A journal bearing, simply stated, is a cylinder which surrounds the shaft and is filled with some form of fluid lubricant. In this bearing a fluid is the medium that supports the shaft preventing metal to metal contact. The most common fluid used is oil, with special applications using water or a gas. This application note will concentrate on oil lubricated journal bearings.
Hydrostatic bearings provide accurate, highly damped, friction free linear and rotary motion. These bearings also average the form errors of the surfaces that make up the bearing components. This averaging allows the bearings to exhibit smaller error motions than would otherwise be possible. The small error motions attainable when hydrostatic bearings are used make them the bearing technology of choice for ultra precise ways and spindles for instruments and machines.
Hydrodynamic Bearing, which are active as the shaft rotates, create an oil wedge that supports the shaft and relocates it within the bearing clearances. In a horizontally split bearing the oil wedge will lift and support the shaft, relocating the centerline slightly up and to one side into a normal attitude position in a lower quadrant of the bearing. The normal attitude angle will depend upon the shaft rotation direction with a clockwise rotation having an attitude angle in the lower left quadrant. External influences, such as hydraulic volute pressures in pumps or generator electrical load can produce additional relocating forces on the shaft attitude angle and centerline position