Technological aspects of manufacturing and preparation of mock-up samples of liquid metal fuses for thermal and switching tests

The advantages of current limiters based on liquid metal self-healing fuses (LMSHF) provoke interest and the need for the development and continuation of research in the direction of creating prototypes and industrial samples of LMSHF, determining the sphere of their application. One of the significant reasons for the lack of the necessary results of experimental research in the literature sources is the technological problems of manufacturing prototypes of LMSHF and preparing them for testing. This is especially noticeable when using fusible elements made of alkali metals that are aggressive to the environment. The proposed approach to solving the technological problems of manufacturing and preparing prototypes for testing is of interest and can be used by scientific groups engaged in research related to LMSHF. The development and discussion of such a technology can contribute to the activation of research towards of creating prototypes, their research aimed at obtaining new practical results.

Combined control of fans of gas cooling units electric drives

The problem of the temperature control at the outlet of gas cooling units of compressor stations of main gas pipelines is discussed. To solve the problemt, a discrete or frequency control of electric motors of fans of gas air cooling devices is used. The problems of electromagnetic compatibility that arise in typical power supply systems of gas cooling installations when connecting electric motors of fans through frequency converters are noted. A combined fan motor control system is considered, in which the electric motors are divided into two groups. The electric motors of the first group are connected to the network directly, the second through frequency converters. By reducing the number of electric motors connected to the network through frequency converters, the negative impact of frequency-controlled drives on the quality of electricity is reduced and the costs of modernization projects are reduced in comparison with the option of the variant using a frequency converter for each electric motor. The energy characteristics of the combined control system are analyzed. The relations that establish the relationship between the temperature difference at the cooling unit and the power of the fan motors for various control methods are obtained. The optimal control algorithm according to the criterion of maximum power saving is proposed, which provides for the interconnected control of the number of discrete-controlled motors and the speed of frequency-controlled drives. The variants of the implementation of the optimal control algorithm are discussed. Analytical expressions for power saving on the fan motor shaft in a combined system compared with a discrete one and a method for estimating energy savings are considered. The obtained results are recommended to be used to assess the technical and economic efficiency of projects for the modernization of electrical complexes of gas cooling units.

Automatic control system of the mechatronic module

The paper discusses a new approach to improving the accuracy of reproducing the task signal by a precision circular transfer table based on the implementation in the form of a mechatronic module. This design eliminates the disadvantages of the traditional design, such as backlash, failure when fixing the face-plate. The mechatronic module is a gearless connection between the face-plate and the electric motor. The new design required a new approach to the operation of the automatic tracking and stage positioning control system. In the process of stage positioning, thermal deformations occur, and therefore, a feature is the inclusion of an additional automatic control system for the cooling of an executive synchronous electric motor with permanent magnets in the rotor. The paper deals with the issue of the interrelationship between the positioning and tracking systems with the thermal deformation compensation system. Simulation of the operation of two systems has been carried out.

Multi-criteria analysis of road bitumen production processes by oxidation of refined petroleum products

Based on the DEA method, an approach has been developed for the multivariate analysis of the road bitumen production processes, allowing obtaining integral comparative assessments that ensure the ranking of processes according to various heterogeneous criteria. The main quantitative characteristics, qualitative indicators, and technological parameters of the oxidation processes are selected to form target functions when solving mathematical programming problems. Based on the CCR and Super Efficiency models of the DEA method, the problems of multivariate analysis of the efficiency of road bitumen production processes for the actual values ​​of the characteristics of raw materials and parameters of technological processes were formulated and solved, a comparative analysis of the estimates obtained for 64 bitumen samples was carried out. The results of the studies carried out make it possible to significantly expand the scope of the DEA method application and create on its basis a software package for multivariate analysis and optimization of bitumen production processes by improving the quality of the final product, reducing the resources for its production and reducing the negative impact on the environment.

Optimization design and operating parameters of induction heat-ing system for hardening

The paper deals with the problem of optimizing the design and operating parameters of an induction heating system for surface hardening of a steel stepped shaft. The problem of optimal design of an inductor is formulated based on a nonlinear two-dimensional numerical model of coupled electromagnetic and temperature fields, developed in the ANSYS Mechanical APDL software. Alternance method of parametric optimization of systems with distributed parameters is used to optimize induction hardening system. MATLAB software has been used for developing parametric optimization subroutine, which was incorporated into the numerical ANSYS model to simulate a process of induction heating. Commonly used a multi-turn solenoid-style coil fabricated from rectangular copper tubing has been used as a hardening inductor. Besides that, an application of profiled copper turns has been investigated. Optimization of induction hardening system described above allows one to substantially improve heating uniformity and enhance metallurgical characteristics of as-hardened stepped shaft. Localized temperature surplus at an upper diameter shoulder has been minimized. At the same time, sufficient austenitization in the fillet area near stepped region (diameter transition) has been obtained.

Riddance jamming of pipeline shut-off valves

The paper conciders the problems of modeling the processes of thermal deformation of valves with an ambient temperature decrease. Some type of wedge valves are exposed to jamming. Heating the valve body is used to eliminate jamming. This problem is common for rigid wedge valves but the reasons not fully explained. Sometimes the valve stem is destroyed due to the significant power of the gate valve electric drives. The aim of the study is to determine the nature of the stress distribution between the structural elements of the valve, which are the cause of jamming with an ambient temperature decrease, and to search for the parameters of the heating process that ensure minimum energy consumption and time. To study the thermal processes in the valve body, a numerical model describing the heat transfer in the structural elements and the fluid is developed. The thermal model is combined with the elastic deformation model. That allows to make compatible calculations without introducing additional errors. The thermal deformations appear in the cooling process and give rise to disproportionate changes in valve dimensions and thermal stresses. Thermal stresses are the cause of jamming. Modeling of the processes of thermal deformation with a decrease in temperature showed that pressure forces of different signs arise in the middle plane of the wedge. At the average height of the horizontal line, there is a compacting pressure and at the lower and upper points there is a stretching pressure. To eliminate the compacting forces local heating was performed in several areas of the body. It was found that the most effective option is to heat the lower hemispherical surface of the body. Heating for thirty minutes reduces the thermal stresses in the wedge and compressive forces to minimum values. For this reason, jamming of the valve is eliminated. For heating the body, a hemispherical induction heater with a magnetic core is provided. The proposed design allows the use of industrial frequency voltage without a step-down transformer and reactive power compensation.

Method for calculating the resistance of an asynchronous squirrel cage motor according to passport data and estimation of its error

A simpler method is proposed for determining the resistances of an induction motor (total inductive resistance, active resistance of the stator and reduced active resistance of the rotor) according to reference data. Three algebraic equations are obtained from the equations of reactive power dissipation and electromagnetic power in the nominal mode and the equation of electromagnetic power in the critical mode: the first is relative to three resistances, the second is the equation of the dependence of the active resistance of the stator relative to the total inductive resistance, and the third is the active resistance of the rotor relative to the total inductive resistance. An iterative method is proposed for solving this system of equations, which gives a small error already at the second step of the calculations. When assessing the error of the method, the specified values ​​of the electromagnetic power and the multiplicity of the maximum torque were used, which are expressed relative to the reference resistances of the control motors. An estimate is given of the total error from the imperfection of the method and the discrepancy between the reference values ​​of the multiplicity of the maximum torque and power on the motor shaft with their refined values ​​calculated from the resistances from the reference book. Based on the calculated resistances in the nominal mode, the dependences of the active and inductive resistances of the motor are constructed using an accurate and approximate method.

Multi-factor analysis and operation optimization for the imple-mentation of foreign economic activity AT an industrial enterprise

The paper is devoted to the urgent problem of increasing the efficiency of foreign economic activity of enterprises of the metallurgical and machine-building industries. To increase the economic efficiency of industrial enterprises functioning in the process of implementing foreign economic activity, the paper proposes an algorithm for multivariate analysis, including the procedure for optimizing the system of interaction between an enterprise and customs authorities. When developing and testing the algorithm, customs operations are considered as critical links that determine the increase of the enterprise foreign economic activity efficiency. The mathematical programming problems are formulated on the basis of the CCR model of the DEA (Data envelopment Analysis) method to carry out a multivariate analysis of the comparative efficiency of import and/or export customs operations. The relative efficiency estimates obtained from solving mathematical programming problems make it possible to identify ineffective or least effective export and import customs operations. Based on directed weighted graphs, the special procedures have been developed to optimize the following parameters of customs operations: time of customs operations, labor costs of the enterprise, financial costs associated with compliance with the established prohibitions and restrictions of foreign trade. The algorithm was tested on the example of an industrial enterprise in the metallurgical industry Arkonik SMZ, which carries out export operations for the sale of lid tape of its own production, as well as import operations for the supply of varnish, which is a necessary technological material to ensure the production process of the tape. The administrative and operational decisions made on the basis of comparative evaluations of the obtained optimization results make it possible to exclude ineffective customs operations of foreign economic activity of an industrial enterprise.

Fuzzy optimization of feedback control at induction heating

The problem of multi-criteria fuzzy-optimal feedback control of an induction heater as an object of technological thermophysics with distributed parameters is considered. A general formulation of the fuzzy optimization problem is given, including requirements for the final and intermediate states and taking into account the fuzziness of competing quality criteria. When solving the problem, interconnected electromagnetic and thermal models of the induction heating process were used. The secondary source method was used to simulate electromagnetic processes, and the differential-difference method was used to simulate thermal conductivity. The numerical method for solving the problem is based on the presentation of the control algorithm in the form of an a priori non-fixed and variable system of rules determined during the heating process. The obtained results of numerical modeling confirm the effectiveness of the proposed fuzzy-optimal method for determining the positional control of objects with distributed parameters.

Two-channel time-optimal control of nonstationary heat conductive process with account for response time of boundary control actions

The task of organization a closed time-optimal control system of linear object with distributed parameters of parabolic type is considered. The object has two lumped internal controls for the power of heat sources excited in the electromagnetic field of an inductor. The proposed method for the synthesis of optimal controllers uses an alternance method for calculating the optimal program controls for each of the control actions. An example of the construction of a quasi-optimal time control system for the process of periodic induction heating of a metal workpiece with constant values of the feedback coefficients calculated for the most characteristic initial spatial distribution is given.