Lubricating greases are semi-fluid or solid lubricants consisting of a thickening agent in a liquid lubricant. They differ from conventional lubricating oils in that they are non-Newtonian in behaviour and will not flow unless stressed under shear beyond a certain value, known as the yield value. It is this ‘non-flowing’ characteristic of greases that enables them to offer certain advantages over lubricating oils and results in their extensive use for the lubrication of rolling contact bearings. This paper outlines the uses and limitations of grease lubrication in rolling bearings. In particular, factors that can influence performance, such as bearing design, speed and temperature, are dealt with in some detail. In addition, new lubrication problems encountered in atomic reactors and aerospace equipment, involving nuclear radiation and inert atmospheres, are discussed, together with steps taken to solve the problems. In conclusion, the paper outlines observations made on the mechanism by which a grease lubricates and also suggests possible future trends in grease development which will be required to cater for the more exacting operating conditions demanded by modern machinery.
The importance of the work of Duncan Dowson for modeling grease lubrication in rolling bearings
