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PurposeThe 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/approachThe 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.FindingsIt 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/valueThe 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.

Purpose -This paper is the third part of a serial studies for constant and variable compensations of the closed-type hydrostatic thrust bearings which has face-to-face recesses couple. The static stiffness of closed-type hydrostatic thrust bearings can then be obtained from the differentiation of recess pressure with respect to worktable displacement. The paper aims to discuss these issues. Design/methodology/approach -In this paper, the double-action restrictors of cylindrical-spool-type and tapered-spool-type are taken into consideration for variable compensation of hydrostatic bearings. Findings -The static stiffness in thrust direction of hydrostatic bearing is determined by the flow continuity equations that are formulated by film flow and compensation flow for each recess, respectively. The type selection and parameter determination of the double-action spool-type restrictors can be obtained from finding results of this study for maximum stiffness in design of hydrostatic bearings. Originality/value -This study reveals that the appropriate range of recess pressure ratio and design parameters of restrictors for the maximum stiffness can be obtained, the avoidance of negative stiffness is also provided.

Purpose -The purpose of this paper is to study the influences of both the number and locations of entry holes on the static and dynamic characteristics of a rigid rotor supported by two double-rows, inherently compensated aerostatic bearings. Design/methodology/approach -The air is assumed to be perfect gas undergoing the adiabatic process and passing through entry holes into the bearing clearance. Air film in the clearance is governed by Reynolds equation including the coupled effects of wedge due to rotor rotation and squeezed film due to rotor oscillation. Findings -The method is used to analyze Reynolds equation, which is then solved by the finite difference method and numerical integration to yield static and dynamic characteristics of air film. The equation of motion of the rotor-bearing system is obtained by using the perturbation method and the eigensolution method is used to determine the stability threshold and critical whirl ratio. Originality/value -The paper considers the eccentricity, rotor speed, and restriction parameter in the analysis of the whirl instability of the rotor-aerostatic bearing system for the comparisons between various designs in the number and locations of entry holes of aerostatic bearings.