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A hydrodynamic bearing with non-uniform herringbone grooves has been developed for use with highspeed motor spindles. The grooves gradually become narrower, shallower and less straight (curved) towards the herringbone centre along axial direction, resulting in an increased pumping effect of the spiral grooves. The optimum dimensions of the grooves for increasing the critical bearing number were clarifi ed theoretically, and bearings with non-uniform herringbone grooves were found to increase the critical bearing number against the half-frequency whirl up to about 50% in comparison to bearings with uniform herringbone grooves. Experiments to investigate the suitability of the proposed bearing for high-speed spindles showed that the maximum rotational speed of a spindle with this bearing was about 20% higher, close to the theoretically predicted 23%, and thus proved that application of this bearing should enable spindles to achieve faster stable rotation as theoretically expected.

MoS 2 -shot coating technology is recently focused as one of potential methods of surface modification to realize a low friction state. In this paper, performances of a small-sized journal bearing with MoS 2 -shot coating, which we aim to apply to a spindle of magnetic recording storage system, are investigated in detail through both of the observation of surface property and experimental approach from the viewpoints of frictional torque, durability against start-stop repetition, and run-out characteristics. In consequence, we can conclude that the MoS 2 -shot coating spindle is suitable for the application of small-sized journal bearing.

Tapered seals are widely used to hold lubricating oil inside the clearance at the ends of fluid film bearings utilized in precise machines such as the spindle motors of HDD systems. This study is aimed at theoretically analyzing the mechanism responsible for leakage from the tapered seal when the sleeve is rotating. Three triggers that cause fluid to leak are found from the theoretical results on the meniscus of the interface (boundary surface of two kinds of fluids) which are regarding to surface tension cooperating with the results from computational fluid dynamics for velocities and pressure fields under axis-symmetric and steady-state conditions. The critical rotational speeds for these triggers to induce leakage are presented. We also report the relationship that the critical rotational speed is nearly inversely proportional to the projected area of the interface.

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