wheel slippage and track damage
NW Mailing List
nw-mailing-list at nwhs.org
Mon Dec 10 17:00:26 EST 2007
Wheel slippage causes local heating of the rail and can cause a shallow pit
or depression in the rail head. The heating causes micro-cracks to grow in
the steel and the repeated 'bang' of a wheel falling into the depression
causes a cyclic impact loading to occur in the rail under the pit. This
all combines into a cyclic fatigue situation where the micro-cracks grow and
join into bigger cracks that lead to rail failure.
In short, wheel slippage causes bad things to occur.
Having said that, the maximum friction occurs between a driving wheel and
the steel rail when a slight amount of slippage occurs between the two.
Thus the better wheel slip controls in a locomotive try to achieve a little
slippage before decreasing the amperage supplied to the affected wheel.
However the trade-off is that the rail is ground off a little faster over
time. This is why you see the rail replacement gangs out on the Elkhorn
grade so frequently- especially when you wish to take photos of moving
trains in daylight.
Engineering is like life; a bunch of trade-offs. Sometimes the best you can
do is trade one not-very-desirable outcome for another not-so-great outcome.
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