Development of a bench-scale liquid metal wiping pilot system for understanding and optimizing the jet wiping process during hot dip galvanizing

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In the case of hot-dip galvanizing, a continuously-moving steel strip is coated with a thin layer of zinc in orderto resist to oxidization. The protective metal is applied in its liquid state, by dipping the substrate into a bath ofcoating. However, at common strip speeds, the liquid layer dragged by the moving web is far too thick anduneven for the applications considered. The final coating thickness is therefore controlled by an air knife,which impinges a two-dimensional high-speed gas jet on the liquid layer. The forces imposed in the liquid bythe air knife jet results in the formation of a runback flow down to the bath, leaving a more uniform andconstant coating thickness dowsntream on the substrate. Nevertheless, operational constraints and processparameter variation can still result in significant coating non-uniformity and excess zinc consumption. Thisresearch program will focus on developing a bench scale galvanizing pilot where a low melting point liquidmetal will be used as an analogue to zinc and a rotating belt arrangement will be combined with an air knife tovisualize the jet wiping process in more detail. State of the art imaging techniques developed at the applicant'slaboratory will be used to visualize the wiping process, coating waviness and solution strategies will beproposed for optimizing the wiping system in terms of process parameters and air knife design. With manyexisting problems at the hot dip galvanizing lines it is difficult to meet the market demands. The results of thisproject are expected to help galvanized strip producers like AM Dofasco to determine, and control theoptimum coating properties that will allow them obtaining the highest productivity and simultaneously achievehigh quality strips with desired product quality. Proper understanding of the jet wiping process and itsinfluence on galvanized product quality has profound impacts on the commercial aspects of hot dipgalvanizing. Based on the current interests in this process optimization, and enhanced productivity (expressedby AM Dofasco hot dip galvanizing lines), an economic impact of $6 million /year is expected from the resultsof this research, which translates to $30 million within five years after completion of this project