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Sheffield, United Kingdom

Zhang K.,Xian Jiaotong University | Meng Q.,Xian Jiaotong University | Chen W.,Xian Jiaotong University | Li J.,Xian Jiaotong University | Harper P.,Tribosonics Ltd
Industrial Lubrication and Tribology | Year: 2015

Purpose - This paper aims to measure the oil film thickness between the roller and the inner ring in roller bearings by the ultrasonic method. The oil film thickness between the roller and the inner ring in roller bearings is a key performance indicator of the bearing lubrication condition. As the oil film is very thin and the contact region is very narrow, measurement of this film thickness is very challenging. A promising ultrasonic method was used to measure this film thickness, and this method was expected to overcome some drawbacks in other methods. Design/methodology/approach - A simplified roller bearing only configured one roller, and an inner ring was built up to investigate this measurement. A miniature piezoelectric element is bonded on the inner surface of the inner ring to measure the reflection coefficient from the layer of oil between the roller and the inner raceway. As the width of the line contact region is smaller than the width of the piezoelectric element, a ray model is used to calibrate the reflection coefficient measured. The quasi-static spring model is then used to calculate oil film thickness from the corrected reflection coefficient data. Findings - The results measured by this method agree reasonably well with predictions from elastohydrodynamic lubrication (EHL) theory. Also, a dynamic displacement of the rig caused by the skid of the roller versus the inner ring was found under light-load and high-speed conditions. Originality/value - This work shows that the oil film between the roller and the inner raceway in roller bearings can be measured accurately by ultrasound and shows a deal method when the contact width is smaller than the piezoelectric element width. © Emerald Group Publishing Limited. Source

Hunter A.,University of Sheffield | Dwyer-Joyce R.,University of Sheffield | Harper P.,Tribosonics Ltd
Measurement Science and Technology | Year: 2012

Interfacial thin liquid films between solid bodies have been measured using ultrasonic reflective techniques in a range of tribological applications such as those present in hydrodynamic bearings, piston rings and mechanical seals (Dwyer-Joyce et al (2004) Tribol. Lett. 17 337-48, Dwyer-Joyce et al (2006) Proc. Instn Mech. Eng. A 220 619-28, Reddyhoff etal (2006) Tribol. Trans. 51 140-49, Harper et al (2005) Tribol. Interface Eng. Ser. 48 305-12). There are two main ultrasonic methods used, the spring model and film resonance techniques. For very thin films (<20μm) a simple quasi-static spring model has been used to show that the proportion of the wave reflected by the liquid layer depends on the stiffness of the layer. This stiffness can be related to the layer thickness and its material properties. In the film resonance technique the incident ultrasonic wave is used to resonate the liquid layer. The frequency of resonance can then be related to the layer thickness. This paper collates four experiments where oil film thickness is measured by both ultrasonic reflection and an independent method. In the first three experiments the film thickness is measured ultrasonically and this measurement is compared to the thickness inferred from the geometry of the surfaces constraining the liquid film. In the final experiment the ultrasonic results are compared to measurements taken using capacitive and verified laser interferometer techniques. Excellent correlation was observed between the measurement methods in all of the experiments. In particular the film resonance technique showed repeatable and consistent results across a wide range of film thicknesses. The spring model showed a degree of agreement for films above a few microns but this relationship diverged as the film thickness approached the magnitude of the surface roughness. © 2012 IOP Publishing Ltd. Source

Brunskill H.,Tribosonics Ltd | Harper P.,Tribosonics Ltd | Lewis R.,University of Sheffield
Wear | Year: 2015

Ultrasonic reflectometry is commonly used in the fields of non-destructive testing (NDT) for crack detection, wall thickness monitoring and medical imaging. A sound wave is emitted through the material using a piezoelectric transducer. This waveform travels through the host medium at a constant speed and is either partially or fully reflected at an interface. The reflected wave is picked up by the same sensor; the signal is then amplified and digitised. If the speed that sound travels through a host medium is known as well as the time this takes, the thickness of the material can be established using the speed, distance and time relationship.Previous work has concluded that the ultrasonic method is too inaccurate to measure wear due to the errors caused by temperature, vibration and the experimental arrangement. This body of work looks at methods to minimise these errors, particularly the inaccuracies introduced from the change in temperature caused by change of acoustic velocity and the thermal expansion of the material, which can be significant in many applications. Numerous case studies are presented using the technique in both laboratory and industrial environments using low cost retro-fittable sensors and small form electronics. © 2015 Elsevier B.V. Source

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