Abstract
Closed bearing units for railway rolling stock shall operate over 800,000 km or during 8 years of operating life (and, in the near future, 1 million km and 10 years) without any maintenance. In order to achieve such high operational indicators, it is necessary, already at the design stage of closed bearing units, to ensure almost absence of wear during the entire specified operating life. This paper reports the results of the optimal design of the elements in the internal geometry of closed bearings based on refined mathematical models using an example of the cylindrical axlebox bearing unit DUPLEX for 1520 gauge rolling stock. The chosen principal mathematical model was a geometrically nonlinear contact problem from the theory of elasticity, which was solved using a finite element method. An original non-linear finite-element model of the multi-contact problem has been developed, taking into consideration the contact deformations rail‒wheel, the deformation of a wheel-set axis, the deformation of the axlebox and bearing rings during contact with all rollers. The model makes it possible to clarify the distribution of loads in the circumferential direction and, accordingly, the maximum load on a roller. The same model could be used, among other things, to analyze the wear of a wheel flange and the effect of gap difference on the bearing wear. A mathematical model and an objective function have been constructed to optimize the profile of a roller (crown, the generatrix of the lateral surface of rotation) considering the accumulation of damage as a result of the irregular loading the roller surface points due to contacts with both the outer and inner rings. The shapes of the roller's face and the ring's operating flange have been optimized that are in contact in the axial direction, which has helped establish that the anthropologically shaped convex face of the roller and the concave flange of the ring are optimal. To simplify the structure technologically, a variant with a conical surface of the flange with the optimal camber value has been accepted instead of the concave flange of the ring
Highlights
Bearings have probably been the most common units of machines and mechanisms throughout the history of technology development up to now
For example, closed bearing units for railway rolling stock must operate over a warranty period of 800,000 km or 8 years of operating life without any maintenance; the failure interval should be at least 1.5 million km; in contrast, conventional axlebox bearings must be serviced after 300,000 km, including oil replacement, rollers rearrangement, analysis of rings for defects; their failure interval is only 600,000 km
Unlike most works, which consider only an isolated contact “roller–ring” or “a row of rollers–rings”, this model makes it possible to refine the distribution of loads in the circumferential direction and, the maximum load on a roller for different designs of the “loader”, and the multi-loading over the rows, the impact of gap difference and distortion
Summary
Bearings have probably been the most common units of machines and mechanisms throughout the history of technology development up to now. For example, closed bearing units for railway rolling stock must operate over a warranty period of 800,000 km or 8 years of operating life (and, in the near future, 1 million km and 10 years) without any maintenance; the failure interval should be at least 1.5 million km; in contrast, conventional axlebox bearings must be serviced after 300,000 km, including oil replacement, rollers rearrangement, analysis of rings for defects; their failure interval is only 600,000 km. In order to achieve such high operational indicators, it is necessary, as early as at the design stage, to ensure a reduction but almost absence of wear over all the specified operating life To this end, it is necessary to apply, practically simultaneously, all possible engineering tools to reduce wear while, at the same time, optimizing elements in the design of a bearing unit applying the refined, rather than simplified, mathematical models
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