Fundamentals of lubrication

Abstract

Lubricants are substances used to minimize the friction and wear of moving parts. Additionally, they can serve to distribute heat, remove contaminants, and improve the efficiency and lifetime of mechanical systems. Lubricants can generally be categorized as liquid, solid, or gaseous. Liquid lubricants consist of base oils such as natural oils, mineral (petroleum) oils, and synthetic oils with combinations of additives that further enhance the properties of the lubricants. Solid or dry lubricants are generally powders or semisolids in the form of a grease or solid-liquid suspension. Gaseous lubricants have a much lower viscosity than liquid or solid lubricants and utilize gasses such as air under pressure. The selection of an appropriate lubricant for a mechanical system requires a thorough understanding of the rheology of lubricants, the effects of additive combinations, and the knowledge of lubrication theory. Lubrication theory is linked to numerous fields of expertise outside of tribology, and without this interdisciplinary aspect, the progression of lubricants and lubrication technologies within the vast array of applications may not have reached the necessary levels of success. The use of liquid lubricants is ubiquitous in most applications, ranging from automotive fluids, to industrial oils, and process oils. Within the lubrication industry, there are over 10,000 different lubricants used around the world. This chapter explores the many aspects of lubricants and lubrication technologies including lubrication fundamentals, rheology of liquid lubricants, liquid lubricant additives, and liquid lubrication theory.