'man, and V. M. Ust'yantsev UDC 666.762.453 Magnesium chromite (magnesia--chromite spinel) is the most chemically resistant compound in relation to molten iron~ilicate slags [i, 2]. Magnesium chromite is one of the basic components of the spinellide of chromite ore and is present in it in the form of a solid solution with other spinellides.The presence of impurities, particularly silicates, in chromite ore has a significant detrimental influence on the quality characteristics of the refractories obtained.Therefore, for the production of refractories with increased resistance the use of purer magnesia--chromite raw material is necessary.Such raw materials include chromite obtained by thermal decomposition of magnesium bichromate.The method of its production was developed by the Ukrainian Scientific-Research Institute for Chemistry [3].We have conducted investigations on the use of synthesized magnesium chromite for the production of magnesia--spinellide refractories.As the result of the fact that the corrosion failure of refractories by slags occurs primarily in the binder, magnesium chromite was introduced into the finely ground component of the charge.To improve sintering of the refractory compositions, titanium magnetite concentrate was added to the composition of the magnesium chromite.Kempirsaisk deposit chromite ore of 3-1 mm fraction and sintered periclase powder of 2-0 mm fraction were used as the granular materials.The chemical and grain-size compositions of the original materials are presented in Tables i, 2.Refractory mixtures containing magnesium chromite sinter with difficulty and therefore the main problem was searching for a method of compacting the refractories.The search for the optimum conditions for obtaining dense parts was made with the use of the methods of mathe matical experiment planning.The open porosity P in %, which must be minimized, was adopted as the parameter of optimization.The independent variables influencing the density of the refractory are: ~, wt. % of sintering addition relative to the basic mixture; x2, temperature of preliminary firing of the magnesium chromite, deg C; x~, firing temperature of the samples, deg C; x4, wt. % of magnesium chromite in the charge; and xs, wt. % of granular chromite ore in the charge.The area of determination was the following: xl = 0.7-1.7%; x2 ~ 700-1500~ x3 = 1650-1850~ x4 = 25-35%; xs = 15-25%.To attain the extreme area the method of steep ascent was used [4]~ In the area close to the assumed extreme the subarea for linear approximation of the function of response was selected.In this subarea there was accomplished a 1/4 replica of the full facto~al experiment 2 s with the generating relationships;The samples were pressed in the form of cylinders with a diameter of 36 mm and a height of 40 mm under a pressure of 150 MPa and fired in the tunnel kilns of Magnesite Combine.Three parallel tests were made at each point of the plan.The regression coefficients with the use of the full factoral experiment or fractional replicas of it are dete...

The MgCr20~--MgAI204 system is a particularly important section for refractories technology in the ternary system MgO--Cr203--AI203; it consists of a continuous series of solid solutions. The properties of magnesium chromite and magnesium aluminate have been studied in some detail, but information published on their solid solutions is limited. The properties of powdered materials are largely determined by such characteristics as the size of the crystallites, the morphology of the aggregates, the specific surface, and the number and size of the pores.

The main factors causing wear of the lining of the converters used in nonferrous metallurgy include intensive impregnation of the refractories with the reagents of the converter melt that leads to zonality (zoning) and the corrosive and erosive action of the circulating melt and fluxes. The abrupt and frequent temperature variations occuring during operation lead to the development of stresses in the refractories at the boundary of the impregnated and the unimpregnated zones because of the difference in their coefficients of thermal expansion and to the formation of cracks and splits (chipped surface). In view of this, decreasing the depth of slag-impregnation (penetration) in the lining would improve its life owing to the decreased size of the sheared-off pieces of the refractory and the smaller surface of interaction between the refractory and the slag.It is known that the composition of the finely milled charge has a significant effect on the quality parameters of the magnesic-spinellid (magnesia-spinellide) refractories and on the specific features of their behavior during service [1][2][3][4][5]. In view of this, it is necessary to carry out additional studies on the specific features of structure evolution of the magnesic-spinellid refractories and on the nature of their impregnation and interaction with fayalite slags as a function of the ratio of the chromium ore and sintered periclase in the dispersed constituent (component) of the charge.In order to conduct these studies, we prepared finely milled systems (compositions) based on the chromium ore belonging to the Kempirsaisk deposit and sintered periclase whose chemical composition is given in Table 1.The composition of the finely milled systems was varied from 100% chromium ore up to 100% sintered periclase maintaining intervals of 20%.Using these systems, we prepared charges containing 35% sintered periclase of the 3-1 mm fraction, 30% sintered periclase of the 1-0 mm fraction, and 35% of one of the aforementioned finely milled constituents. Specimens were prepared using a temporary binder consisting of a preheated (up to 30-40"C) solution of technical-grade lignosulfonates having a density of 1.20-1.24 g/cruZ; the compaction pressure amounted to 130 N/ram 2. Firing was carried out in a tunnel furnace at 1700"C maintaining a 4 h dwell at this temperature. Table 2 shows the properties of the fired specimens.In order to obtain a more detailed evaluation, we studied the nature of pore size distribution in the refractories and the specific features of their impregnation with the fayalite slag and their corrosion. Figure 1 shows the differential curves depicting the pore size distribution. Our studies showed that in the refractory containing the finely milled component consisting, entirely, of the chromium ore, the predominant pore size amounts to I0= 100/~m. As the content of the chromium ore decreases in the binder, the number (fraction) of such pores decreases and the number of the pores measuring l-10 ~m increases. The refractory incorporating the peric...

The cooling of converter linings lengthens their service lifeo A reduction in the temperature of the active surface of the lining impedes the penetration of molten slag and matte into the pores of the refractory masonry, promotes the formation of a crust, and reduces the variation of the temperature in the masonry.An analysis of the heat balance showed that 160 MJ of thermal energy (7% of the total heat input) Is lost through the lining in a coppersmelting converter and up to 320 MJ (11o5%) in a cupronickel converter.The temperature of the active surface of the lining reaches 1250~ sometimes 1350~ The temperature of the lining surface on the melt side decreases slightly and that on the shell side increases to the extent that the lining is eroded.In a 100-mm-thick lining the temperature of the masonry may reach 960~ and that on the side facing the shell 600-700~ In a thick lining the temperature gradient is variable but the temperature field levels out with a decrease in the thickness of the lining.In the zone of the tuyeres the heat flow varies 3-5 kW/m 2. in a 460-380-mm-thick lining, and 8-10 kW/m ~ in a 200-100-mm lining (natural cooling).When the difference between the temperatures of the melt and the active surface of the masonry is 20-50~(measured with an optical pyrometer) for a 400-mm-thick lining the rate of heat transfer from the melt equals 100-250 W/m2odeg K so that the heat transfer coefficient does not exceed 3 W/m2,deg K. tThe data given in this article make it possible to select the most efficient method of cooling the lining of converters for the purpose of lengthening its service life, and they explain some of the contradictions which arise in discussions of the efficiency of given methods of lowering the temperature of the active surface of the lining.The total thermal resistance R t of heat transfer can be divided into three main components; the heat-transfer resistance of the melt R~ the resistenae of the thermal conductivity of the lining and of the clearance between the lining and the shell R%, and the heattransfer resistance of the outside surface of the shell R~. The ratio between them depends on the composition of the matte and slag, the size of the melt bath, the thickness of the lining, the blast condition~, the configuration of the outside surface of the shell, the time of the year, etc. For converters operating in normal conditions R: = 0.5-3%, R% = 60-80%, and R2 = 20-40% so that the temperature of the active surface of the lining can be lowered appreciably by intensive cooling only after significantly increasing the thermal resistance of the melt and decreasing the thermal resistance of the lining and the clearance between the lining and the shell.The influence of the main factors (heat-transfer coefficient, lining thickness, and thermal conductivity) on the ratio between the components of the total thermal resistance is shown in Table i~ The heat-transfer coefficient to the melt is assumed 250 W/m2,deg K and takes into account only the direct cooling of the outside of the masonry....