Greases are semi-solid compounds formulated to protect, seal, and lubricate machine and vehicle components (gears, bearings, chassis, linkages, etc.) and are generally used when oil or fluid lubrication can't be accomplished.
Greases may act as lubricants and sealants in countless applications in an industrial or automotive setting. Grease is ideally used in machinery and engine components that:
Are not in constant operation (Stop and Go operation)
Grease's increased viscosity allows for it to stay in place and does not settle
Do not lend themselves to easy, simple lubrication
Grease may lubricate isolated or difficult-to-access components in industrial machinery
Have worn components
Grease may extend the life of previously worn parts
Greases are generally made up of three main components:
The most important component is the Base Oil itself. The Base oil is what does the bulk of the lubrication between two surfaces. You select a proper base oil similarly to how you would select a fluid lubricant and the application requirement. Base Oil viscosity is the first consideration as well as the type of base oil such as Mineral or Synthetic.
Secondly would be the type of Thickener or "Sponge" that holds the oil in place. There are many different type of Thickeners due to the way they perform in different applications such as high temperatures, high water contact, extended use applications. Currently Lithium Greases are the most popular with is about 80% of the market.
Final consideration would be the additives that are incorporated in the base oil as well as the thickener. Certain additives can provide considerable advantages in one application while being detrimental in another. For example, a grease with high levels of tackiness additive will perform well on the bucket pins of a Backhoe but in an industrial high speed bearing it would create internal friction leading to higher temperature and bearing failure.
Bottom Line, it is very important to select the proper grease for your application and PSC's has broken out the greases in multitude of categories to assist in your selection.