Submerged Entry Nozzle Research Articles

Optimizing of Submerged Entry Nozzle for Bloom Continuous Casting Based on Physical and Numerical Simulation

Herein, a physical model with a geometric similarity ratio of 1:1 and a 3D numerical model of macrosegregation are established to study the initial metallurgy behavior of the 410 mm × 530 mm section bloom continuous casting (CC). The results show that the average wave height, liquid surface velocity, and washing velocity of the five‐port nozzle are greater than those of the straight nozzle, but the center temperature and the temperature gradient at the solidification front are lower. Meanwhile, the diagonally installed five‐port nozzle can avoid the excessive washing effect under the orthogonally installed five‐port nozzle, which improves the minimum subsurface negative segregation index, which is increased from 0.753 to 0.802. For the Steel 45 bloom CC process, when the straight nozzle is changed to the diagonally installed five‐port nozzle, the length of the equiaxed crystal zone is increased from 97.5 to 198.5 mm, and the asymmetry of the solidification structure is improved.

Water Model Experiments on the Influence of Phase Distribution in the Submerged Entry Nozzle Considering Varying Operating Conditions

Continuous casting of steel argon injection into the submerged entry nozzle (SEN) via the stopper is common practice. Nonetheless, the resulting phase distribution in the SEN is still under discussion. The main available casting parameters at the steel plant to determine the flow situation in the SEN are usually the stopper rod position, the argon feeding pressure, the argon flow rate, and the casting speed. To show the potential influence of the phase distribution on the stopper characteristic and on the argon feeding pressure, experiments using a 1:3 scale water model are presented. For the experiment, the water flow rate is scaled using Froude similarity, while the air flow rate is chosen to keep the ratio between the liquid and gas volume flow rate constant. The casting parameters and the pressure at three distinct levels of the SEN are measured. To relate this measurement data to the corresponding phase distribution, two cameras are used to document the phase distribution in the SEN. The images show four major phase distribution patterns. These patterns can be linked to significant changes in the measured pressure levels and the behavior of the stopper.

Effect of Reoxidation on Inclusions Characteristic During Casting in Al‐Killed Steel Containing Rare Earth

To investigate the effect of reoxidation on inclusions characteristic during casting in Al‐killed steel containing rare earth, two industrial heats, including one of steady casting and the other of reoxidation, are performed with sampling from Rheinstahl Heratus, tundish, submerged entry nozzle, and slab. In the present study, air absorption occurs at the submerged entry nozzle and caused the reoxidation of molten steel. As a result, the number of inclusions increases significantly, and nearly spherical Ce2O2S inclusions are transformed to clustered‐like CeAlO3, which increases the average size of inclusions from 3.92 to 9.21 μm, thereby resulting in serious nozzle clogging and slab defects. The results of thermodynamic calculation show that Ce2O2S is transformed to CeAlO3 with total oxygen content increases under different Ce additions, and this transformation of inclusions can be inhibited by controlling the value of [Ce]/[O] above 2.12. Based on the experimental results and the theoretical analysis, the evolution mechanism of inclusions during reoxidation is clarified. This study can provide theoretical guidance to alleviate the harm of reoxidation to Al‐killed RE‐steel from the inclusion‐controlling perspective.

Numerical simulation for EMS induced solidification and inclusion behavior in bloom caster CC mold with bifurcated SEN

A three-dimensional mathematical model has been developed to investigate solidification and non-metallic inclusions behavior in bloom caster mold with bifurcated submerged entry nozzle (SEN) under the influence of in-mold electromagnetic stirring (EMS). An enthalpy porosity approach is applied for the solidification analysis and the stochastic tracking model is used to track the motion of non-metallic inclusions. A numerical investigation has been carried out to study the influence of the stirrer current intensity on turbulent flow, shell generation and inclusion transport. The complex interplay of the induced flow with the inertial impinging jet from the SEN has been investigated. The effect of inclusion density and size on the removal rate of non-metallic inclusion has also been analyzed. The results show that in-mold EMS plays a significant role in solidification and inclusion behavior. With current intensity of 375 A, the inclusion removal rate is higher than that of 0 A, 300 A and 450 A stirrer current. This research suggests that the optimal current intensity of EMS gives a better internal quality of the continuous casting (CC) bloom mold.

The Role of Mold Electromagnetic Stirring in the Dissipation of Superheat during the Continuous Casting of Billets

A two‐phase solidification model coupling mold electromagnetic stirring (M‐EMS) is used to investigate the initial solidification in the mold region of billet continuous casting. One novelty of this numerical study is to quantify how the M‐EMS induces primary and secondary flows, interacting with the jet flows coming from the submerged entry nozzle, and how those flows further influence the dissipation of superheat and the initial solidification. The role of the M‐EMS in speeding up the superheat dissipation in the mold region, known from previous studies and casting practices, is quantitatively verified. Additionally, some new knowledge regarding the M‐EMS is found. The total heat transfer rate from the strand surface to the water‐cooled copper mold is not affected by the M‐EMS; with the M‐EMS, the superheat effect on the solid growth can only be detected in the out‐of‐the‐mold region, while the shell growth inside the mold region is quite independent of the superheat; a strong M‐EMS tends to accelerate the growth of the solid shell in the mold region, but delays its growth in the secondary cooling zones. The aforementioned new findings may only be valid for the case of the current billet casting, to be confirmed for other casting formats/parameters.

Experimental Analysis of a Slab Continuous-Casting SEN with an Inner Flow Divider

In slab continuous-casting machines, the quality of the finished product mainly depends on the hydrodynamic behavior of the molten steel in the cavity of the continuous-casting mold, where the submerged entry nozzle is the central element. Recently, a nontraditional nozzle design was reported, where a solid barrier attached to the inner bottom wall of the nozzle divides its internal volume, particularly around the outlet ports. The solid barrier was named a flow divider. In this work, the effect of the flow divider is analyzed by comparing the performance of traditional nozzles with the performance of nozzles altered with the flow divider. The performance of the nozzles was evaluated experimentally, employing a scaled model of the mold section, using cold water as the working fluid. The shape of the nozzle outlet jets and the fluid flow pattern in the mold cavity were used to determine the performance of the nozzles. In addition, several factors affecting the process stability and the quality of the product were analyzed: the casting speed, the tilt of the nozzle outlet ports, and the injection of gas in the liquid stream entering the nozzle. The analysis showed that for the nozzles with the flow divider, (i) the outlet jets are narrow and symmetric, (ii) the symmetrical double-roll flow pattern in the mold cavity is obtained, (iii) the liquid-free surface is stable and has low distortions, and (iv) the flow divider neither increases the bubble breakage nor the coalescence between them.

Study on Multiphase Flow in a Wide-Width Continuous Casting Mold

The multiphase flow in the mold has a significant impact on the surface quality of the slab. In this paper, the multiphase flow in the mold is studied by establishing a one-quarter scale water mold, with the aid of a high-speed camera and particle image velocimetry (PIV). The oil phase will make the liquid surface velocity around the nozzle smaller. The greater the viscosity of the oil, the greater the critical water model casting speed and the shallower the critical immersion depth of submerged entry nozzle (SEN). Blowing will enhance the turbulence of the flow field in the mold and have a suppressing effect on the surface velocity. However, the vertical velocity of the narrow surface does not change significantly. The randomness of the bubble entering the mold from the nozzle can easily cause asymmetry of the instantaneous flow. The number of bubbles with a diameter less than 1 mm increase with the increase in gas flow rate. The larger the bubble size, the more buoyant around the nozzle when it escapes. The larger the diameter of bubble, the closer the vortex center of the upper circulation is to the nozzle and the closer the center of the lower circulation is to the narrow surface.

Effect of Trace of Oxygen in Ar Gas on Initial Growth of Nozzle Clogging Deposits on SEN for Ti Added Ultra‐Low C Steel Casting

The possibility of reoxidation of Ti‐ultra‐low C (Ti‐ULC) steel by a trace of oxygen in Ar gas, which is injected in a submerged entry nozzle (SEN), is investigated. A commercial‐grade unpurified Ar gas with PO2 = ≈10−4 bar and a purified Ar gas with PO2 = ≈10−18 bar by a set of cleaning kits are employed. Preliminary thermodynamic calculations revealed that the unpurified Ar gas could cause significant oxidation of the Ti‐ULC steel, irrespective of the steel composition, while the purified Ar gas did not oxidize the steel. A series of laboratory‐scale oxidation experiments are carried out using various Ti‐ULC steel samples and the two Ar gases. The oxidation under unpurified Ar gas causes the oxidation of all the samples but only on the surface, in partial agreement with the thermodynamic calculation. The partial agreement between the calculation and the experiment is explained by the availability of oxygen and other metallic elements. It is found that the trace of oxygen in a commercial grade of Ar gas could cause reoxidation of Ti‐ULC steel in an SEN, which may be no better than the reoxidation by CO gas generated by the carbothermic reaction in the SEN refractory. A purity control of Ar gas is recommended.

Numerical Simulation of Flow Field, Bubble Distribution and Solidified Shell in Slab Mold under Different EMBr Conditions Assisted with High-Temperature Quantitative Velocity Measurement

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 Effects of Nozzle Inclination, Area Ratio, and Side-Hole Aspect Ratio on the Flow Behavior in Mold

During the steel continuous casting, the submerged entry nozzle (SEN) plays a crucial role in the fluid characteristic of fluid steel, which further affects the slab quality. In this paper, a nozzle model is developed to study the influences of nozzle inclination, nozzle area ratio, and side hole aspect ratio on the fluid characteristic of fluid steel. The results show that when the nozzle angle increased from 10° to 20°, the impact points of the narrow surface were 0.402 m, 0.476 m, and 0.554 m away from the meniscus, respectively. In addition, when the nozzle area ratio increased from 0.96 to 1.16, it resulted in a significant decrease of the speed of high-temperature liquid steel flowing out of the nozzle. Moreover, when the side-hole aspect ratio was 1.47, the maximum turbulent kinetic energy of the free surface reached 0.00141 m2 s−2. Furthermore, when the aspect ratio was 1.67 and 1.84, a slight difference existed, and the maximum turbulent kinetic energy was almost 0.00095 m2 s−2. The proposed model can provide theoretical basis and guidance for nozzle optimization.

Suppressing initial clog deposits on inner surface of submerged entry nozzle refractory for casting liquid steel: Absorbing CO gas by CO absorbers

A series of experiments and thermodynamic analyses were carried out to find a countermeasure to prevent submerged entry nozzle clogging during continuous casting of Ti-added Ultra-Low C (Ti-ULC) steel, by suppressing CO gas generation in the nozzle refractory. SiO2 and C in usual nozzle refractories proceeded a carbothermic reaction, which generated the CO gas. The CO gas then reoxidized Ti-ULC steel, and a mixture of alumina and FetO–Al2O3–TiOx liquid oxide formed, which was reported to be an initial clog deposit. A concept of “CO absorber” was proposed to absorb the generated CO gas back into the refractory, thereby suppressing the reoxidation. This decreased the thickness of the reoxidation reaction product layer at the interface between the refractory and the steel, which could play as the initial clog deposit. Al4C3, B4C, CaC2, and Al were considered as the candidates for CO absorbers. It was found that B4C was the best candidate thanks to its anti-hydration character, high-temperature stability, and the extent of absorbing CO gas. A series of hot tests were carried out by reacting synthesized refractories in which a certain amount of the candidates were blended. The refractory with 3 mass pct. B4C showed the best result.

Numerical Simulation for Two‐Phase Flow, Heat Transfer, and Inclusion Transport in Bloom Mold Considering the Effects of Argon Gas Injection and Mold Electromagnetic Stirring

A mathematical model based on the Eulerian–Eulerian–Lagrangian method is developed to investigate the two‐phase flow, temperature distribution, and inclusion transport, considering the effect of argon gas injection (AGI) and mold electromagnetic stirring (M‐EMS) in the bloom mold. The magnetic resistance force is adopted to account for the effect of the magnetic field on bubbles. It is demonstrated in the results that when AGI is applied, plumes form near the submerged entry nozzle (SEN) and increase the velocity in the upper part of the mold. While M‐EMS is applied, the swirl flow significantly increases the overall flow velocity and superheat dissipation. In addition, AGI and M‐EMS increase the fluctuation and temperature of the free surface, lower the peak heat flow, and promote inclusions removal. When AGI is applied with M‐EMS, the swirl flow and plumes in the upper part of the mold are weakened due to the interaction between them, and the level fluctuation is lower than that of applying AGI or M‐EMS separately. The heat flow and free surface temperature are more uniform, and the inclusion removal rate further increases. Meanwhile, M‐EMS drives bubble columns to the location between the two ports of SEN and gathers bubbles around the SEN.

Bubble Characterization in a Continuous Casting Mold: Comparison and Identification of Image Processing Techniques

Gas injection is a common practice in numerous metallurgical vessels, and continuous casting mold is one of the examples of such vessels. Argon gas injection into the submerged entry nozzle contributes to increasing the sequence length. However, in some unfavorable conditions, these bubbles become responsible for the occurrence of steel defects such as blister, sliver, and mold slag exposure, etc. Bubbles size distribution in the mold is one of the indicators of cast steel slab quality. Previous studies on estimating the bubble size distribution in mold lack in providing the challenges of automatic image processing (IP) techniques employed to measure the size of the bubbles. On the other hand, bubble size measurement studies performed on other reactors such as bubble columns, etc., are programming intensive and need in-depth knowledge of coding. Some automatic IP techniques also exist which facilitate a user-friendly environment and quick estimation of bubble characteristics. Even though these IP techniques are easy to use, an assessment of their applicability with respect to experiments performed in a particular study is required. Therefore, in this study, details of imaging and automatic IP techniques are discussed through a comprehensive comparative analysis. Three different IP techniques were examined for measuring the bubble sizes, and the performances of these techniques were compared with respect to a newly developed manual benchmark technique. One of the identified techniques, Ellipse Split, was applied to estimate the bubble size distribution at different gas fractions for validation.

Modeling Asymmetric Flow in the Thin‐Slab Casting Mold Under Electromagnetic Brake

Continuous casting (CC) is nowadays the world‐leading technology for steel production. The thin slab casting (TSC) is featured by a slab shape close to the final products and a high casting speed. The quality of the thin slabs strongly depends on the uniformity of the turbulent flow and the superheat distribution, defining the solid shell growth against a funnel‐shaped mold. In most studies, it is commonly assumed that the submerged entry nozzle (SEN) is properly arranged, and the melt inflow is symmetric. However, the misalignment or clogging of the nozzle can lead to an asymmetric flow pattern. Herein, the asymmetry is imposed via a partial SEN clogging: a) a local porous zone inside the nozzle reflects the presence of the clog material; b) the resistance of the clog is varied from low to high values. The solidification during TSC is modeled, including the effects of the turbulent flow. The variation of the flow pattern and the solidified shell thickness are studied for different permeability values of the SEN clogging. These effects are considered with and without the applied electromagnetic brake (EMBr) using an in‐house magnetohydrodynamics (MHD) and solidification solver developed within the open‐source package OpenFOAM.

Numerical Modeling of Transient Two-Phase Flow and the Coalescence and Breakup of Bubbles in a Continuous Casting Mold.

The multiphase flow and spatial distribution of bubbles inside a continuous casting (CC) mold is a popular research issue due to its direct impact on the quality of the CC slab. The behavior of bubbles in the mold, and how they coalesce and break apart, have an important influence on the flow pattern and entrapment of bubbles. However, due to the limitations of experiments and measurement methods, it is impossible to directly observe the multiphase flow and bubble distribution during the CC process. Thus, a three-dimensional mathematical model which combined the large eddy simulation (LES) turbulent model, VOF multiphase model, and discrete phase model (DPM) was developed to study the transient two-phase flow and spatial distribution of bubbles in a continuous casting mold. The interaction between the liquid and bubbles and the coalescence, bounce, and breakup of bubbles were considered. The measured meniscus speed and bubble diameter were in good agreement with the measured results. The meniscus speed increased first and then decreased from the nozzle to the narrow face, with a maximum value of 0.07 m/s, and appeared at 1/4 the width of the mold. The current mathematical model successfully predicted the transient asymmetric two-phase flow and completely reproduced the coalescence, bounce, and breakup of bubbles in the mold. The breakup mainly occurred near the bottom of the submerged entry nozzle (SEN) due to the strong turbulent motion of the molten steel after hitting the bottom of the SEN. The average bubble diameter was about 0.6 mm near the nozzle and gradually decreased to 0.05 mm from the nozzle to the narrow face. The larger bubbles floated up near the SEN due to the effect of their greater buoyancy, while the small bubbles were distributed discretely in the entire mold with the action of the molten steel jet. Overall, the bubbles were distributed in a fan shape. The largest concentration of bubbles was in the lower part of the SEN and the upper edge of the SEN outlet.

Insights into ZrO2- and Al2O3-based submerged entry nozzle clogging for the continuous casting of RE-treating sulfur resistant casing steel

The ZrO2- and Al2O3-based submerged entry nozzle (SEN) clogging during continuous casting of a RE-treating sulfur resistant casing steel is studied experimentally based on morphological analysis and the related thermodynamic calculations. The results show that the ceramic cloggings exists both in the inner-wall and outlet regions of SEN, while the latter is the main reason for terminating the casting with its clogging reaching 77% in the nozzle cross section area. The clogging is caused by RE-containing inclusions from molten steel and reoxidation products by the reaction between RE in molten steel and the initial formed cloggings on nozzle refractory. The possible existence state of RE in molten steel with its content has been discussed, and the clogging mechanism studied in detail. To prevent nozzle clogging, suggestions are given for continuous casting of the RE-treating steel with a modified RE treatment strategy for less solid inclusions and solute [RE] presented in liquid steel during refining process. Additionally, the optimization of nozzle geometry and its refractory materials may help as well.

Significance of Nonmetallic Inclusions for the Clogging Phenomenon in Continuous Casting of Steel––A Review

Nonmetallic inclusions are well known to influence product quality and process stability in the production of steel. A process step that is very sensitive to the presence of nonmetallic inclusion (NMI) is continuous casting. Here, the so‐called clogging phenomenon can occur, resulting in a distinct disruption of the casting process and decreased steel quality. The presence of nonmetallic inclusions considerably contributes to the build‐up of deposits in the submerged entry nozzle provoking instabilities in the flow control system. Numerous research studies have been subject to different clogging mechanisms and related influencing parameters. Interfacial properties significantly influence the behavior of inclusions in the steel–refractory system. The present review demonstrates state of the art concerning the role of NMIs in the appearance of clogging. Particular focus is put on the wetting behavior between the different phases and their consequence for the deposition process. Industrial observations and laboratory methods are summarized and discussed; potential countermeasures are evaluated. A steel group that is especially prone to clogging are Ti‐ ultra low carbon (ULC) steels. An overview of the current understanding of their high clogging tendency and possible influences is presented, considering thermodynamic and interfacial aspects.

Numerical simulation of multi-size bubbly flow in a continuous casting mold using an inhomogeneous multiple size group model

Multi-size bubbly flow in a one-quarter-scale water model of a continuous casting mold was simulated using the inhomogeneous multiple size group (IMUSIG) model. The Sauter mean bubble diameter, gas volume fraction, interfacial area density, turbulence kinetic energy, and velocity field predicted by the IMUSIG and multiple size group (MUSIG) models were compared. The IMUSIG model separated the motions of the small and large bubbles on the basis of two velocity groups, and both models adopted 15 size groups. The results showed that the IMUSIG model better reflected the bubble size distribution near the nozzle. Small bubbles were further transported by the jet flow, which enlarged the bubble cluster range and decreased the gas volume fraction and interfacial area density in the upper part of the submerged entry nozzle, likely diminishing the coalescence rate in this region; consequently, the overestimation of Sauter mean bubble diameter outside the nozzle was corrected. The liquid-phase flow fields predicted by the IMUSIG and MUSIG models were very similar, and the IMUSIG-predicted magnitudes of velocity and turbulence kinetic energy were only slightly lower than the MUSIG predictions; this slight difference is attributable to the expanded bubble cluster range and higher interfacial area density, which weakened the upper recirculation in the IMUSIG model.

Analysis of nozzle clogging position in a continuous casting mold

Abstract In this paper, the flow field of the submerged entry nozzle (SEN) in the continuous casting process is analyzed in detail by numerical simulation. It is found that the front and rear positions of the SEN outlets and the bottom of the nozzle are prone to the accumulation of inclusions. Compared with the actual SEN, the clogging positions with the simulated results are consistent. The composition of nozzle nodules at two different positions is analyzed by scanning electron microscope (SEM), and the inclusions are alumina. The changes in molten steel level characteristics in the mold without and after clogging are compared and analyzed. It is found that the velocity of molten steel near the surface with nozzle clogging reaches 0.483 m/s, the free level fluctuation value of molten steel is 8.9 mm, which is easy to cause steel defects.

Mesoscopic Fluid-Particle Flow and Vortex Structural Transmission in a Submerged Entry Nozzle of Continuous Caster.

Understanding the essence of the flow oscillations within a submerged-entry nozzle (SEN) is essential to control flow patterns in the continuous casting mold and consequently increase the superficial quality of steel products. A numerical study of the mesoscopic fluid-particle flow in a bifurcated pool-type SEN under steady operating conditions is conducted using the lattice Boltzmann method (LBM) coupled with the large eddy simulation (LES) model. The accuracy of the model has been verified by comparing vortex structures and simulated velocities with published experimental values. The LBM modeling is also verified by comparing the “stair-step” jet patterns observed in the experiment. The geometrical parameters and operational conditions of physical experiments are reproduced in the simulations. By comparing the time-averaged velocities of Reynolds-averaged Navier–Stokes equations (RANS) with LBM models, transient mesoscopic fluid-particles and related vortex structures can be better reproduced within the SEN. The visualization of internal flow within the SEN is illustrated through the mass-less Discrete Phase Model (DPM) model. The trajectories show that the LBM–LES–DPM coupled model is good at predicting the transient vortical flow within the SEN. A large vortex is found inside the exit port and continuously changes in shape and size therein. The monitoring points and lines within the SEN are selected to illustrate the velocity variations and effective viscosity, which can reflect the oscillating characteristics even under stable operating conditions without changes at the exit from the SEN. Furthermore, the formation, development, diffusion, and dissipation of the vortex structures from the exit port of the SEN are also investigated using the Q criteria. The comparison of the power spectrum with high-frequency components along the exit port indicates that the flow oscillations must originate from within the SEN and are intensified in the exit port. The mesoscopic LBM model can replicate the fluid-particle flow and vortex structure transmission as well as their turbulence effects inside the SEN in detail.