Fluid Flow-Related Transport Phenomena in Steel Slab Continuous Casting Strands under Electromagnetic Brake

This study is to investigate the effect of electromagnetic brake (EMBr) on fluid flow and particle motion in steel slab continuous casting strands. The effect of slide gate moving on fluid flow pattern was discussed. A strong swirl and asymmetrical flow at the outports and, subsequently, inside the slab mold, was induced by slide gate. The application of EMBr would be a remedy to the swirl flow in the casting mold. Flow pattern has great influence on the trajectories of injected bubbles and nonmetallic inclusions. More bubbles tend to release from the top surface near the wide face opposite to the gate opening side without EMBr; while, they escape at the center place of the slab thickness when the EMBr was applied. Local brake type EMBr has a little effect on the overall removal fraction of nonmetallic inclusions, especially for the small ones. However, EMBr affects the distribution of inclusions on the cross section of the slab, and more inclusions were observed in the sub‐surface layer of the slab.

A kind of composite magnetic field for flow control in slab mold is proposed, in which an electromagnetic stirring (EMS) is carried out near the meniscus and an electromagnetic braking (EMBr) is carried out near the outlet of the submerged entry nozzle (SEN), simultaneously. The yoke for the EMS and the EMBr is made independent from each other, with a ruler type for the EMBr. A three-dimensional model of the magnetic field calculation is established. The simulation results show that the magnetic induction intensity generated with the EMS mainly concentrates in the EMS area. The magnetic induction intensity generated with the EMBr has a large component in the EMS results, which has little effect on the flow of this area. Based on the composite magnetic field calculation results, the three-dimensional numerical simulation of the flow field is carried out, and the flow field obtained is compared to that without the magnetic field but with the EMS and the EMBr only, respectively. The results show that under the composite magnetic field, EMBr and EMS can play their respective roles well under certain conditions, the impact of the jet flow on the narrow face is reduced, and the stirring beneath the meniscus is intensified.

Transient turbulent flow in the mold region during continuous casting of steel is related to many quality problems, such as surface defects and slag entrainment. This work applies an efficient multi-GPU based code, CUFlow, to perform large eddy simulations (LES) of the turbulent flow in a domain that includes the slide gate, SEN, and mold region. The computations were first validated by comparing the predicted surface velocity with plant measurements. Then, seven LES simulations were conducted to study the effects of casting speed, electromagnetic braking (EMBr) field strength, and submerged entry nozzle (SEN) depth on the transient flow. The results show that EMBr has an important influence on flow inside the SEN, in addition to flow in the mold. With EMBr, an “M-shaped” flow profile is seen inside the SEN. The swirling flow behavior in the SEN and ports is more symmetrical at high casting speed and with higher EMBr strength. The position of the SEN ports relative to the peak magnetic field affects the EMBr performance. The results confirm and quantify how applying EMBr greatly lowers both the magnitude and turbulent variations of the surface velocity and level profile.

EMBr (ElectroMagnetic Brake) and in-mold EMS (ElectroMagnetic Stirring) have been developed to control molten steel flow in a continuous casting mold. EMBr is able to stabilize the molten flow in the mold. EMBr is usually used to prevent breakout during high speed casting of medium carbon steel. In-mold EMS is effectively to improve surface quality of the cast such as interstitial free steel by forced flow of the molten steel in front of initially solidifying shell. Suitable molten flow pattern in the mold is depends on its casting condition and components. However, ordinary electromagnetic device has only one function of EMBr or EMS, so a multifunction device which can be selected EMBr or EMS in the mold is desirable. It is difficult to obtain sufficient performance both EMBr and EMS in only one electromagnetic device because the necessary structure of them is different. EMBr needs to generate large magnetic flux density by large teeth of iron core. A lot of small teeth are necessary for EMS to generate travelling magnetic field along the mold side uniformly. The structure and current applied method of the EMBr/EMS multifunction mold has been developed by numerical analysis of electromagnetic field and fluid flow dynamics. The EMBr/EMS multifunction mold has been applied to Kashima No.3 CC.

The flow field, bubble distribution and solidified shell in slab mold are numerically simulated with large eddy simulation (LES) under different electromagnetic braking (EMBr) conditions, assisted with high-temperature quantitative velocity measurement. The calculated velocities on the mold surface are in good agreement with the measured values of the industrial experiment at high temperature with the rod deflection method under different EMBr conditions and different argon flow rates, which verifies the correctness of the model. After EMBr is applied, the flow velocity on the surface of the mold decreases. With EMBr, the velocity on the mold surface first increases and then decreases with the increase in argon flow rate. When the argon flow rate is 10 L·min−1, the jets at the side ports of the submerged entry nozzle (SEN) become disordered, and the liquid level fluctuation near the SEN wall intensifies, which increases the risk of slag entrainment and slag layer breaking and the risk of argon bubbles being captured. When the argon flow rate is 6 L·min−1, the velocity and fluctuation on the mold surface can be significantly reduced by use of double-ruler EMBr; the impact of the jet on the narrow face of the mold is obviously restrained; and the solidified shell thickness increases.

The thin slab casting (TSC) of steel is a type of the continuous casting (CC) with a narrow funnel-shaped mold, characterized by the rapid solidification and fast production rates. A highly turbulent flow impacts on a growing solid shell due to the constant feeding of the fresh hot melt. That strongly affects the solidification profiles and final quality of the TSC slabs. The presented work numerically investigates the solidification inside the TSC mold with the asymmetric flow pattern caused by the misalignment (tilting) of the submerged entry nozzle (SEN). These effects were considered with and without the applied electromagnetic brake (EMBr). The influence of the adjustable EMBr on the asymmetric flow and solidification profiles including turbulent and magnetohydrodynamic (MHD) effects were studied. During consistent series of simulations, the EMBr was varied between the magnetic poles and the time-averaged velocity and temperature fields were collected. The results showed that symmetric EMBr of a local type could partially improve the asymmetry. An optimal braking scenario was found for the casing speed of 5.5 m/min and maximum EMBr value of 180 mT. The solidification and MHD models including turbulence were developed using OpenFOAM®.

Herein, full region (not divided the mold into several parts) fluid flow in a wide slab mold is studied using a one‐quarter scale water model. The particle image velocimetry (PIV) is used to analyze the turbulent features of the flows. The features include the distribution of instantaneous velocity fields, time‐averaged velocity fields, turbulent fluctuation velocity fields, the turbulent kinetic energy (TKE) and its dissipation rate, rate of strain, and the vorticity. There are several findings in this study. The fluid flow in the mold is not always symmetrical even the submerged entry nozzle (SEN) is strictly centered, but the time‐averaged flow structure is symmetric flow. The development of turbulence is relatively sufficient in the lower part of the mold, where the flow velocity is large, and the TKE and its dissipation rate are also large. Regions of positive and negative values signify the direction of the flow rotation with mirror images on both sides of the SEN. The regions of high vorticity are close to jets and decrease as it flows further into the mold.

In steel continuous casting, flow in the mold region is related to many quality problems such as surface defects and slag entrainment. An electromagnetic braking (EMBr) system is a method to control the steel flow field to minimize defects and capture inclusions. The position of the port of the Submerged Entry Nozzle (SEN) and the peak magnetic field both affect the performance of the EMBr. In the present work, an efficient multi-GPU based code, CUFLOW, is used to perform Large Eddy Simulations of the turbulent flow by solving the time-dependent Navier-Stokes equations in a domain that includes the slide gate, SEN and mold region. The computations were first validated by comparing the predicted surface velocity with plant measurements. Subsequently, eight LES simulations were conducted to study the effects of different EMBr values and SEN depths. The flow patterns in various regions are presented. The results show that applying EMBr greatly lowers top surface velocities and turbulent fluctuations.

Effective control of intense turbulence is a crucial challenge for achieving steady production with ultra-high casting speed in thin slab continuous casting. In thin slab casting process, specially designed multi-port submerged entry nozzle (SEN) with four outlets is utilised to ensure an ample supply of molten steel, necessitating the selection and optimisation of suitable Electromagnetic Braking (EMBr) equipment for steel jet control. This study established a comprehensive three-dimensional model of a funnel-type mould, employing a combined experimental-numerical approach to validate and investigate the flow, heat transfer, solidification and electromagnetic behaviour in the mould. The steel grade studied in the simulation is Q235B, and its physical properties were calculated based on its composition with a temperature range of 1450–1826 K. To analyse the influence of high casting speed on the flow and solidification behaviour in the mould, three casting speeds were selected for the study, which were 6, 7 and 8 m/min. The results indicate that the novel Bowl EMBr significantly suppressed the penetration of steel jet and thus enhanced the thickness and uniformity of the solidified shell. As the casting speed increases from 6 to 8 m/min, the solidified shell thickness at the mould exit decreases from 7.91 to 5.94 mm, with the stagnant growth region approaching the mould exit. This highlights the requirement to correspondingly increase EMBr strength under ultra-high casting speed condition to avoid remelting of the shell and the risk of molten steel leakage. The coupled mathematical model established in this study provides guidance for optimising EMBr structures and casting speed under special multi-port SEN conditions, offering recommendations for the rational control of flow, heat transfer and solidification process in the mould.

In this work, the placement of an electromagnetic swirl flow generator (EMSFG) around a submerged entry nozzle (SEN) was proposed as a method for generating a rotating electromagnetic field in a continuous casting (CC) process of steel. First, two kinds of a full type EMSFG and a half type EMSFG were designed based on mathematical modeling. Then, distributions of magnetic flux intensity in an EMSFG as well as distributions of Lorentz force in molten steel were simulated. It was found that the EMSFG structure and electromagnetic parameters have an important effect on magnetic flux intensity and Lorentz force distributions. For both a full type and a half type EMSFG, the magnetic flux intensity and Lorentz force increases as the magnetomotive force increases. Especially, for a full type EMSFG, the magnetic flux intensity is distributed evenly in molten steel. Moreover, the Lorentz force increases along a radial direction in the molten steel in the SEN. However, for a half type EMSFG, the magnetic flux intensity and Lorentz force decreases gradually towards the region without an EMSFG. Consequently, a full type EMSFG with a 44 000 AT magnetomotive force and a 50 Hz frequency is more suitable to apply in the operation of an EMSFG under actual production conditions.

Influences of mould curvature, slide gate, electromagnetic brake (EMBr) position and magnetic forces on steel flow in a slab mould were studied using a mathematical model. Positions of the EMBr include magnets at the same level as the discharging ports of the submerged entry nozzle (SEN) and magnets below the SEN tip. The slide gate induces a biased flow. Regarding the EMBr in the first position, it was found that increasing the magnetic flux density leads to rises of the discharging jets and the elimination of the two upper roll flows with lower roll flows with smaller velocities. In the case of the second position, the EMBr eliminates the effects of the biased flow in the meniscus velocity profile and induces a downward uniform flow eliminating the lower roll flow. In either case, the magnetic flux density does not affect the velocity profile in the discharging ports in the SEN.

Swirling flow submerged entry nozzle technology is one of the important methods to optimise the continuous casting of steel. In this study, a novel swirling flow brick design in tundish was proposed to achieve a swirling flow submerged entry nozzle. Numerical simulations were carried out to investigate steel flow dynamic behaviour in a round mould under the effect of new designs. The results showed that a rotational steel flow was generated inside the submerged entry nozzle by using both two-inlet and three-inlet brick designs. Due to the rotational flow momentum, molten steel from the submerged entry nozzle outlet moved towards the mould wall. Such a flow pattern eliminated the impinging flow in mould, which was generally formed in conventional single-port submerged entry nozzle casting. When using swirling flow brick designs, the whole flow field in the submerged entry nozzle and mould exhibited a dynamic change. As the side-inlet number of bricks decreased from three-inlet to two-inlet, the velocity fluctuation range was reduced from ± 63.3% to ± 8.9%. Moreover, the swirling flow intensity in the submerged entry nozzle was decreased by about 40%. In addition, a high-pressure region above atmospheric pressure was obtained near the submerged entry nozzle wall by using new designs, which is helpful to prevent air from being sucked into the submerged entry nozzle.

The steel/slag interface behavior under a new type of electromagnetic brake (EMBr), vertical electromagnetic brake (V-EMBr), was investigated. The influence of the magnetic induction intensity, the submerged entry nozzle (SEN) immersion depth, and the port angle of the SEN are investigated numerically. The effect of magnetic induction intensity on the meniscus fluctuation of molten alloy is further studied by the experiments. The results show that the meniscus fluctuation is depressed as the magnetic induction intensity is increased, especially for the region in the vicinity of the narrow face of the slab mold. This result is validated by the following experiments. For the influence of the SEN immersion depth and the port angle, the results show that the meniscus fluctuation is suppressed as the values of the immersion depth and the port angle are increased (absolute values for the port angle). However, the influence of the immersion depth and the port angle are not as sensitive as those in the other type of EMBr, e.g., EMBr Ruler. The industrial application of V-EMBr could benefit from this result.

Electromagnetic braking technology plays a critical role in improving the continuous casting yield and optimizing the quality of the continuous casting slab. This paper introduced a novel electromagnetic braking device that integrates a vertical traveling wave magnetic field with a horizontal steady magnetic field, referred to as VTHS-EMBr. The VTHS-EMBr consists of two pairs of vertical magnetic poles that generate the traveling wave magnetic field and a pair of horizontal magnetic poles that generate the steady magnetic field, which were installed on the wide face close to the narrow face of the mold and beneath the submerged entry nozzle (SEN) of the mold. Numerical simulations were conducted to investigate the characteristics of combined magnetic fields with varying vertical traveling wave magnetic induction intensities, wave frequencies, and different horizontal magnetic induction intensities, as well as their effects on the flow behavior of molten steel and meniscus fluctuations in the mold. The results showed that when the motion direction of the vertical traveling wave magnetic field was downward, the electromagnetic braking force increases significantly with higher applied current and frequency. This effect not only effectively reduced the velocity of molten steel in the upward backflow region, mitigated the impact of upward backflow on the meniscus, and significantly suppressed its fluctuation, but also appropriately increased the impact depth of the downward backflow. Under the casting speed of 2 m/min in this study, the VTHS-EMBr demonstrated effective flow control performance. The research on this novel electromagnetic braking technology provides a theoretical basis and technical support for optimizing traditional electromagnetic braking technologies and developing new electromagnetic braking technologies.

In this paper, the fluid flow, slag entrainment and solidification process in a slab mold were studied using physical modeling and numerical simulation. The effect of two types of submerged entry nozzles (SENs) was also studied. The results showed that the surface velocity for type A SEN was larger than that using type B SEN. For type A SEN, the maximum surface velocity was 0.63 m/s and 0.56 m/s, and it was 0.20 m/s and 0.18 m/s for type B SEN. The larger shear effect on the top surface made the slag at narrow face impacted to the vicinity of 1/4 wide face, while the slag layer at the top surface was relatively stable for type B SEN. Increasing the immersion depth of SEN decreased the surface velocity and slag entrainment. For type A SEN, the thickness of the solidified shell at the narrow face of the mold outlet was thin (12.3 mm) and there was a risk of breakout. For type B SEN, the liquid steel with high temperature would flow to the meniscus and it was beneficial to the melting of the mold flux. The thickness of the solidified shell at the narrow face of the mold outlet was increased. Furthermore, the surface velocity was also increased and it was not recommended for high casting speed.