Interface - The Journal of Wheel/Rail Interaction

W/R INTERFACE MANAGEMENT

Management of the Wheel/Rail Contact Interface in Heavy-Haul Operations (continued)

Tangent Track Inspection
The WRCI™ system was used to examine how rail profiles and track conditions contribute to hunting under one type of loaded grain car on specific lines. The system showed that wheels on some of these cars were worn to shapes that produce high contact conicities when contacting certain rail profiles.

Wheel/Rail contact conicity (λ) is defined by Equation: λ = ΔR/2y (4), where ΔR is the rolling radius difference of two wheels on an axle and y is the wheelset lateral shift. Higher values of conicity lead to a higher risk of vehicle lateral instability. Wheel/rail contact conicity is affected by wheel/rail profile shapes that affect the value of ΔR and the clearance between wheel flange and the rail gauge, which affects the value of y.

Table 1 shows the distribution of wheel profiles used to assess the measured rail profiles. The wheel profiles, which were taken from loaded grain cars (with more than 256,000 kilometers of service) that demonstrated lateral instability, demonstrated a tendency to produce higher contact conicities when contacting certain rail profile shapes. Other wheel profiles were taken from other 286k grain cars; service mileages were estimated from their service records.

Because of the asymmetric wear on some of these wheelsets (and the possibility that they could contact either rail depending on the cars’ orientation), the 108 measured wheelsets were mirrored to produce a database with a total of 216 wheelsets. Figure 3 (on prior page) shows an overlay of typical profile shapes from each group of wheels.

Inspection Results

An inspection identified the track sections and rail profiles that produced high contact conicities when contacting certain worn wheel profiles. Figures 6 and 7 show the inspection results for 30.4 km of tangent sections of a heavy haul line. The nominal operating speed on this line is 88 - 112 km/hour, depending on the car types. About 25,000 pairs of rail profiles were measured on the tangent track sections. The Y-axis of Figure 6 indicates the percentage of total rail pairs measured in the tangent track sections. The X-axis denotes the percentage of wheels that exceeded the conicity threshold limit of 0.35, which was selected based on loaded car lateral instability tests conducted at TTC. (The tests concluded that the wheelset conicity of the grain car must be in excess of approximately 0.4 to develop loaded car lateral instability within prevailing operating speeds (5).)

In Figure 6, the bar of <10% indicates that 70% of the rails contacting the wheels in the database caused less than 10% of the wheels to exceed the 0.35 threshold conicity value. In other words, more than 90% of the wheels (new and worn) contacting 70% of the rails produced conicity values below 0.35.

Only about 13% of the measured rail profiles (summation of last four bars circled in Figure 6) in this section of track contacting the wheels in the database caused more than 30% of wheels (last four bars in Figure 6 notated from > 30% to >60%) to exceed the 0.35 threshold conicity value. Therefore, these 13% of rails had a tendency to induce loaded car lateral instability.

Figure 7 shows the locations of the rails that produced higher contact conicities in this section of track. The distance axis shows the measurement numbers in sequence, with a distance interval of 2 meters. The dots show all rails that produced higher contact concities. The numbered blocks show the track sections where a large percentage of the rails produced conicities above 0.35. Subsections 7, 8, 10, and 12 are likely in need of maintenance, because they had a high percentage of exceptions over longer distances (see Table 2).

Figure 8 shows the percentage of all measured rail profiles that exceed the conicity threshold values between 0.25 and 0.5 for the same section of tangent track using the 30% wheel exceedance criterion. The results give an overall view of contact conicity of this track.

Huimin Wu, is Principal Investigator; Semih Kalay, is Vice President Research & Development, Transportation Technology Center, Inc.

References

1) Johnson, K.L., Contact Mechanics, Cambridge University Press, 1985.

2) Burstow, M.C., “Whole Life Rail Model Application and Development for RSSB — Continued Development of an RCF Damage Parametre,” Rail Standard and Safety Board, London, UK.

3) Wu, H., Thompson, R., Lundberg, W., and Hou, K., “Development of an Automated Assessment System for Wheel/Rail Contact Condition Inspection,” Proceedings of 7th World Congress on Railway Research, June 2006.

4) Guidelines to Best Practices for Heavy Haul Railway Operations – Wheel and Rail Interface Issues, International Heavy Haul Association, May 2001.

5) Tournay, H., Wu, H., and Wilson, N., “Investigation into the Root Causes for Loaded Hunting,” Research Report, R-995, Association of American Railroads, Transportation Technology Center, Inc., November 2008.

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