Tapered seal is widely applied to hold lubricating oil inside the clearance at the ends of fluid film bearing utilized in precise machines such as a spindle motor of HDD system. This study aims to analyze theoretically the fundamental working mechanism of tapered seal. Applying the analysis on meniscus of fluid surface due to the surface tension cooperating with the results of computational fluid dynamics for velocities and pressure fields under the axisymmetric and steady-state condition, the mechanism of the sealing ability of the tapered seal is clarified, and an index value which represents the sealing capacity of a tapered seal is introduced. The effects of some design and working parameters, such as the taper angle of the sleeve and the initial fluid volume, on the sealing capacity are discussed through the index value. The role of the barrier film coating on the sleeve surface to the sealing capacity is also studied theoretically.
