Flow Properties of Lithium Stearate-Oil Model Greases as Functions of Soap Concentration and Temperature

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Abstract
Lithium stearate-oil greases having 4, 8, and 12% soap were prepared and flow properties of the greases were investigated, at 0, 25, and 37.8 C. Flow data were obtained with a cone and plate viscometer equipped with automatic programming and recording of shear stress versus rate of shear, and of shear stress versus time at selected shear rates. Flow curves, shear stress versus shear rate, were obtained for an initial and a repeat 300-sec cycle of shear with maxima of 1520 sec−1 and of 15,200 sec−1, Flow curves were measured for highly worked samples, previously sheared at 19,000 sec−1 for 1000 sec. The rate of change of shearing stress required to maintain a constant rate of shear was measured at nine shear rates in the interval from 190 sec−1 to 19,000 sec−1. Similar flow measurements were made on greases containing stearic acid additives. Initial flow resistance, ascribed to soap structural elements, showed temperature and concentration dependence differing from that of the sheared soap, and was destroyed by continued shear or addition of stearic acid. Flow resistance of the sheared samples was dependent on both the magnitude of the shear rate and the time of subjection to the shear.

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