Lubricating Grease

Over the centuries all sorts of materials have been employed as grease, including olive oil and animal fat mixed with lime. The first synthetic calcium soap grease was produced in the 1840s. Today grease is a complex product that is primarily a combination of three ingredients: a thickener, a base oil (also called a lubricating oil or fluid) and performance additives.

Grease can be described as a solid or semi-fluid lubricant consisting of a thickening agent in a liquid lubricant. Other ingredients imparting special properties may be included. Grease consists of a liquid lubricant that is mixed with a thickener. Additives imparting special properties may also be included.

Although it is liquid lubricant (and certain additives) in the grease that provides the necessary lubrication, grease and oil are not interchangeable in their applications. The combination of the thickener, fluid and additives incorporated in grease produce certain properties or characteristics that grease does not share with lubricating oil.

The base oil in grease can be mineral or synthetic, however mineral base oils are used in the majority of greases. The base oil viscosity in grease has a fundamental influence on the lubrication performance of the grease. The base oil viscosity of grease can range from 15 cSt in high speed bearing greases to over 3000 cSt in slow speed, heavy load applications.

Grease thickeners have a significant effect on grease performance. The thickener can be described as a three-dimensional network or matrix throughout the base oil. Examples of thickeners used in grease are metallic soaps such as lithium, calcium and sodium, non-soap thickeners such as polyurea and clay and complex soaps such as lithium complex, barium complex and aluminium complex. The type of thickener used has a fundamental effect on grease performance and characteristics.

Additives in grease have a similar role to additives in lubricating oils. Typical additives used in grease include oxidation inhibitors, extreme pressure (EP) additives, anti-wear additives and corrosion inhibitors.

Grease is used as a lubricant in applications where a continuous supply of oil cannot be provided. In most cases grease lubrication is preferred when: the operating speed is low, extreme pressures are present, the equipment operates intermittently or is subject to reversals of load, the equipment is difficult to access for frequent lubrication, or where leakage of a fluid lubricant cannot be tolerated (e.g. food processing equipment).

Greases are not suitable for applications where the lubricant is used for cooling or where it is required to flush away wear debris and contaminants (as is the case for oils in circulating lubrication systems). At high speeds, agitation of the grease by the rolling elements generates friction and heat that reduces lubrication efficiency and may cause the grease to fail prematurely.