Automatic Control System for Snout Positioning in Hot Dip Galvanization Process

Abstract

Steel is widely used in various applications due to its resistance to mechanical stress and its ductility, as well as having other important features such as weldability, paint adhesion, easy molding and recycling, low cost and ferromagnetic properties. With exposure to humidity and high temperatures, however, rust occurs on the steel surface, causing the material to deteriorate. There are various techniques used to protect steel against corrosion, including Hot-Dip Galvanization, which consists of heating a metallic steel sheet in an oven to approximately 600 °C followed by immersing the sheet in a kettle containing an alloy of molten aluminum, iron and zinc. A rectangular metallic structure, known as an electromechanical immersion tunnel (snout), is used for the transfer of the steel metal sheet from the oven to the bath. It is important to prevent the bath oxidation resulting from the contact of the bath with air (dross) because this phenomenon causes a defect visible in the metallic sheet. This can be minimized by controlling the position of the snout. In this study, a mathematical model was implemented to control the angular and linear position of the snout. The automatic reset mode is activated when the rear roller is replaced, while the automatic mode is always used when there are variations in the zinc bath level. The obtained results confirm the effectiveness of the positioning of the equipment showing a minimization of the time required for new adjustments. This proposal reduces the weight of the scrap generated by 27.54 % and 4.75 % for the formation of PGZN (zinc grains) and PBOR (dross), respectively.