High-power graphite electrode for electric arc furnace

Abstract

The invention discloses a high-power graphite electrode for an electric arc furnace. The high-power graphite electrode comprises an electrode body and an electrode tip, the electrode body comprises a graphite base body, the whole graphite base body is of a drum-shaped cylinder structure, and a through inner hole is formed in the graphite base body to serve as an air hole; a plurality of long-strip-shaped blind grooves are evenly formed in the outer cylindrical surface of the graphite base body, and the long-strip-shaped blind grooves are annularly formed in the outer cylindrical surface of the graphite base body at intervals. The long-strip-shaped blind grooves are filled with superfine graphite filler, and the surface of the superfine graphite filler is flush with the outer cylindrical surface of the graphite base body; the outer cylindrical surface of the graphite substrate and the outer surface of the superfine graphite filler are coated with graphite fiber cloth, the outer side of the graphite fiber cloth is subjected to medium-temperature coal tar pitch dipping treatment, graphitization forming is carried out after secondary roasting to obtain an electrode body blank, and the surface of the formed electrode body blank is coated with a film protection layer. The erosion resistance and oxidation resistance of the graphite electrode can be remarkably improved, the service life of the graphite electrode is prolonged, and therefore the operation cost of the electric arc furnace is reduced.

Description

Technical Field

[0001] The invention relates to a graphite electrode in carbon material technology, in particular to a high-power graphite electrode for an electric arc furnace suitable for an industrial furnace. Background Art

[0002] As a type of equipment that uses the heat generated by electric arc to melt metal, electric arc furnace is widely used in the steel industry and the smelting and processing of non-ferrous metals. Its working principle is based on the high temperature generated by the electric arc formed between the electrode and the charge, thereby achieving the technical purpose of quickly melting the charge. In the electric arc furnace, graphite electrodes play a vital role and are an indispensable part of the arc furnace steelmaking process. They not only have excellent electrical conductivity, but also have the advantages of high temperature resistance, high mechanical strength, low thermal expansion coefficient, high thermal conductivity and relatively low resistivity, and can work stably in extremely high temperature environments.

[0003] During the use of electric arc furnaces, the consumption of graphite electrodes is inevitable. Considering the high energy consumption of electric arc furnaces and the consumable characteristics of graphite electrodes, the use effect and service life of graphite electrodes directly affect the production cost of steel smelting. At present, in addition to the uncontrollable physical loss during storage, transportation and use, graphite electrodes mainly face two types of losses during use:

[0004] The first is the erosion and consumption caused by the contact between the smelting slag and the electrode;

[0005] The second is oxidation loss in high temperature and oxidizing atmosphere environment.

[0006] The above two types of losses will have adverse effects on the use effect and service life of graphite electrodes, and they need to be replaced regularly to maintain the heat treatment efficiency and effect of the arc furnace. If these losses can be effectively reduced, the production cost will be significantly reduced and the operating efficiency of the arc furnace will be improved.

[0007] In practical applications, the erosion of the electrode by smelting slag can be reduced by optimizing the material composition of the electrode, adding protective agents and adopting surface treatment technology. Among them, the surface treatment technology mainly forms an outer protective structure on the electrode surface, including metal film plating, coating and impregnation of anti-oxidation coatings. This method can significantly improve the anti-oxidation ability of the electrode, and it also has a certain effect in dealing with the erosion of smelting slag by smelting slag. However, under the existing technical conditions, the coating and impregnation of anti-oxidation coatings have certain limitations. The uniformity, adhesion and stability of the coating may be affected by the roughness of the electrode surface. In addition, the coating may peel off or burn at high temperatures, thereby reducing the protective effect; and the metal film layer may cause the coating to peel off from the electrode substrate due to the difference in thermal expansion coefficients between the metal coating and the electrode material under high temperature environment, thereby losing its protective effect.

[0008] Therefore, researching and developing a more effective protective morphological structure to improve the erosion and oxidation resistance of graphite electrodes and extend their service life is of great significance for reducing the operating cost of electric arc furnaces and improving production efficiency. Summary of the invention

[0009] The technical problem solved by the present invention is to provide a high-power graphite electrode for an electric arc furnace to solve the shortcomings of the above-mentioned background technology.

[0010] The technical problem solved by the present invention is achieved by adopting the following technical solutions:

[0011] A high-power graphite electrode for an electric arc furnace comprises an electrode body and an electrode head mounted on the electrode body, wherein the electrode body is connected to an electric arc furnace device through the electrode head and energized to realize an arc discharge function;

[0012] The electrode body comprises a graphite substrate, and butt joints are formed at both ends of the graphite substrate, and the electrode head is assembled and connected with the electrode body through the butt joints;

[0013] The graphite substrate is a drum-shaped cylindrical structure as a whole, and the inside of the graphite substrate has a through inner hole as a vent; the graphite substrate is evenly formed with a plurality of long strip blind grooves on the outer cylindrical surface, and the long strip blind grooves are arranged circumferentially at intervals on the outer cylindrical surface of the graphite substrate, and the extending direction is parallel to the axis of the graphite substrate; the long strip blind grooves are filled with ultrafine graphite fillers, and the surface of the ultrafine graphite fillers is flush with the outer cylindrical surface of the graphite substrate;

[0014] The molding density of the ultrafine graphite filler in the long strip blind groove is 1.15 to 1.25 times the molding density of the graphite matrix;

[0015] The outer cylindrical surface of the graphite matrix and the outer surface of the ultrafine graphite filler are wrapped with graphite fiber cloth, the outer side of the graphite fiber cloth is impregnated with medium-temperature coal tar, and after secondary calcination, it is graphitized to obtain an electrode body blank, and the surface of the formed electrode body blank is coated with a membrane protective layer.

[0016] As a further limitation, the electrode body and the electrode head are assembled and connected by a mechanical fixing method, and the mechanical fixing method is a threaded connection;

[0017] Both ends of the air hole are formed with outward-expanding conical openings, and the outward-expanding conical openings are provided with assembly positions with threaded surfaces. The electrode body realizes assembly connection of the electrode head and serial connection of multiple electrode bodies through the assembly positions.

[0018] As a further limitation, the electrode head is made of a high-temperature resistant alloy material, and a passivation protective film layer is formed on the surface of the electrode head; the passivation protective film layer of the electrode head is a chromium oxide film layer, which is formed on the surface of the electrode head by chemical vapor deposition (CVD) or physical vapor deposition (PVD) method.

[0019] As a further limitation, the connection portion between the electrode body and the electrode head is provided with an anti-loosening structure, and the anti-loosening structure may be a locking nut, a spring washer or other mechanical locking device.

[0020] As a further limitation, the outer diameter of the drum-shaped cylindrical structure of the graphite substrate decreases continuously from the middle position to the outer diameters on both sides, and the ratio of the difference between the maximum outer diameter and the minimum outer diameter of the graphite substrate to the length of the graphite substrate is 1:15 to 1:20.

[0021] As a further limitation, the cross-section of the long strip blind groove is rectangular or trapezoidal with the bottom close to the graphite substrate, the bottom width of the long strip blind groove is 10-30 mm, and the spacing between adjacent long strip blind grooves is 30-50 mm.

[0022] As a further limitation, the ultrafine graphite filler comprises ultrafine graphite powder, a binder and water, wherein the particle size of the ultrafine graphite powder is in the range of 50 to 150 nm and the specific surface area is in the range of 18 to 25 m 2 / g, the dosage ratio is not less than 80%, the binder is polyacrylonitrile or polyacrylate, the dosage ratio is 5-15%, and the dosage ratio of water is 5-10%;

[0023] The ultrafine graphite filler is also mixed with carbon fiber with a mass ratio of 3-5% and nano hafnium carbide with a mass ratio of 0-1.5%.

[0024] As a further limitation, the graphite fiber cloth has a thickness of 0.1 to 0.3 mm, a density of 100 to 200 g / m2, is woven in a plain or twill manner, and has 1 to 3 wrapping layers when wrapped around the outer cylindrical surface of the graphite matrix and the outer surface of the ultrafine graphite filler.

[0025] As a further limitation, the impregnating material coated on the outer layer of the graphite fiber cloth is low-quinoline medium-temperature coal tar, and an antioxidant is added to the impregnating material at a mass ratio of 0.7 to 1.5%; the coating thickness of the impregnating material is 0.1 to 0.5 mm; after coating, it is impregnated and formed in a pressure vessel at 180 to 220° C. and 0.5 to 1.5 MPa, and the treatment time is 1 to 2 hours.

[0026] As a further limitation, the membrane protection layer is an anti-oxidation coating formed by coating and dipping; the thickness of the membrane protection layer on the outer cylindrical surface of the electrode body is 100-300 μm, and the thickness of the membrane protection layer on the inner side of the graphite substrate air hole is 0-120 μm.

[0027] Beneficial effects: The present invention relates to a high-power graphite electrode used in an electric arc furnace, which is formed by uniformly forming long strip blind grooves on the outer cylindrical surface of the electrode body and filling them with ultrafine graphite fillers. In addition, through the wrapping of graphite fiber cloth and the impregnation treatment of medium-temperature coal tar, a spatial buffer structure is formed on the outside of the graphite electrode, which can significantly improve the mechanical strength and thermal strain resistance of the outer surface of the electrode, and effectively resist the scouring and erosion of smelting slag; at the same time, the aforementioned combined structure can also provide a stable attachment surface for the membrane protective layer, ensuring the bonding force and stability between the protective layer and the graphite electrode body, preventing it from peeling off or burning in a high-temperature oxidizing atmosphere, further enhancing the structural stability of the electrode in a high-temperature environment, and effectively solving the electrode oxidation problem of graphite electrodes in the smelting process in the prior art. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram of the general assembly structure of a preferred embodiment of the present invention.

[0029] Figure 2 Schematic diagram of the cross section of a graphite electrode according to a preferred embodiment of the present invention.

[0030] Figure 3 for Figure 1 Enlarged schematic diagram of part A.

[0031] Among them: 1. electrode head; 2. assembly position; 3. graphite matrix; 4. air hole; 5. ultrafine graphite filler; 6. graphite fiber cloth; 7. impregnation layer; 8. membrane protection layer. DETAILED DESCRIPTION

[0032] In order to make the technical means, creative features, objectives and effects of the present invention easier to understand, the present invention is further described below in conjunction with specific embodiments. The described embodiments are only part of the embodiments of the present invention, not all of them.

[0033] It should be noted that, in the description of the embodiments of the present invention, unless otherwise clearly stipulated and limited, "multiple" means two or more, and the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integrated connection; it can be a mechanical connection, a chemical connection, or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the internal connection of two elements or the interaction relationship between two elements; for ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to the specific circumstances.

[0034] See also Figure 1 , Figure 2 A preferred embodiment of a high-power graphite electrode for an electric arc furnace is disclosed. In this embodiment, the high-power graphite electrode can be used in an electric arc furnace. The graphite electrode includes an electrode body, and a vent 4 is opened in the middle of the electrode body. The vent 4 is a hole that runs through the upper and lower ends, and both ends are designed with outwardly expanding conical openings. At the corresponding positions of these conical openings, threaded assembly positions 2 are reserved. The assembly positions 2 have three functions:

[0035] Firstly, the electrode body at the end can be assembled and connected with the electrode head 1 through the assembly position 2 at the outer end, and connected with the arc furnace equipment through the electrode head 1 and energized to realize the arc discharge function; this mechanical fixing method ensures good mechanical strength and stability between the electrode body and the electrode head, and facilitates the replacement and maintenance of the electrode.

[0036] Secondly, multiple electrode bodies can be connected in series through the assembly position 2 to form a combined electrode of appropriate length to meet the use requirements of arc furnaces of different lengths;

[0037] Thirdly, multiple electrode bodies connected in sequence can be cooled by air by introducing inert gas through the wind connection hole 4 at the end of the electrode head 1 to reduce the surface oxidation of the graphite electrode. The gas continuously flows inside the wind hole 4 to remove the heat. It has high heat exchange efficiency and good cooling effect, which can extend the overall service life of the graphite electrode body 1.

[0038] In this embodiment, the electrode head 1 is made of a high-temperature resistant alloy material, and a chromium oxide film layer is formed on the surface of the electrode head as a passivation protective film layer, and the passivation protective film layer is formed on the substrate surface of the electrode head 1 by chemical vapor deposition (CVD) or physical vapor deposition (PVD) and other methods. The passivation protective film layer has good high-temperature resistance and chemical stability, can effectively resist the high-temperature oxidation environment in the arc furnace, reduce the oxidation loss of the electrode head 1 in a high-temperature working environment, extend its service life and ensure the stable operation and production efficiency of the arc furnace.

[0039] In addition, the threaded connection design of the assembly position 2 allows the electrode head 1 to have a certain displacement space when subjected to thermal expansion and mechanical stress. This design helps to alleviate the internal stress caused by temperature fluctuations and chemical reactions, thereby further extending the service life of the electrode. In contrast, in other embodiments, the connection between the electrode body and the electrode head 1 adopts an anti-loosening structure, such as a locking nut, a spring washer or other mechanical locking device. These structures ensure that the electrode maintains a stable connection state during long-term operation, preventing the risk of arc instability or electrode falling off due to loose connection.

[0040] The main body of the electrode body is a graphite substrate 3. As an optimized design, the graphite substrate 3 presents the structural characteristics of a drum-shaped cylinder; the cross section of the graphite substrate 3 at any position is circular, the diameter of the middle cross section circle of the graphite substrate is larger than the diameters of the top and bottom cross sections, and the diameter gradually decreases from the center to both sides; specifically in this embodiment, the ratio of the difference between the maximum outer diameter and the minimum outer diameter of the graphite substrate 3 to the length of the graphite substrate is 1:20, that is, corresponding to Figure 1 The ratio of a to b is 1:40. The drum-shaped cylindrical structure of the graphite matrix can ensure that the electrode has sufficient mechanical strength when the air hole 4 is provided, which not only improves the bending strength of the electrode, but also helps to make the thermal expansion uniform at high temperature, thereby extending the service life of the electrode.

[0041] The graphite substrate 3 has a plurality of long blind grooves uniformly formed on the outer cylindrical surface, and these long blind grooves are arranged circumferentially at intervals on the outer cylindrical surface of the graphite substrate 3, and the extending direction is parallel to the axis of the graphite substrate 3. In this embodiment, the cross-section of these long blind grooves is an isosceles trapezoid, the lower base of the trapezoid is located on one side of the graphite substrate 3, the groove bottom width is 24mm, the upper base is located on the other side, the top surface width is 18mm, and the spacing between adjacent long blind grooves is 50mm.

[0042] The long strip blind groove is filled with ultrafine graphite filler 5. Specifically in this embodiment, the ultrafine graphite filler 5 includes ultrafine graphite powder with a mass ratio of 85%, a binder with a mass ratio of 10%, and a binder water with a mass ratio of 5%. The particle size range of the ultrafine graphite powder is 50-150nm, and the specific surface area is 18-25m 2 / g, and the binder is polyacrylate. The ultrafine graphite filler 5 is compacted so that the molding density of the ultrafine graphite filler 5 in the long strip blind groove is 1.15 times the molding density of the graphite matrix 3.

[0043] In another embodiment, the ultrafine graphite filler can also be mixed with carbon fiber accounting for 3-5% of the total mass of the ultrafine graphite filler and nano-hafnium carbide with a mass ratio of 0-1.5%. The addition of carbon fiber and nano-hafnium carbide can further improve the mechanical strength and thermal stability of the electrode. The addition of carbon fiber can enhance the tensile strength and impact resistance of the material, while nano-hafnium carbide helps to improve the high temperature resistance and oxidation resistance of the electrode.

[0044] In this embodiment, the long blind groove not only increases the surface area of ​​the graphite matrix 3, thereby improving the thermal conduction efficiency of the electrode, but also through the filling of the ultrafine graphite filler 5, the electrode can disperse the stress and reduce local wear when it is washed by slag; at the same time, the existence of the long blind groove can produce a thermal buffer area in the interface area between the graphite matrix 3 and the ultrafine graphite filler 5, which also helps to relieve thermal stress and avoid electrode damage caused by uneven thermal expansion.

[0045] During the molding process, the ultrafine graphite filler 5 is surface-polished to obtain a surface flush with the outer cylindrical surface of the graphite matrix 3. At the same time, the outer cylindrical surface of the graphite matrix 3 and the outer surface of the ultrafine graphite filler 5 are stretched and wrapped with a graphite fiber cloth 6. The thickness of the graphite fiber cloth 6 is 0.2 mm and the density is 160 g / m 2 , woven in a twill manner, with two layers of wrapping when the surface is outwrapped, after wrapping is completed, it is pre-fixed with an adhesive and then coated on its outer surface with an impregnating material to obtain an impregnation layer 7, the impregnating material selected for coating uses low-quinoline medium-temperature coal tar as a base material, and an antioxidant accounting for 1.2% of the base material mass is added thereto, the coating thickness of the impregnating material is 0.2-0.3mm, and after coating, it is sent to a pressure vessel for impregnation molding at a set temperature of 200°C and a set pressure of 1.2MPa, and the impregnation molding treatment time is 1-2 hours to ensure that the impregnating material can fully penetrate the graphite fiber cloth 6.

[0046] After the impregnation, the material is sent to the calcination furnace for secondary calcination, and after the secondary calcination, the electrode body is graphitized and formed. After the electrode body is formed, the surface of the impregnation layer 7 is coated with a membrane protection layer 8. The corresponding membrane protection layer 8 can be made of the membrane protection material that can be used for graphite electrodes in the prior art. In this embodiment, the corresponding membrane protection material is an oxidized coating, which is formed by coating. When coating, the outer cylindrical surface is the surface that must be coated, and its corresponding forming thickness should be controlled at 100-300 μm, while the inner surface corresponding to the air hole 4 has a forming thickness of 0-120 μm.

[0047] In this structure, the graphite fiber cloth 6 can be used to enhance the outer surface strength of the aforementioned graphite matrix 3 / ultrafine graphite filler 5, so as to enhance the thermal shock resistance of the graphite matrix, thereby being able to absorb the impact force of the smelting slag to a certain extent; in addition, it can ensure that the adhesion performance of the impregnated material is improved during the secondary roasting process, and obtain an outer surface similar to the anchoring surface effect. This combination of effects enables the traditional membrane protective layer structure with poor adhesion to remain stable in a high-temperature oxidizing atmosphere, and is not prone to peeling or burning. The membrane protective layer structure with excellent performance can effectively enhance the oxidation resistance of the electrode, prevent the electrode from oxidation in a high-temperature working environment, and thus extend the service life of the electrode.

[0048] The high-power graphite electrode for an electric arc furnace of the present invention exhibits excellent performance in practical applications, can effectively resist the scouring and erosion of smelting slag, while ensuring the structural stability and antioxidant ability of the electrode in a high-temperature environment, significantly improving the production efficiency of the electric arc furnace and the service life of the electrode, significantly reducing the operating cost of the electric arc furnace and improving production efficiency.

[0049] The above shows and describes the basic principles, main features and advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A high-power graphite electrode for an electric arc furnace, characterized in that: It includes an electrode body and an electrode head mounted on the electrode body, and the electrode body is connected to the arc furnace equipment through the electrode head and energized to realize the arc discharge function; The electrode body comprises a graphite substrate, and butt joints are formed at both ends of the graphite substrate, and the electrode head is assembled and connected with the electrode body through the butt joints; The graphite substrate is a drum-shaped cylindrical structure as a whole, and the inside of the graphite substrate has a through inner hole as a vent; the graphite substrate is evenly formed with a plurality of long strip blind grooves on the outer cylindrical surface, and the long strip blind grooves are arranged circumferentially at intervals on the outer cylindrical surface of the graphite substrate, and the extending direction is parallel to the axis of the graphite substrate; the long strip blind grooves are filled with ultrafine graphite fillers, and the surface of the ultrafine graphite fillers is flush with the outer cylindrical surface of the graphite substrate; The molding density of the ultrafine graphite filler in the long strip blind groove is 1.15 to 1.25 times the molding density of the graphite matrix; The outer cylindrical surface of the graphite matrix and the outer surface of the ultrafine graphite filler are wrapped with graphite fiber cloth, the outer side of the graphite fiber cloth is impregnated with medium-temperature coal tar, and after secondary calcination, it is graphitized to obtain an electrode body blank, and the surface of the formed electrode body blank is coated with a membrane protective layer.

2. The high-power graphite electrode for electric arc furnace according to claim 1, characterized in that: The electrode body and the electrode head are assembled and connected by a mechanical fixing method, and the mechanical fixing method is a threaded connection; Both ends of the air hole are formed with outward-expanding conical openings, and the outward-expanding conical openings are provided with assembly positions with threaded surfaces. The electrode body realizes assembly connection of the electrode head and serial connection of multiple electrode bodies through the assembly positions.

3. The high-power graphite electrode for electric arc furnace according to claim 1, characterized in that: The electrode head is made of a high-temperature resistant alloy material, and a passivation protective film layer is formed on the surface of the electrode head; the passivation protective film layer of the electrode head is a chromium oxide film layer, which is formed on the surface of the electrode head by chemical vapor deposition or physical vapor deposition.

4. The high-power graphite electrode for electric arc furnace according to claim 1, characterized in that: The outer diameter of the drum-shaped cylindrical structure of the graphite substrate decreases continuously from the middle position to the outer diameters on both sides, and the ratio of the difference between the maximum outer diameter and the minimum outer diameter of the graphite substrate to the length of the graphite substrate is 1:15-1:

20.

5. The high-power graphite electrode for electric arc furnace according to claim 1, characterized in that: The cross section of the long strip blind groove is rectangular or trapezoidal with the bottom close to the graphite substrate, the bottom width of the long strip blind groove is 10-30 mm, and the spacing between adjacent long strip blind grooves is 30-50 mm.

6. The high-power graphite electrode for electric arc furnace according to claim 1, characterized in that: The ultrafine graphite filler comprises ultrafine graphite powder, a binder and water. The ultrafine graphite powder has a particle size range of 50 to 150 nm and a specific surface area of ​​18 to 25 m 2 / g, the usage ratio is not less than 80%, the binder is polyacrylonitrile or polyacrylate, the usage ratio is 5-15%, and the usage ratio of water is 5-10%.

7. The high-power graphite electrode for electric arc furnace according to claim 6, characterized in that: The ultrafine graphite filler is also mixed with carbon fiber with a mass ratio of 3-5% and nano hafnium carbide with a mass ratio of 0-1.5%.

8. The high-power graphite electrode for electric arc furnace according to claim 1, characterized in that: The graphite fiber cloth has a thickness of 0.1-0.3 mm and a density of 100-200 g / m2. It is woven in a plain or twill manner and has 1-3 layers of wrapping on the outer cylindrical surface of the graphite matrix and the outer surface of the ultrafine graphite filler.

9. The high-power graphite electrode for electric arc furnace according to claim 1, characterized in that: The impregnating material coated on the outer layer of the graphite fiber cloth is low-quinoline medium-temperature coal tar, and an antioxidant is added to the impregnating material at a mass ratio of 0.7-1.5%; the coating thickness of the impregnating material is 0.1-0.5mm; after coating, it is impregnated and formed in a pressure vessel at 180-220°C and 0.5-1.5MPa, and the treatment time is 1-2h.

10. The high-power graphite electrode for electric arc furnace according to claim 1, characterized in that: The membrane protection layer is an anti-oxidation coating formed by coating and dipping; the thickness of the membrane protection layer on the outer cylindrical surface of the electrode body is 100-300 μm, and the thickness on the inner side of the wind hole of the graphite matrix is ​​0-120 μm.

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