At present MKN corundum hydraulically hardening compound produced by Borovichi Refractory Combine to TU 14-8-359-80 is used for the outer lining of the nozzles of batch and circulating steel vacuum degassing vessels [I, 2].Wear of nozzle lining of this compound during serive is observed in areas in contact with slag and metal. The basic reasons for wear are penetration and attack of the lining by slag, penetration by metal, erosion action of the moving flows of metal and slag, and sharp thermal shocks at the start and end of vacuum degassing. To increase the life of the lining it is desirable to decrease its porosity and increase the strength and slag resistance.According to [3][4][5][6][7][8] one of the directions in improvement of corundum refractories is addition to the charge of zirconium dioxide. Taking this into consideration, addition of baddeleyite to MKN corundum hydraulically hardening compound to improve the above properties was tested.In conducting the investigations the following original materials were used: fused corundum powder to TU 14-8-384-81 produced by Kazakh Refractory Plant; type PB-2 baddeleyite powder to TU 14-8-393-82; high-alumina cement produced in the experimental Technology Section of All-Union Refractory:Institute meeting the requirments for type Talyum high-alumina cement to TU 6-03-339-78.The chemical analyses* of the original materials are shown in Table i.To obtain comparable results under the same conditions laboratory specimens of concretes were prepared** from corundum hydrauiicaily hardening compounds with additions of 6 and 16%% finely found baddeleyite and also from standard production MKN corundum compound.For all of the compounds s maximum grain size of the fused corundum was 7 mm. in preparation of the specimens the mixtures were moistened with 10% water. The moistened compounds were tamped in split metal molds and held in a humid atmospehre. The hardened specimens had the form of cubes with an edge length of 30 mm. Specimens in the form of 80 mm diameter 35 mm thick disks were prepared for determination of thermal conductivity.The compressive strengths of the specimens after hardening for 3 and 7 days had comparable values for the compound with addition of 6% baddeleyite and MKN compound (21.4 and 25.6 N/mm =, respectively, after 3 days and 30.9 and 26.9 N/mm: after 7 days). With an increase in baddeleyite content in the corundum compound to 16% the compressive strength of the specimens dropped to 17 N/mm 2 after 3 days and to 21N/mm = after 7 days of hardening.The hardened concrete specimens were fired in a batch kiln at 1600~ the service temperature of the lining. The properties of the fired specimens are given in Table 2. An analysis of this data showed that specimens of the corundum compound with addition of 6% baddeleyite possess the best combination of properties (lowest porosity, greatest strength, *The chemical analyses of the materials and the physicotechnical properties of the specimens were determined in the Laboratory for investigation of Refractory Propert...

To increase the service life of vaccum degasser linings abroad hot repairs by guniting are widely used [i-7]. The introduction of guniting of vacutun degasser linings in domestic plants is being delayed primarily by the lack of guniting equipment for these units.Taking into consideration foreign experience the circulation vacutm~ degasser in the No. 1 Oxygen Converter Shop at Novolipetsk Metallurgical Combine was installed with a guniting machine designed for semidry hot guniting of the outer and inner linings of the intake and discharge legs. In connection with this the necessity arose of developing compounds making it possible to hot gunite vacuum degasser linings, which was the purpose of this work.In development of the guniting compounds fused corundum to TU 14-8-384-81 and sintered type PPM-85 periclase to GOST 24862-81 were used as the refractory filler. The binder was Talyum high-alumina cement to TU 6-03-339-78 made in the experimental technology area of AllUnion Refractory Institute. Taking into consideration the recommendations of [8] a plasticizing addition, Druzhkovka Deposit clay, was added to the guniting compounds.In the initial stage of the work laboratory specimens of corundum-and magnesia-type guniting compounds, the chemical and grain size compositions of which are shown in Table i, were prepared. The MKTG-I corundum compound differs from the MKG-I compound in the presence of a sintered titanium-containing addition. In comparison with MPKhBG compound, MPK magnesia compound was characterized by a higher aluminum oxide content.For investigation of the physicotechnical properties concrete specimens in the form of cubes with an edge of 30 mm were prepared from the compounds. In preparation of the specimens the compounds were moistened with water to a plastic consistency and were rammed in split metal molds lubricated with machine oil. The specimens were removed from the molds after hardening for 1 day~ The hardened specimens were fired in a batch kiln at 1600~ with a hold of 4 h. The results of investigation of their physicotechnical properties are given in Table i.Of the corundum composition compounds the specimens of MKTG-I compound with a titaniumcontaining addition had the higher mechanical strength (43.6 N/mm 2) and lower porosity (32.9%). However, MKG-I corundum compound without such an addition is of interest from the point of view of obtaining a heat-resistant gunited coating (15 thermal cycles) and decreasing the changes in linear dimensions in heat treatment (0.13-0.67% growth)~ In the group of magnesia specimens, specimens of MPK compound with an increased aluminum oxide content had the lower open porosity (27.9%) and higher heat resistance (5 thermal cycles). Specimens of MPK and MPKhBG magnesia compounds were characterized by close values of mechanical strength.

In circulating and batch vacuum degassers for steel the outer linings of the intake and return nozzles made of MKN-94 corundum hydraulically hardening compound produced by Borovichi Refractory Compound [i] are subjected to significant wear in service.In [2] a corundum hydraulically hardening compound with addition of baddeleyite making it possible to increase the mechanical strength of the outer lining of the nozzles, to reduce its open porosity, and reduce the rate of wear in service is described.According to [i] the increase in mechanical strength and decrease in open porosity of concrete of corundum hydraulically hardening compound may also be obtained by addition to its composition of titanium dioxide, which promotes sintering of the concrete at the service temperature (1600 ~ but at the same time significant linear shrinkage (1.7%) is observed. The use in preparation of the corundum compound of baddeleyite and titanium dioxide additions leads to an increase in cost of it.Taking this into consideration in this work to improve the physicotechnical characteristics of corundum compound, addition to its composition as the titanium-containing addition of titanium slag, the cost of which does not exceed the cost of fused corundum, in place of a portion of which it is added in preparation of the compound, was tested. The high titanium dioxide content in the titanium slag (more than 80%) provided a basis for expecting that addition of it to the corundum compound will promote an increase in mechanical strength and a reduction in porosity of the concrete in heat treatment, and the presence in the titanium slag of impurities increasing in volume at high temperatures made it possible to expect less shrinkage of the concrete in service than with the addition of pure titanium dioxide.In conducting the investigations fused corundum to TU 14-8-384-81, Talyum high-alumina cement to TU 6-03-339-78 produced in the experimental technology area of All-Union Refractory Institute, and titanium slag to TU 48-10-31-78 were used as the original materials. The chemical analyses of the fused corundum and the high-alumina cement are similar to those described in [2]. The chemical analysis of the titanium slag is* 84.5 TiO=, 4.8 FeO, 5.9 SiO=, 2.1 AI=03, 0.3 MgO, 1.0 Cr=03, and 0.5 MnO and the growth in firing 2.2.For the laboratory investigations specimens were prepared of corundum hydraulically hardening compound (particle size 7-0 ~Lm) with additions of 2 and 5% finely ground titanium slag. For comparison concrete specimens of MKN-94 production compound were also prepared under the same conditions. To prepare the specimens the components of the compounds were mixed, moistened with 10% water, rammed into split metal dies, and held in a humid atmosphere. The concrete specimens had the shapes of cubes with 30-mm edges and of 36-mm-diameter 50-mmhigh cylinders.After hardening for 3 days from the moment of mixing the compressive strengths of the specimens were determined. A portion of the specimens of each composition was fired in a batch...

Extensive studies on the mechanism of the wear of the linings of the vacuum units used for refining of steels have revealed splitting (shear failure) of the products during thermal cycling and erosion of their working layer owing mainly to the characteristics of the process of interaction of the refractories with the metal and the slag (the characteristics such as the depth of impregnation and the quantity of the liquid phase accumulated in the material). In particular, splitting (chipping) of the refractories can occur because of the difference in the coefficients of thermal expansion of the impregnated and the unaffected zones or due to the modifying transformations of the infiltrate that are accompanied by volumetric expansion. The rate of the erosive wear of the refractories is determined to a large extent by the extent of the structural changes occurring in the material adjacent to the working layer owing to the increase in the content of the liquid phase and by the depth of occurrence of these changes that adversely affect the mechanical properties of the material. Table 1 shows comparative data with respect to the total thickness (depth of impregnation) of the reaction zone and the transitional zone in the specimens of the products after their service in the slag belt of a ladle of an ASEA-SKF unit and in the branch pipe (nozzle) of a VP-130 batch-output vacuum installation and, also, the average wear rate and the quality parameters of the refractories.With respect to open porosity and strength, the imported products do not differ significantly from the Soviet products; however, they are subjected to impregnation and wear to a considerably less extent (the insignificant depth of impregnation of the PShKV products is not to be taken as an indicator of quality because of their intensive wear).In order to delineate the reasons underlying such a significant difference in the depth of the impregnated portion, we carried out a comparative study of the pore structure of the refractories, the wetting characteristics with respect to the ladle slag and the steel processed in an ASEA-SKF unit.

One of the main problems in the production of fused and cast refractories is obtaining castings with a dense working layer and a concentrated shrinkage cavity.To obtain this it is necessary to determine the thermal conditions of formation of the casting under which shrinkage porosity is a minimum and solidification of the molten material occurs successively from the working surface of the part.Calculations were made for the purpose of investigation of such thermal conditions.The operation of production of bakor castings was selected as the physical model.The molten bakor was poured into a mold (Fig. i) prepared from sand plates.The mold was placed in a heat box filled with diatomaceous back-up.The temperature of the back-up and the mold was equal to the atmospheric temperature T O . The molten material was overheated by 75~Pouring of the molten material into the mold took 40 sec at a constant rate.Let us solve the undimensional sym/netric problem of construction of the temperature fields in a hardening casting with the following assumptions:i. The thermophysical characteristics of the materials of the mold, the back-up, and the liquid and solid phases of the bakor do not depend upon temperature.For the calculation we take the average values in the temperature range according to the data of [1-4].2. The two-phase zone is not considered.We assume that solidification occurs instantaneously at the solidification temperatue Tso I = ~ (T s + Tg), where T s is the solidus temperature and Tg is the liquidus temperature.3. We neglect free convection in the liquid phase.4. We assume that during the time of pouring as the result of vigorous agitation of the molten material the temperature is uniformly distributed over its volume.In addition it is obvious that the temperature of the surface adjoining the liquid phase acquires the same value.The dimensions, the designations of the zones, and the coordinate axes are shown in Fig. io The conventional designations are T for time, Q for density, c for specific heat, ~ for thermal conductivity, a for the coefficient of thermal diffusivity, h for the specific heat of fusion, ~atm for the coefficient of heat transfer into the atmosphere, ~fil for the time of filling of the mold, v for the rate of filling, v = 2g/Tfil, and g is half the height of the part.In writing the equations and the boundary and initial conditions let us use the dimensionless variables ~ = a~ for time, O = T--To for temperature, ~i = xi/di for the coordinate 7 r~orr0 in the mold or the back-up, ~k = Xk/A for the coordinate in the solid phase, ~f = xf/(l-A) for the coordinate in the molten material, and 6 = A/l for the thickness of the solid phase.To the dimensionless variables the system of equations determining the solution of the problem has the form: The boundary conditions: ~ ~~a.~-,-6 "a~ r a~'All-Union Refractory Institute.