| Abstract: | ![]()
Mobile hydraulic equipment is often subjected to a wide range of operating temperatures, and so must be lubricated with oils with a high viscosity index (VI) in order to maximise efficiency. Formulating high‐VI hydraulic oils is a complex task that requires testing numerous intermediate blends in order to achieve the desired viscosity at both low and high temperatures. With the introduction of the ASTM D 6080 hydraulic oil classification, which defines a separate grade at low and high temperature for high‐VI oils, and further includes VI and viscosity measurements after the sonic shear test, formulating high‐VI hydraulic oils has become even more complex. In order to determine the most effective VI improver to meet a given set of viscosity requirements, a large statistically designed experiment has been carried out. Empirical equations have been obtained that can be used to model the blending efficiency of VI improvers at different temperatures and to estimate their shear stability. This paper shows how the results obtained for 42 hydraulic oils have been used to develop a computer program aimed at facilitating the formulation of high‐VI hydraulic oils. |
