Preliminary Findings:

Journal Bearing Loss of Lubrication

Summary

Fluid film bearings are widely utilized throughout industrial rotating equipment due to their ability to tolerate high operating speeds and loads when compared to rolling element bearings. While there are many benefits to using fluid film bearings, the P-F interval of fluid film bearings is extremely short. Given the short time to failure, fluid film bearing machines must be continually monitored, with the typical monitoring technique used being vibration monitoring.

The conventional technology used to monitor the health of fluid film bearings has historically been proximity probes. While effective, proximity probes require significant resources and downtime to install and maintain. Seeing these limitations, Voyager Dynamics pioneered the use of dynamic strain to monitor the health of fluid film bearings.

Available from Voyager Dynamics, the Voyager FDS sensor, offers an affordable and easy-to-install alternative to proximity probes.

The following are preliminary findings comparing the change in overall response amplitudes of proximity probes and the Voyager FDS sensor to the loss of oil pressure to plain bore fluid film bearings on a 220 lb. laboratory rotor.

Introduction

To simulate a significant fault that could rapidly fail a fluid film bearing the oil supply to the plain bore bearings of the test rotor at the Voyager Dynamics office was shut off while recording continuous data from two orthogonal proximity probes and one Voyager FDS sensor on the inboard and outboard rotor bearings.

During the test, time waveforms were logged from each transducer before and after the oil supply to the bearings was shut off. From these time waveforms, an RMS overall trend was saved with timestamps from each transducer.

The total percent change in RMS overall amplitudes measured by each sensor was calculated from the overall trends to compare the change in amplitude from the proximity probes and Voyager FDS sensor due to the loss of oil supply. It is important to note that the proximity probes were not slow-roll compensated.

The 220 lb. rotor used for this test is center-hung and directly driven by a 5-hp 4-pole motor. The data collected for the test case discussed in these preliminary findings were collected with the rotor balanced to a G12.5, the motor and rotor shifts aligned with within the coupling manufacturer's recommended tolerances, and with worn bearings each with a total diametral clearance of 0.005". 

Overall Vibration Response

Figures 1 and 2 show the change in overall amplitudes measured by the proximity probes and Voyager FDS sensor at the inboard and outboard rotor bearings respectively.

From the data, it was seen that the Voyager FDS Sensors on both bearings measured a significant increase in overall strain amplitudes after the oil pressure to the bearing was lost. Even more significant, it can be seen that while most of the proximity probes did measure a slight increase in overall displacement amplitudes, the inboard X proximity probe measured a decrease in overall displacement after the oil pressure to the inboard bearing was lost.

Conclusion

This initial data shows that the Voyager FDS is not just useful in monitoring the health of fluid film bearings, but that it is the best way to protect fluid film bearings when oil pressure is lost. More continued research is currently ongoing at Voyager Dynamics to better understand the response of these two technologies to a loss of bearing lubrication. This testing will follow the same testing procedures while varying bearing clearance, oil temperature, and rotor balance among other parameters.