Comparison of Electrostatic Fine Powder Coating and Coarse Powder Coating byNumerical Simulations

摘要

Powder coating has several key advantages over liquid coating and fine powder coatingmakes the surface finish quality comparable with liquid coating. This work reports on thenumerical simulation of fine powder coating process in comparison with coarse powdercoating, using a commercial computational fluid dynamic code, FLUENT v6.1. The purpose ofthe study is to understand the gas and particle flow fields inside the coating booth for variousoperating conditions and the effect of reducing particle size on the coating process. The airand powder particle flows in a coating booth were modeled as a three-dimensional turbulentcontinuous gas flow with solid particles as a discrete phase. The continuous gas flow wascalculated by solving Navier-Stokes equations including the standard k-ε turbulence modelwith non-equilibrium wall function and the discrete phase is modeled based on the Lagrangianapproach. In addition to drag force and gravity, the electrostatic force including the effect ofspace charge due to the free ions was considered in the equation of motion and implementedusing user defined scalars and user defined functions. The governing equations were solvedusing second order upwind scheme. This study demonstrates that the use of finer particles ofsize 15 μm or lower can give very smooth and uniform surface finish, which may serve therequirement of automotive top clear coat. This also provides useful information about optimumoperating conditions such as the airflow rate, the applied external voltage and the powdersprayrate. The numerical model can also be used to optimize the gun-booth design for abetter coating efficiency.