MXV RAIL R&D, RAILWAY AGE, MARCH 2025 ISSUE: MxV Rail has been investigating the root cause(s) of asymmetrically hollow worn wheels and will present details of this investigation during the 30th Annual AAR Research Review in April along with the results and findings of many other AAR Strategic Research Initiatives.
Previous research (1) indicated that severely asymmetrical hollow worn wheels run significantly offset from the centerline of the track. Sawley et al. (2) and Fröhling (3) showed that an increase in asymmetrical hollow wear causes an increase in wheel-rail lateral forces. Increased lateral forces will ultimately increase track, track component, and truck component degradation. Cui et al. (4) determined that the maintenance rate for railcars with asymmetric wheel wear may be twice as high as the nominal maintenance rate and demonstrated the potential cost savings achievable by car owners when asymmetric wheel wear is addressed.
The goal of MxV Rail’s research into asymmetric hollow wear is to understand the root cause(s) of severely asymmetrically hollow worn wheels to reduce the occurrence of such wheels. A reduction in asymmetrically hollow worn wheels may be beneficial for both infrastructure and
car owners.
In late 2023, MxV Rail performed an analysis of repeat occurrences of hollow wear at the same axle location within different car types. While other car types repeatedly develop hollow wear in the same axle location, intermodal, stack and vehicular flat railcars were found to have the most repeat occurrences. A previous study (1) showed that these railcar types exhibited more significant asymmetric hollow wear than others. Researchers further investigated the asymmetry of hollow wear at different axle positions for these railcar types, while focusing on the occurrence of hollow wear values greater than 2 mm repeating more than twice.
The number of repeats on the left side of the trucks was subtracted from the number of repeats on the right side of the trucks. This difference was divided by the total number of repeats for the axle position to indicate the relative importance of the bias, and Table 1 (above) shows the results. A negative number indicates a bias with repeats on the left and a positive number indicates the opposite. The intermodal data showed groupings of axles forming part of a truck with either a left or a right bias.
Based on the observed bias occurring within the trucks of intermodal cars, researchers hypothesized that the most worn wheelsets in these trucks may have received a single wheelset changeout, which may perpetuate the asymmetric hollow wear in the truck. An asymmetrically hollow worn wheelset will run with a tracking position offset. Therefore, if this wheelset remains in the truck, it may cause a bias in the wear of the replaced wheelset. This tracking position offset may potentially cause the wheelset replacement to offset its running position to the right, thereby biasing the wear on the replaced wheelset.
A car owner provided data on the car number and truck and axle position for trucks that had a single wheelset changeout. Researchers also obtained more than three years’ worth of hollow wear data for these trucks from wheel profile detectors across North America. The asymmetric pattern that resulted after 1 mm of hollow wear accumulation on the repaired wheelset was compared to the asymmetric pattern on the worn wheelset that remained in the truck.
Table 2 (above) shows the results. Nearly the same portion of trucks had asymmetrically worn wheels either on the same side of the truck, representing 41% of the data, or diagonally opposite each other, representing 39% of the data. The asymmetric wear found on the wheelset that remained in the truck does not appear to drive the bias pattern of the repaired wheelset. Therefore, single wheelset changeouts are not contributory to or a root cause of asymmetric hollow wear within a truck.
References
1. Spangenberg, U., K. Morrison, and S. Cummings. 2022. “Analysis of Asymmetric Hollow Worn Wheels.” Technology Digest, TD022-026. Pueblo, CO: AAR/MxV Rail.
2. Sawley, KJ, D. Oliva-Maal, and J. LoPresti. 1998. “Effect of hollow worn railroad wheels on fuel use and track damage.” Proceedings of American Society of Mechnical Engineers International Mechanical Engineering Congress and Exposition (IMECE), 71–76.
3. Frohling, RD. 2006. “Analysis of asymmetric wheel profile wear and its consequences.” Veh Syst Dyn, 44: 590–600.
4. Cui, Y., Q. He, Z. Zhang, et al. “Using extreme value theory to identify railcar asymmetric wheel wear and its benefit analysis.” Transport 2019, 34: 569–578.
