The Effect of Two-Dimensional Surface Roughness on the Load-Carrying Capacity of a Thin Compressible Gas Film

Abstract

The influence of two-dimensional surface roughness on a very low clearance gas bearing slider is analyzed for conditions typical of current and near term hard disk data storage products. A model lubrication equation including finite width effects, compressibility and molecular slip is first developed and expressed in terms of the product variable, Z = PH. The analytical solution is then obtained by a combined variation of parameters and perturbation expansion method. Results obtained show that the product variable, which is proportional to longitudinal mass flow per unit depth, is not influenced by the details of surface roughness but is instead influenced by the statistics of the roughness distribution. The gas film pressure, however, is found to be a function of both the roughness details and statistics. The bearing load support is increased by the surface roughness, with the roughness first influencing the load through a second order effect.