Вісники та науково-технічні збірники, журнали
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Item Structure and wear resistance of aluminium alloys coated with surface layer laser-modified by silicon carbide(Lviv Politechnic Publishing House, 2018-01-29) Student, Mykhaylo; Pokhmurska, Hanna; Zadorozhna, Khrystyna; Dzyubyk, Andrii; Khomych, Ivan; Karpenko Physico-Mechanical institute of the NAS of Ukraine; Lviv Polytechnic National UniversityModern approaches to ensuring the necessary characteristics of surface of a material with the aim to improve economic and technological characteristics of the structures are considered in this paper. It is shown that aluminium alloys gain wide application in industry. Nevertheless, surface characteristics of materials are insufficiently good for their use in structures which operate under abrasive wearing and boundary friction. The use of the method of surface modification by a concentrated light-beam of energy is of prospect. Analysis of literature data indicates that in the course of laser-modification of surface of an aluminium alloy it is possible to form a material whose operational characteristics are higher than those of the material in its initial state. However, herewith it is important to quantitively estimate properties of the obtained composite layer on the surface of the article as well as to estimate the distinction between the layer and the main metal. The microstructure of laser-modified composite layers of aluminium alloys which had been formed by means of direct blow-in of SiC powder into the melted by laser radiation zone of surface has been investigated. Laser reinforcement of surfaces of aluminium alloys by SiC particles causes pronounced inhomogeneity of structure of surface layers of alloys. It has been shown that preliminary heating of specimens in the course of their laser-treatment increases the depth of the modified layer over the whole zone of treatment and improves the uniformity of distribution of reinforcing SiC particles; however, because of turbulence in the melt there is observed some non-uniformity of distribution of SiC particles in the modified layer. It is found that in the interaction of Al melt with SiC particles there forms plates of Al4C3 carbide at the interface, these plates grow mainly co-axially to the orientations of SiC crystals in the direction to the melt. Besides, in the matrix there takes place partial dissolution of SiC with formation of needle-shaped Al4C3 carbides. During the modification of surfaces of these alloys, in the case of increased concentration of silicium in the melt there is also observed inclusion of pure silicium. Besides, there is also possible the diffusion of aluminium into thin near-surface layer of silicium carbide, the layer separates from SiC crystal (phenomenon of ply separation) when the concentration of aluminium reaches a value of 3–5 %. It is established that the abrasive wear resistance of the non-modified AD35 alloy, which is determined according to the method of rigid abrasive wheel, is by 30–45 % higher than that of B95 alloy. In this case, the deterioration (wear-and-tear) proceeds according to the following two mechanisms: (1) by cutting and (2) by adhesive grafting between the abrasive wheel and the aluminium alloy by tearing out alloy particles from the surface. Optimal regimes of laser reinforcement of surfaces of aluminium alloy by means of fine SiC particles have been determined in this paper; this enabled us to increase 40–70 times the wear resistance of aluminium alloys in comparison with non-modified alloys when they are subjected to friction by rigidly fixed abrasive particles. The same reinforcement almost two times increases the wear resistance in dry reversive friction, and it increases the wear resistance only by 10–25 % in wearing by loose abrasive particles.Item Optimization of welding modes for high-strength low-alloy domex 700 steel(Lviv Politechnic Publishing House, 2017-10-19) Dzyubyk, Andrii; Palash, Volodymyr; Khomych, Ivan; Hrynus, Stanislav; Lviv Polytechnic National UniversityThe microstructure and hardness of the weld joints of DOMEX 700 steel were investigated. As a result, the optimization of the parameters of robotic arc welding in the environment of protective gases was carried out taking into account the size of the energy per unit length. The optimum modes of welding were determined. The size of the deterioration area, where there is a decrease in hardness in comparison with the main metal, for a thickness of 6 mm is 2.36 mm, and for a thickness of 3 mm is 1.51 mm. The parameters of the robotic welding process in the arc mode in the environment of protective gases for the investigated thicknesses of the DOMEX 700 steel were recommended. As a result, the energy-saving conditions for welding performing were achieved ensuring the required technological strength.Item Investigation of magnetically controlled electric arc(Lviv Politechnic Publishing House, 2017-10-19) Biloborodchenko, Volodymyr; Dzyubyk, Andrii; Zabranskyi, Andrii; Lviv Polytechnic National UniversityIn this work, the results of pad welding with the circularly rotating arc existing in an inert gas between a circle cathode with the diameter suitable to dimensions and geometry of a welded surface, with the kinematic characteristics of the motion provided (with the rest equal conditions) by the external magnetic field, are considered. It is shown that the strict theory of an electric arc is insufficient for the description of real physical processes occurred in it under the action of external exciting magnetic fields, and so it does not allow conducting satisfactory technological calculations of the parameters of the pad welding process performed by the arc moved by the external magnetic field. The main problem consists in determining the effectiveness and the direction of superposition of electrodynamic and mechanical forces in it, which resist arc interaction with the magnetic field. Therefore, the aim of the work is to investigate the influence of the induction value В of the transvers magnetic field of a solenoid inductor on predicted kinematic characteristics of the arc. The investigations were conducted with the use of experimental equipment (test bench) consisting of a toroidal inductor with a winding. On the inductor, a nonfusible water-cooled ring copper electrode is mounted. Electrode dimensions agree with the diameter of pad surface. The shielding gas is provided through the system of radially located nozzles with discreet valvular operation, whose work priority is agreed with the arc motion velocity by a control unit. Since the values of abovementioned forces directly conditioned by the presence of a magnetic field in an interelectrode gap, the investigation of its intensity by the electrodynamic method with the help of the measuring instrument for magnetic induction ИМИ-1 was carried out. The analysis of the superimposed surface of the impact of the magnetizing current and the arc gap, which are used at pad welding by magnetically controlled arc, on the field induction shows that the range of their influence as technological mode parameters is quite narrow. Accordingly, for optimal choice of model nomographic solutions and the description of the correlation of parameters of the arc gap and magnetizing current, which provide the technologically suitable induction, an experiment was conducted according to the matrix of simplex-summarized С-С2 design. The investigations of a model extremum shows the acceptable induction value of 850∙10-5Т for the length of the electrode gap of 4 mm and inductor magnetizing current of 6 A. As a result, the proposed design of the test bench satisfies the geometrical parameters of renovated workpiece and enables using the effective repeated thermal pad cycle per unit of the surface by the rotating arc in the stable magnetic field. Settings of the magnetically operated arc, which provide the necessary value of field induction in the inter-electrode gap, can be determined either by nomograph solution, or by the strict statistic models. The influence of the length of the inter-electrode gap on the choice of the induction value is limited by technologically suitable pad current and corresponding length of an arc column. The main setting and controlling parameter of the magnetic field mode is the inductor magnetizing current. The force of resistance to arc motion at the stage of arc development and at the stage of arc steady motion is directly proportional to the value of the pad current. Calculated values of the velocity of arc motion at given values of the pad current are in the range relevant to its steady motion and provide the processes of anode melting without thermal damaging the ring cathode.Item Determination of stresses and ultimate loads for composite plates with elastic inclusions(Lviv Politechnic Publishing House, 2017-10-19) Jaroszewicz, Jerzy; Maksymovych, Olesya; Dzyubyk, Andrii; Nazar, Ihor; Bialystok University of Technology; Lviv Polytechnic National UniversityIn the article, the algorithm for determination of stresses in anisotropic plates with elastic inclusions of another anisotropic material was developed on the basis of complex singular integral equations. The solving of integral equations has been carried out numerically using the method of mechanical quadratures. The strength analysis (calculation of strength) of composite plates with inclusions has been performed using the Hoffman criterion.Item Optimization of conditions of electroslag welding of bandings of rotary units(Publishing House of Lviv Polytechnic National University, 2016) Dzyubyk, Andrii; Dzyubyk, Liudmyla; Zinko, Yaroslav; Biruk, StanislavThe design of banding shells of rotary units is analyzed. It is shown that combined welding and cast manufacturing of bandings is used in the case of large structural sizes. The basic materials (30, 35, 25 HSL and 30 HML), being used in this process, are characterized by the tendency of forming of hardening structures due to the thermal cycle of welding. As a result of this, the cracks in the heat-effected zone, which lead to the destruction of the connection under the influence of welding residual stresses. The analysis of literature sources has shown that the usage of electroslag welding is perspective during the manufacturing and welding of operational cracks. Thus it is important to define the correct parameters of the welding conditions. In the case of electroslag method they are different from the arc methods and are characterized by the larger amount. In the paper the technological process of welding of banding (tread) ring with the external diameter of 4600 mm, wall thickness of 300 mm and wideness of 500 mm, which is made of steel 35. The defining of regime parameters is made using the following recommended techniques: taking into account the chemical composition of the basic metal; according to the nomogram depending on the ratio of the thickness of the metal to the number of electrode wires; using the calculation (design) method according to the conditions of electroslag welding of the banding. Taking into account the tendency of the steel 35 to cracks forming (cracking), the evaluation of the structure and phase composition and mechanical properties of metal of heat-effected zone of the weld. In order to define the microstructure, the cooling rate of the metal in the range of structural transformations was determined and the diagram of anisothermal decomposition of austenite was used. The technique of determination of the metal cooling rate as a result of the influence of thermal cycle of electroslag welding is proposed in the paper. It is based on the usage of special nomograms which characterize the specific features of the process being studied. The cooling rate equals w= 0.1876 degrees per second when using the developed process parameters. Also the investigation of temperature distribution in the cross-section of the weld has been carried out. It is shown that there are no significant deviations of temperature when using the proposed regime parameters. This influences the reduction of the level of residual stresses along the thickness of the weld. The analysis of the diagram of austenite transformation has shown that the structure of the steel 35 in the initial state is ferrite one with the mixture of pearlite and bainite. As a result of welding carrying out the structure will have a similar composition with slightly larger content of perlite and bainite. It was defined that their content in the heat-effected zone is as follows: 39 % for ferrite, 61 % for the mixture of perlite and bainite. At the same time, the investigated technology of electroslag process ensures the slow heating and cooling of the areas around the weld and obtaining of satisfactory mechanical properties of the metal. Therefore, the combined usage of existent techniques of regime parameters determination is expedient. Also it is necessary to carry out the verification of physical and chemical properties of the metal of heat-effected zone in order to prevent the formation of hardening structures.