Bare Tundish Research Articles

Assessment of the Volume Effect and Application of an Improved Tracer in Physical Model of a Single-Strand Bare Tundish

Assessment of the Volume Effect and Application of an Improved Tracer in Physical Model of a Single-Strand Bare Tundish

Physical and Numerical Study on Right Side and Front Side Gas Blowing at Walls in a Single‐Strand Tundish

The compromise between inclusions removal by small bubbles and proper agitation of fluid flow in tundish by gas blown is challenging. The single‐strand tundish without flow control devices (bare tundish) is used to study the effects of side‐wall gas blowing on the flow field. The water model, particle image velocity measurement and computational fluid dynamics simulation are used to study bubble behavior, fluid flow field, and tracer transport. A large horse shoe vortex and a short circuit flow at the bottom are formed in the bare tundish. Gas blowing at the outlet‐side wall of the tundish creates multiple vortices in the right‐side region, with blowing rate and position greatly influencing the surface flow within the tundish. Gas blowing at the front‐side wall creates a large spiral vortex, agitating the fluid in the tundish and improving the flow field. Increasing the blowing rate strengthens the vortex in the right region, but raising the blowing position affects surface flow and creates a counterclockwise flow toward the shroud. In all schemes, gas blowing at a low position on the front‐side wall with a small gas flowrate is the optimized scheme which shows the smallest dead volume and enhances surface flow.

Challenge of Residence Time Distribution Curve in Tundish for Continuous Casting of Steel

The residence time distribution (RTD) curve is a simple and useful method to analyze the flow behavior in the tundish. In the last decades, analysis result acquirement based on the RTD curve has been applied to design and optimize the flow control devices in a simple bare tundish or a multistrand tundish. There are many factors to affect the acquirement and analysis of the RTD curve, such as the tracer, the measuring technology, and the analysis model. In order to find a solution for the above issues, the latest progress and research status of RTD curve are discussed in the fields of water model, mathematical model, RTD analysis model, and measuring technology. After comparison, the KCl solution is a good tracer, and its tracer concentration and volume can be determined by the dimensionless tracer parameter (Dtp). The extended combined model can be applied to analyze the RTD curve by pulse input of tracer, and the mean residence time is the key parameter to identify the difference in fluid characteristics among the strands.

Fluid Flow Characterization of Single-Strand Tundish with Flow Modifiers through Physical Water Model (PWM) and CFD Simulation

The flow behavior in the continuous casting tundish dominates the quality and cleanliness of steel production. In this research, the single strand tundish's fluid flow behavior with different flow modifiers is investigated through numerical and experimental simulation. The numerical; simulation is performed in ANSYS FLUENT 19.2 (commercial package) and experimental through physical water model technique. The flow behaviors of bare tundish and tundish with three different flow modifiers are investigated. The three different flow modifiers deployed are the dam, baffle, and turbulence inhibiter (TI). Fluid flow performance is examined through residence time distribution (RTD) curves, which are derived from the measurement of the tracer concentration at the outlet. Good agreement between the CFD simulation and physical water model experiments is discovered. The results show there is an improvement in residence time and fluid flow (also improved inclusion removal) after the deployment of flow modifiers. There is a 20% improvement in peak and minimum residence time of RTD curves due to flow modifiers application. It is also discovered that the tundish configuration in this research, the tundish with turbulence inhibiter, provides optimal flow characteristics and eventually intended to promote a better level of inclusion removal.

Numerical Investigation of Single-Strand Slab Casting Tundish Flow with Heat Transfer and Inclusion Transport

In continuous casting process, cleanliness of steel can be improved and maintained by promoting the inclusion separation inside the tundish by various means; tundish flow optimization using arrangement of flow control devices inside the tundish is one among them. Three-dimensional computational fluid dynamics simulation of tundish flow is an efficient way to investigate the arrangement of flow control devices. In the present work, three-dimensional isothermal steady-state flow simulations, residence time distribution analysis and inclusion transport simulations of tundish flow are conducted. All the simulation results are validated with experimental measurements reported in literature. Subsequently, the simulations are extended for a non-isothermal flow of the existing tundish in the plant and an additional flow control device, namely a weir with appropriate dimensions is proposed which indicated better steel flow in the tundish with more inclusion separation efficiency as compared to the existing bare tundish.

On the Ladle Shroud Design and Mis-alignment Effects on the Fluid Flow in a Metallurgical Tundish- A CFD Model Study

Two aspects of ladle shroud design in tundish are studied. The two strand tundish is a long and bare tundish i.e. without flow control devices but stopper rods to control flowrate. The 3D CAD geometry, turbulence models, discretisation of governing equations, numerical solution and post processing are performed in a commercial software Siemens STAR CCM+. Compared to the typical pipe ladle shroud, the velocity of impinging stream from the ladle shroud is lower for the trumpet ladle shroud. As a result, the flow stream in the whole tundish shows a contradictory tendency, i.e. the upward stream is more obvious than the downward stream for trumpet shroud and vice visa for pipe shrouds. In industrial production, the ladle shroud often canted to the front wall due to machinery reasons. Therefore, two cases that the misalignment degree of the ladle shroud are 5 and 10 degrees are studied. The results show that the impinging stream flow towards the front side of walls and the flow towards the outlets near the bottom wall and front wall. The horse like vortex that is typically observed in bare tundishes is destroyed. The non-symmetric flow pattern is formed for the severely biased cases which should be paid more attentions from industrial practice.

Physical water model and CFD studies of fluid flow in a single strand tundish

Flow characteristics in a continuous casting tundish is one of the key parameters producing a high quality clean steel. In this study, the fluid flow analyses of a single-strand tundish model were carried out using the commercial CFD software ANSYS FLUENT 14.0 and experimentally verified by physical water model. The realizable k-ɛ equation was utilized to model turbulent phenomenon. The behavior and performance of the flow in tundish with and without flow modifiers were investigated by the residence time distribution (RTD) curves which were obtained from the tracer concentration measurement at the outlet. The results from CFD are in agreement with the experiment results. The results show that the flow modifier plays an important role in increasing residence time and enhancing flow performance which could feasibly promote the inclusion removal potentials in the tundish process. The peak and the minimum residence time of RTD curves of the tundish model with flow modifiers were improved for more than 20%. With the comparison of the four flow modifier configurations (bare tundish, dam, baffle and turbostop) in the current tundish model, it could be concluded that the turbostop could provide the optimal flow characteristic in which could improve the level of inclusion removable.

Transient steel quality under non-isothermal conditions in a multi-strand billet caster tundish: part II. Effect of a flow-control device

A mathematical model was built to simultaneously analyse the effects of non-isothermal conditions and flow-control device on steel quality in a real steelmaking tundish. Liquid steel was used as the operating liquid with a step-input of 23° in a full-scale delta-shaped multi-strand billet caster tundish fitted with a standard impact pad (SIP). The changes in flow pattern and temperature fields of liquid steel in the tundish under isothermal, step-up and step-down conditions were thoroughly studied. Similar to the case of a bare tundish, buoyancy effects were seen to dominate at regions away from the ladle shroud. The presence of SIP modified the flow patterns and resulted into markedly different values of RRI as compared to bare tundish. Finally, the calculated results were qualitatively compared to results obtained from a real steelmaking tundish.

Optimization of flow control devices for a T-type five-strand billet caster tundish: water modeling and numerical simulation

The optimization of flow control devices (FCDs) for a T-type five-strand billet caster tundish was carried out by water modeling and numerical simulation. In water modeling experiments, flow characteristics of the bare tundish and tundish configurations with designed U-type baffles and a round turbulence inhibitor were analyzed using residence time distribution (RTD) curves. Mathematical models for liquid steel in the real plant tundish were established using the fluid dynamics software package Fluent. The flow field, the temperature field, and the RTD curves of liquid steel in the proposed tundish configurations were obtained. The results of numerical simulation and water modeling were validated with each other by the predicted and experimental RTD curves. The results of flow field and temperature field were used to reflect the actual state of a real plant tundish and to choose the optimal FCD. Finally, from the whole performance of the multi-strand tundish, the optimal scheme was determined by combining the results of water modeling and numerical simulation. With the optimal tundish equipped with U-type baffle with deflector holes and round turbulence inhibitor, not only was the flow characteristic of each strand improved, but also the difference of flow characteristics between multiple strands was smaller.

Numerical Investigation of Inclusion Behaviour in a Multi-Strand Tundish During Strand Blockages

Inclusion removal in the continuous casting tundish is an essential technology for production of high-grade steels. In the present study, a three dimensional numerical investigation has been carried out on six strand delta shape tundish. The aim of the work is to investigate the inclusion entrapment and removal phenomenon in a tundish. A parametric study has been carried out to study the behavior of the inclusions in a steelmaking tundish and the results have been compared on the basis of densities and diameters of inclusions. Bare tundish as well as a tundish occupied with Advance Pouring Box (APB) have been studied to predict the transport behavior of inclusion particles. Further, effect of strand blockages has been considered. The turbulent Navier–Stokes equations have been solved to predict the flow velocity distributions and inclusion trajectories were calculated using a Lagrangian particle tracking method. The numerical results were validated using available experimental results and found to be in good agreement. The results indicate that the use of APB has changed the fluid flow pattern and consequently the inclusion particles movement. The density of inclusion particles plays an important role. It has been seen that low dense particles have higher chances to get trapped or removed from tundish. It was also found that larger diameter of inclusion particles have more chances of floatation.

Numerical Modeling of the Fluid Flow in Continuous Casting Tundish with Different Control Devices

Numerical simulations were conducted to study the melt flow under the influence of control devices in a T-type two-strand bloom caster tundish via the open source Computational Fluid Dynamics software OpenFOAM. Three different cases were studied: a bare tundish, a tundish with two pairs of baffles, and a tundish equipped with a turbulence inhibitor and a pair of baffles. Turbulence inhibitor and baffles arrangement showed an improvement of the fluid flow characteristics, yielding lower values of dead volume and higher values of plug flow. With a turbulence inhibitor, the velocity of metal which flows directly toward the tundish floor is smaller and the turbulence kinetic energy of the melt top surface is lower than the other two arrangements.

Ladle Shroud as a Flow Control Device for Tundish Operations

The performance characteristics of a tundish, such as the flotation of inclusions and slag entrainment, are largely influenced by the fluid-flow phenomena. Physical modeling in water is widely used to understand the fluid flows in a tundish and as a tool to improve, control, and design procedures for high-quality steel processing operations. These approaches were used to study the performance of fluid flow for a new design of ladle shroud. The new design for a dissipative ladle shroud (DLS) was studied, using a one-third scale, delta shaped, four-strand tundish. The results were compared with those achieved with the conventional ladle shroud. Different cases have been analyzed, including a conventional ladle shroud (LS) with a bare tundish and a tundish furnished with an impact pad. Similarly, the new design of the shroud (DLS) was studied under equivalent conditions. The physical experiments included the use of particle image velocimetry (PIV) and conductivity tracer techniques. The PIV measured the instantaneous velocities at the outlet of the DLS and the LS at different flow rates, showing the detailed jetting characteristics of water leaving the two types of ladle shroud. Residence time distribution (RTD) curves were also obtained for the different flow arrangements previously mentioned, and the dispersion of a colored dye tracer was observed at different intervals of time during tundish operation and analyzed using the video visualization technique.

Modelling performance of four‐strand, 12 t, delta shaped continuous casting tundish fitted with different flow modifying arrangements for better steel quality

The performance of a 12 t, delta shaped, four‐strand, billet casting tundish was investigated using a full scale (1∶1) isothermal model using water as the simulating fluid for steel. Three different modelling experiments were carried out. Quantifiable parameters like ‘number of slag beads’ in transient physical modelling of slag entrainment, or ‘residual ratio of inclusions’ (RRI %), in steady state mathematical modelling of inclusion removal and ‘mean residence time’, ‘dead volume fraction’, etc., in steady state mathematical computation of residence time distributions, were used as the performance indicators. Results for three different flow modifying dam arrangements were considered and compared with those of a bare tundish. Computational fluid dynamic analysis showed that different flow modifying dam arrangements significantly alters the flow pattern within the tundish. On the basis of these performance indicators, the best arrangement was identified. The assumption in this paper that similar conclusions can be drawn from experiments carried out either in transient or in steady state conditions was verified. It was shown that both transient physical modelling experiments and the steady state mathematical predictions, point to the same conclusion.

Effect of Shape and Flow Control Devices on the Fluid Flow Characteristics in Three Different Industrial Six Strand Billet Caster Tundish

Fluid flow phenomenon in a tundish depends upon the shape of tundish. The change in the shapes can bring drastic change in the flow pattern and thus effect the fluid flow characteristics in the tundish. The signifiacnt effect of flow control devices on fluid flow phenomenon is also noticed. In the present work, investigation of fluid flow phenomenon was performed for the symmetrical half of a six strand tundish. Fluid flow pattern gets altered by changing the shapes of tundish and pouring chamber. The impact of this change results in a development of various flow patterns. These flow patterns are analysed for capturing the better inclusion flotation. The mathematical model has been validated by the experimental results of Singh and Koria for a single strand bare tundish.

Modeling Study of the Influence of Subflux Controller of Turbulence on the Molten Steel Flow in Tundish

The objective of the study is to diagnose the current condition of the two-strand tundish. The investigated object is a “T”-type tundish. The nominal capacity of the tundish is 7.5 tonne of liquid steel. By the mathematical simulation, fluid flow and heat transfer of molten-steel in a tundish of a billet caster under different conditions (bare tundish and tundish with flow control device) are analyzed. Three variants of subflux controller of turbulence configurations in the tundish are tested. Numerical simulations of are carried out with the finite-volume commercial code FLUENT using the realizable k- turbulence model. Liquid steel velocity, temperature, turbulent kinetic energy and Residence Time Distribution (RTD) characteristic have been obtained as a result of mathematical calculations. The RTD curve is used to estimate the different volumes such as plug volume, dead volume and mixed volume inside the tundish. The ratio of mixed to dead volume, which indicates the mixing capability of a tundish, is estimated.

Numerical Investigation of the Fluid Flow in Continuous Casting Tundish Using Analysis of RTD Curves

A detailed mathematical procedure of the optimization of the fluid flow in a tundish water model with and without flow control devices (weir and dam) was carried out using the commercial CFD code FLUENT 6. 0. The (k-ɛ) two-equation model was used to model turbulence. The residence time distribution (RTD) curves were used to analyze the behavior of the flow in tundish. The location of flow control devices in the tundish was studied. The results show that the flow modifiers play an important role in promoting the floatation of nonmetallic inclusions in steel. Comparing the three geometric configurations that are considered (bare tundish, weir, weir + dam), the tundish equipped with the arrangement (weir+dam) is a best and optimal geometric configuration of tundish.

Modeling of Fluid Flow and Residence Time Distribution in a Four-strand Tundish for Enhancing Inclusion Removal

The introduction of the appropriate size and precise location of flow control devices such as dam, turbulence inhibitor, etc., helps to modify the flow pattern and minimizing short circuiting and dead zone. Beside this, these also create the surface directed flow and maximize the residence time available for the flotation of inclusions and assimilation of the reaction products from the molten steel into the slag phase. These can be products of deoxidation, reoxidation, precipitation, emulsification and/or entrainment of refractory components into the melt and thus encompass both indigenous and exogenous inclusions. To this end, both the numerical and physical simulations were carried out mainly for three cases: a) in absence of flow control devices (i.e., bare tundish), b) in the presence of a dam, and c) with the application of turbulence inhibiting device (TID) and dam combination in the existing tundish configuration. The commercial CFD (computational fluid dynamics) package FLUENT® was used to predict the flow field prevalent in the water model tundish at steady state, whereas in the experimental program, both Particle Image Velocimetry (PIV) techniques for flow measurements and tracer dispersion experiments for concentration measurements were applied in the present study. Among all types of configurations applied in the present study, a combination of TID with holes+a dam work reasonably found to be an optimum configuration of the four-strand tundish regarding inclusion floatation. A superior strand similarity is also achieved in this configuration. Also the predicted time averaged horizontal and vertical components agreed within ±10% with the experimentally derived ones.

Numerical Simulation of Flow-induced Wall Shear Stress to Study a Curved Shape Billet Caster Tundish Design

Wall shear stress due to flow of the molten steel in the tundish is one of the factor for erosion of refractory walls which decides sequence length of a tundish. The flow-induced shear stress on the wall of a six strand curved type billet caster tundish has been computed by a 3-D mathematical model. The location of predicted peak wall shear stress was found to be same as observed in the plant after a sequence. Different design parameters of the tundish such as wall inclination angle, curvature radius, and tundish width are studied by analyzing the flow-induced wall shear stress. The role of a pouring chamber is assessed with respect to the wall shear stress. It was found that vigorous circulation around the inlet stream from shroud plays a major role in deciding the extent of the wall shear stress. Use of pouring chamber resulted in lesser wall shear stress than that of a bare tundish. The peak shear stress was found to be decreasing as any of the design parameters increased within a range. A modification in design parameter of the tundish can reduce the wall shear stress, thus may help to improve the sequence life of the tundish.

Dissipation of Turbulent Kinetic Energy in a Tundish by Inhibitors with Different Designs

Turbulent flow of liquid steel and its control is studied using different geometries of turbulence inhibitors. Four designs of turbulence inhibitors were characterized through experiments of tracer injection in a water model and mathematical simulations using the Reynolds Stress Model (RSM) of turbulence. Inhibitor geometries included octagonal‐regular, octagonal‐irregular, pentagonal and squared. A layer of silicon oil was used to model the behaviour of tundish flux during steel flow. Fluid flows in a tundish using these geometries were compared with that in a bare tundish. Experimental and simulation results indicate that the flow in a bare tundish and a tundish using turbulence inhibitors open large areas of oil close to the ladle shroud due to strong shear stresses at the water‐oil interface with the exception of the squared inhibitor. Oil layer opening phenomena are explained by the high gradient of the dissipation rate of turbulent kinetic energy. Using the squared inhibitor the kinetic energy reports a high gradient from the tundish floor to the free bath surface as compared with other geometries.

Water Modeling of Optimizing Tundish Flow Field

In the water modeling experiments, three cases were considered, i. e., a bare tundish, a tundish equipped with a turbulence inhibitor, and a rectangular tundish equipped with weirs (dams) and a turbulence inhibitor. Comparing the RTD curves, inclusion separation, and the result of the streamline experiment, it can be found that the tundish equipped with weirs (dams) and a iurbulence inhibitor has a great effect on the flow field and the inclusion separation when compared with the sole use or no use of the turbulent inhibitor or weirs (dams). In addition, the enlargement of the distance between the weir and dam will result in a better effect when the tundish equipped with weirs (dam) and a turbulence inhibitor was used.