SU833367A1 - Mixture for heat insulation of metal surface at steel casting - Google Patents

Description

 (54) MIXTURE FOR THERMAL INSULATION OF A METAL MIRROR DURING STEEL CASTING

The invention relates to ferrous metallurgy, in particular to compositions of the mixtures used for thermal insulation of a metal mirror during steel casting. In domestic practice, three main groups of heat insulating mixtures are used: on the basis of ash, expanded or crude vermiculite, and also expanded perlite. The ash of thermal power plants as a heat insulating material is inferior to expanded perlite and vermiculite, since its bulk weight is 5-10 times more and, accordingly, more heat absorption by the mixture. The best grades of expanded vermiculite by volume weight (80–120 kg /) and thermal conductivity at 500 ° C (0.140, 15 kcal / mh degree) approach the expanded perlite, but melt too quickly at the interface with the liquid metal. The practice confirms the advantages of the mixtures on the basis of perlite, especially when using the downward-wided molds with heat-insulated plates. In these conditions, saving on the head trim is achieved only when using the perlite graph 1% mixture. A mixture containing 4-7 vol.% Amorphous graphite is known, the rest is expanded perlite 2. However, at such a low content of graphite, the heat-insulating properties of the mixture are low: the mixture is sintered at high temperature, a deep shrinkage shell is formed in the ingot. Also known is a mixture containing amorphous graft, silica and expanded perlite g. The addition of silica does not significantly alter the thermal insulation properties of the perlite-graphite mixture, since the main component of perlite is silica, and therefore the introduction of an additive of silica is equivalent to the use of heavier grades of perlite, which does not increase the thermal insulation mixtures. In the factories of the USSR, a heat-insulating mixture based on expanded perlite and ground coal, mainly anthracite, is used. The heat-insulating capacity of this mixture needs substantial improvement. Closest to the proposed technical essence and the achieved result is a mixture for thermal insulation of a metal mirror during steel casting, containing 10–20% by volume of carbon-containing additives, namely amorphous graphite and 80–90% by volume of expanded pearlite Z. The mixture is characterized by a significant removal of fine fractions of perlite when the mixture is supplied to the mirror of a liquid metal, as well as by the gradual burnout of graphite and, as a result, by the sedimentation of the mixture. On large ingots (more than 10 tons), until the end of metal crystallization, the thickness of the mixture layer decreases by 30-50%, which noticeably reduces its effectiveness. Since the decrease in the thickness of the layer of the mixture proceeds slowly, it does not affect the quality of small weights, but negatively affects the quality of large ingots, which crystallization ends 2.5-3.0 hours after the metal is filled into molds. The study of a perlite-graphite mixture with 12 vol.% Graphite under a binocular microscope (magnified 10 to 60 times) shows that the angular mirrors of the perlite are shaped like a polyhedron, approaching a sphere, with only a small fraction of graphite plates sticking on the verge of perlite grains, the rest are located between them. At the same time, the voids between the pearlite grains, which are 40–50% of the volume of the mixture, are only partly filled with graphite. This is due to the gas permeability of the mixture, the gradual burnout of graphite on the metal mirror and the fusion of pearlite grains that are not separated by more graphite, which leads to a shrinking of the heat insulating properties. The purpose of the invention is to improve the heat transfer properties of the mixture and reduce the head trimming of the ingots. The goal is achieved by the fact that the mixture for thermal insulation of a metal mirror during casting with tat, including expanded perlite and carbon-containing additives, contains amorphous graphite and thermoanthracite as a carbon-containing additive in the following ratio of ingredients:% amorphous graphite 4-6 T er MO anthraxit 10-12 Expanded perliteEverything else. In addition, the mixture contains thermoanthracite with a grain size of 0.2-0.4 parts of the grain size of the exfoliated perlite. The choice of thermoanthracite is determined by the shape of its particles, which, like that of perlite, approaches spherical, and its inertness relative to the oxygen of the air (thermoanthracite burns in a stream of oxygen at a temperature not less than), unlike graphite, which particles with a small thickness relative to to the volume they have a large surface, while thermoanthracite with the same volume of grain has a surface many times smaller, which, in turn, prevents the oxidation of thermoanthracite. The required fractional composition of thermoanthracite was established when studying the structure of mixtures under a binocular microscope. For dense packing of the particles of the mixture (the main condition for its stability and reduction of the drift removal), the size of the thermoanthracite particle located inside the cube is 0.4 diameters of the perlite particle, and if it is located inside a tetrastra, the tops of which are Perlite grains are about 0.2 of a diameter of perlite particles. Experiments have shown that with a larger fraction of thermoanthracite, the mixture loosens, while the smaller fraction becomes non-uniform, since thermoanthracite accumulates in the lower layers of the mixture. At the same time, thermoanthracite cannot completely replace graphite, since thermoanthracite particles, in contrast to amorphous graphite, do not adhere to the surface of pearlite grains. When the content of amorphous graphite and thermoanthracite is below the lower limits, sintering of the mixture on the ingot mirror and deterioration due to its heat insulating properties are observed, and when the content of the above ingredients is above the upper limits, there is no significant improvement in the heat insulating properties, and the danger of carburizing the ingots increases. In tab. I shows the proposed and known fs mixtures compositions. Expanded perlite with a saturated weight of 60 kg / m, anthracite fines MO fines (subjected to crushing and amorphous graphite of Krasnorsky place of birth, are used as starting materials. Fractional composition of starting materials, rials,%: -. Grain size, mm 10 Exfoliated Ter perlite More than 630 629-500 499-400 399-315 314-250 249-200 199-160 159-125 Less than 125 Fractional composition of graphite of such and thermoanthracite To test the stability of mixtures in relation to specimen and burnout, their carbon-containing components Pour into a crucible layer 50 m thick and subjected to calcination in silicate The electric furnace at 1180 C for 1 hour and 10 minutes, the results of the experiments are given in Table 2. Here are the results obtained using the proposed and known mixtures for insulating the metal in the profit of 50 kg ingots (after filling out

Amorphous graphite 4 Thermoanthracite 10 Perlite expelled 86 ant cit

Table I

12

6 12 82

88 SIC liquid steel in-profit pristivuyut 500 cm mixture). The results of the calcination of the mixtures in the furnace when they heat the metal in profit are generally identical. Mixes I and 2 do not sinter when calcined in the profit of the ingot, which determines their improved thermal insulation properties and, as a result, obtaining the minimum depth of the shrinkage shell (34-35 mm). As shown by studies of the structure of mixtures I and 2 (after exposure to high temperatures)) under a binocular microscope, 4-6.% Of graphite is enough to deposit graphite plates on the surface of pearlite grains, and 10-12% by volume of anthrathic anthracite provide compaction of the mixture and prevent the penetration of its oxygen in the air. The prevention of the oxidation of the carbon-containing component and the associated lack of sintering of the mixture is the main condition for improving the heat-insulating properties of the mixture when insulating large ingots. This condition is achieved with the use of the proposed heat insulating mixture. Due to the increase in the heat insulating properties of the proposed mixture, a reduction in the head cut of ingots is observed by 1-2%, the consumption of expensive and scarce graphite is reduced by half, and the discharge of the pier in the atmosphere of the workshop is reduced. It is preferable to use pre; lagged mixture for insulating the profits of large ingots (weighing more than 10 tons).

not an ingot

Depth of the Shrinking Invention Formula

Claims (1)

1. A mixture for thermally insulating a metal mirror during steel casting, including expanded perlite and a carbon-containing additive, due to the fact that, in order to reduce the head trim of the ingots, it contains amorphous and thermoanthracite as a carbon-containing additive the following ratio of ingredients, vol.%: Amorphous graphiteA-6 Thermoanthracite 10-12 Expanded perlite 2 ,. The mixture according to claim 1, characterized in that it contains thermo. Table 2 anthracite with a grain size of 0.2-0.4 parts of a grain size of expanded perlite. Sources of information accounted for in the examination 1, Steel, 1972, No. 10, p. 901-903 2, USSR Author's Certificate No. 589067, cl. In 22D 7/10, 1976. 3, USSR Author's Certificate No. 470354, cl. B 22D 7/10, 1974. 4, Technological instructions for steel casting. Makeevka, metallurgical plant them. CM. Kirov, 1975. 5, USSR Author's Certificate No. 348288, cl. In 22 1E 27/06, 1970.