Mihaiela Isac

Ladle Shroud as a Flow Control Device for Tundish Operations

The performance characteristics of a tundish, such as the flotation of inclusions and slag entrainment, are largely influenced by the fluid-flow phenomena. Physical modeling in water is widely used to understand the fluid flows in a tundish and as a tool to improve, control, and design procedures for high-quality steel processing operations. These approaches were used to study the performance of fluid flow for a new design of ladle shroud. The new design for a dissipative ladle shroud (DLS) was studied, using a one-third scale, delta shaped, four-strand tundish. The results were compared with those achieved with the conventional ladle shroud. Different cases have been analyzed, including a conventional ladle shroud (LS) with a bare tundish and a tundish furnished with an impact pad. Similarly, the new design of the shroud (DLS) was studied under equivalent conditions. The physical experiments included the use of particle image velocimetry (PIV) and conductivity tracer techniques. The PIV measured the instantaneous velocities at the outlet of the DLS and the LS at different flow rates, showing the detailed jetting characteristics of water leaving the two types of ladle shroud. Residence time distribution (RTD) curves were also obtained for the different flow arrangements previously mentioned, and the dispersion of a colored dye tracer was observed at different intervals of time during tundish operation and analyzed using the video visualization technique.

Effect of flow modifiers on liquid metal cleanliness in four-strand delta shaped billet caster tundish

Abstract Mathematical modelling was performed on a full scale aqueous model of a delta shaped four-strand billet caster tundish that is in operation at the RTIT (QIT) plant in Sorel-Tracy, Que., Canada. The tundish already uses a large and shallow impact pad designed by the McGill Metals Processing Centre (MMPC) and has proved to be quite successful. In the present study, 12 different combinations of flow modifiers were researched, each of which consisted of the standard impact pad (SIP) and two dams located in between the inner and outer strands. In addition, the size of the SIP was varied in four steps, and its performance was evaluated. The residual ratio of inclusion (RRI) was calculated for all 18 designs, and the best configuration was identified. Mathematically predicted RRI values were verified with existing water model data for a couple of designs.

Applications of Computational Fluid Dynamics (CFD) in iron- and steelmaking: Part 1

Abstract After presenting a review of some applications of computational fluid mechanics (CFD) to ironmaking processes in Part 1, the authors now explore the use and extent of CFD in steelmaking and steel casting processes. Steelmaking processes generally include the basic oxygen furnace, electric arc furnace or equivalent, the ladle and continuous casting and incorporating a tundish and moulds. All these steelmaking processing steps involve highly coupled complex transport phenomena. The use of CFD to model such processes has been an active area of research for the last three decades. Many models have been developed to predict mixing behaviour, slag foaming, gas–liquid interactions, multiphase flows, as well as heat and mass transfer aspects. In the present review, the role of CFD in modelling steelmaking operations is reviewed, discussed and critiqued.

Effect of vertical alignment of ladle shroud on transient steel quality output from multistrand tundish

Abstract Slight misalignments of the ladle shroud in a multistrand continuous casting tundish can lead to significant differences in the amounts of slag entrained into individual moulds during transient operations. In this full scale water modelling work, the effects of ladle shroud alignment on steel quality was measured in terms of ‘slag’ entrainment into the individual moulds. The ladle shroud was purposefully biased by about 4–5° off vertical, and the numbers of ‘slag particles’ entering individual strands of the four‐strand billet caster were measured during a ladle change and compared with the no bias condition. Given the great sensitivity of steel quality to this slight misalignment during a ladle change, possible remedial actions are discussed for equivalent steel plant operations.

Effect of submergence depth of the ladle shroud on liquid steel quality output from a delta shaped four strand tundish

Abstract Physical and mathematical modelling was performed in a full-scale water model tundish to study the effect of the submergence depth of the shroud on melt flow and liquid metal quality. In the full-scale water model tundish, slag entrainment tests were performed at various immersion depths of the shroud. Polyethylene beads (920 kg m−3) were used to simulate the slag phase and the number of beads collected in each submerged entry nozzle during a ladle change, indicated relative performances in terms of slag entrainment. A three-dimensional mathematical model was developed and contours of turbulence (turbulent kinetic energy (TKE) contours) were examined at different depths of submergence of the ladle shroud. At low depths of submergence there is high turbulence within the tundish and this causes more slag entrainment. On the contrary, at high submergence depths there is very low turbulence and hence amount of slag entrained is less. Tundish operations with higher submergence depth of the shroud may eliminate the use of turbulence inhibitors and thereby reduce refractory consumption and cost.

Models and Equations for Atomic Transport Coefficients of Liquid Metals: Viscosity and Self-Diffusivity

The current article presented appropriate models using a new parameter recently introduced by the authors to accurately predict the atomic transport coefficients, i.e. viscosity and self-diffusivity, of liquid metallic elements at their melting points. The models for both the meltingpoint viscosity and self-diffusivity are expressed in terms of well-known physical quantities; atomic mass, atomic volume, melting point, melting-point surface tension, and the new parameter T ξ . Moreover, the authors derived expressions for the temperature dependence of the atomic transport coefficients of liquid metallic elements in terms of melting point temperature. These two models give very good agreement with experimental data for various metallic liquids. Using the models, self-diffusivities were predicted for liquid aluminum, calcium, and magnesium.

In-Situ Sensors for Liquid Metal Quality

Abstract The development of effective methods for directly measuring liquid metal quality, prior to casting and final solidification, has long been a goal for Process Metallurgists. For aluminum, which is generally much cleaner than steel, it is first necessary to concentrate the inclusions by filtering the metal through a porous frit, before then freezing the remaining metal, and subjecting it to microscopic examination (e.g. PoDFA). An alternative method is to take a sample of metal, freeze it, and then dissolve the metal to release the particles (inclusions) through elutriation (the Slime Technique). The only true on-line, in-situ, methods are the Ultrasonic Liquid Metal Sensors (such as the Mansfield Molten Metal Sensor), and the Electric Sensing Zone Methods (such as LiMCA and ESZ-pas). Currently, perhaps the most reliable, but least satisfying, technique is to wait for customer complaints to identify problems. JFE has developed an ultrasonic, on-line, system that registers larger inclusion clusters in rolled steel sheets as they are produced. Alternatively, many steelmakers will use PDA (Pulse Discrimination Analysis) on a small surface of solid steel, to arrive at conclusions concerning inclusions less than 10 microns. Unfortunately, this ignores the much larger inclusions normally present within a steel melt that are responsible for compromising metal properties. The late Professor Iwase was a strong believer in the development of good techniques and methods to monitor and control metallurgical processes, including those related to metal quality. This review is dedicated to his memory, and to his strength of perseverance.

Mathematical Modeling and Microstructure Analysis of Low Carbon Steel Strips Produced by Horizontal Single Belt Casting (HSBC)

The horizontal single belt casting (HSBC) process has been proposed as an efficient, economical, and environmentally friendly alternative approach to the production of ferrous alloys. Low carbon steel strips were cast using the HSBC simulator apparatus to study the characteristics and properties of the as-cast steel strips. Three-dimensional computational fluid dynamics simulations using ANSYS FLUENT 14.5 were also performed. Numerical predictions were validated against experimental casting results. Microstructural analyses and as-cast surface texture studies were conducted on low carbon steels.

The Computational Fluid Dynamic (CFD) Modeling of the Horizontal Single Belt Casting (HSBC) Processing of Al-Mg-Sc-Zr Alloy Strips

Al-Mg-Sc-Zr alloys have shown exceptional potential as structural materials for transportation applications. These alloys have proved to be good candidates to be processed as thin strips via the horizontal single belt casting (HSBC) process. The HSBC process is a near-net-shape casting technology, which involves casting molten metal directly into thin strips, close to the final product thickness, at higher cooling rates than conventional continuous casting and thin-slab casting processes. It offers an efficient, economical, and environmentally friendly approach to the production of metal strips. Fluid mechanics and associated heat transfer are important aspects of any casting process, and the novel HSBC process is no exception. Three-dimensional computational fluid dynamics simulations using ANSYS FLUENT 14.5 were performed, in order to assess the importance and effects of the various operational conditions of the HSBC process. This enabled process parameter optimization. Numerical predictions were validated against experimental casting results.

The Design of a New Casting Process: From Fundamentals to Practice

Abstract Section 4.7 makes use of the preceding sections to propose a new casting system, called HSBC, or Horizontal Single Belt Casting, to produce steel sheet products. Following a review of Conventional Continuous Casting and Thin Slab Casting processes, the process overview goes to Near-Net –Shape-Casting processes. The two NNSC processes analyzed are TRC (Twin Roll Casting), and HSBC (Horizontal Single Belt Casting). The section presents the latest research on fluid flows, solidification, and heat transfer in moving mold machines, as well as predicted heat fluxes, based on perfect and imperfect thermal contact. Similarly, this section reviews solidification and strip microstructures in NNSC. Following an analysis of fluid flows and the design of liquid steel delivery systems, presenting the potential of the HSBC process from fundamentals to practice, the authors conclude that the HSBC system will most likely usurp current CCC slab caster operations in the years to come.