Rolling bearings

Rolling bearings generally comprise two bearing rings with integral raceways. Rolling elements are arranged between the rings and roll on the raceways. Rolling elements can be balls, cylindrical rollers, needle rollers, tapered rollers or barrel rollers. The rolling elements are generally guided by a cage that keeps them at a uniform distance from each other and prevents them coming into contact with each other. In needle roller bearings and ribless spherical roller bearings, the cage also ensures that the rolling element axis is positioned correctly. Where bearings can be dismantled, the cage holds the rolling elements together and gives easier fitting of the bearings. For particular applications, rolling bearings with a full complement of balls, cylindrical rollers or needle rollers may be used.

Every roller bearing design has characteristic features that make it especially suitable for specific bearing applications. It is not possible to draw up generally valid rules for the selection of the bearing type as several factors usually have to be considered and weighed up. In addition to load and speed, attention must also normally be paid to influences such as temperature, lubrication, vibrations, fitting, maintenance etc. In many cases, at least one of the main dimensions of the bearing – usually the bore diameter – is already defined by the design of the adjacent construction.

The bearing size is determined primarily by the magnitude and type of load – dynamic or static – the bearing load carrying capacity and the requirements for operating life and operational reliability of the bearing arrangement. Rotating bearings are subjected to dynamic stresses. Bearings are subjected to static stresses if there is only very slow relative motion between the bearing rings, if swivel motion occurs or if loads occur in a stationary condition. Where external dimensions are identical, roller bearings can in general be subjected to higher loads than ball bearings. As a result, ball bearings are usually used for small and moderate loads, whilst roller bearings are frequently used for higher loads and larger shaft diameters