Stability of rotor supported on powder lubricated journal bearings with surface pockets

Conventional oil lubricated journal bearings experience a degradation in the lubrication properties of oil at high temperatures thereby making the use of oil lubricants impractical in a hot working environment. Under these conditions, powder lubricants can be used for the successful operation of the rotor-bearing system. Whirl instability is a serious problem for rotors supported on journal bearings which restrict the system to be operated at high speeds. Surface modifications in the form pocket in the bearing can be used to improve the performance. A sudden change in film thickness caused by the presence of pocket in the bearing will generate hydrodynamic pressure which will support the external load and may influence the stability of the rotor supported on such bearings. The objective of this paper is to explore the stability characteristics of powder lubricated journal bearings employing pockets of different shapes (rectangular, trapezoidal, elliptical, and parabolic). It is observed that though the pocket of all shapes increases the whirl stability of a rotor-shaft system, the rectangular shape is the most effective among all. Therefore, such bearings may be given a rectangular pocket to increase the stability of rotors.