Influence of the number of feeding holes on the performances of aerostatic bearings

Purpose - The purpose of this paper is to study the influence of number of feeding holes on the performance of aerostatic bearings with spindle rotation. In traditional design of aerostatic bearings, the selection of hole numbers is dependent only on spindle size. However, when the hole numbers of air feeding are enough, the performance of the aerostatic bearing cannot be enhanced by increasing the hole numbers. Design/methodology/approach - The Reynolds equation is utilized to model the air film within bearing clearance at constant temperature and the state equation of adiabatic process is for air feeding within bearing clearance. The finite difference method with relaxation algorithm is utilized to determine the pressure distributions from discretized and coupled equations of flow continuity. The eccentricity, spindle speed, and the number and arrangement of feeding holes are considered in the analyses to determine the load capacity, attitude angle, and flow rate for the comparisons between various designs of aerostatic bearings. Findings - It is seen from the simulation results that the aerostatic bearing designed with a small number of feeding holes and without locating at bearing bottom is most suitable for the spindle operating at high speed, while the bearing designed with a large number of feeding holes is suitable for the spindle operating at low speed, and the load capacity is increased with the increasing number of feeding holes for low journal speed. Originality/value - The paper proposes an extensive database as a critical requirement in the design for number and arrangement of feeding holes of aerostatic bearings for the spindle operating at low or high speed.