Investigation of Slider Disk Contact in Air-Helium Gas Mixtures

Transcription

1 Investigation of Slider Disk Contact in Air-Helium Gas Mixtures Researchers: Zhengqiang Tang, Visiting Graduate Student, UCSD Pablo A. Salas, Postdoctoral Fellow, CMRR Advisor: Frank E. Talke, Professor, CMRR and MAE Department. October 25,

2 Introduction Outline Research Objectives Models -- New Air Bearing Design -- Air Bearing Simulator (CMRR CODE) -- Asperity Contact Model Results Summary 2

3 Introduction Advantages of helium filled HDDs [1]: Less dense Smaller temperature increase Less turbulence Laminar flow Less windage loss Inert property Helium filled HDDs Disadvantages of helium filled HDDs: Hermetically sealing technology Reliability issues of heads and disks [1] Nan Liu, Jinglin Zheng, and David B. Bogy, Thermal flying-height control sliders in hard disk drives filled with air-helium gas mixtures. 3

4 Research Objectives Investigate the physical properties of air-helium gas mixtures. Investigate the steady static performance of a new air bearing surface in air-helium gas mixtures. Investigate the dynamic performance (flying height, contact force between the slider and disk) in air-helium gas mixtures. 4

5 Research Method Air bearing simulator Slider/disk contact model Air-helium gas mixture slider/disk contact air bearing pressure slider rough disk surface X Y Z 5

6 0.7 mm New Air Bearing Surface 0.85 mm Bottom view of the air bearing design Number of nodes: 65, 378 Number of elements: 130, 345 To generate the mesh, there must be a smooth transition from one step height to the next. 6

7 Air Bearing Simulator (CMRR Code) An air bearing simulator [2] was used for the simulation of the flying characteristics of the new slider. The pressure distribution is obtained by simultaneously solving the dynamic Reynolds equation and slider equilibrium equations. Steady static simulator Dynamic simulator Air bearing pressure distribution [2] Wahl M., 1994, Numerical and Experimental Investigation of the Head/Disk Interface, PhD Dissertation, University of California, San Diego. 7

8 Contact Model The contact models developed by Kogut and Etsion [3] and Suh et al. [4] were used to calculate contact force, friction force and adhesive force. The results of contact, friction and adhesive forces are incorporated in the dynamic air bearing simulator. [4] [3] Kogut L, and Etsion I A static friction model for elastic plastic contacting rough surfaces. ASME J. Tribol., 126, [4] Suh A.Y., Polycarpou A.A., 2008, Adhesive contact modeling for sub-5-nm ultralow flying magnetic storage head-disk interfaces including roughness effects, Journal of Applied Physics 97:

9 Physical Properties of gas mixtures [5] G. A. Bird, Molecular gas dynamics and the direct simulation of gas flows. New York: Oxford Univ. Press,

10 Physical Properties of gas mixtures Viscosity: μ [6] B. E. Poling, J. M. Prausnitz, and J. O Connell, The properties of gases and liquids. 5 th ed. New York: McGraw-Hill,

11 (λ-λ A )/(λ H -λ A );(μ-μ A )/(μ H -μ A ) Physical Properties of gas mixtures mean free path viscosity Fraction of helium in the gas miture α The normalized mean free path and viscosity of the air-helium gas mixtures as a function of helium percentage. 11

12 Physical Properties of gas mixtures The Reynolds number: ρ/µ, s/m Fraction of helium in the gas miture α 12

13 Results Steady static simulation results -- Flying height at the pivot point -- Flying height at the transducer -- Maximum pressure on the slider Dynamic simulation results -- Minimum flying height -- Maximum contact force 13

14 Relative change of FH and max pressure Steady Static Simulation Results flying height at pivot point flying height at transducer Maximum pressure on slider Fraction of helium in the gas miture α Normalized to the value at α = 0. The flying height at pivot point at α = 0 is 40.2 nm The flying height at transducer at α = 0 is nm The maximum pressure at α = 0 is MPa 14

15 Dynamic Performance in gas mixture 15

16 Minimum flying height, nm Dynamic Simulation Results N N N N N Fraction of helium in the gas miture α The minimum flying height decreases with increasing fraction of helium in the gas mixtures at different applied shocks. 16

17 Maximum contact force, N Dynamic Simulation Results N N N N N Fraction of helium in the gas miture α The maximum contact force increases with increasing fraction of helium in the gas mixtures at different applied shocks. It significantly increases after the fraction of helium reaches about

18 Summary The Reynolds number decreases with the increase of helium fraction in gas mixture. The lower Reynolds number is associated with less turbulence. For the steady static simulation, with the increase of helium fraction in gas mixture, we observe: The flying height at pivot point decreases; The flying height at transducer increases. The maximum pressure on slider decreases. For the dynamic simulation, with the increase of helium fraction in gas mixture, we observe: The minimum flying height decreases; The contact force at the head disk interface increases. 18

19 Thank You! 19