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...

Flame gunniting is one of the most effective and promising methods of restoring worn linings of various metallurgical assemblies [I]. However, to date the theory of heat-mass exchange, which makes up the essence of flame gunniting, has been only weakly developed.In particular, this refers to the theory of the calculation of non-steady-state temperature fields (defining the thermal-stress fields) in the region where the gunnite coating is applied, particularly when geometrically complex forms of worn recesses are to be filled with the gunniting mass.In recent years the Leningrad State Board of the Nickel Industry has intensively been developing a standard package of applied programs for a broad class of tasks in the calculation of one-and two-dimensional temperature fields in various multilayer solids (of the type of linings for metallurgical assemblies) with moving boundaries.The package envisages the possibility that various recesses are present in the solids (simulation of worn sections of the lining) filled with a solid mass.Thermal boundary conditions of a general form are used and from these the traditional first-, second-, and third-order conditions follow as partial conditions.The thermophysical properties of the gunnite coating and of each of the materials forming the layers of the lining are considered as dependent on the temperature in accordance with arbitrarily specified laws. An arbitrary law of change with time in the rate of growth of the gunnite coating is assumed.The initial temperature field, nonuniform in the general case, is two-dimensional.It is assumed that there is heat exchange between the lining and the surrounding medium after the gunniting is completed.Calculations may be done in a rectangular or cylindrical system of coordinates depending on the geometry of the lining and the site of the wear in it.The package has a developed modular structure and is built up in such a way that the programmer can easily replace modules and at the stage of editing the program can connect in new modules corresponding to individual functions (for example, setting the law of increase in the thickness of the gunnite coating with time).In the case of a user who is not a programmer, thereis a large prepared set of programs which makes it possible to solve a wide range of problems and to provide for the setting of different conditions of the original data.For economy of machine time when working through the variants of the process which are identical at the initial stage of the calculations, the possibility is envisaged of a magnetically stored memory file of the current intermediate state and the next semivariant continuation of the calculations.The algorithmic language is Fortran. The software is designed for an OS ES computer.The package of programs will be completed in 1984.It is next assumed that there will be a subsequent improvement of the program provision for the calculation of the temperature fields during flame gunniting which will provide the research engineer with wide opportunities for carrying o...

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...