Interface - The Journal of Wheel/Rail Interaction

WHEEL SHELLING

Implementing an Anti-Shelling Wheel Profile (continued)

Improved Steering
The design, known as the Anti Shelling Wheel (ASW) profile, is superimposed onto the AAR1B in Figure 3a. The extra metal in the flange root can be clearly seen, as can the tread roll-off. Both of these features increase the ΔR that can be obtained in curves compared to the AAR1B, although the tread roll-off is a lesser contributor. The ASW profile had even more metal in the flange root than did the QCM-Heumann profile, as can be seen in Figure 3b. As a result, the ASW profile would be able to generate even stronger steering moments than the QCM-Heumann profile.

The advantage of a stronger steering moment is that it can somewhat reduce the angle of attack on the lead axle in a truck, which in turn can reduce the lateral creep forces acting in the wheel/rail contact patch. In terms of the shakedown diagram, this results in a lower traction coefficient, which helps to move the contact condition to the left, away from the shakedown limit. The tread roll-off on the ASW resulted in higher contact stresses when in contact with a low rail than would occur with the AAR1B, but not so high as to exceed the shakedown limit. This was viewed as an acceptable trade-off, since the contact stresses were still much lower than those that would result from a false flange contacting the low rail. The effective conicity of this wheel was identical to the AAR1B, for lateral displacements of 6 mm or less from track center. Greater displacement caused contact to occur at the bottom of the flange root area, resulting in higher effective conicity.

The results obtained from CN and CP were different. CP’s ASW profiles showed undamaged treads and minimal tread and flange wear after 150,000 km, whereas CN’s ASW profiles exhibited a band of cracks near the tread centerline. The differences could possibly be explained by the fact that wear on CP’s wheels was evenly spread across the tread because CP was grinding its tangent rail to two separate profiles. Flexible trucks, which can take advantage of the stronger steering moment produced by the ASW profile to reduce angle-of-attack, were also in use on much of CP’s coal fleet. CN was using conventional trucks, and grinding to a single tangent profile which happened to concentrate wheel/rail contact right at the start of the tread roll-off.

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