Modeling of inclusion removal in a tundish

Abstract

Mathematical models have been developed to predict the removal of alumina inclusions from molten steel in a continuous casting tundish, including the effects of turbulent collisions, reoxidation, flotation, and removal on the inclusion size distribution. The trajectories of inclusion particles are tracked through the three-dimensional (3-D) flow distribution, which was calculated with the K-ε turbulence model and includes thermal buoyancy forces based on the coupled temperature distribution. The predicted distributions are most consistent with measurements if reoxidation is assumed to increase the number of small inclusions, collision agglomeration is accounted for, and inclusion removal rates are based on particle trajectories tracked through a non-isothermal 3-D flow pattern including Stokes flotation based on a cluster density of 5,000 kg/m 3 , and random motion due to turbulence. Steel samples should be taken from as deep as possible in the tundish near the outlet and several residence times after the ladle is opened, in order to best measure the Al 2 O 3 concentration entering the submerged entry nozzle to the mold. Inclusion removal rates vary greatly with size and with the presence of a protective slag cover to prevent reoxidation. The random motion of inclusions due to turbulence improves the relatively slow flotation of small inclusions to the top surface flux layer. However, it also promotes collisions, which slows down the relatively fast net removal rates of large inclusions. For the conditions modeled, the flow pattern reaches steady state soon after a new ladle opens, but the temperature and inclusion distributions continue to evolve even after 1.3 residence times. The removal of inclusions does not appear to depend on the tundish aspect ratio for the conditions and assumptions modeled. It is hoped that this work will inspire future measurements and the development of more comprehensive models of inclusion removal.These validated models should serve as powerful quantitative tools to predict and optimize inclusion removal during molten steel processing, leading to higher quality steel.

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

“…For the inclusion motion in tundish, studies have been carried out to investigate the inclusion removal under the effects of various factors such as flow control devices, tundish geometries, gas bubbling rates, and inclusion sizes. [1][2][3][4][5][6][7][8] After inclusions move from the tundish into the SEN, their deposition on the SEN wall can lead to nozzle clogging. In order to understand the deposition location and mechanism, computational fluid dynamics (CFD) studies have been carried out to investigate the inclusion transport in turbulent steel flows and its deposition on the SEN walls.…”

State of the art in the control of inclusions during steel ingot casting

“…[25,26] The fundamentals of alumina sintering into clusters [30,68,207] need further investigation, though fractal theory has been used to describe the cluster morphology (features). [208,209] Inclusion agglomeration can cause clogging problems in both nozzles and ingot runners. An example is shown in Figures 37(a) [17] and (b) [18] of alumina inclusions clogging a submerged entry nozzle in continuous casting.…”

Numerical Simulation of the Molten Steel Flow in the Tundish of CSC Machine / Symulacja Numeryczna Przepływu Ciekłej Stali W Kadzi Pośredniej Urządzenia COS

“…Flow in the tundish is also greatly affected by the ladle-tundish nozzle geometry and gas in the ladle stream. Problems related to surface turbulence can be reduced by avoiding excessive argon levels in the ladle stream and by using fully-shrouded and immersed nozzles [2,4].…”

“…If the liquid level is too shallow, high-speed, asymmetric flow may produce vortexing, which can entrain surface slag down into the mould. Generally summarize, for the designing of a tundish arrangement, it is necessary to look for the highest plug flow volume fraction with a minimum dead volume and perfect mixing zones [4,5]. An important mechanism for inclusion elimination from liquid steel is that of simple flotation, whereby the particle is separated if it rises as the result of its buoyancy to contact the slag and is then absorbed by the slag.…”