Thin film hydrodynamic lubrication of flying heads in magnetic disk storages

Typical hydrodynamic lubrication problems commonly encountered in the ultrathin spacing between a computer flying head and a magnetic disk are reviewed. In magnetic disk storages, minimizing the spacing between the head and disk is essential to promote the largest possible increase in magnetic bit density. In the small (nearly 1.0 μm) spacing that has recently been attained, the rarefaction effects owing to the molecular mean free path become dominant. Specifically, in this paper the three governing equations resulting from the first- and second-order slip-flow models and from the linearized Boltzmann equation are compared. Next, some numerical approaches to eliminating the instability in pressure distribution in the high bearing number region are described. Surface roughness effects are also a principal concern in thin spacing. A mixed lubrication model which enables the analysis of the start/stop operation and the average film thickness theory for one- and two-dimensional roughnesses is summarized. Finally, from the viewpoint of practical head design, the slider dynamic characteristics and related slider design factors are discussed.