Research On Characteristics Of Lubricant Film Flow And Depletion On Head Disk Interface

With the advent of the era of big data, people demand higher storage capacityof hard disk. Among all the new technology, reducing flying height of recordinghead and the adopting heat assisted magnetic recording(HAMR) technologies areeffective ways to improve the density of hard disk storage. However these twotechnologies damage the lubricant coating on the magnetic disk. In order tomaintain the best tribological performance and flying flight stability of slider athead/disk interface(HDI), the thickness of the lubricant on disk surface must keepuniform. Therefore, investigating the reason behind lubricate loss under slidinghead and the heat source and puting forward the method to reduce the loss, is ofvital significance to improve the reliability of head disk interface.Based on Navier-Stokes equation and continuity equation, we the lubricantflow loss theoretical model was deduced in this study. First, the air bearing pressurewas solved at HDI based on Reynolds equation which is modified by F-K model.Then, the lubricant film thickness equation was deduced under the flying sliderconsidering van der Waals force, surface tension and external forces on film surface.Finally, the film thickness equation was established under heat source. Due to theintroduction of heat, evaporation should be considered in the equation. At the sametime, the viscosity of lubricant related to film thickness and temperature wasinvolved in the study, so the theoretical model was improved.After solving the distribution of air bearing force under plant slider anddouble-track slider, the film thickness deformation under the two types of sliderswas sloved. The main factors that trigger the film flow through remove the physicsin the equation were confirmed. For different working conditions of hard diskdrives, the effects of different parameters on film deformation including initialthickness of lubricating film, flying height of slider and the speed of the disk wereinvestigated and the corresponding ways to reduce the film thickness deformationwere porposed.The theoretical model of lubricant deformation under heat source was based onthe technology of HAMR. By comparing the temperature distribution under single-layer glass disk and multilayer disk, the necessity of using multilayer disk to buildthe model were confirmed. By comparing the effects of each physics in the equation,it is concluded that evaporation is the main reason for lubrication loss. Then the effects of some parameters of HAMR on lubrication film deformation wereanalyzed, including the initial film thickness, laser power, spot size and molecularweight of the lubricant. Through investigating the reasons of film thickness changewith parameter change, methods to reduce the loss of lubricant were put forward.After solving the film thickness change under slider and heat source condition,the recovery of lubricant was discussed. On the basis of film thickness deformationequation, lubricant recovery equation was deduced. Using the results of filmthickness changes under slider and the heat source as the initial conditions, therecovery time and recovery rate of lubricant were investigated and the reason oflubricate recovery were illuminated. Finally the effects on initial lubricant filmthickness, temperature and polar end group of lubricant on lubricant recovery timeand rate were studied. Methods of fast recovery for lubricant were put forward.