Computational Fluid Dynamics Investigation of the Static Pressure at the Blade in a Blade Coating Process

Abstract

The process of coating textiles with a blade coater has been investigated with CFD (Computational Fluid Dynamics) software. The simulations have uncovered a pressure drop in the area between the edge of the knife and the textile. This drop can be explained by the varying height of the flow channel which is made of the knife and the textile in conjunction with the no slip condition that is applied to the walls. In the simulations this drop became arbitrarily deep with increasing viscosity leading to negative absolute pressure levels. This may be a hint that the no slip condition is not valid in this scenario that involves shear rates of the order of 103/s and dynamic viscosities of around 10 to 100Pas. With a proposed slip condition for the textile the pressure drop became less pronounced. At the same time the flow rate through the gap between knife and textile was reduced leading to a thinner coating. This can be a hint that a slip between coating material and textile can cause distortions in the coating up to a complete disruption which is reported frequently by the industry. This could eventually be avoided by reducing the varying height of the flow channel. Alternatively a vertical lift of the textile due to the negative pressure was taken into account. This lift appeared only with low tensions of the textile of about 1N/m and showed no influence on coating thickness and pressure drop.

Keywords

CFD simulation coating process no-slip condition processing rheology

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