Wetting Line in High-Speed Free Jet Coating, 1999 Coating Conference Proceedings

John A. Roper III

Dow Chemical Company

Pekka Salminen & Robert Urscheler

Dow Europe S.A.

Douglas W. Bousfield

Paper Surface Science Program

Dept. of Chemical Engineering

The achievement of a steady wetting line between the free jet and moving paper web is needed for optimum operation of free jet coaters. Earlier work has demonstrated the influence of pump speed, jet angle, and coating speed on the jet stability. These results have been interpreted as due to a balance between the kinetic energy of the jet and the air pressure generated by the moving paper web. Our objective in this study was to further our understanding of the balance of these forces through the use of computational fluid dynamic (CFD) modeling of the jet applicator combined with pilot coater studies. As part of our pilot trials we wished to directly measure the position of the coating wetting line to determine the amount of deflection of the jet under different process conditions. We used a laser sensing device that was able to reproducibly determine the position of the jet within 0.1-0.2 millimeters. The effects of pump speed, jet angle, coating speed, coating solids, coating pigment, thickener, and base paper were investigated. Pump speed and jet angle had the largest influence on the deflection of jet position with deflections of up to 2-3 millimeters from the zero point. These measurements have been compared with the results of the CFD model. We found that the calculated deflections were of the same magnitude as the experimentally observed deflections. The effect of jet angle, however, was not as great in the calculated results.