnated tar. After the graphitization, ie after the usual thermal treatment at a temperature of 2600 ° C. to 2800 ° C., the jacket component 2 and the core component 3 are non-positively connected to one another by this carbonized impregnation.

The coating component 6 can furthermore also be formed by thermoplastic material, for example a so-called green mass, ie a mixture of pitch and tar, which softens during operation, that is to say at higher temperatures, and flows in pores and interspaces and thus adhesion caused between the core component 3 and the sheath component 2. A thermoplastic coating component 6 also compensates for the stresses that can occur because the second graphite of the core component 3 has a higher coefficient of thermal expansion than the first carbon material of the jacket component 2. To the extent that identical parts are present in the embodiment according to FIGS. 3 and 4 with the embodiment according to FIGS. 1 and 2, the same reference numerals are used; to the extent that functionally identical, structurally slightly different parts are present, the same reference numerals are used with a prime, without the need for a new description in each case.

The electrodes 1 'shown in FIG. 3, assembled to form an electrode string, have jacket components 2' with core components 3 '. The core component 3 'each has at its lower end a frustoconically widening section which bears in a corresponding area of the box 7' against the jacket component 2 '. As a result, the core component 3 'is held in the direction of the axis 5 against slipping out of the casing component 2' in one direction - upwards in FIG. 3. In the other direction - downward in FIG. 3 - the core component 3 'is secured by the nipple 9. The jacket component 2 'is provided on its outside with a known annular coating 16, which serves to reduce the side burn-up.

A so-called wick 17 made of an electrically conductive material can be arranged in the core component 3 'in a conventional manner, concentric to the axis 5. In this exemplary embodiment, no appreciable annular gap is formed between the core component 3 'and the casing component 2'. In order to reduce thermal stresses between the casing component 2 'and the core component 3' at high temperatures, the core component 3 'can be provided with slots 18, preferably running in the longitudinal direction, as can be seen from FIG. 4. For the materials the same specifications apply as for the exemplary embodiment according to FIGS. 1 and 2.

In the exemplary embodiment according to FIG. 5, the parts which are identical to the exemplary embodiment according to FIGS. 1 and 2 are provided with the reference numbers used there. Insofar as individual parts are merely modified in terms of design, they are identified by the same reference numerals, which are each provided with a double prime, without the need for a new description.

In the exemplary embodiment according to FIG. 5, the core component 3 "of the electrode 1" has blind holes 19 running radially to the axis 5 on its outside, into which so-called locking bolts 20 are inserted, which bear against the inner wall 21 of the jacket component 2. These locking bolts 20 can be formed from pitch that inflates and then carbonizes during operation of the electrode 1 ″, that is to say at higher temperatures. The inflation bolts 20 are pressed against the inner wall 21 by the inflation. The carbonization then hardens them off, so that overall a non-positive connection between core component 3 "and jacket component 2 is achieved. A connecting pin 22 with the same effect can be arranged concentrically to the axis 5 between the nipple 9 "and the adjacent core component 3", which in aligned blind holes 23, 24 in the end face 13 "of the nipple 9" and the adjacent end face 14 "of the core component 3 "is used. Locking bolts 20 and connecting bolts 22 are therefore also electrically conductive. 6, the jacket component 2 '"and the core component 3"' of an electrode 1 '"can also be connected to one another by a dovetail connection 25. For this purpose, the jacket component 2'" are parallel in the inner wall 21 '" Undercut grooves 26 running to the axis 5, into which dovetail-shaped webs 28 formed on the outer surface 27 of the core component 3 '' engage.

It applies to all exemplary embodiments that the features which are described in each case only for one exemplary embodiment can also be used in the other exemplary embodiments. In practice, the individual electrodes 1 or 1 'or 1 "or 1"' are supplied individually by the manufacturer of the electrode - each with a nipple 9, 9 "- and assembled on the melting furnace to form an electrode string consisting of several electrodes by adding an electrode 1 or 1 'or 1 "or 1'" again in accordance with the erosion.

Claims

claims 1. Electrode for electrometallurgical processes with - A jacket component (2, 2 ', 2' ") made of a first graphite, - A core component (3, 3 ', 3", 3 "') made of a second graphite and - At least one connecting element for connection to a further electrode (1, 1 ', 1 ", 1'"), characterized in that the second graphite of the core component (3, 3 ', 3 ", 3'") has a lower specific electrical Resistance and a higher bulk density than the first graphite of the shell component (2, 2 ', 2' "). 2. Electrode according to claim 1, characterized in that the first graphite has a specific electrical resistance of 6.5 to 9.0 Ωμm and a bulk density of 1.5 to 1.64 g / cm ³ and that the second graphite has a specific electrical resistance of 4.5 to 6.4 Ωμm and a bulk density of 1.65 to 1.75 g / cm ³ . 3. Electrode according to claim 1, characterized in that fastening means for connecting the jacket component (2, 2 ', 2' ") and the core component (3, 3 ', 3", 3' ") are provided. 4. Electrode according to claim 3, characterized in that the fastening means are formed by a coating component (6) arranged between the jacket component (2) and the core component (3). 5. Electrode according to claim 3, characterized in that the fastening means are formed by locking bolts (20) arranged in blind holes (19) of the core component (3 "), against the jacket component (2). 6. Electrode according to claim 4, characterized in that the coating component (6) is designed to be electrically conductive. 7. Electrode according to claim 1, characterized in that as a connecting element formed at one end of the jacket component (2, 2 \ 2 ") to the core component (3, 3 ', 3", 3' ") tapering frustoconical recess with a Internal thread (8) for receiving a double-conical pin (9, 9 ") with External thread (10) is provided. 8. Electrode according to claim 7, characterized in that the pin (9 ") and the core component (3") are connected to one another by means of a connecting bolt (22). 9. Electrode according to claim 1, characterized in that the jacket component (2 ') has a coating (16). 10. Electrode according to claim 1, characterized in that the core component (3, 3 ', 3 ", 3'") has a layer of metal or metal alloys. 11. Anspmch electrode 2. characterized in that the specific electrical resistance of the first graphite is 20% to 25% higher than the specific electrical resistance of the second graphite. 12. Electrode according to Anspmch 2, characterized in that the bulk density of the second graphite is 9% to 10% higher than the bulk density of the first graphite. 13. Anspmch 7 electrode, characterized in that the core component (3, 3 ', 3 ", 3'") consists of the same graphite as the pin (9, 9 "). 14. Anspmch 1 electrode, characterized in that the jacket component (2) is designed as a hollow cylinder and the core component (3) as a cylinder, that the jacket component (2) has an inner radius R; and an outer radius R _a and the core component (3) has a radius R _k and that for the ratio of the radii to each other: 0.3 <R _k / (R _a - Ri) <3.0. 15. Electrode according to Anspmch 14, characterized in that the following applies to the ratio of the radii to one another: 0.3 <R _k / (R _a ^• * ^■ Ri) <0.8.