Interface - The Journal of Wheel/Rail Interaction

W/R INTERFACE MANAGEMENT

Management of the Wheel/Rail Contact Interface in Heavy-Haul Operations (continued)

Wheel/Rail Profile and Track Gauge Maintenance
Based on the findings from the track inspection, recommendations related to the control of rail profiles, the control of track gauge, and the development of a new wheel profile have been made.

Rail grinding in tangent track sections is necessary, not only to remove surface defects such as corrugations and RCF, but also to reduce the propensity of vehicle lateral instability. The tangent rails tend to wear into a shape with a flat head. This shape moves the contact position from the rail crown region to the rail gauge region as the wheelset moves laterally. This can result in high contact conicity and cause plastic flow at the gauge corner.

Based on analysis of the rail inspection data, slightly lowering the tangent rail shoulder (to crown up the railhead) can improve vehicle lateral stability. With careful design, the grinding template for use on tangent track can ensure that crowning of the railhead is achieved. Correctly positioning the grinding templates should also be emphasized when grinding tangent track. Overcutting the rail gauge corner is not recommended, however, because it produces concentrated contact at the wheel tread, which can lead to hollow-worn wheels. The grinding interval also needs to be properly programmed. Rail grinding should be conducted before the tangent rails wear into shapes that can produce high contact conicities.

The track gauge in tangent track needs to be carefully controlled during the rail installation, especially on lines with concrete ties. Plastic metal flow on the gauge face of the rail can be prevented by reducing wheel contact at the rail gauge corner region through proper rail grinding.

Controlling Rail Profile on Curves
The outer rail on curves generally wears into a shape that produces conformal contact with worn wheels. Significant rail gauge corner cutting on the high rails of curves must be avoided during rail grinding in order to reduce the development of a severe two-point contact pattern for all passing wheels and also to reduce the “wear in” period for new wheels.

The wheel/rail contact pattern on curves may have no direct relationship to vehicle lateral instability. However, the contact pattern or the wheel wear pattern on curves may contribute to the formation of undesired worn wheel shapes that can produce high contact conicities. Significant rail gauge corner cutting on the outer rails of curves may not only degrade vehicle curving performance, but may also produce concentrated wear at the wheel tread and induce high contact conicity. Crowning of the inner railhead on curves is also recommended to reduce the risk of rail rollover and to maintain required rolling radius on curves.

Rail inspection further indicates the need to design a new wheel profile in order to improve the contact pattern of the new wheel / worn high rail in curves. The new wheel profile should correct the severe two-point contact pattern that is currently common when a new wheel contacts the worn outer rail of curves. Tests of a new wheel profile that were conducted in revenue service showed that the new wheel wore less and developed a better wear pattern than the current standard wheel.

The wheel/rail contact inspection technique that is presented in this article qualitatively assesses rail wear and the risk of RCF by assessing the influence of wheel/rail contact on vehicle performance and the wheel/rail interface. Analysis is based primarily on wheel/rail profile geometries and static wheel loads. Further development will include creepage and dynamic wheel/rail forces from a large population of cars with varying performance characteristics in order to quantitatively assess rail wear and the initiation of RCF.

This technique of managing wheel/rail contact will be implemented on track geometry inspection cars, ensuring that both track geometry and wheel/rail contact conditions will be inspected at regular intervals. With this, a more complete evaluation of track conditions can be used to determine the need and priority for rail maintenance.

References
1) Wu, H., Madrill, B., and Kalay, S., “New Wheel Profile Design and Preliminary Service Test Results,” Technology Digest, TD-06-023, Association of American Railroads, Transportation Technology Center, Inc., September 2006.

Huimin Wu, is Principal Investigator; Semih Kalay, is Vice President Research & Development, Transportation Technology Center, Inc.

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