Coating Weight Reduction Technology in Gas Wiping of Hot-Dip Galvanizing on Steel Strip

Abstract

In the gas wiping process used in hot-dip galvanizing, the coating thickness has two thinning limits. The first is the limit due to splashing of the liquid film of molten zinc, and the second is the thinning limit of the wiping capacity of the equipment.

In this study, we investigated the possibility that wiping efficiency is reduced by the effect of zinc solidification due to gas jet cooling by conducting a gas wiping experiment under various temperature conditions.

A galvanized steel strip with a width of 100 mm was immersed in a molten zinc bath in the air atmosphere. The steel strip was heated by induction heating or a gas burner, and the wiping gas was also heated.

The results clarified the fact that high temperature conditions improved gas wiping efficiency. It is suggested that high wiping efficiency is prevented by an increase in viscosity due to an increasing solid volume fraction in the liquid zinc film surface caused by microscopic solidification. In addition, it was also found that the development of the initial alloy layer reduced the amount of liquid phase, which inhibits wiping.