Powder coating process parameters for a transfer efficiency model

The trajectories of charged powder particles in a powder coating system are governed by the electrostatic, gravitational and aerodynamic forces acting on the particles. A mathematical model of particle trajectories inside a powder coating booth must consider (1) the aerodynamic flow field, (2) particle size and charge distributions, (3) the electrostatic field distribution, and (4)the geometry of the target. Our approach is to employ a grid generation and flow solver to examine the air flow pattern and an iterative technique where the Charge Simulation Method can be used to compute the electric field strength and the Method of Characteristics can be used to compute the charge density in the gun-to-target region. The electrostatic forces due to the deposited powder layer and image charge are to be taken into account to determine if the particle will deposit on the substrate or not. The model is applied to the geometry of a high-voltage electrode consisting of a long thin rod with a hemispherical end cap and a grounded flat disk substrate. An experimental system to measure transfer efficiency, with the ability to control various parameters effecting transfer efficiency, has been developed to verify the theoretical model. The simulation results can provide valuable information concerning particle deposition and optimization of transfer efficiency. This paper describes (1) system parameters involved in modeling the transfer efficiency, (2) an approach to develop such a model with preliminary data on the simulation of particle track, and (3) experimental data on the real-time measurements of first pass transfer efficiency.