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A study of mold flux entrapment and gas entrainment in an ingot casting process

Time: Wed 2021-06-09 14.00

Location:, Stockholm (English)

Subject area: Metallurgical process science Materials Science and Engineering

Doctoral student: Jun Yin , Materialvetenskap

Opponent: Professor Yogeshwar Sahai,, Ohio State University, USA

Supervisor: Mikael Ersson, Materialvetenskap; Pär Jönsson, Processer

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The focus of this work is to study the gas entrainment and mold flux entrapments during the ingot filling process based on physical and numerical modelling.

The formation of the free surface was investigated in the uphill teeming method, which illustrates a dynamic change at a quasi-steady state. The influence of several turbulent models on the result was studied. The Reynolds stress turbulence model predictions show a good agreement to the experimental result compared to predictions using k-ԑ based turbulence models. It was found that the Weber number at the free surface is smaller than 12.3, when the inlet velocity is 0.5 m·s-1. This indicates a minor chance for mold flux entrapments, based on previously reported results. 

In order to reach a calm free surface using an even high inlet velocity, the side teeming process is proposed. A rotational flow field was found to be generated in the side teeming process, due to the horizontal teeming of the molten steel. A vortex cannot be found in the side teeming process because of the weak strength of the swirling flow. However, surface disturbances can be seen close to the wall of the mold, but they are small and vanish at lower teeming velocities.

An optimization of the filling angles in the side teeming process was studied to reduce and eliminate the surface disturbances at the edge of the mold. The result showed that the 90 degrees filling angle results in a calm free surface without surface disturbances. Therefore, this design is recommended to use in the ingot casting process.

The trumpet was also studied in this work to better understand the gas entrainment phenomenon. Water model experiments were carried out to measure the gas entrainment rate during a quasi-steady. Numerical simulations were performed and the results showed a good agreement to the experimental results. The formation of a big bubble was observed at the bend, which is due to the generation of a low-pressure region. Finally, an angled runner design was constructed to ease the gas entrainment rate. The results showed that the 30-degree angled runner can result in less entrained gas in the horizontal runner and lower hump height compared to the traditional design.