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.

CFD analysis of blade coating from a reservoir onto a horizontal substrate using a homogeneous two‐phase model

“…The performance of the present model is demonstrated through comparisons with two earlier studies. [21,22] Both these studies used a FEM approach to solve a singlephase free surface flow problem. The solution domains used in the present work match those in Schmidt et al [21] and Mitsoulis and Athanasopoulos [22] except for the addition of regions where the air above the free surface is modelled.…”

“…In the area of numerical modelling of blade coating, many studies are based on a single-phase liquid model with a free surface and solved using a finite element method (FEM) with commercial or in-house codes. [7,[13][14][15][16][17][18][19][20][21][22][23] Many of those studies used non-Newtonian fluid properties. [13,[15][16][17][18][20][21][22][23] Some studied the effect of blade shape.…”

“…[7,[13][14][15][16][17][18][19][20][21][22][23] Many of those studies used non-Newtonian fluid properties. [13,[15][16][17][18][20][21][22][23] Some studied the effect of blade shape. [15,17,20,22,23] Others included models for particle motion within the coating, [19,20] accounted for blade displacement, [15,20,23] or included substrate deformation and elasticity.…”

“…[15,17,20,22,23] Others included models for particle motion within the coating, [19,20] accounted for blade displacement, [15,20,23] or included substrate deformation and elasticity. [23,24] In the FEMbased studies listed, two works [20,21] describe the specification of the contact angle (the angle between the free surface tangent and the blade surface). One FEM-based study coupled shell theory and lubrication flow theory.…”

Computational fluid dynamics (CFD) and its application to textile technology

“…The CFD model can hence be used to optimize the mixing tank design for this process. Schmidt et al (2009) analysed the commonly used blade coating process with a CFD simulation. One of the main findings was that pressure decreased with viscosity in the coating material in the area underneath the blade's edge.…”