Interface - The Journal of Wheel/Rail Interaction

INTERFACE OPTIMIZATION

Tools and Techniques for Optimizing the Wheel/Rail Interface
By Gary P. Wolf • July, 2007

Much has been written and said about the need to optimize the interface between the wheel and rail, but with the growth of heavy axle load traffic, the mandate for optimum performance is greater than ever. Balancing the wheel/rail equation and optimizing interaction can only be done through engineering analysis and the application of technology.

Task 1. Measuring and Defining Rail Parameters

Those charged with managing or maintaining a railway understand that rail (and its shape or profile) is the one asset that is entirely under their control. Wheels are another story. Unless a railway is a closed-loop operation, the interchanged wheels that pass through the system every day represent a wide range of conditions, shapes and profiles. With such uncontrollable variability in wheel conditions, it is imperative to control the rail profile in order to maximize its asset life, and minimize the risk of derailment. Of course, you know the adage: “If you can’t measure it, you can’t manage it.” Fortunately, there are tools that can accurately measure the profile and wear characteristics of rails and wheels.

Initially, only crude mechanical tracing devices were available to measure rail profiles. These devices were cumbersome, lacked accuracy, and did not capture any digital data on the profile shape. Today, however, there are a number of optical and laser-based devices that can measure the surface profile of the rail to an accuracy of thousandths of an inch at speeds up to 60 mph. These instruments can store the data digitally for analysis and reference to other measurements.

Optical Rail Measurement vehicles, such as those used by Advanced Rail Management Corp. (ARM), utilize a high-speed laser-measuring system to take a “snapshot” of the head and base of the rail every 5 to 15 feet on freight lines, and down to every foot or less, as required, in curves on transit and high-speed lines. Wear measurements on the ARM vehicles (see Figure 1), which utilize ORIAN laser measurement systems designed by KLD Labs, are accurate to approximately 0.001 inches across the running surface of the rail. From this profile snapshot, the software can determine the type and weight of rail, and the amount of side and top wear from its as-new condition. The system can also determine the gauge-face angle and cant of the rail, and calculate the percent of gauge wear, head loss and other programmable parameters. (Figure 2 shows the typical view of a left and right rail in a curve, and associated wear statistics. Figure 3 shows the predictive wear line for a given curve.)

By comparing historical data obtained from periodic measurement runs with gross rail tonnage, users such as ARM can identify gauge-face, vertical or the overall percentage of head wear per million gross ton miles. Through regression analysis, software can predict when the rail will reach its wear limits. Rail grinding templates can be superimposed over the measured rail profiles to plan the grinding strategy and determine the appropriate metal-removal rates.

Optical Rail Measurement can also be combined with track geometry measurement systems to accurately measure gauge, crosslevel and alignment, and precisely identify the locations at which exceptions are identified.

Task 2. Measuring the Wheels
For more than a century now, mechanical personnel have carried various AAR-approved wheel gauges in their coveralls. While the gauges are accurate, there is potential for error, as measurements are often taken under difficult conditions — under vehicles, in low light, with the users in awkward positions. While these “go/no-go” gauges serve a useful purpose, these types of static wear measurements do not address the overall wheel shape and the contact pattern the wheel makes with the rail.

PAGE 1 OF 4 | NEXT PAGE >