The Ink Metering Process with Two Counterrotating Rollers - Simulation and Experiment.

A two roller inking unit is presented. The ink is separated, accelerated and metered at one single nip. The focus is put on the simulation of the metering process and on its experimental verification. A finite-element analysis (FEA) is applied to simulate the ink flow. The rollers are modeled as rigid rollers, counterrotating with various speed differentials. The material properties of the ink are characterized by the density, the surface tension and the viscosity. Here the power-law model is applied to express the viscosity. The values used are taken from measurements with a conventional sheetfed offset ink. The simulations deliver an inverse dependence of the metered inkfilm thickness ratio from the roller's speed ratio. These results could be verified by experimental data retrieved from a self designed metering device. Further aspects of the FEA, especially concerning the surface tension, are discussed as well as the quality of the metered ink film (smoothness, ribbing). Methods of introducing a rubber roller into the simulation are offered. All in all it is shown that commercial software applying FEA can be used to predict the metering behavior of the two-roller unit and that it can be incorporated into the design process of an inking unit.