Interface - The Journal of Wheel/Rail Interaction

W/R INTERFACE MANAGEMENT

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

Improving Vehicle Curving Performance
A track inspection was conducted on a 261-km, heavy-haul line, 25.6 km of which contained curves. All measured rail profiles were stored in three files named Sections 1, 2 and 3. The wheel profile database described in Table 1 was used in the curved track rail inspection.

Contact conformity is a parameter used to evaluate bogie curving performance. The conformity of a wheel contacting the outer rail on a curve is a measure of the maximum gap between the wheel flange root and the rail gauge corner when the wheel is in flange contact with the rail, as shown in Figure 7. A large gap can lead to severe two-point contact, resulting in a larger rolling radius difference between the two contact points. This wheel/rail contact pattern can result in poor wheelset steering on curves and can generate high wheel/rail interaction forces, which increase wear and RCF on wheels and rails. Poor wheelset steering can also induce high gauge-spreading forces that can degrade the track.

Figure 8 shows simulation results for a hopper with a 32.4-tonne axle load negotiating a 291-m radius curve, under three wheel/rail interface lubrication conditions. The total rolling resistance, also called wear index, is an indication of the energy consumed in the wheel/rail interface. (It is measured by the traction forces at the wheel/rail interface and the creepages).

ΔRRD2 in Figure 8 is the rolling radius difference between two contact points at the wheel tread and flange on the outer rail when curving. As ΔRRD2 is larger than 6 mm, the total rolling resistance increases almost linearly with ΔRRD2.

Table 2 lists the section length and the length of the curves (only counting the curves with a radius less than 873 meters). The smallest curve radius on this line is 291 meters. The threshold gap value (d in Figure 7) used to evaluate the contact conformity in this inspection was 0.5 mm.

Figure 9 shows the distribution of contact conformity exceptions (i.e., where d> 0.5 mm) for the curves in this line with radii smaller than 873 meters. It shows that 20% to 30% of the wheels in the wheel database exceeded the contact conformity threshold when contacting 65%, 78% and 86%, respectively, of the rail profiles measured in curves of these three sections of track.

Of the wheels in the wheel database, 21.3% were new standard wheels; 14.8% had 56,000 km of service. Previous research has indicated that the current standard wheel profile can produce severe two-point contact when contacting the worn outer rail on curves. The rolling radius difference between the two contact points on the outer rail can be up to 12 mm (1).

Consequently, the poor conformity of wheel/rail contact, shown in Figure 9, was mainly caused by the new, or nearly new, wheels. Figure 10 shows the typical contact pattern produced by a standard wheel profile when contacting the worn high rail profiles in curves with radii of 291 m, 436 m and 873 m on this line. On the other hand, the worn wheels generally produce relatively conformal contact when contacting the worn outer rails on this route.

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