Abstract
Numerical simulation of flake orientation during droplet impact on substrates in spray painting processes
Highlights
Effect pigments are widely used in industrial spray painting processes for imparting colour and coating appearance, enabling e.g. metallic effect coatings that are very popular in the automotive industry
A dynamic contact angle model that is suitable to the spray painting process was proposed and validated by the experimental observations
Some numerical treatments have been applied, ensuring accurate calculation of derivatives and stable solution by solving the flake motion equations, which makes the simulation of the flake movement possible in a practical sense
Summary
Effect pigments (flat, 5 – 40 μm broad flakes) are widely used in industrial spray painting processes for imparting colour and coating appearance, enabling e.g. metallic effect coatings that are very popular in the automotive industry. It is already well known that the initial pigment/flake orientation in the paint layer, primarily at the early stage of the film formation and before the subsequent solvent evaporation and baking, influences the final metallic effect significantly. It is strongly suspected that processes during viscous droplet impact have a decisive influence on pigment orientation. Mainly large droplets (e.g. D > 500 μm) with low viscosity under hydrophilic/hydrophobic surface conditions were investigated. Different outcomes of droplet impact on dry/wet substrates were analysed [4]. The air entrapment by droplet impact was studied [3]. The contact angle models that have to be applied in the numerical simulation were studied and discussed in detail [7,8]
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