Continuous hot-dip coating technologies

Abstract

The industrial production of hot dip galvanized steel started with naval parts in France in 1854, however, significant industrialization started only in 1938 when Tadeusz Sendzimir patented his continuous hot dip coating line. Since then, the industry is “galvanized” in the sense of fulfilling new industrial needs with higher quality products produced with less energy consumption and lower CO2 emission.
Most production lines are fundamentally designed for the incoming material group, meaning the structure of the continuous hot-dip galvanizing line depends on the production and processing technology of flat steel strips. Manufacturing lines therefore process hot-rolled and cold-rolled flat steel strips. These lines significantly differ from each other in the entry sections together with the cleaning sections in front of the furnace and in the through-pass heating furnaces. Different pickling, passivation, degreasing, heating, and reduction processes are required for cold-rolled and hot-rolled flat steel coils. Therefore, the main types of galvanizing lines are driven by the microstructural givens of the steel and the level of the upstream processing as well as the applied coating type. Table1 shows the different commercial groups of finished products for which the relevant production technology is determined. The composition of melting will develop a multi-strata coating based on a nanostructure of the intermetallic compound in between the substrate steel and the overlay formed in less than a second. The overlay is mostly a solid solution of Zn-Al, yet we can create even an intermetallic compound, binary and ternary eutectic-based overlay as well.
We can say that the hot-dip coating technology controls nano-scale processes so that to ensure a Giga-scale consistent product output. In this article, the structure of the main hot dip galvanizing lines will be discussed focusing only on the general introduction of the function of different machine sections.