Measuring Paint Droplet Size, Velocity, and Charge-to-Mass Ratio Distribution for Electrostatic Rotary Bell Spray Simulation

Abstract

High-speed electrostatic rotary bells are widely used in the automotive industry as they provide high quality paint films with better transfer efficiency compared to air-atomizing guns. However, due to its highly turbulent spray pattern, transfer efficiency is still not ideal, i.e. some portion of paint will not reach intended target surfaces and becomes overspray. Numerical simulation of the electrostatic spraying process provides a tool to model this process as well as a way to optimize transfer efficiency. Currently, the state-of-the-art simulation model can simulate the flying trajectories of paint droplets from the edge of the rotating bell cup to the target surfaces. It requires some input information to start the simulation. The input information includes paint droplet size, velocity, and charge-to-mass ratio. Due to its large number of droplets, distributions based on droplet diameters are used to represent the entire droplet population. This paper describes experimental and mathematical methods to measure and calculate paint droplet size, velocity, and charge-to-mass ratio distributions. The resulting information can then be organized and used as the input data files for Electrostatic spray painting simulation.