KEITH BROCKWELL (Fellow, STLE; Deceased) and WALDEMAR DMOCHOWSKI (Member, STLE)
National Research Council
Institute for Aerospace Research
Ottawa, Ontario, Canada
SCAN DECAMILLO (Member, STLE)
This article presents a report on an investigation into the performance characteristics of a steadily loaded pivoted shoe journal (PSI) bearing that is lubricated with ISO VG 32 and VG 68 oils. The article describes a testing machine on which the experimental investigation was performed. Measurements of shaft torque, pad temperature distributions, oil inlet and outlet temperatures, oil flow rate, and eccentricity have all been recorded as functions of load and speed. The experimental results from both test oils are presented in graphical form and are compared with theoretical predictions obtained from the author's computer model of the PSI bearing. These results showed that the thicker ISO VG 68 oil provided thicker oil films. However, it also had higher bearing temperatures and power losses. A good correlation between the theoretical and experimental results has been found. Theoretical analysis of the bearing friction losses indicate that shear losses predominate and churning losses account for approximately 20% of the total losses.
When it comes to lubricating pivoted shoe journal (PSJ) bearings, the lubricant grade is typically based on the application. Low-speed/high-load applications often use ISO VG 68 oil to maintain a thicker oil film, whereas the majority of high-speed/low-load applications use light turbine oil, ISO VG 32, to keep pad temperatures and power losses at manageable levels. In between, there are cases where lubricant grade benefits overlap. There are also reasons to consider a change from the recommended lubricant, which may be the case in an upgrade or when different applications (e.g., a gearbox and compressor) share a common lube system. In such situations, the changes in bearing performance need to be assessed.
A number of authors have presented steady-state results from experimental work on PSJ bearings. This includes studies of bearing and bulk oil temperatures, over a wide range of bearing sizes, speeds, and unit loads (Brockwell, et a1. (1), (2); Simmons and Dixon (3); Simmons and Lawrence (4); DeChoudhury and Masters (5); DeChoudhury and Barth (6). Others have measured shaft-to-bearing displacements, also over a wide range of operating conditions (Brockwell and Kleinbub (7); Pettinato and DeChoudhury (8); Tripp and Murphy (9). All of the studies mentioned are based on tests using light turbine oils.
The purpose of this article is to fill a gap in the literature by providing information from PSJ bearing tests comparing bearing performance using ISO VG 32 and ISO VG 68 oils. Shaft torque, bearing and bulk oil temperatures, and shaft displacements have been recorded for various loads and speeds. Comparisons are made between the experimental results and theoretical predictions.
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