A Primer on Grease Testing for Performance and Condition Monitoring Michael D. Holloway 5th Order Industry LLC Highland Village, TX Max Martinis Whitmore Manufacturing LLC and Jet-Lube Rockwall, TX Grease manufacturers use one set of tests to characterize greases and provide useful information for technical data sheets, while end-users rely on a different set of tests to monitor the condition of inservice greases. This paper begins with a review of grease chemistry. It then explores the tests that are used for each purpose – grease selection and condition monitoring of greased bearings. Conventional as well as new tests are presented. Components There are three components of a grease - the base oil, the thickener, and performance additives. Traditionally, the base oil was considered the major component. In many conventional greases, it can be from 70 to 95% of the grease. For this reason, many bearing manufacturers consider the base oil viscosity to be a predominant factor in grease selection and approval for their products. The fact remains that, with recent technological developments in the two other components (thickeners and performance additives), the base oil has become less of a determining factor and more of a component that can have synergistic effects with other components. The second component is the thickener. This is what gives the grease its body. The thickener is typically how grease is characterized. Producing a thickener can be a complicated process. One manufacturer may attempt to produce one type of thickener for grease only to have it fall short in performance compared to other products of the same thickener type. The raw materials and the manufacturing process will dictate if a thickener will provide superior or marginal performance. Thickener types include simple metal soaps, complex soaps, synthetic organic thickeners, and inorganic gelling agents. Thickeners can account for between 2 and 40% of a grease formulation. The performance additives incorporated into the grease formulation provide specific functionality such as rust and corrosion resistance, oxidation resistance, anti-wear characteristics, extreme pressure handling, and even improved lubricity. These chemicals, both solid and liquid, can account for between 1 and 25% or more of the final grease formulation, depending on what performance criteria and targets need to be met. Table 1 lists the various general types or classes of base oils, thickeners, and performance additives.
- 26 NLGI Spokesman | VOLUME 84, NUMBER 4 | September/October 2020