Year

1997

Degree Name

Master of Engineering

Department

Department of Materials Engineering

Abstract

The requirement for high quality steel especially high steel cleanliness has increased in recent years due to the rapid development of new technologies such as thin strip casting and new products such as ultra low carbon steel for deep drawing quality, which require high steel cleanliness. This has led to the development of the role of the tundish to enhance the removal of inclusions from steel. Two mathematical models have been developed to investigate the effect of various operating parameters on the removal efficiency of inclusions in a tundish. The first model was applied to predict the removal efficiency of the particle in a tundish without gas injection. Both models assumed that the fluid flow in the tundish consists of three regions; plug flow , mixed flow and dead flow region. In the plug flow region of flrst model, it was assumed that the removal efficiency of the particle was governed by Stoke rising velocity. The removal of partide in the mixed flow region was assunried to follow the kinetics of the flrst-order law. The dead region was not involved in the partide transfer process. The second model was devebped to predwt the rennoval effidency of particles in a tundish bubbled by gas. The transfer process of partk^le in the plug and dead flow region were assumed similar to the first model. In the mixing region, it was assumed that the removal of particles mainly occurs due to the adhesion of indusion to bubbles. The flotation rate of the partide therefore was assumed to be governed by collision efficiency between particles and bubbles. Cold model experiments were carried out to validate the proposed mathematical models. It was found that, the results from the first mathematical model were in good agreement with the results obtained from cold model experiments for a tundish without gas injection. Both mathematical and cold model experimental results showed that the efficiencies of particle removal in a tundish slightly increased with increasing fluid depth and decreased with increasing casting rate. It was also found that the removal efficiency of the particles was greatly dependent on the particle size. As predicted by the mathematicat model for removal of particles in a tundish bubbled by gas, the renrwival efficiency of partides in tfie tundish increased with increasing gas flow rates injected in tundish. Cold nrKXiel experiments showed the similar pattern wifri this mathematical prediction. Cold model experiments also indicated that at high gas flow rate the removal of particles decreased t)ecause of the reentrainment of the particles.

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