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Research Papers: Magnetic Storage

Lubricant Depletion and Disk-to-Head Lubricant Transfer at the Head-Disk Interface in Hard Disk Drives

[+] Author and Article Information
Rohit P. Ambekar

Department of Mechanical Engineering, University of California, Berkeley, CA 94704rohit.ambekar@hitachigst.com

David B. Bogy

Department of Mechanical Engineering, University of California, Berkeley, CA 94704dbogy@cml.me.berkeley.edu

C. S. Bhatia

Department of ECE, National University of Singapore, Singapore 117576, Singaporeelebcs@nus.edu.sg

J. Tribol 131(3), 031901 (May 27, 2009) (8 pages) doi:10.1115/1.3139045 History: Received October 16, 2006; Revised April 14, 2009; Published May 27, 2009

As the head-disk spacing reduces in order to achieve the areal density goal of 1Tb/in.2, the dynamic stability of the slider is compromised due to a variety of proximity interactions. Lubricant pickup by the slider from the disk is one of the major reasons for the decrease in the stability as it contributes to meniscus forces and contamination. Disk-to-head lubricant transfer leads to lubricant pickup on the slider and also causes depletion of lubricant on the disk. In this paper, we experimentally and numerically investigate the process of disk-to-head lubricant transfer using a half-delubed disk, and we propose a parametric model based on the experimental results. We also investigate the dependence of disk-to-head lubricant transfer on the disk lubricant thickness, lubricant type, and the slider air bearing surface (ABS) design. It is concluded that disk-to-head lubricant transfer occurs without slider-disk contact and there can be more than one timescale associated with the transfer. Furthermore, the transfer increases nonlinearly with increasing disk lubricant thickness. Also, it is seen that the transfer depends on the type of lubricant used and is less for Ztetraol than for Zdol. The slider ABS design also plays an important role, and a few suggestions are made to improve the ABS design for better lubricant performance.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

ABS designs used for experiments: (a) Femto A and (b) Femto B. Both have a design flying height of 3.5 nm.

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Figure 2

Time history of lubricant depletion and transfer volumes for Femto A with Zdol lubricant

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Figure 3

Angular distribution of the lubricant

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Figure 4

Data fit to lubricant depletion volume showing two time scales (y1 and y2 correspond to 16 Å and 12 Å initial Zdol lubricant thicknesses, respectively)

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Figure 5

(a) and (b) Angular distribution and transfer history for a high value of K1, respectively

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Figure 6

Total lubricant depletion and transfer after 30 min along with data fits for two instances of Femto A

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Figure 7

Volume rate of lubricant transfer as a function of disk lubricant thickness as predicted by evaporation model of (5)

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Figure 8

Effect of lubricant type on the lubricant depletion and transfer

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Figure 9

Effect of ABS design on the lubricant depletion and transfer

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Figure 10

(a) and (b) Mass flow lines across ABS for Femtos A and B, respectively, as obtained from static simulations in CMLAIR

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Figure 11

Schematic showing sudden expansion of air under the airbearing

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Figure 12

Maximum expansion ratios for Femtos A and B

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Figure 13

Lubricant depletion volume and rms AE signal at different rpm: (a) Femto A and (b) Femto B (disk lubricant 16 Å Zdol)

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Figure 14

Critical clearance and minimum flying height for Femtos A and B

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