Abstract:
Over 80 percent of bearings are grease lubricated world over due to many
advantages and ease of application. It is a semisolid lubricant which offers the
advantages of two lubricating groups viz. lubricating oils and solid lubricants.
Lubricating greases are intermediate in their properties between liquid lubricants
(oils) and solid lubricants. Grease can be defined as "A solid to semi fluid product of
dispersion of a thickening agent in a liquid lubricant. Other ingredients imparting
special properties may be incorporated" (ASTM D 288, Standard Definitions of
Terms Relating to Petroleum). Greases are thixotropic materials under normal
conditions. Owing to their semisolid nature and are not thrown out of open
lubrication points by centrifugal forces, and thus can be applied to unsealed
lubrication points. However, when the load is increased and a critical value has been
reached, the grease gets deformed and may start flowing like ordinary lubricating oils.
Mechanical stable greases used in goos sealed bearings do not leak out even reaching
near critical loaded conditions. Grease is often expected to perform as a seal,
corrosion inhibitor, shock absorber, water resistance and a noise suppressant.
