Mixing rheometry for studying the manufacture of lubricating greases

The overall objective of this work was to evaluate the manufacture of lubricating greases through the mixing rheometry technique, by studying the effect of some processing variables such as rotation speed, intensity and duration of the homogenization treatment and thermal profile applied, in terms of the power-draw characterization and rheological behaviour of the final product. With this aim, lithium lubricating greases were prepared by inducing the saponification reaction between 12-hydroxystearic acid and hydrated lithium hydroxide within a naphtenic lubricating oil medium in an open vessel. The saponification reaction occurred until neutralization by stirring with a control led-rotational speed mixing rheometer using an anchor impeller. Different rotational speeds were selected. Finally, a highly intensive homogenization treatment was applied using a rotor-stator turbine in order to reduce crystal sizes. Different homogenization treatments and cooling profiles were applied on the incipient greases. The manufacture of lubricating greases was always followed through the evolution of torque with processing time. The experimental results obtained demonstrate that the mechanical behaviour of a lubricating grease strongly depends on some of the processing variables studied. Some exponential models have been proposed to evaluate the influence of the processing variables on both the consistency index and the linear viscoelastic plateau modulus of the lubricating greases. (c) 2004 Elsevier Ltd. All rights reserved.