What does basic dynamic load rating C mean for railway axle bearings?

Jan Babka, SKF Global Railway Application Competence Center Manager explains: What basic dynamic load rating C means for railway axle bearings. The main parameter that expresses the ability of any bearing to withstand load is the parameter called basic dynamic load rating 'C'. The definition can be found in any bearing catalogue: It is the load that the bearing can theoretically endure for one million revolutions without starting to develop on its raceways the damage called spalling. In the case of an axle bearing, this parameter 'C' can always be found on the drawing, usually in the upper right corner. Typically, its value is around 1 000 kN, which corresponds to about 100 metric tons. If we want to compare this load to something, we can say that it is approximately: the weight of three fully loaded trucks or weight one fully loaded typical American railway freight wagon. So if we hypothetically put one such fully loaded American railway freight wagon on one wheelset bearing with C of 1000 kN, it would be able to be rotated for one million revolutions without getting spalling. Fortunately, such a wagon has eight bearings. An axle bearing has a certain advantage over bearings in other applications. Because its size and thus the size of its basic dynamic load rating C is predetermined by the fact that it is mounted on a relatively large railway axle. Although it doesn't look like that, if we look at a heavy freight wagon, for example, the thick railway axle ensures that the railway axle bearing is usually relatively lightly loaded. This is specifically manifested by relatively low values of the contact pressures compared to bearings in other machines, the most heavily loaded railway ones have a contact pressure of around 1400 MPa, while, for example, ACBB for F1 – 5 GPa. Now I will ask you a provocative question: if we say that railway axle bearings are under-loaded, does that mean that we can increase their load without any problems? The answer is 'YES, but only under certain conditions'. And we could simply express this condition by saying that we have to ensure that the rolling process inside the bearing takes place as close as possible to laboratory conditions. This means in particular: So that no dirt gets into the grease That the right type of grease is used To keep the grease in great condition So that the axle journal and the axlebox do not deform the bearing rings in an unacceptable way Only then will we be able to rely on the relatively high basic dynamic load rating C, which expresses the ability to withstand high loads. And it follows that an absolutely necessary condition for increasing the axle load is always a consultation with a bearing expert.