Influence of forced convection on solidification and remelting in the developing mushy zone

Liu

et al. 2020

Metall Mater Trans B

The electromagnetic brake (EMBr) is a well-known and widely applied technology for controlling the melt flow in the continuous casting (CC) of the steel. The effect of a steady (DC) magnetic field (0.31 T) in a CC mold is numerically studied based on the GaInSn experiment. The electrical boundary conditions are varied by considering a perfectly insulating/conductive mold or the presence of a conductive solid shell, which is experimentally modeled by 0.5 mm brass plates. An intense current density (up to 350 kA/m 2) is induced by the EMBr magnetic field in the form of loops. The electric current loop tends to close either inside the liquid bulk or through the conductive solid. Based on the character of the induced current loop closures, the turbulent flow is affected as follows: (i) it becomes unstable in the insulated mold, forming 2D self-inducing vortex structures aligned with the magnetic field; (ii) it is strongly damped for the conductive mold; and (iii) it exhibits transitional behavior with the presence of a solid shell. The application of the obtained results for the real CC process is discussed and validated.

Section: Introductionmentioning

confidence: 88%

Electric Current Distribution During Electromagnetic Braking in Continuous Casting

Liu

et al. 2020

Metall Mater Trans B

“…The striking influence of uniform transverse magnetic fields on liquid metal flows in ducts with various wall conductance ratios was observed in the early studies of Cuevas et al [1,2] The ability of DC magnetic fields to dampen fluctuations in highly turbulent flows is supposed to have attractive application potential for flow control in continuous casting, for example, to prevent undesired remelting of the solidified shell. [3][4][5] However, the magnetic field effect is anisotropic and, thus, could become rather complex. Studies on mixed convection, which represents a superposition of buoyancy and forced convection, found both a stabilizing and a redistributing impact.…”

Section: Ensuring the Quality Of Continuous Cast (Cc)mentioning

confidence: 99%

“…According to Eq. [5] for the magnetic field, applied in the normal direction to the mold's wide face, the Lorentz force will act in the vertical plane only. The distribution of the Lorentz force function L F L ; u ð Þin the vertical center plane is investigated in Figure 14 together with the magnitude of the magnetic force and the induced current density to distinguish wherever its action is important or not.…”

Section: Action Of the Lorentz Forcementioning

confidence: 99%

Generation of Reverse Meniscus Flow by Applying An Electromagnetic Brake

Karimi-Sibaki

et al. 2021

Metall Mater Trans B

A numerical study is presented that deals with the flow in the mold of a continuous slab caster under the influence of a DC magnetic field (electromagnetic brakes (EMBrs)). The arrangement and geometry investigated here is based on a series of previous experimental studies carried out at the mini-LIMMCAST facility at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR). The magnetic field models a ruler-type EMBr and is installed in the region of the ports of the submerged entry nozzle (SEN). The current article considers magnet field strengths up to 441 mT, corresponding to a Hartmann number of about 600, and takes the electrical conductivity of the solidified shell into account. The numerical model of the turbulent flow under the applied magnetic field is implemented using the open-source CFD package OpenFOAM®. Our numerical results reveal that a growing magnitude of the applied magnetic field may cause a reversal of the flow direction at the meniscus surface, which is related the formation of a “multiroll” flow pattern in the mold. This phenomenon can be explained as a classical magnetohydrodynamics (MHD) effect: (1) the closure of the induced electric current results not primarily in a braking Lorentz force inside the jet but in an acceleration in regions of previously weak velocities, which initiates the formation of an opposite vortex (OV) close to the mean jet; (2) this vortex develops in size at the expense of the main vortex until it reaches the meniscus surface, where it becomes clearly visible. We also show that an acceleration of the meniscus flow must be expected when the applied magnetic field is smaller than a critical value. This acceleration is due to the transfer of kinetic energy from smaller turbulent structures into the mean flow. A further increase in the EMBr intensity leads to the expected damping of the mean flow and, consequently, to a reduction in the size of the upper roll. These investigations show that the Lorentz force cannot be reduced to a simple damping effect; depending on the field strength, its action is found to be topologically complex.

“…Refractory properties are important for the heat transfer, wear, and thermal stress resistance of a material [52,53]; gas bubble formation [54]; and clogging rate, among others. SEN clogging causes an asymmetric flow pattern, parasitic solidification at an SEN, hook formation at a meniscus, local shell thinning, and breakouts since the forced convection plays a crucial role in solidified shell formation [55,56].…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2021

Metals

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.