An Improved Air Film Model for Studying the Tilt Characteristics of Aerostatic Thrust Bearings

Abstract

In this study, an improved mass-spring model that treats the lubricating air film as distributed springs is proposed to calculate the static and dynamic angular stiffness of aerostatic thrust bearings. The proposed model refines the traditional mass-spring model by introducing the spatially varying mechanical properties of the air film and the frequency-dependent behavior of dynamic coefficients. Axial and tilt characteristics are coupled through distributed equivalent air springs, where spring coefficients are determined by the static air pressure and the transient perturbation pressure. On the basis of the improved model, a fast calculation method for static and dynamic angular stiffness is presented by periodically extending the axial characteristics of a single symmetric sector instead of utilizing the full model. The results from the fast calculation method with a single symmetric model show good agreement with those obtained from the Reynolds equation and computational fluid dynamics method with a full model, while reducing computation time by 88.0% in static analysis and 98.6% in dynamic analysis. Moreover, the applicability and limitations of this model are investigated, indicating that it has a broader applicability in dynamic angular stiffness analysis compared with static analysis. Within the applicable range, the static and dynamic designs of the thrust bearing are performed. The effects of air film thickness, orifice diameter, and orifice location on axial and angular stiffness are analyzed. This research establishes an efficient approach for the analysis of tilt characteristics in aerostatic bearings. Furthermore, the limitations of the proposed model provide valuable guidance for the appropriate application of the mass-spring model in the dynamic study of spindles within mechanical systems.