Frosty Tech has posted a article "Ball Bearings Vs. Sleeve Bearings".
Since ball bearings are the favored type of bearing system we´ll begin with them. Essentially ball bearings consist of two hardened metal rings, one inside the other, separated by a set number of perfectly spherical steel balls spaced equilaterly with a bearing cage. The balls run along concave grooves set into each of the rings. Ball bearings can be found in everything from the washing machines to your hard drive to the little fans which keep your computer cool 24X7.Read more
The ball system requires a thin film lubricant for most high speed applications. What lubrication there is, is for friction reduction, heat dissipation, corrosion prevention, and long bearing life. While the balls make contact with the bearing cage, most of the friction in the system is limited to the tangents of the individual balls as they rotate around in the race ways. The balls have surface finishes on the order of 2-3 microinches and the raceways of 6-10 microinches. With such finely tuned components, proper lubrication leads to quieter performance, less torque and the most important for our situation - long life.
