Abstract: Application of Greases for Gear Lubrication in Powertrains

Author Info: Benedikt Siewerin, Thomas Tobie, Karsten Stahl

Greases as lubricants are a relatively small application field for gears in powertrains compared to widely used oil lubrication. However, greases have many advantages that make them very interesting for certain machines, when special operating conditions occur. Due to their thickener, greases can build larger lubricant films in tooth contact, the adhesion properties of greases on the tooth flanks allow a reduced expenditure of sealing up to open running gear drives, and the maintenance can be reduced as well. Grease lubrication can also ensure the lubrication of the gear flanks, regardless of the spatial position they are in. During the design process of such a gearbox, the engineer can choose between different ways of applying the grease: Besides dip lubrication, it is also possible to execute spray lubrication or initial application on the tooth flanks. All these lubrication types show different performances concerning the lubricant supply to the gear mesh and thus, the main tribologically influenced failure modes on gears, such as scuffing, macro pitting and slow-speed or sliding wear. This paper presents an overview of the latest results from several research projects that have investigated many greases of different base oils, thickeners, and additive packages concerning the gear lifetime. It summarizes the main results and discusses recommendations for an optimal use of the lubricating grease.

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Abstract: Organic Solid EP Additive for Lubricating Greases

Author Info: Devin Granger, Renato Baptista de Oliveria, Shoshana Sakolsky

Solid extreme pressure (EP) additives are commonly used in greases for demanding applications. Many solid EP additives are inorganic minerals, e.g. molybdenum disulfide (MoS2), and, as these additives need to be mined, production is limited by mineral vein location and accessibility. Bio-based organic additives, as opposed to petroleum-based products, have the potential for wider availability and improved logistics. Lack of familiarity with organic solid EP additives lowers the visibility and adoption of these materials, despite lower color and improved ecotoxicology versus some mineral additives.

Described here is the comparison of laboratory performance of a bio-based organic solid EP additive, MoS2, and graphite using 3 additive-free base greases of common formulation characteristics: ISO viscosity grade 220 group I base oils combined with lithium 12-hydroxystearate, lithium complex or aluminum complex thickeners to achieve NLGI grade 2. A variety of EP and wear tests were conducted to compare performance of the additive versus industry standard EP additives.

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