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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. Multi-slot type gas wiping nozzle was proposed for improving coating weight controllability, and investigated using numerical simulations recent years. We made two types of 3-slot wiping nozzle and measured 2-dimentional free-jet characteristics with a hot-wire anemometer. Then, gas wiping model experiments with paraffin wax coating were carried out. We found that a gap between main and auxiliary slot has significant effect on the jet stream characteristics. Although each slot gas pressure conditions were the same, velocity distribution of the jet becomes sharp if the gap is narrow. The coating thickness after 3-slot gas wiping decreased with a sharp pressure gradient of the jet.

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.

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