In recent years there has been a significant increase in torch guniting as an effective method of repair of the linings of metallurgical furnaces. One of the significant advantages of torch guniting as compared to other methods of repair of linings is its prospects for mechanization and automatic and the possibility of its use for linings which have cooled little.It is obvious that success in mechanization and especially automation of torch guniting depends to a significant degree upon the depth and extent of scientific and technical knowledge of this process, the conditions of its occurrence, and the characteristics and conditions determining its effectiveness. In particular, an important role is played by knowledge of the nonsteady temperature fields of the lining during application to it of the guniting. Space and time changes in the temperature of the lining and the applied gunited coating influence similar changes in the thermal stresses in the lining and the coating, leading in unfavorable cases to cracking of them.To calculate the nonsteady temperature fields of the linings of metallurgical furnaces in torch guniting, a program was developed for the EC computer.The basis of the program is the algorithm for solution of a problem equivalent to the problem of the temperature field of a growing multilayer plate. The program calculates the unidimensional nonsteady temperature field of a flat wall consisting of an arbitrary number of layers of different materials. The thermophysical properties (thermal diffusivity, thermal conductivity, specific heat, apparent density) of each of the materials in the general case are known functions of temperature T. It is assumed that at the start of guniting the temperature distribution across the lining thickness is specified in the form of a continuous piecewise-linear function.The algorithm assumes that from the initial moment, during the specified time interval the hot gunite coating grows uniformly on the surface, but (in the general case) nonuniformly?with time. The rule of growth of the coating thickness is assumed to be known. On the surface of the coating, in the general case, the rule of change in its temperature with time during guniting is specified. Upon completion of guniting the lining cools, liberating heat according to the Newton--Richman rule. On the side of the lining facing within the metallurgical furnace, the coefficient of heat transfer is assumed to be dependent upon the surface of the applied coating and time (the convective and radiation components of heat transfer are taken into consideration), while on the outer surface of the lining the coefficient of heat transfer is assumed to be dependent only upon temperature.The assumptions and the limitations related to them on the range of use of the calculations using the given algorithm, caused by such an idealization of actually very complex conditions and processes of heat propagation in the coating and the lining during torch guniting, are sufficiently clear from that presented above and therefore are n...

Increasing the effectiveness of using fuel and the energy efficiency of heating equipment is an important national economic problem whose resolution in the country is attracting a great deal of attention. This problem faces the refractories industry, which every year uses more than 3 million tons of standard fuel. The complexity of the problem in the production of refractories is connected with the variety of furnace designs, schedules and methods of operation, and the different levels and potential for heat-engineering improvements of the plant. An all-round analysis of the factors affecting the consumption of fuel enables us to identify the main means of reducing it, to develop measures of increasing the effectiveness of using fuel in furnace installations.The first point is the need to update still further the industry' s kilns and furnaces, the introduction of modern eontraflow-recuperative firing units (PROA) instead of outdated designs (annular, gas-chamber, periodic, etc. ), which have higher (sometimes by several orders) fuel consumptions with low levels of mechanization.Of all the possible furnace schemes, the PROA is heatwise the best, providing the minimum fuel consumptions to be obtained [1]. In the ideal case (isoentropic process) PROA, realizing the contraflows with an inversion of heat exchange at maximum temperatures, in a fixed working schedule, do not require expenditure of fuel, using as a working instrument the energy introduced at a single time during their starting up [2]. Although existing PROA schemes (tunnel, rotary, shaft furnaces) are still not perfect, their advantages are obvious compared with other forms, This fact was one of the causes of the wide use of PROA in world practice, including the refractories industry of the USSR, where they constitute approximately one-half of the furnace stock and are responsible for firing the largest part of refractories output.

The degree of optimization of the process of guniting of the linings of metallurgical equipment is determined to a great degree by the possibility of regulating and controlling the working characteristics of the guniting stream. In connection with this there is much interest in investigation of the aerodynamics and heat exchange in two-phase streams (jets) with a high concentration of solid polydispersed guniting particles, particularly in a mathematical description of the guniting stream and an investigation of its aerodynamic characteristics.The guniting jet is formed in the following manner. Through the two coaxial channels to the mouth of the torch are supplied oxygen (through the outer orifice) and the guniting mixture by a flow of compressed air (through the inner orifice).In the inner stream the concentration of the addition is very high and the flow rate of the air and the rate of movement of the gas suspension is much less than the flowrate and rate of movement of the oxygen at the mouth of the torch.It is known that at a certain distance from the orifices the streams are mixed to a sufficient degree and in the main portion they may be considered as a single gas stream with a mixture.Therefore in development of the calculation method a free axially symmetric nonisothermal subsonic stream with a polydispersed solid addition was considered. In the general case, the guniting mixture may contain particles of materials differing in size, densities, and thermophysical characteristics.The basis of the proposed method of calculation of the guniting stream was [1-3].One of the methods of an analytical description of two-phase jet flows used at present is the method of integral relationships of the boundary layer with specified universal functions of distribution of the parameters in the transverse sections of the streams.In jet flow the rule of preservation of the longitudinal component of the full impulse Io is fulfilled;where R(x) is the radius of the stream at a distance of x from the orifice in m, p_ is the density of the gaseous phase in kg/m 3, ug is the velocity of the gaseous phase in ~/sec, r is the current value of the radius of the ss in m, S is the number of fractions of the solid particles, n. is the concentration of particles of the i-th fraction in a unit of volume in l i/m ~, u i is the velocity of movement of the particles of the i-th fraction in m/sec, m. is the average weight of a particle of the i-th fraction in kg, m i = (4/3)~6~pi, Pi is th~ density of the particles of the i-th fraction in kg/m ~, 6. is the average diameter of the particles of the i-th fraction in m, and i is the number of theZfraction of the guniting mixture.Here and subsequently, 0, m, and ~ designate the values of the parameters at the nozzle edge, on the axis, and on the outer edge of the stream.For the i-th fraction the rule of the preservation of its mass flow rate Qi,o is preserved:

An increase in the service characteristics of refractory parts may be obtained by plasma spraying of a heat-resistant powder material on their surface. The powder material, sprayed in the jet of a low-temperature plasma, melts and is applied to the surface in the form of individual fine particles. Each particle, striking the surface of the base, is deformed, spreads, and solidifies on it. Adjoining one another, the particles form a coating, the quality of which is determined to a significant degree by the level of the thermal stresses and deformation in the base and the coating during spraying and subsequent cooling.The condition of the plasma sprayed refractory coating was investigated on bases in the form of plates assuming the existence in the system of unidimensional temperatures fields.The problem of determining the stresses in such a system is a problem of the disconnected quasistatic theory of thermal elasticity for a two-layer free plate with a thickness changing with time and a temperature gradient across the thickness. Such a problem for a single layer plate with a constant thickness and constant thermomechanical characteristics has been considered in the literature [4]. However, with large changes in temperature, which occur in the base and the coating in plasma spraying, the mechanical properties of the materials depend significantly upon temperature. Taking this into consideration , we assume that the moduluses of elasticity Ez and E2, Poisson's ratios ~z and v2, and the coefficients of linear expansion ~z and ~2, respectively9 of the base and the coating are functions of the temperature T: Et = Ez(T), E2 = E2(T), ~z = ~x(T), ~2 = ~2(T), az = ~z(T), ~2 = a2(T). xx --.y ------ l--v t [T(z, t)]where To is the initial temperature of the base, t is time, c~ z), c~ z), c~ 2), c~ =) are constants determined from the boundary conditions of the base and the coating, and E is the variable of integration.The direction of the coordinate axes is shown in Fig. i. With z = H, equality of the thermoelastic displacements on the side of the base and the sprayed coating must be observed. This condition leads to the next:The constants for each moment of time cx and c= must be determined from the zero boundary conditions for the stresses at the boundaries of the plate. Disregarding the boundary effect, we write:From this we find that:All-Union Refractory Institute.

One of the most important means of increasing labor productivity, economy, and rational utilization of material and labor resources in modern metallurgy is reducing the time for repair of the worn linings of metallurgical equipment, mechanization and automation of this process, and economy in refractory materials.In recent years it has become obvious that one of the promising methods in this direction is [I] the torch guniting method. The effectiveness of the guniting process is determined to a large degree by the occurrence of the components of its heat-and mass-exchange processes, in particular the heating of the refractory material particles in the jet and heating of the lining.The wide introduction of torch guniting in metallurgy provides a tremendous saving and therefore at present metallurgists of many countries of the World are displaying active interest in it. However, until now the theory of the guniting process has been developed very weakly and in essence has a fragmentary character. The many publications on torch guniting contain essentially a presentation of specific production experience and descriptions of narrowly specific results of experimental production investigations, the basis of which is practical experience and experience in the study, including theoretical, of similar or related phenomena and processes and also intuitive concepts of the rules of torch guniting. Some publications have been devoted to theoretical investigations but as a rule they consider only individual particular problems in a simplified setting.The need for development of the theory of guniting and, in particular, of the theory of the heat-and mass-exchange processes composing the essence and determining the effectiveness of torch guniting has been maturing for a long time. An experimental solution of these problems is difficult because of the difficulty and complexity in the development and use of a large flame stand (with a flame carrying the solid phase) and also the large variety of technological, geometric, and other characteristics of metallurgical equipment causing in turn wide variation in the conditions of repair of points of wear of the lining.In connection with this, in the State Institute for the Design of Nickel Industry Plants and the All-Union Institute for Refractories an attempt has been made to develop a universal physicomathematical model and software for the common system computer for calculation of a combination of complex heat and mass exchange processes which are the basis of torch guniting of metallurgical equipment. Below is given a brief description of the model developed and individual practical significant results obtained during computer experiments with it.The general model consists of three particular physicomathematical models. The first describes the temperature and velocity field of the gaseous and solid (polydisperse) phases of the guniting flame, the second the conditions of heat exchange of the portion of the lining being gunited with the external in relation to it medium, and the thi...