Because wheel axle bearings have a direct impact on train safety, sensor-equipped bearings that monitor the bearings' condition have also been developed, and these have been put into practical use on freight trains. For the bearings used in drive units that are operated in conditions of severe vibration, NSK's proprietary and extremely reliable bearings have been used for many years. In addition to incorporating measures to prevent seizures between the roller and the rib, these bearings have ultra-hard cages treated with soft-nitriding.
The bearings used in the traction motor must also conform to requirements for extended maintenance intervals, and NSK has therefore developed cages that have excellent grease replenishment capability, and also incorporate a fail-safe design. As a result, the company has brought into commercial use bearings with a grease-life more than twice that of conventional models. In addition, NSK has resolved what was a maintenance-related issue of electrical corrosion prevention with ceramic-insulated bearings and resin-insulated bearings. NSK has the certification of the Association of American Railroads (AAR) for its RCT-sealed, tapered roller bearings for freight car axles.
In order to successfully develop highly reliable bearings for railway vehicles and to improve their performance, NSK is aware of the importance of gaining a sound understanding of the actual usage conditions of such bearings, as well as of the need for tests and experiments that accurately recreate those conditions.
Therefore, in this field, the company has always devoted its energies towards the establishment of measurement technologies using actual equipment and assessment techniques for simulations. As examples, the company measures the motion of the roller in the cylindrical roller bearings of the axles of Shinkansen trains in actual operation, and it measures the rolling element load distribution when the axle box is distorted. NSK has established high level analytical techniques and design technologies through the application of these measurement technologies and the feedback obtained from them. The company now aims to establish simulation evaluation technologies that will permit highly accurate reconstructions of actual operating conditions. On another issue, in relation to the monitoring of operational conditions, which will continue to be seen as very important from the point of view of safety, NSK has successfully established sensor technologies and put them into actual use.
NSK develops and sells a wide variety of bearings for use in railway vehicles, including for wheel axles, drive units and traction motors. These bearings feature high performance, high reliability and long maintenance intervals to help support rail companies in their mission to facilitate a safe, fast and reliable arrival at the destination.
NSK bearings have a long history in Japan's Shinkansen bullet trains, starting with the first 0 series, right up to the latest N700 series. The company supplies two different types of Shinkansen wheel axle bearings: the grease-sealed type and the oil bath lubrication type.
Spherical Roller Bearings
Cylindrical Roller Bearings
Spherical roller bearings resist seizure, maintain dimensional stability, can support high radial loads and moderate axial loads, and resist wear in spite of constant vibration, misalignment and shock loads.
By virtue of the line contact between rolling elements and raceways, cylindrical roller bearings have high radial load capacity and are suited for high-speed applications.