Continuous Casting Machine Research Articles

Impingement Density Analysis on Heat Transfer and the Appearance of Edge Cracks in Conventional Slab Using Hydraulic Nozzles

In this work, the fluid dynamics and heat transfer of two hydraulic nozzles used in the secondary cooling of the conventional slab continuous casting machine were analyzed. Impingement density maps, the jet opening angle and heat flux associated with different operating conditions (impingement distance, pressure) were experimentally determined. The opening angle and impingement density footprint were found to vary considerably in shape and magnitude with varying operating pressure and distances. Finally, it was found that when short operating distances are used, a greater heat extraction gradient occurs in the major axis of the impingement footprint, which promotes edge-cracks in the slab in plant.

Movement speed of the directional crystallization front of aluminum in a cylindrical crucible under different MHD-stirring modes

To improve the quality of continuous cylindrical ingots of aluminum and its alloys produced in continuous casting machines, MHD-stirring is implemented in the hot top of the mold. For this purpose, poloidal and toroidal flows are excited in the molten metal. These flows significantly affect heat the transfer from the hot metal entering the hot top of the mold to the cooling zone, where thecrystallization front is formed. The experiment showed that the toroidal flow first reduces the speed of the advance of the crystallization front, and then, as the rotating field magnitude increases, the speed ceases to change noticeably. The poloidal flow also first reduces the crystallization front speed, but somewhat faster than the toroidal flow, and there is a minimum on the curve of the dependence of the front advance speed on the traveling field magnitude, after which the crystallization front speed begins to increase. It has been found that under the combined action of travelling and rotating magnetic fields, the speed of advance of the crystallization front first decreases, and then increases.

Effect of slab width on choice of appropriate casting speed in steel production

In steel continuous casting (CC), the choice of the appropriate speed at which the slab is cast can be influenced by many different factors and phenomena. While the slab thickness seems to have the biggest impact, other features like the slab width have been consistently overlooked. In fact, the slab width practically limits the casting speed via the mass flow constraint which governs the input and output balance at the tundish. Here, we present a case study that aims at analyzing steel production data from the perspective of casting speed constraints. By studying the speed fluctuations of an industrial CC machine, we identify a strategic regime change toward a stricter consideration of the mass flow constraint. The regime change manifests itself in a significant increase in the correlation between the actual casting speed and the maximal speed associated with the mass flow constraint. On the surface, taking greater account of the input and output balance at the tundish has reduced the productivity of the continuous caster; however, one can argue that the lessened yield is compensated by a diminished risk of eventual slab breaking. From the perspective of this trade-off, we establish a visualization technique that enables us to pinpoint the boundary beyond which one strategic regime becomes economically more advantageous than the other.

Improvement of the secondary cooling mode for continuous casting of round billets at Ural Steel JSC

Formation of hot cracks on continuously cast round billets is the frequent problem in metallurgical production. The article presents the results of a study of the macrostructure, surface quality and technology of continuous casting of round billets with a diameter of 455 mm, produced at the bloom caster of Ural Steel JSC. The main defects of such billets are identified as surface cracks of “combined” type, namely, transverse cracks (the share among the billets with defects is 9.1%), cracks of the mesh form (the share among the billets with defects is 8.3%). The main reasons for the unsatisfactory quality of the ingot are determined: increased overheating of metal in the tundish, which can be partially compensated by reduction of the casting speed, and intensive cooling of billet surface in the first segments of secondary cooling, which increase thermal stresses in metal with consequent heating of surface layers. It was decided that the most effective way to minimize billet defects is to improve the secondary cooling technology in compliance with the regulated casting temperature and speed procedure. Thermal calculations of billet solidification are conducted. It was revealed that overcooling of billet surface occurs in the first segments of secondary cooling under the existing secondary cooling modes and temperature and speed modes of casting, which leads to additional thermal and phase stresses. In the third segment of the secondary cooling zone, heating of the billet surface is observed due to the heat of the central part. Rational flow rates of cooling agent for the secondary cooling segments of the bloom continuous casting machine are proposed. They include expansion of the active section of secondary cooling with a reduction of cooling agent consumption in the first segments will reduce the thermal cycling processes in the hardened crust and minimize the likelihood of cracking. The work was conducted under financial support of the RF Ministry of Science and High Education (project No. FZRU-2020-0011).

Generation of Time-Series Working Patterns for Manufacturing High-Quality Products through Auxiliary Classifier Generative Adversarial Network.

Product quality is a major concern in manufacturing. In the metal processing industry, low-quality products must be remanufactured, which requires additional labor, money, and time. Therefore, user-controllable variables for machines and raw material compositions are key factors for ensuring product quality. In this study, we propose a method for generating the time-series working patterns of the control variables for metal-melting induction furnaces and continuous casting machines, thus improving product quality by aiding machine operators. We used an auxiliary classifier generative adversarial network (AC-GAN) model to generate time-series working patterns of two processes depending on product type and additional material data. To check accuracy, the difference between the generated time-series data of the model and the ground truth data was calculated. Specifically, the proposed model results were compared with those of other deep learning models: multilayer perceptron (MLP), convolutional neural network (CNN), long short-term memory (LSTM), and gated recurrent unit (GRU). It was demonstrated that the proposed model outperformed the other deep learning models. Moreover, the proposed method generated different time-series data for different inputs, whereas the other deep learning models generated the same time-series data.

Estimation of the boundary condition of a 3D heat transfer equation using a modified hybrid conjugate gradient algorithm

Billet production is for the most part completed in a continuous casting machine. To produce a billet of suitable quality, the secondary cooling control system needs to provide an appropriate value of water flow rate. At present, most secondary cooling control methods are based on a heat transfer model for the billet, the accuracy of which can directly impact the cooling effect and further affect its quality. In practice, it is difficult to determine the heat flux at the billet’s boundaries due to the complexity of continuous casting. Therefore, this study focuses on identifying the boundary conditions for the 3D heat transfer model of a billet with a linear coefficient. First, we transform the identification of boundary conditions into an optimization problem, prove the Lipschitz continuity of the cost function of the optimization problem, and obtain the Lipschitz constant. Second, based on the Lipschitz continuity of the cost function, we present a modified hybrid conjugate gradient algorithm (MHCGA) to solve the optimization problem and then prove the global convergence of this MHCGA. Compared with other methods, the results of the simulation experiments clearly show that this MHCGA can reduce running time and iteration number. Third, to eliminate the ill-posedness of the inverse problem for identifying the boundary condition, we combined a regularization method with MHCGA. Simulation experiments confirmed that this method can effectively estimate the boundary conditions. Finally, the experimental data from a steel plant verified the validity of our method, and the prediction results of the shell thickness were confirmed by the nail shooting method.

An automated system development to control the device for supplying slag-forming mixture into mould of CCM

The mechanism of feeding slag-forming mixture (SFM) with a pneumatic drive has a number of disadvantages associated, in particular, with the uneven supply of the mixture into mould. To eliminate the drawbacks, mixture feeding device with an electric drive was designed to eliminate them. In order to ensure control of the SFM feeding process, an automated system has been developed that provides real-time information on the technological process of feeding the mixture into the mould of continuous casting machine, including speed of rotation of screw drive motors and movement of carriage, the level of the mixture in the bunkers and its consumption, temperature of the metal and slag. A software and hardware complex (SCADA-system) has been developed, which makes it possible to analyze the components of the mixture in the “online” mode and take into account the effect of changes in the supply of each of them on its composition. The dependence of the mixture consumption rate on the casting rate has been established, which can be displayed on the screen in the current mode. Application of the SCADA-system made it possible to control the developed SFM feeder both in manual and automatic modes. It was shown that the implementation of the developed automated SFM feeding device in the steelmaking production of Ural Steel, JSC will secure decreasing the SFM consumption by 2.8% and decreasing downtime by 5% due to increasing efficiency of fault detection with a total implementation cost of 200 thous. rubles.

Increase of durability of CCM rollers by electric arc surfacing method with use of promising surfacing materials. Part 1. Structure, phase composition and properties of deposited layers

Experimental compositions of flux-cored wires for electric arc surfacing of rollers of continuous casting machine at JSC OEMK named after A.A. Ugarov. To improve the properties of the deposited layers, refractory components were introduced into the charge of the base wire ASM 4603-SA: micro- and nanodispersed powders of tungsten carbide (3–12 %), as well as hexagonal boron nitride powder (0.1–0.2 %). A complex of studies of the structure, composition and properties of the deposited layers has been carried out. An increase in the content of the refractory WC additive in the ASM 4603-SA charge from 3 % to 12 % promotes an increase in the hardness of the deposited layer from 48.9 HRC to 55.1 HRC. The maximum hardness of the deposited layer is set for the specimen deposited with the ASM VI wire – 57.1 HRC. It was found that the phase composition of the deposited layers consists of solid solutions based on α-Fe and γ-Fe iron. The maximum amount of α-Fe was found in the layer deposited with ASM VI wire (84 %). It is shown that the structure of the deposited layers consists of martensite grains surrounded by interlayers of austenite.

Analysis of a New SEN Design with an Inner Flow Divider

To minimize the product imperfections due to slag entrapment and surface defects, the fluid flow pattern inside the mold must be symmetric, commonly named double-roll flow. Thus, the liquid steel must enter into the mold evenly distributed. The submerged entry nozzle (SEN) is crucial in product quality in vertical steel slab continuous casting machines because it distributes the molten steel from the tundish into the mold. This work evaluates the performance of a novel bifurcated nozzle design named “SEN with flow divider”. The symmetry at the outlet ports is obtained by imposing symmetry inside the SEN. The flow divider is a solid barrier attached at the SEN bottom inner wall, the height of which slightly surpasses the upper edges of the outlet ports. The performance analysis is done first using numerical simulations, where the Computational Fluid Dynamics (CFD) technique and the Smoothed Particle Hydrodynamics (SPH) approach are used. Then, experimental tests on a scaled model are also used to evaluate the SEN performance. Numerical and physical simulations showed that the flow divider considerably reduces the SEN outlet jets’ broadness and misalignment, producing compact, aligned, and symmetric jets. Therefore, the SEN design analyzed in this work is a promising alternative to improve process profitability.

Improvement the Round Bloom Continuous Casting Technology at JSC “Ural Steel”

The results of assessment of macrostructure and surface quality of round blooms 455 mm in diameter, cast on 4-strand continuous casting machine (CCM) at JSC “Ural Steel” are presented. The analysis of technological casting parameters of round blooms 455 mm in diameter (from steel grade “2”) at bloom caster of JSC “Ural Steel” are completed. Violations in casting temperature and rate parameters, which deteriorate thermal conditions of solidification and quality of continuous casting blooms, have been revealed. The main causes of unsatisfactory bloom quality have been determined, which are the increased overheating of cast metal and irrational secondary cooling mode. The results of the experiment to evaluate the surface temperature dynamics of a round bloom in the secondary cooling zone are presented, which confirmed the inefficiency of the secondary cooling mode for the defect-free bloom formation. As a result of thermal calculations of round blooms solidification of 455 mm in diameter, rational coolant flow rates by secondary cooling sections for bloom caster of JSC “Ural Steel” have been proposed. Optimized secondary cooling parameters provide a softer secondary cooling of the round bloom, which reduces the probability of the surface and internal defects development.

Development of a Steel Plant Rescheduling Algorithm Based on Batch Decisions

During the steelmaking and continuous casting process in the steel plant, it is common to encounter delays that affect initial planning. Furthermore, continuous casting machines themselves can lose much of their performance in the event of closure of one or more of their casting strands. The situation that is generated, far from being a planning problem, forces consideration of a vision of cost analysis when deciding changes in the planned sequences. This study presents a detailed analysis of the different circumstances that can cause strands closures or sequence breaks, their consequences and the different options available to minimize losses. Finally, an algorithm capable of analyzing the workshop situation and making the most favorable decision to optimize production is proposed, analyzed and compared with the efficiency of the original scheduling method in a real steel plant. The new algorithm proves its efficiency in all situations, with a time-saving average of 26.41 min per decision taken.

ПОДДЕРЖАНИЕ КАЧЕСТВА СВИНЕЦСОДЕРЖАЩИХ ТЕПЛОНОСИТЕЛЕЙ В ПЕРСПЕКТИВНЫХ ТЕХНОЛОГИЯХ ПЕРЕРАБОТКИ ОРГАНИЧЕСКОГО И НЕОРГАНИЧЕСКОГО СЫРЬЯ

The unique properties of heavy liquid metal coolants (low chemical activity when interacting with air, organic compounds, water and water vapor, high boiling point, low vapor pressure) allow them to be used both in the first circuits of fast neutron reactor plants and in heat exchangers used for processing various organic and inorganic raw materials. Such devices can be either recuperative or mixing type. The latter additionally have the following advantages: lower cost and simplicity of construction; no heat transfer surfaces that can be subject to corrosion and contamination; reduced dimensions due to a larger specific heat transfer surface. The greatest degree of study relates to liquid metal pyrolysis of solid substances, direct contact distillation of aqueous solutions without preliminary preparation, improving the efficiency of continuous casting machines due to the replacement of water with lead-bismuth eutectic. The results of research in support of the above processes are presented. The methods of maintaining the quality of lead-containing heat carriers do not have fundamental differences for the conditions of reactor installations and in relation to promising technologies for processing organic and inorganic raw materials. At the same time, the requirements for devices for implementing these methods in promising technologies for processing various raw materials are significantly lower: in general, a sensor for measuring the thermodynamic activity of oxygen and a device for entering gas (hydrogen-containing or oxygen-containing) mixtures in the coolants.

Optimization of the Continuous Casting Process of Hypoeutectoid Steel Grades Using Multiple Linear Regression and Genetic Programming—An Industrial Study

Štore Steel Ltd. is one of the major flat spring steel producers in Europe. Until 2016 the company used a three-strand continuous casting machine with 6 m radius, when it was replaced by a completely new two-strand continuous caster with 9 m radius. For the comparison of the tensile strength of 41 hypoeutectoid steel grades, we conducted 1847 tensile strength tests during the first period of testing using the old continuous caster, and 713 tensile strength tests during the second period of testing using the new continuous caster. It was found that for 11 steel grades the tensile strength of the rolled material was statistically significantly lower (t-test method) in the period of using the new continuous caster, whereas all other steel grades remained the same. To improve the new continuous casting process, we decided to study the process in more detail using the Multiple Linear Regression method and the Genetic Programming approach based on 713 items of empirical data obtained on the new continuous casting machine. Based on the obtained models of the new continuous casting process, we determined the most influential parameters on the tensile strength of a product. According to the model’s analysis, the secondary cooling at the new continuous caster was improved with the installation of a self-cleaning filter in 2019. After implementing this modification, we performed an additional 794 tensile tests during the third period of testing. It was found out that, after installation of the self-cleaning filter, in 6 steel grades out of 19, the tensile strength in rolled condition improved statistically significantly, whereas all the other steel grades remained the same.

Дослідження дефектів поверхні труб із недеформованої безперервнолитої заготовки

Defects of outer and inner surfaces of hot-rolled tubes of various steel grades and sizes manufactured on tube-rolling unit with a continuous mill (TPA 30-102) at Interpipe Nikotube LLC from a nondeformed continuously cast billets produced by MZ Dniprostal LLC have been studied. Characteristic genetic and morphological signs of defects were revealed which makes it possible to reliably classify them, identify cause of defect formation and recommend measures to eliminate them. Defects on the outer and inner surfaces of tubes are of metallurgical origin and associated with quality of initial continuously cast billets (a consequence of violation of the smelting and continuous casting technology). Defects on the inner surface of tubes were caused on defects in the axial zone of original billets (unacceptable porosity, looseness, chemical inhomogeneity, liquation stripes and cracks, etc.) and are classified as steel-smelting films and bulges. It was found that displacement of the thermal center of crystallization (a feature of the machines for continuous steel casting of curvilinear type) had an additional negative effect on quality of the inner surface of the studied tubes. Defects on the outer surface of tubes are tears of burning in places of accumulation of low-melting inclusions and their eutectics, as well as steel-smelting scabs on rolled dirt and gas bubbles. Likelihood of formation of scabs on outer surface of the studied tubes over rolled crust introversions is not excluded. The study results will allow manufacturers to reliably classify defects, promptly reject tubes with unacceptable defects of metallurgical origin and minimize supply of low-quality products to consumers. These results will later be included in the classifier of defects in tubes manufactured on the TPA 30-102 unit from nondeformed continuously cast billets. The results of the study of natural signs of defects of metallurgical origin in the tube surface will be useful for elaboration of measures aimed at improvement of the technology of manufacturing initial tube billets. Keywords: tube surface defects, continuously cast billets, microstructure, rolled contamination, low-melting inclusions, eutectic, gas bubbles, decarburization, liquation.

Experimental determination of the shell thickness within the primary cooling zone in the continuous casting process

ABSTRACT The correct thickness of the shell solidifying within the primary cooling zone of the continuous casting machine is among the most important parameters assuring the safe operation of the casting process. The main problem is related to the fact that the actual measurement of the thickness of steel solidifying in the mould is impossible. Available continuous casting process monitoring systems allow us to calculate its approximate value on the basis of the mould wall temperature reading, and often these systems ensure failure-free steel casting. In this paper, the authors show the results of long-term research carried out when assessing anomalies occurring during the steel continuous casting process. As a result of this research, shell thickness was measured experimentally. On the basis of experimental data, a new model was proposed to describe heat transfer in the primary cooling zone.

Modernization of a rolling table before gas cutting machine of bloom CCM

The results of the analysis of the design of the intermediate rolling table in front of the gas cutting machine of the four-strand continuous casting machine (CCM-1) of the electric steelmaking shop of JSC Ural Steel are presented. It is shown that as a result of exposure to high temperatures (due to the unsuccessful location of the gear motor near the high temperature zone), the operability of the gear coupling of the gear motor is often disrupted. To improve the performance of the intermediate rolling table CCM-1, it is proposed to modernise it by installing a pull-down device on each strand directly in front of the gas cutting machine, the working element of which is a drive roller located above the rolling table. Rotation of the roller is carried out from an individual electric drive, and its pressing to the workpiece – by means of a hydraulic drive through a system of levers. This makes it possible to perform all 28 rollers of the rolling table non-drive ones, without changing their location. As a result of the modernization of the intermediate rolling table CML-1 in front of the gas cutting machine, it was possible to simplify its design and reduce the complexity of maintenance and repair by 64 hours per year. Replacing 28 drive rollers with non-drive rollers increases the reliability of their operation, allows you to increase the repair period of operation and thereby reduce the cost of operating costs. In addition, reducing the number of electric motors from 28 to 4 provides significant energy savings. Calculations show that the implementation of design solutions leads to a reduction in the cost of one ton of steel by 0.05 %, an increase in product profitability by 0.19 % and an increase in labor productivity by 0.41 %. Additional capital expenditures of about 1 million rubles are recouped in less than 3 months.

Transport of heat and material properties in continuous casting of steel

Liquid steel solidifies within a containment of a continuous casting machine and moves in axial direction as the solidified shell is withdrawn towards the end of the machine. A mechanical model for computing the deformation of the solidifying steel in the roll containment is developed based on the beam theory and on a ferro-static pressure load. The material properties of the steel at high temperatures result from high temperature constitutive equations including creep for the solidified shell between the rolls. The temperature distribution within the solidified shell is computed based on the thermal boundary conditions as in the secondary cooling zone water is spread onto the surface of the steel shell and heat is removed. The solidified steel shell thickness increases along the machine containment up to the point of total solidification. A suitable discretization of the region by the finite beam elements is used to get a suitable mechanical model. The ferro-static pressure acts inside of the solidified shell and causes some bulging of the shell between the roll containment. As there is a slow axial motion of the solidifying shell the numerical modeling of the transport e.g. of heat and of the creep strain, which is computed in each time step, has to be as accurate as possible as a lot of time steps are necessary. Different numerical strategies have been analysed with respect to the accuracy of the computation results.

Interrelation of CCM (Steel Billet Continuous Casting Machine) Tube Steel Casting Parameters and Hot-Rolled Plate Quality

The quality of the hot-rolled plate up to 36 mm thick was estimated by the percentage of rolled products, sorted due to the presence of a surface defect "Non-metallic inclusions", and internal defects, detected by ultrasonic plate control. The analysis of the data on the total sorting of hot-rolled plates demonstrated that the amount of sorting differs significantly on the melting from which each series of tubular metal casting commenced, compared to all the other melting in the series. The sorting of the sheets rolled from the metal of the first in a series of melting proved to be 1.9 times higher than that of the metal of all other melts. The main reason (in 68% of cases) of sorting is the presence of non-metallic inclusions on the surface of the plates. The effect of sorting of hot-rolled plates on non-metallic inclusions of various parameters has been studied: the duration of the intermediate ladle-heating; the length of time from the end of the heating of the intermediate ladle, prior to the beginning of the casting; lining temperatures of the intermediate ladle before the beginning of casting; duration of filling the intermediate ladle; the filling rate of the intermediate ladle with metal; mass of metal in the intermediate ladle before the beginning of casting into the crystallizer; chemical composition of metal; overheating of the metal over the liquidus point at the beginning, middle and end of the casting. On the sorting of flat products for non-metallic inclusions, of all the parameters considered, a statistically significant effect is due only to the overheating of the metal above the liquidus point, which varies in the range from 19 to 35 ° C. In order to obtain an acceptable quality of both the surface of slabs and the surface of hot-rolled plates for non-metallic inclusions, the first in a series of melts recommends overheating of the metal in the intermediate ladle above the liquidus temperature of 30-35 ° C.

Sensorless electric drive of the mixture supply system in the mold of the continuous steel casting installation

The system of automatic feeding of the slag-forming mixture into the mold of the continuous casting machine was investigated in this article. The necessity of using a slag-forming mixture in the process of steel production has been substantiated. The proofs are given that the consumption of the slag-forming mixture significantly affects the cost of the final product. The quality level of the final product depends on the uniformity and consistency of the mixture supply to the crystallizer. Therefore, the actual direction is the automation of the process of feeding the slag-forming mixture into the mold of the continuous casting machine. The description of the developed automatic installation, which implements the supply of slag-forming mixture, is presented. The necessity of using a sensorless electric drive for moving the trolley has been substantiated. A simulation model of a bogie electric drive with a vector control system based on sensorless determination of the angular speed of the engine has been developed. The description of the method for determining the angular speed of the motor based on the known values of phase voltages is given. The simulation of the developed electric drive system in the Matlab Simulink program, confirming the adequacy of the developed system. The introduction of a sensorless electric drive into the system for feeding the mixture into the mold of the continuous casting machine will increase the reliability of the entire system and reduce its weight and dimensions.

New material-saving technologies of pipe rolling on pilgrim units

In this work, based on the analysis of the process of hot pilger rolling of pipes of a wide range of sizes and grades from a round continuous cast billet, new and improved existing metal-saving technologies have been developed to reduce metal losses in the pilger head.Using scientific and patent sources of information in the field of pilger rolling and its mathematical modeling with the calculation of tables for rolling pipes of a wide range of sizes from a round continuous-cast billet with a diameter of 385-470 mm, metal losses into technological scrap on a pilgerstan are determined: a seed and a pilger head.On the basis of the results of the theoretical determination of metal losses in the process scrap on the pilgerstan: the seed and the pilger head, a forecast was made to reduce the weight of the pilger head, which was used to develop new material-saving technologies for pilger rolling of pipes, both thick-walled with D / S = 6 - 12.5, and thin-walled with D / S = 12.5 - 40. Metal losses in the pilger head are the main factor of increased metal consumption coefficients on pilger units, which reduces their competitiveness in comparison with other units when using round continuously cast billets as a starting material.The forecast for the reduction of metal losses in the pilger head made for the first time makes it possible to estimate the reserves for reducing the mass of the pilger head both by eliminating the underflow of the liner and trimming of the pipe end adjacent to the pilger head, and by means of individual parts of its profile part and predicting its decrease to the minimum possible size, ensuring the removal of the pipe from the mandrel using a gate device.To reduce the weight of the pilger head when rolling thick-walled pipes, it is recom-?ended to use improved technologies for butt-end rolling and rolling of the pilger head on the free section of the mandrel.The results of the studies and the proposed new material-saving technologies can be used on pilgrim units when rolling thick-walled (D / S = 6 - 12.5) and thin-walled (D / S = 12.5 - 40) pipes of a wide range of brands (carbon, alloyed, highly alloyed and special) from both continuous casting machine and forged and centrifugally cast billets, as well as ingots.