Statistical modelling of coating layer thickness distributions: Influence of overspray on coating quality

This paper investigates the layer formation in spray coating processes. Based on a Monte-Carlo simulation, a stochastic model of the coating layer thickness distribution was derived. It couples the stochastic process of droplet deposition on the particle surface with the droplet shape constructed from a spherical cap model and the droplets wetting properties (contact angle). The model was successfully shown to be able to replace the simulation. A parameter study revealed recommendations for designing a coating process, which were in agreement with the works from other authors. The model was then used to investigate the influence of overspray on the coating quality in comparison with experiments. It was found that the presence of over spray not only reduces the process efficiency but also increases the coefficient of variation of the resulting layer thickness distribution. This was caused by an increase in droplet size due to a predominant drying of small drops. It was also found, that a higher solid content of the spray solution increases the coefficient of variation, not only due to a decreased number of droplets, but also due to a greater variability in the layer thickness each droplet introduces. (C) 2017 Elsevier B.V. All rights reserved.