Analysis of accumulated lubricant for air-helium gas mixture in HDDs

Abstract

For higher areal density, full helium as well as air-helium gas mixtures are currently being investigated as candidates for use in advanced drives. Moreover, the head mechanical spacing and the amount of accumulated lubricant on the bottom surface of the slider should be reduced for higher areal density. To analyze the characteristics of accumulated lubricant under these conditions, gas property equations for binary gas mixtures as functions of helium fraction ratio and temperature were derived. Accumulated lubricant equations were derived by considering the attractive forces, such as the dispersive and polar effects. An increase in the helium fraction ratio reduces the small shear stress on the bottom surface of the slider, which leads to a decrease in lubricant transfer capability. As a result, the amount of total lubricant transfer and accumulation are increased markedly. Also, with a decrease in lubricant thickness, the amount of accumulated lubricant increases greatly with a high helium fraction ratio. In conclusion, the HDI problems induced by lubricant transfer should be considered in full helium-filled or air-helium gas mixture drives.