Continuous Steel Casting Process Research Articles

Type-2 fuzzy hybrid expert system for prediction of tardiness in scheduling of steel continuous casting process

This paper addresses an interval type-2 fuzzy (IT2F) hybrid expert system in order to predict the amount of tardiness where tardiness variables are represented by interval type-2 membership functions. For this purpose, IT2F disjunctive normal forms and fuzzy conjunctive normal forms are utilized in the inference engine. The main contribution of this paper is to present the IT2F hybrid expert system, which is the combination of the Mamdani and Sugeno methods. In order to predict the future amount of tardiness for continuous casting operation in a steel company in Canada, an autoregressive moving average model is used in the consequents of the rules. Parameters of the system are tuned by applying Adaptive-Network-Based Fuzzy Inference System. This method is compared with IT2F Takagi–Sugeno–Kang method in MATLAB, multiple-regression, and two other Type-1 fuzzy methods in literature. The results of computing the mean square error of these methods show that our proposed method has less error and high accuracy in comparison with other methods.

Mathematical Modeling of Behaviour a Liquid Steel Flow and a Non-Metallic Inclusions in the One Strand Wedge Type Tundish with a Subflux Turbulence Controller and a Low Dam

The numerical modelling technique is successfully used for simulation of liquid metal movement and behaviour of non-metallic inclusions in the continuous casting devices. The CFD (Computational Fluid Dynamic) method allows information on physical, chemical and hydrodynamic phenomenon in the metallurgical processes to be obtained. In the continuous steel casting process, where the tundish performs the function of a device batching steel to the mould, the monitoring especially of non-metallic inclusions is very essential because a quantity of non-metallic inclusions in the liquid steel limit the quality of final steel product. The paper presents the results of computing simulation of behaviour a liquid steel flow and non-metallic inclusions in the one-strand tundish with stopper rod system. The subject of simulation was a one-strand tundish of a nominal capacity of 30 tons. The tundish is used in the polish steel mill to process of continuous casting slabs. In the paper authors analysed two tundish i.e. tundish with a low dam and tundish with a subflux turbulence controller and a low dam. The Ansys-Fluent® program was used for solved mathematical model of casting process. The computer simulations were performed for unsteady and nonisothermal conditions. The population balance model was used to description of non-metallic inclusions growth process. As a result of computations, fields of liquid steel flow, fields of secondary phase volume fraction, fields of volume fraction for particular bins and non-metallic inclusions growth curve were obtained.

Influence of Different Oxides on the Viscosity of Fluorine-Free Mold Fluxes

Mold fluxes play an important role in the steel continuous casting process. Mainly, they must prove adequate lubrication between the solidified steel shell and the copper mold. Thus, the knowledge of mold flux viscosity with the temperature is a relevant property for industry applications in order to prevent operation problems and product defects. On the other hand, for environmental reasons, the replacement of fluorine by non-pollutants compounds, is one of the objectives in the design of new compositions for these slags. In this paper, the viscosity is calculated in the range: 1250-1400 ¼C applying two models based on their chemical composition and another one using the differential thermal analysis technique. The results obtained with this model showed a good correlation with respect to other traditional models using the chemical composition of the mold flux to estimate the viscosity. The aim is to observe the effect of different oxides on the viscosity of mold fluxes. One of the mold powders was designed with a chemical composition similar to a commercial one (containing 10 wt% of fluorine), while the others powders were fluorine-free (containing boron and lithium). It should be noted that a fluorine-free powder with a viscosity similar to the powder with fluorine was produced replacing 10 wt% fluorine by 4 wt% Li2O and 6 wt% B2O3.

Thermal Shock Behavior of Porous Nozzles with Various Pore Sizes for Continuous Casting Process

Thermal shock behavior of porous ceramic nozzles with various pore sizes for continuous casting process of steel was investigated in terms of physical properties and microstucture. Porous nozzle samples with a composition of Al 2 O 3 -SiO 2 -ZrO 2 were fabricated by adding various sizes of graphite as the pore forming agent. As the graphite size increased from 45~75 to 150~180 μm, both the resulting pore size and the flexural strength also increased. A thermal shock test was carried out at temperatures (ΔT) of 600, 700, 800, and 900℃. Microstructure analysis revealed a small number of cracks on the sample with the largest mean pore size of 22.32 μm. In addition, increasing the pore size led to a smaller decrease in both pressure drop and elastic modulus. In conclusion, controlling the pore size can enhance thermal shock behavior.

Novel online temperature control system with closed feedback loop for steel continuous casting

Based on a basic water cooling model, a novel model with closed feedback loop was developed for online temperature control system (OTCS) to control the strand surface temperature online during steel continuous casting process. The OTCS considered the temperature delay to the casting speed and water flowrate and combined the feedback control model with feed forward control model for the control of secondary cooling water. The online feed forward control with the temperature of molten steel in the tundish and the temperature of cooling water was also considered. A fine adjusting temperature region and an optimal temperature region were applied to the OTCS to avoid big temperature fluctuation during control process and to shorten the adjusting time. A single point OTCS was applied to a slab continuous caster, showing that the slab surface temperature was well stabilised at the target temperature under the control of the OTCS in continuous casting process. During tundish change or big variation of casting speed, the low slab surface temperature could be quickly controlled to the target temperature again by the OTCS within 7 min. The industrial application indicated that the OTCS could reduce the slab surface cracks and aid in increasing productive efficiency in continuous casting.

철강 연주공정에서 데이터마이닝을 이용한 품질제어 방법에 관한 연구

The smelting and the continuous casting of steel are important processes that determine the quality of steel products. Especially most of quality defects occur during solidification of the steel continuous casting process. Although quality control techniques such as six sigma, SQC, and TQM can be applied to the continuous casting process for improving quality of steel products, these techniques don't provide real-time analysis to identify the causes of defect occurrence. To solve problems, we have developed a detection model using decision tree which identified abnormal transactions to have a coarse grain structure. And we have compared the proposed model with models using neural network and logistic regression. Experiments on steel data showed that the performance of the proposed model was higher than those of neural network model and logistic regression model. Thus, we expect that the suggested model will be helpful to control the quality of steel products in real-time in the continuous casting process.

Study of the behaviour of mould powders for continuous casting by using the heating microscope

Mold powders, initially fly ash based, were introduced about 40 years ago in the steel continuous casting process. Nowadays, also synthetic powders consisting of mixtures of various minerals are used. The aims of the powders, when added to the free surface of the liquid steel in the mold, can be summarized as follows: thermal isolation of the steel surface, in order to prevent its solidification; protection of the steel surface from the oxidation; lubrication and heat transfer control between the mold wall and the solid steel shell; absorption of non-metallic inclusions coming from the steel. The purpose of this work is to characterize the thermal behavior of some mold powders for continuous casting when they are subjected to different heating cycles: heating rate of 30°C/min up to the sample fusion; heating rate of 80°C/min up to the sample fusion; instantaneous or "flash" heating, which allows to heat the sample in few seconds. On the basis of predetermined time or temperature intervals applied, this study yielded to different results, like the melting temperature, the presence of crystallizations, and the phenomena that occur in the material.

Development of Electromagnetic Swirling Flow in Immersion Nozzle in Continuous Casting Process of Steel

Swirling flow in an immersion nozzle is effective on improving quality of casting block and casting speed in continuous casting process of steel. However, a refractory swirl blade installed in the nozzle is liable to cause clogging, which limit the application of the process. In this study a new process is proposed, that is a rotating electromagnetic field is set up around an immersion nozzle to induce a swirling flow in it by Lorentz force. New types of swirling flow electromagnetic generator are proposed and the effects of the structure of the generator, the coil current intensity and frequency on the magnetic field and on the flow field in the immersion nozzle are numerically analyzed.

The effects of casting speed on steel continuous casting process

A three dimensional simulation of molten steel flow, heat transfer and solidification in mold and “secondary cooling zone” of Continuous Casting machine was performed with consideration of standard k−e model. For this purpose, computational fluid dynamics software, FLUENT was utilized. From the simulation standpoint, the main distinction between this work and preceding ones is that, the phase change process (solidification) and flow (turbulent in mold section and laminar in secondary cooling zone) have been coupled and solved jointly instead of dividing it into “transient heat conduction” and “steady fluid flow” that can lead to more realistic simulation. Determining the appropriate boundary conditions in secondary cooling zone is very complicated because of various forms of heat transfer involved, including natural and forced convection and simultaneous radiation heat transfer. The main objective of this work is to have better understanding of heat transfer and solidification in the continuous casting process. Also, effects of casting speed on heat flux and shell thickness and role of radiation in total heat transfer is discussed.

Evolution of Control Models for Secondary Cooling in Continuous Casting Process of Steel

AbstractSecondary cooling control is an important factor in the continuous steel casting process. This paper reviews popular control models and analyzes their principles and characteristics. On the basis of the review, this paper proposes a new concept called “effective‐superheat” and a new control model called “synthetical model dynamic control method based on online temperature measurement.” The model, which combines the advantages of the popular models reviewed, not only allows steady, accurate and dynamic control of slab surface temperature, but also provides the temperature profile and the end of the liquid pool. In addition, this paper also discusses the current problems with secondary cooling control and the related development trends, which may be helpful for further development of secondary cooling control technology and informationization of the continuous casting process.

NUMERICAL MODELLING OF NON-METALLIC INCLUSIONS SIZE DISTRIBUTION DURING LIQUID STEEL FLOW THROUGH A CONTINUOUS CASTING SLAB TUNDISH

The article presents the results of computer simulations of non-metallic inclusions behaviour in a slab tundish. The tundish is equipped with a dam with two holes. The authors employed the CFD (Computational Fluid Dynamics) numerical modeling technique to demonstrate changing process of non-metallic inclusions size distribution. The computer simulations were performed for non-isothermal and non-steady conditions of continuous steel casting process. As a result of computations, time characteristics of changing volume fraction for particular group of non-metallic inclusions were obtained.

Numerical simulation of two-fluid flow and meniscus interface movement in the electromagnetic continuous steel casting process

This paper presents a mathematical model and numerical technique for simulating the two-fluid flow and the meniscus interface movement in the electromagnetic continuous steel casting process. The governing equations include the continuity equation, the momentum equations, the energy equation, the level set equation and two transport equations for the electromagnetic field derived from the Maxwell's equations. The level set finite element method is applied to trace the movement of the interface between different fluids. In an attempt to optimize the casting process, the technique is then applied to study the influences of the imposed electromagnetic field and the mould oscillation pattern on the fluid flow, the meniscus shape and temperature distribution.

Decomposition kinetic of carbonaceous materials used in a mold flux design

Mold fluxes develop important functions during steel continuous casting process. To obtain a free-defect product the melting rate of mold flux is an important property to be controlled. The melting rate depends on the reactivity of carbonaceous material added to these powders as carbon source. In this article, the decomposition kinetic of two carbonaceous materials added to mold flux: petroleum coke and synthetic graphite, was analyzed. By measuring mass loss at different heating rates the decomposition reaction was determined on both types of materials. Applying several kinetic models of non-isothermal decomposition, the average activation energy E = 48 kJ/mol to mold powder with 15 wt% coke and E = 67 kJ/mol to one with 15 wt% graphite was determined. A first order of reaction (n = 1) associated to the decomposition process was assumed to both types of materials. The lower activation energy presented by mold powder-15 wt% petroleum coke indicated a higher reactivity of this material. A higher level of variation of E and n values with decomposition degree and temperature observed in the powder with petroleum coke was associated to a less thermally stable material along with a more complex degradation process.

The Effect of Temperature Fluctuation on the Formation of Billet Surface Defect in the Initial Solidification Area

The heat transfer in steel continuous casting process under mold oscillation was calculated, and temperature fluctuation phenomena was found in the initial solidification area, the maximum value was approximate 16 °C. The effect of different continuous casting parameters on temperature fluctuation were analyzed, and the temperature fluctuation was considered to be a key factor to the formation of oscillation marks. The Index of Temperature Fluctuation(ITF) was proposed to predict the effect of temperature fluctuation on the formation of billet surface defects.

Simulation of heat transfer in steel billets during continuous casting

This work is focused on the development of computational algorithms to create a simulator for solving the heat transfer during the continuous casting process of steel. The temperatures and the solid shell thickness profiles were calculated and displayed on the screen for a billet through a defined continuous casting plant (CCP). The algorithms developed to calculate billet temperatures, involve the solutions of the corresponding equations for the heat removal conditions such as radiation, forced convection, and conduction according to the billet position through the CCP. This is done by a simultaneous comparison with the kinematics model previously developed. A finite difference method known as Crank-Nicholson is applied to solve the two-dimensional computational array (2D model). Enthalpy (HI,J) and temperature (TI,J) in every node are updated at each step time. The routines to display the results have been developed using a graphical user interface (GUI) in the programming language C++. Finally, the results obtained are compared with those of industrial trials for the surface temperature of three steel casters with different plant configurations in different casting conditions.

Simulation factors of steel continuous casting

The factors involved in simulating the continuous casting process of steel and the effects of the factors on the thermal behavior were investigated. The numerical methods and the influence of some assumptions were also analyzed, such as nodes used to discretize the steel in array size and computing time to obtain good approaches. The results show that some of these factors are related with the design of the continuous casting plant (CCP), such as geometrical configuration, and the operating conditions, such as water flow rate, heat removal coefficient in the mold, casting times, and casting speed in the strand, which affect the heat removal conditions over the temperature and solidification profiles.

Numerical Simulation of Steel Flow and Behaviour of Non-Metallic Inclusions in the Six-Strand Tundish with Stopper Rod System

The numerical modelling technique is successfully used for simulation of steel flow and behaviour of non-metallic inclusions in the tundish. The CFD (Computational Fluid Dynamic) method allows information on steel motion, flow, flow turbulence and steel temperature distribution in the tundish to be obtained. In the continuous steel casting process, where the tundish performs the function of a device batching steel to the mould, the monitoring of steel flow is very essential because steel flow has influence on the behaviour of non-metallic inclusions. The paper presents the results of computing simulation steel flow and flotation of non-metallic inclusions in the six-strand tundish with stopper rod system. The subject of simulation was a six-strand tundish unprovided with flow control devices. The tundish is used in the polish steel mill to process of continuous casting billets. The Fluent program was used for solved mathematical model of casting process. The numerical simulation of steel flow was performed for whole test facility without the “symmetry” boundary condition. As a results of numerical simulation maps of directions flow and temperature of steel, Residence Time Distributions curve type of (F) and (E) and distributions of non-metallic inclusions between slag phase and particular tundish outlets has been obtained.

A Simple Model to Calculate Dendrite Growth Rate during Steel Continuous Casting Process

In the current paper, the relationship between the casting speed and the dendrite growth during steel continuous casting process was studied; and a simple mathematical model to calculate the primary dendrite growth rate according to the casting speed was developed. The model was used to predict the distribution of the dendrite growth rate along width direction and casting direction during a continuous casting process, indicating a dendrite growth rate of 0.1–3.0 mm/s, which is much higher than that in regular ingot casting. The dendrite growth rate fluctuates along casting direction because of the different cooling intensity in each zone of the continuous caster; and the distribution of the dendrite growth rate along width direction was non-uniform due to the uneven transverse distribution of cooling intensity. The predicted results agree well with the measurements.

Numerical Simulation of Steel Flow Through a One Strand Slab Tundish with Steel Flow Control Devices

This paper presents the results of a computing simulation of steel flow in a one strand slab tundish. The tundish is used in a Polish steel mill to process continuous cast slabs. Fluent® was used to solve the mathematical model of the casting process. For verification of the mathematical model and results of the numerical simulation, experimental research during continuous steel casting process was conducted. The effect of the industrial experiment was characteristic of a change in chemical elements when steel grades were changed in the course of the casting sequence. The internal geometry of the considered object was changed by two types of flow control devices, i.e., subflux turbulence controller and gas permeable barrier. From these calculations of residence time distribution of steel curve (RTD) the influence of argon blowing and use of the subflux turbulence controller on steel flow in the tundish have been obtained.

Modelado del Proceso Convencional de Colada Continua de Aceros Libres de Interticios

The purpose of this work was to develop a mathematical model able to simulate the continuous casting process of IF steel (Interstitial Free).and to determine the optimum operating conditions. The model formulation involves the momentum equations of liquid and solidified materials coupled with the temperature evolution of the slab. The differential equations and boundary conditions are numerically solved using the finite volume technique with appropriated boundary conditions for each region of the casting machine. The model predictions were compared with industrial data for conventional continuous casting conditions and extended to IF steel.