Measured Performance of Tilting-Pad Journal Bearings over a Range of Preloads—Part I: Static Operating Conditions

Abstract

This article presents the measured static characteristics for five tilting-pad journal bearings with a range of preload factors. The bearings had five shoes with static forces applied both on the pad and between pads. The journal diameter was 70 mm, with a length-to-diameter ratio of 0.75, a pivot offset ratio of 0.50, and a nominal assembled radial clearance of 81.3 μm. The rocker-backed pads have nominal radial machined clearances of 176.8, 114.3, 91.4, 73.7, and 61.0 μm. These clearances constitute a range of preloads from −0.333 to 0.540. Most tilting pad bearings are intentionally designed with positive preloads, although with pivot wear and/or pad and pivot distortion or machining tolerances, bearings can operate with zero or negative preloads. Measured results for bearings with negative preload factors have not previously been available. Measurements reported here were made for a variety of speed-load conditions encompassing a Sommerfeld number of 0.1 to 4.5. The measured parameters are eccentricity magnitude, attitude angle, film thickness, and temperatures sufficient to define thermal boundary conditions. Also measured are oil supply pressure, flow rate, and on-shaft pressure profiles. The focus of the work presented herein is to quantify the influence of preload on film thickness, maximum pad temperature, and eccentricity magnitude and attitude angle. Measurements showed preload had a moderate influence on operating eccentricity but not on attitude angle. Negative preloads resulted in the greatest temperature rise, although all temperature rises were relatively small.