Magnitude of loadThe magnitude of the load is one of the factors that usually determines the size of the bearing. Generally, roller bearings are able to support heavier loads than similar-sized ball bearings (fig. 1) Bearings with a full complement of rolling elements can accommodate heavier loads than corresponding bearings with a cage. Ball bearings are typically used in applications where loads are light to normal. Roller bearings are used in applications where loads are heavier.
Direction of load
NU and N design cylindrical roller bearings, needle roller bearings and toroidal roller bearings can support pure radial loads only ( fig. 2 ). All other radial bearings can accommodate some axial loads in addition to radial loads (→ Combined loads ).
Thrust ball bearings and four-point contact ball bearings ( fig. 3 ) are suitable for light or normal loads that are purely axial. Single direction thrust ball bearings can accommodate axial loads in one direction only. For axial loads acting in either direction, double direction thrust ball bearings are needed.
Angular contact thrust ball bearings can support normal axial loads at high speeds. Here, the single direction bearings can also accommodate simultaneously acting radial loads, while double direction bearings are normally used only for purely axial loads ( fig. 4 ).
For normal to heavy loads that are purely axial and act in one direction only, needle roller thrust bearings, cylindrical and tapered roller thrust bearings are suitable. Spherical roller thrust bearings ( fig. 5 ) can accommodate axial loads in one direction only as well as radial loads. For heavy alternating axial loads, two cylindrical roller thrust bearings or two spherical roller thrust bearings can be mounted in pairs.
A combined load consists of a radial and axial load acting simultaneously. The ability of a bearing to accommodate an axial load is determined by the contact angle a. The greater the angle, the higher the axial load carrying capacity of the bearing. An indication of this is given by the calculation factor Y, which becomes smaller as the contact angle a increases. The values of the angle a or the factor Y are listed in the relevant product chapter.
The axial load carrying capacity of a deep groove ball bearing depends on its internal design and the operational internal clearance (→ Deep groove ball bearings ).
For combined loads, single and double row angular contact ball bearings and single row tapered roller bearings are most commonly used, although deep groove ball bearings and spherical roller bearings are suitable ( fig. 6 ). In addition, self-aligning ball bearings and NJ and NUP design cylindrical roller bearings as well as NJ and NU design cylindrical roller bearings with HJ angle rings can be used for combined loads when the axial component is relatively small ( fig. 7 ).
Single row angular contact ball bearings, single row tapered roller bearings, NJ design cylindrical roller bearings, NU design cylindrical roller bearings with an HJ angle ring and spherical roller thrust bearings can accommodate axial loads in one direction only. For axial loads that alternate direction, these bearings must be combined with a second bearing. For this reason, universally matchable angular contact ball bearings (→ Bearings for universal matching ) and matched sets of tapered roller bearings (→ Matched bearing sets ) are available.
When the axial component of the combined load is significantly large, a second bearing, free of radial load may be necessary. In addition to thrust bearings, some radial bearings, e.g. deep groove ball bearings or four-point contact ball bearings ( fig. 8 ) are suitable. To make sure that the bearing is subjected to a purely axial load, the bearing outer ring must be mounted with radial clearance.
When a load acts eccentrically on a bearing, a tilting moment occurs. Double row bearings, e.g. deep groove and angular contact ball bearings, can accommodate tilting moments, but paired single row angular contact ball bearings and tapered roller bearings arranged back-to-back, are more suitable ( fig. 9 )