Technological features of continuous lines for hot-dip galvanizing of a steel strip

The article describes technological features of a continuous hot-dip galvanized steel strip used in domestic enterprises. Basic technological operations of the galvanizing process are discussed, such as preparation of the strip surface, its thermochemical treatment, melt galvanizing, formation of the coating with air knives, cooling of the strip after galvanizing, editing and finishing of the galvanized strip. It is shown that furnaces of both vertical and horizontal types are installed in new units. Advantages and disadvantages of vertical-type furnaces compared with the horizontal ones are considered. It is shown that the peculiar feature and the advantage of modern units of hot-dip galvanizing is a continuous modular design that allows to produce a strip with different types of coatings at one unit. The use of various types of zinc coatings can improve technological and operational properties of the galvanized sheet. Chemical compositions and application fields of the four most common zinc-based coatings, namely zinc, zinc-iron, zinc-aluminum and aluminum-zinc compound are analysed. It is stated that on modern lines of hot dip the galvanizing coating is applied to the strip on both sides. However, currently, technologies of one-sided zinc coating on a steel strip are developed, the application of which will reduce the consumption of expensive zinc, and consequently, the cost of the finished product. Some promising methods and equipment for unilateral galvanizing are shown and described.