Production of top skimmings in hot dip galvanizing

Abstract

Whereas skimming is a well-known by-product of hot dip galvanizing, it has never been deeply investigated, neither well accounted for, by galvanizers. Physical reasons justify that the proper units, for the operating costs of skimming, are g/m² or more generally weight per unit surface, instead of weight percentage of the loaded Zn. Indeed, with such a unit, results would largely depend on the average coating thickness. A stepwise regression analysis on skimming, produced daily on four industrial lines of Arcelor, shows that it is highly correlated to the line speed. Skimming costs will inherently increase with the line productivity for a defined thickness. The explanation of that fact is not fully clear because very low Zn oxide is found in the skimming which mainly consists of pure Zn. The wiping process is however suspected. Future work is required to try to establish a full modelling of the skimming production including Fe dissolution as well as the oxidation at wiping and the skimming practice.