Flange Climb Derailment Criteria and Wheel/Rail Profile Management and Maintenance Guidelines for Transit Operations (2005) / Chapter Skim
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Pages 12-30
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From page 12... ...
The distance that the wheel can stay in contact with the rail in the section with maximum flange angle during flange climb depends on the length of L0, wheel L/V ratio, and wheelset AOA. 3.1.3 Wheel Tread Taper The wheel tread taper, which results from the wheel radius reduction from flange root to tread end (Figure 3.3)
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From page 13... ...
For the convenience of both wheel/rail contact analysis and vehicle modeling, it Figure 3.1. Flange angle and flange forces.
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From page 14... ...
Profile measurement becomes especially important for diagnosing problems due to poor wheel/rail interactions, such as poor vehicle curving, vehicle lateral instability, flange climb derailment, and excessive wheel/rail wear. However, the measurements are only useful when they are properly taken.
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From page 15... ...
, which significantly changed the wheel tread slope. When the rotated wheel profile is used to calculate the contact geometry with a rail, the calculated contact situation would also be different from the real condition.
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From page 16... ...
They are generally related to the following issues: • Making maintenance decisions • Studying wear processes and wear rates • Studying contact conditions • Studying wheel/rail interactions Often, in maintenance decisions, not only the profile shapes are considered but also the surface conditions. In transit operations, flat spots on the wheel surface are one of the common reasons for wheel re-profiling.
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From page 17... ...
Most profile contour measurement devices now have software that can quickly process a large group of measured wheels and provide results for wheel flange height, flange thickness, tread hollowing, and other geometry parameters on a spreadsheet. The rail head material loss computation requires that the measured rail profiles have a correct orientation relative to the new rail template; previous measurements at the same location can be used to confirm the accuracy of the computation.
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From page 18... ...
3.3.2.1 Maximum Contact Angle The maximum wheel/rail contact angle depends on the maximum wheel flange angle and the maximum angle of the rail gage face. A wheel profile with a higher flange angle can reduce the risk of flange climb derailment and can have much better compatibility with any new design of vehicle/truck that may be introduced in the future compared to wheels with lower flange angles.
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From page 19... ...
Whether wear or RCF occurs depends on the lubrication conditions, tangential forces at the contact patch, and the hardness of the wheel and rail steels. 3.3.2.4 Effective Conicity on Tangent Track Lateral instability is more likely to occur when there is high wheelset conicity (the ratio of RRD between the left and right wheel over the wheelset lateral displacement)
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From page 20... ...
Although the critical value can be varied by vehicle types, generally the effective conicity should be no higher than 0.3. Note however that RRD and wheelset conicity has no effect on the hunting speed of trucks equipped with independently rotating wheels.
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From page 21... ...
wheelset lateral shift relative to the track will nearly cause wheel flanging for this wheel and that the 1:40 taper is maintained in this lateral shift range, an RRD of 0.015 in. will be obtained.
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From page 22... ...
Although research is ongoing in this area, potential methods for controlling this form of RCF may include the following: • Optimizing wheel/rail profiles to improve vehicle steering by – Reducing the width of the contact band in the rail gage shoulder or – Increasing the wheel conicity in the flange root area, which gives a smoother transition of contact from rail head to the gage shoulder; • Optimizing vehicle suspension stiffness to improve vehicle steering; • Applying friction modifiers and/or lubricants to the rail head to reduce wheel rail forces; and • Using harder rail steels. Hence, compatible wheel and rail profiles are critical for a system to reach desirable contact patterns.
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From page 23... ...
3.4.2 Stable Contact Conditions -- Stable Worn Shapes of Wheel and Rail Stable contact is considered to be the desirable equilibrium condition. When this stage is reached after the wearin period, wear rate and contact stress should be relatively low due to a conformal contact situation at both wheel tread/rail crown and wheel flange throat/rail gage areas.
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From page 24... ...
The associated wheel and rail profiles may include these conditions: • Thin flange • Low wheel flange angles • Hollow wheels 24 • Low rail gage angles • Low rail with field side contact • Significant loss of rail cross section When wheels and rails wear into the critical shape, they should be either re-profiled or replaced. 3.5 WHEEL RE-PROFILING Wheel truing is a process for re-profiling the wheel shape and removing surface defects like flats, spalls, and shelling.
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From page 25... ...
3.5.2 Surface Finish Requirements Several systems have reported flange climb derailments occurring at curves or switches in yards just after the wheels had been trued. This type of derailment may have been a result of the required maximum flange angle not being obtained, but was more likely caused by excessive wheel surface roughness after wheel truing.
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From page 26... ...
Under this condition, the existing worn wheel/rail shapes should be taken into consideration when designing the new wheel profile, for example when adopting a new wheel profile with a higher flange angle to replace the existing low-flange-angle wheel. If the profile change is significant compared to the existing design, it is likely that an interim profile (more than one, when necessary)
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From page 27... ...
, the template gages usually do not have the whole shape of the rails. 3.7.5 Rail Lubrication after Grinding Slight lubrication immediately after rail grinding can reduce the wheel flange climbing potential, just as lubrication after wheel truing can.
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From page 28... ...
(3.4) where ∆G = the variation of rail gage from the standard value and can be both positive and negative based on the variation direction, C C G f G B fa s a= + + = − −0 2 2 2 ∆ ∆ C G B fs s s0 22= − − 28 ∆f = the variation of wheel flange thickness from the value for the new wheel, which is generally negative due to wear, and Ga and fa = the actual gage and flange thicknesses, respectively.
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From page 29... ...
Newark City Subway (Light Rail Line) Restraining rail is installed on curves with a radius less than 600 ft.
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From page 30... ...
They are also affected by the vehicle and track conditions in that system, most often vehicle suspensions, track geometries, and lubrication. In many cases, the improvement of vehicle performance or wheel/rail wear relies on the combined improvement in wheel/rail profiles, track maintenance, and lubrication.
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