Aerostatic porous bearings have been successfully applied to various precision devices such as machine tools and measuring equipment to achieve a higher accuracy of motion. However, aerostatic porous bearings have a disadvantage in that they are prone to cause pneumatic hammer instability. Therefore, to avoid this instability, a surface-restricted layer that has permeability smaller than the bulk of the porous material is usually formed on the bearing surface. In this paper, the dynamic characteristics of aerostatic porous journal bearings that have a surface-restricted layer are investigated numerically and experimentally. The effects of permeability in bulk porous materials and of a surface-restricted layer on the bearing characteristics are discussed using two kinds of porous material: graphite and metal. It was confirmed that aerostatic porous metal bearings with relatively large permeability could achieve large values of dynamic stiffness and damping coefficients using a low permeability, surface-restricted layer.

Issue Section:
Hydrodynamic Lubrication
Keywords:
aerostatic journal bearing, porous bearing, surface-restricted layer, dynamic characteristics, damping, elastic constants, graphite, machine bearings, permeability, porous materials
Topics:
Bearings, Graphite, Journal bearings, Permeability, Porous materials, Stiffness, Metals, Clearances (Engineering), Damping
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