Numerical simulation of molecularly thin lubricant film flow due to the air bearing slider in hard disk drives

Abstract

In this paper we numerically study the evolution of depletion tracks on molecularly thin lubricant films due to a flying head slider in a hard disk drive. Here the lubricant thickness evolution model is based on continuum thin film lubrication theory with inter-molecular forces. Our numerical simulation involves air bearing pressure, air bearing shear stress, Laplace pressure, the dispersive component of surface free energy and disjoining pressure, a polynomial modeled polar component of surface free energy and disjoining pressure and shear stress caused by the surface free energy gradient. Using these models we perform the lubricant thickness evolution on the disk under a two-rail taper flat slider. The results illustrate the forming process of two depletion tracks of the thin lubricant film on the disk. We also quantify the relative contributions of the various components of the physical models. We find that the polar components of surface free energy and disjoining pressure and the shear stress due to the surface free energy gradient, as well as other physical models, play important rolls in thin lubricant film thickness change.

Three-dimensional deformation analyses of the ultra-thin liquid film surface (linearized analyses for the steady state)

“…6 and 7 show, when the disk speed increases, the deformation h L decreases and is nearly constant along the disk running direction, x, almost everywhere except at the applied position of the pressure or the shearing stresses. Similar situation occurs in the head-disk interface in more realistic configuration (Wu 2006;Kubotera and Bogy 2007). For more realistic air bearing sliders over the liquid distributed pressures and shearing stresses are calculated by the molecular gas film lubrication (MGL) equation Kaneko 1988, 1990;Kang et al 1999).…”

“…For such a situation, the long wave equation for the ultra-thin liquid, which is the time evolution equation for the shape and deformation of thin liquid films and includes surface tension and surface forces such as van der Waals forces (Oron et al 1997), has been modified considering the velocity of the moving solid and pressure and shearing stresses applied at the surface. The generalized long wave theory was used to examine the instability of the head-disk interface (Fukui et al 2004(Fukui et al , 2005a and deformations of ultra-thin but continuous liquid films (Yorino et al 2004a, b;Wu 2006;Kubotera and Bogy 2007;Fukui et al 2007).…”

Frequency domain analyses of a thin liquid film surface by repetitively applied stress (dynamic response analyses by the long wave equation)

“…The basic equation was extended to the head disk interface (HDI) problem by considering the moving boundary wall (disk), and the time evolution of the ultrathin liquid (lubricant) is calculated in the time domain under the static pressure and shear stress produced by an air bearing slider (Yorino et al 2004;Wu 2006;Kubotera and Bogy 2007). The deformation is generally small when the boundary wall (disk) moves and the disjoining pressure is not negligible, so that the linearized equation for small deformation can be used, and simple but instructive characteristics have been obtained both analytically and numerically (Fukui et al 2007(Fukui et al , 2010a.…”

Dynamic Behavior of a Thin Liquid Surface by Repetitively Applied Stress (Numerical Analyses by the Long Wave Equation)

“…The basic equation was extended to the HDI problem by considering the moving boundary wall (disk), and the time evolution of the ultra-thin liquid (lubricant) is calculated in the time domain under the static pressure and shear stress produced by an air bearing slider (6)(7)(8) . Since the deformation is generally small when the boundary wall (disk) moves and the disjoining pressure is not negligible, the linearized equation for small deformation can be used, and simple but instructive characteristics have been obtained both analytically and numerically (9,10) .…”