Vol 49, No 1 (2019)

Abstract—Inspection of the gas-exhaust system at arc furnaces of capacity 3–10 t in the casting shops of manufacturing enterprises reveals problems responsible for copious gas and dust emissions in the production buildings, with degradation of the air quality. This is mainly associated with structural shortcomings of the systems for gas and dust evacuation from the furnace chamber through the exhaust channel, working window, and gaps between the housing and roof and also between the edges of the holes in the upper section and the electrodes within the holes. In particular, the moving joints between the rotary hoods and the gas-exhaust lines in such systems do not ensure reliable sealing. Accordingly, an improved design of the hood-rotation mechanisms has been proposed, with two sand barriers preventing the atmospheric emission of harmful emissions between the moving components. In the design of an industrial prototype, a method is developed for calculating the energy parameters of the drive in the improved system. A 1 : 10 scale model of the system is built to check the design and the theoretical equations. By means of a measuring system consisting of a tensoresistive converter, an ac amplifier, an analog–digital converter, and a computer, the load on the model’s drive on switching from the working position to the rest position and back is determined, for two cases: with and without sand barriers to seal the mobile components. The drag in the two sand barriers on rotation of the moving element amounts to 20–26% of the total load on the drive, depending on the angular velocity of the cantilever with the hood. According to the theoretical formulas, this figure is 17–23% for hood-rotation mechanisms in arc furnaces of capacity 3–10 t. Video recordings of the smoke fluxes from the model through the gaps between its housing and the roof during simulations of steel production confirm the reliability of the sand barriers, which ensure complete sealing of joints in the hood-rotation mechanism. Practical use of the proposed design improves gas–dust evacuation from the working zone of smelting furnaces used in the foundry.

Abstract—The influence of nonuniform boundary conditions on the cooling rate of stainless steel in continuous casting of cylindrical billet is investigated. Nonuniformity of the boundary conditions over the billet perimeter is assumed. The longitudinal cooling rate is assumed constant within the cooled sector of the billet. The presence of heat fluxes between cooling sectors is assumed. The gradients of the temperature and the thermal stress that develop in the solidifying billet are compared at different cooling rates in the secondary-cooling zone. The thermal stress is compared with the permissible value for each grade of steel, so as to determine cooling conditions corresponding to permissible thermal stress. The results indicate that the cooling rate affects the appearance of external and internal defects in the continuous-cast cylindrical billet. It is also found that the nonuniformity of the boundary conditions affects the temperature fields in the solidifying continuous-cast cylindrical billet. The results are presented in graphical form and analyzed in detail. A mathematical model is developed to calculate the temperature fields in the solidifying billet, on the basis of the nonsteady heat-conduction equation. The thermal stress is calculated by familiar methods that permit the determination of the stress that appears between cooling zones in the solidifying billet. The results may be used to develop cooling conditions that correspond to permissible thermal stress. By that means, the frequency of internal and external defects in the solidifying continuous-cast cylindrical billet may be decreased.

Abstract—The influence of the solidification of high-strength moderately alloyed steel on the mechanical properties of the castings is studied experimentally. The low-temperature strength is of particular interest, since it determines the reliability and performance of cast products. The impact strength, work of crack development, and fiber content in the fractures are plotted as a function of the test temperature. Three production technologies for castings are considered: (1) casting in a thin-walled mold with forced water–air cooling that varies over the ceramic-layer height (casting with external cooling); (2) casting in the same conditions with the introduction of solid microcooling particles in the liquid steel (casting with complex cooling); (3) casting in a sand (liquid-glass) mold (the control technology). The results indicate that the impact strength is higher in the first two cases, over the whole temperature range. The variation in impact strength is smoother in those two cases; and the sharp decrease in impact strength seen in the control samples is not evident. The work of crack development W_cd also depends on the casting conditions. Serial curves show that the steel cast in the first two cases is less inclined to brittle failure (greater cold strength). Analogous results are obtained in studying the fiber content of the fractures.

Abstract—In textbooks on the metallurgy of iron, the chapter regarding the processes in the blast-furnace hearth must be supplemented with information regarding the calculation of the total energy of the composite blast, which determine the size of the combustion zone ahead of the tuyeres; and the total mechanical energy of the hearth gas, which characterizes the penetration depth of the hearth gas with respect to the furnace axis and the temperature at the center of the hearth. Constant monitoring of these total-energy values is required in the blast furnace. Those readings must be compared with the values for the best operating periods.

Abstract—Although Russia has considerable reserves of manganese, the quality of its manganese ore is relatively poor. (Its mean Mn content is 9–23%, with a high content of harmful impurities, primarily phosphorus). In terms of economic security, it is essential to create a Russian source of manganese. This entails enrichment of the lean manganese ore; the development of effective technology for producing manganese ferroalloys from the resulting concentrates; and improved methods of removing phosphorus from manganese concentrates. In the production of manganese ferroalloys from ore, about 50% of the manganese is lost. Numerous byproducts are formed in this process. The processing of such byproducts not only reduces the demand for the initial ore but also increases the efficiency of ore processing and decreases the environmental impact.

Abstract—Two types of mechanical characteristics of structural steel in uniform and nonuniform force fields are presented. In the science of metals and alloys, assignment by type is a fundamental concept. An analytical apparatus is developed for finding relations between the fracture resistance and basic mechanical characteristics of the metal, so as to assess the structural viability of steel in nonuniform force fields with annular stress concentrators, under uniaxial tension. The structural viability of steel with regular stress concentrators is assessed, and their low-temperature embrittlement is estimated.