Vol 62, No 7-8 (2018)

We designed and produced a working model of new four-roll mill with the use of additive technologies. The model has two driven working rolls and two driven auxiliary rolls for screw rolling of round billets. Plasticine billets were rolled in the model mill to show that the four-roll screw rolling is possible. The experimental rolling was simulated by using the QForm software. The accuracy of computer simulations was estimated by comparing the dimensions of the billets obtained after rolling and as a result of computer simulations. We simulated the procedure of rolling of a round billet of alloyed steel both in a four-roll mill and in a three-roll mill with radial-shear rolling. According to the results of computer simulations, it was shown that the variations of the diameter along the length of the billet and the total work required to realize shape-forming are lower for the four-roll mill.

Solid-phase reduction of nickel oxide is an important process stage in nickel production. The mathematical model of the steady-state operation of the apparatus is an important component, which allows determining the optimal operating mode of the rotary tube furnace (TRK). The automated software application ReactOp is capable of generating a mathematical model of the reactor on the basis of hydrodynamic and thermal models supplemented by the mechanism of chemical transformations, kinetic parameters, thermal and physical properties, and heat transfer parameters. The software complex is equipped with a user-friendly interface, which allows to interactively generate a runtime program based on the mathematical model.

The software application ReactOp has built-in programs enabling numerical solution of differential equations and solution of inverse chemical kinetics problems, and is capable of providing statistical performance analysis and finding the optimal control solutions based on the methods of non-linear programming.

The paper is dedicated to the development of a mathematical model of the steady-state TRK operation. Production of nickel from ores involves several stages of processing raw materials, wherein a corresponding intermediate product is obtained at each stage. As a result of the oxidizing roasting of the nickel flotation concentrate, a roasted product is obtained mainly comprising nickel oxide and other impurities, such as compounds of copper, cobalt, iron, sulfur, as well as rare and precious metals. This stage is followed by the process of solid-phase reduction of nickel oxide in the rotary tube furnaces aimed at obtaining a coarsened, mostly reduced product, which can be further subject to anode electric melting. The latter process allows reducing the consumption of electricity and a reducing agent.

The paper further provides the results of mathematical modeling of the reduction process of oxidized copper-nickel ore concentrate in the rotary tube furnace.

We consider principle of operation and a procedure of evaluation of the constructive, energy, and force parameters of the drive of a new system of unloading of a shaft lime-gas furnace. The proposed method enables us to determine the power of the electromechanical drive of the system with the rational number of knives-scrapers required to guarantee the desired productivity of a vertical-type furnace with the maximum possible uniformity of the unloading of burnt lime over the perimeter of a moving hearth with regard for the mechanical characteristics of the loose material and the design parameters of the unit.

Three stages of metal desulfurization in a ladle during production of low-sulfur pipe steel grade DNV SAWL 485 FD in the PAO MMK oxygen converter workshop are analyzed: the first stage is the treatment of semiproduct during metal delivery from a converter with solid slag-forming mixture; the second stage is steel processing in a ladle-furnace unit under a “white” slag; the third stage is the injection of fluidized lime into steel in a ladle-furnace unit. The relative amount of sulfur removed at different stages of treatment is compared. The greatest amount of sulfur, i.e., approximately three quarters of the total amount, is removed in the ladle-furnace during the second and third stages in the ratio 1:1.33. Dependences are revealed for the degree of metal desulfurization on the ratio of the lump lime weight to fluorspar weight, the specific consumption of fluidized lime and the intensity of its injection in the argon stream, are revealed for the second and third stages. Rational values are recommended for parameters in order to improve metal ladle desulfurization efficiency.

Route maps for the production cycle of operation and repair of continuous casting machine slab rolls in the Azovstal’ and Il’ich Metallurgical Combines (Mariupol’) are presented. It is shown that the complete roll operating cycle in horizontal, curvilinear, and radial sections of the secondary cooling zone as their diameter changes as a result of wear, grinding, and surfacing, makes it possible to increase roll running time, to reduce purchasing expenditure, technical servicing, and restoration. It is established that an increase in secondary cooling zone roll life with diameter 380–270 mm with unchanged composition of the basic and surfacing metal is provided by surfacing technology with formation of a corrosion-resistant surface layer of individually deposited welds with a gap between adjacent welds.

The structure and microstructure of impact fracture specimens of the heat-affected zone (HAZ) of low carbon micro-alloyed high-strength pipe steel welded joints are investigated. Correlation of structure parameters and fractographic characteristics of the failure micro-mechanism channel is established, providing information about elementary acts of failure, i.e., the dimensions of ductile and brittle microcracks.

Expansion of gas-thermal spraying technology applications in various industries such as oil and gas, chemical, mechanical engineering, aviation, rocket building, agro-industrial, etc., can be achieved by obtaining a given set of operating properties with control of coating structure and phase composition. Direct control of the coating structural and phase composition is only possible after a complete establishment of a relationship between the factors determining the structural inheritance of the initial powder material and factors that influence a change during the coating deposition. Parameters and regimes of gas-thermal deposition technology should be substantiated not only empirically, but also scientifically. These processes have not been sufficiently studied in a materials science respect. In addition, information provided by raw material producers (fractional composition, chemical composition, powder material production technology, and less often flow parameters and bulk density) is not provided in its entirety. This work demonstrates the relationship between powder material production technology and features of coating structure formation by the High Velocity Air-Fuel (HVAF) deposition process of Fe-Cr14-Ni6-Si3 (iron-based) powder material used extensively in the oil and gas industry.

Methods of ladle furnace slag stabilization are analyzed. It is shown that increasing the Al₂O₃ content of slag to higher than 18% results in chemical stabilization of slag. It is revealed that if the Al₂O₃ content is less than 30 wt.%, the refining properties of the slag do not degrade. When that content is exceeded, Al₂O₃ behaves similarly to SiO₂, i.e., reduces the desulfurization ability of slag and makes it more corrosion aggressive. The most favorable content of Al₂O₃ in slag is from 12 to 25%, the properties of slag varying from basic to acidic. If the Al₂O₃ content is higher than 14%, the probability of formation of MgO–Al₂O₃ refractory spinel on the surface of refractory products increases, thereby increasing the durability of ladles and vacuum chambers.

Domestic technological and design developments in the area of special electrometallurgy has made it possible to organize production of a wide range of hollow ingots by electroslag remelting (ESR). The properties of these metal ingots fully comply, and for a number of indices exceed, the specifications laid down for thermal and nuclear power plant objects. This makes possible to use them not only in a deformed but also in a cast condition. Results of theoretical and experimental studies of individual physical processes associated with assimilation of ESR for hollow ingots demonstrate new possibilities for controlling their quality and improving the economic efficiency of the production process. Methods are developed for controlling physical and structural heterogeneity of hollow ESR-ingots made from alloy steels with mutual movement of the ingot, consumable electrode (CE), and crystallizer, and also with the use of a reduced frequency alternating current.

The contemporary state of oil and gas complex development gives rise high consumer specifications for the quality and reliability of pipe products. Continuous growth of recovery volumes, including the development of new fields and new industrial production regions, severe climatic conditions when the air temperature reaches minus 40–60 °С, the demand for cost efficiency of new pipeline construction, an increase in operating pressure up to 8.4–15 MPa, as well as ensuring corrosion resistance and reliability of main pipelines, all constantly raise the level of specifications requirements for pipe quality. Connected with this are new trends in the requests and needs of companies for extraction and transportation of hydrocarbon energy sources. Today these companies wish to obtain not only pipes that meet world quality standards, but also products suitable for the temperature conditions of oil production and transportation and the characteristics of extracted raw material chemical composition, and with a reduction in pipe product customer expenditure.

Autoclave ammonia leaching of silver from low-grade copper concentrates is studied with use of Zhezkazgan concentrates of the following composition, %: 9.55 Cu, Fe 4.84, S 5.6, 27.03 Si, 109.6 g/ton Ag. According to X-ray phase analysis the main minerals present in the concentrate are, %: 29 quartz (SiO₂ ), 33 plagioclase ((Ca, Na)(Al, Si)AlSi₂O₆ ), 16 mica, 10 chalcocite (Cu₂S), 2 chalcopyrite (CuFeS₂ ), and 7 pyrite (FeS₂ ).

It is shown that during ore processing in which gold and silver are in close association with sulfide minerals, precious metals are not extracted by cyaniding even after ultrafine grinding. The proportion of such persistent raw materials is more than 30% of the total ore reserves containing precious metals in the world. Use of the most common technologies of autoclave sulphuric acid and neutral leaching for quantitative oxidation of gold and silver containing sulphides in this case is limited due to the formation of argentojarosite, inert with respect to the cyanide ion. In order to avoid its formation and to increase the degree of leaching silver directly at the autoclave stage, its extraction in ammonia is investigated.

With direct autoclave leaching copper extraction into solution is 93–97%, while silver extraction is not observed in some experiments, which may be due to the sorption activity of aluminum and silicon compounds present in the concentrate. Preliminary mechanical activation and surface resynthesis have a favorable effect on recovery rates of copper and silver in solution. An additional operation of concentrate silica removal provides extraction of 97% copper and 83% silver into solution with [NH₄OH] = 7 mole/dm³, L:S = 10:1, τ = 3 h, pO₂ = 0.6 MPa, t = 140°С.

Prospects are considered for the use of materials based on refractory metals for manufacturing high-temperature engineering components. Leading manufacturers of refractory metals and alloys offer a wide range of materials based on tungsten and molybdenum. Data are provided for the mechanical properties of refractory metals and alloys at room and elevated temperature. Dispersion strengthening with refractory metal carbides or oxides is used to improve material operating properties.

Currently dispersion-strengthened composite materials are used increasingly widely in special engineering industries. The main obstacle in the way large-scale implementation of these materials are high cost and the problem of providing a strong bond between particles and matrix under conditions of uniform particle distribution within a matrix. A method is proposed in this work for liquid-phase preparation of highly reinforced dispersion-strengthened composite material based on an aluminum alloy matrix reinforced with discrete ceramic particles. The technology developed makes it possible to reduce the cost of the dispersion-strengthened composite material obtained, in particular as a result of not using powder components and preparing composite material in a single stage. In this case a strong interphase boundary is provided between matrix and filler.

The structure of the silver-substituted hydroxyapatite and tricalcium phosphate powders is confirmed by the methods of X-ray phase diffraction analysis and IR spectroscopy. Silver-substituted hydroxyapatite coatings consist of large particles of round shape and the presence of nanoparticles is also detected. The silver-substituted tricalcium phosphate coatings are formed by fine particles and nanoparticles are detected on the entire surface of the coating. Both types of coatings exhibit hydrophilic properties. The adhesion of silver-substituted tricalcium phosphate coatings is almost twice higher than the adhesion of silver-substituted hydroxyapatite powder coating. The obtained coatings are of interest as antimicrobial coatings for intraosseous dental and orthopaedic endoprostheses.