Use of rotating machinery to convert raw power into useful work is a fundamental
block of modern industrialized civilization. This rotating machinery
is involved in almost every facet of life, be it the crank shaft in the engine of a
tractor used to harvest soy beans, the hub on a bicycle, or the turbine/generator
unit in a hydro-power station delivering electricity to the electrical grid. Regardless
of their scale and use, rotating machines have some similarities: they
all have at least one rotating part and that rotating part must be separated from
the stationary portion of the machine by some sort of bearing. This bearing
provides an easily sheared layer that allows the surface of the rotating part
(shaft) to slide relative to the stationary part. This interface and the surfaces
which bound it are central to the study of Tribology, the study of surfaces in
relative motion including friction, lubrication and wear.
In the case of large rotating machines such as steam turbines, hydro-electric
turbines and other electrical power generators the machine’s shaft is most commonly
isolated from the stationary equipment through the use of journal bearings.
To maintain low friction and minimize wear of the surfaces, these journal
bearings are filled with lubricant.