Estimates for the pressure and thermal distortions of coating dies for use in design and simulation.

摘要

A coating die is used for distributing liquid in order to apply a uniform film on a solid surface. The fluid flowing through the die cavity can exert a pressure of up to 500,000 Pascal on the die body. This liquid pressure can distort the die and lead to a non-uniform slot opening, which in turn causes non-uniformity in the coating thickness. Distortion of the die can also occur during non-isothermal operation of the die; this is an undesired consequence of delivering liquids at a different temperature than the die itself. The distortions undergone by the die both due to liquid pressure and non-isothermal conditions should be within the manufacturing tolerances for the slot heights in order to maintain uniformity in the coating.;The deformation exhibited by a coating die due to pressure loadings is modeled both two-dimensionally and three-dimensionally. A two-dimensional model has lower computational load and is preferred for die design. For the two-dimensional analysis of a coating die, the finite element method is used to determine the deflections due to pressure loadings with a focus on slot heights. A model of low computational load is also developed based on beam theory, and its results are compared with those of the two-dimensional finite element analyses predictions. The beam model is incorporated in a die design and simulation program in which flow and slot deformations are coupled. Two-dimensional finite element analyses due to non-isothermal conditions are also performed on the coating die to give an estimate of the die deflection due to temperature variations within the die. A three-dimensional coating die with varying inner cavity area is modeled and analyzed to check its predictions with those of the two-dimensional finite element analyses and beam theory results.;In the literature reviewed, flow distribution is fully coupled to die deformation only for extrusion dies. Extrusion dies are used for extruding melted polymers of very high viscosity. Therefore, the deflections are much larger for extrusion dies than for coating dies. Mechanical adjustments can be used to manage the large deflections in the case of extrusion dies whereas coating dies have to be designed for small deflections comparable to manufacturing tolerances. This is the first time where a coupled analysis has been done for a coating die. This research provides the slot deflections for a coating die subjected to pressure loadings that vary throughout the die length. The model of flow distribution coupled with die distortion incurs low computational load and is intended for use in design and simulation programs. Die design guidelines are developed based on examination of the die dimensions and flow parameters having the greatest effect on slot deflections.