Interface - The Journal of Wheel/Rail Interaction

FLANGE CLIMB

Flange Climb and Independently Rotating Wheels
(continued)

When these vehicles were run through the simulated curve, LRV2 (the low-floor, three-car body system) produced much higher L/V ratios than the other vehicle. As Figure 2 indicates, LRV2 with IRWs (shown in blue) derailed at 45 mph, just above the Nadal's value, while the same vehicle with solid axles (shown in purple) operated well above Nadal's value without derailing. The reason for this is that the solid axles applied a longitudinal force, but the IRWs did not.

LRV2 also produced much higher L/V ratios than LRV1. This occurs because no steering moment is produced when the independently rotating wheelset is pushed into flange contact. A conventional wheelset, conversely, tries to steer itself back to reduce the angle of attack. "As you push it into flange contact, there is a large increase in the rolling radius of the flanging wheel and that tries to pull it around to reduce the angle of attack," Elkins said. But with IRWs, that effect doesn't occur. "When you push it into flange contact, there is no moment trying to reduce the angle of attack. So you get a much higher angle of attack."

Vehicle and wheel profile design
These simulations indicate that vehicle design can have a significant effect on the potential for flange climb derailment, and that articulation and suspension systems must be carefully designed to work with IRWs. They also indicate that wheel profiles can also play a role in a wheelset's ability to resist derailment.

Longitudinal steering forces are a function of rolling radius difference between left and right wheels. The larger the rolling radius difference, the larger the steering forces. Wheel/rail conicity also plays a role.

A wheelset shifts laterally to equalize the paths traveled by the inner and outer wheels. This lateral shift is inversely proportional to wheelset conicity, Elkins said. Wheel taper and conicity also play a role in wheelset steering and flange contact in curves. Wheels with a 1: 40 taper (0.025 conicity) can negotiate no more than a 1-degree (approximately 5,800-foot radius) curve without making flange contact. Wheels with a 1: 20 taper (0.05 conicity) can accommodate a 2-degree (approximately 2,800-foot radius) curve before making flange contact. Whereas some custom wheel profiles (with 0.2 conicity) can accommodate a 580-foot radius curve before making flange contact.

Like wheel-flange angle, the wheel profile can represent a significant factor in flange climb derailments, Elkins said. "If you're not in flange contact, you can't have a flange-climb derailment."

This article is based on "Wheel/Rail Interaction: Flange Climb Derailment and the Effects of Independently Rolling Wheels," a presentation by Nicholas Wilson, Scientist - Transportation Technology Center, Inc., and John Elkins, President of RVD Consulting, Inc., at Interface Journal and Advanced Rail Management's Rail Transit '04 Wheel/Rail Interaction Seminar.

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