Fluid dynamic bearing device and storage disk driving device using the same

Abstract

A fluid dynamic bearing device includes a shaft and a sleeve, with the shaft or the sleeve having a greater hardness being smoothed to have about 0.02 μm or less of the arithmetical average of the surface roughness. The hardness of the shaft or the sleeve having a greater hardness is a Vickers hardness of about 100 Hv or greater at a portion that is arranged to come into contact with the other of the shaft or the sleeve. Further, the hardness of the other of the shaft or the sleeve is a Vickers hardness of about 600 HV or smaller at a portion arranged to come into contact with the shaft or the sleeve having a greater hardness. A clearance of a radial gap defined between the shaft and the sleeve S is about 1.3 μm to about 2.5 μm. Other gaps defining the fluid dynamic bearing portion are configured such that the rotor hub (or the thrust plate) and the sleeve do not come into contact with each other at a thrust dynamic bearing portion when the shaft is slanted as much as possible relative to the sleeve in a state that the rotor is lifted to a rated flying height.

Dependencies are inferred from the claim text.