Interface - The Journal of Wheel/Rail Interaction

TTCI TECH OVERVIEW

Meeting the Industry’s Technology Goals

The wheel/rail interface must be managed in order to increase the life of rail and rolling stock components and to reduce in-service failures. This was one of the primary messages delivered at the Association of American Railroads/Transportation Technology Center, Inc.’s 14th Annual Research Review. The research that was presented covered a range of topics directed toward meeting the industry’s technology goals, and many of them fell within the realm of wheel/rail interaction.

“Understanding what’s going on at the wheel/rail interface moves us from reactive to proactive maintenance,” said Lisa Stabler, BNSF’s Assistant Vice President for Quality and Reliability Engineering. “We’ve seen that unless there is a smoking gun, like a burned-off journal or a broken rail, a service failure is likely caused by an interaction.”

Wheel/rail interface management includes the design and maintenance of wheel and rail profiles, friction control, and automated measurement of wheel/rail interaction, said Semih Kalay, TTCI’s Vice President for Research and Development. Automated wayside and onboard systems are being used to inspect rail and joint bars and to measure rail stresses and track strength.

Automated wayside or onboard vehicle health monitoring systems are also being used to monitor the condition of rolling stock and to identify poorly performing vehicles, which increase derailment potential and the overall stress state of the railway. Condition monitoring enables railways and car owners to schedule the necessary maintenance on a proactive basis, thereby reducing risk and maintenance costs, he said.

Wayside condition detectors, such as acoustic bearing and cracked wheel detectors, performance detectors (such as truck hunting, truck performance and wheel impact load detectors), and wayside machine vision technology (such as wheel profile and brake shoe modules) are able to report on vehicle and vehicle component condition in lieu of visual inspections.

Condition Monitoring
Condition monitoring systems have enabled researchers to compare wheel tread temperatures to hot and cold wheel detector readings in order to determine limits for thermally related wheel tread damage.

“Research has shown, for example, that average wheel temperatures are approximately 150 degrees less than tread temperatures,” said Harry Tournay, TTCI Senior Scientist. The goal is to use wayside detectors to relate wheel temperature to brake conditions, including applied hand brakes and stuck or inoperative brakes.

The overall objective of automated vehicle health monitoring and inspection systems is to use the best available technology to identify poorly performing equipment and potential safety problems before they cause rail damage or accidents. Continuous streaming video is also being used to identify missing or damaged car safety appliance components.

The TTCI reported that since the implementation of wayside detection and technology systems, the broken rail accident rate was 7.6% lower. The broken wheel accident rate was 17.2% lower. The combined broken wheel and rail accident rate per million miles was reduced by nearly 10%.

Between 1997 and 2006 there were 72 train accidents attributed to truck hunting in the U.S. Between 2006 and 2008, the period in which the Advanced Technology Safety Initiative (ATSI) truck hunting program (which relies on the implementation of detector-based condition monitoring) was launched, there have been no train accidents attributed to truck hunting on mainline track in the U.S.

Vehicle/Track Interaction
Among the objectives of the Strategic Research Initiatives of the Wheel/Rail Interface Management project is to investigate the root causes of loaded car hunting, and to develop recommended standards and practices to eliminate the problem.

“The symptoms of loaded car hunting include the failure of adapter pads on M-976 trucks during hunting,” Tournay said (see Figure 1).

Tests showed that hunting of loaded cars is the result of the inertial and suspension characteristics of the carbody interacting, dynamically, with the self-centering properties of the wheel running on tangent rail.

“Normally, the warp restraint of the truck is sufficient to stabilize the wheelsets,” Tournay said. Under the action of loaded hunting, however, the wheelsets, constrained relatively softly by the adapter pads, excite the carbody in yaw. This saturates the friction of the wedges in the truck suspension, breaking-down the truck warp and reducing, substantially, the wheelset constraint, leading to wheelset hunting.

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