Like for ball bearings, a distinction between bearings that support radial loads and those that support axial loads can be made. Radial needle roller bearings with or without inner ring just support radial loads and are designed for medium loads with intermediate speeds. They are used especially for transmissions and in generally in mechanical engineering. By renouncing the inner ring, installation size can be reduced additionally. In this case, the shaft serves as the raceway, though – to reach the complete load capacity, the shaft has to be hardened and grinded within the range of 58-64 HRC. This is also the case for needle roller and cage assemblies, which exclusively consist of cages and needle rollers. Here, bearings directly run on the shaft and the housing respectively.
However, axial needle roller bearings just support axial loads; this is applicable because of a solid cage, in which several needle rollers run safe. Here, you can also find various designs and components. Thus, axial needle roller and cage assemblies can be combined with different kinds of axial bearing washers, depending on load carrying capacity of the substructure. Multi row needle roller and cage assemblies for highest load ratings are used in axial piston pumps for example, while models with integrated washers are used in elevating tools and in ancillary components of track vehicles.
Finally, there are also needle roller bearings that combine radial and axial rolling elements. For lower axial loads, a combination of balls and needle rollers is proper (series NKIA/NKIB/NX/NKX); for higher axial loads, a combination of cylindrical rollers and needle rollers is most suitable (series NKXR). Combined bearings can be mounted in a quite uncomplicated way and are easy to handle. Additionally, less installation space is needed, because only one compact combined system instead of two separate bearings can be installed. Therefore, combined bearings are mostly used in applications, where installation space is limited.
Needle roller bearings in a full complement design do not have a cage. Fixation of rollers either takes place through self hold or through a tube, which is just pressed out by the shaft during the mounting process. Full complement needle roller bearings can be used in applications, where low speeds and extremely high loads occur.