Trends in gear oil additives

Abstract

AbstractOf the total amount of additives produced and sold in the world, gear oil additives are the second largest group, after the engine oil additives. According to the purpose of the finished lubricant, these additives can be classed as either additives for automotive gear lubricants or additives for industrial gear lubricants. Although the main function of such additives is the same for both types of lubricants, namely to reduce friction and wear and avoid surface fatigue, permanent deformation of the tooth, and excessive wear, the requirements that these lubricants have to meet are different. The most important specifications for automotive gear lubricants are, in the USA, API GL‐1—GL‐6, and MIL L 2105 A—2105 D, respectively, whereas in Europe manufacturers tend to have taken GL‐4 or GL‐5 as a basis, and added their own supplementary requirements. Industrial gear lubricants are manufactured according to US Steel 224 specification, DIN 51517/3, and AGMA 250.04. The gear oil additives themselves are based on sulphur and phosphorus chemistry, but other chemicals are introduced into the additive packages to ensure oxidation stability, anti‐corrosion protection, copper compatibility and better seal compatibility. Boron compounds are shown to improve the antiwear and extreme‐pressure properties of the lubricants, as well as oxidation stability, thermal stability and detergency. Rig and bench tests demonstrate the benefits of adding boron compounds to fully formulated GL 5 oils and to classic sulphur‐phosphorus additive packages for automotive and industrial gear oils.