Fundamental Study on Oil Leakage from Tapered Seal at Ends of Fluid Film Bearing for Precision Equipments

(Theoretical Study on Critical Rotational Speed for Oil Leakage)

Abstract

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.