Bearings. Journal principles

Hydrodynamic principles for gas bearings are similar to those involved with Hquid lubricants except that gas compressibility usually is a significant factor (8,69). With gas employed as a lubricant at high speeds, start—stop wear is minimized by selection of wear-resistant materials for the journal and bearing. This may involve hard coatings such as tungsten carbide or chromium oxide flame plate, or soHd lubricants, eg, PTFE and M0S2. 

Externally pressurized gas journal bearings have the same principle of operation as hydrostatic liquid-lubricated bearings. Any clear gas can be used, but many of the design charts are based on air. There are three forms of external flow restrictors in use with these bearings pocketed (simple) orifice, unpocketed (annular) orifice, and slot. 

If the effects of lubricant inertia can be neglected, then the performance of a journal bearing is determined by the entrainment velocity, the sum of the surface velocities of the rotor and the bearing. Applying this basic principle, the system shown in fig. 2b has exactly the same behaviour as that in fig. 2c where ... 

Archeological evidence dating to before 1400 B.C. shows the use of tallow to lubricate chariot wheel axles. Leonardo da Vinci discovered the fundamental principles of lubrication and friction, but lubrication did not develop into a refined science until the late 1880 s in Britain when Tower produced his studies on railroad car journal bearings in 1885. In 1886 Reynolds developed this into a theoretical basis for fluid film lubrication (1). 

---