RU2753817C1 - Method for protection of graphite electrode from oxidation - Google Patents

Abstract

FIELD: metallurgy.SUBSTANCE: invention relates to ferrous and nonferrous metallurgy, namely to methods for protection of electrodes of electric arc furnaces from oxidation under high temperatures. The technical result is achieved by the fact that in the method for protection of a graphite electrode from oxidation by supplying a protective medium containing an antioxidant component during operation of the electric furnace, the protective medium is supplied to the side surface of the electrode in form of a water suspension containing 10 to 12% wt. of the antioxidant component in form of active magnesium hydroxide through a spraying water-cooling ring to form a protective coating with a thickness of 0.2 to 0.4 mm. The protective medium is also applied below the electrode contact node and the spraying water-cooling ring is attached at a fixed height from the surface of the furnace.EFFECT: increase in the resistance of graphite electrodes to oxidation during operation under high temperatures, as well as efficiency and availability of the method for industrial application.2 cl, 2 dwg, 1 tbl

Description

The invention relates to ferrous and non-ferrous metallurgy, and in particular to methods of protecting the electrodes of electric arc furnaces from oxidation.

During the operation of graphite electrodes on electric arc furnaces, there is intense erosive destruction of the side surfaces of the electrode due to intense oxidation of graphite due to heating at high temperatures, which leads to a decrease in its diameter in the working part and an increase in the current density in this area of the electrode [Yachikov I.M., Kolokoltsev V.M. Reducing the consumption of graphite electrodes in arc furnaces with forced cooling / Electrometallurgy, 2008, No. 8 p. 23-26].

A number of groups of methods have been developed to protect electrodes from oxidation.

Known methods of protecting graphite and carbon electrodes from oxidation by impregnating their surface with solutions of various components. For example, a method in which the electrodes are impregnated with an aqueous solution of sodium polyphosphate with an average degree of polymerization of 4-6 with a concentration of 18-20% and maleic acid with a concentration of 005-0.1 wt. % at 90-100 ° C. (Av. Certificate No. 1699909, IPC С01В 31/02, published on 23.12.1991). The general disadvantages of these methods include the use of a multicomponent composition, which complicates the process of preparing a solution and, accordingly, preparation of production. In addition, the use of a solution leads to an increase in the electrical resistance of the electrode, which is unacceptable, especially in the zone of contact with current leads.

Another group includes methods in which an antioxidant protective coating is applied to the lateral surface of the electrodes by spraying, dipping or brushing, for example, by spraying in the form of aqueous solutions of a nitride-borophosphate composition (Pat. Republic of Belarus No. 11708, IPC С09К 15/00, С01В 31/00 , published 2009.04.03) or with a brush with the consistency of a liquid slurry of the composition, based on a high-alumina material with the addition of carbon powder and orthophosphoric acid (RF patent No. 2006189, IPC Н05В 7/08 (1990.01), С25С 7/02, С25В 11/12, published 1994.01.15).

The disadvantages of the methods include the complexity, both in the preparation of a multicomponent composition, and in applying a coating to the electrodes. In addition, a common disadvantage of the known methods is that the processing of the side surfaces of the electrodes with various inorganic compounds or the application of these compounds to the prepared surface followed by heat treatment is carried out beforehand before the start of melting. This lengthens and complicates the melting process.

In the third group of methods of protection of electrodes is carried out by cooling them with water. A decrease in the temperature of the electrodes leads to a decrease in the rate of the processes of interaction of the electrode material with the furnace atmosphere. The process of heat removal can proceed due to the presence of an upper water-cooled metal cylinder, to the flat lower end of which a consumable graphite electrode is attached (Gudim Yu.A., Zinnurov I.Yu., Kiselev A.D. Steel production in arc furnaces. Structures, technology, materials: monograph. - Novosibirsk: Publishing house of NSTU, 2010, 547 p.) or during evaporation of water sprayed on the surface of these electrodes, for example, using a device consisting of a spray ring fixed on the electrode holder formed by a pipe supplying cooling water and equipped with spray nozzles facing the surface of the electrodes (Mokhov V.A., Yachikov I.M. Modeling the waste of a graphite electrode in an arc furnace using evaporative cooling. Theory and technology of metallurgical production. 2011, No. 11, pp. 189-195).

The disadvantages include the low efficiency of the method, since only the upper part of the electrode is subjected to water cooling.

A known method of protecting electrodes from oxidation by applying a heat-resistant coating containing titanium dioxide and sodium silicate during the operation of the furnace, on the part of the electrode surface located below the contact unit (Ed. St. No. 401024, IPC N05B 7/06, publ. 05.07. 1974). The known method makes it possible to protect the lower part of the electrode located in the under-roof space from oxidation by exhaust gases due to the coating with a layer of refractory ceramic coating (thickness of the protective layer 0.2-2.0 mm).

The disadvantage of this method is the complexity and low degree of protection of the electrode from oxidation (the consumption of electrodes for melting is reduced by 10-15%).

The technical result of the present invention is the development of a more efficient and affordable for industrial application in comparison with the prototype method for increasing the resistance of graphite electrodes to oxidation during operation at high temperatures by combining cooling and applying a protective coating on the side surface of the electrodes during the operation of the furnace.

The specified technical result is achieved in that in the method of protecting the graphite electrode from oxidation by supplying during the operation of the electric furnace a protective medium containing an antioxidant component to the side surface of the electrode, according to the invention, the protective medium is supplied in the form of an aqueous suspension containing 10-12 wt. % of the antioxidant component in the form of active magnesium hydroxide through a spray water-cooling ring to form a protective coating with a thickness of 0.2-0.4 mm.

In this case, the protective medium is applied below the contact assembly of the electrode, and the spray water cooling ring is attached at a fixed height from the surface of the furnace.

FIG. 1. Scheme of applying a protective coating

FIG. 2. Installation for studying the change in the mass of the electrode

The electrode protection process is carried out as follows (Fig. 1). A suspension consisting of water and 10-12 wt. % active magnesium hydroxide to ensure maximum cooling of the electrode surface as it is lowered outside the furnace due to the evaporation of water contained in the suspension, and on the other hand, the formation of a dense protective film 0.2-0.4 mm thick, which provides antioxidant protection of the electrode inside the furnace space by eliminating the interaction of graphite with the atmosphere of the furnace. If the amount of active magnesium hydroxide in the suspension exceeds 12 wt. %, this increases its viscosity and can lead to clogging of the nozzles when spraying. If its share is less than 10 wt. %, the film thickness will be less than 0.2 mm.

Due to the fact that the electrodes have some porosity. As a result of spraying the suspension, part of the active magnesium hydroxide, which is ultrafine particles, clogs the pores, and part forms a dense film. At temperatures above 350 ° C, active hydroxide decomposes into magnesium oxide and water. Since it is ultradispersed, the resulting magnesium oxide film remains on the surface and is partially sintered. Its protective properties are preserved. With a coating thickness of less than 0.2 mm, the protective effect decreases sharply, with a thickness of more than 0.4 mm, the effectiveness of the coating remains almost unchanged.

In order to check the protective properties of a coating based on active magnesium hydroxide against interaction with oxygen on the surface of a graphite electrode, tests were carried out under laboratory conditions. For testing, samples were cut from the electrode, on which, after heating to a temperature of 200 ° C, a protective coating of various thicknesses was applied; the coating was not applied to the reference samples. The tests were carried out on the setup shown in FIG. 2, at a temperature of 900 ° C. Each sample was individually suspended with a platinum wire from an electronic balance (BJIA-200-M) and placed in the reaction zone of the oven. The balance was used to record the change in the mass of the test samples during heating.

Installation for studying the change in the mass of the electrode (Fig. 2) includes:

- Tamman oven (4);

- graphite heater (5), isolated from the working space of the furnace with an alundum cover (6);

- a tungsten-rhenium thermocouple (7) located above the sample and designed to measure its temperature;

- corundum capillary for air supply (8);

- test sample (9) attached to the VLA-200-M balance (10);

- rotameter RM-A-0.063G U3 (11), designed to control the flow of gases.

The technological parameters of the tests are given in the table. After heating to a predetermined temperature (900 ° C), the weight loss was recorded in the course of firing as a function of time. As can be seen from the table, the waste of the electrode without coating was 16%. With a film thickness of about 0.1 mm, the waste reduction effect is negligible. Starting from a coating layer thickness of about 0.2 mm, waste is reduced by about 30%, almost unchanging with increasing thickness. Therefore, a coating thickness of 0.2-0.4 mm is optimal. Its increase has almost no effect on oxidation, but increases the consumption of hydroxide. optimal. Its increase has almost no effect on oxidation, but increases the consumption of hydroxide.

The proposed method makes it possible to increase the reliability of the operation of electric arc furnaces while reducing the consumption of electrodes and to speed up the process of applying a protective coating.

Claims (2)

1. A method of protecting a graphite electrode from oxidation by supplying a protective medium containing an antioxidant component during the operation of an electric furnace to the side surface of the electrode, characterized in that the protective medium is supplied in the form of an aqueous suspension containing 10-12 wt. % of the antioxidant component in the form of active magnesium hydroxide, through a spray water-cooling ring to form a protective coating with a thickness of 0.2-0.4 mm. 2. A method according to claim 1, characterized in that the protective medium is applied below the contact assembly of the electrode, and the spray water cooling ring is attached at a fixed height from the surface of the furnace.

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