Volume 27, Nº 1 (2023)

This paper investigates the cutting forces arising when using a single abrasive grain. Analytical studies were carried out using a model of a single abrasive grain in the form of a rod with a radiused apex acting on the workpiece material. The slip-line method (method of characteristics) was used to calculate the deformation intensity of a plastically edged workpiece material under the action of a single grain. Mathematical models were developed for the following factors: plastic deformation of the material, edging of the stagnated zone and its friction against the grain surface when moved upwards in the form of chippings, grain friction against the plastically deformed material, and the action of the dynamic component of plastic deformation. The significance of the dynamic component in the overall balance of forces related to plastic deformation was established by determining the ratio of dynamic stress on the break line and shear yield point. This dependence calculated for D16T and 30HGSA materials showed the feasibility of accounting for the dynamic component of the cutting force under the velocity of a single grain impacting the workpiece surface of above 50 m/s. Graphs depicting the relative grain force and the relative depth of grain penetration are given. The proposed calculation method for cutting forces using a single grain can be used to determine the total force of interaction between the single grain and the work-piece material. In order to adopt the defined processing method and the workpiece material, the number of grains in contact, the contact duration, and the cutting speed should be found. On this basis, the process performance and the quality of the workpiece surface can be calculated.

The authors demonstrate the potential of a methodological approach for monitoring the damage kinetics and evaluating the load-bearing capacity of composite structural elements based on the method of acoustic emission. This methodology was developed by specialists of the Blagonravov Mechanical Engineering Research Institute of the Russian Academy of Sciences. The methodology was implemented for a fatigue test of an aircraft panel represented by a complex hybrid structure with a lining made of layered composite and a cellular internal structure of aluminum foil with polymeric filler that has a continuous layered structure in the gripping area. Fatigue tests were carried out at 4 Hz from the zero-loading cycle with an amplitude of 145 kN. To record the accumulation of damages, R15–AST transducers by Mistral (USA) and an A-line 32D 8-channel acoustic emission system by Interunis-IT LLC were used. Comparing the weight content of location impulses with their threshold values in energy clusters characterizing the kinetics of micro-, meso-, and macro-damages of the composite material structure made it possible to determine the bearing capacity of the aircraft panel at respective stages of damage kinetics. The results of the acoustic emission diagnostics are given for the examined aircraft panel during cyclic loading, including the coordinate location of acoustic emission sources, accumulation of acoustic emission events by channels, the dynamics of partial activity changes, and weight content of location impulses at damage evolution stages of a composite material. Therefore, the acoustic emission diagnostics of the aircraft panel made it possible to identify the areas of intensive damage accumulation in the hybrid structure of the panel and control the actual bearing capacity by defining the extent of its damages at various scale and structural levels during cyclic loading. The described methodology of using acoustic emission diagnostics for monitoring the damage kinetics and actual bearing capacity of highly loaded composite elements extends the research potential of the acoustic emission method.

This work is aimed at improving the performance of various handling equipment by optimizing the transportation cycle, e.g., decreasing the time of acceleration and deceleration by damping load oscillations, increasing the steady-state motion speed, and decreasing the time of pauses. The object of modeling is an overhead crane with a capacity of 15 ton, a stroke of 15 m, and three degrees of freedom. A Lagrange equation of the first kind as a non-linear heterogeneous system was used. A mathematical analysis of the damping process was carried out by energy balance modeling. As a result, the optimal amplitude and frequency of damping impulses required to change the suspension length within 5% were obtained. These impulses have a maximum frequency of three oscillations per second and are supplied in a reversed phase to load oscillations. According to calculations, energy costs for damping load oscillations are below 3–4% of the lifting motor power. It is shown how damping is implemented in manual control, and coefficients are calculated to define the amplitude of changes in the load and arm suspension length. The ranges of changes in these coefficients comprise 0.85–0.9 and 1.1–1.15 for setting the amplitude and frequency of damping impulses when using an automatic system. On this basis, a load oscillation damping system for a moving overhead crane is developed. Options are proposed for the damping system: by an operator or an automatic control system. The mathematical model of a crane is suitable for studying various types of equipment. Due its high efficiency and relatively low cost, the proposed method of damping is recommended when designing new equipment or improving the existing equipment.

In this study, we analyze the results of calculating the resistance of substation earthing equipment taking operational factors into account. The resistance of a substation earthing system was estimated using both calculation (methods of equipment operating factors, generalized parameters and induced potentials) and instrumental (ammeter-voltmeter) methods. During operation, the resistance of the studied earthing system was found to increase in comparison with the rated values, thus reducing its overall efficiency. The resistance of substation earthing equipment measured experimentally by the ammeter-voltmeter method showed the relative error of the considered calculation methods to reach 48, 46.7 and 28.6%, respectively. With the purpose of increasing the calculation accuracy of earthing equipment resistance by the method of induced potentials, it was proposed to use an operating factor. Thus, during the substation operation period of 10, 10–20 and over 20 years, the resistance of the earthing system increases by 1.02–1.1 times due to corrosion. It was shown that the installation procedure and maintenance checks (conducted at least every six years) increase the resistance of earthing systems by 1.02 and 1.05 times, respectively. Lightning discharges and short-circuit currents affect the corrosion rate of earthing systems, thereby increasing their resistance by 1.01–1.03 and 1.03–1.05 times, respectively. Therefore, the operating factor value may range from 1.115 to 1.274. The use of the operating factor in calculating the resistance of an earthing system by the induced potentials method increased the overall calculation accuracy, with the relative error not exceeding 3%. This corresponds to the normative and technical requirements stipulated by the Federal Grid Company of the Unified Energy System of Russia.

The authors develop a system of optimal planning of power consumption in the Republic of Altai local grid system based on a large proportion of renewable and alternative generating power sources. The studies were carried out using the linear programming method for power consumption patterns used by generating consumers. Power consumption charts by seasons and hourly retrospective rows of weather data by wind current velocity and solar insolation over 2021 were used as source data. Wind turbines, solar photovoltaic facilities, hydro-power plants, and energy accumulators were considered as local power consumption facilities to calculate electricity generation. The article provides calculation results for electricity generation in winter, since this is when a higher power deficiency is observed. It was shown that power consumers in the region under study can independently install additional generating power sources in the form of wind turbines, solar photovoltaic facilities, hydro-power plants, and energy accumulators due to electricity deficiency. Their combined generation mitigates the unpredictability of power generation by renewable sources. The authors propose a method that allows generating consumers to minimize their material and financial expenses and reduce the carbon footprint. The significance of the study consists in the substantiation of a hybrid power supply system with a high proportion of renewable and alternative power sources, which is implemented in the Republic of Altai and can be reproduced in other local energy systems with similar weather conditions.

This work investigates possible options for replacing the main separator of steam power boilers to ensure their maximal service life. Separators of drum-type boilers are reviewed in terms of their advantages and disadvantages. An analysis of two steels – WB36 and 16GNMA – is carried out by comparing their performance characteristics, chemical composition, and welding procedures. Possible technical solutions for replacing overaged drum boilers are analyzed from the technical and economic perspectives. Three options were selected for replacing the separator: a similar drum made of imported grade WB36 steel; an alternative option with a small drum and a bank of off-mounted cyclones; a drumless option based on a multi-stage evaporation cycle and a bank of cyclones. The materials currently used in separators, i.e., 16GNM and 16GNMA, are compared with imported WB36 steel. It was found that each option had its own advantages and disadvantages, which should be analyzed according to the following parameters: weight and dimensions; assumed need in lifting equipment; hydraulic losses; assumed changes in automatic boiler equipment; relative costs associated with designing, analysis, and risk management. Therefore, the presented recommendations for selecting a drum replacement option are essential for extending the service life and ensuring the reliable and safe operation of boiler equipment.

The aim was to develop a procedure for obtaining an electrode paste of needle coke in case of thermophysical action in the extruder circuit to produce graphitized carbon electrodes with the required structure and properties for thermal furnaces. To study the properties and composition of electrode pastes and electrodes, X-ray powder diffraction, electron microscopy, infrared spectroscopy, and calorimetry analysis were used. To evaluate the electrode behavior upon its heating in a melt, mathematical and statistical analysis was used. The data were processed using standard MS Office programs. Experiments with graphitized carbon materials were conducted in a calorimetric laboratory at the Scientific Center for Problems of Processing Mineral and Man-Made Resources, Department of Metallurgy, Saint Petersburg Mining University (Russia), using a developed proprietary prototype of the extruder. The conditions and technological parameters for processing electrode pastes were defined and substantiated (rate of extrusion and electrode paste flow, pressure, and heating rate within the defined temperature range to achieve stable structural indicators of electrodes). According to XRD data, the proposed method of thermophysical processing of an electrode paste via a special extruder within 550–620°C and a die pressure of 60–80 MPa provides an evenly directed structure of needle coke with an average needle thickness of 12–20 nm and a length of needle phases of 5–10 mm. The behavior of electrode samples was examined in the furnace melt within 1500–1700°C. The obtained stable levels of the thermal-expansion coefficient (0.3·10-6 °C-1) and specific electrical resistance (4.5–6.0 μmOhm·m) were manifested in reduced electrode sublimation, low losses of overall weight at the electrode end, decreased oxidation, and reduced damage on its side. The proposed electrode structure ensures stable heat and electrical conductivity, as well as high heat capacity, which levels are equivalent to those of imported electrodes and electrode pastes.

The aim of the study was to examine the chemistry, kinetics and mechanism of oxidizing roasting of a typical sample of sulfide copper-cobalt ore. The research object was sulfide copper-cobalt ore with the following main minerals: pyrite, pyrrhotite, chalcopyrite, sphalerite, tremolite, silicon dioxide, talc, siderite and calcite. The methodology involved high-temperature X-ray phase analysis (100–900°C), thermogravimetry, differential scanning calorimetry and mass spectrometry of the released gas (30–1100°C, heating rate – 5–20°C·min-1, air flow rate – 30 cm3·min-1). The chemistry, kinetics and mechanism of oxidizing roasting of sulfide copper-cobalt ore with a particle size of <0.1 mm were studied. It was found that the process can be represented as a set of seven elementary reactions: five exothermic reactions (at 398–445, 394–488, 440–498, 433–549 and 451–562°C), corresponding to the intense combustion of iron, copper and zinc sulfides, and two endothermic reactions (at 651–664 and 743–927°C), associated with the decomposition of residual copper and iron sulfates. Kinetic analysis (Kissinger and Augis-Bennett methods, identification of the reaction model by reference function and iterative optimization) of differential scanning calorimetry data in connection with the above reactions showed that the limiting stage of the latter is nucleation and crystal growth. The values of activation energy, pre-exponential factor and Avrami parameter ranged between 140–459 kJ·mol-1, 1.41·104–3.49·1031 with-1 and 1.0–1.7, respectively. It was established that crystallization of the products of elementary reactions is accompanied by an increase in the number of nuclei; new phase nuclei can be formed both on the surface and in the bulk of ore particles. The crystal growth is one-dimensional and is controlled by a chemical reaction at the interphase boundary or by diffusion of reagents. The results obtained can be applied in the practice of oxidizing roasting of sulfide ores and concentrates.

31 января 2023 года Валерий Михайлович Салов отметил 80-летие.