Wetting and spreading characteristics of oil droplet impact on textured surfaces

During the lubrication process in machining operations, the texture formed on the surface of the machined part influences the lubrication performance at the interface. Therefore, it is crucial to determine the influence of surface texture properties on the adhesion and spreading characteristics of lubricant droplets impacting on the wall. This study investigates the effects of surface texture characteristics, peak and valley characteristics, and the Weber number on the morphological evolution and kinetic behaviour of oil droplets after impacting a rough wall surface, through capturing the kinetic behaviour of oil droplets against a textured metal wall using high-speed camera experiments. The results show that the shape of the convex structures on the surface, the orientation of the grooves, and the peak-and-valley characteristics of the surface topography can result in different spreading characteristics and oil film oscillations during the impact process of oil droplets. The spreading coefficients of the oil droplets in the direction perpendicular to the texture are almost identical when the oil droplets impact the textured surface at both the peak and valley positions, and the heights of the droplets are nearly the same. When the oil droplet is spread in different directions along the cutting texture wall, if the transverse wave width ξ_∥ is less than the longitudinal wave height ξ_⊥, the spreading coefficient of the oil droplet in the vertical texture direction at the same time is greater than the texture direction in the initial stage of spreading, and the maximum spreading factor of the oil droplets in the vertical texture direction in the stabilisation stage gradually increases with the decrease of ξ_⊥ and the increase of ξ_∥. The spreading coefficient of oil droplets in the vertical groove direction increases with increasing We, and the minimum droplet height decreases with increasing We. The research content of this study provides fundamental support for an in-depth understanding of the kinetic behaviour of solid-liquid interface complexes and lubrication-related mechanisms.