CCM Mold Research Articles

Numerical simulation of the efficiency of free and forced mixing of liquid metal in a CCM mold

Numerical simulation of the efficiency of free and forced mixing of liquid metal in a CCM mold

Simulation of a new process of mixing liquid metal in CCM mold with rotating cooling jacket with vertical ribs

The article proposes a new technology of filling the CCM mold with liquid metal and mixing it. The original patented device consists of a closed bottom nozzle and a rotating jacket. Experimental studies of liquid metal flow in a mold are long, complex and time-consuming, therefore, in the work was used mathematical modeling by numerical method. The objects of research are the hydrodynamic and thermal flows of liquid metal during the new process of steel casting into a CCM mold of rectangular cross-section, and the result is a spatial mathematical model that describes the flows and temperatures of liquid metal in the mold. To simulate the processes occurring during the metal flow in the mold, the authors used a specially crea­ted software package. The theoretical calculations are based on the fundamental equations of hydrodynamics, the equations of mathematical physics (equation of thermal conductivity taking into account mass transfer) and a proven numerical method. The area under study is divided into elements of finite dimensions, for each element a formulated system of equations is written in a difference form. The result is the velocity and temperature fields of the metal flow in the mold volume. According to the developed numerical schemes and algorithms, a calculation program was compiled. The paper considers an example of calculating the steel casting into a mold of rectangular cross-section and flow diagrams of liquid metal over various mold sections. Vector flows of liquid metal in various mold sections are clearly presented for different rotary speed of the rotating jacket. The authors identified the areas of intense turbulence and presented the results of the problem numerical solution in graphical form by diagrams of the velocity fields of liquid metal flows and their temperature over various mold sections.

Modern approaches ensuring rational conditions for continuously cast billet formation in a billet CCM mold.

The development of technology and technology of continuous steel casting actualizes the improvement of the control system of casting processes and diagnostics of the formation of continuously cast billets. The conditions determining the stability of continuous cast billet forming process in billet CCM mold are considered: the correspondence of liquid steel mass entering the mold and the outgoing billet mass; ensuring the specified intensity and uniformity of billet cooling in the mold sleeve; ensuring a rational level of friction in the crystallizer. It is shown that, on the one hand, heat transfer in the mold is largely determined by the correspondence of the billet shrinkage and the internal profile of the mold, but, on the other hand, it is noted that it is impossible to obtain a universal profile that creates optimal conditions for the formation of billets from all grades of steel with arbitrary temperature-speed parameters. Therefore, the concept of a universal crystallizer assumes that rational conditions of heat removal are achieved due to additional influences. The basics of diagnosing of heat exchange processes in the crystallizer are presented, based on the computational processing of the current ACS signals about the cooling water temperature drop in the crystallizer and its flow rate. It is noted that this system, unfortunately, does not guarantee the detection of local unevenness of the heat removal in the crystallizer and needs to be improved by providing the possibility of assessing the billet faces cooling uniformity. Modern approaches to optimize internal profile of crystallizer sleeves, choice of materials for coating inner surface of sleeves, choice of parameters of mold swinging system and diagnostics of parameters of force interaction between crust of forming billet and mold sleeve are briefly considered on issue of friction rational level establishing. The creation of a “universal” crystallizer with an increased number of control systems and the creation of a system for optimization of casting processes for specific conditions are identified as possible directions for the development of approaches to ensure rational conditions for the formation of continuous cast billets in the crystallizer of a billet caster.

Thermal Design of CCM Mold with Slotted Water Cooling Channels

Thermal Design of CCM Mold with Slotted Water Cooling Channels

Simulation of the Heat-Transfer Conditions in a CCM Mold

Simulation of the Heat-Transfer Conditions in a CCM Mold

Mathematical Simulation of CCM Mold Filling with Liquid Metal during Its Feeding from Rotary Submerged Nozzle

Mathematical Simulation of CCM Mold Filling with Liquid Metal during Its Feeding from Rotary Submerged Nozzle

Mathematical modeling of filling the CCM mold with liquid metal during its supply from a rotating submersible nozzle

Experimental studies of the flow of liquid metal in CCM mold are long, complex and labor consuming process. Therefore, mathematical modeling by numerical methods is increasingly used for this purpose. The article considers a new technology for liquid metal supply into a mold. The authors present original patented design of the device, consisting of direct-flow and rotating bottom nozzles. The main results of investigations of the melt flow in the mold are considered. The objects of research were hydrodynamic and heat flows of liquid metal at new process of steel casting into a CCM mold of rectangular section. The result is spatial mathematical model describing flows and temperatures of liquid metal in the mold. To simulate the processes occurring during metal flow in the mold, special software was designed. Theoretical calculations are based on fundamental equations of hydrodynamics, equations of mathematical physics (equation of heat conduction taking into account mass transfer) and proven numerical method. The area under study was divided into elements of finite dimensions; for each element, resulting system of equations was written in difference form. The results are fields of velocities and temperatures of metal flow in the mold volume. A calculation program was compiled based on developed numerical schemes and algorithms. An example of calculation of steel casting into a mold of rectangular cross-section, and flow diagrams of liquid metal along various sections of the mold are given. Vector flows of liquid metal in different sections of the mold are clearly presented at different angles of rotation of the deep-bottom nozzle. The authors have identified the areas of intense turbulence. Metal flows of the described technological process were compared with traditional metal supply through a fixed bottom nozzle.

Simulation of a new method for supplying and stirring liquid metal in a CCM mold

A significant influence on stability of the process of filling the CCM mold with liquid metal is exerted by the structural and technological schemes and designs of used devices, modes and parameters of filling the mold with the melt. All this is due to the features of the devices used and the improvement of their design. The high requirements for such devices have determined the need to create new devices designs to reduce the time spent on preparation for work and maintenance and to improve the quality of resulting metal billets. In scientific literature, including patents, more and more articles and materials are devoted to the development of new and improvement of the existing methods of supplying and stirring liquid metal in CCM and devices for their implementation. Experimental studies of liquid metal flow in CCM are a long, complex and laborious process. Therefore, mathematical modeling by numerical methods is increasingly used for this purpose. The authors have proposed a new technology for pouring liquid metal into a mold and a device for its implementation due to the use of effect of a deep-bottom submersible nozzle rotating in the mold with eccentric outlet holes. The purpose of this work is to simulate by proven numerical method a new process of filling a rectangular CCM mold with liquid steel and stirring it. Based on the developed numerical schemes and algorithms, a calculation program was compiled. The article describes an example of calculating the steel casting into a mold of rectangular cross-section and flow diagrams of liquid metal in it.

A review of domestic and foreign experience of steel treatment in CCM tundishes

The modern steelmaking facilities melt as a rule a semi product, which is further subjected to various processes of refining in steel ladle. Recently an additional treatment of the metal in CCM tundish became widespread in the domestic and foreign practice. A tendency of transforming tundish into a multifunctional metallurgical reactor was noted, since more and more technological operations are transferred in it, including alloying, stirring, various methods of heating, modifying and removal of nonmetallic inclusions. Examples of comprehensive utilization of a bloom CCM tundish at some Japanese plants of Kobe Steel in Kakagava presnted, at which the metal is filtered when going through holes in the two partitions thus effectively removing nonmetallic inclusions. New variants of metal blowing off in the tundish by inert gas developed by domestic specialists considered, including a technology for metal blowing off by an inert gas and a facility for the inert gas supply through the stopper of the tundish. Supply of inert gas through the stopper results in efficiency increasing of degassing and nonmetallic inclusions removal as well as submerged nuzzles service time increase, which is particularly important at casting of steels with high content of aluminum. Examples of solutions of metal treatment in tundish by cored and aluminum wire given. Schemes of cored wire introduction into tundish and liquid steel treatment in a CCM mold considered. Considerable attention was given to the problem of metal temperature control in tundish, including by an electric arc, induction and plasma heating. List of domestic and foreign plants presented, implemented facilities of steel plasma heating in the CCM tundish. It was noted, that steel chemical heating in tundish can be applied at unforeseen problems arising at casting.

Determination of melting temperature of slagmaking mixtures for billet CCM mold by differential thermal analysis method

At PJSC “Izhstal” continuously casted billets with sections of 125*125 and 140*180 mm are produced at a CCM of radial type, manufactured by STS firm, Italy. At the casting by a closed stream it is recommended to use import Steelin ML/P-280, Steelin ML/LM-280, Steelin ML/HC-230 slag-making mixtures (SMM) in the mold. At present within the import substitution program, pilot-industrial test are carried out at the plant to use SMM of domestic production. To ensure a stable process of casting and obtain quality continuously casted billet it is important to know the operation properties of SMM, including the range of melting, which is characterized by temperatures of SMM softening and melting. The value of the characteristics influences the thickness of the liquid slag layer on the surface of liquid steel in CCM mold. The properties mentioned above were determined by a differential thermal analysis at a automated facility ВТА-983. The difference of temperatures between the sample and the standard, measured during heating and cooling with continuous speed, was the registered parameter. By application the differential thermal analysis method the temperatures of softening and melting of granulated SMM of Intoflux GB 1040/H and Intoflux GB 1220/A grades were determined. Based on the results of the analysis, the softening temperature of the Intoflux GB 1040/H grade SMM was determined as 755 °C, the softening of Intoflux GB 1220/A grade SMM takes place in the temperature interval of 645-803 °C. The temperatures of commencing of crystal phases melting of the mixtures studied were 825 and 925°С for Intoflux GB 1040/H grade SMM, 1097 and 1206 °C for Intoflux GB 1220/A grade SMM. Based on the results of pilot-industrial tests, the Intoflux GB 1040/H grade SMM was recommended for usage at casting medium-carbon and high-carbon steels as a substitution of import SMM of Steelin ML/HC-230 grade.

Assessment of the efficiency of non-metallic inclusions removal through the use of centrifugal force at different stages of steel production

Methods for the removal of non-metallic inclusions from steel at various stages of its production are considered: in a teeming ladle, a tundish and a CCM mold. It is proposed to classify methods of non-metallic inclusions removal into two groups: mechanical (inert gas blowing, application of electromagnetic stirrers, etc.) and physical and chemical (modification of non-metallic inclusions, slag treatment, rational deoxidation modes). Particular attention is paid to methods aimed at creating a vortex in the metal, inside which non-metallic inclusions are transported to its axis. The aim of the work is to determine the efficiency of use centrifugal forces to remove non-metallic inclusions at different stages of steel production. To assess the centrifugal force effectiveness, it has been analyzed the transfer time of non-metallic inclusions of various sizes to the vortex axis in the teeming ladle of 50 tons capacity, a rotary chamber of tundish (chamber capacity is 2.0 tons) and the CCM mold of 160 mm in diameter. For typical angular velocities being observed during electromagnetic stirring, the values of the metal inertia moment and the kinetic energy of its rotational motion have been calculated. According to the calculations, the smallest transfer time of inclusions is achieved in the teeming ladle. However, vortex creation in it requires a significant energy. The use of centrifugal force in the mold, although it does not require such a high energy, is also not efficient enough due to the low angular velocity of the vortex, limited by a risk of violating the crust formation in the mold. The possibility of using the kinetic energy of the jet flowing from the teeming ladle to the rotary chamber of the tundish has been assessed.

Видалення неметалевих включень за рахунок використання відцентрових сил у промковші МБЛЗ

На підставі проведеного огляду методів видалення неметалевих включень зі сталі в процесі позапічної обробки й безперервного розливання сталі запропоновані їхня класифікація на дві групи: механічні й фізико-хімічні. До першої групи запропоновано віднести методи, що передбачають зміну картини циркуляційних потоків у ковші таким чином, щоб прискорити спливання НВ у шлакову фазу або їх вловлювання спеціальними керамічними фільтрами.

Development and Implementation of the System for Determining the Actual Level of Metal and Thickness of Slag Mixture in the Bloom CCM Mold at JSC “OEMK”

Achieving a higher quality of continuously-cast billets is possible by using a nuclear-type electromagnetic sensor instead of the traditional sensor to measure the level of metal in the mold. A combined use of two types of sensors makes it possible to control the thickness of the slag-forming mixture on the metal surface. The paper describes the experience of implementing a metal level measurement system with electromagnetic sensor at the bloom CCM of the Oskol Electrometallurgical Plant.

Mathematic simulation of atomic structure of multicomponent oxide-fluoride melt for continuous casting machines

Determination of relation between oxides melts properties, based on silicates and calcium alum-silicates and magnesium and their chemical composition and structure is an important condition to provide a rational slag mode in a continuous casting machines mold. A mathematical simulation of slag melts and casting powders accomplished. The oxide-fluoride system was chosen for the simulation, for which the structure after solidification was determined by experiment. Results of molecular-dynamic simulation of CaO–SiO2–Al2O3–MgO–Na2O–K2O–CaF2–FeO system, correspondent to industrial casting powders composition, used during steel casting for slag formation in a CCM mold (35.35 % SiO2; 30.79 % CaO; 8.58 % Al2O3; 1.26 % MgO; 13.73 % CaF2; 7.57 % Na2O; 0.88 % K2O; 1.82 % FeO). Taking into account the concentration, a re-calculation was accomplished to mole shares and correspondent number of ions in the model for each component calculated. Simulation of the 8-component oxide-fluoride melt with 2003 ions size in the main cube (a side length of 31.01 Å) was accomplished at the experimentally determined temperature of solidification onset (1257 K) under periodic boundary conditions and fixed volume. The Coulomb interaction was taken into account by the Ewald–Hansen method. The time step was 0.05t0, where t0 = 7,608×10–14 sec is the internal unit of time. The melt density was taken as 3.04 g/cm3 based on the experimental data. The inter-particle interaction potentials were chosen in the Born–Mayer form. According to the simulation results, the structure of sub-crystalline groups of atoms present in the melt at the temperature of the onset of solidification was determined. A discussion of the simulation results and their comparison with the literature data presented.

Optimization of Thermal Performance of CCM Mold

A physical simulation technique was used to study the processes of heat transfer between solidifying metal and CCM mold during continuous casting of steel. Variation trends have been established with respect to the amount of heat transferred from liquid metal to solidified crust, from billet surface to the mold tube, and from the mold tube to cooling water. Practical recommendations were suggested concerning an increase in heat transfer efficiency for the described stages of heat transfer from solidifying metal to cooling water.

Influence of Different Factors on Withdrawal Speed of Continuous Cast Billet

The influence of the St.3sp, 40 and 85 steel grades chemical composition, temperature of the metal in the tundish ladle, billet cross-sectional dimensions (150 × 150 and 152 × 170 mm), the sulfur content in the metal on the speed of withdrawal of the billets from the CCM mold has been investigated. It was established, that the change of the metal temperature in the tundish ladle of the CCM has the greatest effect on the billet withdrawal speed, the change of carbon content in the steel and the billet cross-sectional dimensions influence in less extend, and the sulfur content in the cast steel does not affect at all.

MODEL STUDIES OF HYDRODYNAMIC CHANGES OF STEEL FLOWS IN MOLD OF SLAB CCM DURING SUBMERGED NOZZLES REPLACEMENT

The analysis results of trends and modern techniques of research in the field of steel continuous casting are highlighted which are aimed at finding and eliminating of factors that have a negative impact on the surface quality of continuous cast billets. It is shown that the existing concept of creating quick change systems of submerged nozzles, which are used on the slab CCM, leads to the formation at the each stream of machine during serial casting of 20 heates of substandard portion of the billet with 30 – 40 m of length, formed as a result of unstable hydrodynamic conditions in the mold. The research results are given for the physical model of changes of trajectory and speed of the metal flows into the CCM mold, which are related with submerged nozzles replacement in the process of serial casting of steel. Recommendations to reduce duration of the negative impact of this factor on the con­ditions of cast billet formation are offered. Using control-measuring system with strain gauge transducer, it was found that the fluid flows velocity difference at the opposite narrow walls of the mold model, causing a violation of the thermal conditions of crust formation of con­tinuous casting billet, in the case of once-through submerged nozzles can reach 2.0 – 2.3 and for non-pressure hollow-bottom nozzles with two lateral holes separated by divider – 1.2 – 4.0. Information about the trajectory symmetry breaking of circulation circuits of melt flows in the mold, caused by conducting of operation of outworn submerged nozzle replacing, also was obtained using high speed video materials. During the research the visualization of water flows trajectories, which simulated the molten steel in the mold model, was provided by intro­duction of air through a channel of model of stopper-monoblock of the tundish, so that the input of argon during casting was simulated. The obtained information allowed to develop a new principle of construc­tion of system of submerged nozzles quick change which consists the combined and parallel implementation of individual stages of refracto­ries replacement by its structural elements (manipulator, teeming and pushing devices). It allowed to reduce the time required to replace a outworn submerged nozzle and to increase the yield during the produc­tion of slab billets on CCM.

Pilot Implementation of the Technology and Equipment for Feeding Cooling Inoculators Into the CCM Mold at Severstal

In the steel production at the Severstal Cherepovets Metallurgical Combine, we conducted pilot tests of equipment and technology in the continuous casting and simultaneous application of slag-forming mixtures and inoculators as a fraction. We observed improvement in the macrostructure in the axial zone of the ingot as a consequence of a more intensive cooling, as well as by increasing the number of crystallization sites. As an alternative to the method of introducing discrete inoculators, we propose a method and develop equipment designed to deliver a continuous ribbon chiller in the mold of the continuous caster. We determine the main parameters of the equipment and technology for introducing the ribbon into the mold of the continuous caster.

USAGE OF UNEVEN ESTIMATED NETS FOR MATHEMATICAL MODELING OF THE PROCESSES OF CONTINUOUS CAST BILLET FORMATION IN A CCM CRYSTALLIZER

The discrete analog of diff erential equation of heat conduction allowing applying irregular computational net for the mathematical modeling of continuous casting was proposed. This method of meshing allows taking into account the distribution of temperature gradients in the model. It improves accuracy of the approximation and adequacy of the computation results. The mathematical model of crystallization and shrinkage of slab in CCM mold was developed. Application of irre gular computational net allowed using the elements of size of 1 – 2 mm in modeling. The researches of slab cross-section profi le distortion under the influence of the mold were conducted on the basis of this model. Calculation of the geometrical profi le allows to specify the conditions of the thermal and mechanical interaction of the solidified shell with the mold walls and to solve the task of determination of optimal mold taper of CCM, ensuring reduction in number of slabs aff ected by surface and subsurface cracks.

DIAGNOSTICS OF ELECTROMECHANICAL DRIVE OF THE CCM MOLD OSCILLATION MECHANISM

The vibrometry method of diagnosing the destruction of the eccentric shaft of the oscillation mechanism drive of the continuous casting machine mold was developed based on the research of influence of fatigue fracture of the shaft on the amplitude-frequency characteristic and the vibration level of the oscillation mechanism. Using the Shengli theory to determine the current crack length of the eccentric shaft, the dependence of the shaft stiffness variation with time was derived. The study of this dependence has shown that decreasing shaft stiffness leads to the increase of total vibration level and spectrum of fluctuations of the drive of mold oscillation mechanism. The obtained results allowed to establish the discernment boundaries of status (integrity) of the eccentric shaft of the drive of the mold oscillation mechanism by the vibration level depending on the rotational speed of the motor shaft on the basis of GOST ISO 10816-1-97. The proposed vibrometry method for diagnosing the drive of the CCM mold mechanism is focused on the use of widely available portable vibration analyzers.