- ItemInfluence of diamond component based on wurtzite boron nitride on wear resistance of cutting tool(Lviv Politechnic Publishing House, 2020) Volkogon, Volodymyr; Avramchuk, Svitlana; Fedoran, Yuriy; Kravchuk, Andrii; Pavlychuk, Tetiana; Antonyuk, Viktor; Avramchuk, Kateryna; I. M. Frantsevich Institute for Problems of Materials Science of the National Academy of Sciences of Ukraine; National Technical University of Ukraine “Igor Sikorsky Kyiv Polytechnic Institute”The article is devoted to the study of the influence of the diamond component in a composite superhard material based on wurtzite boron nitride on the stability of the tool during turning of hardened steels in the mode of smooth turning and when processing intermittent surfaces. The aim of the work is to study the influence of the content of the diamond component in the composite superhard material based on wurtzite boron nitride on the stability of the tool. Based on the analysis of the main patterns of changes in the coefficient of friction depending on various factors, the evaluation of composites containing diamonds of different dispersion in comparison with other materials of this class. The results of the study of the technical level of composite polycrystalline superhard materials based on wurtzite boron nitride of different composition and determination of the efficiency of their use as a cutting tool in the machining of hardened steels are presented. The intensity of wear of composites in the cutting tool during processing of hardened steels is experimentally determined. It is established that the presence of a diamond component in the composite significantly affects the stability of the tool in the conditions of smooth turning due to heat dissipation in contact with the processed material. In the processing of hardened steels with the presence of shock loads, the phase state of the matrix component of the composite plays a decisive role. The obtained research results make it possible to determine the optimal composition and conditions for obtaining a composite material of the system “boron nitride – diamond”, which provides the most effective application of the cutting tool in practice.
- ItemFeatures of repair welding of power hydrocylinder elements(Lviv Politechnic Publishing House, 2020) Dzyubyk, Andrij; Nazar, Ihor; Dzyubyk , Liudmyla; Lviv Polytechnic National UniversityAt present, the use of power hydraulic cylinders is an integral part of most industrial equipment. They provide translational and horizontal movements, replacement of goods, fixation, etc. These devices are necessary elements of the equipment where application of the corresponding level of effort is applied. Often hydraulic cylinders are created specialized to perform certain types of work. It should be noted that part of the elements of the power cylinder in the manufacture is combined with welding. Such integral connections provide rigidity of installation, tightness of a design, fatigue strength at multicycle loadings. Difficult operating conditions, significant workloads, the presence of various external factors often leads to the destruction of individual elements of the cylinder. At the same time, the cost of repairing equipment that involves replacement with new power devices is quite high. This causes the implementation of repair and restoration work carried out at specialized enterprises. However, in the case of repairs, there are often a number of problems that require prompt resolution in the production environment. These should include the provision of basic materials with similar physical and chemical properties, the establishment of welding modes, the selection of the necessary welding materials, the use of appropriate techniques for conducting the arc process, etc. Therefore the repaired welded design of the case of the power hydraulic cylinder needs additional studying for weldability of separate elements among themselves, formation of a zone of thermodeformation influence. In general, the repaired hydraulic cylinder should meet the installation operating requirements depending on the purpose. The design of the considered hydraulic cylinder of the press installation is rather technological from the point of view of maintenance of automation of welding process. It contains long welds of a simple ring configuration. At the same time, the significant linear dimensions and the presence of a cylindrical surface cause some complexity in the implementation of processes. The construction material of the power hydraulic cylinder is low-carbon low-alloy steels. The analysis of technological weldability indicates a tendency to crack due to the thermal cycle of welding. The simulation of welds of the power hydraulic cylinder is performed in the work. The number of rollers was taken into account when obtaining butt welds. A compa ative analysis of different electrode materials with different doping systems is done. The most applicable welding materials by chemical composition and properties of the weld metal are determined. According to the literature data and the results of comparative analysis, the optimal range of cooling rate of the main material of the hydraulic cylinder was established. The properties and structure of the zone of thermal influence of the butt welds of the power hydraulic cylinder have been studied. The magnitude of deformations and stresses caused by the thermal cycle of welding of the hell structure of the hydraulic cylinder liner is investigated. The admissible parameters of the zone of plastic deformations during butt welding are determined.
- ItemOptimization of vibratory conveying upward by inclined track with polyharmonic normal vibration(Lviv Politechnic Publishing House, 2020) Vrublevskyi, Ihor; Hetman Petro Sahaidachnyi National Army AcademyThe paper is devoted to the research of vibratory conveying of piece goods along an inclined track, performing harmonic longitudinal and polyharmonic normal vibrations. It is considered the conditions of reaching maximum conveying velocity at specified values of frequency and amplitude of longitudinal vibrations – the conditions of maximum dimensionless conveying velocity, depending on several dimensionless parameters in the moving modes without hopping. These dimensionless parameters are the inclination angle parameter – a ratio of an inclination angle tangent to a frictional coefficient, the intensive vibration coefficient – a ratio of the longitudinal amplitude of vibration to the amplitude of the first harmonic of normal vibration and frictional coefficient. Maximal conveying velocity is achieved at the certain values of normal vibration amplitudes and values of phase difference angles between longitudinal and normal vibrations, which are called optimal, and their values are dependent on these two dimensionless parameters, while maximum normal vibration acceleration should be equal to the gravitational acceleration. The research was made by approximate harmonic balance method and by numerical step-by-step integration method, which allows performing calculations with any given accuracy. The results obtained by the two methods are compared. To determine the maximal and optimal values of elevation angles, there are calculated the maximal value of the inclination angle parameter at which the value of dimensionless velocity is equal to zero, and the value of the inclination angle parameter at which a particle moves to a specified height in the minimum time. The optimal values of amplitudes of harmonics of polyharmonic normal vibration are determined in dependence on the inclination angle parameter with the number of harmonics from four to seven. The graphs of these dependencies are presented and the most important values of dimensionless parameters are presented in the table.
- ItemSimulation modelling of dynamic processes due discontinuous frictional treatment of the flat surfaces(Lviv Politechnic Publishing House, 2020) Gurey, Volodymyr; Korendiy, Vitaliy; Kuzio, Ihor; Lviv Polytechnic National UniversityFriction treatment refers to surface strengthening (hardening) methods using highly concentrated energy sources. In the course of this processing in the surface layers of the processed surfaces of parts the strengthened layer with nanocrystalline structure is formed. The formed layer has specific physical, mechanical, chemical properties, as well as improved performance properties, which are significantly different from the base metal. A highly concentrated energy source is formed in the contact area of the tool-part due to the high-speed friction (60–90 m/s) of the tool on the treatment surface. Frictional treatment of flat parts according to the kinematics of the process is similar to grinding. The strengthening process was carried out on an upgraded surface grinder. The tool is a metal disk made of stainless-steel. Transverse grooves are formed on the working surface of the tool to intensify the process of forming a strengthened (reinforced) layer with a nanocrystalline structure. The grooves form additional shock loads in the contact area of the tool-treatment surface of the part. These shock loads increase the shear deformation of the metal of the parts’ surface during treatment, which affects into formation the quality parameters of the parts’ surface and surface layer. To study the friction treatment process, the calculation scheme of the elastic system of the machine was developed. A simulation model for the study of dynamic processes that take place during the friction treatment of flat surfaces was built. This model gives possibility to determine the displacements and velocities of the machine table on which the part is fixed and the tool, and to determine their mutual displacement and also calculate the reaction of the machine table.
- ItemLocalization of steel fractures based on the fractal model of their metallographic images(Lviv Politechnic Publishing House, 2020) Zhuravel, Ihor; Mychuda, Łesia; Zhuravel, Yurii; Lviv Polytechnic National UniversityThere are a number of tasks that require assessment of the condition of the material and its mechanical characteristics. Such tasks may arise at the production stage, when there’s a need to control the content of various components of the material, strength, hardness, etc. Also similar tasks arise during exploitation of materials, which is especially relevant today, when most of the responsible products and structures in the field of nuclear energy, chemical industry, machine-building industry are on the verge of wearing down. Previously defectoscopy methods were mainly used to assess the reliability of such materials and products. These methods provided information on the presence or absence of a defect. But to prevent accidents, information about the pre-defective state of the material itself and the degree of its degradation is needed. Approaches involving methods and means of solid state physics, mechanics, chemistry, materials science and other scientific disciplines have become more informative for describing the state of degradation. However, these methods are quite laboursome and time consuming and cannot be applied to transient processes. Therefore, it is important to develop a method that would be based on the analysis of the microstructure of the material would allow to obtain its numerical mechanical characteristics. This approach would be used at the production stage of materials to determine their components and mechanical characteristics and at the stage of exploitation to determine the degree of degradation of the material. It is known that the fractal dimension of each microstructure of the material is an indicator of its qualitative characteristics. Thus, the numerical value of the fractal dimension establishes the relationship between the structure and the mechanical properties of the material. In this work the method of localization of fractures of heat resistant steels on the basis of fractal models of metallographic images is developed and its advantages in comparison with other known approaches are analyzed.