Slewing bearing service life

In antifriction slewing bearing technology, theoretical life is a well-known term. Due to a multitude of influential factors, nominal life acc. to DIN/ISO281 cannot in practice be taken as an absolute value but as a reference value and design guide. Not all slewing bearingswill reach their theoretical life, although most will generally exceed it,often by several times.Theoretical life criteria cannot be applied directly to large-diameter slewing bearings, particularly with slewing bearings performing intermittent slewing motions or slow rotations.In most applications the speed of rotation in the race will be relatively low. Therefore, the smooth operation and precise running of the slewing bearing are not adversely influenced by wear or by the sporadic occurrence of pittings. It is,therefore, not customary to design large-diameter slewing bearings destined for slewing or slow rotating motion on the basis of their theoretical life. For better definition, the term “service life”was introduced. A slewing bearing has reached its service life when torque resistance progressively increases, or when wear phenomena have progressed so far that the function of the bearing is jeopardized.Large diameter antifriction bearings are used in highly diverse operating conditions. The modes of operation can be entirely different such as slewing over different angles, different operating cycles, oscillating motions, or continuous rotation. Therefore, apart from static aspects,these dynamic influences have to be taken into account.
The slewing ring service life determined with the aid of the curves shown is only valid for bearings carrying out oscillating motions or slow rotations. This method is not applicable to:
– slewing bearings for high radial forces,
– slewing bearings rotating at high speed,
– slewing bearings having to meet stringent precision requirements.
In such cases UWE bearing will carry out the calculations based on the load spectra including the speed of rotation and the percentage of operating time.We must clearly distinguish between the operating hours of the equipment and the actual rotating or slewing time. The various loads must be taken into account in the form of load spectra and percentages of time. For service life considerations another influential factor not to be neglected is the slewing angle under load and without load.For an approximate determination of the service live of a slewing bearing, service life curves are shown next to the static limiting load diagrams.This does not apply to profile bearings types 13 and 21.These service life curves are based on 30,000 revolutions under full load. They can also be employed to determine the service life with different load spectra or to select a bearing with a specified service life.