RU2271345C1 - Method of manufacturing corundum refractory products - Google Patents

Abstract

FIELD: refractory materials.

SUBSTANCE: invention relates to manufacture of corundum refractory articles based on mullite-corundum binder and used in linings of heat assemblies employed in variant industry fields. Method of invention comprises preparation of blend by way of moistening grainy corundum constituent with suspension of activating mullite-forming additive in industrial-grade lignosulfonate aqueous solution followed by mixing with finely ground corundum constituent, formation of articles from thus prepared blend, drying thereof, and firing at 1200-1500°C. Activating mullite-forming additive is finely ground silica/alumina mixture in eutectic weight ratio 94.5/5.5, respectively, used in amount 2-4% of the weight of total content of corundum constituents.

EFFECT: reduced power consumption on production of corundum refractory products due to lowered (by 200-500°C) firing temperature and reduced refuse.

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Description

The invention relates to the refractory industry, and in particular to a method for the manufacture of corundum refractory products based on a mullite-corundum bond used in the linings of thermal units used in various industries.

A known method of manufacturing corundum refractories, including the preparation of a mixture by mixing granular corundum with a finely ground component containing corundum and activating mullite-forming additives, followed by moistening the mixture with an aqueous solution of technical lignosulfonate, pressing products from the resulting mixture, drying and calcining them at a temperature of 1750 ° C. Moreover, as an activating mullite-forming additives, the mixture contains distensillimanite concentrate and quartz sand in an amount at which the ratio of SiO ₂ : Al ₂ O ₃ in the finely ground part of the charge is 1: 1.67-2.26 (I.I. Kabakova et al. The production of dense heat-resistant corundum refractories for induction channel furnaces // Refractories, 1974, No. 10, p.13-17).

The corundum products obtained in a known manner are characterized by a compressive strength of 79-130 N / mm ² , an open porosity of 9.5-13.3%, heat resistance in the 1300 ° C mode — water 15 heat exchange, the temperature at which deformation begins under a load of 0.2 N / mm ² 1750 ° C.

Products have a structure in which large corundum grains are surrounded by a vitreous shell, and the binder is represented by two phases - corundum and mullite.

The disadvantage of this method is the significant energy consumption for its implementation associated with a high firing temperature of 1750 ° C. In addition, due to the equality of the values of the firing temperature and the temperature of the onset of deformation of the products under load, firing defects in deformation and cracks are inevitable.

Closest to the invention is a method of manufacturing corundum refractory products, including the preparation of a mixture by wetting the granular corundum component with a suspension of an activating mullite-forming additive (clay) in an aqueous solution of technical lignosulfonate, followed by mixing with other components of the mixture, including with finely ground corundum component, molding the products drying and firing them. To moisturize corundum grains in a known method using 7-9 wt.% Suspension, which contains 2-4 wt.% Clay. As a finely ground component, isometric single crystals of aluminum oxide 1-10 μm in size are used, which are successively mixed with the remaining clay in an amount of 1-13 wt.% And an aqueous solution of triethanolamine and methyl cellulose (USSR Author's Certificate No. 1133247, IPC C 04 V 35/10 , publ. 07.09.84).

Products obtained in a known manner have an open porosity of 13-17%, tensile strength in bending 49.9-58.4 N / mm ² , the temperature of the onset of deformation under a load of 1720-1740 ° C.

In the known method, clay is used as an activating mullite-forming additive, the total amount of which in the charge is from 3 to 17 wt.%. As is known, clay contains a large number of fusible impurities that adversely affect the quality of refractory products, in particular, the temperature of the onset of deformation under load decreases.

The two-stage introduction of clay into the mixture in the known method creates the conditions for the formation of mullite both near the grain boundaries and in the binder of the refractory. However, the crystallization of primary mullite proceeds in the presence of a large amount of a liquid phase, caused by impurities, which separates corundum and mullite grains, not allowing crystalline aggregates to strengthen the structure to fully form. To increase the degree of sintering and achieve higher strength corundum refractories in the known method, it is necessary to firing products at a temperature of not lower than 1700 ° C.

High-temperature roasting of corundum products requires large energy costs for the implementation of the method, and is also the reason for the marriage of products resulting from deformation and cracking during firing due to the small difference between the temperature of the onset of deformation under load and the firing temperature.

The invention solves the problem of reducing energy consumption for the production of corundum refractory products by reducing the firing temperature while maintaining the required level of product properties.

The technical result that can be obtained by using the invention is to achieve high strength refractory corundum products at a lower firing temperature, increasing the temperature of the onset of deformation of the products under load, as well as reducing firing defects.

The specified technical result is achieved by the fact that in the method of manufacturing corundum refractory products, including the preparation of the mixture by wetting the granular corundum component with a suspension of an activating mullite-forming additive in an aqueous solution of technical lignosulfonate, followed by mixing with a finely ground corundum component, molding the products from the resulting mixture, and drying them according to the invention in the preparation of the mixture as an activating mullite-forming additives use finely ground mixture silicon oxide and aluminum oxide in a eutectic ratio, wt.%: 94.5 SiO ₂ and 5.5 Al ₂ O ₃ , in an amount equal to 2-4 wt.% of the total content of corundum components, while the products are fired at a temperature 1200-1500 ° C.

The use of an activating mullite-forming additive in the form of a finely ground mixture of silicon and aluminum oxides in a eutectic ratio, when it is introduced directly onto corundum grains, increases the degree and rate of physicochemical processes during the formation of the structure of corundum refractory, which reduces the firing temperature of corundum products.

A low temperature eutectic containing 94.5 SiO ₂ and 5.5 Al ₂ O ₃ has a melting point of 1540 ° C. It is known that in multicomponent systems the temperature of the appearance of the eutectic melt is significantly reduced. In this regard, at a temperature of the order of 1200 ° C, secondary mullite crystallizes at the contacts of corundum grains. Since the amount of the liquid phase is small, mullite crystals form direct bonds with corundum grains, and a strong crystalline frame of corundum products is formed. Depending on the amount of the eutectic mixture, the hardening process increases to a temperature of 1500 ° C.

The choice of the limits of the content of the mixture of eutectic composition is due to the following. A decrease in the amount of the mixture of less than 2 wt.% Of the total amount of corundum components leads to the formation of an insufficient number of direct bonds in the structure of the refractory and, as a consequence, to a decrease in the strength of the products. Exceeding the amount of the mixture by more than 4 wt.% Entails an increase in the amount of secondary mullite and the liquid phase, an excess of which leads to loosening of the structure and a decrease in direct bonds, which also negatively affects the strength of the products.

Firing at temperatures above 1500 ° C is not economically feasible. Lowering the firing temperature below 1200 ° C does not provide the necessary degree of sintering, as evidenced by the insufficient strength of the products.

The firing of corundum refractory products at temperatures 200-500 ° C lower than in the known methods, will significantly reduce the cost of implementing the proposed method.

Thanks to the use of cleaner components in order to activate sintering, compared with clay, the deformation temperature of products under load increased in a smaller amount. At the same time, the interval between the temperature of the deformation of products under load and the temperature of their firing widened, which eliminates the firing marriage for deformation and cracks.

The method according to the invention was carried out as follows. Corundum refractory products were prepared from a mixture, wt.%:

granular electrocorundum, fractions 3-1 mm 35.0 fractions 1-0 mm 36.0 finely ground electrocorundum, fractions less than 0.09 mm 29.0 fine mixture of silicon and aluminum oxides in eutectic ratio, wt.%: 94.5 SiO ₂ and 5.5 Al ₂ O ₃ , fractions less than 0.09 mm 2.0-4.0 (over 100%) aqueous solution of technical lignosulfonate density 1.18 g / cm ³ 3.9-4.5 (in excess of 100%).

Initially, a suspension of the indicated finely ground mixture of oxides in an aqueous solution of a technical lignosulfonate technical was prepared, which was thoroughly mixed. The resulting suspension was moistened with granular corundum, after which a finely ground corundum component was introduced and mixed again.

The products were molded at a pressing pressure of 70 N / mm ² , dried and calcined at temperatures of 1200, 1400 and 1500 ° C. The exposure time at the final temperature was 6 hours.

After firing, products were inspected in order to identify firing defects. As a result of inspection, the firing marriage for deformations and cracks was not found.

Physico-ceramic properties of corundum refractories were determined on the samples according to existing GOSTs and methods. Property indicators are given in the table.

The table shows that the products made according to the invention have a sufficiently high strength (more than 50 N / mm ² ) at temperatures of 1200, 1400 and 1500 ° C. High strength indicates sintering of products. Obtained in a known manner, products at the same firing temperatures have low strength (less than 30 N / mm ² ), which indicates their insufficient sintering and the need to further increase the firing temperature. The temperature of the onset of deformation under load in products manufactured by the proposed method is 10-20 ° C higher than in products obtained by the prototype method. The remaining properties satisfy the requirements of TU 14-8-556-87 * (* Reference. Refractory products, materials and raw materials. - M .: Metallurgy, 1990. p.63), presented to corundum products of a similar composition containing at least 90% Al ₂ About ₃ . The marriage rate is reduced by 9-11%.

Thus, the proposed method allows to reduce energy consumption for the production of corundum refractories by reducing their firing temperature by 200-500 ° C while maintaining the required level of properties for corundum refractories, as well as to increase the temperature of deformation under load and to exclude marriage of firing products.

* bending σ

Claims (1)

A method of manufacturing corundum refractory products, including the preparation of a mixture by moistening a granular corundum component with a suspension of an activating mullite-forming additive in an aqueous solution of a technical lignosulfonate, followed by mixing with a finely ground corundum component, molding products from the resulting mixture, drying and firing them, characterized in that in preparation As an activating mullite-forming additive, a finely ground mixture of silicon and aluminum oxides is used in a eutectic ratio ., and weight%: 94,5 SiO ₂ and 5,5 Al ₂ O ₃ in an amount of 2-4% by weight of the total content of corundum components, wherein calcination is carried out at product temperatures 1200-1500 ° C..