Reduction of dross in galvanized sheets through automatic control of snout positioning in continuous operation

Abstract

Hot-dip galvanizing is a common industrial process in which sheet steel is immersed in a molten zinc alloy bath. After solidification, a thin zinc-rich layer is formed on the steel surface, which protects the substrate in corrosive environments. A rectangular metallic structure known as a snout is used for the transfer of the steel sheet from the furnace to the bath. In this study, an automatic control is implemented for the angular and linear position of the snout aiming to reduce surface defects in sheets (zinc grain) due to top and bottom dross. A mathematical model is developed for set point calculations, and on–off controllers are used and tested for industrial continuous operation. The results confirm the effectiveness of the positioning of the equipment enabling reduction of the transition time from around 5 min to a few seconds, resulting in a 24.57 % reduction in non-conformances due to zinc grains and 4.56 % reduction in non-conformances due to dross in the processed materials.