Bulletin PNRPU. Mechanical engineering, materials science

The occurrence and propagation of cracks in products made of heat-resistant nickel alloys during surfacing, welding and additive technologies associated with the use of highly concentrated energy sources is a significant problem that reduces the quality of products. The tendency to form hot cracks in welding and surfacing is determined by the composition and quality of the alloys, structural factors - grain size and structural heterogeneity, composition of filler materials and welding and surfacing technology. When surfacing at low speeds, the rate of crystallization of the weld metal decreases, its area, width and the high-temperature weld zone increase, which causes a decrease in the intensity of the build-up of the welding stresses, which relax in a large volume of the weld and near-shock zone. The paper presents the results of the investigation of the influence of the parameters of the argon-arc and laser surfacing regime on the structure formation, properties and propensity of high-temperature nickel alloys to crack formation under different methods of surfacing. Alloys with a large structural heterogeneity, especially due to dendritic liquation and predominantly with larger grains, have an increased tendency to form hot cracks. The structure of nickel alloys, given a balanced chemical composition, is not always a guarantee of good crack resistance. As practice and results of research show, the choice of technology and parameters of the surfacing regime is often crucial. It has been established that the argon-arc surfacing of a nickel alloy in combination with an additional ultrasonic action creates a modifying effect of increasing the phase dispersion. The combination of favorable structural parameters - fine-grained g-solid solution and increased dispersion of g¢-phase, which is realized under argon-arc surfacing with additional ultrasonic action at optimal conditions, leads to an increase in the microhardness and heat resistance of nickel alloys. Cracks and porosity under the optimal surfacing regime are not fixed.

The production of cast billets of high accuracy, the surface of which does not require additional machining, is one of the priority production tasks. Investment casting is a method that solve this problem. In the production of melted models by cold pressing of powders of waxy compositions, high dimensional geometric parameters of molded articles are achieved, characterized by the absence of shrinkage defects. However, the elastic response of the compacted material is a disadvantage of this method of forming extended sections of the melted models. This, in some cases, leads to an increase in the dimensions of the compact in the longitudinal pressing direction by 0.7-1.2 %, and in the transverse direction by 0.4-0.5 %. This effect is difficult to predict due to the uneven distribution of density in the volume of the resulting compacts. To design a tools, we need to manage the dimensions of extended compacts, including those with a variable cross-section and complex configuration. The purpose of our experiment is that we want to establish the possibility of controlling the magnitude of the elastic response of an extended section of a melted model obtained by extruding a waxy powder powder through the mouthpiece without preheating it. In this paper we present the results of a series of experiments on the regulation of the magnitude of the elastic response of a material during the simulation of the process of obtaining extended compacts obtained by extrusion through a mouthpiece. The extrusion velocity was a variable parameter in the experiment. The parameters recorded are: the load created in a cylindrical piston filled with a waxy material fraction, the temperature of the extruded material, the density and the magnitude of its elastic response along the length of the resulting compact. The unevenness of the distribution of properties is reduced due to a change in the rate of formation of compacts, this allowed us to predict the final dimensions of the molding, which are important for the design of press tools.

Gas-dynamic design of the centrifugal compressor stage begins with the selection of the basic dimensions based on certain rules - the rules of primary design. The Universal modeling method is developed at the St. Petersburg Polytechnic University and is successfully used in design practice. Its recommendation for the impeller entrance dimensions focuses on the relative velocity minimization. The blades’ inlet angle is selected from the condition of non-incidence entrance. Recommendations are justified when designing stages with medium and large flow rates. The comparison of primary design principles by universal modeling Method (minimizing the speed at the entrance to the impeller and providing a no incidence entrance on the design mode, while the inlet blade angles are small, long inter-blade channels, the loss coefficient is increased) and Clark firms (optimizing the shape of the inter-blade channels by increasing the inlet angle of the blades and increasing the flow coefficient by reducing the height of the blades on the design mode, while there is a positive incidence angle and large kinetic energy at the entrance) was made. The analysis is based on the example of a stage with a design flow rate coefficient 0.015 and a loading factor 0.70. The results of stages calculations by the program inviscid quasi-three-dimensional calculation of 3 DM.023 and the program of the Method of universal simulation was compared. Analysis of velocity diagrams and calculations of the characteristics of low-flow stages showed that, due to small blade angles, the impeller loss factor is large, but can be reduced when the proposed new recommendations for primary design are fulfilled.

The enterprises applying technologies with low consumption of resources when receiving metalwares designs most of which important criterion for evaluation of quality is nonvolatile operational durability have considerable competitive advantages The developed technology is directed to recovery of operational characteristics of steel details, including extended, having signs of wear, a metal building-up on their surface. Process is realized as a result of local heating of a steel detail by combined use of powers of arc and aluminothermic influences. The lack of information on such process, structures and properties of the received buiding-up and its connection with parts material defines relevance and demand of results of researches. The main purpose of work is definition of the thermal mode of such impact on a zone of metal building-up of steel elements design at which the required geometrical, structural and strength characteristics received product are reached. Local heating in the considered process can be provided by means supply to a surface of product of heat resulting from joint arc and aluminothermic influence from the extended core electrode (CE), that consists from steel lengthy cover in which thermite filler is concluded. The last represents mix of fractions of oxide of iron, reducer and additives These materials - waste of the machine-building enterprises and metallurgical complex, its utilization is difficult. Process allows to provide return of these materials to production. The main purpose of using the termite material, that fills the cavity of the extended core is to regulate the temperature and supply metal to the building-up zone of the resulting material on the surface of the part - the basis. Slag, formed as a result of the aluminothermic component of the thermal effect on the fusion tub, slows the rate of heat removal from the last. Temperature influence in a zone of contact of the build-up metal with basis is regulated by the current, tension and time of their stay in a zone of thermal influence. After crystallization the chemical analysis of build-up material zone is carried out, the structure, strength and dimensional and geometrical parameters of received product are defined. During the experiment is established. compliance of chemical composition of build-up metal of a zone of thermal influence to the material of basis executed from St3 defined in accordance with GOST 380-2005. Comparison of traditional structures with the structures received in the experimental way has established a number of insignificant distinctions. The parameters of the thermal effect on the joint area of the build-up metal with the basis are determined, at which it corresponds to the required strength and dimensional-geometric characteristics.

The actual task is to develop a technology that allows the finishing of surfaces of difficult-to-profile parts made of hard-to-work materials obtained by electro erosion treatment. The purpose of the work is an experimental study of the application of electrolyte-plasma polishing technology for finishing surface of parts obtained by the method of copying and piercing erosion processing. As the processed material, structural alloyed steel 38Х2Н2МА in accordance with GOST 4543-71 was chosen. Electrical discharge machining processing of the sample was carried out on an Electronica smart CNC echo sander. Experiments on electrolyte-plasma polishing of experimental samples after Electrical discharge machining were carried out on a laboratory installation "Polytech-15" with a power of 15 kW. The method of electrolytic-plasma polishing is based on electro-discharge phenomena in the "metal-electrolyte" system, while the workpiece is an anode. Polishing of metals occurs in the stress range 200-350 (V) and current density of 0.2..0.5 (A/cm2). At a voltage of more than 200 (V) around the anode, a stable thin (50-100 μm) vapor-gas shell forms during the transition from bubble boiling to film anode. The electric field strength in the gas-vapor cladding reaches 104-105 (V/cm). Near the microprotrusions, the electric field strength increases, and in these areas microplasma discharges migrating over the surface arise, which provide a complex chemical and physical effect on the surface material of the article. In the course of the study, the change in the roughness of the treated surface was studied. The paper shows the possibility of applying electrolyte-plasma polishing technology to improve the quality of the machined surface of 38Х2Н2МА steel after Electrical discharge machining . It is established that the use of electrolyte-plasma polishing technology within 5 minutes of operation allowed to reduce the roughness of the surface processed by the Electrical discharge machining surface by an average of 5 times. It is shown that in order to obtain a roughness of the machined part surface with a value of Ra 1.6 μm, it is more efficient to use a combination of Electrical discharge machining technologies at regimes No. 2 and electrolytic-plasma polishing.