Wall Of Submerged Entry Nozzle Research Articles

Numerical study on steel flow dynamic behaviour in a round mould under the effect of a swirling flow brick design in tundish

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.

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.

Transient simulation of melt flow, clogging, and clog fragmentation inside SEN during steel continuous casting

Clogging of submerged entry nozzle (SEN) during continuous casting of steel is an undesirable phenomenon leading to different problems like flow blockage, slag entrainment, nonuniform solidification, etc. A transient numerical model for nozzle clogging based on an Eulerian-Lagrangian approach was developed and it covers the main steps of clogging: (a) formation of the first oxide layer by chemical reactions on the steel-refractory interface; (b) motion of non-metallic inclusions (NMIs) due to the turbulent melt flow towards the SEN wall; (c) interactions between the melt, the NMI, and the wall; (d) formation and growth of the clog by the deposition of NMIs on the clog front and the flow-clog interactions; and (e) detachment/fragmentation of a part of clog due to the flow drag force. Clogging in an industrial scale SEN was simulated. The simulated clog front was compared with real as-clogged SENs. The modeling results have successfully explained the SEN clogging induced transient flow phenomenon in the mold region, i.e. the transition from the stable to an unstable and non-symmetrical flow.

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.

Effect of submerged entry nozzle wall surface morphologies on boundary layer structure and alumina inclusions transport

During the Al-killed steel continuous casting process, the molten steel corrosion and the accumulation of alumina inclusion deposits affect the submerged entry nozzle (SEN) wall surface, including the surface morphologies of the smooth wall, porous refractory wall, and clogged wall. The SEN wall surface morphology affects the boundary layer structure and alumina inclusions transport. In this study, a physical modeling method was adopted, and the surface morphologies simulation was realized by filling up the natural porous refractory material and inserting the real clog material in the polymethyl methacrylate SEN model. The velocity in the boundary layer was measured using the particle image velocimetry (PIV) technology, and the alumina inclusions transport path in the boundary layer was calculated by MATLAB software. The MATLAB codes combined the velocity data from the PIV measurement results and the inclusion transport equation. The four-quadrant analysis showed that sweep and ejection events existed in the boundary layer. The fluctuations of the velocity and the turbulent kinetic energy in the normal direction were increased in the porous refractory and the clogged wall boundary layer when the sweep and ejection events existed. The transport of the alumina inclusions with a diameter of 1–15 μm was affected by the ejection and the sweep events. The alumina inclusions moved toward the boundary in the sweep event. During the sweep event, the transport path of alumina inclusions with 1 μm diameter was close to the boundary; the alumina inclusions were more easily attached to the boundary. The alumina inclusions escaped from the boundary in the ejection event. In the porous refractory and the clogged walls, the alumina inclusion transport path in the normal direction was increased. When the SEN wall’s morphologies changed from smooth wall to porous refractory wall and clogged wall, the sweep event area proportion increased from 10.17% to 39.77%, and the ejection event area proportion decreased from 32.96% to 9.24%. Moreover, the sweep event’s probability increased from 25.83% to 28.24% when the morphologies of the SEN wall changed from smooth wall to porous refractory wall and clogged wall, which will increase the alumina inclusion deposition rate in the porous refractory wall and the clogged wall boundary.

Modeling Study of EMBr Effects on the Detrimental Dynamic Distortion Phenomenon in a Funnel Thin Slab Mold

The turbulent phenomena occurring in the thin slab mold affect the final product quality. Therefore, it is essential to carry out studies to understand and control their occurrence. Current research aims to study the electromagnetic brake (EMBr) effects on the flow patterns in a funnel thin slab mold. The objective is to prevent the detrimental phenomenon known as dynamic distortions (DD) of the flow, applying the EMBr in the typical horizontal position (H-EMBr) and a new vertical position close to the narrow faces (V-EMBr). The fluid dynamics are simulated using the Reynolds stress model (RSM), the Volume of Fluid (VOF) model and the Maxwell equations in their magnetohydrodynamics (MHD) simplification. The results show that the H-EMBr effectively counteracts the DD phenomenon by reducing the submerged entry nozzle (SEN) ports' mass flow rate differences. The EMBr reduces the highest meniscus fluctuations from −10 to ±3 mm with a field intensity of 0.1T and almost 0 mm for higher field intensities. In contrast, the V-EMBr configuration does not reduce or control at all the DD phenomenon, even though eliminating the upper roll flows does not diminish the meniscus fluctuation amplitudes and induces new small roll flows close to the SEN's wall.

Effect of interfacial reaction behaviour on the clogging of SEN in the continuous casting of bearing steel containing rare earth elements

The problem of the clogging of submerged entry nozzle (SEN) in the continuous casting of bearing steel containing rare earth (RE) elements is studied in this paper. The composition, formation process, growth mode and cause of the clogging at the interface of the molten steel and the refractory of SEN were analysed in detail during the process of molten steel casting. The results showed that the graphite dissolution process on the inner wall of SEN can improve the wettability between the molten steel and the refractories, which provides convenient conditions for the reaction and adhesion of RE and its compounds on the inner wall of the SEN. Clogging compounds at different locations had different compositions. The main compositions at the interface between the molten steel and the refractories were consisting of cerium aluminate compounds, while the outer walls of the SEN mostly consisted of cerium sulfide compounds. With the growth of clogging, the laminar flow interface layer on the inner wall of the SEN will gradually increase, which further accelerates the clogging, and ultimately affects the continuous casting. Therefore, the prevention of clogging in the SEN of RE steel can be mainly carried out by inhibiting the formation of initial clogging in the early stages and by inhibiting the reaction of the SEN materials.

Anti-fouling of submerged entry nozzle with electric current pulse

An effective method for anti-clogging of submerged entry nozzle (SEN) was developed by imposing an electric current pulse (ECP) between the SEN and the stopper in the continuous casting process. The morphologies and components of the adhered inclusions on the inner wall of SEN were examined. The size distribution and amounts of inclusions in the steel slab were measured and compared before and after treatment with ECP. After ECP treatment, the tap hole of SEN was only slightly clogged, the inner wall became smooth and the thickness of adhered inclusions decreased by about 50%. The ECP effect was also reflected in the inclusion amounts of the formed steel slab, which decreased by approximately 30% compared to the non-treated sample. These improvements were attributed to the ECP transferring excess negative charges to the molten steel side and maintaining a low or even a zero electric potential difference between the SEN and molten steel, which decreased the wettability and the interaction between the two phases.

A transient model for nozzle clogging

This model has been developed for transient simulation of clogging (also called as fouling) in submerged entry nozzle (SEN) during continuous casting. Three major steps of the clogging have been taken into account: (a) transport of non-metallic inclusions (NMIs) by turbulent melt flow towards the SEN wall; (b) interactions between melt and wall, and the adhesion of the NMI on the wall; (c) formation and growth of the clog by NMI deposition. The computational domain is divided into bulk and near-wall regions. An Eulerian-Lagrangian approach is employed to calculate the transport of NMIs by the turbulent flow; a stochastic near-wall model is adopted to trace particles in the turbulent boundary layer (near-wall region). The early stage of clogging is modeled by the dynamical change in wall roughness, while the late stage of the clogging is modeled by building a layer of porous clog region from the wall. This layer is called as ‘clog’, and it continues to grow by attaching more NMI particles. To evaluate the model, a laboratory experiment, which was designed to study the clogging of SEN during steel continuous casting, is simulated. It is verified that the model can reproduce the experiment: the calculated clogged section of the nozzle is qualitatively comparable with as-clogged sections in laboratory experiments; the calculated mass flow rate through the nozzle agrees with the experimentally-monitored result as well. New knowledge is obtained. (1) Clogging is a transient process interacting with the melt flow, and it includes the initial coverage of the nozzle wall with deposited particles, the evolution of a bulged clog front, and then the development of a branched structure. (2) Clogging is a stochastic and self-accelerating process. Finally, model capabilities/limitations, uncertainties for choosing the modeling parameters such as mesh size, Lagrangian time scale, the correction factor in the interpolation of clog permeability are studied and discussed.

A Study on the Nonmetallic Inclusion Motions in a Swirling Flow Submerged Entry Nozzle in a New Cylindrical Tundish Design

Different sizes and shapes of nonmetallic inclusions in a swirling flow submerged entry nozzle (SEN) placed in a new tundish design were investigated by using a Lagrangian particle tracking scheme. The results show that inclusions in the current cylindrical tundish have difficulties remaining in the top tundish region, since a strong rotational steel flow exists in this region. This high rotational flow of 0.7 m/s provides the required momentum for the formation of a strong swirling flow inside the SEN. The results show that inclusions larger than 40 µm were found to deposit to a smaller extent on the SEN wall compared to smaller inclusions. The reason is that these large inclusions have Separation number values larger than 1. Thus, the swirling flow causes these large size inclusions to move toward the SEN center. For the nonspherical inclusions, large size inclusions were found to be deposited on the SEN wall to a larger extent, compared to spherical inclusions. More specifically, the difference of the deposited inclusion number is around 27 pct. Overall, it was found that the swirling flow contains three regions, namely, the isotropic core region, the anisotropic turbulence region and the near-wall region. Therefore, anisotropic turbulent fluctuations should be taken into account when the inclusion motion was tracked in this complex flow. In addition, many inclusions were found to deposit at the SEN inlet region. The plotted velocity distribution shows that the inlet flow is very chaotic. A high turbulent kinetic energy value of around 0.08 m2/s2 exists in this region, and a recirculating flow was also found here. These flow characteristics are harmful since they increase the inclusion transport toward the wall. Therefore, a new design of the SEN inlet should be developed in the future, with the aim to modify the inlet flow so that the inclusion deposition is reduced.

Numerical and Physical Study on a Cylindrical Tundish Design to Produce a Swirling Flow in the SEN During Continuous Casting of Steel

A new tundish design was investigated using both water model experiments and numerical simulations. The results show that the Reynolds Stress Model simulation results agree well with the Particle Image Velocimetry-measured results for water model experiments. A strong swirling flow in the Submerged Entry Nozzle (SEN) of the new tundish was successfully obtained, and the tangential velocity in the region near SEN inlet could reach a value of around 3.1 m/s. A high value of the shear stress was found to exist on the SEN wall, due to the strong swirling flow inside the SEN. This large shear stress leads to the dissipation of the rotational momentum of the steel flow. Thus, the maximum tangential velocity of the steel flow decreases from 3.1 m/s at around the SEN inlet to 2.2 m/s at a location close to the SEN outlet. In addition, the near-wall region has a high pressure, which is larger than the atmospheric pressure, due to the centrifugal effect. The calculated swirl number, with the value of around 1.6 at SEN inlet, illustrates that the current design can produce a similar strong swirling flow compared to the swirl blade method and the electromagnetic stirring method, while this is obtained by simply changing the steel flow path in tundish instead of using additional device to influence the flow.

Design of a Submerged Entry Nozzle for Thin Slab Molds Operating at High Casting Speeds

A submerged entry nozzle (SEN) for thin slab casters operating at casting speeds as high as 7.5 m/minute was developed based on fundamental grounds of boundary-layer theory and water modeling experiments. Experimental techniques included tracer injection to observe overall fluid flow patterns, high speed video camera and image analysis to follow dynamic changes of meniscus levels and particle image velocimetry to measure water speeds in the mold. This design was compared with two other SEN designs of nozzles under current commercial use at various thin slab casters. Direct comparisons of mathematical simulations and experimental results among the three SEN's evidenced that this new SEN yields very stable flows which are independent from casting speed and nozzle immersion depth. Fluid flow developed by this SEN consists of a double roll pattern without generation of superficial vortices. The two other SEN's yield instable discharging jets due to and excessive shearing effects with the surrounding fluid inducing severe dissipation of kinetic energy which promotes severe tailing effects inducing strong meniscus oscillations. The proposed design has reported good industrial performances and a longer operating life because the slag protection belt suffers less wear thanks to smaller velocities of the bath in contact with the SEN wall.

Kinetic Modeling on Nozzle Clogging During Steel Billet Continuous Casting

In the current paper, a kinetic model was developed to study the entrapment of inclusions in the molten steel flowing through a Submerged Entry Nozzle (SEN) during billet continuous casting process. The trajectory of inclusions was calculated by considering the drag force, lift force and gravitational force. The entrapment locations of inclusions on SEN wall were predicted. The effects of nozzle diameter, casting speed, billet dimension, and inclusion diameter on SEN clogging were quantitatively discussed. The results indicate the inclusions with diameter larger than 100 μm are not able to be entrapped by the nozzle wall; and the entrapment probability will increase quickly with decreasing size of inclusions. The distribution of the entrapped inclusions along the nozzle length is non-uniform and the volume fraction of inclusions in the clogging materials should be considered in order to more precisely predict the accumulated weight of molten steel that can be poured before the nozzle is fully blocked by clogging. Under the conditions assumed: 150 mm×150 mm billet, 2.0 m/min casting speed, approximately 25°C superheat, 1 m length of the SEN (Al2O3–C materials), 20 μm inclusions diameter in a single size, 30 ppm T.O and 40 mm nozzle diameters, the prediction shows that ~351 ton steel can be poured for the current billet continuous caster.