The purpose of this study is investigation of the patterns of occurrence of the system of macro and microcracks in the rocks during rapid cooling for their effective softening.Methodology. The solution of the problem of crack system development is based on the fact that, as a result of rapid cooling in the surface layer of the rock, the tensile stresses are developed. The stretched layer acquires potential energy, depending on the modes of thermal influence and rock properties. At a certain point, the energy of the stretched layer starts to be spent on the forma tion of new surfaces of the growing system of macro and microcracks.findings. A model of behavior of the surface layer of rocks in the conditions of thermal shock by cooling is proposed. This model takes into account the development of a fracture macrocrack system and a microcrack system that move in the layer behind the cooling front. The dependence has been obtained that allows determining the penetration depth of a macrocrack system in the rock depending on the thermal exposure regimes and the physical and mechanical properties of the rocks. The formation of a microcrack system in the stretched cooled surface layer which changes its strength properties is experimentally proved. It is shown that the system of macrocracks moves into the array with deceleration and penetrates into the rock deeper than the thickness of the cooled layer, while microcracks are formed within the extended cooled layer. It is shown that the penetration depth of the macro crack system into the rock is practically independent of the mode of thermal shock by cooling and is determined by the physical and mechanical properties of the rock and the time of exposure. Increasing the potential energy of the stretched rock layer due to an increase in the temperature difference between heating and cooling ("toughening" of the thermal shock regime) leads mainly to an increase in the density of a cracking net on the rock surface. originality. For the first time the development of a crack system rather than a single crack in a rock during rapid cooling was considered. The model of the rock surface layer behavior under the conditions of rapid cooling is proposed. The geometric aspects of the initiation and propagation of a macrocrack system into the rock due to thermocycling loading are considered. The fact of initiation of a microcrack system along with macrocracks which change the strength properties of rock in the formation zone is proved.Practical value. The analytical dependence is obtained that allows determining the penetration depth of a crack system in rocks as a result of thermal shock by cooling. This dependence makes it possible to estimate the size of the damaged by macro and mi crocracks zone of a rock, as well as the degree of rock softening depending on its physical and mechanical properties and thermal shock modes of cooling. The results are used in real technological processes with thermocycling impact such as preparing rocks for mechanical destruction, hydraulic fracturing, ...
Purpose. To establish analytical dependences for calculating the characteristics of the ash suspension and the velocity of constrained settling of coal and quartz depending on the particle size and density of the medium, which is necessary for calculating the design and determining the operating modes of hydraulic devices for extracting coal from water mineral suspension of fly ash from thermal power plants. Methodology. The research was carried out on the basis of a cellular suspension model and classical concepts of constrained particle motion in laminar and turbulent flow. For analytical evaluation of the characteristics of the suspension, the defining correlations and the Wend formula for viscosity were used. The Ergun equation and correlation analysis methods were used to calculate and analyze the speed of constrained movement of ash suspension particles. Findings. Approximating nonlinear functions are obtained for determining the speed of constrained movement of coal and quartz particle size up to 4 mm in an ash suspension with a density of 1.31.8 g/cm3. It is shown that, for both settling and ascending of coal, there is a direct relationship between the velocity and particle size, in both cases it is nonlinear. For any coal size, the speed of ascent depending on the suspension density is of extreme nature; the rational density range is 1.551.8 g/cm3 with a maximum of 1.65 g/cm3. The established dependencies allow us to determine the size of coal and quartz particles, taking into account the counter-flow of the liquid phase, as well as the boundary size. Originality. For the regime of weak-turbulence flows there were established dependences and approximation equations of the constrained movement speed of coal and quartz particles the main components of the water suspension of fly ash from the Novo-Kramatorska TPP, depending on the size and density of the ash suspensions with changes in the characteristics of the medium depending on density. The frames of the Stokes description of processes are established. It is shown that the movement of the liquid phase in a counter-flow with precipitating particles is effective for surfacing of thin coal classes. Practical value. The described approach can be used for analytical evaluation of the characteristics and velocity of constrained movement in various water suspensions of discrete solid particles in weak-turbulence flows. The advantage is a wider coverage of hydraulic equipment operating modes. The results obtained are necessary for designing and determining the technological modes of operation of various hydraulic devices in the technology of complex processing of fly ash from TPPs.
The purpose of the work is to invent a method and develop a tool for effective drilling of strong and especially strong rocks with the least expenditure of both energy and money for the drilling tool. Currently, in rocks, the most time-consuming and expensive is drilling wells in strong and especially strong rocks. Despite numerous attempts to solve the problem of drilling strong rocks, an effective solution to this problem has not yet been found. The problem is that the introduction of drilling tools into these rocks requires considerable effort and work to destroy these rocks. This requires high strength and durability of the drilling tool, which is limited by the properties of known materials used. The solution to this problem may be to strengthen strong and drill wells in particularly strong rocks by transferring them to a stressed state or creating a grid of cracks in them, which will significantly reduce the effort and work to introduce the tool into the rock, as well as its abrasive wearout. This article proposes a new method and device for creating cracks on the mine face surface in durable rocks for their further drilling by cutting. A brief description of the new method of impact-cutting drilling of strong rocks is given. Sketch drawings of a previously unknown device for impact-cutting drilling of strong rocks are provided and a description of its work is given. The advantages of this method and the device are indicated – in solving the problem of drilling strong rocks.
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