Flow Visualization Studies in Scaled-Up Gravure Grooves and Cells

Gravure coating and printing are processes that are capable of producing thin coatings or fine patterns on substrates at high speeds by using a cylinder engraved with sub-millimeter scale grooves (for coating) or cells (for printing). A scaled-up groove and cell were built to study flow inside actual gravure grooves and cells during the emptying process. For the experiments with a scaled-up groove, a flat glass plate is passed horizontally over the groove under fully flooded conditions, and a large eddy is observed whose strength depends on the angle between the groove and the direction of the moving top. If the moving top is changed to glass with a convex curved surface, a recirculation is also obtained inside the groove when the top approaches the groove. Then, the recirculation becomes separated from the other fluid inside the groove and follows the top as it leaves the groove. For the experiments with a scaled-up cell, a glass top with a convex curved surface is passed horizontally over the cell. The results reveal that the larger the capillary number and the larger the thickness of liquid on the lands, the larger the amount of liquid remaining inside the cell after the moving top passes over the cell.