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Izvestiya. Non-Ferrous Metallurgy

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No 3 (2023)
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Metallurgy of Nonferrous Metals

5-16 577
Abstract

The utilization of modern automated control systems in copper cathode production offers the opportunity for remote access to control and regulate the electrolytic process parameters. This, in turn, enhances production efficiency while reducing energy costs. The significant parameters in copper electrolytic refining encompass the temperature and composition of the electrolyte, the circulation rate of the electrolyte, the level of sludge, and the frequency of short circuits occurring between the electrodes and the current density. These parameters directly impact the quantity and volume of cathode sludge. The occurrence of short circuits within the bath arises from the growth of dendrites, necessitating the monitoring of voltage, composition, and temperature of the electrolyte. Regular analysis of the electrolyte's composition and the accumulation of sludge volume at the bottom of the electrolyzer is also necessary. The intensification of the electrolysis process primarily involves increasing the current density, reducing the electrode spacing, enhancing the quality of electrodes, improving the electrolyte circulation system, and further mechanizing and automating the process and its auxiliary operations. These efforts contribute to increased productivity. The objective of this study is to expand the capabilities of automated process control systems by incorporating sludge level control sensors. This aims to mitigate irrecoverable losses resulting from dendritic sludge short circuits on the electrodes located in the lower section of the electrolyzer, utilizing new software. A sludge level control method to prevent short circuits has been investigated, and control software employing float-type level sensors has been developed. This measure is projected to decrease energy consumption by 15–20 % and can be effectively implemented in the production of electrolytic copper at the copper smelting plant in Lao Cai, Vietnam.

17-26 594
Abstract

Silicon and silicon-based materials find extensive applications in metallurgy, microelectronics, and other emerging industries. The field of use of synthesized silicon varies based on its morphology and purity. This study employs voltammetry, galvanostatic electrolysis, and scanning electron microscopy to examine the impact of KI surfactant (in mol %) to 66.5KF–33.3KCl–0.23K2SiF6 melt at 750°C on the electrowinning kinetics of silicon ions and the morphology of silicon deposits formed on a glassy carbon electrode. The findings demonstrate that the addition of potassium iodide to the KF–KCl–K2SiF6 melt at a concentration of 2 mol % induces changes in interfacial tension at the boundary between the glassy carbon, melt, and atmosphere. Consequently, the wetting of the glassy carbon with the melt decreases, leading to a reduction in the actual working surface area and, consequently, a decrease in cathode current while maintaining current density. Taking into account this effect and employing an algebraic estimation of the influence of the melt meniscus shape, it is postulated that the addition of KI does not significantly affect the kinetics of the cathode process. Nevertheless, the impact of KI addition on the morphology of electrodeposited silicon is mentioned. During the electrolysis of the KF–KCl–K2SiF6 melt, fibrous silicon deposits with arbitrary shapes are formed on the glassy carbon electrode, whereas the addition of 2 and 4 mol % of potassium iodide to the melt leads to the agglomeration and smoothing of silicon deposits under the same electrolysis conditions (cathode current density: 0.02 A/cm2, electrolysis duration: 2 h). The obtained results indicate the potential to manipulate the morphology of electrodeposited silicon for specific applications in various fields.

Metallurgy of Rare and Precious Metals

27-37 441
Abstract

This article describes studies on improving reprocessing technology gold production cementate (GPC) formed in refining section of chemical metallurgical shop at JSC Uralelektromed, in order to increase the extraction rate of targeted metals into marketable products, diversification of production, achievement of economic effect due to increasing content of precious metals (PM) in individual concentrates. The optimization of GPC reprocessing technology includes intensification of leaching of initial material and filtration of produced pulp, in order to increase the extraction of gold and platinum group metals (PGM) into solution and decrease the circulated PM. This would allow individual products (crude PM) to be obtained with minimum material loss and labor consumption. It is possible to increase rhodium content in concentrate and to reduce its circulation by preliminary oxidating annealing at the temperature above 500 °C. At this temperature hardly soluble trioxide Rh2O3 is formed on rhodium surface, insoluble in aqua regia, thus allowing it to deposit in the form of individual product. The influence of temperature and composition of gaseous phase was established upon oxidizing annealing of initial raw stuff (t = 500÷750 °C) on the composition of rhodium trioxide concentrate (15÷45 % Rh2O3). Reprocessing flowchart of gold production cementate was developed and tested on commercial scale, allowing for the simultaneous production of several products: deposited gold (Au ≥ 98 %), deposited silver (Ag ≥ 98 %), PGM concentrate (Pt ≥ 45 % and Pd ≥ 15 %), rhodium concentrate (Rh = 15÷45 %).

Foundry

38-53 363
Abstract

The utilization of computer simulation software for casting process simulation is becoming essential in the advancement of casting technology in aviation and other high-tech engineering fields. With the increase in the number of computational cores in modern CPUs, the use of multi-threaded computations is becoming increasingly relevant. In this study, the efficiency of multi-threaded computations in modeling casting processes was evaluated using finite element method casting simulation software ProCast and PoligonSoft, which utilize parallel computing architectures with distributed (DMP) and shared (SMP) memory, respectively. Computations were performed on Intel and AMD-based computers, varying the number of computational threads from 4 to 32. The calculation efficiency was evaluated by measuring the calculation speed increase in the filling and solidification of GP25 castings made of ML10 alloy, as well as the complex task of filling and solidification modeling nickel superalloy casing castings with radiation heat transfer simulation. The results indicate that the minimum computation time in ProCast software is observed when using 16 computational threads. This pattern holds true for both computing systems (Intel and AMD processors), and increasing the number of threads beyond this point does not make a practical difference. The performance decrease in this scenario can be attributed to the low-performance energy-efficient cores in systems based on Intel processors or the decrease in core frequency and full loading of physical cores in systems based on AMD processors. Multi-threading the modeling task in PoligonSoft software is less efficient than in ProCast, which is a result of the shared-memory architecture used in PoligonSoft. Despite the significant difference in parallel efficiency, the task of GP25 casting solidification in both PoligonSoft and ProCast is solved in a time close enough to be considered sufficient.

54-66 474
Abstract

Aerospace, manufacturing, and shipbuilding industries strive to enhance their competitiveness by optimizing material utilization and improving production processes. The investment casting process offers the capability to fabricate intricate and precise components using a diverse range of alloys. However, this method is not without its drawbacks, including high manufacturing costs and a significant rate of defective castings, which can reach up to 30 %. These defects primarily arise from the stresses imposed on the wax patterns and ceramic molds, leading to their distortion. To address this issue, efforts have been made to reduce stress by employing compacted wax powders for the production of investment patterns. However, stress relaxation in the wax patterns remains a concern as it can result in elastic deformation of the compacted material and subsequent alterations in the final product dimensions. To mitigate this issue, a series of tests were conducted with the objective of studying stress relaxation under constant compression strain, as described by the Kohlrausch equation. The obtained results provide valuable insights that enable the prediction of the ultimate dimensions of patterns created using different grades of wax.

Pressure Treatment of Metals

67-78 400
Abstract

In order to simulate the pressing of hollow profiles made from aluminum alloys, the previously developed design algorithms for the pressing tool and the QForm software were utilized. The objective of this study was to enhance the quality and decrease the design timeintervals for pressing tools used in the industrial production of aluminum alloy profiles. A novel design procedure for a combined tool, along with the technology of semi-continuous pressing with welded hollow profiles made from aluminum alloys, was proposed. This was achieved using the QForm software, which enables efficient calculations and adjustments of pressing parameters and tool geometry through a dialog interface. The developed algorithm and design procedures enable the drawing of hollow profiles, technological calculations of pressing parameters, selection of a suitable horizontal hydraulic press, matrix and splitter design, determination of strength parameters, assessment of equipment load, and preparation of working drawings for the pressing tool. In order to validate the effectiveness of the design procedure, it was applied to typical hollow profiles fabricated on a commercial scale. Two variations of the pressing tool design were examined. Simulation results obtained from QForm Extrusion software, specifically designed for pressing analysis, revealed that the initial design of the tool, with predetermined technological parameters and geometry of the splitter and matrix channels, resulted in uneven flow of profile elements and temperature distribution. However, by adjusting the tool parameters, it was possible to achieve a straight profile exit from the matrix and a uniform temperature distribution across its cross section. Industrial verification of the designed tool, utilizing a 33 MN hydraulic horizontal press for pressing profiles made from alloy 6063, demonstrated that significant modifications to the matrix and splitter were not necessary. By employing the proposed pressing tool design, batches of products were successfully manufactured in compliance with the required technical specifications, while reducing the design time intervals of the pressing tool by approximately 50 %.

79-88 497
Abstract

This article describes the features of determining strain curves in true stress–true strain coordinates, using samples of circular cross section from Al–Cu–Mg–Zn aluminum alloy. The calculation and experimental methods of determining true stresses and strains were compared Calculation methods based on the condition of volume constancy may not reflect actual regularities of deformation at the stage of strain localization in the considered material. Nevertheless, the use of systems of digital image correlation (DIC) allows measurements of both the geometrical sizes of deformed sample and strain fields on its surface to be performed, including on the sample neck. It was demonstrated that the measurement error of the sample diameter by the coordinate field was 0.02 mm at the instance of destruction. In order to improve the measurement precision, an increase in the recording frequency in proportion to increase in strain rate was proposed, as well as measuring the surface coordinates from both sides of the sample. It is also possible to supplement the strain curves obtained by DIC optical systems with the measurements of true fracture stress, and the true fracture strain determined by calculations on the destructed sample. The presented methods of analysis of plastic flow by direct measurement of field displacements and strains allow actual regularities between true stresses and strains at the interval of irregular plastic strain to be established. This cannot be achieved by analytical conversion of conventional curve. The obtained hardening coefficients and strain curves can be used for simulation and design of machinery structures and parts.



ISSN 0021-3438 (Print)
ISSN 2412-8783 (Online)