Wheel/Rail Interaction ’08:
Data to Information
(Part 2 of 2)
Part 1 of this article examined efforts to optimize vehicle and track component performance through various testing, monitoring and simulation programs. Part 2 continues on the theme of “data to information,” further exploring such programs and the operational benefits they engender.
Maintaining a Safe Neutral Temperature (SFT) on CWR has been an ongoing challenge for railways. Because of the danger of track buckling, which occurs at high temperatures, and rail breaks, which occur at low temperatures, railways and suppliers have been working to develop a practical, reliable and affordable means of measuring and monitoring the neutral temperature on CWR.
Canadian National worked with IDERS Engineering to develop a wireless system to monitor the SFT on CWR in order to detect track buckles and rail breaks, and emerging problems that are related to temperature changes, tonnage, track and surfacing work.
CN wanted a low-cost tool that would provide lifetime accuracy without the need for ongoing calibration — a tool that was rugged and robust, required no service or service parts, that was easy to install, and could be interrogated wirelessly, said IDERS President Bradley Brown.
To be acceptable to CN, an SFT measurement system needed to provide accurate measurements in all weather conditions (-40 degrees C to +70 degrees C) and require no ongoing service or calibration requirements. The system must provide an “instant” wireless SFT read-out that can be read at speed by roadmasters, tampers or defect detection cars (up to 20 mph).
The IDERS SFT measurement system, which is currently being implemented on CN, utilizes a sensor that is mounted to the rail and calibrated with known strain or SFT. As the stress-free temperature rises, the rail and sensor stretch. This change in dimension produces a drop in sensor resonant frequency, which is proportional to the change in strain. As the stress-free temperature drops, the rail and sensor compress. This change in dimension produces an increase in sensor resonant frequency which is proportional to the change in strain.
CN hopes that the SFT measurement system will enable track crews to find and fix problems on a proactive basis, and will provide CN and contract crews a verification and quality control tool.
Target Profiles for Rail Grinding
The removal of metal at the right time and in the right place is a fundamental aspect of rail maintenance work. This sounds simple enough, but it’s easier said than done.
The early days of rail maintenance often saw excessive metal removal in order to correct surface irregularities and defects that had, or would, cause severe problems. Today, rail maintenance practices have taken great steps toward becoming preventive measures. In contemporary rail grinding programs, thin layers of metal are removed at regular intervals to keep rail profiles within tight tolerances and prevent the types of conditions that require significant metal removal, said Wolfgang Schoech, Manager External Affairs at Speno International SA. (See Target Profiles for Rail Grinding: A Never Ending Story.)
An effective “preventive” approach requires the “right” profile or profiles to be applied. Since rails are installed at different locations and traffic characteristics change, there isn’t a single profile that suits all conditions. In Europe, profiling started with aiming at the as-rolled shape of new rails. “Experience showed that this “re-profiling” was not always the best solution,” Schoech said. As a result, various, more specialized profiles were developed. These profiles have undergone long in-track testing and today a number of unique profiles are routinely ground.
European railroads currently employ a number of specific profiles, including wear-reducing asymmetric profiles, fatigue-reducing anti-headcheck profiles, and various profiles increasing running stability. Occasionally, no existing profile best fits a certain scenario and an entirely new profile must be developed. This was recently the case for Banverket, a heavy-haul railroad in northern Scandinavia. Banverket undertook a meticulous process to develop the rail profile that best matched its hollow-worn wheels, in order to optimize both wheel and rail service life, he said.
“Ongoing creation, and revision of rail profiles is intrinsic to ensuring that grinding remains a preventive measure, that metal removal be minimized, and that rail service life be fully exploited,” Schoech said.
Evaluating the Risk of Wheel Climb
For many years now, the L/V ratio has been the industry standard for evaluating wheel climb risk; in recent years, the expanding network of wayside detector units has made it easier than ever before to take accurate and frequent L/V measurements. Recent research funded by the Federal Railroad Administration (FRA) and performed by the National Research Council of Canada’s Centre for Surface Transportation Technology (CSTT) suggests that additional parameters may be necessary to accurately gauge wheel climb potential in certain scenarios.
Common knowledge, supported by L/V measurement data, holds that one-point contact carries less risk of wheel climb than two-point contact, said Yan Liu, Senior Engineer at the NRC-CSTT. However, using only the L/V ratio to model this condition presents a technical dilemma. Under two-point contact conditions, the standard L/V ratio loses its essential meaning because the total lateral and vertical force between the wheel and rail is shared by both points of contact. Therefore, when the L/V of a two-point contact wheel is measured by a wayside detector, the data does not represent the true L/V of the wheel in a potential wheel climb scenario.
Using a formula (V2/V) that includes both points of vertical force on a non-conformal wheel, in conjunction with the standard L/V ratio, the NRC-CSTT research demonstrates a more reliable measure of the wheel climb potential of a two-point contact wheel, Liu said.
The NRC-CSTT research also modeled various lubrication conditions to better understand the effects of gauge-face and top-of-rail (TOR) lubrication on wheel climb potential. This battery of simulations indicated in all of the scenarios tested (loaded and empty cars, one- and two-point wheel contact, and varying levels of lubrication) that lower friction at the gauge-face results in lower overall wheel climb potential.
The NRC-CSTT simulations can also be applied to further study on cant deficiency, car types, and truck characteristics to develop a more thorough understanding of wheel climb dynamics, Liu said.
"Managing Wheel/Rail Interaction on Rail Transit Systems"
"Tuning in to the Systems Approach"
"Examining Wheel/Rail Interaction"
"Examining Wheel/Rail Interaction on Rail Transit Systems"
"Improving Truck Designs to Reduce Forces Transmitted to Track"
"Design Considerations to Meet the M976 Specification"
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