Mechanism Studies On Combined Effects Of Surface Roughness And Accommodation Coefficient On The Lubricating Characteristics Of Air Bearing Film In The Head/Disk Interface

As a part of the computer hardware system, the hard disk drive (HDD) plays an important role in saving and remembering information and data. The head floats on the disk along with the slider when the head/disk system works. This is because the disk rotates with a high speed with the driving of the main shaft, which can carry the air into the slider and the disk interface, and in turn, will satisfy the head float above the disk without damaging the track of the disk. The distance between the slider and the disk is called flying height which determines the storage capacity of HDD. With the HDD’s storage capacity improving, the flying height has been reduced to several nanometers which require modifying of the gas film lubrication equation properly.Based on the simplified molecular gas film lubrication (MGL) equation which was proposed by the group, this paper proposes a modified MGL equation, in which both surface roughness and accommodation coefficient (AC) are considered. In the modified equation, flow factor of the film, the shear flow factor and pressure flow factor are introduced. Then combined effects of surface roughness and AC on the characteristics of gas film lubrication are investigated comprehensively.In the modified MGL model, precise second order (PSO) model is selected to fit the Poiseuille flow and Couette flow, which not only improves the accuracy of the solution results, but also ensures the efficiency of computing. The least square finite difference (LSFD) method is used to solve the modified MGL equation and the specific implementation process is given in detail.According to the modified MGL equation and solving method, this paper investigates the effects of various accommodation coefficients, surface roughness values and surface roughness modes combinations of the head and the disk on the pressure distributions, carrying capacities and the pressure center of the film. What’s more, reasonable explanations are given for the phenomena presented by calculating. Numerical results are shown as follows.The pressure distributions and carrying capacities of the film increase with the increase of AC in various surface roughness combinations of the head and the disk. For a given surface roughness, the pressure distributions and carrying capacities of the film for the case of head rough only are higher than the case of the disk rough only. Besides, the pressure center moves towards the trailing edge of the slider with the increase of AC in various surface roughness combinations of the head and the disk.In addition, variations of AC of the head and the disk have reverse effects on the pressure distributions and the degree is different. The pressure distributions decrease obviously with the decrease of the disk’s AC, while the pressure distributions increase slightly with the decrease of the head’s AC. Moreover, various AC and surface roughness mode combinations of the head and the disk also affect the pressure distribution of the film obviously. On the one hand, transverse roughness mode of the head will lessen gas leakage along the length direction of the slider, and in turn, will result in the pressure distribution of the film increase. On the other hand, longitudinal roughness mode of the head will intensify gas leakage along the length direction of the slider, and in turn, will result in the pressure distribution of the film decrease.