3-inch crack in the plate can grow into a so-called "cupid's bow" crack, as
part A of figure 3.14 shows. Its name is derived from the bowlike shape the
crack assumes when the two ends turn outward toward the rim.
plate is easily detected by a careful inspection of the wheels. However, if
such a crack is neglected, it can extend through the rim, as part B of
figure 3.14 shows, and cause the wheel to fail.
f. Tread worn hollow.
A gage is provided for condemning wheels for
worn hollow treads, as shown in figure 3.15. When the two ends of the gage
touch the rim and the flange but the bottom nipple on the gage does not
touch the tread, the wheel has reached the condemnable limit and must be
removed from service. The real limit of a tread worn hollow defect is the
height of the flange and this is what the gage is based on. Wheels should
not be condemned for having treads worn hollow before the gage limit is
g. Out of round.
If a wheel has a worn spot in the tread more than
3/64-inch deep, it is out of round and has reached the condemnable limit. A
wheel with this defect causes damage to the track, equipment, and lading
when the train is traveling at high speeds.
Figure 3.16 shows the gage
applied to a defective 33-inch wheel.