b. Shell-out (Rule 71--AAR symbol 71).
Although the true cause of the shell-out defect has
not been defined, it is probably caused by foreign
material in the wheel tread. The name of this defect
is derived from the fact that it looks somewhat like
an inverted oyster shell with a high center. The
same gage is used as for a slid-flat defect, and the
same measurements condemn the wheel from
further freight and passenger service. The same
rough riding and rail damage occur with this defect
as with a slid-flat defect.
c. Seams (Rule 72--AAR symbol 72). Seams
are manufacturing defects; they run lengthwise
around the wheel and cause either the flange or the
rim of the wheel to break off. Any seam detected
Figure 2.5. Measuring Slid-Flat Spot.
within 3 3/4 inches of the flange condemns the wheel from further service. Part of a wheel with a seam defect
is shown in figure 2.6.
Figure 2.6. Seam Defect.