Bulletin PNRPU. Mechanical engineering, materials science

This article shows the calculation results for effective power of the welding arc with bipolar rectangular current pulses of 50 Hz by weld sizes on АА1060 aluminum alloy of 4 mm thickness at a welding speed of 2.5 mm/s. The average pulse current showed no changes and was 170 А, and reverse polarity pulses duration was set at three levels - 20, 25, and 30 %. As a result of numerical experiments based on a mathematical model, it was determined that the effective power decreases from 2,080 to 1,843 W. The reason is a decrease in the average pulse current of reverse polarity from 50 to 30 А. This indicates a higher thermal efficiency of the reverse polarity arc which shall be estimated by the specific effective power per 1 А of current. To account for the plasma gas flow contribution to the effective arc power, we used the proposed formulas for the power from the electrode sheaths. As the result, for all welding conditions, we have obtained a stable value of the plasma gas flow specific effective power of 3.28 W/А at an average algebraic deviation of 4.4 %. This tends to the simple formulas for effective power calculation. The average effective efficiency is 75 % for the direct polarity arc and 65 % for the reverse polarity arc. The reverse polarity pulses efficiency coincides well with the obtained efficiency for the reverse polarity arc with a consumable electrode, if we subtract the power transferred to the article by electrode metal droplets. The obtained efficiency values make it possible to calculate the penetration for bipolar rectangular current pulses and consumable electrode welding.

The article presents the results of studies of the mechanism of changing the dimensional accuracy of precision parts such as bearing rings, which arise due to the asymmetry of the plots of residual stresses relative to the main axes of the transverse and longitudinal sections of the rings that occur during relaxation. The production of precision rolling bearings of accuracy classes 6 and higher, which are widely used in various machines and aggregates, is particularly critical for the stabilization of geometric parameters. Even a slight change in size over a certain time interval leads to a sharp loss of accuracy of these bearings. The existing technology and known methods of stabilizing geometric parameters, such as heat treatment, low-temperature tempering, artificial aging, are ineffective, since their use in practice leads to high-energy costs, and the degree of refinement of geometric dimensions and shapes is insignificant. Therefore, work on improving the technology of stabilizing the geometric parameters of precision bearings is very relevant. The object of research in this work is the rings of the bearing assembly of the belt tensioner of the car (tensioning rollers) of the following types 2108-1006120-01, 2112-1006120-01. The control of the studied parameters of the parts was carried out using the following equipment, namely: the MAR 3 diffractometer, the FARO ARG EDGE coordinate measuring machine. Studies show that the stabilization of the dimensions of the parts, as well as the values of deviation from roundness (ovality), occurs on the 15th day after the application of the proposed method of relaxation of residual stresses in precision parts such as bearing rings based on the propagation of ultrasonic energy through a special liquid (cavitation effect).

The problem of the reliability at the promotion of modern advanced types of API pumps was investigated. Pumps that are still rare in the Russian Federation. The difference of the design and pumps use is presented and the typical failures of new model sucker rod pumps are discussed. The review of fatigue fractures of threaded connections is carried out for the search of effective methods for microstructure control and quality assurance. The classical procedure for determining failures has been shown, including examination of the quality of the rod, metallographic examination of bars typical for the oil industry and fractography. Based on review of pumps had different operating conditions noted the similarity of destruction and are fixed regularities. To explain the systematic nature of the failure is performed a calculation by the modified Inglis formula. At paper is tabularly presented nonlinear stress distributions at microvolumes under the API tapered thread profile. The most significant stresses under the thread roots are considered in detail and here is shown in five times higher stresses in respect to the body of the rod behind the thread. The reasons and constructive factors are counted. The main conclusions are made about the criticality of deviations of the objects microstructure, despite the same origin of the studied metal objects from one manufacturer, JSC "Omutninsky Metallurgical Plant". The correlation of the types of microstructure and the run life time between failures is shown. Clarified the acceptability of various microstructures away from stress concentrators and criticality in the root of the thread. It is concluded that it is necessary to control the critical deviations of the microstructure in the area of stress concentrators to ensure quality. A review and assessment of approaches for quality assurance of threads API pump parts is carried out. Highlighted especially effective improvements, discussed the possibility of their combination. The insufficiency of the classical methods of metallurgy for solving the quality improving problem of the investigated objects is explained.

The main stages of obtaining sealing gaskets from thermally expanded graphite are presented. A method for obtaining a mathematical model of the dynamics of the process of cutting these gaskets on press equipment is proposed. The procedure for obtaining a model consists of two interrelated stages. At the first stage, using the experiment, the dependence of the technological force of the cutting process on the movement of the working body was obtained, which has a number of features due to the specific properties of thermally expanded graphite. A schematic diagram of the experiment and its results are presented, which are approximated in the form of analytical dependencies based on the least squares method. The calculation scheme of the dynamics of the cutting process is developed, taking into account the dynamic relationship between the engine, the Executive body in the form of a crank-slide mechanism of the press and the processed material. Taking into account the accepted assumptions, a dynamic model reduced to the crank shaft is constructed and its main geometric, mass, and power parameters are calculated. The main stages of operation of press equipment in the cutting process are considered. The main parameters are summarized in the corresponding table, the elements of which are used in compiling the generated mathematical model. At the same time, the design and technological features of the press are taken into account and the stages of its operation (working and idling) are highlighted. The structure of the system of equations of motion is nonlinear and takes into account the characteristic and type of technological cutting force, the analytical value of which is obtained on the basis of experiments. The solution of these equations is implemented using the DYNAMIC software module using the fourth-order Runge-Kutta method. A number of module elements are presented in the article. As an example, a graphic illustration of one of the calculation results is given. Based on the results of the research, conclusions are made.

The paper presents the results of the investigation of the angles of twisting of cardan shafts and the efficiency of the cardan transmission. The task of the investigation is to improve the methodology for calculating the angle of twist of the cardan transmission and the efficiency of the cardan transmission using theoretical and experimental investigations, and for this it is necessary: to test the cardan transmissions characterized by variable values of torque and braking torques and changes in the design parameters of the cardan transmission in each experiment , calculate the experimental errors. For investigations, a needle-bearing gimbal test bench was used, which generates torque using an electric motor, and the loading device is hydraulic, where the gimbal drive is loaded with a hydraulic pump and an adjustable throttle. To prevent overheating of the working fluid in the hydraulic system, there is a heat exchanger, and to prevent exceeding the working pressure, a safety valve is installed, which is controlled by an electrocontact pressure gauge, which, if the working pressure is exceeded, is triggered and directs the flow of working fluid into the hydraulic tank and the pressure in the hydraulic system drops. As a result of experimental investigations to identify the influence of the length of the cardan transmission, the angle of misalignment of the shafts of the cardan gear, the load and the rotational speed of the cardan gear on the angle of twisting of the cardan shaft and the efficiency of the cardan gear, as a result of which regression equations were obtained for determining the angle of twisting from the listed higher parameters and efficiency of cardan transmission for their introduction into an improved method for calculating cardan transmission.

The relevance of the presented work is due to the study of materials with desired properties. This makes it possible to increase the operational characteristics of the units of mechanisms. In this paper, the processes of structure formation in metal-glass materials obtained by powder metallurgy are considered. For this, the authors use the method of obtaining a composite material based on carbonyl iron powder VK-1 and glass. The paper considers the production of glass powder by grinding, mixing with iron powder and subsequent pressing of the resulting powder using a hydraulic press and sintering in a protective atmosphere. Broken container glass of BT-1 brand is presented as a glass filler. The article describes the technique and stages of obtaining metal-glass materials. Substantiations are given for the choice of the matrix (carbonyl iron powder) and the reinforcing component (broken glass powder). The work establishes a connection between the composition and structure of the obtained composite materials and their properties. During the study, parameters such as the concentration of the glass powder and the sintering temperature were varied. The properties under study were hardness and porosity after sintering. Mathematical modeling and processing of the results obtained were performed using the STATISTIKA 10 software package. Microstructural analysis of the obtained samples was carried out using a KEYENCE-VHX digital optical microscope. The main conclusions about the reasons for the obtained dependences are formulated. The practical significance lies in obtaining new materials with enhanced antifriction properties. It is shown that with an increase in the sintering temperature, up to 1100 °C, an increase in hardness, a decrease in porosity and the formation of a new phase of fayalite (FeSiO4) are observed.