2017 Volume 57 Issue 6 Pages 1087-1093
This paper presents a study of the gas wiping process, which is used in coating processes to control the final coating weight applied on a substrate. The wiping process is one of the factors which limit the maximum line speed of continuous galvanizing lines (CGL). In recent years, a multi-slot type wiping nozzle was proposed to improve gas wiping performance, and was investigated by numerical simulation. Here, the impinging jet characteristics of a 3-slot nozzle are investigated by experimental and numerical analysis, focusing on the mixing process of the jets and the distribution of the impinging pressure of the mixed jet. The gas wiping capability was tested in model wiping experiments with a molten paraffin coating. The results confirmed that the impinging pressure distribution of a 3-slot nozzle with a relatively low auxiliary jet velocity is sharper than that of a single-slot nozzle, and this makes it possible to reduce the coating weight. Conversely, when the jet velocity of the auxiliary slots approaches that of the main slot jet, the width of the impinging pressure distribution spreads and the coating weight increases. The turbulent kinetic energy of the flow field changes depending on the velocity of the auxiliary jets, and the energy distribution decides the width of the mixed jet flow.