Interface - The Journal of Wheel/Rail Interaction

WRI '08 SEMINAR OVERVIEW

Wheel/Rail Interaction ’08: Data to Information
Part 1 of 2 (continued)

Rail Testing
The AAR and FRA have jointly funded a revenue service “mega site” testing program to help North American freight railroads implement heavy axle load (HAL) operation and mitigate its effects on track degradation. Track-related experiments at mega sites on Norfolk Southern and Union Pacific coal lines supplement the HAL testing at FAST (Facility for Accelerated Service Testing) by providing a wider range of track, subgrade, operating and environmental conditions.

The revenue service experiments were designed to quantify how HAL operation affects track component degradation, to test new designs and track materials, and to improve track maintenance procedures in order to reduce the forces applied to the track. The performance of premium rail, including resistance to wear and defect growth, under heavy axle loads in revenue service was also evaluated.

The Eastern mega site was established on four (6.8- to 10-degree) curves on a 55-MGT, timber-tie track with excellent gauge-face lubrication and top-of-rail lubrication friction control. Operating speeds are 20 - 30 mph. The Western mega site was established on three (1- to 2-degree) curves on a 240-MGT, concrete-tie track with 141-pound premium rail with fair gauge-face lubrication and no top-of-rail lubrication friction control. Operating speeds are 50 mph.

Dingqing Li, Senior Principal Engineer at the Transportation Technology Center, Inc., reported that (assuming a maximum 5/8-inch gauge-face or head wear), all test rails have exhibited excellent wear performance with a minimum estimated wear life of:

• 2,800 MGT for a 2-degree curve with “fair” gauge-face lubrication and no TOR friction control.

• 1,000 MGT for a 10-degree curve with “excellent” gauge-face and TOR friction control.

• 560 MGT for a 5-degree curve with no lubrication (39-ton axle loads).

Rolling Contact Fatigue (RCF) was not an issue at up to 150 MGT, Li said. While no RCF appeared in rails in a 1-degree curve after 610 MGT, significant RCF did occur on the low rails of 2-degree test curves at the UP site within 300 - 350 MGT. Contributing factors include:

• Very dry rail surface (friction coefficient above 0.5).

• Poor geometry at welds. (More than half of the RCF defects were concentrated around plant welds.)

• Under-balanced speed, which caused higher normal and tangential wheel/rail forces on low rails, particularly on the 2-degree curves.

Other possible factors include wheel and rail profiles, and the warp stiffness of trucks.

Generally, Li said, all premium rails in the tests have exhibited excellent wear performance under HAL operation. No internal defects or broken plant welds were identified during the test. Without preventive grinding, RCF started to become significant on the low rails in 2-degree curves after 300 - 350 MGT. All of the premium rails in the tests showed work-hardening effects, with hardness measurements of more than 400 BHN.

Vehicle Testing
Efforts are also underway to quantify and improve the performance of railway vehicles and components. TTX Company, for example, has established an ongoing R&D program to evaluate trucks and truck components at the TTCI facilities in Pueblo, Colorado. TTX’s research there is focused upon improving the performance of cars and components, and on lowering the operating costs for cars used in the TTX fleet. The basis for much of the testing is from the AAR Manual of Standards and Recommended Practices, Chapter XI service worthiness test standards and procedures. The recent M-976 standards for the interchange of 110-ton cars has led to a growing number of adapter-pad equipped cars entering the TTX fleet.

TTX began voluntary compliance with the S-286 specification for free interchange of 286,000-pound gross rail load (GRL) cars in 2003, and is currently engaged in an extensive R&D effort to monitor and quantify the performance of M-976 trucks on all TTX car types.

As the M-976 trucks in the fleet have begun accumulating significant mileage, TTX R&D has also engaged in a test program to compare standard roller bearing adapters to adapters with pads, along with the baseline curve negotiation data, said Jon Jeambey, TTX’s Director of Research and Development. Distance-measuring lasers have been added to the instrumented wheelsets to record wheelset angle-of-attack in order to help researchers understand the role of adapter pad motions during curving.

TTX has determined that adapter pads are a key performance component of its truck designs. M-976 truck types and side bearing types are familiar to TTX, but this is the first widespread use of adapter pads since the articulated doublestack cars in 1986 – 1992 era.

“We’re concerned by how little we know about the function of adapter pads,” Jeambey said.

Tests of adapter pads in the early 1990s indicated that the pads’ properties had both positive and negative effects. While they reduced wheel shelling in TTX service tests and lowered wheel/rail forces in most cases, decreased truck warp restraint and high-speed instability (and an assumed short life due to constant flexing of the pads) prevented TTX from approving their use in its fleet.

TTX plans future testing of M-976 truck designs to determine pads’ influence on rolling resistance, speed stability and truck warp in curves with high rail lubrication.

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