Development of a Hydraulic Shroud Nozzle Manipulator with Robust Force Control in Continuous Casting Process

Abstract

The shroud nozzle is used to transport the molten steel from the ladle to the tundish in the continuous casting process. A hydraulic manipulator transfers the shroud nozzle and connects it to the collector nozzle installed on the bottom of the ladle. During the nozzle connection, however, the misalignment between the shroud nozzle and the collector nozzle frequently occurs due to the initial position error of the ladle, unexpected external forces on the nozzle, etc. In case the nozzle is not aligned properly, there is air-inflow into the molten steel through the crevice, and this results in the defect of steel products by oxidation. In addition, if the nozzle tightening force is not enough to hold the shroud nozzle while the molten steel flows into the nozzle, the nozzle vibration occurs by the irregular flow of the molten steel and it gives rise to another air-inflow to the molten steel. POSCO currently uses the remote operated manipulator for the shroud nozzle manipulation, but this cannot measure and control a fine nozzle alignment appropriately. In this paper, we designed and controlled a novel 5-DOF hydraulic manipulator to solve the nozzle misalignment problem. Each joint of the manipulator contains a torque sensor which enables to detect the external forces exerted to the shroud nozzle, and this is utilized to measure the misalignment. Moreover, the nozzle misalignment can be adjusted in real-time by the proposed force integral controller using joint torque sensors.