Optimizing Wheel and Rail Profiles
on Amtrak's Northeast Corridor (continued) Wear is only one parameter for evaluating
wheel/rail performance. Another is "effective
conicity," which represents a weighted average of the rolling radius difference.
When tapered wheels in tangent track are shifted sideways, the contact point
on one wheel moves toward the flange throat of the wheel, while the contact point
on the other wheel moves toward the field side. This creates rolling radius difference
in which one wheel is rolling on a bigger radius than the other. Rolling radius
difference on a fixed axle generates longitudinal creep forces that initiate
a steering moment, which usually steers the wheelset away from the curve and
back toward the center of the track. As the wheelset passes the centerline of
the track, a steering moment is generated in the reverse direction, forcing the
wheelset back toward the curve. Depending on the damping in this system, this
movement will either be damped within three or four cycles or it will lead to
a flange-to-flange, hunting motion.
Designing a New Wheel Profile
CSTT also looked at
wheel/rail conformality — whether there was typically
one- or two-point contact on the corridor — by positioning a wheel on rail
in a curve (see Figure 2). Gaps greater than 0.4 mm between the two points of
contact — one toward the top of the rail and one toward the gauge corner
or face of the rail — constituted non-conformal, two-point contact. Gaps
of 0.4 mm or less were considered conformal contact. Very small gaps of less
than 0.1 mm between the profiles were considered closely conformal contact.
Wheel profiles on the Acela fleet generated non-conformal two-point contact,
a condition that is dominated by wear. A large percentage of the wheels on Amtrak
locomotives, however, generated non-conformal single-point contact, which is
generally associated with high stress, hard gauge-corner contact and rolling
contact fatigue. These locomotives are believed to be responsible for a disproportionate
amount of contact fatigue.
DECEMBER 2004 "Designing Amtrak's
Wayside Train/Track Interaction Detection System" READ
ARTICLESEPTEMBER
2004
"Developing an Enterprise Asset Management System for Amtrak’s Northeast
Corridor" READ
ARTICLE
SEPTEMBER 2004 "Monitoring Vehicle/Track Interaction
on Amtrak's NEC" READ
ARTICLE
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CSTT also looked at
wheel/rail conformality — whether there was typically
one- or two-point contact on the corridor — by positioning a wheel on rail
in a curve (see Figure 2). Gaps greater than 0.4 mm between the two points of
contact — one toward the top of the rail and one toward the gauge corner
or face of the rail — constituted non-conformal, two-point contact. Gaps
of 0.4 mm or less were considered conformal contact. Very small gaps of less
than 0.1 mm between the profiles were considered closely conformal contact.
