New Wiping Techniques to Efficiently Produce Suitable Coating Layers: at High Speed in the Hot Dip Galvanising Process

The objective of this project was to find an innovative way to efficiently wipe suitable coating layers at high speed in the hot dip galvanising process. Three technical fields were examined with the support of numerical modelling, with the aim of an industrial scale trial. Contrary to our first thoughts, no thinner gauges could be obtained if the drag-out is lower: laboratory trials have shown that pre-wiping is worthless because of the natural ability of the strip to drag liquid out of the bath. First, a pilot line trial at CRM presented the hydrodynamic foil wiping technique as an interesting solution for high speed galvanising. Second, a rotating permanent magnets' approach, adjacent to the bath level, was analysed and evaluated in a small laboratory scale trial. Third, an electromagnetic technique was tested on CRM's pilot line where both wiping efficiency and finish quality have to be improved. Also a strong disturbance force, normal to the strip's plane, demands stabilisation developments. In the numerical field, a wiping model was developed and adapted for each technique with some limitations.