Vol 19, No 2 (2018)

The article considers the questions of determination of contact stresses in the chain transmission hinges that need to be known for assessing their wear resistance, because the wear and tear of hinges is the most common type of damage to the chain gears. In this context the main attention was paid to determining the required clearance between the bushing and the pin of roller chain drives. This gap largely determines the character of the distribution and magnitude of contact stresses in the hinge, and, consequently, the durability of chain drives. A method of calculation of the maximum contact stresses in the chain transmission hinges is developed. It is shown that decreasing clearance in the hinges increases the contact angle between the pin and the bushing and reduces the maximum contact pressure. However, for the actual angles of contact the contact stress greatly exceeds the allowable average unit pressure, causing increased wear of the hinges. One of the possible solutions to this problem is the use of transition fits in hinges, in which the gaps and interferences are relatively small. When pressing the pins into in the bushings, due to cutting microasperities from the contact surfaces, the interference in the connection virtually disappears. Examples of determining gaps and contact stresses in the chain transmission hinges are provided.

The paper describes the scientific and technical basis of the vacuum-free plasma method for obtaining silicon carbide realized by DC arc discharge between graphite electrodes. In a series of experiments the energy supplied to the system was changed by increasing the duration of arc discharge with the constant value of current intensity (165 A); two precursor types were used: a mixture of silicon powder with X-ray amorphous carbon in the microfiber form in the first case and with carbon powder in the second case; the mass ratio in the initial mixture was Si:C = 2:1. As a result of the evaluation of the synthesis product quantitative composition, the experimental parameters that allow to achieve the maximum content of the target silicon carbide phase (up to 45%) are determined. Moreover, it was possible to determine the parameters when the only impurity phase in the product was graphite; as a result, the purification of the product from unbound carbon and thereby obtaining silicon carbide with ~99% content was successfully performed by atmospheric furnace heating at a temperature of 900 °C. This result is ensured by two factors: the presence of carbon fibers in the initial reagents mixture and a sufficient level of the supplied energy of about 216 kJ/g.

This article is devoted to the desription of аpython library based on symbolic regression methods for control systems synthesis problem. Control sysnthesis is becoming more and more relevant, gaining particular importance in view of the rapid development of robotics. Usually, practicians and engineers apply template-type regulators when modeling, and then select optimal parameters for them. At a time when the computing power of PC’s has reached its peak, and programming languages have become extremely expressive due to the high level of abstraction and the vastness of libraries, it is better to implement the synthesis in the form of a library. Python was chosen as the language for synthesis implementation. According to the authors of the article, Python is a convenient language for programming matrix and vector calculations thanks to the numpy package. Moreover, the share of projects written in Python in the web service for hosting Github has been steadily increasing recently, which indicates the support of the language from the developer community. This article describes how to use the package to solve the problem of control synthesis. The authors provide the description of the symbolic regression method, the network operator and algorithms for finding the optimal solution using the principle of small variations of the basic solution. In the experimental part of the article, an example of how to use the library to solve the problem of synthesis of control of a mobile robot moving on a planewith obstacles is considered.

Reinforced concrete elements of the Zagorsk-2 pumped storage station structure had got into unexpected stress-strain state after unequal settlement and bending of the structure crosswise of the flow as a result. Cracks emerged in the load bearing reinforced concrete elements and the reinforcement crossing the cracks suffered significant tensile stresses. Important to mention, that the main reinforcement is arranged along the flow. There was a cofferdam designed and constructed across the reverse channel, which allowed to decreasethe water level and remove water from the channel to provide stabilized position of the powerhouse. After stabilization of the powerhouse, it was planned to level the powerhouse by the compensation grouting method.Based on the finite element soil-structure model of the powerhouse, the stress-strain state of reinforced concrete elements subject to unequal settlement and during the levelling operations was determined.The results of the stress-strain state analysis were compared with the actual in-situ stress data obtained by the “reinforcement de-stressing” method. According to the results of the analysis, it is necessary to strengthen the RC load bearing structures of the Zagorsk-2 powerhouse.In the article, the main design proposals for strengthening the RC load bearing structures of the Zagorsk-2 powerhouseby the external carbon fibre reinforcement are given and justified.

Using stay-in-place cement board forms for construction of residential buildings of reinforced concrete is one of the effective methods of modern construction. In the process of production of construction materials despite tight control some defects in structures may form. In this regard, the reliability assessment of the construction technology in terms of quality is an essential task. To assess the reliability of the construction technology the methods of visual examination of building structures and instrumental measurement of detected defects were used. Mathematical processing of the quantitative characteristics of the qualitative parameters is performed by methods of mathematical statistics with the confidence α = 0,95. The study established the most common defects of building structures erected with the stay-in-place cement board forms, as well as identified the cause-and-effect relationships of their formation. The probability of simultaneous failure of the task by the quality parameters of at least one characteristic varies from Qmin = 0,082 to Qmax = 0,161 with the average value Qcp = 0,119, the admissible value specified in building code being Qmin = 0,2. Overall, the technology of constructing reinforced concrete residential buildings with stay-in-place cement board forms corresponds to the level of reliability according to the quality parameters set by the project documentation.

Goal. Metal frame supports SVP-22 with round timber lagging and backfilling of the voidsof unsupported space with chock support is used in the workings of unstable ores and rocks at the Orlovsky mine. When filling the voids with a chock supportmanually, people are located in an unsupported part of the working, therefore this operation is hazardous and laborious. The purpose of the work is to select and test the backfill material for voids of unsupported space, which ensures a decrease in diffusion and oxygen seepage to the centers of spontaneous ignition of the ore bodies under conditions of intense oxidation of sulphide ores at the Orlovsky deposit. Methods. Foaming non-combustible materials (“Blockfil” phenolic two-component resins) were tested in the experimental works at the Orlovsky mine for backfilling the voids when supporting the mine workings by metal frame supports with a round timber lagging. Results. It has been established that the use of phenolic resins as backfilling will reduce the intensity of the oxidation reaction and prevent self-heating of the ore to critical temperatures, and also prevent or slow down the process of heating ofmine air from the heated surface of the ore body to temperatures exceeding the design values. Conclusions. The use of phenolic resin “Blockfil” to fill the voids ensured the absence of deformation of the elements of the metal frame support and the safety of mining, and also allowed to reduce the intensity of the oxidation reaction and prevent self-heating from the ore to critical temperatures and prevent or slow down the process of heating the mine air from the heated surface of the ore body to temperatures, exceeding the design values.

Purpose. The purpose of this work was to examine various aspects of the physico-chemical heap leaching technology at the Mkuju River in Tanzania. The objectives of the study were to determine the basic geotechnological conditions of the Mkuju River uranium deposit, conduct laboratory work on the study of various technological parameters and rock characteristics, as well as a thorough analysis of geotechnological zoning. Methods. The objectives of the research have been solved using the generally accepted methodological approaches to solving problems on ores with a disturbed and undisturbed material structure that have been selected from wells drilled at the Mkuju River Mine in Tanzania, which are being explored and exploited for uranium. Results. Based on the conducted studies, the main geotechnological and geological-hydrogeological conditions, natural factors and their influence were determined. Also, laboratory studies helped determine the technological parameters and their optimal values. The conclusion. Underground leaching is influenced by a large number of factors, and the study of geotechnological conditions of deposits is the basis for a quantitative and qualitative assessment of the interrelationships of natural and industrial components of the natural-industrial system. In this case, after determining the factors the adaptation of the in situ leaching method to specific geological and hydrogeological conditions is established.