Andrea Trivella

Identification of Discharge Coefficients of Orifice-Type Restrictors for Aerostatic Bearings and Application Examples

In this chapter is described an experimental study conducted in order to identify the supply hole discharge coefficients of externally pressurized gas bearings. Tests were carried out over specific hole, feed pocket and air gap size ranges on pneumatic pads with two types of air feeding systems: annular orifices (inherent orifices) and simple orifices with feed pocket. Air consumption and pressure distributions were measured as a function of supply pressure and air gap height. Discharge coefficients were approximated by an experimental formula based on the Reynolds number and the feeding system geometry. The validity of the formulation found in the study was verified by comparing the numerically calculated pressure distribution with the experimental distribution measured on different pad types. The numerical pressure distribution was calculated using equations for air flow through the supply holes and the Reynolds equations for the air gap.

High speed rotors on gas bearings: design and experimental characterization

Gas bearings are employed in a variety of applications from micro systems to large turbomachinery. As they are free from contaminants if supplied with clean air, gas bearings and pneumatic guide-ways are often used in food processing, textile and pharmaceutical industries. The new research works are focused on expanding the applications of gas bearings, in particular at very high speeds. Dental drills for example operate at speeds of over 500 krpm and it seems that a limit for gas bearings without cooling is 700 krpm [1]. Nevertheless in [2] a spindle with 6 mm diameter that operated at 1.2 million rpm is described.