Influência da geometria da válvula submersa no escoamento do aço no molde de lingotamento contínuo e suas implicações na qualidade superficial de placas

Abstract

Consumers of the steel industry are continuously looking for steels with a high degree of cleanliness and excellent surface quality. To meet this demand, it is necessary that the production process develops controls that reduce or eliminate occurrences of surface defects. Many defects can be originated in the continuous casting stage, and some of these defects can be directly attributed to the inefficient control of steel flow conditions the mold, especially in the meniscus region. The flow at the meniscus region can be controlled by many parameters and operational conditions. One of the variables that significantly affect flow control in this region is the submerged entry nozzle geometry. In this work, the effects of shape and angle of the submerged entry nozzle outlet port on the steel flow in the continuous casting mold were measured using the experimental nail board, which provides information about direction and fluid velocity in the meniscus region, and through mathematical and physical modeling, to obtain the factor F, that brings an indicative of turbulence in the mold. Through evaluations of quality of the final product, it was identified that the submerged entry nozzle with oval outlet and angle of -15 ° presented lower indexes of occurrence of defects like powder inclusion and longitudinal crack. Surface velocity measurements using the experimental technique of nail board and factor F also indicated that the submerged entry nozzle with oval outlet presented the best flow, since the superficial velocities and factor F for the other nozzles were very low, with a tendency to vortex formation. Submerged entry nozzles with circular outlets and angles of -15° and -25° presented surface velocity values in the order of 0.17 and 0.20m/s respectively and factor F in the order of 1.0N/m. The valve with the best quality result (Oval outlet and angle of -15 °) presented surface velocity values in the order of 0.27m/s and factor F in the order of 3.8N/m respectively. Therefore, for the conditions tested, these are ideal values for the best flow condition and less defect formation in the final product.