Vol 25, No 4 (2021)

The aim was to study the effects of technological residual stresses on the bending stiffness of cylindrical parts of shafts and axes. Experiments were conducted for elongated cylindrical specimens made of steel grade 35 with a diameter of 30 mm using boring and turning methods. Specimens were annealed in a protective medium to remove initial residual stresses. Experiments were carried out using an Amsler laboratory hydraulic testing machine and VK8 grade hard-alloy matrices. The experiments showed that, for an extremely low degree of relative crimping of 0.1 to 0.5%, the size of the layer with tangential residual compression stresses gradually decreases. The stiffness of such cylindrical workpieces remains almost unchanged. An increase in relative crimping (from 0.5 to 1.2%) leads to a decrease in resi dual compression stresses on the part surface. The layer thickness with tangential residual compression stresses starts to increase. This leads to a decreased residual buckling and an increased bending stiffness. It was found that the degree of relative crimping has no effect on the variation of distribution depth of axial residual stresses. Optimal distribution of tangential residual compression stresses can be reached by increasing their depth. A linear relationship was found for relative crimping of 0.1 to 1.0%. The highest bending resistance was recorded for specimens strengthened by residual crimping of about 1.0%. By processing workpieces using enveloping deformation with crimping of 0.1% and loading them with a transverse force of 0.6 kN, bending distortion can be decreased and the strength of parts can be increased by 5 times. It was found that the bending stiffness of cylindrical shafts is greatly affected by residual compression stresses. The bedding depth of residual stresses has various effects on the stiffness of cylindrical parts. Thus, correct use of strengthening enveloping deformation can form a high-quality surface layer on parts with the pre-defined distribution of residual stresses.

The possibility of installing photoelectrical solar units inside domical structures with the maintenance of their power generation level was investigated; an optimal distance between a photoelectrical solar unit and the transparent walls of the respective domical structure was determined. The experiments were carried out at the North-Eastern Federal University in the central part of the Republic of Sakha (Yakutia) by determining reduction in the electrical energy efficiency of photoelectrical solar units when changing their location. An optimal distance for installing such units within transparent domical structures was found based on graphical interpretations and gradients. The authors obtained reference parameters for light flux reduction, the generation power of a photoelectrical solar unit when changing the operation medium, and the optimal distance of a photoelectrical solar unit inside a domical structure for reducing the surface contamination of the unit. It was found that, when photoelectrical solar units are operated within a transparent domical structure, the power generation falls by 25.61% as compared to actual results in open space. It was found that an increase in the distance between the transparent walls of the domical structure and the unit led to a decrease in the power generation by ~23.01% and the light flux power by 5.224% at 1.5 m. This method of installing photoelectrical solar units can be used in the construction and designing of smart home systems and autonomous power generation facilities in northern regions of Russia.

The aim was to assess the technological feasibility of generating sodium cyanide by coal gasification, to study the effects of the process parameters (temperature, experiment duration, coal type) on the concentration of sodium cyanide in the resulting solutions, as well as to identify optimal modes of the process. Experiments were carried out on a laboratory setup consisting of a tubular cylindrical furnace equipped with a working compartment in the form of a corundum tube. Lignite and charcoal, preliminarily crushed to increase the specific surface area, were investigated. A solution of sodium cyanide was produced by sorption of gaseous hydrocyanic acid (a syngas component) with a sodium carbonate solution. A NaOH solution (pH = 10) installed in an ice bath was used in the system of absorbers. The content of sodium cyanide in the solution was determined by the titrimetric method. The HSC Chemistry 5.1 software package was used for thermodynamic calculations. During the gasification of charcoal in the temperature range 600–800oC, sodium cyanide solutions with a concentration of 0.03–0.08 wt% were obtained. An increase in temperature from 600 to 900oC led to a 4-fold decrease in the concentration of sodium cyanide in an alkaline solution, under the same duration of the experiments. A regression equation was derived for the dependence of the NaCN concentration in solution on the temperature of coal gasification and the duration of the process. It was shown that the generation of sodium cyanide by coal gasification under laboratory conditions yields sodium cyanide concentrations in solution comparable to those used for gold cyanidation at gold recovery plants. The installation of sodium cyanide generation lines directly at the production areas of gold recovery plants will reduce the production costs by eliminating expenses for purchasing, transporting and storing reagents.

We apply mathematical modelling to study heat transfer processes during fire refining of blister copper in a ladle-furnace unit. A ladle-furnace unit was designed to test the refining technology using bottom blowing in a bubble mode by gaseous reducing agents (hydrocarbons) and an oxidiser. Mathematical modelling allows the properties of a real process to be described based on mathematical formalisation of physical laws and regularities. It was proposed to use gaseous reducing agents, rather than expensive residual fuel, as a liquid-reducing agent. The use of gaseous reducing agents in the bottom blowing mode produces higher technical and economic indicators of the process. In addition, some technological operations were transferred directly to the ladle, thereby eliminating the need for re-melting and heating of refined copper. One of the identified problems was the need to maintain the predetermined thermal regime, which provides the very possibility of both performing refining operations and introducing a gaseous reagent (determining the hydro-gas-dynamic parameters) into the melt during bottom blowing. An original method for considering the thermal effects of chemical reactions in mathematical models was presented using an example of exothermic reactions during oxidative refining. The use of two different methods of analysis allowed a comprehensive assessment of the influence of the main exothermic reactions on the thermal regime of the refining process. The presented mathematical models can be used for determining the specific effect of various technological parameters (composition and fuel consumption, temperature and degree of blast enrichment, lining design, etc.) on the dynamics of changes in the temperature field of the melt and the technical and economic parameters of melting as a whole.