ABSTRACT
The primary purpose of the lubrication of machine elements is to protect surfaces in contact against damage and wear and to reduce friction in most cases. Another auxiliary role of lubrication includes heat dissipation. Effective lubrication is usually achieved by the formation of a film between the surfaces in contact. Formation of a liquid lubrication film depends on some physical properties of the lubricants, notably surface tension or wettability and viscosity. However, one can broadly put lubricants into the common categories of lubrication by gas, liquid film lubrication, boundary lubrication, and solid lubrication. In most mechanical systems, more than one of these lubricant films are active at the same time to provide effective lubrication. The lubrication of shafts in sleeve or journal bearings has been well studied in the last two centuries because these components are so widely used in power generating machinery and railroad equipment.
