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Title: Modelling shell and oscillation mark formation during continuous casting via explicit incorporation of slag infiltration
Author: Ramirez Lopez, Pavel Ernesto
ISNI:       0000 0004 2682 3566
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2010
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The development of reliable numerical models is vital to improve the quality of continuously cast products and to increase the productivity of the casting machine. In order to provide accurate predictions, these models must include detailed descriptions of the physical phenomena occurring inside the mould, such as metal flow, heat transfer and solidification. However, these topics are often treated separately during modelling due to their complexity. This has a negative impact on the accuracy of the predictions. To address this issue, a numerical model capable of coupling the flow dynamics with both the heat transfer to the mould walls and solidification has been developed. The 2‐dimenional model is based on a commercial CFD code that solves the Navier‐Stokes Equations coupled with a Volume of Fluid interface tracking technique for the multiphase system slag‐steel‐air under transient conditions within a conventional slab mould. The use of an extremely fine mesh in the meniscus region (~50 μm) allows, for the first time, the explicit calculation of liquid slag infiltration into the shell‐mould gap. Heat transfer through the solid mould faces and mould oscillation were also included in the model to provide a more realistic representation of the process. The model developed was tested in two case studies. In the first case, the predicted values were compared to prior numerical models and laboratory experiments directed to casting of conventional slabs. Excellent agreement was found for characteristics such as slag film development and heat flux variations during mould oscillation. Furthermore, predicted values for shell thickness, consumption and heat flux were also found to be in good agreement with plant measurements. The findings of this case study provided improved, fundamental understanding of the mechanisms involved in slag infiltration and solidification inside the mould and how these affect key process parameters, such as powder consumption and shell growth. The second case study consisted of a sensitivity study, where casting conditions (e.g. casting speed, mould cooling, steel/slag properties and oscillation settings) were varied in the simulations to determine their effect on both powder consumption and the formation of defects. The simulations predicted the initial formation of typical casting defects known as oscillation marks, without the aid of any external data fitting. The key result drawn from the sensitivity study was the determination of simple rules for the calculation of consumption, heat flux and defect formation as a function of the casting conditions. This opens the possibility of using the model as a diagnostic tool and for process optimisation.
Supervisor: Lee, Peter Sponsor: CONACYT ; SEP ; FIDERH ; CORUS ; EPSRC
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral