Extensional Rheology: New Dimension of Characterizing Automotive Fluids

Paper #:
  • 2017-01-0364

Published:
  • 2017-03-28
Abstract:
A variety of performance fluids and lubricants are used in automobiles and in automotive manufacturing processes. These include engine oils, driveline fluids, paints, forming lubricants, and many others. Controlling the rheological properties of these fluids is crucial to achieve desired performance and product qualities. In this study, we have applied Extensional Rheometry to gain a new insight on the performance of automotive fluids. Traditionally, rheological experiments focused on the study under shearing flow. However, the real operations contain both shear and ‘extensional’ (or ‘elongational’) flow components. In this paper, we have investigated the extensional behavior of automotive fluids using a Capillary Breakup Extensional Rheometer. (The extensional viscosity express how “sticky” the fluid is, whereas shear viscosity means how “slimy” the fluid is.) The operation contains 3 basic steps: (1) fluid sample is placed between two plates, (2) Then the two plates are separated rapidly, (3) after the plate movement stopped, laser micrometer monitors the diameter of the gradually thinning fluid filament as a function of time. During the measurement, the fluid temperature was precisely controlled with an external circulator. We added a high-resolution, high-speed digital imaging system to observe fluid deformation process in-situ. The raw data of filament break-up behavior gave significant insight of the fluid properties. The model fitting analysis was used to determine the extensional viscosities. Excellent stability and repeatability of the technique was apparent with the trials using polybutane viscosity standard oil. The experimental data and analysis are presented for a variety of automotive fluids, including fully-formulated driveline fluids. The effect of lubricant additives are also presented which clearly showed the influence of surfactant and polymer additives to the extensional behavior. The study showed that Extensional Rhemometry can provide very useful information to the automotive fluid systems.
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