Design optimization of flow control device for multi-strand tundish

The fluid flow phenomena in tundish have a strong influence not only on the uniform of composition and temperature of bath, but also on the separation of non-metallic inclusions, especially for the multi-strand tundish. A water model of a multi-strandtundish has been set up based on the Froude number and Reynold number similarity criteria. The effect of dam+weir and baffle on the uniform of composition and temperature of bath for different nozzles has been studied. The residence time distribution curves of the fluid flow were measured by SG800. Comparing the photos of the flow pattern in tundish, the optimum arrangement of baffle+dam was obtained. This new structure is benefit not only to uniform the temperature among different SENs (submerge entry nozzles) but also to separate the non-inclusions from the liquid steel, it can be widely used in multi-strand tundish.     

Fluid Flow in Tundish Due to Different Type Arrangement of Weir and Dam

Tundish is an important metallurgical reactor in the continuous casting process. In order to control the fluid flow in tundish and thus take full advantage of the residencetime available for the removal of inclusions from molten steel, the effect of weir and dam on the fluid flow has been studied in a water model based on the characteristic number Froude and Reynold number similarity criteria. The residence time distribution curves of the flow were measured by SG800. The optimum arrangement of darn and weir and the nonstationary flow in tundish were discussed. The results show that the combination of weir and dam is benefit for the flow pattern in tundish, weir can prevent the upper recirculating flow, dam can cut off the bottom flow and turn to upwards, it is advantageous to separate the nonmetallic inclusions. Furthermore, it is important to exceed the critical depth of bath during exchange ladles, not only for the inclusion floatation but also for avoiding tundish slag drainage earlier.     

Influence of flow control devices on metallurgical effects in a large-capacity tundish

The influence of flow control devices on metallurgical effects in a large-capacity tundish has been studied carefully with elements tracing, sampling and theoretical prospecting. The results from the studies are (1) in the continuous casting of clean steel, bad control of tundish operation may deteriorate the cleanliness of steel; (2) the cleanliness of steel is deteriorated mainly at the unsteady state; (3) large amount of macro inclusions come from the top slag and the refractory of tundish; (4) installing dam and weir can improve the cleanliness of steel and lighten the influence of steel fluctuation; and (5) the result of theoretical calculation suggests that the inclusions larger than the critical size of 92.6 μm can be floated out from the tundish bath completely.     

Dissymmetric flow phenomenon in a multistrand tundish

The dissymmetric flow phenomenon exists in a symmetric multistrand tundish. It was studied by the physical simulation experiment. The fundamental flow characteristic of dissymmetry was analyzed. The asymmetry of the flow field, the temperature field, and the inclusions distribution without flow-control devices (FCDs) were compared with those with FCDs. It is proved that the asymmetry of the flow and temperature field along the outlets at the long range is more obvious. The symmetric FCDs installation has a slight effect on the dissymmetric temperature field, simultaneously, the symmetry of the average residence time and the fluid flow pattern has improved, and the fluid flow in the tundish has been more reasonable. In case of a symmetric multistrand tundish having a large volume, the influence of the dissymmetric phenomenon should be considered and the flow behaviors in the whole tundish should be studied completely.     

Improvement of tundish shape and optimization of flow control devices for sequence casting heavy steel ingots

The metallurgical effect of a round tundish used to cast heavy steel ingots in machine works at present was evaluated through water modeling experiments. The flow control devices of the improved oval tundish, which was used instead of the round tundish, had been optimized. The results show that the residence time of the round tundish is short, its inclusion removal efficiency is too low, and it has more dead zones and an unreasonable flow field. Compared with the round tundish, the improved oval tundish with the optimized weir and dam has a better effect:its minimum residence time is prolonged by 38.1 s, the average residence time is prolonged by 233.4 s, its dead volume fraction decreases from 26% to 15%, and the ratio of plug volume fraction to dead volume fraction increases from 0.54 to 1.27. The inclusion removal efficiency also increases by 17.5%.     

Mathematical modeling of fluid flow,heat transfer and inclusion transport in a four strand tundish

Mathematical simulation was used for trouble-shooting and optimization. By the mathematical simulation, fluid flow and beat transfer of molten-steel in a four-strand tundish of a billet caster under different conditions (bare tundish and tundish with flow control device) were analyzed, The results showed that (1) the tundish with flow control device (FCD) has an important effect on the fluid pattern and temperature distribution; (2) the unsteady, solving method was used to model the inclusion motions at different time perthds, and it showed that the FCD is advantageous to separate the nonmetallic inclusions. According to the simulation results, the main problem existing in the industry preduction was found, and some helpful rneasurements were executed. Consequently, the large nonmetallic inclusions were separated, and the content of total oxygen was reduced. The qualily of steel was greatly improved.     

Inclusion’s Removel Mechanism in Liquid Steel of Continuous Casting Tundish

Three dimensional velocity distribution and turbulence energy dissipation of the steel in tundish are calculated. Then, the mathematical model of collision removal and flotation removal is established. In this collision mode,the rate constants of all types of collision are concluded, the change rate of inclusion number density is obtained.The quantitative calculation shows that it is violent turbulence at the inlet area of tundish and that collision is the main removal type to those inclusions with radius from 0 to 25μm.The collision of inclusions has two effect: one is to decrease the number of small inclusions, the other is to increase the number of big inclusions.To calculate the removal of inclusions, both collision and flotation should be considered. At last, the result of industrial experiment proves the collisien model is true.     

Application of Computational Fluid Dynamics to analysis of metallurgical process for continuous casting tundishes

A series of simulations by mathematical and physical modeling on fluid flow, mass and heat transfer in continuous casting tundishes have been carried out. It was found by computational fluid dynamics (CFD) simulation that in most cases tundish flow must be treated as a non-isothermal reactor due to the existence of temperature difference between the transport ladle and the tundish.The critical conditions when the non-isothermal flow in the tundish can not be neglected have been found by CFD simulation and water modeling. A direct measurement in a 40 t tundish has confirmed the simulation results.     

Modeling study on fluid flow and inclusion motion in 6-strand bloom caster tundishes

The behavior of fluid flow and particle motion in a 6-strand bloom caster tundish was investigated by a water model and numerical simulation. Compared with a device without flow control, the tundish with flow control has an important effect on the fluid flow pattern and inclusion removal. It is revealed that by non-isothermal process, which is real production condition, the fluid flow in tundish shows a strong buoyancy pattem, which drives particles to move upwards. The particle removal was quantitatively studied by mathematical and physical simulations.     

Large-eddy simulation of the compressible flow past a tabbed cylinder

The compressible flow past a tabbed cylinder has been studied numerically using large-eddy simulation for a free-stream Mach number M∞=0.75 and a Reynolds number based on the diameter Re=2×105. Because of the passive control of the flow past a tabbed cylinder, the mean drag coefficient of tabbed cylinder is less than that of a corresponding circular cylinder with a drag reduction up to 33%. The fluctuating lift coefficient is greatly suppressed to be nearly zero. Drag reduction due to the shearing process prevails over that due to the compressing process in this flow. Through investigating the mechanisms relevant to passive control of the tab, it is found that suppression of the shear layer instability can lead to a higher-base-pressure distribution, which can reasonably be associated with drag reduction and suppression of the lift fluctuations. The analysis of convective Mach number and self-sustained oscillations phenomenon inside the shear layers indicates that both the compressible effect and high-frequency forcing result in suppression of the shear layer instability of tabbed cylinder.