Paper 11: Capacitance Measurements and Oil Film Thickness in a Large-Radius Disc and Ring Machine

Harper

2008

Tribology Transactions

Face seals operate by allowing a small volume of the sealed fluid to escape and form a thin film between the contacting parts. The thickness of this film must be optimised to ensure the faces are separated, yet the leakage is minimised. In this work the liquid film is measured using a novel ultrasonic approach with a view to developing a condition monitoring tool. The trials were performed in two stages. Initially tests were based on a lab simulation, where it was possible to compare ultrasonic film thickness measurements with optical interference methods and capacitance methods. A direct correlation was seen between ultrasonic measurements and capacitance. Where ultrasonic and optical methods overlap, good correlation is observed, however the optical method will not record film thickness above ~0.72m. A second set of trials was carried out, where the film thickness was monitored inside a seal test apparatus. Film thickness was successfully recorded as speed and load was varied. The results showed that while stationary the film thickness varied noticeably with load. When rotating however, the oil film remained relatively stable around 2 m. During normal operation of the seal, both sudden speed and load changes were applied in order to initiate a seal failure. During these events, the measured film thickness was seen to drop dramatically down to 0.2 m. This demonstrated the ability of the technique to predict failure in a face seal and therefore its aptitude for condition monitoring.

Section: Acoustic Materials Propertiesmentioning

confidence: 99%

“…Electrical resistance and capacitance have proved useful methods in general film thickness measurement, as have optical methods. However, both these approaches require modifications (electrical contacts and an optical window, respectively) to the bearing machinery that hinder their practical application to seal monitoring [4][5][6][7][8].…”

Section: Introductionmentioning

confidence: 99%

A New Approach for the Measurement of Film Thickness in Liquid Face Seals

Reddyhoff

Harper

2008

Tribology Transactions

“…Researchers have used a range of techniques to monitor lubricant film thickness such as optical [6,7], capacitance [8,9] and eddy currents [10]. These approaches have the attraction that they provide additional information to the traditional techniques (and acoustic emission), and offer the potential to give early warning of failure and/or other diagnostic information.…”

Section: Introductionmentioning

confidence: 99%

Monitoring of Lubricant Film Failure in a Ball Bearing Using Ultrasound

Zhang

Drinkwater

2006

Journal of Tribology

A lubricant-film monitoring system for a conventional deep groove ball bearing (type 6016, shaft diameter 80 mm, ball diameter 12.7 mm) is described. A high frequency (50 MHz) ultrasonic transducer is mounted on the static outer raceway of the bearing.The transducer is focused on the ball-raceway interface and used to measure the reflection coefficient of the lubricant in the 'contact' ellipse between bearing components. The reflection coefficient characterises the lubricant film and can be used to calculate its thickness. An accurate triggering system enables multiple reflection measurements to be made as each lubricated contact moves past the measurement location.Experiments are described in which bearings were deliberately caused to fail by the addition of acetone, water and sand to the lubricant.Ultrasonic reflection coefficient was monitored as a function of time as the failure occurred. Also monitored were the more standard parameters, temperature and vibration. The results indicate that the ultrasonic measurements are able to detect the failures before seizure. It is also observed that, when used in parallel, these monitoring techniques offer the potential to diagnose the failure mechanism and hence improve predictions of remaining life.

“…Electrical resistance and capacitance have proved useful methods, as have optical methods. However, both these approaches require modifications to the bearing machinery that frequently preclude their application outside of the laboratory [1][2][3][4][5]. One method that shows potential for non-invasive oil film measurement is the use of ultrasonic reflection.…”

Section: Introductionmentioning

confidence: 99%

“…Combining (1) and (3) gives a relationship between reflection coefficient and liquid film thickness. This has subsequently been used to measure the oil film in rolling element bearings [17], hydrodynamic journal bearings [18], piston ring liner contacts [19], and thrust pad bearings [20].…”

Section: Introductionmentioning

confidence: 99%

The Phase Shift of an Ultrasonic Pulse at an Oil Layer and Determination of Film Thickness

Reddyhoff

Kasolang

Proceedings of the Institution of Mechanical Engineers, Part J:

et al. 2005

Published paper KeywordsOil film thickness measurement, ultrasound, phase difference, phase shift, ultrasonic reflection AbstractAn ultrasonic pulse incident on a lubricating oil film in a machine element will be partially reflected and partially transmitted. The proportion of the wave amplitude reflected, termed the reflection coefficient, depends on the film thickness and the acoustic properties of the oil. When the appropriate ultrasonic frequency is used, the magnitude of the reflection coefficient can be used to determine the oil film thickness. The reflected wave, however, has both a real and an imaginary component, and both the amplitude and phase are functions of the film thickness. The phase of the reflected wave will be shifted from that of the incident wave when it is reflected. In the present study this phase shift is explored as the film changes and is evaluated as an alternative means to measure oil film thickness. A quasi-static theoretical model of the reflection response from an oil film has developed. The model relates the phase shift to the wave frequency and the film properties. Measurements of reflection coefficient from a static model oil film and also from a rotating journal bearing have been recorded. These have been used to determine the oil film thickness using both amplitude and phase shift methods. In both cases, the results agree closely with independent assessments of the oil film thickness. The model of ultrasonic reflection is further extended to incorporate mass and damping terms. Experiments show that both the mass and the internal damping of the oil films tested in this work has a negligible effect on ultrasonic reflection. A potentially very useful application of the simultaneous measurement of reflection coefficient amplitude and phase is that it the data can be used to negate the need for a reference. The theoretical relationship between phase and amplitude is fitted to the data. An extrapolation is performed to determine values of amplitude and phase for an infinitely thick layer. This is equivalent to the reference signal determined from measuring the reflection coefficient directly, but importantly does not require the materials to be separated. This provides a simple and effective means of continuously calibrating the film measurement approach. 1