Grease is defined as a semisolid lubricant that generally consists of a soap emulsified with mineral, synthetic or vegetable oil. The characteristic feature of grease is that has a high initial viscosity, which upon the application of shear, drops to give the effect of an oil-lubricated bearing of approximately the same viscosity as the base oil used in the grease. “Grease” is sometimes used to describe lubricating materials that are soft solids or high viscosity liquids (but these materials do not have the shear-thinning properties of classic grease). Petroleum jellies, for example, are not generally classified as greases.
Greases are applied to mechanisms that can only be lubricated infrequently and where a lubricating oil would not stay in position. They also act as sealants to protect against water and incompressible materials. Also, grease-lubricated bearings have greater frictional characteristics due to their high viscosity.
There are a variety of characteristics of lubricating greases, which can be important in meeting the needs of industry and specific on-the-job requirements, including:
The categories of grease are typically referred to as the following grease types:
- Lithium grease
- Lithium complex grease
- Aluminum complex grease
- Polyurea grease
- Clay/bentonite grease
- Overbased calcium sulfonate grease
- Sodium Grease (Soda Soap)
Below is a brief description of each grease type, followed by where it is usually used.
Lithium is the most common grease type used globally. It is a simple soap grease that becomes smooth textured and is stable to heating. A light, general-purpose grease for home and industrial use. Lithium grease is used in plain/rolling-element bearings in: compressors, fans, centrifugal pumps, chassis parts, U-joints, water pumps on passenger cars, track rollers, and commercial lawn mowers, underground mining machinery, crushers, vibrating screens, centralized lubrication systems. It is also used for chairs, guides, hinges, cables, track, and slides.
Lithium Complex Grease
Lithium complex greases are complexes of multiple soaps, offering additional properties over a lithium grease, such as utility in higher temperature applications. It works well in automotive, construction and general industrial applications like automotive chassis, shackle joints, pins and ball joints, wheel bearings, and construction and mining equipment.
Aluminum Complex Grease
Aluminum complex grease is widely used in food and beverage processing plants because it can be made food grade grease using food grade white mineral oil or synthetic hydrocarbon. Aluminum complex greases are applicable in steel mills and mining applications because of their superior water resistance properties and ability to perform at high temperature. It is also used as a protective, anti-rust film in in food processing equipment, as a release agent on gaskets or seals of tank enclosures, and as a lubricant for equipment and machine parts that may come into incidental contact with food. Aside from the food industry, aluminum complex grease is also used in steel mills, mining, general machine and part lubrication, cold rolling mills, hot rolling tables, paper mills, and wet and dry ends.
Polyurea grease is a non-soap thickened grease that is becoming widely accepted as the best option for long life applications such as electric motor bearings, automotive and off highway constant velocity (CV) joints, roller and ball bearings, steel mill roller tracking, and high-speed spindles and fans.
Clay or Bentonite Grease
Clay (bentonite) is a popular non-soap thickened grease. These smooth-textured greases are good for high temperature/short interval applications, as they have outstanding heat resistance. They are also good for applications where frequent relubrication is needed.
Overbased Calcium Sulfonate Grease
This is “newer” technology, and the Overbased Calcium Sulfonate (OBCS) chemistry not only functions as a thickener but also as an anti-wear and EP agent and corrosion inhibitor. OBCS is an outstanding multi-purpose grease with few shortcomings or weaknesses. It is used in heavy mobile equipment, marine equipment and cables that are exposed to salt water, in wet and dry end bearings of paper machines, in the roller bearings of slab and steel mills, and in the centralized lubrication systems of automotive services.
Sodium Grease (Soda Soap)
Sodium greases are a generally fibrous textured, stringy greases that have been used as standard wheel bearing greases for years. They are low-cost greases that offer good shear stability and rust protection. However, due to their very poor water resistances, many industries have moved away from using sodium greases.
There are many applications where using oil as a lubricant is not practical or possible. Rolling bearings, for example, are almost always lubricated with grease. There are several different types of grease (as noted above) each having many variations and custom formulations, depending on the application.