SU1016908A1 - Method for preparing heat insulating mixture for steel casting - Google Patents

Abstract

A METHOD FOR OBTAINING A TESHLYIZOLATING MIXTURE FOR CASTING THE EXPERIENCE, which consists in firing wastes of starch pathogen production (Agrimus) with an oxygen excess factor of 0.50-0.92 and a temperature of 175-750 C.

Description

Co-11 The invention relates to ferrous metallurgy, and in particular to methods for the partial shading of mixtures for steel casting. There are known methods for producing heat insulating mixtures for steel casting, which consist in the following: raw materials: combustible (powdered aluminum, charcoal, peat graphite, etc.), oxidizers (nitrate, carbonates; oxides, etc.), refractory fillers (perlite , vermiculite aluminous materials, fireclay, forces rolls, etc., catalysts (fluorides, oxides, etc.) are thoroughly crushed and in a powdery form with observance of safety measures are mixed and dried lj, 2J. The main disadvantage of the known methods is the high cost of mixtures, which is obtained from the use of expensive materials (aluminum, graphite, etc.) and the need to use special equipment for grinding the mixing and drying of the starting components in an explosion-proof design. In addition, the lack of methods. This is a limited raw material base of the outgoing components and, accordingly, a shortage of materials: graphite5 fluorspar, powdered aluminum, etc. The method for producing a heat insulating mixture for casting steel according to the invention consists in burning the waste of starch and steel production (Agrimus) at an oxygen excess factor of 0.500, 92 and a temperature of 175-750 ° C. Agrimus is a waste product of starch and furfural from vegetable raw materials (corn kernels, sunflower seeds, buckwheat and rice husks, pulp) and contains 24–26% ash, and steel – hydrolytic lignin. The size of particles of agrimus is less than 1 mm. In the process of burning agrmus by the invented method, carbon black — carbon black — is derived from the lignin carbohydrate. Due to the lack of oxygen to completely burn the lignin in the agrimus, after firing it produces a mixture consisting of ash, soot and lignin. At the same time, the firing temperature should not be lower than 175 ° C - the temperature during the lignin flame, since at a temperature of less than 175 ° C, the lignin will not burn 8 and, therefore, there will not be any black carbon. At the same time, the firing temperature should be no higher than the temperature at which carbon black begins to burn. At temperatures above 750 ° C, secondary soot formation processes are possible, among which carbon black carbonation is particularly undesirable, and soot interaction with water vapor. . The optimum firing temperature is 500 ° C, since at this temperature the agrimus lignin self-ignites and the CO / CO ratio is less than 0.1. Agrimus roasting parameters, which allow to obtain mixtures suitable for use in steel casting, are given in the table. As follows from the table, roasting agrimus at temperatures of 175–750 ° C and oxygen excess coefficients of ei 0.50–0.92 allows to obtain mixtures containing 40–80% aoly, 15–30% carbon black, 5–30% volatile ( hydrolyzed lignin), which can be used in steel casting. The limits of the oxygen excess factor Oh are chosen so that the content of ash and soot obtained during the roasting of agrimus corresponds to their content in the ash-graphite mixtures used in practice. The mixture obtained from roasting agrimus, consisting of ash, soot and volatile (hydrolytic lignin), is a ready-made mixture for steel casting, which can be used both to isolate the metal mirror during siphon steel, and to insulate the profitable part of the ingot when siphon casting and casting on top. The calorific value of the mixture depends on the volatile content and can vary from 0 to 4000 kcal / kg (the calorific value of pure agrimus). Since the mixture obtained by the proposed method may contain different amounts of ash, soot and volatile and, accordingly, have different slag-forming, lubricating. and exothermic properties, the parameters of the method of obtaining mixtures are selected on the basis of the goal of ensuring maximum efficiency in the application of mixtures for a specific purpose. For example, when casting large (12–18 t) ingots from above, it is desirable not only to reduce the thermal losses of the ingot with the help of the heat insulating mixture but also to give an additional amount of heat to the profitable part of the ingot. In this case, the oxygen excess factor is chosen to be 0.5 from the condition of obtaining the maximum amount of volatiles in the mixture, ensuring its eco-thermality. In siphon steel casting, it is desirable to have a relatively high ash content, since part of it should melt and fill the gap between the ingot and the mold, and part of it should provide heat insulation of the ingot. It is impractical to have a higher volatile content since all the same, these volatiles, under conditions of oxygen deficiency, do not completely burn out in the intrasubular body, but will be consumed in the form of smoke. This condition is satisfied by the method of obtaining mixtures at about 0.92. By varying the firing temperature, the required amount of soot is provided, when i the maximum and at the minimum amount of soot is obtained. U) and the oxygen excess factor of 0 less than 0.5%, the soot content during roasting is higher than 30%, which creates the danger of carbonization of the metal of low carbon steel grades. The content of soot is 15% corresponds to, 92, with Ct. More than 0.92 is not effective protecting the ash in the resulting mixture from melting upon contact with the liquid metal, since the soot content will be less than 15%. The optimal composition of the mixture: 50-60% ash, 20-25% soot and 20-25% volatile corresponds to 6 0.7, the temperature . firing 500 ° C. Optimum values of C6 0.7, C allow you to simultaneously obtain both siphon mixtures for fine and therefore stronger calcined fraction, and the mixtures for casting are superlarge and therefore weaker under the same conditions the calcined fraction of agrimus mixtures. Consequently, it is sufficient to sow by fraction of the mixture obtained under optimal conditions in order to produce mixtures of two kinds in one process. The mixtures obtained by the proposed method showed extremely high thermal insulation properties during testing. For example, with a mixture layer on the metal mirror, for 40 minutes from the end of the casting, the surface temperature of the mixture did not exceed, while its lower surface was in contact with the liquid metal. The thermal conductivity coefficient under these conditions was 0.05 W / m-grad, the thermal conductivity coefficient of the perlite-graphite mixture was 0.23-0.32, and the ash-graphite mixture was 0.52-0.57 W / m-grad; The heat capacity of the mixture is determined by the heat capacity of its components and is 0.1-0.2 kcal / kg. K depending on the specific composition. In the practical use of the method according to the invention, it is advisable to use cyclone type aggremars, in which the agrimus is fed from above and the oxidizer on the side. Since a large amount of heat — 4000 kcl / kg — is generated during the combustion of agrimus with long-term storage, no additional heat sources are required. The temperature in the combustion chamber is regulated by the water cooling of the cyclone shell. Cooling of the mixture after the combustion chamber to a temperature of 170 ° C, at which the ignition of the mixture is prevented, is produced by water vapor. Example 1. An agrimus is fed to a cyclone combustion chamber at a rate of 25 kg / min, oxygen at 7 or air at 35 m / min. The temperature in the combustion chamber is 175 s, the calcining time of the agrimus particles. corresponds to the time-their fall and is 15-20 seconds. The resulting composition of the mixture,%: ash 40, soot 30, lignin 30. Example 2. Cyclone combustion chamber: 50 g / min of agrimus is supplied, 90 m / min of air is supplied through side burners. The temperature in the combustion chamber is 500 s, the firing time of the agrimus particles is 5-8 s. The composition of the resulting rmesi. %: ash 55, 21, lignin 24 .. Example Z. In a cyclone installation, agrimus is burned at a flow rate of 100 kg / min, air flow is 250 m / min at a temperature of firing time of agri5 particles of Musa 3-5 s. The composition of the resulting mixture,%: ash 80, soot 15, lignin 5 The prepared mixture is packaged in bags for delivery directly to the casting department of the steelmaking shop. Upon receipt of heat-insulating mixtures by the proposed method, an increase in the efficiency of their use in casting steel and a reduction in cost are achieved. 1. In the mixtures obtained by the proposed method, soot is formed as a carbonaceous substance, which is superior in its protective lubricating properties to other carbonaceous materials. 2, The invented method provides the best refractory ash of the ash with carbonaceous material in comparison with limestone methods, since soot is formed as a result of thermal decomposition of carbon directly on the surface of each particle. It does not need an excess of soot. 3. It is eliminated the need to grind the mixtures obtained by the proposed method, since both the large and small particles of Agrimus crumble to the same extent from the surface with soot and, therefore, the fractional composition of the mixtures is selected from the point of view of their most effective use, and not according to the condition of production of the mixtures. This significantly increases the efficiency of application of the mixtures, especially when casting drill 8, where the technological limitations on the fractional composition are significantly lower than for siphon casting of steel. Preparation of ash-graphite, ash-coke, ash-coal, perlite-graphite, etc. mixtures in the usual way require, firstly, an excess of carbonaceous material, secondly, thorough grinding of the starting components. Consequently, the advantages of the mixtures obtained by the proposed method include the reduction of dustiness and the improvement of working conditions during their preparation and use. As a result of applying the proposed method, the number of flaws, cracks and captivity on the ingot is reduced by 3 times, which reduces the amount of stripping before the next rolling. The resulting heat insulating mixtures are fed into the mold in the same way as all other mixtures, i.e. in bags to the bottom of the mold or hung at a distance of 100,250 mm from its lower section during siphon casting of steel. When casting the mixture from above, they sit down in bags or by pressing from a special device on the metal mirror immediately after ingot casting. The economic effect of this method is due to the difference in the cost of heat-insulating mixtures for casting, which are obtained by known and proposed methods and amounts to 0.37 rubles. . per 1 ton of steel.

175

5-10 20-30

500

5-10 20-30

40 42 47 49

30 30 27 26

30 28 26 25

500

0.7 500

0,9 750

0.92

8 Continued tavshshts

Claims (1)

. A METHOD FOR PRODUCING A HEAT-INSULATING MIXTURE FOR STEEL Pouring, which consists in the burning of starch-waste production waste (agrimus) with an oxygen excess coefficient of 0.50-0.92 and a temperature of 175-750 ° C.