Behavior of a Tilting–Pad Journal Bearing With Different Load Directions

Abstract

Tilting–pad journal bearings (TPJBs) are widely used in rotating machinery to support the rotors efficiently at elevated speeds under light/heavy loadings. Because of the importance of this machine component, many authors have published several theoretical and experimental studies, to evaluate the influence of clearance, lubricant temperature, oil flow-rate and thermal effects on behavior of TPJB. However, the investigations of the influence of loading direction on properties of TPJB are very limited. In bearing models as well as in experimental tests, the load is often assumed along the vertical direction only and the geometry of the bearing is the same for each pad, which corresponds to an axial symmetry of the bearing. This paper presents first a theoretical analysis of the influence of the load direction on both the static and the dynamic behavior of a five-pad TPJB with a non-uniform clearance: that is, the different bearing configurations in the range between load-on-pad (LOP) and load-between-pads (LBP) are investigated. Then, the analytical results are compared with experimental measurements. The tests were performed with a nominal diameter of 100 mm and a length–to–diameter ratio of 0.7, using a suitable test-rig, in which it is possible to apply the static load in any direction. The procedure for the estimation of the bearing geometry from experimental measurement of the non-uniform clearance profile is also described. The results show that the load direction has considerable effects on both the static and the dynamic characteristics of the TPJB. Besides, the influence of load directions is stronger on the dynamic characteristics of tilting pad bearing than on the static ones.