What are the differences between rail shapes that produce higher contact conicities and those that produce lower contact conicities? The profiles shown in Figures 1a and 1b illustrate the differences that can result in significant changes in conicity. The rail profiles that produced high conicity were selected from the rail group that produced more than 60% of the wheel exceptions shown in Figure 2 (See Part 1). The rail profiles that produced low conicity were selected from the rail group that produced less than 10% of the wheel exceptions shown in Figure 2.

The differences between these two groups of rail profiles can clearly be seen. The rail profiles that produced low contact conicities have a relatively low rail shoulder compared to the rails producing higher contact conicities. Rails with considerable plastic flow at the gauge face of the rail (see Figure 1b) can also contribute to high contact conicity associated with reduced flange clearance.

The contact conicity of worn wheels can be very dependent on the shape of the rail profile. Figures 3a and 3b show the high contact conicity that is produced by a representative worn wheel profile (selected from the group labeled >256,000 service km) contacting with two rail profiles. Both rail profiles have higher rail gauge shoulders. The rail profile shown in Figure 3b also has plastic flow at gauge face. The same worn wheel produces lower contact conicities when contacting rails with lower gauge shoulders (see Figure 4). New wheels tend to produce lower contact conicities when contacting both new and worn tangent rails (see Figure 5).

Note that the contact conditions shown in Figure 3 can also produce high contact stress due to a single, small contact area. When a vehicle experiences lateral oscillation, it not only transmits high forces into the truck structure, it also generates higher tangential force and creepages at the wheel/rail interface, which increases wear and the risk of rolling contact fatigue (RCF).

At certain locations, tight gauge also contributed to high contact conicities. The standard track gauge spacing of 1435 mm (56.5 inches) is measured at 15.6 mm (5/8 inches) from the top of the rail. Tight gauge conditions, combined with worn wheel profiles, can result in the rail gauge corner contacting a wheel at the flange throat. This is caused by small lateral wheelset shifts that are caused by track perturbations, vehicle dynamic movements, or a combination of both. This can result in higher conicity contact conditions and vehicle lateral instability. Tight gauge, which can be caused by improper installation, is exacerbated by metal plastic flow toward the gauge face of the rail, and/or rail movement.

A track geometry inspection identified a number of track sections with tight gauge conditions. Figure 6 illustrates the reverse correlation between the conicity exceptions and the variations in track gauge. The line of 30% of exceedance of wheels was the reporting criterion used in the inspection. Once above, it indicates that more than 30% of the wheels used in the assessment contacting the rail at that location exceeded the conicity threshold of 0.35.