Performance Experiments with a 200 mm, Offset Pivot Journal Pad Bearing

Journal bearings are an important design option, particularly appropiate for high-speed rotating machinery applications. This paper presents results from an extensive program of experimental work with a 200 mm, five-shoe, tilting-pad bearing of this type. The tilting pads were fitted with offset pivots; this is in contrast to most previous work which has concentrated on bearings with pads which have centrally mounted pivots. The new results obtained for the offset pivot pad bearing are compared with recently published, equivalent results for the same bearing fitted with center pivot pads. A substantial temptature reduction in bearing tempature is revealed for the offset pivot case.

Introduction

Tilting-pad, hydrodynamic journal bearings are widely used in industry for a range of machinery and are particularly appropiate for high-speed applications. In many cases, center pivot pads are used and prove very satisfactory. Pressure to design and operate machinery capable of operating at enhanced speeds and loads puts a premium on cooler-running bearing design. For this reason, offset pivot pads which lead to significantly cooler bearings and increased hydrodynamic film thickness are frequently employeed as a design option. Published experimental work with tilting-pad journal bearings has concentrated on bearings with center-pivoted pads and a recent paper (1) presented a new set of comprehensive data for such a five-pad, 200 mm diameter bearing.

The purpose of this new paper, which complements the one refered to above, is to present additional results particular to offset pads and compare these results with the already available center pivot findings. So far as the authors have been able to determine, with one exception, no similar experiments involving a journal bearing fitted with offset pivot pads have been previously reported. Hence, it is hoped that results of this paper will be of interest both to the academic community and to industry supplier and users.

The exception mentioned above is an interesting paper by Brockwell et al. (2) mainly concered with a rather different journal bearing, namely a tilting-pad, leading edge groove (I.EG) bearing. For comparison purposes, Brockwell and his colleagues included some experiments with a 100 mm, conventional, i.e., non-LEG, offset pivot, journal pad bearing.