Cold model study on inclusion removal from liquid steel using fine gas bubbles

A water model study was undertaken to investigate inclusion removal from liquid steel using fine gas bubbles, which were created by injecting air into a shroud nozzle just underneath the slide gate. The water flow rate was varied in the range of 2.0-3.2 m(3) hr(-1), which is equivalent to 1.77-2.83 m s(-1) of the linear velocity at the exit of the shroud nozzle. The ratio of gas to liquid flow rates was varied in the range of 0-12 % by volume. Polyethylene, PVC and ABS particles were used to imitate the inclusion. The characteristics of the bubble formation varied with the gas inlet position along the shroud: the closer the slide gate, the better the mixing between the gas and liquid phases. This was dependent on the slide gate opening: the smaller the opening, the more turbulence and hence the better mixing of the gas and the liquid. The relative removal efficiency was fairly independent of such variables as liquid flow rate, i.e., linear velocity, the slide gate opening (up to 58 % by area), and inclusion concentration. However, this was greatly affected by the wettability, i.e., contact angle of the inclusion with the liquid: the larger the contact angle, the higher the efficiency. It is concluded that the governing factor which determines the removal efficiency of the inclusion from liquid steel is the wettability of the inclusion with the steel, and the idea proposed in the present study should be an effective means for production of clean steels.