Fluid dynamic pressure bearing for spindle motors and storage disk drive devices and having ridge portions between grooves in the fluid dynamic pressure bearing

摘要

A fluid dynamic bearing having a shaft (12) and a bearing sleeve (11) rotatably supported relative to each other. At least one of the shaft and the bearing sleeve is made of steel or stainless steel made of by weight C: 0.6˜1.20%; Si: 1.0% or less; Mn: 1.0% or less; Cr: 10.5˜18.0%; Mo: 1.0% or less; S.: 0.03% or less; and Fe. The dynamic pressure bearing surface (20) is formed by ridges (22) remaining in between multiple dynamic pressure grooves (21) formed by electrochemical machining.