STUDY OF A GAS THRUST BEARING WITH SUPPLY GROOVES

Abstract

Plane externally pressurized thrust gas bearings for high speed spindles are considered. The behavior of the rotor-bearing system is studied both numerically and experimentally. A numerical model based on Reynolds equation is used to simulate the static and dynamic behavior of the system. Flow rate equation through inlet orifices is coupled with Reynolds equation. The flow rate is calculated by considering an experimentally determined discharge coefficient, that is function of holes diameter and local clearance. To increase stiffness are studied thrust bearings presenting a circumferential groove situated at the same radius of the supply holes. The influence of the groove on stiffness and stability is discussed. Simulations are made to evaluate the influence of supply holes diameter and of axial clearance on bearing characteristics. Two thrust bearings are studied experimentally. They are composed by a symmetric couple of disks facing the rotor flange. The internal and external diameters of the disks are 52 mm and 110 mm and equipped with 8 holes of diameter 0.35 mm on a circumference of diameter 65 mm. A thrust bearing present a rectangular section circumferential groove, located at the same radius of the orifices, of width 0.7 mm and thickness 10 Pm. Comparisons between simulated and experimental stiffness are presented. NOMENCLATURE b critical ratio = 0.528 S C conductance d c discharge coefficient S d supply orifice diameter F axial force acting on the rotor (comprehensive of rotor weight) G mass flow rate h axial clearance 0 h axial clearance in central position g h groove depth K axial stiffness ISBN 4-931070-07-X T k temperature coefficient 0 T / 293 m rotor mass N number of orifices on each bearing disc P absolute pressure S P supply absolute pressure q inlet mass flow rate per unit surface Re Reynolds number 0 R gas constant = 287.6 m 2 /s 2 K r radius g r groove radius o r supply holes circumference radius S orifice section 0 T absolute temperature in normal condition t time g w groove width z axial coordinate P air viscosity N U air density in normal condition -angular coordinate Z rotational frequency