The axle load acts on the box unit and has shock-pulse nature when the car is moving, that can lead to a mutual change in the surface positions of the roller ends with the edges of the bearing races. The ways are proposed to optimize the internal geometry of the radial and end contact elements of the roller bearing of the axle box unit. It is proposed to eliminate the occurrence of possible conditions that lead to the movement of bearing rollers into the thrust and locking of bearing rollers by increasing the minimum limit in the axle clearance of the axle box.

In order to improve the working capacity and life of bearing units, the dimensional analysis of the inner geometry of a cylindrical radial bearing was carried out. The assembly component, composed by the outer diameter dimensions of the raceway of the inner race, the inner diameter of the outer race and the two diameters of the rollers, was considered as a dimension chain. It is recommended, in order to reduce wear and friction losses, to produce the diametrical dimensions of the roller according to the fifth accuracy degree. It is established that the cause of the axial clearance between the roller and the double-flanged race is the distance between the contact points on the right and left flanges with the horizontal position of the roller, as well as the diagonal distance. Tolerances for ring dimensions, for such a combination, are recommended to accept with respect to accuracy degree 6.