Environmentally Acceptable Ester-Based Hydraulic Fluids

In industrial applications, hydraulic drives are used when large forces or torques need precise control and in the case of mobile equipment where power density and weight become crucial. To perform the drive's functions over the system's lifetime, the hydraulic fluid must be considered as a system component starting with the design of the drive application. Due to a societal increase in environmental consciousness in the late 1980s, regulatory agencies started demanding that these fluids be rapidly biodegradable and nontoxic. This excluded most mineral oil from consideration. Currently, vegetable oils, a variety of synthetic esters, special hydrocarbons and polyglycols are being used for these applications. This chapter gives an overview of ester-based hydraulic oils. The focus is on the influence of different alcohol and fatty acid components on the properties of the basic oils. With regard to hydraulic applications, the rheological behavior and the aging stability are especially important. These properties can be examined by a lot of ASTM and DIN standardized test methods. Furthermore, IFAS has developed special experimental setups and procedures for investigating the aging stability or the content of ester-based oils in hydraulic systems.