Measured Temperature Characteristics of 152 mm Diameter Pivoted Shoe Journal Bearings with Flooded Lubrication^©

KEITH BROCKWELL (Member, STLE)
National Research Council, Institute for Aerospace Research, Ottawa, Ontario, Canada K1A OR6

SCAN DECAMILLO (Member, STLE)
Kingsbury, Inc, Philadelphia, Pennsylvania

WALDEMAR DMOCHOWSKI (Member, STLE)
National Research Council, Institute for Aerospace Research, Ottawa, Ontario, Canada K1A OR6

The steady-state performance characteristics of journal bearings sometimes impose limitations on the operation of high-speed rotating machinery. Such limitations in bearing performance might be the result of one or more of the following: inadequate load carrying capacity, unacceptably high operating temperatures, and inefficient component performance. Lowering operating temperatures helps to boost the bearing's load and/or speed capability, and reducing bearing power loss and/or oil flow requirements improves machine efficiency.

In response to the need to improve bearing performance, the authors have conducted extensive testing of the pivoted shoe journal (PSJ) bearing. This paper describes work from the first phase of the study, in which the effects of independent design and operating variables on the metal temperatures of flooded lubricated, PSJ bearings are examined experimentally. These variables include pivot location, load orientation, shaft speed, and bearing load. In conclusion, it is shown that some of the independent variables have a significant influence on bearing performance, after comparing pad temperature profiles, isotherms, and maximum temperatures.

The study was performed on a rig that measures steady-state performance under light to moderately heavy unit loads, and comparatively high operating speeds. These conditions are representative of modem-day rotating machinery, particularly new turbine and compressor designs.

Introduction

As operating speeds have increased to improve the performance of rotating machinery, bearing designs have been pushed to their absolute limit. For example, steam and gas turbine designers are now considering the use of pivoted shoe journal (PSJ) bearings for applications operating in excess of 100 mJs. And compressor designers have intentions of operating PSJ bearings at speeds approaching 120 m/s. The dramatic increase in temperature and power loss of a 0.43 m diameter PSJ journal bearing operating in the turbulent regime has been well documented (1). This is one of a number of studies of the steady-state performance of the center pivot PSJ bearing with flooded lubrication (2)-(7). Unfortunately, other studies of offset pivot PSJ bearing designs with flooded lubrication are not so well documented (8), (9).

Tests conducted on a center pivot PSJ bearing with flooded lubrication have shown that pivot design is influential in affecting bearing steady-state performance (7). It was found that the spherical seat bearing has higher operating temperatures and power losses, and also consistently ran with a higher shaft eccentricity, than the key seat bearing. There have been other studies of the spherical seat PSJ bearing (2), (3), (5), (10), (11), and a similar number of studies of the line contact pivot PSJ bearing (4), (6), (9), (12), (13).

This is the first of a series of papers describing a new experimental and theoretical study that is intended to extend the speed and/or load capabilities, and to improve the efficiency, of PSJ bearings. The work was performed on 0.152 m (6 in) diameter PSJ bearings with rolling contact pivoted pads. This pivot is different from other types of pivot, in that the back of each pad is machined to a radius that is slightly smaller than the radius of the supporting ring. This allows each pad to roll in the supporting ring, so that their angle of inclination can change to accommodate changes in bearing operating conditions. Gardner and U1schmid (1) tested a bearing with this type of pivot, and noted that the shift of the contact point is relatively small, in comparison to the pad circumferential length. Apart from this study, there seems to have been only one other published work on the rolling contact pivot bearing (8).

This paper describes work from the first phase of the study, in which the effects of a number of independent design and operating variables on the operating temperatures of flooded lubricated PSJ bearings are examined experimentally. These variables include pivot location, load orientation, shaft speed and bearing load. The study was performed on a test rig that simulates the operating characteristics of bearings now used in modern-day rotating machinery.

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