UBC Theses and Dissertations
Rheological characterization of fumed silica lubricating greases Zakani, Behzad
Lubricating greases have been widely used for rail lubrication systems. For an efficient grease pump design, it is important to study grease shear viscosity and it is also crucial to analyze grease yielding behavior to determine its consistency on rail surface. Among all rheological properties measured through experiments, yield stress is an ill-defined property, which investigation of a reproducible method for its determination can be invaluable. As the flow properties of a material will be usually influenced by the changes in environment temperature, studying the effects of temperature on the rheological properties of grease are important. In this study, different rheological measurements and visualization techniques, previously developed to study a wide range of materials, have been performed to characterize fumed silica based lubricating greases manufactured by L.B. Foster Rail Technologies Corp. Using commercial rheometers and different approaches to determine the yield points of these materials, it was revealed that the values obtained by curve fitting on steady-state flow curves, creep, amplitude sweep crossover and stress ramp-up were roughly similar. The microstructure of this grease was analyzed using Scanning Electron Microscope (SEM) on Cryo and non-Cryo modes. Besides visualizing a new thickener microstructure, it was shown that the heterogeneous structures developed by small fumed silica agglomerates lead to the formation of greases with higher shear viscosities. Finally, thermo-rheological analysis of these samples revealed that these materials follow neither Arrhenius equation nor time-temperature superposition principle.
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