Published: Jan 2010
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THE MAJOR FUNCTION OF LUBRICATING OILS IS the reduction of friction and wear by the separation of surfaces, metallic or plastic, which are moving with respect to each other. The oils also act as carriers for many special chemicals such as corrosion inhibitors, antiwear agents, load-carrying friction modifiers, and foam suppressors. Performance requirements can also include cooling, the dispersion and neutralization of combustion products from fuels, and the transport of contaminants to a filter. The high-quality and improved properties of present-day lubricants have enabled engineers to design machines with higher power-to-weight ratios that generally have higher stresses, loads, and operating temperatures than before. Thus, it has been possible to develop automobile engines, turbines, gear sets, etc. that are capable of higher speeds and higher specific power output per unit weight of machinery. In a very different field, lubricants with increased resistance to the effects of radiation have been developed for nuclear power stations. From a historical standpoint, solvent-refined paraffinic oils have been the most widely used base stock for lubricating oil applications. In recent years, alternative refining processes such as catalytic isomerization and deep hydrogenation have been developed to yield higher purity base oils that are better suited to withstand severe operating conditions. Research in the field of additives has, in turn, produced lubricant formulations that can operate under the higher piston-ring belt temperatures of super-charged automotive diesel engines and provide the dispersion required to prevent the formation of low-temperature sludge in gasoline engines for stop-start, short-distance motoring. Despite the increasing temperatures, loads, and other requirements imposed on lubricants, mineral oils are likely to continue to be employed in the foreseeable future for the majority of automotive, industrial, and marine applications. However, in the aviation field, synthetic lubricants are used extensively. There are also a growing number of critical automotive, industrial, and marine applications where the use of synthetic lubricants can be justified on the basis of total performance or fire resistance.
Sauer-Danfoss, Ames, IA