Том 49, № 7 (2019)

Relatively flexible cylindrical parts (shafts and axles) may be straightened by loads produced by different stresses in different distributions. A promising method is straightening by flexure under a distributed load, with subsequent strengthening of the workpiece by surface plastic deformation based on transverse rolling between flat plates. The goal in the present work is to determine the stress state of the workpiece in transverse straightening so as to select the best type of load and treatment conditions. The mathematical analysis is based on the theory of an elastoplastic solid; ANSYS Workbench software is employed. Effective methods of loading in the transverse straightening of cylindrical parts are determined. Analytical calculations yield the residual stress corresponding to straightening of the cylindrical parts. The residual stress required for straightening depends on the initial flexure, the material in the workpiece, and its size. The stress state of cylindrical parts is determined for different types of transverse loading. The flexural stress for straightening of a shaft under a distributed load is less than the stress due to a transverse force. To straighten a rod (diameter 10 mm, length 200 mm) with initial flexure 0.5 mm, flexural stress of about 370 MPa must be created. In the transverse straightening of cylindrical parts, flexure under the action of a distributed load is an effective loading method. Limiting flexural coefficients of 5.3–5.5 are obtained for all values of the shaft rigidity in straightening by transverse flexure under a distributed load when l/L = 0.8. The proposed mathematical model correctly determines the residual stress corresponding to straightening of the cylindrical parts. The formula derived for calculating the total flexure and determining the effective load may be recommended for practical use in production conditions so as a ensure precise straightening of relatively flexible parts such as shafts.

The use of zinc-bearing (galvanized) scrap as a batch component in electrosmelting produces dust from which nonferrous metals may be extracted. However, the behavior of chlorine and its components in electrosmelting dust containing zinc and lead has not been adequately studied. Research shows that chlorine and its compounds in electrosmelting batch and hence in the arc-furnace emissions must be regarded as a hazard because they form highly toxic organic compounds: dioxins and furans. They are released to the atmosphere not only as gas but also as in adsorbed form on the surface of the dust particles. According to the available data, their concentration is 5–500 ng/kg of dust, depending on the smelting parameters. The formation of dioxins and furans in arc furnaces is analyzed, as well as their behavior in captured dust. With 1.3% chlorine in electrosmelting dust, 99.9% forms relatively safe compounds—mainly chlorides—but the remainder forms dioxins and furans. The quantity of dioxins and furans adsorbed on the surface of dust particles is 474 ng/kg of dust. Dioxins and furans are powerful environmental toxins (first hazard class) and therefore raise the hazard status of the dust from the fourth to the third class (or higher). That must be taken into account in handling the dust. In addition, the dioxins and furans are transported to the environment by dust particles, onto which the chemicals are sorbed. Therefore, electrosmelting dust whose surface contains adsorbed dioxins and furans may carry these toxic materials into living organisms. Means of decreasing dioxin and furan emissions in electrosteel production are considered. Methods of dust processing characterized by low environmental impact and resource conservation are also discussed. In particular, the possibility of using milk of lime to irrigate the exhaust gases from the arc furnace is analyzed. This method is found to lower the content of dioxins and furans to acceptable levels. The effectiveness of the proposed methods is assessed.

A mathematical model is proposed for an arc furnace in electrosmelting. So that the model will describe furnace behavior as accurately as possible, research on this topic is analyzed, and basic design principles are formulated. Specifically, the starting point is to derive the equivalent circuit of the furnace. Cassie’s nonlinear differential equation for the conductivity, which has been widely adopted by researchers, is employed in formulating the mathematical model of the arc. In the model, we use calculations of the circuit parameters on the low-voltage secondary side of the transformer and also draw on literature data. To investigate furnace behavior at different times, different values are adopted for the time constant of arc conductivity. By that means, the nonsteady state of the regions close to the electrodes under the influence of external perturbations may be taken into account. The variation in temperature, variation, and pressure of the gas in the furnace during the electrosmelting process is also taken into account. This approach permits realistic description of the furnace behavior with nonsteady arc combustion at different stages of the process; assessment of the possible control parameters; and determination of the requirements on the control system. The basic structure of the model of a three-phase ac arc furnace is derived. MATLAB Simulink software is used in all the calculations of the circuit components and in modeling. The structure includes an ac voltage source; the resistances and inductances on the secondary side of the transformer; the corresponding short-circuit resistances and inductances; and a model of the ac arc. The model is used for dynamic analysis of the arc as an electrical object. Specifically, the dependence of the voltage on the current (the volt–ampere characteristic) is determined. The shape of the volt–ampere characteristic determines the arc combustion, the regions where the arc exists and is stable, and correspondingly the quality of control. The volt–ampere characteristic is investigated with different voltages on the secondary side of the transformer and different arc lengths and also for different values of the time constant of arc conductivity. The model also permits analysis of the static characteristics. The current dependence of the arc length is nonlinear at various voltage stages of the transformer. Recommendations are made regarding the selection of the control signals. Control systems are devised for different stages of smelting. For example, in the initial stage (melting), the control system must minimize the number of disruptions when the region of arc existence is small and must limit the power introduced. Simulation shows that, when the process is nonsteady, adaptive control signals must be used, because they are able to adjust to the continuously changing state of the arc furnace.

According to research in the electrosmelting shop at AO EVRAZ ZSMK, the partial (up to 55%) replacement of chunk iron by hot-briquetted iron in rail-steel production is feasible and economically efficient. The phosphorus content in the steel is decreased by 0.003%, with constant content of nonferrous impurities. The use of hot-briquetted iron does not affect the productivity of the arc furnace. The consumption of power, natural gas, and coke increases when hot-briquetted iron is introduced in the metal batch. However, that may be compensated by the price difference between chunk iron and hot-briquetted iron.

The production of differentially thermally strengthened general-purpose and special-purpose rails has been introduced at AO EVRAZ ZSMK. This technology is used, for instance, for rails that are reliable at low temperatures, high-speed rails, and rails characterized by increased wear resistance and contact-fatigue life. The plan is to increase the range for rails operating at extremely high speed and especially high stress. With timely maintenance, the properties of the new rails should ensure a life corresponding to a gross load of 2–2.5 billion t.

The operational wear of rails is analyzed and the actual wear is determined in measurements within the OAO RZhD network and in the laboratory. The wear resistance of rail steel is investigated as a function of the chemical composition and the microstructure (specifically, the dispersity). The microstructure of rail steel with different wear resistance is investigated by means of an electron microscope. Metallurgical approaches to improving the wear resistance of steel are described. Operational measures are also noted.