Effects of diffusion on lubricant distribution under flying headon thin-film disks

Lubricants on thin-film disks have large effects on head–disk interface characteristics. They reduce head and disk wear while thick lubricant film increases friction force between them and lubricant transfer onto head surfaces. Therefore, we have to know the lubricant behavior in many cases. Lubricant depletion due to disk rotation has been studied very well. However, the effects of flying heads have not been understood systematically until now. We developed a simulation program to numerically calculate the change in lubricant thickness under a flying head on a thin-film magnetic disk. The program included the effects of centrifugal force, shear stress from the air due to disk rotation with a flying head, and the effect of lubricant diffusion. We first calculated a change in lubricant thickness under a flying head using previously published data without the effect of diffusion. Calculated results showed fairly good agreement with the published experimental data with very high peaks on both sides of the flying head rails. With the introduction of diffusion effects, these peaks became moderate and the calculated result agreed very well with the experimental data. The coefficient of diffusion obtained to best fit to the experimental data was close to that reported in a literature. We analyzed the effects of air shear stress patterns under flying head on the change in lubricant distribution. We found that the side shapes had large effect on the distribution. We also confirmed that our program could calculate lubricant depletion on rotating disks without a flying head.