Bananas - defects in the jet stripping process

The problem of coating steel by passing it through a bath of molten alloy is considered. The thickness of the coating is determined by the operating conditions of the process, including the speed of travel, temperature of the sheeting and the air pressure and shear from the air knives that operate to strip off excess liquid alloy. During the process, on wider sheets and those with thicker coatings, there sometimes appear defects - known as bananas. These appear at the edges and curve upwards. These regions are almost completely devoid of any coating and hence are not suitable for sale. The group revisited previous work before considering several processes that may be relevant to the problem. These included a two-dimensional model allowing variation in air pressure across the sheet, a study of the backflow generated by the air knives and the Marangoni (surface tension) effect near the edge of the sheet.