Experimental Evaluation of the Forces in Bevelled Blade Coating, 1994 Coating Conference Proceedings

N. Triantafillopoulos, N. Altug

Previous analyses of bevelled blade coating have considered many different forces that act on the blade and affect coat weight. These forces include (a) the hydrodynamic lubrication lift, either under the blade surface or in the blade nip, (b) the impulse force arising from the coating layer striking the blade, and (c) the lateral force acting along the direction of web movement. The objective of this work was to determine experimentally the total dynamic force (TDFe) acting on the blade and compare it with the magnitude of each of the analytical forces listed above. The TDFe was determined at three different web speeds up to 300 m/min in a pilot coater with an applicator roll. This study demonstrated that coat weight development in bevelled blade coating is controlled mainly by the impulse force and, secondarily, by the hydrodynamic lift. If one only considered the lubrication flow in the blade nip by itself, hydrodynamic lift could not account for the whole TDFe, i.e., it was less than 47% of the TDFe. Results indicated that the impulse force was responsible for about 90% of the TDFe, its contribution increasing with web speed. The remaining 10% was accounted for by the lateral force and the hydrodynamic lift acting on the surface of the blade upstream of the blade nip. Within the speed range studied, the lateral force at the blade nip represented approximately 4 to 8 percent of the TDFe. The “pressure” force, originally included in the impulse model, should be omitted from calculations of the impulse force.