RU2149190C1 - Method of preparing charge material for metallurgical conversion - Google Patents

Abstract

FIELD: ferrous metallurgy, particularly, preparation of iron charge for steel melting in electric arc furnaces. SUBSTANCE: method includes preliminary filling of charging box of casting machine with filler, subsequent pouring on filler of liquid iron and action on filler with force to overcome buoyancy force. Filler is used in the form of solid additives possessing magnetic properties. Solid additives are acted upon just after pouring of liquid iron with sign-varying, alternating or constant magnetic field for 1-6 s with intensity of magnetic field within 0.01-50 T. As a result, ingots of charge material of stable composition is produced for metallurgical conversion. EFFECT: higher technical-and-economic indices of steel melting process. 3 tbl

Description

 The invention relates to ferrous metallurgy, and in particular to the production of metal smelting for steelmaking in electric arc furnaces.

 A known method of producing a semi-finished product for a metallurgical redistribution in the form of a billet comprising preloading iron ore pellets into the molds of a casting machine and then pouring them with molten cast iron (a.s. N 985063 - analog). The disadvantage of this method is the uneven distribution of pellets, especially in molds with ingots weighing up to 18-23 kg

 There is also a method of producing a charge for electric melting, including the formation of a workpiece from metallized pellets and a weighting additive, in which the workpiece is formed by filling a mold pre-filled with metallized pellets, molten iron in an amount of 0.8-8.0 kg per 1 kg of pellets (a. S. N 805634, C 22 B 1/00 - prototype). When pellets are filled with 25-30% of the working volume of the trough, the latter are in the upper part of the ingot, which leads to the loss of the pellets and to an unstable composition of the resulting blanks, to obtain a semi-finished product with a high density, approaching a heavy scrap. The use of such a semi-finished product in electric furnaces can cause the formation of a dense layer of a metal charge, which has a reduced melting rate and limits the possibility of intensifying the operation of powerful electric furnaces, which ultimately negatively affects the furnace performance and the quality of the smelted steel, as well as reducing the yield of the semi-finished product.

 The closest technical solution is a method for producing a semi-finished product for a metallurgical redistribution, includes its formation from a solid filler and a liquid iron-carbon alloy. The semifinished product is formed by loading a solid filler onto the surface of a liquid iron-carbon alloy pre-cast into a mold and immersing it in the liquid phase under the influence of a force exceeding the lifting Archimedean force by at least 5%. As a solid filler, oxidizing agents are used with the total amount of oxygen necessary for the oxidation of 5-95% carbon and the complete oxidation of the remaining components with an oxygen affinity greater than that of carbon (prototype patent No. 2075516, C 21 C 5/52, 5 / 04 and also C 22 B 1/00, filing date 04.03.94).

Upon receipt of the charge for electric melting according to the prototype, it occurs that the pellets in the trough volume are distributed unevenly due to the apparent density of cast iron and pellets (8 g / cm ³ and 3.0-3.5 g / cm ^3, respectively).

 The upper part of the ingot contains very little cast iron and a lot of pellets; the lower part of the ingot, on the contrary, consists almost entirely of cast iron and almost does not contain pellets. In the upper part of the ingot, the pellets are very weakly bonded by cast iron and when the ingot falls from the filling machine onto the railway platform, the pellets separate from the ingot and form a talus that is non-magnetic and does not load with the ingots during loading. With subsequent overloads, an additional scree forms again, which with further redistribution leads to a deterioration in the technical and economic indicators of the process. As a result, ingots contain insufficient amount of oxygen introduced by pellets for oxidation of pig iron impurities, and the oxidation period of steel smelting in electric furnaces increases by 10-15%.

 When the pellets are filled with pellets in the aforementioned manner, this material is spilled outside the pellet limits of about 20-30%, and the distribution of pellets over the cross-section of the ingot occurs unevenly, which leads to significant current surges during melting in electric furnaces. In addition, it is quite difficult to implement this method.

 The technical task is to ensure the stability of the composition of the charge material and improve the technical and economic indicators of the process of steelmaking in electric arc furnaces.

 The technical result is achieved in that in a method for producing a charge material for a metallurgical redistribution, which includes pre-filling the molds of a filling machine with a filler, its subsequent pouring with molten cast iron and exposure of the filler to a force that overcomes the Archimedean force, in which solid additives having magnetic properties, and the effect on solid additives is carried out immediately after pouring liquid cast iron alternating, variable or constant a magnetic field for 1-6 seconds with a magnetic field providing a strength in the range of 0.01-50 T.

 Solid additives (filler) with magnetic properties can be obtained in two ways: without firing method and using firing.

 Such materials are obtained in the form of pellets or briquettes. The composition of the initial charge includes materials with magnetic properties, for example, iron ore concentrates, firing of magnetic enrichment, waste from the metal industry, etc.

Also, binders, which can be of both organic and inorganic origin, are included in the initial charge. The main requirements for binders are:
lack of content of harmful elements in their composition for subsequent redistribution;
the binders should provide a filler with a strength of 5-20 kg / okt., which is quite enough so that there is no destruction during transportation and loading.

 The third component of the charge is various additives, fluxes, alloying materials, etc., required for further processing.

 The calcination method allows to expand the range of materials used that do not have magnetic properties, but containing iron oxides. The provision of magnetic properties is carried out during the firing process in a reducing or oxidizing atmosphere.

 The firing method allows to obtain a cleaner filler due to a significant reduction in the consumption of binders.

 Fillers with magnetic properties were obtained in two ways: non-firing method and using firing. Fillers in the form of pellets were obtained on a laboratory granulator, and briquettes on a manual press. The firing was carried out in a laboratory furnace with a variable atmosphere.

 Upon receipt of non-calcined pellets and briquettes, iron ore concentrate and binders - lime were used.

 After receiving the briquettes and pellets were kept in the air for 6-10 days to obtain the necessary strength properties.

 Upon receipt of the filler by roasting, iron ore, flux and a bentonite were used. The provision of magnetic properties was carried out during firing in a reducing atmosphere. The chemical composition of the materials used is shown in table 1.

 The proposed method does not change the casting technology of cast iron and can be used on existing conveyor filling machines with technical improvements.

 This is as follows. The dosing device releases a strictly defined portion of the filler into the mold of the casting conveyor, then liquid cast iron is poured to fill the remaining volume of the mold. When cast iron is poured, a magnetic field (alternating, alternating or constant) is applied until the cast iron in the mold is hardened. The exposure time of the magnetic field in the proposed method can vary from 1 to 6 seconds, this is usually sufficient to complete the transition of liquid iron to solid-liquid or solid in the mold. In addition, the preform obtained in this way will already approach the place of intensive cooling with water. And the force of the magnetic field acting on the filler was calculated from the condition of rigid retention of this filler inside molten iron until it becomes a solid state. Magnetic induction is 0.01-50 T, which is confirmed experimentally. Such a run of magnetic induction is necessary in order to compensate for the volumetric, weight and other factors of the filler itself. In addition, the geometric dimensions of the obtained filler may vary due to the technological features of the process for their preparation, as well as the composition of the filler may be heterogeneous.

 To confirm the proposed method, experiments were conducted. A few molds were taken and permanent and variable magnets made. The filler in the mold was filled in portions manually, and under the mold were electric magnets. When cast iron was poured into the mold, the electric magnet began to work and kept the filler in liquid cast iron. The operating time of the magnets ranged from 1 to 6 seconds. Then the electric current was turned off and water was supplied for cooling. All time intervals of the proposed method in the experiments were the same as on a real casting conveyor. In this way, about 12.5 tons of charge material was obtained, which, in its external and internal structure, met all the requirements proposed for it. The experiments showed that, if desired, the structure of the charge material can be varied over a fairly wide range.

 Conducting pilot melts for remelting charge material in the steelmaking workshop of the joint venture AK Tulachermet. The charge material was used in the smelting of steel 45 in a 10-ton electric arc furnace with a main lining and a transformer capacity of 4 MW. A total of 4 experimental swimming trunks. All charge material for one melt was fed into the furnace with three filling baskets opening from below. The charge material was loaded together with small scrap into the upper part of the first and second filling baskets, and lime at their bottom. Only scrap metal was loaded into the third basket. The amount of charge materials used in the filling during pilot melting is shown in table 2.

 The charge from the first filling basket was loaded onto a “swamp”, consisting of a small amount of metal (0.5-1 t) and slag remaining from the previous smelting, and the electric furnace was turned on. In the course of melting, the second and third charge baskets were made to charge the base twice. After the formation of a common melting crater under the electrodes, an active boiling of the bath was observed with the formation of foamy slag shielding electric arcs.

After obtaining the desired chemical composition in the furnace and at a metal bath temperature of 1650-1680 ^o C, the metal was poured into a steel pouring ladle and transferred to VMNLZ.

 Table 2 shows some indicators of the experienced swimming trunks.

The analysis of the obtained experimental data when replacing steel scrap in the charge of an electric furnace with up to 30% of charge material allows us to draw the following conclusions:
due to the exact predetermined weight ratio between cast iron and filler in the charge material, to obtain the necessary carbon content in the furnace bath after complete melting;
due to the increased density of the charge material compared to scrap metal, to increase the productivity of the unit;
combine the melting process with the oxidative period of the melting, i.e. reduce the time spent by the metal in the furnace;
through active dosing during the melting process to improve the quality of the metal.

Claims (1)

 A method of producing a charge material for a metallurgical redistribution, including pre-filling the molds of a filling machine with a filler, its subsequent pouring with molten cast iron, and the force acting on the filler to overcome the Archimedean force, characterized in that solid additives with magnetic properties are used as filler, and the effect on solid additives are carried out immediately after pouring liquid cast iron with an alternating, alternating or constant magnetic field for 1 to 6 s with strength of the magnetic field that provides power in a range of 0.01 - 50 T.

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