As market forces drive up the gross weight on rail, railroads continue moving toward increased usage of heavy axle load (HAL) equipment, namely 286,000 lb and 315,000 lb GWR vehicles that provide more competitive and efficient transportation. According to the AAR's Universal Machine Language Equipment Register (UMLER) database, since 1995, at least 70% of vehicles built each year were HAL vehicles. 2005 had 49,923 more HAL vehicles running on the North America railroad system than the previous year. This practice can result in significant overall savings in operating costs. However, HAL equipment can also accelerate wear and damage to the railroad infrastructure and have a greater potential for truck warping and vehicle dynamics problems. Thus, keeping rolling stock and track safe while ramping up the usage of HAL equipment presents a significant challenge. Wheel Impact Load Detector (WILD) SuperSites, developed by Salient Systems Inc. (SSI), provide real time monitoring and alarming on excessive axle loads and vehicle dynamics. SuperSites are important tools in the scientific study of HAL vehicles and the monitoring of heavy haul operations. This paper provides a snapshot of results of studies conducted on Union Pacific (UP) HAL routes and demonstrates how HAL loads affect the rolling stock, the track, and the wheel/rail interaction. The heavier the load, the higher the impact of the defective wheels to the track; therefore, heavily loaded vehicle routes (such as the coal route from the Powder River Basin to Kansas City and the primary intermodal route from Los Angeles to El Paso) need to be monitored more proactively to avoid track structural damage.
Decades of measuring friction conditions at the wheel-rail interface have resulted in widely varying answers produced by different measurement methods and devices. This variation is a result of many factors, some of which are difficult to quantify and control, especially under field conditions. One of these variables is the presence of an unknown 3rd body layer material, whose accumulation on the wheel and rail surfaces affect the value of independent tests performed to quantify the nominal state of wheel on rail in actual operating conditions. This paper describes a series of tests undertaken to understand the creation of the 3rd body layer from the starting point of clean wheel and rail surfaces and how that can lead to new standard practices for field testing. A 2 × 2 matrix of wheel and rail conditions is defined to help formalize the discussion of the production and measurement of the 3rd body layer. Case 1 is the nominal virgin state of the two materials. This is actually fairly hard to produce. Almost any process and/or handling will leave some films on both surfaces. Lab tests typically start in this state after cleaning/degreasing the surfaces following machining or sanding. Cases 2 and 3 are potentially the same (clean wheel or rail), however, the more likely case is Case 2 where some existing location on actual track is chosen to determine its current state, thus the use of a Tribometer using a clean wheel. Case 4 represents the nominal state of most track with passing vehicles where the current environmental/ambient conditions encourage a particular set of 3rd body wear products. This formalization helps reveal the prior common practices that have produced assumptions of what is the ‘correct’ value and how that has created a bias in one’s thinking of what really exists in normal revenue service. This issue is particularly consequential in attempting to quantify the benefit of the friction modifiers that are being adopted across the railroad industry.
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