RU2109073C1 - Method of metal melting in dc arc furnace - Google Patents

Abstract

FIELD: electrothermics, in particular, DC arc and plasmarc furnaces. SUBSTANCE: method includes loading of a part of charge of next heat, just before tapping of melt from furnace, onto bottom electrodes through melt. Charge contains materials satisfying the conditions of formation of contact between charge and bottom electrodes by chemical composition, material sizes and quantities and having no easily oxidizing materials. It is desirable to supply a part of charge of next heat in the amount of 1-3% of the total weight of next heat. EFFECT: provision of melting of complex alloys in DC arc and plasmarc furnaces with reliable operation of bottom electrodes. 2 cl

Description

 The invention relates to the field of electrometallurgy and can be used in arc and plasma direct current furnaces.

 Known methods of melting in DC arc furnaces, in which a charge is loaded into the furnace, an electric arc is ignited between the graphitized electrode and the charge, the electric circuit of the power source being closed through a graphitized electrode, a charge, a conductive hearth [1] or hearth electrodes. For reliable electrical contact between the hearth and the charge, a part of the melt of the previous melting (swamp) is left on the hearth, onto which the charge is loaded [1, 2].

 The disadvantage of this method is that directly alloyed steels and alloys cannot be smelted directly in the furnace, since after loading a fresh charge into the swamp and starting a new smelting, the alloying elements of the previous smelting, for example chromium, interact with the oxides usually contained in the charge and are oxidized. Thus, up to 10-25% of alloying elements are lost.

 These disadvantages are absent in the method of operation of the DC arc furnace described in [3] and taken as a prototype. It includes conducting one after another in a direct current arc furnace melts, each of which contains loading the charge, heating and melting it by passing current through the mixture and at least one hearth electrode, completely draining the finished melt from the furnace.

 The prototype has drawbacks in that, after the melt is drained, part of the slag from the melt, which prevents electrical contact between the hearth electrodes and the charge, enters the hearth electrodes. From time to time, arcs light up between the hearth electrodes and the charge, destroying the hearth electrodes and the hearth of the furnace. In some cases, the electric contact of the charge with the hearth electrodes is completely absent. This reduces the reliability of the furnace.

 The basis of the invention was the task of developing a method of melting metal in a DC arc furnace, in which the formation of a slag layer between the hearth electrodes and the charge would be unlikely.

 This is achieved by the fact that in the known method of melting metal in a direct current arc furnace, including loading the charge, heating and melting it with an electric arc while passing current through the charge and at least one hearth electrode, draining the finished melt from the furnace and loading the charge for the next melting according to the invention immediately before draining the melt from the furnace to the hearth electrodes through the melt part of the charge from the charge of the subsequent melting, containing materials that satisfy the conditions for the formation of contact between in charge and hearth electrodes in chemical composition, size and quantity and not containing easily oxidized alloying elements.

 In addition, on the hearth electrodes before draining the melt serves the mixture of the subsequent melting in the amount of 1-3% of the mass of the mixture of the subsequent melting.

 The invention allows for reliable contact between the electrode and the mixture, to increase the reliability of the furnace.

 The invention consists in the following.

 When a portion of the charge is fed through the melt to the hearth electrodes, there is no slag at the junction of the hearth electrode with the melt. It floats on the surface of the melt. The mixture partially sinks in the molten part of the head of the hearth electrode, freezes it and welds to it. A charge slide is formed above the hearth electrode, and the slag, returning after the metal is drained into the furnace, surrounds the hearth electrode and does not fall into the zone of electrical contact. To load the mixture into the melt, 1-3% of the fine mixture, for example, low-carbon iron, which does not contain easily oxidized alloying elements, is selected from the subsequent filling. Filling such a mixture into the finished melt does not in any way affect its chemical composition or temperature, since the mixture does not have time to melt in a short time before discharge. If necessary, the composition of the charge can be specially introduced material that most meets the conditions of the invention in terms of chemical composition, size, quantity.

 The invention is not illustrated by the drawing, since the charge can be arranged in many known ways: manually, through the furnace door, through openings in the arch located above the hearth electrodes, from bunkers, etc. When mastering the melting method, the charge was loaded onto the hearth electrodes using filling cars.

 An example implementation of the method was carried out on a direct current arc furnace with a capacity of 20 tons. Ferrochrome melt with a chromium content of 16% was prepared on the furnace. As the charge, we used metallized pellets with an iron oxide content of about 10%, ferrochrome with a chromium content of 60%, the furnace had two hearth electrodes, to protect which 100-150 kg of soft iron bars were used in the charge, which were fed to the hearth electrodes at 50- 75 kg using a filling machine. Smelting of metal from such a charge can be carried out only with a complete discharge of the melt, since the joint melting of ferrochrome and pellets leads to a large loss of chromium. The application of the invention allowed to completely drain the metal and provide good contact of the bottom electrodes with the charge when returning to the furnace after draining a large amount of slag and loading 16 tons of metallized pellets into the furnace. In the process of melting, iron oxides were reduced with carbon, and ferrochrome was loaded into the deoxidized bath. After melting and heating the metal, soft iron bars were loaded onto the hearth electrodes and the metal was completely drained immediately without slag. Slag contains a certain amount of ferrochrome oxides, which are reduced with carbon. The absorption of chromium was about 100%. Such a process was only possible using the claimed invention.

Literature
1. Okorokov G.N., Donets A.I. et al. "Heating became a direct current discharge at a baking plant." 1 N 0038920X Steel, N 5, 1994, p. 38.

 2. Shalimov A.G. "Current trends in the use of direct current electric furnaces for steelmaking abroad." 1 N 0038-9201 Steel, N 5, 1994, p. 40-42.

 3. Zakomarkin M.K. Malinovsky V.S., Lipovetsky M.M. "DC steelmaking furnace with a capacity of 25 tons at Izhstal Production Association. I N 0038-920X, Steel, N 4, 1991.

Claims (2)

 1. A method of melting metal in a direct current arc furnace, including loading the charge, heating it and melting it with an electric arc while passing current through the charge and at least one hearth electrode, draining the finished melt from the furnace and loading the charge for the next melting, characterized in that immediately before the melt is discharged from the furnace to the hearth electrodes, a part of the charge from the charge of the subsequent melting is fed through the melt, containing materials that satisfy the conditions for the formation of contact between the charge and the hearth of the electrode mi by chemical composition, size, quantity and not containing easily oxidized alloying elements.  2. The method according to p. 1, characterized in that on the bottom electrodes before draining the melt serves charge subsequent melting in the amount of 1 to 3 wt.% The charge of the subsequent melting.