Youichi Kawakubo

Head crash process of magnetic coated disk during contact start/stop operations

To increase the recording density of rigid magnetic disk files, it is important to understand and prevent the Head Crash problem. In Winchester type head-disk interfaces, Head Crash is most liable to occur during Contact Start / Stop (CS/S) o-erations. Head wear or disk wear after Head Crash were reported by past researchers. But the Head Crash process itself has not been made clear. In this study, friction force and acoustic emission(AE) signal during CS/S operations are measured until Head Crash. The results show that the piling up of disk binder on a head surfase is the main reason of Head Crash. It is triggered by the intrusion of wear particle into the head-disk interface. From these results, more durable magnetic coated disks will be developed in the future.

Lubricant behavior and pin wear on thin-film magnetic disks

Transparent-pin wear tests with in-situ microellipsometer measurement were performed on thin-film magnetic disks with different lubricants. We found that pin wear started when the decrease in the lubricant thickness at the pin slide-path leveled-off and that pin wear sometimes started when the lubricant thickness was still larger than that of the adsorbed lubricant. These mean that the free lubricant on the disk surface is not replenishing the real points of pin-disk sliding. Consequently, we considered that the replenishment of free lubricant to the real points of pin sliding is more important than the fact whether the average lubricant thickness exceeds the adsorbed lubricant thickness or not. Tests on disks with different lubricants show that the lower the lubricant viscosity, the greater the lubricant loss and the smaller the pin wear. We find that a low-viscosity-lubricant is better in replenishing free lubricant to the real points of sliding than high-viscosity-lubricant is.

Effects of sliding pin shapes on change in thin-film disk lubricant thickness

To analyze lubricant loss by head sliding, change in lubricant thickness during sliding under a flat-circular-surface pin (FC pin) on a thin-film magnetic disk is compared with that of a spherical-surface pin (S pin). Lubricant pick-up onto the PC pin was much smaller than that onto the S pin. And the amount of lubricant loss under the FC pin was smaller than that under the S pin. We consider the cause of this is the difference in the angle of the side wall at the trailing edge of the pins.

Head contact pressure and slow speed sliding test on coated magnetic disks

An analytical method to determine apparent contact pressure between a coated magnetic disk and head during show speed sliding is proposed. Results of analysis show that as sliding velocity increases, contact force gradually decreases but apparent contact pressure peaks at a velocity slightly lower than that of the trailing edge take-off. In this study, a slow speed head sliding test was performed to compare the analytical and experimental results. Validity of contact pressure analysis was confirmed through friction force measurement during the test. However, disk lifetime change with sliding velocity did not coincide with that of the peak contact pressure. This indicates that the contact pressure has little effect on the sliding test lifetime.

Velocity dependence of lifetime and temperature rise during pin-on-disk type sliding tests on coated magnetic disks

The velocity dependence of disk lifetime and temperature rise before failure during a pin-on-disk type sliding test on coated magnetic disks was investigated in detail The disk lifetime decreased with increasing sliding velocity, with less velocity dependence at lower velocities than at higher velocities. The temperature rise just before disk failure was measured using an infrared microscope and was calculated using the measured coefficient of friction. The discrepancy between measured and calculated temperature rise and the reason for the velocity dependence in the disk lifetime are discussed.