It serves many purposes, but the ultimate goal of a lubricant is to reduce unwanted friction (the resistance encountered when solid surfaces slide against each other). This friction reduction is accomplished by separating two solid surfaces with a thin layer of lubricant.

Friction, unabated, can cause many problems for machinery. Every metal surface within a machine, no matter how finely finished, will have some degree of roughness, with high points called asperities. As the surfaces move past each other, these asperities come into contact and catch on one another.

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As the asperities catch and move, they rip each other apart, causing abrasions and adhesion, and in some scenarios, they can even weld and seize together. The pieces of metal torn from the component surfaces become free-moving particulates and are introduced to the machine’s lubrication system, causing further problems. Additionally, friction produces heat which, if unchecked, can quickly degrade the lubricant and cause catastrophic machine failure.

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Beyond friction reduction, lubricants can also provide:

• Heat control — The heat created by friction is absorbed and transferred by the flowing lubricant. Additionally, heat generation is reduced by the lubricant’s reduction of friction.

• Contamination control — Grease and other lubricants can be used to create a seal between a machine’s internal components and the external environment, which prevents the ingress of contamination. In addition, lubrication circulating within a machine can carry contaminants to a tank, sump or filter, where they can then be removed.

• Protection against chemical attack — Lubricants and their additives can coat the surfaces of machine components, protecting them from corrosion, such as rust.

• Transfer of energy — Hydraulic oil, because of its in-compressible nature, is used to transfer energy within a hydraulic system.