The effects of basecoat bell application parameters on elements of appearance for an automotive coatings process

This research investigated the effects of basecoat (BC) bell application parameters on the appearance of automotive vehicles. A full factorial two-level DOE matrix was created to test the impact of four BC bell zone variables on appearance: flow rate, shaping air, voltage, and bell speed. Paint age was a covariate in the analysis. Panels were sprayed with waterborne BC followed by solventborne clearcoat and cured vertically at 144°C. The appearance was characterized by measuring the DOI, surface waviness, and multiangle color. Flow rate, bell speed, and shaping air were found to have the most impact on surface waviness. In addition, four interactive effects were also found to be significant. Three of these interactive effects included flow rate in combination with the other parameters. The results of this study indicate that particle size and fluid atomization play a key role in paint appearance. Decreasing the flow rate and/or increasing bell speed lead to a smoother finish, but are also correlated to a darker appearance at near specular angles, whereas the opposite is true at far specular angles.