Derivation of Rarefaction-Modified Reynolds Equation Considering Porosity of Thin Lubricant Film

1997 ◽  
Vol 119 (4) ◽  
pp. 653-659 ◽  
Author(s):  
Yasunaga Mitsuya ◽  
Zhisheng Deng ◽  
Masahiro Ohka
Keyword(s):  
Reynolds Equation ◽  
Lubricant Film ◽  
The Other ◽  
Magnetic Head ◽  
Permeable Material ◽  
Magnetic Medium ◽  
Magnetic Disk ◽  
Head Slider ◽  
Liquid Lubricant ◽  
Modified Reynolds Equation

A new lubrication model is derived for solving ultra-thin gas lubrication problems encountered in the analysis of a magnetic head slider flying over a magnetic disk coated with giant-molecule lubricant film. In this model, the liquid lubricant film is replaced with a permeable material, and the boundary between the gas and liquid is subject to two kinds of velocity slippage: one due to the rarefaction effect and the other to the porous effect. Using this model, a rarefaction-modified Reynolds equation is derived considering the permeability of the running surface. This equation is then applied to the lubrication of head sliders flying over a magnetic medium. An interesting condition is found to arise wherein total apparent slippage seems to disappear due to the cancellation of the two slippages and the permeability effects are larger for a slider having a steeper pressure gradient.

Dynamic Analysis of the Rarefaction-Modified Reynolds Equation Considering Porosity of Thin Liquid Lubricant Film

1999 ◽  
Vol 121 (4) ◽  
pp. 864-871 ◽  
Author(s):  
Yasunaga Mitsuya ◽  
Zhisheng Deng ◽  
Masahiro Ohka
Keyword(s):  
Reynolds Equation ◽  
Mean Free Path ◽  
Lubricant Film ◽  
Correction Coefficient ◽  
Dynamic Problems ◽  
Head Slider ◽  
Liquid Lubricant ◽  
Damping Coefficients ◽  
Modified Reynolds Equation ◽  
Velocity Region

A rarefaction-modified Reynolds equation was derived to solve dynamic problems of a thin liquid lubricant film coated on a sliding surface. Applying the perturbation method, a calculation procedure based on FEM was formulated to obtain the stiffnesses and damping coefficients of gas lubricating films over a permeable liquid lubricant. Calculations were performed for a specified flying head slider. First, the effects of the permeability and porosity correction coefficients, which serve to increase the molecular mean free path, were presented focusing on landing on/off characteristics. Next, the effects of those on the stiffnesses and damping coefficients were demonstrated using the frequency domain. The results showed that the permeability and porosity correction coefficient increasingly had an influence on the landing on/off characteristics more in the higher velocity region, and that the permeability was effective in increasing the damping of lubricating films.

Detection of the Asperity Contact Between Sliding Surfaces by Monitoring the Excitation of Resonant Oscillation Using the Fiber Wobbling Method

2007 ◽  
Author(s):  
Shintaro Itoh ◽  
Kenji Fukuzawa ◽  
Yuya Hamamoto ◽  
Hedong Zhang ◽  
Yasunaga Mitsuya
Keyword(s):  
Viscoelastic Properties ◽  
Lubricant Film ◽  
Solid Surfaces ◽  
Asperity Contact ◽  
Magnetic Head ◽  
Magnetic Disk ◽  
Disk Interface ◽  
Starting Point ◽  
Lubrication Performance ◽  
Lubricant Films

In the head disk interface (HDI) of a magnetic recording system, lubrication caused by a monolayer thick lubricant film is necessary to achieve stable relative motion between a magnetic disk and a magnetic head. Viscoelastic properties of lubricant films should be clarified for improvement of lubrication performance, however, measurement methods have not been established yet. In this study, we present a new method precisely detecting the starting point of asperity contact of sliding solid surfaces in order to measure viscoelastic properties of the molecularly thin lubricant film on the magnetic disk.

The Effect of Porosity on the Head-Media Interface

2000 ◽  
Vol 123 (3) ◽  
pp. 555-560 ◽  
Author(s):  
James K. Knudsen ◽  
Kenneth E. Palmquist
Keyword(s):  
Experimental Data ◽  
Porous Layer ◽  
Reynolds Equation ◽  
Velocity Slip ◽  
Element Model ◽  
Liquid Lubricant ◽  
Slip Effects ◽  
Porosity And Permeability ◽  
The Media ◽  
Modified Reynolds Equation

A lubrication model for the head-media interface is presented which includes the effect of porosity in the media coating. Experimental data is shown which illustrates the reduction in head-media spacing as porosity is increased. A modified Reynolds equation is derived to account for the effects of coating porosity. Other authors have considered a very thin porous layer to simulate a liquid lubricant or surface microstructure on a nonporous substrate. This study considers a porous layer that can be much larger than the bearing clearance. Darcy’s law is used in the porous layer. Velocity-slip effects, resulting both from rarefaction and the porous boundary, are considered. The modified Reynolds equation is applied to a simple capillary model of a porous layer as an illustrative example. The modified Reynolds equation was incorporated into a finite-element model for the head-media interface. Computations show reduced head-media clearance as porosity and permeability are increased in agreement with experimental data.

Optimum Design of Magnetic Head Slider Under Static and Dynamic Operation Conditions of Hard Disk Drive

1999 ◽  
Author(s):  
Yasuhisa Hattori ◽  
Hiromu Hashimoto ◽  
Masayuki Ochiai
Keyword(s):  
Objective Function ◽  
Hard Disk Drive ◽  
Optimum Design ◽  
Hard Disk ◽  
Disk Drive ◽  
Magnetic Head ◽  
Head Slider ◽  
Dynamic Operation ◽  
Operation Conditions ◽  
Design Variables

Abstract The aim of this paper is to develop the general methodology for the optimum design of magnetic head slider for improving the spacing characteristics between head slider and disk surfaces under the static and dynamic operation conditions of hard disk drive and to present an application of the methodology to IBM 3380-type slider design. In the optimum design, the objective function is defined as the weighted sum of minimum spacing, maximum difference of spacing due to variation of radial location of head and maximum amplitude ratio of slider motion. Slider rail width, taper length, taper angle, suspension position and preload are selected as the design variables. Before the optimization of magnetic head slider, the effects of these five design variables on the objective function are examined by the parametric study, and then the optimum design variables are determined by applying the hybrid optimization technique combining the direct search method and the successive quadratic programming (SQP). From the results obtained, the effectiveness of optimum design on the spacing characteristics of magnetic head slider is clarified.

Two Dimensional Modified Reynolds Equation Including Pressure Dependent Viscosity Effect

2012 ◽  
Author(s):  
Jung Gu Lee ◽  
Alan Palazzolo
Keyword(s):  
Reynolds Equation ◽  
Elastohydrodynamic Lubrication ◽  
Fluid Film ◽  
Maximum Pressure ◽  
Elastic Solids ◽  
Pressure Distributions ◽  
Pressure Dependent Viscosity ◽  
Modified Reynolds Equation ◽  
Dependent Viscosity ◽  
Modified Equation

The Reynolds equation plays an important role for predicting pressure distributions for fluid film bearing analysis, One of the assumptions on the Reynolds equation is that the viscosity is independent of pressure. This assumption is still valid for most fluid film bearing applications, in which the maximum pressure is less than 1 GPa. However, in elastohydrodynamic lubrication (EHL) where the lubricant is subjected to extremely high pressure, this assumption should be reconsidered. The 2D modified Reynolds equation is derived in this study including pressure-dependent viscosity, The solutions of 2D modified Reynolds equation is compared with that of the classical Reynolds equation for the ball bearing case (elastic solids). The pressure distribution obtained from modified equation is slightly higher pressures than the classical Reynolds equations.

Dynamic characteristics of a magnetic head slider

1985 ◽  
Vol 21 (5) ◽  
pp. 1509-1511 ◽  
Author(s):  
Y. Mizoshita ◽  
K. Aruga ◽  
T. Yamada
Keyword(s):  
Dynamic Characteristics ◽  
Magnetic Head ◽  
Head Slider
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