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12 CHAPTER 3 RECOMMENDED MANAGEMENT AND MAINTENANCE GUIDELINES OF WHEEL/RAIL PROFILES FOR TRANSIT OPERATIONS In this section, the guidelines for management and Wheel tread taper maintenance of wheel/rail profiles for transit operations are Coordinates of wheel profile recommended. The guidelines cover the following issues: New wheel profile drawings 3.1.1 Wheel Flange Angle Wheel/rail profile measurement and documentation Wheel flange angle is defined as the maximum angle of the Wheel/rail profile assessment wheel flange relative to the horizontal axis, as illustrated in Wheel re-profiling Figure 3.1. Wheel profile design As discussed in Chapter 2, maximum flange angle is Ground rail profile design directly related to the wheel L/V ratio required for wheel Effect of gage and flange clearance on wheel/rail flange climb. A higher flange angle has a lower risk of interaction flange climb derailment. Therefore, it is very important to Wheel/rail profile monitoring program clearly denote the flange angle in the wheel drawing. In a given manufacturing tolerance range, the flange angle In order to better understand and apply the guidelines, related should not be smaller than a specified minimum required technical definitions are briefly introduced. Specific techniques value. (or software) mentioned in this report are only used as exam- ples and do not indicate endorsement of specific products. 3.1.2 Wheel Flange Length 3.1 REQUIREMENT FOR NEW WHEEL Wheel flange length (Len) is defined as the length of PROFILE DRAWINGS flange starting from the beginning of the maximum flange angle to the point where flange angle reduces to 26.6 degrees Wheel profile drawings represent the designed shapes for (see Figure 3.2). new wheels. Adoption of a wheel profile design for a specific Also discussed in Chapter 2, wheel flange length is related transit operation requires careful consideration of the vehicle to the distance limit of flange climb. A longer flange length and track conditions that the new wheel profile will experi- has a lower risk of flange climb derailment. Therefore, it is ence. When building a new system or a new line in particular, equally important to clearly denote the flange length in wheel selecting a proper wheel profile at the start is very important drawings. for the long-term stability of the system, which is indicated by It is also useful to denote the maximum flange-angle good vehicle performance and low-wheel/rail-wear rates. length L0. In Section 2.7 of Appendix B, the two phases Therefore, the requirements for the wheel profile drawings, of flange climb related to L0 and Len are discussed. The described below, are not only for manufacturer use but also for distance that the wheel can stay in contact with the rail in wheel profile designers to recognize the important parameters, the section with maximum flange angle during flange and for staff in transit operation and maintenance to understand climb depends on the length of L0, wheel L/V ratio, and the features of the wheel profile(s) used in their system. wheelset AOA. For the purpose of wheel manufacturing, wheel profile draw- ings generally have all dimension descriptions required for the machine production of such a profile. In this section, only those 3.1.3 Wheel Tread Taper parameters that currently are not shown or not required on the drawing are emphasized. They are the following: The wheel tread taper, which results from the wheel radius reduction from flange root to tread end (Figure 3.3), Wheel flange angle provides wheels with a self-centering capability and also Wheel flange length helps wheels steering on curves. However, high slope of

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13 Figure 3.1. Flange angle and flange forces. Figure 3.2. Notation of wheel flange length. taper can increase the risk of vehicle hunting above certain speeds. When a straight line is designed for the wheel tread, a ratio 3.1.4 Coordinates of Wheel Profile of radius reduction versus length can be used to denote the taper. For some wheels designed with arcs in the tread sec- The designed wheel profiles are generally described by a tion, an equivalent slope may be approximated. series of circular arcs and straight lines. For the convenience of both wheel/rail contact analysis and vehicle modeling, it Figure 3.3. AAR-1B wheel profile drawing.