A particular solution of a linear variant of the dynamic thermal elasticity problem is considered in application to modeling the conditions of surface hardening of metal products by an energy pulse. The authors determined the equation of medium motion with the model of temperature pulse tested earlier for compatibility with special cases of the equations of parabolic and hyperbolic thermal conductivity. The problem of loading a flat plane of a short circular cylinder (disk) with a temperature pulse is presented. Pulse is a consequence of adopted structure of the volumetric power density of the heat flux, the time multiplier of which has the form of a single wave of the Heaviside function. Classical thermoelastic displacement potential and the method of its division into the product of independent variables functions were used to construct the thermal stress tensor. Differential equations for multiplier functions and their general solutions were found. Natural boundary conditions were set for the components of thermal stress tensor, and their tasks were solved. The obtained solutions are in the form of segments of functional series (the Bessel function in radial coordinate and the exponential function in axial coordinate). The article considers a numerical example of loading a disk made of 40KhN steel which has the mechanical properties sensitive to temperature treatment. Maple computer mathematics package was used in the calculations. Approximate solutions take into account the first 24 terms of the functional series. Estimation of the example makes it possible to explain the presence of stress peaks and stress intensity as a consequence of mutually inverse processes of temperature stress growth and reduction of elasticity coefficients with temperature rise. The numerical example warns against relying only on estimates of solutions to thermoelasticity problems without taking into account the plastic and viscous properties of the material.
Аннотация. В настоящей работе исследованы процессы обезуглероживания периклазоуглеродистых и алюмопериклазоуглеродистых ковшевых огнеупоров. Процессы обезуглероживания протекают уже на стадии сушки и разогрева футеровки после ремонта, при ее тепловой обработке на газовых или электрических стендах. Эти процессы наносят непоправимый ущерб огнеупорам еще до ввода ковша в непосредственную эксплуатацию (до контакта с расплавленной сталью). Одним из направлений повышения стойкости углеродсодержащих огнеупоров против окисления является применение антиоксидантов (Al, SiC, Si и др.), которые вводят в состав сырьевой смеси на стадии изготовления. Их действие основано на приоритетном окислении по сравнению с углеродом. Антиоксиданты действуют в определенном температурном интервале, что открывает широкие возможности по разработке энерго-и ресурсосберегающих температурных режимов тепловой обработки футеровки. Проведен термогравиметрический анализ периклазоуглеродистых и алюмопериклазоуглеродистых безобжиговых смолосвязанных огнеупоров марок AMC 78-8/7HG, RI-MC175LC (фирма RI); MayCarb 284-AX (фирма MAYERTON), используемых при выполнении рабочих слоев футеровок сталеразливочных ковшей. Термогравиметрический анализ образцов огнеупоров осуществили на дериватографе LABSYS evo TG DTA DSC 1600 при нагреве до температуры 1100 °С со скоростью 15 °С/ мин. Рентгенофазовый анализ выполняли на рентгеновском дифрактометре XRD-6000. Результаты термогравиметрического анализа представлены в виде дериватограмм. Установлено, что максимальная скорость окисления углерода во всех случаях достигается при температуре 700 -750 °С. Следовательно, в целях реализации малообезуглероживающего первого разогрева ковша после ремонта для огнеупоров исследуемых марок рекомендуются температурные режимы, включающие низкотемпературные (до 500 °С) выдержки футеровки.
In this paper, the processes of decarburization of periclase-carbon and aluminum-periclase-carbon ladle refractories were investigated. Decarburization processes take place already at the stage of drying and heating the lining after repair, during its heat treatment on gas or electric stands. These processes cause irreparable damage to refractories even before the ladle is put into direct operation (before contact with molten steel). One of the ways to increase resistance of carbon-containing refractories against oxidation is the use of antioxidants (Al, SiC, Si, etc.), which are introduced into the composition of the raw mixture at the manufacturing stage. Their action is based on priority oxidation compared to carbon. Antioxidants act in a certain temperature range, which opens up wide opportunities for development of energy- and resource-saving temperature modes for lining heat-treatment. The authors made mogravimetric analysis of periclase-carbon and aluminum-periclase-carbon non-ignited resin-bonded refractories of AMC 78-8/7HG, RI-MC175LC (RI); MayCarb 284-AX (MAYERTON) grades used in the execution of working layers of steel ladle linings. Thermogravimetric analysis of refractory samples was carried out on a LABSYS evo TG DTA DSC 1600 derivatograph when heated to a temperature of 1100 °C at a speed of 15 °C/min. X-ray phase analysis was performed on an XRD-6000 X-ray diffractometer. The results of thermogravimetric analysis are presented in the form of derivatograms. It was established that the maximum rate of carbon oxidation in all cases is reached at a temperature of 700 – 750 °C. Therefore, in order to implement a low-carbonizing first heating of the ladle after repair, temperature modes are recommended for refractories of the studied brands, including low-temperature (up to 500 °C) lining exposure.
Now in metallurgical production energy resources demand is almost completely satisfied by gaseous fuel. Biogas obtained during organic waste processing is considered as an alternative and cheaper type of fuel. The experience of biogas application has shown that in most modern burners decrease of efficiency and limitation of the range of load regulation is observed. To apply biogas in an industrial environment, it is necessary to develop burners and the methods of its combustion, which provide a high combustion efficiency, as well as a higher energy conversion efficiency. The authors have used the results of gas analysis of biogas obtained in the process of anaerobic decomposition process of organic waste in the reactors of a bioenergy plant. Methods of mathematical statistics with the use of regression analysis of experimental data were used to assess the indicators of the energy efficiency of the gas burner. The possibility of using biogas and landfill gas in the process of roasting, blast-furnace smelting, production of rolled products and steel, as well as heat treatment of metal has been experimentally proven. The properties and composition of biogas at the outlet of the methanogenesis reactor of the bioenergy plant “EcoVoltAgro” are described. A new design of a gas burner is proposed. In this model the efficiency of mixture formation and the completeness of combustion of the flow of a methane-containing gas mixture are significantly increased (up to 32 %) due to the effect of rotation of the perforated pipelines of the gas inlet pipe. On the basis of the results of the full-scale experiment, the optimal values of the gas-air mixture supply rate, the temperature of the supplied air, the volume fraction of methane were determined in order to obtain the largest width of the zone of deviations of the permissible concentrations of carbon dioxide. The use of the designed gas burner provides energy-efficient combustion of biogas in metallurgical furnaces, kilns, and dryers, as well as in any steam and hot water boilers.
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