Thermo-molecular gas-film lubrication dynamics considering boundary temperature and ambient gas (2-DOF numerical analysis by t-MGL equation)

Abstract

The static and dynamic flying characteristics of a slider in a hard disk drive have become an important consideration owing to recent increases in recording density. In the present paper, the characteristics of a plane inclined slider (Case 1) and a step slider flying in either air or He (Case 2) over a running boundary wall with local temperature distributions are analyzed using the thermo-molecular gas-film lubrication (t-MGL) equation. For a plane inclined slider (Case 1), the fundamental static and dynamic characteristics are analyzed numerically and are examined through two limiting approximations: the approximation for infinite bearing number and the incompressible short bearing approximation. For a step slider (Case 2), the decreases in the minimum spacing for a slider flying in He are significant because the mean free path of He, ?He, is approximately three times that of air, ?air. The increases in the minimum spacing due to laser heating are negligible in both air and He because the heat spot size is very small. Moreover, the decrease in the minimum spacing produced by thermal deformation (projection height, dmax) by laser heating in the thermal fly-height control slider is reduced by the total additional pressure of (1) MGL pressures produced by the air-film wedge effect, (2) t-MGL pressures produced by the applied temperature distribution, and (3) van der Waals attractive pressure due to the ultra-small spacing. The spacing fluctuation in He caused by a running wavy disk is smaller than that in air, because the inlet-to-outlet spacing ratio (h1/h0) in He is larger than that in air.