No abstract
Accelerating production processes with the use of heating equipment that operates under the action of various corrosive agents requires the development of refractory materials that will provide effective and reliable operation. Increased demands are placed on the refractory linings under such conditions. In particular, the refractories should possess a high strength, which is one of the decisive criteria of the working capacity of the heating plant during prolonged operation.The Ukrainian Institute has developed highly refractory, volume-constant corundum concretes [i] which can be recommended for unfired, monolithic linings in various high-temperature units working in reducing, neutral, and oxidizing gaseous atmospheres at service temperatures of 1800-1900~Studies carried out at IPP AN UkSSR showed [2-6] that ceramics and refractories are classified with the nonlinear-elastic systems.This agrees with data in [7][8][9]. In particular, from the results given in [8,9] it follows that ignoring the nonlinearity of the diagrams during their treatment leads to considerable errors in determining the strength.Experimental investigations of the strength properties of corundum concretes were carried out on equipment at IPP AN UkSSR using the methods stated in [2][3][4][5].The specimens were tested according to the four-point bending scheme on equipment designed on the basis of the RM-101M rupture machine.The arrangement of the equipment is shown in Fig. 1. It has special supports with distances of 50 and 30 mm between the internal points of application of the loads, and i00 and 60 mm between the loads. These supports are different from those described in [2,5] in that the rollers i transmitting the force onto the specimen 2 are arranged on the plates (in Fig. I not shown) which can be rotated around cylindrical rods coaxial with the specimen.Electromagnets are used to fix the initial position of the rollers. A rigid plate dynamometer 3 is built into the support~ and the deformations of this are measured with strain gauges, and the bending meter 4, designed on the basis of the small inductive displacement sensor which was designed in IPP AN UkSSR, is built into the support.As a result of improvements made to the metering circuit it is possible to register, on two-coordinate potentiometers, the deformation diagrams not only with the use of the strain gauges (P--a, see Fig. I) glued to the specimen in the compression zone 5 and in the tension zone 6, but also with the aid of the bending meter 4 (P--~, see Fig. 1).In order to study the acoustic emission (AE), diagnosing the development in the specimens of cracks during deformation, use is made of a special instrument [6]; and we developed a metering-information system which ensures the measurement in a stated range of frequencies of the parameters of acoustic emission (total number of impulses, their intensity, amplitude, and the number of elementary events --acts of acoustic emission); in addition, a synchronized signal is transmitted to one of the channels about the change i...
CONCLUSIONSAll refractory materials are with advantage divided into two groups in terms of the characteristics of their mechanical behavior, viz., brittle refractories for which the degree of brittleness X = i, and relatively brittle refractories with X < i. The method and means of determining the strength of refractories should be decided in accordance with the degree of their brittleness.A criterion is proposed for the resistance of refractories to thermal stresses which takes into account the effective relation between the stresses and deformation.It was shown that in the case of materials of equal strength, rigidity, and coefficients of linear expansion the thermal-shock resistance is greater for the material with the lower degree of brittleness. LITERATURE CITED
Intensifying the chemical process by increasing the temperature of the thermal decomposition of carbonate raw material in a fast gas stream has made it necessary to develop highly effective refractory materials including high-refractory concretes designed for making the unfired monolithic lining of various zones in thermal aggregates, in particular of the reactors in the production of industrial carbon. The refractory materials used for the lining must be characterized by high strength, thermal-shock resistnace, and constancy of volume during use.On the basis of laboratory and production studies a composition has been developed for a corundum concrete in a hydraulic binder made from high-alumina cement. The unfired specimens of corundum concrete were characterized by high strength and thermal-shock resistance, and an insignificant increase in volume on heating. As the coarse-grained concrete filler we used electrosmelted corundum and the multicomponent, finely dispersed part consisted of hlgh-alumina cement grade VGTs-70, GK alumina, a binding additive, and an addition of highly refractory oxides.With the aim of refining the composition of this corundum concrete, we used the method of mathematical planning of an experiment with quantitative, variable factors to establish the regression dependences between the proportion of individual components of the finely dispersed part and the properties of the corundum concrete mixture and, in the construction of the composition-property diagram, to find the coordinates of the points corresponding to the optimum value of the property to be studied. The method makes it possible to describe a model of the subject of the study by an equation of the form:where y is the function to be studied; x i are variation facotrs (i = i, 2, ..., k); x, --x~ is the concentration in the finely dispersed part of the concrete, respectively, of highalumina cement, GK alumina, binding additive, and the oxide addition.Using a simplex-grid method the choice of the optimal composition of highly refractory corundum concretewhich has the maximum crock strength (y, function) with corresponding limitations on the linear dimensions and the thermal-shock resistance (functions Y2 and ya) can be made. In the planning of the experiment with quantitative factors charaeterizlng the compositions of the mixtures (total concentration of components, 100%), we used the so-called Sheffe simple simplex-grld to optimize the properties of the mixtures and to construct the composition-property diagrams [i].In the k-dimenslonal space where k is the number of components of the mixture xi, the condition of the total concentration of mixture components (100%) in natural units has the form:I where the number of components of the mixture of the system, x i varies from 1 to k.With the transition from the natural to the coded values of the factors the condition of the sum of concentrations of the components of the mixture takes the form:
The necessity to use slide gates in steelcasting ladles was brought about by the development of continuous casting and the ex-furnace refining of steel, more particularly by the protracted stay time of the melt in the ladle, the high temperature, and the corrosive propperties of the slag [I].The specifications of the refractory plates of a slide gate are dictated by the actual conditions of service.The main causes of gate failure are the encrustation or erosion of the steelcasting channel, melt leakage between the plates, and the solidification of the steel in the channel after the closure of the gate [2]. It is well known [i, 3] that the casting of steel with a high Mn/Si ratio through slide gates presents certain difficulties.The optimal technological parameters in the production of refractory materials for slide gates can be determined therefore only on the basis of an analysis of the interaction of the molten steel with the refractory.The diversity and complex nature of the processes which accompany the corrosion of refractories by the molten steel and slag makes it necessary to use a different method of analyzing the steel and slag resistance in every concrete case [4][5][6][7][8][9].Since in none of the known methods of determining the metal resistance is the experiment carried out in conditions approaching those in the industrial process tests were carried out with the in-service determination of the properties of the refractories.
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