b. Passenger car axle, 1940-design (solid-friction or roller bearing). The principal difference between the
1940-design axle and the earlier standard axle is the absence of the "black collar" and the raised wheel seat.
Figure 2.23 is a diagram of the 1940-design passenger car axle designed for use with roller bearings. Table III
contains the new dimensions for it.
Notice the absence of the end collar on the roller bearing axle, a
characteristic of all journals designed for roller bearings.
c. All-purpose tubular axle (friction and roller bearings). The dimensions, when new, of the distance
between the wheel seats of tubular axles (table IV) are larger than the same dimensions on solid axles (table III).
Note in the diagram in table IV, the dotted lines inside the solid contour lines; these outline the outer surface of
the hollow in the axle.
2.17. AXLE WEAR LIMITS
Much of the wear of axles takes place on the journal. Because of the weight and friction concentrated on
it, the journal tends to wear and become smaller in diameter and longer. As the journal wears, its load limit
decreases until it reaches a point where it is no longer safe and must be removed from service. As the journal
lengthens, more lateral movement is permitted, and this excessive sidesway is dangerous.
The wear limits for the three types of axles are shown in tables II, III, and IV. By comparing these with
the new dimensions, you can see that axle wear is considered critical and the tolerances are small. However,
axles may be turned on a lathe to restore the original contours or to refinish the journal. Small scratches can be
removed and the axle returned to service. When a defect is severe enough the axle must be removed and
restored; when any limit of wear is reached, it must be scrapped. The following paragraph explains axle defects.
As with wheels, the standards for axle wear limits and defects are defined in the AAR Wheel and Axle
Some of the major and more frequently occurring defects are explained in the following
subparagraphs, and the AAR symbols for them are given. When an axle is condemned, the appropriate symbol
is marked on it to identify the defect or cause for removing the axle from service.