ABOUT INFLUENCE OF FACTIOUS COMPOSITION OF CHARGE MATERIALS AND MODES OF PRESSING ON HIGH-QUALITY INDEXES OF INTERMEDIATE PRODUCT OF MAGNESIA REFRACTORIES

Abstract

The development of the refractory industry in the field of new generation magnesia refractories is possible on the basis of a deep scientific study of the physicochemical mechanics and petrology of the formation processes of this type of refractories. Improving the quality of magnesia refractories begins with an increase in the content of magnesium oxide, an increase in the size of periclase crystals and the density of periclase powders. The effect of the fractional composition of charge materials, as well as pressure and holding time during pressing, on the properties of a semi-finished product of magnesia refractories was investigated. The study of fused magnesite powder was performed on laboratory cylinder samples. The optimal grain composition was selected on the basis of theoretical considerations that the densest packing is reached in a ratio of 7:3. To moisten the mixture, an aqueous solution of technical lignosulfonate was used. The powders were mixed in a laboratory mixer (mass moisture 2,2–2,4%) to form their most rational coagulation structure. The porosity of the products depends not only on the forces and conditions of the molding, but also is determined by the ratio of grain sizes of the mass. The production of refractory samples was carried out by the method of semi-dry pressing on a laboratory hydraulic press PSU-250 with a pressing force of 2500 KН. A slightly moistened powder mass is loaded into the mold, which the press compresses in the vertical direction. After completion of the pressing process, the product (raw) is pushed out of the mold and the pressing cycle is repeated. There are two ways to stabilize the properties of raw materials in hydraulic presses. When pressing refractory masses in the pressure range of 10-200 MPa, the relationship between the density of the raw material and the pressing pressure is expressed by A.S. Berezhny formula. The compressed air contained in the mass, expanding, creates tensile forces and forms tears in the raw material. Therefore, it is advisable to remove air from the mass, which occurs during a pause at the end of pressing. The low strength of the raw material after pressing is due to the presence of air shells around each grain, which are removed with great difficulty during pressing. The decrease in the porosity of the semi-finished product during pressing has a positive effect on the exposure time at maximum pressure.