Experimental Analysis on Coating Weight Controllability of a Multi-slot Gas Wiping Nozzle

Abstract

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.

Jet Flow Characteristics of 3-Slot Nozzle in Gas Wiping Process at Continuous Galvanizing Line

“…A previous study 9) by some of the same authors indicated that the distance between the main slot and the auxiliary slots has a remarkable influence on the formation of the jets after the three jets merge. In particular, wiping performance was improved by shortening the distance between the main slot and the auxiliary slots.…”

“…Although the simulation results indicated that the maximum impinging pressure of the 3-slot nozzle is higher than that of the 1-slot nozzle, the coating weight after wiping with the 3-slot nozzle was thicker than that after the 1-slot nozzle. Takeda et al 9) first investigated the jet flow characteristics and wiping performance of 3-slot nozzles in an experimental analysis with a paraffin wiping apparatus. The results showed that the jet formation after mixing of the three jets changes depending on the shape of the nozzle tips, and as a result, wiping performance might improve or deteriorate, depending on the nozzle design.…”

“…The impinging pressure distribution was measured under several pressure conditions using the 3-slot nozzle used in the previous studies, [9][10][11] and wiping performance was examined by using the same model wiping apparatus as in the previous studies. In addition, the process of jet formation with the 3-slot nozzle was analyzed in detail by computational fluid dynamics (CFD).…”