An innovative evaluation technique for assessing metallic color matching performance in Electrostatic Rotary Bell Sprayers (ERBSs): a methodology based on droplet size distribution

Abstract Electrostatic Rotary Bell Sprayers (ERBSs) are pivotal in automotive painting, offering high efficiency and superior surface finishes through a dual-phase atomization process. Various factors significantly influence droplet size distributions, including rotational speed, paint rheology, and flow rate. Previous studies concluded that the geometry of the rotary cup also plays a critical role, as different designs can yield varied atomization outcomes. Rayleigh’s theory underpins the understanding of ligament formation and the conditions affecting droplet disintegration. Yet, it falls short of addressing the complexities introduced by colloids and particulate flakes in metallic paints. This is particularly important, as metallic flakes' density and orientation within paint droplets are critical for color appearance. In this paper, we provide a new framework to investigate the color-matching performance of various rotary cups using laser diffraction and droplet size analysis. Many studies previously used droplet size distributions and colorimetry to assess cup performance; however, in this study, an integrated approach is utilized to demonstrate how droplet size distribution data can be analyzed, post-processed, and used to predict the color-matching performance of various cups.