Wear of high-fired periclase-spinel refractories in the roof of a double-bath steel-melting furnace

Conclusions Periclase-spinel products prepared from magnesite powders which are pure in chemical composition and beneficiated Kempirsaisk chromite possess an increased resistance (30% higher than in ordinary periclase-spinel brick) during service in the roof of a double-bath steel-melting furnace, operating with oxygen blow in the bath. Their wear in general occurs as a result of the fusion of the working surface. The mechanism of this wear is explained by the metasomatic processes which lead almost to complete replacement of the periclase and chrome-spinel by ferritic spinels.The increase in the resistance of the experimental periclase—spinel refractories is helped by the structure with the direct bond between the grains which retards the access of silicates and slags inside the textural elements. This exerts a favorable influence on the change in structure of the refractory during service, especially in the transition zone in which additional sintering and crack formation leading to scaling of the experimental refractory hardly develops.On the basis of the results of the research we recommend that refractory enterprises set up various technological production lines for making periclase-spinel products from pure Satkinsk magnesite powders (94–96% magnesium oxide) and beneficiated Kempirsaisk chromite (59–60% chromium oxide) using high-temperature firing in a tunnel klin. The use of high fired periclase-spinel products with a direct bond between the grains would increase the resistance of the roofs of metallurgical furnaces operating with the use of oxygen and increasing their outputs.Translated from Ogneupory, No. 5, pp. 28–33, May, 1973.     

Production technology of high-density periclase-spinel roof materials

Conclusions High-density periclase-spinel refractories can be produced from a body of magnesite powder containing 94–96% magnesium oxide and Kempirsai chromite by high-pressure molding and high-temperature firing in a tunnel kiln. The product is strong with good thermal stability and high onset temperature of deformation under a load. The structure of the refractory is improved as a result of the formation of a large proportion of direct intergranular bonds between the periclase and spinel.It is planned to produce experimental industrial-scale batches of periclase-spinel roof refractories and to subject them to trials in the roof of open-hearth furnaces in continuous operation.Translated from Ogneupory, No. 8, pp. 39–44, August, 1973.     

Testing porous periclase — Spinel products in the lining of a rotary kiln burning magnesite

Conclusions The life of porous periclase-spinel products in the most badly worn section of the sintering zones of rotary kilns used for firing caustic dust is 50–100% greater than the average life of the lining in this zone made from chrome-magnesite and magnesite-chromite products.The increased wear resistance of the experimental periclase-spinel products is probably explained by the reduction in the rates of zone formation owing to the features of the phase composition and the structure of the refractories, and also the appreciable strength and comparatively low thermal conductivity.It is desirable to use perous periclase-spinel products for lining the sintering zones of rotary kilns used for firing magnesite, mainly in the most badly worn sections having a temporary fused area (skin).Translated from Ogneupory, No. 1, pp. 30–35, January, 1973.     

Magnesia products from powders containing more than 94% MgO

Conclusions Using magnesite powders with large contents of magnesium oxide we obtained high-quality magnesite and periclase-spinel products. Periclase-spinel products obtained from the above powders satisfy the requirements of GOST for the PShSP type of product for the roofs of open-hearth furnaces and electric steel furnaces. Their thermal shock resistance is 7–15 water-heat cycles, compared with 5–7 heat cycles for ordinary periclase-spinel products, which is due to their structural features.Translated from Ogneupory, No. 1, pp. 54–58, January, 1969.     

Magnesite-chromite products from high purity magnesite and chromite

Conclusions Products made from magnesite and chromite with low-impurity oxide concentrations possess better thermal factors than ordinary periclase-spinel refractories: refractoriness under load: 1700°C and above; bending strength at 1300°C 2.5–3 times greater; deformation 3–4 times; and the rate of deformation at steady-state creep is about a half.The periclase-spinel products with low quantities of impurities have an increased thermal-shock resistance, which is achieved by adding small quantities of chromite to the granular part of the batch in combination with the additions made to the dispersed constituent.The products develop a direct bond between the crystals of periclase, i. e., periclase-spinel, in which two types of direct bond exist between the periclase and the spinels: the contact between crystal and crystal, and the contacts in the form of shells and edgings of spinels around the crystals of periclase. In the latter case, the development of a direct bond between the crystals is more complete which is contributed to by the replacement in the silicate part of monticellite by dicalcium silicate.Translated from Ogneupory, No. 2, pp. 32–37, February, 1971.     

Testing refractories containing magnesite — Chromite clinker in the roofs of open-hearth furnaces

Conclusions Roof refractories made using magnesite-chromite clinker obtained from caustic magnesite in the comparative tests had better factors, and a more homogeneous structure than periclase-spinel, and ordinary magnesite-chromite roof refractories. The wear resistance of the roof refractories (in millimeters per heat) made by the proposed technology, using clinker, is 25% higher in average experimental campaigns compared with the three previous campaigns.Translated from Ogneupory, No. 5, pp. 23–27, May, 1971.     

Industrial production of dense powder from Satkinsk magnesite beneficiated by flotation

Conclusions The beneficiation by flotation of Satkinsk magnesites of the fourth grade with fine mutual growth of minerals allows us to obtain from them a product containing (calculated on the calcined substance) 94.0–96.5% MgO, 0.3–0.4% SiO₂, and 1.40–2.87% CaO.A technology was developed for producing dense powder from the magnesite beneficiated by flotation, specifying combined fine grinding of it with caustic magnesite in a tube mill, briqueting on smooth roller presses, and burning the briquet in a rotary kiln.In industrial conditions using the beneficiated (flotation) and briqueted Satkinsk magnesite, firing in a rotary kiln, we obtained high-quality powder with an apparent density of 3.13–3.32 g/cm³, with a developed direct bond in the periclase crystals. The powder of all fractions is homogeneous in chemical composition, does not contain free calcium oxide, and may be used completely without aging for producing magnesite refractories for critical locations in furnaces.Translated from Ogneupory, No. 2, pp. 5–11, February, 1972.     

Characteristics of heat-insulating refractories produced by some foreign companies

Conclusions Studies were made of heat insulating aluminosilicate products produced by certain companies. The articles are divided into four groups. It is found that within the limits of any one group there is a substantial spread in the properties: strength, apparent density, and temperature of deformation.The main form of raw material for producing insulating products is kaolin, including beneficiated kaolin. Out of 22 specimens investigated eight contained no more than 0.64% Fe₂O₃, which is important for the service of the products in reducing atmospheres; the semiacid and kaolin products contained iron oxide varying in the range 1.0–1.5%.The use of pure kaolins and low-ash combustible additives in the production of insulating refractories contributes to the production of refractories with a low concentration of fusible impurities.Translated from Ogneupory, No. 8, pp. 57–59, August, 1972.     

Firing roof refractories by setting products of a single grade

Conclusions A study was made of the firing process in a high-temperature tunnel kiln set with roof refractories of one and two grades. The firing loss when the products were placed in 3–4 rows (on edge) is slight but sharply increases in the two lower rows of the lattice setting using products of a single grade. The setting of the roof refractories over the height should consist of no more than four rows (on edge) which with a kiln channel height of 1.1 m is possible by using a setting of periclase-spinel refractories with an undersetting of chrome-magnesite products.The firing of the roof refractories should be done in a 7-column setting using products of two grades with a column thickness of 0.23 m and a length of 2.6 m.The possibility of using lattice settings in specialized kilns with a low channel height should be considered separately.Translated from Ogneupory, No. 1, pp. 11–19, January, 1971.     

Obtaining fused magnesia-alumina spinel and using it to produce magnesite-spinel roof refractories

Conclusions A method was developed for producing fused spinel which, when used in place of chromite as a component of the charge for basic refractories, yields roof products characterized by enhanced refractoriness under load, and also by low creep at elevated temperatures. This ensures high factors for the other properties. The preliminary testing of the refractories in the roofs of electric-steel melting furnaces demonstrated an increase in their wear resistance by 26–33% compared with the resistance of the currently supplied periclase-spinel refractories, which are used normally in these conditions.Translated from Ogneupory, No. 4, pp. 12–17, April, 1973.     

Production and service-testing of refractories based on flotation-concentrated magnesite

Conclusions Flotation-concentrated magnesite and pure and concentrated chromite were used for producing high-temperature fired magnesite, magnesite-chromite, and periclase-spinel refractories which, compared with ordinary types, contained less silicates and, more direct bonds between the high-refractoriness minerals so that their refractoriness under a load and their thermal strength were higher.In the lining of 100-ton converters for steel, the durability of the experimental magnesite refractory produced from concentrated magnesite and tar-impregnated was 19% better than that of ordinary tarbonded magnesite brick.In the lining of the tuyere zone and of the zone above it in 20-ton and 30-ton converters for copper and nickel, the durability of the experimental magnesite-chromite and periclase-spinel refractories produced from concentrated magnesite and concentrated and pure chromite was 30–35% better than that of ordinary MKhS and PShS type refractories.Translated from Ogneupory, No. 1, pp. 11–15, January, 1976.     

Effects of different particle size of spinel and Y2O3 additive of the periclase-spinel refractory on the sintering densification and corrosion resistance to copper smelting slag

In order to analyze the sintering densification and copper smelting slag corrosion resistance of periclase-spinel refractories, the periclase-spinel refractories were prepared with fused magnesia, magnesia-rich spinel, industrial alumina, and yttrium oxide as the main raw materials. The different particle sizes of spinel in material and with or without Y₂O₃ additive were studied. The study demonstrated that: (1) The different particle sizes of spinel in periclase-spinel refractories can result in different effects. Adding particle spinel to the refractory can improve the strength and corrosion resistance of the periclase-spinel refractories. The addition of spinel and magnesia powders in the matrix resulted in cracks due to the great difference of coefficient of thermal expansion between magnesia and spinel. The reduction in bulk density and strength of the material decreased slag penetration resistance because of its poor sintering properties. While adding the alumina in the matrix can further fill the crack and prevent slag penetration by the volume expansion of in-situ reaction to form spinel. (2) The periclase-spinel refractories can be reacted with Cu slag to form a Mg₂FeO₄ insulating layer as the iron ion becomes oxidized. Adding Y₂O₃ in periclase-spinel refractories can result in grain boundary phase reconstruction, which can promote sintering densification, improve the slag physical infiltration resistance, and improve the chemical corrosion resistance of materials.     

Research in the production of periclase-chromite refractories from beneficiated raw materials

Conclusions Laboratory and technological investigations of periclase-chromite refractories produced from beneficiated starting materials were carried out for the purpose of defining more precisely the required grainsize distribution of the starting components of the mix. The structural characteristics (the nature of the porosity, the development of a fragmented macro- and microstructure, and the formation of a direct intergranular bond) were analyzed in relation to the composition and grain-size distribution of the mix.The process of the formation of direct chrome-spinel-periclase bonds depends primarily on the firing temperature. The degree of the development of direct bonds can be regulated, however, by varying the composition of the mix in addition to which the process can be intensified by adding some of the chromite to the fine-ground part of the mix and increasing the proportion of coarse-grained chromite. An increase in the molding pressure and a decrease in the upper limit of the coarseness of the granular chromite also contribute to the formation of direct bonds.To ensure that the properties of the refractories, more particularly the thermal-shock resistance, are as required and that the standard specifications for the Cr₂O₃ content are met the proportion of the granular chromite in the mix must be 10–15% and that of the fine-ground component 5–10%. It will be necessary to verify the compositions in production conditions and to investigate the durability of the refractories in service.Translated from Ogneupory, No. 7, pp. 30–38, July, 1978.     

The effect of composition of granular and dispersed constituents of magnesite-chromite and periclase-spinel products on their properties and behavior under the action of iron oxides

Conclusions The composition of the dispersed and granular constituents greatly affect the properties of periclase-spinel and magnesite-chromite articles.With the introduction of chromite in the dispersed phase of the articles, the refractoriness under load may be increased by about 70°. The spalling resistance is also increased.Magnesite-chromite articles with the introduction of part of the chromite in the dispersed phase has much less tendency to embrittlement under the action of iron oxides even with a higher total content of chromite than articles containing chromite only in the granular part.With a reduction in the content of chromite in the granular part (so that the total content of chromite in the article does not exceed 25–30%) we can get quite a satisfactory life for the articles in regard to the embrittling action of the iron oxides.The manufacture of refractories of this type may also prove to be favorable with the use of magnesites with a somewhat higher content of calcium oxide.High physicochemical factors for the articles may be obtained by making the periclase-spinel articles with the addition of aluminous materials in the dispersed or granular phase.Comparative study of the properties shows that the periclase-spinel articles compared with the magnesite-chromite (with one and the same composition of dispersed phase) has a higher refractoriness under load, a lower porosity, lower gas permeability, and a much lower tendency to embrittlement under the action of iron oxides, although the spalling resistance of periclase-spinel refractories, as is well known, is lower.Translated from Ogneupory, No. 1, pp. 44–52, January, 1966.     

Some results of the installation of a technology for periclase-spinel refractories

The characteristics of periclase-spinel refractories and mixtures with an additive of synthesized spinel produced by the Magnezit Company are presented. The best refractories are produced from spinel synthesized by block melting and casting into molds and by sintering caustic magnesite and aluminum-containing slag. The possibility of manufacturing spinel-containing mixtures using waste periclase-spinel refractories is considered. Replacement of part of the mixture by a spinel-containing material improves considerably the physicomechanical parameters of the mixture.Translated from Ogneupory i Tekhnicheskaya Keramika, No. 9, pp. 31 – 33, September, 1996.     

Properties of spinels formed in highly fired periclase — Spinel refractories

Conclusions In high-temperature firing of periclase-spinel refractories one of the principal aims of a rational technology is achieved: the formation of spinels of magnochromite composition, with the crystal structure of a normal spinel and a high melting point.In such products the modified chrome spinel relates to magnochromite in composition whilst having the structure of normal spinel. The melting point of the modified chrome spinel exceeds 2100°C. The secondary spinels correspond in composition, or are close to, magnochromite. They have the structure of the mixed spinel with a very low degree of rotation, and a melting point of 2050–2070°C.Translated from Ogneupory, No. 8, pp. 41–44, August, 1972.     

Periglase-spinel refractories based on magnesite powder from caustic dust

Conclusions Periclase-spinel products in whose batch ordinary magnesite powder of fractions 3-1 mm is replaced with powder of the same fraction but obtained by burning caustic magnesite without sintering additives are satisfactory as regards all factors except thermal-shock resistance, and meet the requirements of GOST 10888-64.The resistance and wear of the experimental periclase-spinel products in the roof of an open-hearth furnace are about the same as for ordinary roof magnesite-chromite refractories.Translated from Ogneupory, No.5, pp. 12–13, May, 1970.     

Dynamic method for determining the coefficient of transverse deformation of refractories at high temperatures

Conclusions We developed a direct dynamic method and constructed apparatus for determining the coefficient of transverse deformation of refractory materials.We studied the temperature dependence of the coefficient of transverse deformation of magnesite, dinas, periclase-spinel and high-alumina refractories.Translated from Ogneupory, No. 7, pp. 47–50, July, 1969.     

Improved technology for producing certain magnesite refractories and a statistical method for evaluating their properties

Conclusions As a result of improving the technology for manufacturing certain magnesite refractories we improved their quality and reduced the loss. Comparatively good qualitative factors and enhanced wear resistance in service are possessed by roof products made by a combined periclase-spinel and magnesite-chromite technology, incorporating in the batch both granular chromite and chromite milled together with magnesite powder.The comparatively low loss and the excellent property factors are typical for steel casting nozzles made on the basis of magnesite powder obtained by burning magnesite in shaft furnaces. Mathematical statistical techniques were used to determine the distribution and mutual relationships between the property factors of some magnesite products. The marked mutual relationship between the quality factors indicates the possibility of using statistical methods for evaluating some properties of these products.Translated from Ogneupory, No. 5, pp. 8–14, May, 1973.     

Effect of some technical factors on the spalling resistance of periclase-spinel refractories

Conclusions The thermal-shock resistance (spalling resistance) of periclase-spinel refractories increases 1.6–2.0 times when the chromite and finely milled magnesite are added separately to the batch. The main technical factor leading to an increase in the stable spalling resistance of the products is the application of a layer of ground chromite to the coarse grained part of the magnesite in the batch and its bonding. The strength and apparent density of the articles under these conditions are somewhat diminished, and there is roughly a 1% increase in porosity.The increased spalling resistance of periclase-spinel refractories when the chromite is added separately to the batch is due to the formation of a special submicrocracked structure, ensuring a reduction in the thermal expansion and elastic characteristics, an increase in the deformation prior to destruction (/E) and a damping decrement () of the material, and restriction and retarding of the rate of capillary liquid suction by the products.Translated from Ogneupory, No. 5, pp. 31–39, May, 1968.