The influence of process parameters on flow-field characteristics and coating properties in nanocomposite spray deposition

Abstract

The spray deposition process serves as an essential approach for enabling the highly efficient and cost-effective production of nanocomposite coatings. However, it is crucial to conduct a parameter analysis of this process to ensure that high-quality coatings can be fabricated stably. For this purpose, an air-atomized spray system has been developed, and this paper investigates the influence of process parameters on flow-field characteristics and coating properties. Considering that the feeding rate of nanocomposite ink and the distribution ratio of compressed air are key parameters affecting the spraying effect, the velocity and pressure distributions of the flow-fields, as well as the surface morphologies of the coatings, were measured. The results indicate that increasing the air distribution ratio allocates more air to compress the flow-fields, leaving less air for atomizing and delivering the nanocomposite droplets. This leads to an overall decrease in droplet velocity, with the maximum velocity magnitude dropping from 150 to 100 m/s. The compressive effect on the flow-fields becomes more pronounced, causing the elliptical spray patterns to elongate, with the maximum eccentricity reaching about 0.9. Besides, the maximum pressure drops from nearly 350 to below 100 Pa, resulting in a more uniform pressure distribution. The elongated elliptical patterns and uniform pressure distribution facilitate the formation of a more even coating over a larger area. Notably, at lower ink feeding rates, increasing the air distribution ratio results in coatings with a surface roughness between 1 and 1.5 μm. However, a higher feeding rate leads to more large droplets, reducing the compressive effect of shaping air and increasing the surface roughness of coatings to around 3 μm. Experimental findings can provide insights for setting process conditions of spray deposition to facilitate the production of nanocomposite coatings.