A COMPARISON OF PARTICLE IMPACT IN GAS-SOLID AND LIQUID-SOLID EROSION

The sizes of craters formed on cylindrical, electro-polished, OFHC copper erosion specimens subjected to impact by closely-sized glass beads, average diameter 540 mu m, suspended in diesel oil in a slurry-pot erosion tester operating at nominal rotation speeds of 18.7, 14.0 and 9.35 m s(-1) have been compared with those produced in an identical apparatus operating at the same speeds, in which the glass beads were suspended in air. Crater sizes were measured at the cylinder stagnation line and at location angles of 15 degrees, 30 degrees, 45 degrees, 55 degrees and 65 degrees on either side of it. Impact craters formed under liquid-solid erosion conditions were found to be smaller than those formed in gas-solid erosion at the same nominal test speed. Crater sizes were related to impact velocities using diameter measurements from craters produced under slow loading conditions. The differences in normal impact velocities during gas-solid and liquid-solid erosion are discussed and the values compared with predictions from a mathematical model. The relative retardation of impacting particles in liquid-solid erosion is ascribed to fluid dynamic effects on particle velocities and trajectories, including squeeze-film retardation of particles immediately prior to impact. In both air and diesel oil the effective free-stream velocity was found to correspond with the nominal test speed. Impact crater eccentricity was measured for tests conducted at 18.7 m s(-1) in air and diesel oil. Eccentricity was consistently greater for craters formed in diesel oil. Ripple pattern formation, owing to the displacement of material by plastic deformation, during the wear of copper subjected to repeated impact by glass beads suspended in diesel oil at 18.7 m s(-1), is reported.