Steel In Tundish Research Articles

Effect of Inflow Rate Variation on Intermixing in a Steelmaking Tundish during Ladle Change‐Over

The intermixing of dissimilar grades of steel in tundish during the ladle change‐over is a problem of growing interest. During sequential casting of different grades, it is important that the intermixing of the grades is kept to a minimum. Present work deals with computational and water model studies of the three‐dimensional turbulent fluid flow in a multi‐strand tundish during ladle change‐over process. The physical investigation has been carried out by conducting experiment on a 1:4 scale model of tundish. The numerical simulations have been carried out with the help of educational version of ANSYS Fluent, using the Volume of Fluid (VOF) method and incorporating standard k–ɛ turbulence model. The numerical model has been validated with the results of physical investigation and is found to be in good agreement. Further, the numerical model is used to study the ladle change‐over process considering effect of inflow rate on grade mixing and interface positions, i.e., different bath height positions in tundish with and without advance pouring box (APB). It has been observed that the use of APB is not helpful in reducing the intermixed time while increase in flow rate of new grade steel decreases the intermixed amount.

Effect of Turbulence Inhibitor on the Molten Steel Flow in Tundish

The flow pattern and temperature distribution of molten steel in tundish were calculated by CFD and heat transfer method. Comparing the tundish flow field and the temperature field of empty packet and turbulence inhibitor installed, the role of turbulence inhibitor in tundish was analyzed, and the advantages and disadvantages of turbulence inhibiter were illuminated. The results show that: the turbulence inhibitor can eliminate the short circuit flow at tundish bottom, stabilize flow, and homogenize molten steel composition; but the turbulence inhibitor can consume energy of molten steel, and reduce the temperature of molten steel in the tundish. Without the turbulence inhibitor, the surface minimum temperature is far from the narrow corner, it is not easy to knot cold steel; installing turbulence inhibitor can raise the molten steel temperature near inlet, steel flow will scour inlet refractory intensively, service life of which shortens.

Effect of Parapet Hole on Tundish Flow Field

According to the actual operating parameters of tundish in a steel mill, the flow pattern and temperature distribution of molten steel in tundish were studied by CFD and heat transfer calculation method. Changing the height of parapet hole, the effect of parapet hole on flow field and temperature field were simulated. The simulation results show that: the parapet hole height has large influence on flow recirculation position, which can impact surface temperature and outflow temperature of molten steel. When parapet hole height increases, the recirculation vortex moves towards the surface of molten steel in outflow zone, surface temperature rises, but outflow temperature decreases near the narrow wall. Comprehensive analysis show that, when the parapet hole height is 480mm, surface temperature is high, molten steel will not solidify at corner; the reduction of molten steel temperature is small at outflow hole.

Numerical Calculation for Temperature Field in Two Exits Tundish

According to the operating parameters of a tundish for continuous casting in a steel mill, the temperature distribution of molten steel in tundish was studied by the method of numerical calculation. Change the flow orifice area of slag wall, simulation calculation for the effect of various slag walls on the temperature distribution of molten steel in tundish was done. Through the calculation and analysis of tundish longitudinal section and the surface temperature distribution, temperature uniformity of molten steel in tundish was determined. The calculation results show that: the slag wall can obviously deduce temperature difference between the top and the bottom of molten steel in tundish; small flow orifice area of slag wall can promote the temperature uniformity of molten steel after slag wall.

Numerical Simulation of Flow Field in the Tundish with Two Outlets

According to the operating parameters of continuous casting tundish in a steel mill, the flow patterns of liquid steel in tundish were studied by the method of numerical simulation. Changing the flow orifice area of slag wall, to simulate and calculate the influence of slag wall on the flow field in tundish. Through calculating the steel flow vector, to analyze the uniformity of steel flow in tundish, by calculating the inclusions distribution to analyze the effect of blocking slag wall holding inclusions. The simulation results show that: the slag wall can obviously deduce the short circuit flow of steel liquid in tundish bottom. With the flow orifice area is reduced, and the turbulence brisk between two slag walls, and liquid surface is easy to roll; the ability of slag wall holding inclusions enhances, but too small flow orifice area will prompt inclusions passing the slag wall.

Numerical Simulation of Fractal Agglomerating-Growth of Al2O3 Inclusions in Tundish

Based on the Al2O3 inclusion analysis of low-carbon aluminum killed steel in tundish of a domestic steel company and fractal theory analysis, a mathematical model of fractal agglomerating-growth of Al2O3 inclusions in tundish was established. The results indicated that: large swirl flows exist in both sides of inlet, space between weir and dam, and large zone above outlet, in which monomer and agglomerated inclusion particles accumulate easily; the agglomerated inclusions with hydrodynamic diameter of 6 — 9.8 μm were quickly generated less than 16 s, but those inclusions with hydrodynamic diameter more than 11 μm were difficult to form; the number density of agglomerated inclusion rapidly increased first, then slowly reduced, so the form and quantity distribution of agglomerated inclusions can be controlled by controlling the residence time of inclusion particles in tundish.

In the Tundish Flow State in the ANSYS Simulation

Through the establishment of ANSYS tundish steel liquid flow finite element model analysis of finite element method in simulating the flow field in tundish for applications. comparison with and without flow control device of liquid steel in tundish flow characteristics the results have guiding significance for practical production.

Designing of a Novel Shroud for Improving the Quality of Steel in Tundish

In present 92.8% of world steel production is casted on continuous casting machine. The key phase of continuous casting is tundish. Beside of refining effect of slag phase also steel flow in tundish is very important factor. The main causes for inclusion formation and contamination of the melt include reoxidation of the melt by air and carried over oxidizing ladle slag, entrainment of tundish and ladle slag, and emulsification of these slags into the melt. These causes are due to generation of turbulence in the melt. Although turbo stop lowers the turbulence in some extent. But it is not capable of totally decrease of turbulence specially during lowering of metal bath at the time of ladle exchange operation, cause contamination of the steel melt in tundish. So in the present work it has been focused to develop a novel shroud which have significant role to supply of steel from ladle to tundish at slow rate to avoid turbulence, emulsification and formation of slag eye in tundish to produce quality steel in a sustained manner.

A Compensation Model of Continuous Temperature Measurement for Molten Steel in Tundish

A compensation model has been proposed to reduce errors caused by the immersion depth of the sensor and the time lag of continuous temperature measurement for molten steel in tundish, which is based on the limited data fitting method and data fusion technology. According to the heat transfer analysis of sensor, the thermal model has been bulit to determine the temperature variation function. The parameters of the compensation model are recognized by generic algorithm, which combines the determine function, the molten steel mass in the ladle and pouring time. The processing of error compensation is divided into three stages: tracking, holding and compensation. When the processing is stable, the measured temperature error is small, and the measured temperature is regarded as accurate value and tracked. For the end of pouring stage of the ladle, the temperature error is caused by the immersion depth of the sensor, and the measured temperature before sharp decreasing is considered as real temperature and held. For the temperature increasing stage after ladle changed, the measured temperature is compensated online. The application results show that the error between the compensation temperatures and the actual ones have been decreased to ± 2 °C, and the time lag could be shortened from 3 – 5 min to 40 s by applying this model.

Infrared Continuous Temperature Measurement System for Molten Steel in Tundish

In order to detect the liquid with high temperature, a new kind of continuous temperature measuring system for the molten steel in continuous casting tundish was developed, combining infrared measurement with optical fiber conduction technologies. It overcomes the disadvantages of the existing disposable fast thermocouple such as intermittent measurement, frequent replacement, and experiential insertion position and depth, which can provide a favorable guarantee for the closed loop temperature-related control of the continuous casting production. It is demonstrated that the measurement lag is well solved because the unique single-layer compound outer protection tube with inner sighting tube is adopted, and the system has the advantages in long service life and high measurement precision. In addition, the cost is reduced by 20%~50% compared with the other similar products. The main performance indexes of the system are response speed 3~5s, longest continuous measuring time up to 70h, and average error ±3°C.

Influence of Steel Grade on Oxidation Rate of Molten Steel in Tundish

The influence of steel grade on the oxidation rate of molten steel in tundish was studied by conducting oxidation experiments on the Ti and Ti–Al deoxidized molten steel and comparing the obtained oxidation rates with that of the Al deoxidized molten steel as measured in a previous report. In the still state, the oxidation rate of the Ti deoxidized molten steel is faster than those of the Ti–Al deoxidized molten steel and the Al deoxidized molten steel, showing dependence on the steel grade. This means that in the still state, while the oxidation rates of the Ti–Al and Al deoxidized molten steel are controlled by the mass transfer of oxygen in the oxide film, the oxidation rate of the Ti deoxidized molten steel is controlled by the mass transfer of O2 gas in the gas phase because the surface is not covered with oxide films. In addition, in the stirred state, the oxidation rates of the Ti and Ti–Al deoxidized molten steel become faster than that of the Al deoxidized molten steel in the region where the O2 gas partial pressure exceeds 10 kPa. This dependence on the steel grade can be explained by the mechanism of accelerating the mass transfer in the gas phase due to active iron evaporation in the Ti and Ti–Al deoxidized molten steel, in which the surface disturbance is larger than that in the Al deoxidized molten steel.

タンディッシュ内における溶鋼の酸化速度に及ぼす鋼種の影響

The influence of steel grade on the oxidation rate of molten steel in tundish was studied by conducting oxidation experiments on the Ti and Ti-Al deoxidized molten steel and comparing the obtained oxidation rates with that of the Al deoxidized molten steel as measured in a previous report. In the still state, the oxidation rate of the Ti deoxidized molten steel is faster than those of the Ti-Al deoxidized molten steel and the Al deoxidized molten steel, showing dependence on the steel grade. This means that in the still state, while the oxidation rates of the Ti-Al and Al deoxidized molten steel are controlled by the mass transfer of oxygen in the oxide film, the oxidation rate of the Ti deoxidized molten steel is controlled by the mass transfer of O2 gas in the gas phase because the surface is not covered with oxide films. In addition, in the stirred state, the oxidation rates of the Ti and Ti-Al deoxidized molten steel become faster than that of the Al deoxidized molten steel in the region where the O2 gas partial pressure exceeds 10 kPa. This dependence on the steel grade can be explained by the mechanism of accelerating the mass transfer in the gas phase due to active iron evaporation in the Ti and Ti-Al deoxidized molten steel, in which the surface disturbance is larger than that in the Al deoxidized molten steel.

Influence of Turbulence Controller on Flow Mode of Molten Steel in Tundish

According to tundish for thin slab caster in a steel factory, 1:3 water modeling and numerical simulation were established. By measuring RTD(Residence time distribution) curves of fluid flow in tundish, real residence time, plug flow volume fraction and dead zone fraction were computed, influence of turbulence controller structure on flow mode of molten steel in tundish were studied. The results show that fluid flow in tundish can be improved, if turbulence controller has reasonable structure. A reasonable turbulence controller structure was obtained. Water modeling results agree with numerical computing results well.

Hydrodynamic and Mathematical Simulations of Flow Field and Temperature Profile in an Asymmetrical T-type Single-strand Continuous Casting Tundish

To further remove mini-size nonmetallic inclusions and improve surface quality of stainless steel slab at No. 2 Steelmaking Plant of Shanxi Taigang Stainless Steel Company Limited, the flow field and temperature profile of molten stainless steel in an asymmetrical T-type single-strand continuous casting tundish with a capacity of 18–20 tons have been investigated by both hydrodynamic and mathematical simulations. The influences of height for low-wall of turbulence inhibitor, dam height, weir depth, distance between dam and weir, submerged depth of ladle shroud and casting speed on flow field in the tundish have been studied in a 1 : 3 reduced scale hydrodynamic model. The streamlines, velocity vector fields and temperature profiles are also mathematically simulated.The hydrodynamic modelling results indicate that height for low-wall of turbulence inhibitor, dam height and weir depth are three important structural parameters on flow field of molten stainless steel in the tundish. The optimization of the three parameters can improve dispersed plug zone and reduce dead zone effectively. Changing casting speed can improve turbulent flow, and thus reduce dead zone of molten stainless steel in the tundish. As a result, five groups of optimized structural parameters of the tundish have been recommended, which can reduce volume fraction of dead zone down to 15–30% and increase volume fraction of dispersed plug zone to more than 20%. In addition, it is verified that the optimized groups of structural parameters of the tundish can maintain their advantage at different casting speeds in a narrow range.The mathematical modelling results suggest that heat losses around the tundish must be considered in order to accurately simulate the streamline, velocity vector field and temperature profile. The calculated temperature drop of molten stainless steel between inlet and outlet of the tundish is about 4.4 K; the maximum temperature drop in the whole tundish is about 10 K. The modification of flow filed by changing structural parameters of the tundish can slightly affect temperature profile of molten stainless steel in the tundish.

Numerical simulation of flow phenomena and optimum operation of tundish

To enhance the quality of grade 20 carbon-steel on the continuous casting production line, the mechanism of forming blowholes and non-metallic inclusions in billets and numerical simulation of flow phenomena about liquid steel in tundish were studied. The results show that the configuration and operation of tundish play an important part in quality assurance of grade 20 carbon-steel products. By optimizing the configuration of the tundish, the depth of liquid bath in tundish is enhanced, the impact of liquid steel is decreased, and the residence time of liquid steel is lengthened, which is useful for eliminating inclusions and blowholes and improving the service life of tundish. Improving the pouring and tapping operation of liquid steel can avoid the contact of liquid steel with air, and decrease re-oxidation. Strict control of the superheat degree of casting liquid steel can decrease the non-metallic inclusion content of the re-oxidation in billets and reduce the erosion of tundish. The inclusions and blowholes in the continuous casting grade 20 steel billets are reduced to a great extent and qualification rate is enhanced from 60% to 80%.

Reoxidation Behavior of Molten Steel in Tundish.

It is necessary to clarify the reoxidation factors and quantitatively determine the contribution of each factor to the reoxidation of the molten steel to prevent the contamination in the tundish. In this study, the molten steel in tundish has been sampled in production scale experiment and from the composition change of the molten steel the amount of reoxidation of the molten steel teemed from the first ladle into an actual tundish has been quantified by factor as divided into initial teeming stage and stable casting stage. By applying the reaction rate model of oxidation by air which was developed on the basis of the basic experiment, the amount of oxidation by air in the tundish has been predicted successfully. Comparison of the amounts of oxidation by air calculated from the change in the N content with the experimentally determined amounts of oxidation has shown that it is difficult to judge whether or not the molten steel is oxidized from the N absorption behavior alone.

Numerical and Modeling Analysis of Fluid Flow and Heat Transfer of Liquid Steel in a Tundish with Different Flow Control Devices.

Fluid flow and heat transfer of liquid steel in a two-strand tundish of a slab caster were analyzed using water modeling and numerical techniques. Three cases were considered: A bare tundish, a tundish equipped with a pair of weirs and a pair of baffles (arrangement W&B) and a tundish equipped with a turbulence inhibitor and a pair of baffles (arrangement TI&B). The water modeling, under isothermal conditions, indicated the existence of a strong bypass-flow for the bare tundish and the W&B arrangement while the TI&B arrangement reported a longer minimum residence time and higher plug flow characteristics. Numerical results verified the trend mentioned with the water model. The numerical study showed also that cold and hot steel affected considerably the flow patterns of steel due to the existence of buoyancy forces. In the case of a step-input of cold steel, bypass-flow was intensified for the bare tundish and the tundish with a W&B arrangement. When a step input of hot steel is introduced into the system buoyancy forces make the steel to flow preferentially near the free surface. The tundish with a TI&B arrangement showed the best flow characteristics with not splashing and negligible turbulence. This arrangement shows a slower response to thermal disturbs coming from the input making the tundish a less exposed reactor to the temperature changes and the consequent changes in flow patterns usually found in real casting operations.

Effects of Tundish Cover Powder and Teeming Stream on Oxidation Rate of Molten Steel in Tundish.

The oxidation rate of the molten steel covered with the tundish cover powder and the molten steel being teemed was measured and the reaction mechanism was investigated as a basic study to quantify the oxidation rate of molten steel at different parts in an actual tundish. The oxidation rate of the molten steel covered with the tundish cover powder is proportional to the partial pressure of O2 gas in the gaseous phase and the reciprocal number of thickness of tundish cover powder and can be explained by mass transfer control model of O2 gas in the layer of tundish cover powder. The oxidation rate of stirred molten steel and molten steel being teemed is proportional to the partial pressure of O2 gas in the gaseous phase and the 0.45th power of the stirring energy per unit area and can be rationally explained by a control model of mass transfer of O2 gas in the gaseous phase in which an increase in the reaction interface area due to stirring is considered.

Effect of Stirring on Oxidation Rate of Molten Steel.

As basic research to quantify the oxidation rate of molten steel in tundish, oxidation experiments were performed on nonkilled molten steel sand aluminum-killed molten steel on laboratory scale, and the effect of stirring on the oxidation rate was studied. The following conclusions were derived. The oxidation rate of the nonkilled molten steel by air is not affected by stirring and is controlled by the diffiusion of O2 gas in the gas phase. Stirring changes the oxidation rate because of breaking the oxide film in the oxidation process of the aluminum-killed molten steel by air. The oxidation rate of the aluminum-killed molten steel in the still state is controlled by the diffusion of oxygen in the oxide film, while the oxidation rate of the aluminum-killed molten steel in the stirred state is controlled by the diffusion of O2 gas in the gas phase.

Technology for Cleaning of Molten Steel in Tundish.

Sheet and coated steel have been demanded to meet quality requirements of ever increasing severity in recent years. Reduction in nonmetallic inclusions is an important challenge in this respect. Protection on the molten steel in the tundish against contamination is of special importance in not only improving steel product quality, but also avoiding immersion nozzle clogging and increasing the number of sequence-cast heats. To supply molten steel with high cleaniliness in a stable manner, the cleaning behavior of the molten steel in the tundish was investigated and mechanism whereby the molten steel is kept clean in the tundish was quantified. Based on the results achieved, technology was studied for keeping the molten steel clean in the tundish.