THE INFLUENCE OF THE SQUEEZE FILM ON PARTICLE IMPACT VELOCITIES IN EROSION

The results of a study of the cushioning effect of the fluid between an approaching solid particle and a planar surface are reported. Solutions are obtained for the equations that describe the motion of the fluid in the squeeze film between the particle and the surface. It is shown that the pressure required to exude the fluid from between the impinging particle and the target is of sufficient magnitude to markedly reduce the impact velocity below the value predicted by the potential flow solution. In some cases the particle is stopped prior to impact by the cushioning effect and a criterion for the assessment of the effect, expressed in terms of the particle Reynolds number and the particle and fluid densities, is presented. Significant retardation immediately prior to impact is found for all particles and approach velocities in liquid solid erosion. The effect of the squeeze film on particle trajectories after impact is discussed. The predicted functional form of the results is confirmed by experimentally determined values of impact velocity of spherical glass and steel particles suspended in various liquids deduced from the examination of crater sizes.