Effects of roughness orientations on thin film lubrication of a magnetic recording system

Abstract

In this paper, the relations expressing the effects of roughness orientations and molecular mean free path on the roughness-induced flow factors are derived. Such consideration of the effects of roughness orientation on bearing performance is necessary when rotary actuators are used in magnetic recording systems. Using the perturbation approach and the coordinate transformation, the flow factors are derived and expressed as functions of the roughness orientations, the Peklenik numbers, the standard deviations of roughness heights of each surfaces, the inverse Knudsen number and the film thickness ratio of the lubrication film, where h/ sigma is the ratio of average film thickness to standard deviation of the composite roughness. Two orientation coefficients are proposed to reveal the combined effects of Peklenik number and orientation angle and the change of flow factors is analysed as the orientation coefficients vary. Finally, the static performance of a magnetic recording head flying above a rotating disc under the ultra-thin-spacing condition is analysed with roughness and rarefaction effects taken into account. The effects of surface characteristics of the moving surface on load capacity are more significant than those of the stationary surface.

Investigation on Effect of Surface Roughness Pattern to Dynamic Performance of Mems Resonators in Various Types of Gases and Gas Rarefaction

“…To lower the external SFD and improve the Q-factor, a lower ambient pressure (p) is introduced within the thin gap spacing (h 0 ), thus the effect of gas rarefaction becomes important [2]. Also, the effect of surface roughness [3] becomes an important factor to be discussed because of the large surface area and volume ratio under gas ambient conditions. To model the SFD, the conventional Reynolds equation [4] was derived using the conventional lubrication theory.…”

“…Fukui and Kaneko [5] derived the modified Reynolds equation with Poiseuille flow rate (Q P ) to model the effect of gas rarefaction. Also, the surface roughness effect can be solved by (1) mixed average film thickness functions [6], (2) average flow factors [3,[7][8][9][10] for all surface roughness pattern directions, and (3) using the fractal model [11] to generate functions for random surface roughness. To consider the surface roughness patterns, Patir and Cheng [12] first proposed the modified Reynolds equation using flow factors.…”

Interactive Effects of Rarefaction and Surface Roughness on Aerodynamic Lubrication of Microbearings

“…White et al [ 18 ] introduced the transverse sinusoidal roughness pattern to study the influence of surface roughness on steady-state pressure profiles of wedge bearing by variable grid implicit finite difference method and found that the load capacity could be decreased to a limiting value at higher bearing numbers. For the applications of perturbation technique and mapping function, Li et al [ 19 ] studied the effects of roughness orientations and rarefaction on static performance of magnetic recording systems. The results demonstrated that the flow factors changed with the orientation angle and Peklenik number, and the effect of moving surface on surface characteristics is more significant than that of the stationary surface.…”

Effect of surface topography associated with arbitrary velocity direction on the lubrication film thickness in elliptical contacts

“…Much attention has been attracted for this problem, and the stochastic and deterministic rough-surface EHL models have been developed. The stochastic rough-surface EHL models were commonly used in early research studies (Patir and Cheng, 1978; Greenwood and Tripp, 1970/1971; Li et al , 1995; Chen et al , 2007; Majumdar and Hamrock, 1982; Zhu et al , 1990; Letalleur et al , 2002; Akbarzadeh and Khonsari, 2010; Liu and Wang, 2000; Harp and Salant, 2001). In these studies, a separate model was commonly developed considering the asperity contact and the film lubrication as two parts, which were linked with a load-sharing concept.…”