Y. H. Jung

Motions of Air Bubbles Trapped in Grooved and Plane Journal Bearings of Operating Fluid Dynamic Bearings

We investigated the motion of air bubbles trapped in grooved and plane journal bearings of operating fluid dynamic bearings (FDBs) by using the finite volume method and the volume of fluid method. The motion of a trapped air bubble in grooved journal bearing is mostly determined by surface tension and the pressure difference due to the wedge effect of the groove. Also, the motion of trapped air bubbles in plane journal bearing is mostly determined by surface tension and the Coutte flow. A novel design of FDBs was finally proposed to expel the air bubbles trapped in grooved journal and plane journal bearings out of operating FDBs.

Effect of the Cross-Sectional Shape of Recirculation Channel on Expelling Air Bubbles in the FDBs of HDD Spindle Motors

Fluid dynamic bearings (FDBs) are applied to most of the spindle motors of computer hard disk drives (HDDs) since FDBs provide better dynamic characteristics, such as lower vibration and noise, than ball bearings. However, a weakness of FBDs is instability arising from air bubbles in the oil lubricant of FDBs. One possible solution to expel the trapped air bubbles out of FDBs is to include recirculation channel (RC). RC is designed to balance the pressures between upper and lower parts of FDBs and to circulate the oil lubricant as well as to expel air bubbles out of FDBs. This paper experimentally and numerically investigates the behavior of the air bubble in oil lubricant of operating FDBs due to the design of the RC. We created the FDBs with transparent cover and performed the experiment to visually observe the behavior of trapped air bubbles. Also, we numerically studied the phenomena of expelling the air bubble. The flow field of FDBs is calculated by the Navier-Stokes equation and the continuity equation. And we numerically explained that large pressure difference between upper and lower regions of RC and fast flow velocity along RC expel the air bubble out of FDBs. This research can be effectively utilized to develop robust FDBs by expelling the air bubbles out of FDBs.Copyright

Behavior of Micron-Sized Air Bubble in Operating FDBs by Using the Discrete Phase Modeling Method

Fluid dynamic bearings (FDBs) have been applied to the spindle motor of a computer hard disk drive (HDD) because FDBs provide better dynamical characteristics of lower vibration and noise than ball bearings. However, one of the weaknesses of FBDs is the instability arising from the air bubble in oil lubricant of FDBs. Air bubbles are formed and trapped in oil lubricant by the inappropriate process of oil injection or the external shock. Trapped air bubbles decrease the rotational accuracy and the stability of a rotor-bearing system in such a way to generate non-repeatable run-out (NRRO) and to decrease the stiffness and damping coefficients of FDBs. It is important to predict the path of air bubbles in oil lubricant and to design FDBs in such a way to easily expel air bubbles out of operating FDBs.Copyright