23rd International Colloquium Tribology - January 2022 355 Observation of Grease Flow by Particle Image Velocimetry Haruka Iki Lubricants R&D Dept., ENEOS Corporation, Yokohama, Japan Department of Mechanical Engineering, Graduate School of Engineering, Kanto Gakuin University, Japan Kazumi Sakai Lubricants R&D Dept., ENEOS Corporation, Yokohama, Japan Reo Miwa Department of Mechanical Engineering, Graduate School of Engineering, Kanto Gakuin University, Japan Ryosuke Sato Department of Mechanical Engineering, Graduate School of Engineering, Kanto Gakuin University, Japan Norifumi Miyanaga Department of Mechanical Engineering, Graduate School of Engineering, Kanto Gakuin University, Japan 1. Introduction Grease characteristics are one of the most important factors that determine performances of rolling bearings. For example, it is known that bearing torque is influenced by grease flow on raceways as well as by viscosity of the base oil[1]. Furthermore, bearing noise is occurred when the thickener passing over the raceway and homogeneous dispersion of thickener is indispensable for effective noise reduction in bearings[2]. Thus, it is important to understand the flow properties for grasping the bearing performance and designing grease formulation logically and efficiently. Sakai et al. [3], visualised grease fluidity and large scale distribution in ball bearings by neutron imaging technology. However, there are few methods that could reveal grease microscopic behavior on raceways, and consequently it is difficult to grasp the complicated behavior of grease accurately. Therefore, in this study, using Particle Image Velocimetry (PIV), the observation method of flow property was established and the difference in grease flow depending on the thickener type was investigated. 2. Methodology PIV is an optical method of flow visualizations. Tracer particles are added in fluids, and speed and direction of the flow are calculated from the motion of tracer particles. Fig.1 shows the schematic image of experimental device used in the PIV analysis. By using a ball-on-disk type lubrication tester (steel ball and glass disk), the flow of grease was observed by taking pictures from above the disk with a high-speed camera after ball passing. Tested greases were composed of poly-α-olefin as base oil and urea-based thickeners. As for the urea-based thickeners, different types of thickeners -alicyclic, aliphatic (C8, C18)were also examined. 3. Results and discussion By the PIV method, grease flow towards outside of the raceway and flow back on the raceway after ball rolling were observed. Furthermore, aliphatic urea greases adhered less and were actively flowing on the raceway, whereas the flow of the alicyclic type was slow when the rotation speed is low. These results suggest that the grease flow strongly depends on the thickener type and that these differences affect bearing performance. References [1] M. Nitta, T. Tsuda, H. Arai, K. Sakamoto and K. Sakai, “Effect of Transition Point of Viscoelasticity of Diurea Grease and Molecular Structure of Thickner on Running Torque of the Ball Bearing” Tribologist, 61, 10 (2015) 699-708. [2] K. Matsubara, D. Dong and T. Endo, “Low Noise Greases for Bearings”, NLGI Spokesman, 72, 6 (2008) 25-34. [3] K. Sakai, Y. Ayame, Y. Iwanami, N. Kimura and Y. Matsumoto, “Observation of Grease Fluidity in a Ball Bearing Using Neutron Imaging Technology”, Tribology Online, 16, 2 (2021) 146-150. 356 23rd International Colloquium Tribology - January 2022 Observation of Grease Flow by Particle Image Velocimetry Fig. 1: Schematic of experimental device