Continuous Casting Machine Research Articles

Improvement of the metal casting process and refractory equipment design in the intermediate ladle ‒ open jet ‒ the continuous billet caster mold's installation

The steel flow and refractory arrangement of the intermediate ladle (IL) ‒ open jet (OJ) ‒ continuous casting machine (CCM) mold's installation are regarded in the article. The specifics of the metal flow controlling are mentioned. The structural features of the continuous billet caster which maintain the effective metal flowing through the IL ‒ OJ ‒ CCM mold installation are presented. The improving of the installation design allows the expedient metal flows and provides the billets' quality upgrading.

Mathematical Modeling of Cooling of a Continuously Cast Ingot for Reducing Heat Losses

We consider thermal processes running in the course of cooling of a continuously cast ingot in a continuous billet casting machine with regard for the heat of phase transformations. For the solution of the problem of rational utilization of the heat of melts, we propose to improve the technology of continuous casting of steel, which would make it possible to use the heat of the liquid core of an ingot for leveling the temperature field over its cross section and guarantee the minimum losses of the heat at the exit of the continuous billet-casting machine. We develop a mathematical model of cooling of continuously cast ingots in a two-dimensional space representation with regard for the release of the heat of crystallization in the two-phase zone. The numerical realization of the model is performed with the help of the implicit difference scheme of coordinate-wise splitting. The adequacy of the model is checked by analyzing the convergence of the experimental and numerical data according to the Fisher, Student, and Mann–Whitney criteria. In modeling, we simulated the control action in the zone of secondary cooling. It is established that, in the case of application of the control action in this zone, the surface temperature increases by 160°C, while the average mass temperature increases by 100–160°C. We choose criteria for the rational modes of cooling of continuously cast ingots. To preserve the heat content of an ingot, it is proposed to use heat insulation after the zone of water–air cooling. We determine relationships between the parameters affecting the surface temperature of the ingot and represent them in the form of nomograms. It is shown that, before the machine of gas cutting, as a result of heat insulation in the zone of air cooling, the ingot is thermostatted as a result of which the temperature of its most vulnerable zones (corners and surfaces) increases. It is established that, for the rational modes of casting of steels, the ratio of the length of the zone of heat insulation to the total length of the continuous billet casting machine varies within the range 0.3–0.6. To determine the heat losses in the process of subsequent cooling of the ingot in air after leaving the zone of machine gas cutting, according to the existing technology of transportation of slabs to compression, the time of modeling was set equal to 90–105 min. To preserve the heat content of the ingot and level temperatures over its cross section, it is also necessary either to use a thermally insulated transmission roller conveyer or to hold ingots in a thermostat.

Boundary-Condition Selection in Simulating the Secondary-Cooling Zone in the Continuous-Casting Machine

Methods of specifying the boundary conditions in the secondary-cooling zone of the continuous-casting machine are compared in simulating slab solidification. Experimental data are used to assess the correctness of the models. The results of simulation are different when using the mean heat-transfer coefficient for the section of the continuous-casting machine and the local heat-transfer coefficients for the zones with and without coolant. The modeling results are compared with experimental data for the surface temperature of the continuous-cast ingot at the center of its broad face.

RESEARCH OF THE BEHAVIOR OF MACROSTRUCTURE DEFECTS OF THE PRE-DEFORMED CONTINUOUS CAST BILLETS DURING ROLLING

The most significant trend in recent decades in the field of continuous casting of steel billets is a partial transfer of the process of deformation of the exposure to the field of complete solidification (rolling mill) in the area of two-phase (solid-liquid)state (technological line of CCM). However, the implementation of such two-stage deformation of the continuous cast ingot leads to the need for changes to the methodology of physical simulation of the behavior of defects (surface and bulk) in the course of the subsequent rolling, first and foremost, in terms of the correct choice of their geometric shape and spatial orientation. The paper presents the results of a study of the influence of spatial orientation of the surface defects and continuity of the macrostructure of the metal axial region deformed in the line of the continuous casting machine using layered physical models. An experimental study performed in the conditions of deformation of reduced billets by two schemes with rolling simulation scale1:5: in smooth rolls, simulating the process of groоvelles rolling as applied to the first two stands of the crimp group of medium-section mill 300; in the first and second pairs of rectangular grooves of breakdown stand of the mill 500/370 of PJSC “Donetsk Metal Rolling Plant”. According to the multiplicity of the problem, the universal design of physical models was developed to simulate the spatial location of both surface and internal defects. Studies have shown that in case of rolling of physical models with extract ratio over 2.0 and an angle of misalignment defects imitators close to 60° their complete “healing” is possible. In turn, decrease in the angle to 30° contributes to greater extraction of the defect-simulator and only a small decrease in their width. In the case of total misalignment of defect-simulators (angle 90°) there is a broadening of the defects and their deposition to the initial length after tilting by 90°. The obtained experimental data allowed understanding of the mechanisms of “healing” defects integrity of metal depending on magnitude of the total extracts, the angle of misalignment of the longitudinal axis of the defect with the rolling direction and the distance of their occurrence from the longitudinal-transverse plane of symmetry.

The NLMK’s Experience of Operating Slab CCM Molds with Improved Wall Design

NLMK’s experience in operating the continuous casting machine (in steel shop 1) with a mold with multi-taper working surfaces and wear-resistant thermal-spray coating is described. The changes to the design of the working surfaces that contribute to the formation of slab crust of uniform thickness are described.

Producing Structural-Steel Bar from Continuous-Cast Billet

The expanded use of continuous-cast billet in the production of structural-steel bar is considered. The quality of 135 × 135 mm continuous-cast billet produced on a standard continuous-casting machine and the bar derived from it is evaluated. At more recently built plants, the production of quality bar from continuous- cast billet requires total extension of the order of 6–7. On the basis of the analysis developed in the present work, it is possible to determine the maximum critical bar cross section such that the required properties are ensured.

ON MODELING PROCESSES IN CONTINUOUS CASTING MOLD

The work focuses on modeling of processes occurring in the mold with a new patented cooling system in continuous casting ma chine, in particular, at temperature drop in metal of the stock and in the wall along the height of the mold, on which quality of the resulting billet depends. In the review, works are referred in which slag- forming mixtures (SFM) are investigated that affect heat flow from stock metal to the mold. Foreign authors put emphasis on “soft” cooling of the mold by selection of the SFM. Improvement in process of stock metal cooling in the mold is primarily aimed at improving quality of slab surface, increasing resistance of the mold and increasing productivity of machine, which, according to several authors, can be achieved by mathematical modeling of the process. The problem of mold cooling depends directly on convective motion of liquid steel in the mold, which is considered in a number of works of foreign authors. Use of the principle of heat pipes operation in cooling system of the machine mold, in particular, using porous material with water and air operating medium, as well as the question of liquid droplets evaporation on nanostructured super-hydrophilic surfaces, draws attention of researchers. Cooling of the mold at metal casting speeds of more than 7 m/min, accompanied by an increase in heat flux density, is an urgent task and is considered by a number of authors. Interrelation of the main parameters of the process is determined using Rayleigh dimension theory. Temperature gradient in metal of the mold wall is determined as the main parameter, depending on casting speed (time of stock metal forming in the mold), properties of poured metal (heat capacity, heat conductivity), thermal conductivity of the mold wall, and temperature drop in molded metal. Exponents for similarity criteria are determined taking into account available experimental data on dependence of heat flux density on accepted speed of steel casting, steel parameters. The ratio ∆ t c / t c (where ∆ t c is an average temperature difference across the wall thickness, tc is an average value of a wall temperature) for the mold with the existing and the new (patented) cooling system allows us to determine temperature difference in metal of the billet, which in two compared cooling systems of the mold comprises ∆ t м1 = 450 °С and ∆ t м2 = 231 °С, and the ratio – ∆ t м1 /Δ t м 2 is 1,95 times. Decrease in metal temperature drop ∆ t м2 indicates more “soft” cooling of the mold with a new cooling system.

DYNAMIC LOADS INFLUENCING ON ELEMENTS OF MULTI-MOTOR HYDRAULIC DRIVE OF CCM COOLER

Based on dynamic model of multi-motor drive of continuous casting machine (CCM) coolers, mathematical model is formed and evaluation of low- frequency dynamic processes occurring in the drive is performed. Model of the coolers drive is an eight-mass dynamic system with elastic connections between masses. Description of links takes into account presence of gaps and damping properties in them. Active load in dynamic model is described by mechanical characteristic of hydraulic drive. The cooler moving beams and cooling metal mass are regarded as reactive loads. Motion of all masses of the model is described through the system of second-order differential equations. Integration of differential equations was carried out by Runge-Kutta method. To analyze influence of various­ factors on loads that arise in cooler drive, a software program was written. Evaluation of dynamic processes in the CCM cooler drive shows that dynamic component of load in the elements of machine for vertical displacement of mobile beams is of a significant value. Dynamic response factor K d in the drive elements reaches 2.2 – 2.3. Analysis of the factors influencing dynamic processes in the cooler drive reveals that the optimum ratio of masses of metal located in cooler and moving beams of the cooler is close to 1.6 – 1.7. The minimum dynamic coefficient is close to 1.5. The nature of change in drive dynamics due to viscosity of working fluid of hydraulic drive is smoothly decreasing linear dependence with a minimum corresponding to fluid viscosity value of 4·10–5 m2/s. Speed of vertical displacement of the moving beams of the coolers also affects dynamic processes that arise in their drive. At the same time, the dynamic response factor is higher with the higher speed. Within the limits of change in speed of movement of the moving beams of the cooler referred to in the paper, K d varies from 2 to 2.2. Dynamic model of multi-motor hydraulic drive of cooler of a walking-type used in the work makes it possible to analyze low-frequency dynamic processes occurring in hydraulic drive. As a result, it be comes possible to identify degree of influence of various design and power conditions of operation of hydraulic drive on low-frequency oscillations in it and, to develop optimal design solutions in terms of its operability using calculating tool.

Development of a New Horizontal Continuous Casting Machine Construction for Nonferrous and Precious Metal Billets

The work is devoted to development of a new design of horizontal continuous billet casting machine (HCBCM) for non-ferrous and precious metals. The possibility of calculation and design of horizontal casting machine elements by means of computer simulation using the software created is demonstrated. Based on the proposed methods of calculation and design as well as analysis of mathematical modeling results, new designs of HCBCM elements are created that enhance the efficiency of the machine. Appraisal trials of HCBCM structural elements created are performed successfully to measure the effectiveness of this work and introduction into production.

Design Engineering of Refractory Components for Use in Refining Continuous-Cast Steel

We perform physical and mathematical modeling of tundish hydrodynamic processes in the 4-strand continuous bloom casting machine at the EVRAZWest Siberian Metallurgical Complex. Aphysical model of the tundish is used for qualitative assessment of melt mixing processes. A qualitative assessment of nonmetallic inclusion removal efficiency in the tundish is provided for models that employ refractory components in a variety of different configurations. We develop recommended design parameters for full-height refractory dividers in the tundish.

Elastoplastic Flexure of Round Steel Beams. 1. Springback Coefficient

Round steel beams are widely used in metallurgy, manufacturing, and construction. It is often irreplaceable in the production of machines and mechanical equipment on account of its excellent corrosion resistance and remarkable strength. Cylindrical springs for road and railroad vehicles are manufactured from round beams by means of special bending machines. Round beams also serve as blanks in the production of seamless pipe for the oil and gas industry. Stepped round beams are used as rollers in rolling and straightening mills. Steel rebar is manufactured from round beams of similar size. Outside Russia, the main producers of continuous-casting machines for the production of round billet are SMS Demag (Germany), Danieli (Italy), SMS Concast (Switzerland), and Siemens VAI (Austria). Russian producers include AO Chusovskii Metallurgicheskii Zavod, PAO Chelyabinskii Metallurgicheskii Kombinat, AO Volzhskii Trunbnyi Zavod, OAO Nizhneserginskii Metizno-Metallurgicheskii Zavod, AO Chepetskii Mekhanicheskii Zavod, PAO Severskii Trubnyi Zavod, and PAO Taganrogskii Metallurgicheskii Zavod. In the manufacture of parts from round beams and their use, they often experience elastic or elastoplastic flexure or complex torsion and flexure. In the present work, we propose an analytical method of calculating the residual curvature of round steel beams in elastoplastic flexure. In the calculations, the residual curvature of the round beam after flexure and the bending moments of the beam cross section in flexure are determined as a function of the beam radius, the Young’s modulus, the yield point, and the hardening modulus of the steel. The results may be widely used at manufacturing and metallurgical plants.

Comparación y Efecto del Homogenizado en Billets de Aluminio AA 6063

The lack of comparative studies about the distribution of the main alloying elements along aluminum billet´s AA 6063 widely use in extrusion companies to produce aluminum profiles, It makes necessary to counterpoise the difference between homogenized billet produced in horizontal continuous casting machine and a billet produced in vertical semi-continuous casting process. Applying spectrometric tests to quantify the weight percent of main alloying elements, brings out its own nature of each production process on every billet. Nevertheless, helped out by a metallographic test reveals in one billet the negative effect of an inadequate process of homogenization after the heat treatment process T5 in the aluminum profiles that holds it back to reach an adequate Webster hardness related to quality assurance. It reflects that is not enough to have a billet with a uniform chemical composition but the importance of an adequate billet´s heat treatment in order to be use in the extrusion process.Keywords: AA 6063, Billet, Comparison, Homogenized

Temperature Differences in the Mold of a Continuous-Casting Machine with a New Cooling System

Attention focuses on the processes in the mold of a continuous-casting machine when using a patented new cooling system. In particular, the temperature differences in the steel billet and in the wall over the mold height are of interest in modeling the casting processes, because those differences affect the quality of the billet produced. A literature review covers research on the slag-forming mixture, which affects the heat flux from the billet to the mold. Non-Russian authors highlight mild cooling of the mold in selecting the slagforming mixture. Improvement of billet cooling in the mold permits improvement in the surface quality of the slab, extension of mold life, and increase in productivity. According to numerous authors, that may be accomplished by mathematical modeling of the process. The mold cooling depends directly on the convective motion of liquid steel in the mold, a topic addressed by many non-Russian authors. Researchers have considered systems in which the heat pipes in the cooling system of the mold are based on porous material, with water and air as the working fluid, and those in which liquid droplets on nanostructured superhydrophilic surfaces are evaporated. Mold cooling at steel casting rates higher than 7 m/min, accompanied by increase in the heat-flux density, is of great importance, as reflected by the number of studies published. The relations between the basic process parameters are determined by means of Rayleigh dimensionality theory. The basic parameter selected is the temperature difference in the metal mold wall, which depends on the casting rate (the time that the billet is in the mold), the properties of the steel (specific heat, thermal diffusivity), the thermal conductivity of the mold wall, and the temperature difference in the cast steel. In determining the exponents in the dimensionless relations, the available experimental data regarding the dependence of the heatflux density on the casting rate and the parameter of the steel are taken into account. On the basis of the ratio Δtme/tme obtained (where Δtme is the mean temperature difference over the wall thickness and tme is the mean wall temperature) for molds with the existing and new (patented) cooling systems, the temperature difference in the steel billet may be determined. For the two cooling systems compared, Δtme1 = 450°C and Δtme2 = 231°C. Consequently, Δtme1/Δtme2 = 1.95. The smaller temperature difference Δtme2 indicates milder cooling of the mold with the new cooling system.

Improving the quality of continuously cast slabs: by means of the pinch roll drive of the horizontal part of a continuous casting machine

The aim of this research is to help reduce the share of cast slabs with extensive macrostructural defects by changing the structure and the control system of the straightener drive. The article describes the results of a passive experiment. On the basis of these results, requirements have been formulated to the structure and the control system of the straightener drive, a control philosophy developed and a new functional block diagram proposed. The study has been carried out for the curve-type continuous caster operated by one of the major Russian steel producers. The experimental study involved a statistical analysis of the pinch roll drive load sharing data registered by the current monitoring system, as well as the data provided by the sample testing laboratory on the main internal defects found in slabs. The theoretical study included the application of analytical and numerical solutions to algebraic equations, as well as structural modelling. The results of this research were tested on a prototype electric drive for the continuous caster pinch rolls. The authors offer some recommendations on the design of the automatic drive for the pinch rolls installed in the horizontal section of the secondary cooling zone, which also include a technique for calculating the load torques on the straightener pinch rolls, a functional block diagram and a control algorithm for the pinch roll drive installed in the horizontal section of the secondary cooling zone. An average of 50% improvement has been seen in load sharing between the pinch roll drives of the secondary cooling zone. The maximum axial stresses in the slab have reduced four times. There has been an average of 16% improvement in the slab macrostructure for all types of defects and a 13% improvement in terms of axial defects.

НАПРАВЛЕНИЯ РАЗВИТИЯ ПРОИЗВОДСТВА МЕЛКОСОРТНЫХ ЗАГОТОВОК ДЛЯ ПОЛУЧЕНИЯ ДЛИННОМЕРНОГО ПРОКАТА

The aim of the work is to study the technological features of the transfer of metallurgical enterprises to the production of small-size and wire metal products from continuously cast billets. The main parameters of the rolling technology are considered: the size of the billet, the choice of the location of the continuous casting machine, the transfer scheme of continuously cast billets to small- size and wire mills. It is shown that when using a continuously cast square billet with a size of 130x130 mm and 150x150 mm, direct combination of a continuous casting machine with a rolling mill is almost impossible due to the difference in the speed of continuous casting and the roughing group of the mill. The performed calculations show that the scheme of cutting the billets and combining with the intermediate furnace is technologically feasible, however, further heating of the billets leads to significant energy losses. It has been established that an effective option for combining the continuous casting machine with a rolling mill is to use a complex of equipment with a furnace-thermostat for a billets 120 m long. This flowchart reduces the energy consumption for heating the billets by at least 53%. The proposed technology of combining the continuous casting machine with a rolling mill will provide metal savings by reducing the thickness of the scale to 0.4-0.73 mm (an average of 1.1% of the mass of the billet), improve its quality by reducing the depth of the decarburized layer from 1.1 mm to 0.3 mm. The technology provides for the transportation of liquid steel in the ladle from the steel-smelting shop, casting on the continuous casting machine, identification of defects in the billets in a hot condition, supply of the billets with a temperature of 8500С to high-temperature furnaces for heating and subsequent rolling.

Підвищення ефективності процесів суміщення лиття-прокатування за рахунок збільшення швидкості кристалізації металу в машині безперервного лиття заготовок.

Підвищення ефективності процесів суміщення лиття-прокатування за рахунок збільшення швидкості кристалізації металу в машині безперервного лиття заготовок.

Utilizing Industry-oriented Finite Element Codes in the Design of Virtual Steel Mill Concept

Standard industry-oriented finite element codes offer a great degree of versatility and computational efficiency. These software tools in hands of control process engineers help to establish new concepts of control strategies, leading to an effective or autonomous operation. However, their use in continuous casting industry is usually limited to isolated case studies due to missing communication layer interfaces and data processing tools within steel mill infrastructure. Systematic breaking of these barriers would lead to novel concepts of distributed parameter system identification and control system design using off-line or co-simulation control schemes. This marks the way towards virtual technological nodes as a part of a more general concept of virtual steel mill with continuous casting machine at its very heart.

Improvement in billets quality from billet caster by roller suspension of secondary cooling zone stiffening

Presently, continuous casting machines are widely used in metallurgical industry for production of high quality billets. And the maximum economic and resource-saving effect is achieved by the use of continuously casting small-section billets. Proceeding to the continuous casting has tightened the requirements for product quality and the main objective has become to determine the factors influencing the billet quality. It is necessary to design competently a zone of secondary cooling, for improvement of quality of production. Having changed her design and as a result the loadings operating on a zone of secondary cooling will decrease and the rigidity of a design will increase.

СХЕМА НАПРЯЖЕННО-ДЕФОРМИРОВАННОГО СОСТОЯНИЯ НЕПРЕРЫВНО-ЛИТОГО СЛЯБА В ТЕХНОЛОГИЧЕСКОЙ ЛИНИИ МНЛЗ

The aim of the work is to develop a model of the deformation-stressed state of a continuous-cast billet, taking into account its behavior in the continuous casting machine line. A new physical model of the ingot crust bending process in the inter-roller gap has been proposed. The model is based on the regularities of the change in the deformed state of the surface of the crust under the action of ferrostatic pressure. It is established that the crust undergoes a cyclic alternating deformation in the process of moving it across the inter-roller gap. It is shown that the surface of the crust comes into contact with the surface of the roller before approaching the inter-roller gap. This causes the appearance of an anomalous area with a constant curvature of the crust at the final stage of its buckling. The second anomalous deformation zone of the ingot crust is the junction zone of the previous crust and the subsequent inter-roller gap, where the crust instantly changes its curvature. In combination with the flat scheme of the stress-strain state, a physical model is presented, which makes it possible to identify in each of the inter-roller gaps the zone of maximum values of the tensile strain rate. Identifying the zone of maximum values of the tensile strain indicator and comparing it with the maximum allowable one allows determining and correcting the length of the inter-roller gaps of the continuous casting machine.

ТЕРМОСТАТИРОВАНИЕ НЕПРЕРЫВНОЛИТОГО СЛИТКА В МНЛЗ ДЛЯ ОБЕСПЕЧЕНИЯ ПРЯМОЙ ПРОКАТКИ

The paper describes mathematical modeling of the temperature field of a continuously cast cast ingot with a zone of thermal insulation in a two-dimensional spatial representation to ensure direct rolling. Currently, the cooling and solidification modes of a continuous cast ingot do not ensure an even distribution of temperatures across its cross-section, the difference between the surface and the center at the exit from the caster at different drawing speeds can be up to 500 °С. In order to maintain the heat of the melt and to ensure an even distribution of temperatures over the ingot section, it is proposed to use thermal insulation instead of air cooling in the air-cooled zone of the continuous casting machine, which will reduce (or eliminate) the intermediate heating of the ingot in heating furnaces before rolling. A mathematical model of the cooling of a continuously cast ingot is described, taking into account the evolution of the heat of crystallization in a two-phase zone and the equalization of the temperature along its cross section. The numerical realization of the model was carried out by the method of splitting by coordinates in the programming language C++. The adequacy of the model was verified by the convergence of the calculated and experimental data. To estimate the temperature equalization by its cross-section, a numerical experiment was conducted in the thermal insulation zone, as a result of which a temperature field of a continuously cast ingot along the length of the continuous casting machine was obtained at casting speeds of 0.6 to 1.4 m/min. The efficiency of temperature equalization over the section of the ingot was determined when using the heat insulation zone in comparison with air cooling. Based on the simulation results, it is established that the heat content of the ingot due to the use of the heat of the liquid phase is increased by ~ 30%, which makes it possible to apply direct rolling.