Experimental evaluation of surface roughness variation of ductile materials due to solid particle erosion

Abstract

The present research is related to an experimental analysis of the changes in surface roughness of ductile materials exposed to solid particle erosion. Physical data were obtained by an impingement jet facility for erosion times of 2.5, 5 and 10 h and wall inclination angles of 10, 20, 30 and 40°. Aluminium 5754, copper and brass (70%Cu-30%Zn) wall samples were subjected to erosion by quartz sand and spherical glass bead particles with a number mean diameter of 235.4 and 211.5 µm, respectively. Air velocity at the exit of the jet was approximately 26 m/s whilst particle velocity was about 9.5 m/s at the same location. Air velocity measurements (single phase flow) were performed at the exit of the impingement jet by using a one-component laser Doppler anemometer (LDA). To allow measurements of particle motion, a combined method of shadow imaging and particle image velocimetry (PIV) was applied. Particle images were recorded by a double shutter CCD-Camera with macro optics together with background illumination and the particle velocity field was calculated by PIV using a successive refinement of the interrogation area. Global erosion was quantified by weighing the mass of samples before and after each experimental run. Two-dimensional roughness profiles were acquired by optically scanning the surface of each sample after erosion and compared to the initial state of the surface. Changes in the material surface were assessed in the region with most pronounced erosion in terms of three roughness parameters: namely, arithmetic average height (Ra), mean spacing at the mean line (RSm) and standard deviation of the roughness angle (Δγ). Additionally, insights on the importance of wall roughness on particle behaviour in confined gas–solid flows as well as on modelling particle–wall interaction with rough walls are presented. Regarding the jet flow, results demonstrated the influence of inclination angle on air and particle velocity profiles. The optical measurements showed the influence of solid particle erosion, inclination angle and particle shape on the temporal evolution of surface roughness of the analysed materials. Finally, the experimental data allowed for the development of a simple correlation to estimate the dependency of Δγ on solid particle erosion and inclination angle as a function of time.