Effect of Electromagnetic Frequency on the Flow Behavior in Mold during Bloom Casting

Considering solidification, a large eddy simulation (LES) model of two-phase flow was established to simulate the thermal–magnetic flow coupled fields inside a jumbo bloom. The magnetic field was calculated based on Maxwell’s equations, constitutive equations, and Ohm’s law. An enthalpy–porosity technique was used to model the solidification of the steel. The movement of the free surface was described by the volume of fluid (VOF) approach. With the effect of electromagnetic stirring (MEMS), the vortices in the bloom tended to be strip-like; large vortices mostly appeared in the injection zone, while small ones were found near the surface of the bloom. It is newly found that even though the submerged entry nozzle (SEN) is asymmetrical about the bloom, a biased flow can also be found under the effect of MEMS. The reason for this phenomenon is because the magnetic force is asymmetrical and transient. A high frequency will reduce the period of biased flow; however, the frequency should not be too high because it could also intensify meniscus fluctuations and thus entrap slag droplets in the mold. The velocity near the solidification front can also be increased with a higher frequency.

Asymmetric Flow Control in a Slab Mold through a New Type of Electromagnetic Field Arrangement

This research aims to investigate the control effect of asymmetric flow in a slab mold using a novel magnetic field arrangement: freestanding adjustable combination electromagnetic brake (FAC-EMBr). Three scenarios (submerged entry nozzle moves to the narrow face, wide face of the slab mold, and rotates 10°) were studied using three-dimensional numerical simulation. The results show that the magnetic field generated by the FAC-EMBr system can effectively cover three key zones in mold and that the magnetic flux density in the zone cover by a vertical magnetic pole can be adjusted according to the actual flow condition. The FAC-EMBr can effectively improve the asymmetric flow in a mold and near the narrow surface caused by the asymmetric arrangement of the nozzle and can effectively inhibit the occurrence of the flow deviation phenomenon and stabilize the steel/slag interface fluctuation. At the same time, FAC-EMBr has obvious inhibition effects on the surface velocity and can optimize the asymmetric distribution of the surface velocity and the upper reflux velocity caused by the asymmetric arrangement of the nozzle. This study can provide theoretical evidence for the development and utilization of a new electromagnetic brake technology.

A Simulation Method for the Optimization of Cooling Water Slot Structure in Slab Continuous Casting Mold Combined With SEN

The temperature field in the full 3D finite element mold model combined with submerged entry nozzle(SEN)(Full SEN-3D FEMM) is simulated with Fluent of ANSYS 18.0 Package to apply the maximum heat flux density on the heat face of mold copper plate obtained through this simulation to the element model of the copper plate, and thermal stress and strain simulations on the copper plate and stainless back ones are conducted with Workbench of ANSYS 18.0 Package to confirm the reasonable designing factors for the water slot structure on the copper plate. The maximum heat flux densities on the wide and narrow heat faces of the copper plates are given on the initial shock areas of molten steel flux injected through SEN. With constant heat flux density on the heat face, the more the thickness of copper plate increases, the more the max- and min temperatures increase and the difference between them decreases. Elastic and plastic deformations on the copper plate are made during continuous casting(CC) process; the former occurs around the water slots and the latter around the heat face with the highest temperature, which regards 20-18-17 as the most reasonable one among 4 plans for the water slot structure.

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.

On Modelling Parasitic Solidification Due to Heat Loss at Submerged Entry Nozzle Region of Continuous Casting Mold

Continuous casting (CC) is one of the most important processes of steel production; it features a high production rate and close to the net shape. The quality improvement of final CC products is an important goal of scientific research. One of the defining issues of this goal is the stability of the casting process. The clogging of submerged entry nozzles (SENs) typically results in asymmetric mold flow, uneven solidification, meniscus fluctuations, and possible slag entrapment. Analyses of retained SENs have evidenced the solidification of entrapped melt inside clog material. The experimental study of these phenomena has significant difficulties that make numerical simulation a perfect investigation tool. In the present study, verified 2D simulations were performed with an advanced multi-material model based on a newly presented single mesh approach for the liquid and solid regions. Implemented as an in-house code using the OpenFOAM finite volume method libraries, it aggregated the liquid melt flow, solidification of the steel, and heat transfer through the refractory SENs, copper mold plates, and the slag layer, including its convection. The introduced novel technique dynamically couples the momentum at the steel/slag interface without complex multi-phase interface tracking. The following scenarios were studied: (i) SEN with proper fiber insulation, (ii) partial damage of SEN insulation, and (iii) complete damage of SEN insulation. A uniform 12 mm clog layer with 45% entrapped liquid steel was additionally considered. The simulations showed that parasitic solidification occurred inside an SEN bore with partially or completely absent insulation. SEN clogging was found to promote the solidification of the entrapped melt; without SEN insulation, it could overgrow the clogged region. The jet flow was shown to be accelerated due to the combined effect of the clogging and parasitic solidification; simultaneously, the superheat transport was impaired inside the mold cavity.

Interfacial Heat Flux Estimation in a Funnel Shaped Mould and Analysis of Solidification Characteristics in Thin Slab Continuous Casting

An inverse heat transfer model based on Salp Swarm optimization algorithm is developed for prediction of heat flux at the hot faces of a mould in thin slab continuous casting. The industrial mould considered in this work is a funnel-shaped mould having complex arrangement of cooling slots and holes. Significant variations of heat flux along the casting direction, as well as across the width are observed. Subsequently, the obtained heat flux profile estimated by the inverse method is used to analyse the fluid flow and thermal characteristics of the solidifying steel strand inside the mould. Three different recirculatory zones are present due to molten steel flow, affecting the thermal and solidification characteristics significantly. The effect of these recirculatory flows on remelting phenomenon, and consequent formation of thinner shell at the mould outlet leading to quality control issues in the casting process have been discussed. Another practical issue of depression in the wide face shell thickness at the mould outlet has been identified, and its cause has been related to the location of the Submerged Entry Nozzle and the high speed of the molten steel inflow.