Submerged Entry Nozzle Research Articles

Effects of Submerged Entry Nozzle Bottom Shape on the Size Distribution of Argon Bubbles in a Steel Continuous Casting Slab Strand Using Multiple‐Size‐Group Approach

Herein, the effects of the bottom shape of the submerged entry nozzle (SEN) on the molten steel flow and size distribution of argon bubbles are analyzed in a steel continuous casting slab strand using multiple‐size‐group approach. The type of nozzle bottom includes the well bottom, flat bottom, and mountain bottom. Most of argon bubbles are larger than 4.5 mm inside the SEN and the mold at the three types of nozzles. The frequency distribution of bubbles inside the SEN increases from 28.29% to 32.65% and 35.74% for 5.0–5.5 mm bubbles and decreases from 53.71–50.49% and 47.38% for 5.5–6.0 mm bubbles with the nozzle bottom varied from the flat to mountain and well shape, respectively. The number density of argon bubbles with 4.0–5.5 mm diameter in the mold decreases and increases for 5.5–6.0 mm bubbles with the nozzle bottom varying from the well to flat and mountain shape, respectively. In addition, the results of the industrial trials show that inclusions adhesion and aggregation at the bottom of the nozzle are eliminated using the flat bottom SEN casting. Meanwhile, the mechanism of SEN clogging under the different types of nozzle bottoms is analyzed.

Control of macrosegregation at the steel gradient transition by submerged entry nozzle and mold electromagnetic stirring

Control of macrosegregation at the steel gradient transition by submerged entry nozzle and mold electromagnetic stirring

Influence of Submerged Entry Nozzles on Fluid Flow, Slag Entrainment, and Solidification in Slab Continuous Casting

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.

Numerical Study on Characteristic Positions and Transition of Flow Patterns in a Slab Continuous Casting Mold

The flow pattern in an opaque mold cannot be readily visible, and worker experience plays a major role in controlling it, even though it has a significant impact on slab quality in a continuous casting (CC) mold. An Eulerian–Eulerian two‐fluid model is used to comprehensively study the two‐phase flow of argon and molten steel in a slab CC mold. The positions of vortex centers in upper/lower recirculation zones and the impingement point of jet flow on the narrow face of mold are identified and their distribution is analyzed. The interactive effects of casting speed, argon flow rate, and immersion depth of the submerged entry nozzle (SEN) on the flow pattern inside the mold are revealed. 2D and 3D flow pattern regimes are plotted and the boundary lines and boundary surfaces are fit with exponential functions and ternary functions, respectively. To obtain a double roll flow in the slab CC mold investigated, the relation among argon flow rate (), casting speed (), and the immersion depth of the SEN () should satisfy, .

Online Supervisory System for In-Process Optimization of Calcium Additions by Continuously Monitoring the State of Non-metallic Inclusions Inside Low-Alloyed Liquid Steels

A decision support system was developed using supervised machine learning (ML) approach for optimization of calcium (Ca) additions by continuously monitoring the physical state of non-metallic inclusions (NMIs) inside low-alloyed liquid steels. In this work, two instances were considered to design the base algorithm for the proposed supervisory system: (1) Clogging of submerged entry nozzle (SEN) during continuous casting of steels due to accumulation of solid oxide non-metallic inclusions (NMIs) and (2) Ca treatment during secondary steelmaking for modification of oxide NMIs from solid to liquid state to avoid SEN clogging. At first, experimental investigations were carried out on liquid steel samples from three low-alloyed Ca-treated steel grades from the same steel family to evaluate the characteristics of solid oxide NMIs that cause SEN clogging. In the next step, data-driven models were developed using an in-house ML algorithm trained primarily with process data for calculating the value of the newly proposed dummy parameter ‘Clog.’ These models, after testing, were architected to develop a supervisory system based on experimental investigations and data-driven models. The objective of this proposed supervisory system was to predict the optimum quantity of Ca needed for successful modification of NMIs from solid to liquid state to avoid SEN clogging based on the forecasted ‘Clog’ value. Finally, industrial data from ~ 3000 heats were tested to verify the results obtained from the developed supervisory system. The results confirmed that this novel supervisory system could predict the optimum class of Ca for all studied steel grades with 95 to 98 pct accuracy. The integration of this online supervisory system in steel production is expected to minimize operators’ corrective actions in achieving realistic control of Ca additions.

Assessment of URANS-Type Turbulent Flow Modeling of a Single Port Submerged Entry Nozzle (SEN) for Thin Slab Continuous Casting (TSC) Process

The numerical methods based on the unsteady Reynolds-averaged Navier–Stokes (URANS) equations are robust tools to model the turbulent flow for the industrial processes. They allow an acceptable grid resolution along with reasonable calculation time. Herein, the URANS approach is validated against a water model experiment for the special single port submerged entry nozzle (SEN) design used in the thin slab casting (TSC) process. A 1-to-2 under-scaled water model was constructed, including the SEN, mold, and strand Plexiglas segments. Paddle-type sensors were instrumented to measure the submeniscus velocity supported by videorecording of the dye injections to provide both qualitative and quantitative verification of the SEN flow simulations. Two advanced URANS-type models (realizable k–ε and shear stress transport k–ω) were applied to calculate velocity pattern on meshes with various resolutions. An oscillating single jet flow was detected in the experiment, which the URANS simulations initially struggled to reflect. The dimensionless analysis of the mesh properties and corresponding adjustment of the boundary layers inside the SEN allowed to resolve the flow pattern. The performed fast Fourier transform (FFT) verified a good numerical prediction of the flow frequency spectrum. The corresponding simulation strategy is proposed for the industrial CC process using the URANS approach.

Improving the comprehensive properties of ZrO2–C materials with aid of TiO2 addition

Owing to the harsh working condition, the ZrO2–C materials used in the slag line in the submerged entry nozzle are confronted with serious slag erosion. In order to solve this issue, different amounts of TiO2 addition ranging from 0 to 6 wt% are added and their effects on the erosion resistance of ZrO2–C materials in addition to phase composition, microstructure, physical properties and high-temperature mechanical properties are investigated in this work. When the sintering temperature is above 1400 °C, fine TiC grains and SiC whiskers are in-situ formed and distributed around ZrO2 particles, which can reinforce the matrix and improve the strength of ZrO2–C materials. With the amount of TiO2 addition increasing, the cold strength of ZrO2–C materials increases while the high-temperature strength slightly decreases. Combining with the erosion resistance, the optimum amount of TiO2 in ZrO2–C materials is determined to be 4 wt%, in which the cold compressive strength (46.13 MPa), the cold modulus of rupture (35.12 MPa) and the residual strength after thermal shock (15.01 MPa) reach the maximum. Based on this, the promotion mechanism of erosion resistance is further discussed with aid of molecular dynamics simulation.

Experimental Analysis of the Influence of the Sliding-Gate Valve on Submerged Entry Nozzle Outlet Jets

This work studies how the sliding-gate valve (SGV) modifies the features and the dynamic behavior of the outlet jets for flat-bottom and well-bottom bifurcated submerged entry nozzles (SENs) used in continuous casting machines. Three conditions for the SGV were studied: no obstruction, moderate obstruction, and severe obstruction. The experimental study used a scaled model, employing cold water as the working fluid. A high-frequency analysis of the flow inside the SEN’s bore arriving at the outlet ports was performed by employing the particle image velocimetry (PIV) technique. Low-frequency measurements of the volumetric flow at the exit port were obtained by splitting the exit jet into four quadrants and employing digital flowmeters. It was observed that reducing the SGV clearance increases the turbulence of the flow inside the SEN bore, but the flow displays ordered rather than erratic fluctuations. Flowmeter measurements showed that, regardless of the level of obstruction in the SGV, the outlet jets on flat-bottom and the well-bottom SENs have dynamic behaviors and features with significant differences. This finding is relevant because the flow distribution inside the outlet ports is directly related to the jet’s wideness, affecting the recirculation pattern inside the mold and, therefore, the quality of the finished steel slab.

Investigating the Origin of Non-Metallic Inclusions in Ti-Stabilized ULC Steels Using Different Tracing Techniques

Since steel cleanness comes to the fore of steel producers worldwide, it is necessary to understand the formation mechanism and modification of non-metallic inclusions (NMIs) in more detail. One central point is the identification of the source of especially interfering NMIs to prevent their evolution in the future. The present study applies two approaches to determine the source of NMIs in Ti-stabilized ultra-low carbon (ULC) steels—the active and the passive tracing. Both approaches are applied to an industrial experiment. The active tracing technique is focused on investigating the clogging layer formation in submerged entry nozzles and, hence, the origin of alumina particles. This method adds rare earth elements (REEs) directly to the melt to mark pre-existing deoxidation products at a certain point of the steelmaking process. The main concern of the passive method, the so-called REE fingerprint, is the determination of the source of mesoscopic NMIs. For the REE fingerprint, the pre-existing concentration of REEs in different potential sources and the investigated NMIs are measured by using an inductively coupled plasma mass spectrometer (ICP-MS). The resulting patterns are compared after normalizing the contents to chondrites, and the NMIs’ origins are identified. Concerning the EDS analysis and the resulting patterns from the REE fingerprint, the mold slag and, respectively, the casting powder were the sources of the investigated NMIs.

Stabilizing Flow of Molten Steel in Mold during Slab Continuous Casting through Electromagnetic Swirling Flow in Nozzle

Bias flow of molten metal in slab mold caused by unstable flow from submerged entry nozzle can deteriorate the slab quality during continuous casting. In this study, a novel electromagnetic swirling flow in nozzle (EMSFN) technique, which utilizes electromagnetic force to stabilize the flow in the nozzle and subsequently control the flow in the mold, is proposed. The mechanism for controlling unstable flow through EMSFN is explored through numerical simulation and water model experiments. In the results, it is shown that the molten steel is rotated under the effect of magnetic field and flows into the mold along the upper edge of the nozzle outlet, which weakens the impact of molten steel on the bottom of nozzle and stabilizes the outflow from nozzle. The flow field is consistently symmetrical on both sides of the nozzle. The impact depth of molten steel flowing down along the narrow sides of the mold on both sides is greatly reduced. The surface velocity on both sides of the nozzle changes uniformly. The range of surface velocity variation with EMSFN is only 10% of that with a conventional nozzle. The EMSFN technique can help prevent slag entrapment and improve the flotation of inclusions and bubbles.

Mathematical modeling of the effect of SEN outport shape on the bubble size distribution in a wide slab caster mold

Herein, the effects of outport shapes of the submerged entry nozzle (SEN) on the size distribution of argon bubbles were studied in a wide slab caster mold by the mathematical modeling. The Eulerian–Eulerian model coupled with Multiple-Size-Group (MUSIG) approach were used to solve equations of the two phase flow and polydispersed bubbly flow in the mold, respectively. The effect of the SEN outport angle and shape on the distribution of the molten steel flow, argon gas volume fraction, and argon bubble size were investigated. The outport shapes of the SEN included large rectangular, small rectangular, square, trapezoid, and runway. Results showed that the speed of molten steel increased within the range of 260 mm from the SEN, and decreased within the range of 550 mm from the narrow face with the outport angle of SEN increased from 20° to 45°. The bubble diameter was 5.7 mm at 255 mm distance from the SEN along the mold width at different outport angles. The average speed of molten steel at the outport of SEN decreased from 0.91 to 0.72 m/s with the outport shape changed from small rectangular to runway, trapezoid, square and large rectangular. The average diameter of bubbles was approximate 5.2 mm at the outport for the five types of nozzles, and increased from 3.2 to 3.45 mm inside the mold with the outport shape changed from the runway to square, trapezoid, large rectangular and small rectangular, indicating the rate of bubble breakup was larger with the runway and square SEN casting.

Simulation of the fluid flow in continuous casting copper slab mold for different SEN design

The quality of continuously cast slabs largely depends on the processes taking place in the mold. In continuous casting of copper and its alloys the solidification process is almost completed within it. This paper presents a comprehensive optimization of the submerged entry nozzle design by combining physical and mathematical modeling with further comparison of obtained results with the actual process. The article studies the critical features of hydrodynamic processes in copper slab by physical and mathematical modeling during continuous casting. To ensure the efficiency of liquid pool homogenization, it seems appropriate to direct some metal upwards through openings in the SEN to the liquid meniscus. The optimal configuration of the SEN is the one where 35% of the liquid flows upwards to heat the melt meniscus and slab upper corner zones and 65% of liquid metal moves downward to the liquid pool bottom.

Tracing of Deoxidation Products in Ti‐Stabilized Interstitial Free Steels by La and Ce on an Industrial and Laboratory Scale

The continuous casting of Al‐killed Ti‐stabilized interstitial free steels is often affected by clogging. By today, the mechanism behind this phenomenon is not entirely clarified. The active tracing method, which involves the direct addition of rare‐earth elements (REEs), enables tracking of nonmetallic inclusions (NMIs) over process time. Due to the high oxygen affinity of these elements, preexisting NMIs are partially reduced and marked by this tracer. Using scanning electron microscopy with energy‐dispersive spectroscopy, it is possible to differentiate such labeled NMIs from particles formed at later stages in the process by the absence of these tracing elements. Active tracing is used in industrial and laboratory settings to trace preexisting alumina NMIs with La or Ce. In the investigation, it is revealed that the number of small NMIs increases after the addition of REEs, and subsequently, the size increases again after FeTi is alloyed. In both settings, traced and untraced Al–Ti oxides are found. The separation tendency of traced NMIs is studied over time by analyzing the composition of the slags. Furthermore, the impact of deoxidation products on the formation of the clogging layer within the submerged entry nozzle is investigated, indicating that these NMIs contribute to its formation.

Numerical Simulation of Flow and Argon Bubble Distribution in a Continuous Casting Slab Mold under Different Argon Injection Modes

A three-dimensional model is established to investigate the effect of argon injection mode, argon flow rate and casting speed on the gas–liquid two-phase flow behavior inside a slab continuous casting mold. The Eulerian–Eulerian model is employed to simulate the gas–liquid flow, and the population balance model is applied to describe the bubble breakage and coalescence process in the mold. The numerical simulation results of the bubble size distribution are verified using the water model experiment. The results show that the flow field and bubble distribution are similar between the argon injection at the upper submerged entry nozzle (SEN) and tundish upper nozzle (TUN), while the number density is larger for the argon injection of TUN. The coalescence rate of bubbles and the bubble size inside the mold increase with increasing argon flow rate. When the argon flow rate exceeds 4 L/min, the flow pattern of liquid steel changes from double-roll flow to complex flow, with aggravation of the level fluctuation of the top surface near the SEN. When the casting speed increases, the bubble breakup rate increases and results in a decrease in the size of bubbles inside the mold. At a high casting speed, the flow pattern tends to form double-roll flow, and the liquid level at the narrow face of the top surface increases.

Physical modeling and numerical investigation of fluid flow and solidification behavior in a slab caster mold using hexa‐furcated nozzle

AbstractSlag entrapment from metal–slag interface during continuous casting operations has been a major area of concern for steelmakers globally. The presence of inactive regions in the upper region of the mold poses another challenge. Proper flow behavior of the molten metal coming out of the nozzle in the mold is required to overcome these challenges. Nozzle design greatly affects the flow pattern of the molten steel inside the mold. The present investigation is an attempt to study the flow and solidification behavior in a slab caster mold with the use of a novel‐designed hexa‐furcated nozzle using numerical investigation results. The casting speed and submerged entry nozzle (SEN) depth are varied to study the effect of these parameters on minimizing the inactive zones in the mold and the steel/slag interface fluctuations. The results show that the interface fluctuation increases at higher casting speed and lower SEN depth. The residence time distribution (RTD) analysis was also performed for different cases to investigate the flow behavior. The validation of the fluid flow and RTD curve inside the computational domain is carried out with the use of physical modeling.

X-ray Imaging of Two-Phase Flow Regimes in a Liquid Metal Swirling Downward Flow With Side Wall Gas Injection

The formation and behavior of gas bubbles is experimentally investigated in a liquid metal downward pipe flow, a configuration that largely corresponds to the situation in a submerged entry nozzle (SEN) in the continuous casting process in steel making. The experimental mockup is operated at room temperature using the ternary alloy GaInSn as model fluid. Argon gas is injected through an orifice located in the SEN wall. The gas distribution in the pipe is visualized by means of the X-ray radiography. The set-up is completed by an electromagnetic stirrer, which is used to create a swirling flow in the tube. Depending on the volume flow rates of the gas and the liquid metal, as well as the intensity of the swirl flow generated by the stirrer, 4 flow regimes are observed: (1) the formation of an almost stationary gas pocket in the region below the injection point without any electromagnetic stirring, (2) a twisted void zone along the side wall, (3) a straight void zone in the center of the pipe, and (4) a bubble chain in the core of the pipe flow. The experiments reveal that the wetting conditions at the inner SEN wall have a decisive influence on the resulting flow regime.

Numerical Analysis of Slag–Steel–Air Four-Phase Flow in Steel Continuous Casting Model Using CFD-DBM-VOF Model

Argon injection is usually applied in the continuous casting mold to prevent submerged entry nozzle (SEN) clogging. However, the stability of the slag–steel interface is affected by the injected gas, even leading to the formation of the slag eye. A computational fluid dynamics–discrete bubble model–volume of fluid (CFD-DBM-VOF) model is established to predict the argon–slag–steel–air four-phase flow in the continuous casting mold. The bubble behavior is treated with the Lagrangian approach considering bubble coalescence and breakup. The movement behavior of the slag–steel interface is analyzed with and without argon blowing, validated with the water model. The results show that the large bubble tends to float up into the slag–steel interface near the SEN with argon injection, resulting in fluctuations in the slag–steel interface near the SEN. The bubble distribution, flow field, fluctuation height of the slag–steel interface and configuration of the slag eye in the mold are analyzed. Furthermore, the effect on the casting speed, gas flow rate and thickness of the slag layer is obtained based on the result. The mathematical prediction results showcase a combination of well-established phenomena and newly generated predictions.

Physical and Numerical Simulation Study on Structure Optimization of the Inner Wall of Submerged Entry Nozzle for Continuous Casting of Molten Steel

The submerged entry nozzle (SEN) plays an important role in the continuous casting production process. It is a cast refractory pipe fitting installed in the lower part of the tundish and inserted below the molten steel level of the mold. It not only affects the speed of molten steel flow, but is also prone to nodules and affects production. In the present work, the flow behavior of molten steel in a traditional nozzle and that in a new type of nozzle whose inner wall was distributed with arrays of hemispherical crowns were studied by means of both physical simulation (using a water model) and numerical simulation (using ANSYS CFX) based on the prototype of a production continuous casting slab mold. Both experimental and numerical simulation results show that, compared with the traditional nozzle, the impact depth generated by the new-type nozzle in the mold is reduced by 21.06–26.03 cm, the impact angle is reduced by 14–17 degrees, and swirl flow was generated inside the new-type nozzle, which not only improves the flow characteristics inside the submerged entry nozzle and changes the dead zone size in the submerged entry nozzle, but also improves the velocity distribution at the outlet of the nozzle and minimizes the possibility of nodulation. In addition, in contrast to the traditional nozzle that generates flat body-shaped jets of molten steel flow, the new-type nozzle produces baseball glove-shaped jets that penetrate shallower into the molten steel bath in the mold, which significantly reduces the outlet velocity and is conducive to the floating of inclusions.

Performance Features of Submerged Entry Nozzle in High-Speed Casting on Thin-Slab CC Machine

Performance Features of Submerged Entry Nozzle in High-Speed Casting on Thin-Slab CC Machine

Optimization of Port Angle for Narrow‐Width Mold Flow Field under High Casting Speed Based on Large Eddy Simulation and High‐Temperature Measurement of Velocity

Herein, the flow field of the mold through numerical simulation and high‐temperature measurement is studied, and discussed the effects of casting speed and port angle on the flow field of the 880 mm wide mold. The velocities near the mold surface of the numerical simulation are in good agreement with those of the high‐temperature measurement. As the casting speed continues to increase, the surface flow velocity of the mold also increases. When the casting speed increases to 1.8 m min−1, the flow pattern of the mold exhibits a strong double‐roll flow, the strong jet increases the risk of argon bubbles being captured by the solidification front inside the mold. As the port angle of the submerged entry nozzle (SEN) gradually increases, the surface flow velocity of the mold gradually decreases. By appropriately increasing the port angle of the SEN to 20°, the surface flow velocity of the mold decreases, and the stability of the molten steel–slag interface improves. At the same time, there is no significant change in the distribution of argon bubbles, and the removal rate of inclusions is the highest.