Prediction of fiber coating thickness via liquid-phase process

Two kinds of fiber coating processes, free coating and obstructed coating, are investigated theoretically and experimentally. In the free coating process, the entrainment of Newtonian liquid film onto a vertical fiber, which is continuously withdrawn from a coating liquid bath, is considered. A dimensionless analysis is applied to identify dimensionless groups governing the system in this process and the coating thickness is determined by two dimensionless parameters, Capillary number and Goucher number, and the fiber radius. The obstructed coating mechanism is studied numerically. The shear rate acting on the fiber surface is proportional to the fiber draw speed in an unpressurized applicator and can be minimized in a pressurized applicator through the applied external pressure. The calculated results were compared with the experimental data in the obstructed coating process and a good agreement was obtained.