Bulletin PNRPU. Mechanical engineering, materials science

Hydro jet pumps are used in many branches of engineering. They are designed for pumping liquid, gaseous or gas-liquid mixtures. Although hydro-jet setups have a relatively low efficiency factor (about 30 %), they demonstrate obvious advantages over, for example, multiphase pumps due to simplicity of their design and operation, the absence of moving mechanical parts and, as a consequence, high reliability. For the most part, designing of flow ducts of hydro-jet pumps is carried out by applying the engineering methods of single-phase flow computation, which are based on the laws of conservation of energy, mass, momentum and semi-empirical relationships. However, the results of their application for evaluating multiphase flows are highly approximate. A more efficient approach to optimization of the duct system of Hydro jet pumps is the mathematical modeling of flows using modern software packages adapted to problems of hydro- and gas dynamics. The paper presents the results of mathematical modeling of hydro-jet pump operation under conditions of pumping gas-liquid mixtures. The simulation was performed using the STAR-CCM + software. The problem was solved in the Euler coordinates using the Volume of Fluid (VOF) model of a multiphase flow. A turbulent flow of gas-liquid mixture is described in the framework of the k-ε model assuming that there is no chemical interaction between the phases, and the first approximation does not take into account the surface tension forces. In the calculations made, water was used as the liquid phase, and air, which is an ideal gas - as the gas phase. A few variants of computation of flow ducts with cylindrical and annular active nozzles are considered. A comparative assessment of the pump efficiency is carried out. It has been shown that the most effective model is the pump, in which the flow duct is fitted with an annular nozzle and the gas and liquid are fed separately through the two passive inlets.

This paper presents study of short-term strength and ductility of stainless steel samples PH1, obtained by selective laser sintering on the installation Eosint M280 at different heat treatment modes. The study was to determine the optimal mode of heat treatment and the direction of growing samples (horizontal or vertical). Tests were carried out from alloy PH1 according to GOST 1497 with the construction of conditional diagrams of tensile and determination of the following characteristics: conditional time resistance;, conditional yield stress; residual elongation; relative contraction; static modulus of elasticity in tension . Characterization of mechanical properties of the alloy PH1 in the tensile test on the installation LFMZ100 were conducted on cylindrical specimens made of heat-treated work pieces obtained by selective laser sintering. Tests on the modulus of elasticity were carried out according to GOST 25.502-79. The rate of loading determining the strength was 1,25 mm/min loading Rate in determining the flow characteristics was 0,125 mm/min the Tests were performed until fracture of the samples. Analysis of the results showed that the performance characteristics of the samples reach a maximum value in obtaining their horizontal orientation than the characteristics obtained by the vertical direction of growing samples. Studies of the structure and physical and mechanical properties of the alloy PH1 showed that this alloy has higher strength characteristics compared to analogues obtained using casting, rolling and solid-phase sintering technologies. The obtained characteristics of short-term strength and plasticity, conventional tensile diagrams can be used in strength calculations and in determining the modes of testing for low-cycle fatigue of parts made of alloy PH1.

Fluoroflogopit type molded glass-ceramic materials are promising alternatives to traditional refractories for electrolysers in non-ferrous metallurgy. The use of cast glass-crystalline fluoroflogopite-type materials in the electrolysis method of producing metallic magnesium allows us to solve several urgent problems associated with the rapid deterioration of the lining of electrolyzers. First of all, when using glass-crystalline fluoroflogopite-type materials, the cost of repairs and diagnostic equipment downtime are reduced, the purity of the main products increases, since the glass-crystalline fluoroflogopite-type materials practically do not interact with the components of the electrolysis bath medium. Long service life is ensured by low surface wettability of molten mica-crystalline fluoroflogopite-type materials by molten liquid magnesium. However, the existing technological solutions and technological process parameters do not provide the necessary level of yield of products and are largely dangerous for the environmental situation and the health of production personnel. The article specifies the dimensional parameters of the technological process of obtaining cast micaceous crystalline materials, which provide an increase in the yield of useful products, as well as help to enhance the environmental safety of this production. The practical utility of such solutions as preliminary granulation of charge mixtures before loading into a single-phase melting electric arc furnace and using a multi-level exhaust gas cleaning system is shown. It is shown that the choice of optimal dimensional parameters of the technological process allows to neutralize the effect of the most dangerous byproduct hydrogen chloride to a level that allows to preserve the health of workers and prevent irreparable environmental damage to the territory of the enterprise and nearby settlements simultaneously with increasing productivity and product quality.

The development of new technologies for the manufacture of products from aluminum alloys, providing improved performance and high economic performance, is an urgent task. The use of additive technologies (АТ) or technologies of layer-by-layer synthesis for the manufacture of metal structures makes it possible to significantly accelerate the solution of problems of technological preparation of production and production of finished products. The use of filler wire as a working material allows you to get rid of the problems associated with the low productivity of existing methods, the high cost of the equipment used, the limited types of materials used, due to the use of powder systems. The use of the layer-by-layer synthesis method allows the use of wrought aluminum alloys for the preparation of complex shaped products. The use of new alloys for additive production will provide complex critical structures with improved performance characteristics. High performance characteristics are provided by the formation of a given structure and metal properties of the structure (determined by the residence time of the metal in the molten state, the size of the fusion zone between the layers, the rate of heating and cooling of the metal in the lower layers, etc.). Constant heating of the molded product when applying layers may make it difficult to obtain the required dimensions of the deposited layers and the desired structure of the metal obtained To solve many problems of surfacing aluminum alloys, to improve performance with high quality allows plasma surfacing with direct current of reverse polarity. Plasma surfacing with reverse polarity current provides cleaning of the surface of the previous layer from contamination due to the effect of cathode sputtering, good wetting and spreading of the liquid metal with minimal surface heating. This ensures the production of layered materials with a favorable structure without internal defects. The paper presents the results of the study of the additive formation of products from an aluminum alloy 1580 system aluminum-magnesium-scandium using plasma surfacing current of reverse polarity. Selected modes of welding, ensuring the formation of layered blanks without internal defects. It is established that plasma surfacing provides the relative stability of the structural and phase composition of the material of the layers under the influence of thermal cycles as the blank is formed. A slight increase in the volume fraction of hardening and excess phases was recorded. Marked loss of zinc in the weld metal while maintaining the content of the remaining elements. It has been established that the strength characteristics of the deposited metal are at the level of the properties of the cast material, yielding to the deformed; at the same time, the ductility of the weld metal significantly exceeds the ductility of castings - by 2-3 times, and the ductility of annealed rolled semi-finished products - by 1.5 times.

Enamel coatings are characterized by high resistance to aggressive media, gas and atmospheric corrosion, organic and mineral acids in a wide range of temperatures, and have good hygienic properties. The service life of enamel coatings can be significantly reduced in violation of the integrity of the coating. The problem of the occurrence of enamel coating defects that destroy the integrity of enamel is considered. Among the defects of enamel coatings “enamel bubble” and “foreign inclusions” are most common and the characteristics of defects depend on the chemical composition of the enamel and the temperature of the heating and aging processes in the furnace. The purpose of the work is to establish the influence of time and temperature of burning on the structure and defects of the enamel coating. Defects of the surface of the enamel coating were studied using metallographic studies and methods of scanning electron microscopy. Elemental analysis of coatings was studied by X-ray energy dispersive microanalysis. Samples of enamel coatings were thermally treated at temperatures of 820 °C, 830 °C, 840 °C, 850 °C, 860 °C, and 880 °C and for a time of 2 minutes, 3 minutes, 4 minutes, and 5 minutes. The chemical composition of the enamel coating defects is shown. The influence of temperature and heat treatment time on the structure and defect of the enamel coating has been established. It is shown that with an increase in firing temperature from 820 °C to 880 °C, the enamel bubble defect becomes pronounced, the enamel cellular structure begins to be more clearly seen, the size of the bubbles gradually increases, the number of bubbles of relatively small size becomes larger. An increase in heat treatment time from 2 minutes to 5 minutes leads to the enlargement of bubbles, the cellular structure of the enamel becomes more pronounced. Long-firing will not lead to the correction of coating defects. The optimal technological parameters of heat treatment of enamel coatings were established: firing temperature of 820 °C and firing time 2...3 minutes.