Interface - The Journal of Wheel/Rail Interaction

W/R INTERFACE MANAGEMENT

Management of the Wheel/Rail Contact Interface in Heavy-Haul Operations
(Part 1)
By Huimin Wu and Semih Kalay • October, 2009

Wear and rolling contact fatigue (RCF) of rails and wheels are common problems under heavy-haul operations. Increasing axle loads can increase the capacity of a railway system, but also can increase the stress state of the system. A root cause of RCF and excessive wear on rails and wheels is the high energy input into the wheel/rail interface, indicated by high levels of contact stress, tangential forces and creepages (1, 2). Reducing the energy input into the wheel/rail interface is a key strategy to reducing wear and RCF.

Wheel/rail contact conditions significantly influence vehicle performance, wheel/rail wear and the formation of RCF. To manage the wheel/rail interface, wheel/rail profiles and wheel/rail contact conditions must be measured and analyzed, and wheel/rail maintenance practices must be carefully controlled.

A wheel/rail contact interface management technique that has been developed and applied in North American heavy-haul service includes three major elements:

• Development of an automated wheel/rail contact inspection system for conducting system-wide wheel/rail contact inspection.

• Identification of undesired wheel/rail contact conditions causing vehicle performance problems and excessive wear and RCF on both wheels and rails.

• Guidance for wheel and track maintenance to correct the identified wheel/rail contact problems.

This technique applies the fundamentals of wheel/rail contact computation to the evaluation of wheel/rail contact from a systematic point of view.

Wheel/Rail Contact Inspection System

The Transportation Technology Center, Inc. (TTCI) developed an automated wheel/rail contact inspection (WRCI™) system (3) under the Association of American Railroads’ Strategic Research Initiatives Program. Figure 1 illustrates the data measurement and processing flow of the WRCI™ system. This measurement system can be installed on a railway car, as shown in Figure 2. The WRCI™ can perform real-time assessment of wheel/rail contact conditions, using rail profiles that are measured by the system and compared to pre-collected wheel profiles from more than 200 representative wheelsets. The pre-collected wheel profiles, which are drawn from cars that normally travel over the route being inspected, have varying degrees of wear. A GPS system is used to correlate the rail measurements to the track locations. The operating speed is proportional to the measurement interval and currently reaches 70 km/hr with a measurement interval of 3 meters. Track curvature, wheel loads and track gauge are taken into consideration in the assessment. The likely effects of wheel/rail contact on vehicle performance are predicted based on assessment results. Wheel/rail contact conditions can be quickly assessed in order to provide an overall view of wheel/rail contact conditions on a system and determine the need for rail reprofiling.

In the WRCI™ system, the wheel/rail contact parameters are assessed by placing each wheelset profile that is stored in the database on each measured pair of rails. The wheel profiles are moved laterally, relative to the rail profile, and the program calculates the following contact parameters:

• Contact positions on each rail.

• Maximum contact angle.

• Rolling radius difference on curves.

• Effective conicity on tangent track.

• Contact conformity.

• Contact stress.

Contact position is particularly important, as it detects the contact position on the low rail in curves, and the risk of rail rollover derailment. Figure 3 shows that 38% of the wheels used in the inspection contacted the inner rail on a curve at a point more than 55 mm from the rail gauge. The WRCI™ system produces an exception alert if this contact pattern continues for a specified distance — 30 meters, in this instance

The maximum contact angle relates to the risk of flange climb derailment. A low contact angle can be caused by rail rotation due to weak track or fastening system. A low contact angle can also be caused by wheels contacting rail at the rail lip, as shown in Figure 4, which can lead to poor vehicle curving performance.

Contact conformity and rolling radius difference provide an indication of vehicle curving performance under prevailing track conditions. Contact conicity indicates vehicle lateral stability at high speed. Contact stress and its distribution provide an indication of wear and risk of RCF.

Exception reports are produced for the track sections (specified in both distance and GPS coordinates) where pre-defined criteria have been exceeded and where distances exceed user-defined lengths. Information on track curvature and measured rail gauge are also included in the exception report.

PAGE 1 OF 2 | NEXT PAGE >