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Slag carry-over during the draining of molten steel from a teeming ladle is numerically studied here. Two-phase isothermal transient 3D Computational Fluid Dynamics simulations were employed to simulate the draining process. Two nozzle diameters, two nozzle positions and three slag heights were considered. From mass balances, the slag carry-over in terms of mass flow rate was obtained for each of the above variables. Besides, the draining times of the teeming ladle were estimated from theoretical considerations and CDF simulations, and compared.

Slag carry-over during draining of molten steel from teeming ladles is an important industrial issue given it affects the quality of the solid steel. Main problems of slag carry-over are [

Tapping of molten steel without slag carry-over is a difficult task due to the formation of a draining vortex [

In this work, the slag carry-over during molten steel draining from a teeming ladle (see

The flow of an isothermal incompressible Newtonian fluid and the mass conservation are represented by the Navier-Stokes equations and the continuity equation,

respectively [

A mass balance in the teeming ladle yields the following expression, which tracks the time evolution of the molten steel height:

h m s ( t ) = h m s 0 − ( 1 2 ( D 1 D 2 ) 2 C D 2 g ) t (1)

where h_{ms}_{0} is the initial height of molten steel, C_{D} is the nozzle discharge coefficient, g is gravity, and t is time.

On the other hand, the teeming ladle becomes empty when the molten steel height and the slag height become null. In this case, the draining time from Equation (1) is given by:

t d = 2 h m s 0 + h s ( D 1 D 2 ) 2 C D 2 g (2)

A cylindrical teeming ladle in which D_{2} = D_{3} (see

NAME | SYMBOL | VALUE |
---|---|---|

Ladle diameter | D_{2 } | 3.0 m |

Nozzle diameter | D_{1 } | 0.05, 0.1 m |

Nozzle discharge coefficient | C_{D } | 1.0 (dimensionless) |

Initial molten steel height | h_{ms}_{0 } | 0.75 m |

Slag height | h_{s}_{ } | 0.1, 0.15, 0.2 m |

Molten steel density | ρ_{ms}_{ } | 7100 kg∙m^{−3 } |

Slag density | ρ_{s} | 2500 kg∙m^{−3} |

and 1295 s of elapsed time for slag heights of 0.2, 0.15 and 0.10 m, respectively. Besides, for the centered position of the nozzle (

On the other hand,

Related to the mass flow rate of slag from the ladle for the 0.1 m diameter centered nozzle,

Slag layer thickness (m) | Draining time (s), Equation (2) | Draining time (s) for centered position, CFD simulations | Draining time (s) for off-centered position, CFD simulations |
---|---|---|---|

0.10 | 1498.6 | 1470.0 | 1480.0 |

0.15 | 1542.1 | 1520.0 | 1526.0 |

0.20 | 1584.3 | 1570.0 | 1570.0 |

Slag layer thickness (m) | Draining time (s), Equation (2) | Draining time (s) for centered position, CFD simulations | Draining time (s) for off-centered position, CFD simulations |
---|---|---|---|

0.10 | 374.7 | 372.0 | 376.0 |

0.15 | 385.5 | 378.0 | 382.0 |

0.20 | 396.1 | 390.0 | 390.0 |

of 0.15 - 0.20 and 0.1 m, respectively. For the 0.1 m diameter off-centered nozzle,

Finally, the draining times were determined from Equation (2) and from CFD computer simulations, considering a molten steel height of 0.75 m and a nozzle discharge coefficient of 1.0. These draining times are shown in

The slag carry-over from a teeming ladle was numerically studied. Two nozzle diameters, two nozzle positions and three slag heights were considered in the 3D transient isothermal CFD computer simulations. The following conclusions arise:

1) Slag carry-over in terms of mass flow rate is significantly increased as the nozzle diameter is increased.

2) Starting time of slag carry-over increases as the slag height decreases.

3) Mass flow rate of slag is slightly larger for the nozzle centered position than that corresponding to the off-centered position.

4) Draining time depends inversely on the nozzle diameter. As the nozzle diameter is increased, the draining time is decreased.

Flores-Sanchez, D. and Barron, M.A. (2017) Numerical Analysis of Slag Carry-Over during Molten Steel Draining. Open Journal of Applied Sciences, 7, 611-616. https://doi.org/10.4236/ojapps.2017.711044