Lubricant Migration Simulations on the Flying Head Slider Air-Bearing Surface in a Hard Disk Drive

Kubotera, H.; Bogy, David B.

doi:10.1109/tmag.2007.902975

Cited by 9 publications

(4 citation statements)

References 5 publications

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“…This approach enables us to predict lube migration without a complicated lubricant analysis, such as that in references [10,11]. We found that the lubricant could flow backward to the slider surface from the trailing edge and stay around the stagnation line.…”

Section: Introductionmentioning

confidence: 85%

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Air Bearing Design to Prevent Reverse Flow from the Trailing Edge of the Slider

Aoki

2009

Tribol Lett

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A simulation approach that relies on an analysis of the flow patterns closest to an air bearing surface (ABS) was used to predict the lubricant accumulation on the ABS of a head slider. The lubricant accumulation patterns obtained through the simulation were in good agreement with experimental results and with our experimental apparatus. We used this method to study and analyze flow pattern droplets close to the trailing edge of a number of sliders and found that there was a reverse flow from the slider's trailing edge on both sides of the trailing pad and behind the read/write element, which could result in a lubricant accumulation on the slider surface close to the trailing edge of a slider and thus lead a transient slider vibration and magnetic-signal loss in a hard disk drive. Further simulations and analyses revealed that the reverse flow is dependent on the depth of slider surface on adjacent to the trailing edge of the slider, and that if the depth is less than a critical depth, which is dependent on the velocity of the disk, the reverse flow could be eliminated. On the basis of these findings, we propose a new ABS design concept for effectively suppressing the reverse flow of lubricants from the trailing edge of the slider. In this concept, the slider has a ''smooth flow pad'' and the depths of outlet recesses are specified as being smaller than the critical depth. It was confirmed by both simulation and experiment that lube accumulation on the slider surface is obviously decreased and the reliability of a hard disk drive with this air bearing design is consequently improved.

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Section: Introductionmentioning

confidence: 85%

“…Kubotera and Bogy [10,11] have numerically studied lubricant migration on an ABS by taking into account air bearing pressure, air bearing shear stress, Laplace pressure, the dispersive component of the surface free energy, and disjoining pressure.…”

Section: Introductionmentioning

confidence: 99%

Air Bearing Design to Prevent Reverse Flow from the Trailing Edge of the Slider

Aoki

2009

Tribol Lett

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“…When the flying height of the slider is decreased to a magnitude approaching the thickness of the lubricant layer, the interaction of the airflow and lubricant layer leads to increasing lubricant movement (Dai et al 2004;Fukui et al 2007; Kubotera and Bogy 2007;Marchon et al 2007;Wu 2006). This lubricant movement induces either some lubricant accumulation on the slider air-bearing surface or dripping of lubricant into the air-bearing surface from the slider's sidewall.…”

Section: Introductionmentioning

confidence: 99%

Simulation on contact between the droplet and the slider at head-disk interface based on water-hammer pressure model

Aoki

2008

Microsyst Technol

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To understand the cause of read/write error due to lube accumulation, a model to simulate the slider's response to the contact impact, which can occur between a lubricant droplet on the disk and a slider, was developed. The contact impact model is based on the water-hammer pressure model with an additional damping force, where the wave-shock pressure is assumed to function as the contact pressure, and the damping force defines the damping characteristics of the impact which are due to the lubricant's high viscosity and squeeze between the droplet and slider contact area along the slider local velocity direction. The transient contact impact is dependent on lube droplet density, disk velocity, pitch angle of the slider, and contact area between the droplet and the slider. The measured read/write signal jump due to lube pickup can be explained by the simulation results. This modeling and simulation are helpful to us in understanding the read/write signal loss due to a lube droplet at head disk interface.

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“…Inspired by this finding, many papers, mostly numerical analyses, have been published on the deformation and instability of the lubricant layer in the framework of continuum theory [3,4,[6][7][8][9][10]. It is generally agreed [4,8,10] that the shear force induced by the air flow is a dominant factor determining the lubricant dynamics. However, in all of these studies, the shear force was represented by either an oversimplified model [4,6] that contains only the Couette flow component or a model based on the first-order slip theory [8].…”

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confidence: 99%

Air-Bearing Shear Force in the Head–Disk Interface of Hard Disk

Liu

Bogy

2009

Tribol Lett

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The air-bearing shear force in the head-disk interface (HDI) of hard disk drives is a dominant factor determining the motion and instability of the lubricant layer, which plays an important role in drive reliability. In this communication, an analytical formula, which is applicable to the flow of an arbitrarily rarefied gas in the HDI and is more general than that based on the first-order slip theory, is presented based on the Boltzmann equation. When a hard sphere model is used for the air molecules, the formula reduces to that based on the first-order slip theory, and it thus validates previous studies based on the latter formula.Keywords Air bearings Á Head-disk interface Á Shear force Á HDD reliabilityThe head-disk interface (HDI), as shown in Fig. 1, is the region between a slider and a disk in hard disk drives. The slider, carrying a read-write transducer at the trailing edge, flies over the disk which rotates and has a local speed U around 10-30 m/s. A specifically designed pattern called the air-bearing surface (ABS) exists on the slider's surface facing the disk. In the HDI, the flow of air, setup by the moving disk and compressed by the ABS, creates pressure that balances the suspension load on the slider, and it serves as a cushion layer to stabilize the motion of the slider and reduce contact between the slider and the disk. To further reduce the possibility of the slider's impact on the disk, and mitigate its effect when contact occurs, a layer of lubricant, with thickness of about 1 nm, is coated on the disk. In modern hard disk drives, the minimum flying height of the slider has been reduced to less than 5 nm. This leads to strong interactions between the slider, the air flow, and the lubricant. Experiments have shown that the lubricant, due to its mobility, deforms and creates specific patterns due to these interactions [1,2]. It has also been experimentally observed that the lubricant in some cases transfers from the disk to the slider [3], which decreases the effect of the lubricant as a protecting layer for the disk and may alter the performance of the slider. Thus, despite its very small thickness, the lubricant layer plays an important role in the reliability of hard disk drives [4].Although the thickness of the lubricant layer is often less than 1 nm, experiments have shown that it can still be modeled using continuum theory with a modification to its viscosity [5]. Inspired by this finding, many papers, mostly numerical analyses, have been published on the deformation and instability of the lubricant layer in the framework of continuum theory [3,4,[6][7][8][9][10]. It is generally agreed [4,8,10] that the shear force induced by the air flow is a dominant factor determining the lubricant dynamics. However, in all of these studies, the shear force was represented by either an oversimplified model [4,6] that contains only the Couette flow component or a model based on the first-order slip theory [8]. Wu [8] compared results based on these two models and showed that the approach to mo...

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Lubricant Migration Simulations on the Flying Head Slider Air-Bearing Surface in a Hard Disk Drive

Cited by 9 publications

References 5 publications

Air Bearing Design to Prevent Reverse Flow from the Trailing Edge of the Slider

Air Bearing Design to Prevent Reverse Flow from the Trailing Edge of the Slider

Simulation on contact between the droplet and the slider at head-disk interface based on water-hammer pressure model

Air-Bearing Shear Force in the Head–Disk Interface of Hard Disk

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