Truck Warp: The Causes and
Cures – Part 1 of 2(continued)
Warped trucks are most evident when executing
a curve, during which they produce excessive squealing caused
by flange contact against the outer rail, and a deeper
groaning sound on the inner rail as the wheels slip across the railhead. Truck
Performance Detectors (TPDs) can accurately detect warped trucks by the characteristic
pattern of wheelset forces they generate, rather than by their acoustical attributes.
While noise alone may be cause for concern in some instances, there are other,
more significant consequences. For starters, warped trucks cause excessive wear
on components. At worst, they can cause rail rollover derailments. Figure 3 shows
a typical plot of the lateral wheel forces produced under a normally steering
truck. Note that the leading axle always produces higher forces than the trailing
axle. This is because the leading axle always attacks the outer rail of a curve
at a higher angle of attack than the trailing axle. Visualize a truck as a square
box trying to move through a curved trough. The leading edge is always going
to be bumping into the outer edge of the trough. However, the forces on the trailing
axles are usually benign, as the trailing wheelset maintains a nominal radial
alignment with the center of the curve. When a truck warps, however, both axles
are aligned sharply against the outer rail of the curve in a severe angle of
attack. This creates significant flanging forces against the rail resulting in
excessive wear to both the wheel and rail. Since the wheel is exerting excessive
flanging forces against the outer rail, a similar and opposite reaction occurs
against the inner rail of the curve.
AUGUST 2004 "Effects of
Rail Cant on Wheel/Rail Forces and Derailment
Potential" READ
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While noise alone may be cause for concern in some instances, there are other,
more significant consequences. For starters, warped trucks cause excessive wear
on components. At worst, they can cause rail rollover derailments. Figure 3 shows
a typical plot of the lateral wheel forces produced under a normally steering
truck. Note that the leading axle always produces higher forces than the trailing
axle. This is because the leading axle always attacks the outer rail of a curve
at a higher angle of attack than the trailing axle. Visualize a truck as a square
box trying to move through a curved trough. The leading edge is always going
to be bumping into the outer edge of the trough. However, the forces on the trailing
axles are usually benign, as the trailing wheelset maintains a nominal radial
alignment with the center of the curve. When a truck warps, however, both axles
are aligned sharply against the outer rail of the curve in a severe angle of
attack. This creates significant flanging forces against the rail resulting in
excessive wear to both the wheel and rail. Since the wheel is exerting excessive
flanging forces against the outer rail, a similar and opposite reaction occurs
against the inner rail of the curve.
