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Note that the designed wheel flange angle currently used relocating the contact band. Under these conditions, the
in North American transit operation ranges from 60 to 75 ground rail design must take the wheel shapes in the system
degrees. TCRP Report 57: Track Design Handbook for Light into consideration to ensure that the objectives will be
Rail Transit (11) proposed a wheel flange of 70 degrees achieved.
based on Heumann's design. The APTA Passenger Rail Ground rail profiles can be designed differently for
Safety Standard Task Force Technical Bulletin (12) provided straight and curved tracks. This is likely to be the case for
guidance on reducing the probability of wheel-climb derail- high speed operations because of a strong emphasis on lat-
ment, suggesting a minimum wheel flange angle of 72 eral stability on straight track. On straight track, the goal is
degrees (suggested tolerances are +3.0 degrees and -2.0 mainly to achieve low effective conicity, thereby raising
degrees). the speed at which vehicle hunting could start. In curved
A new wheel profile may be requested for a completely track, the main emphasis may be placed on improving
new rail system starting with new wheels and new rails. The vehicle steering and reducing lateral forces and rolling
design emphasis under this condition is to establish desirable resistance.
starting wheel/rail contact features to help new vehicles meet
their performance requirements. Simulations and trial tests
should be conducted on vehicles with the new wheel profiles 3.7.1 Ground Rail Profile for Straight Track
under the specified operating conditions to ensure that the
specified requirements have been meet. The likely wear In straight track, high values of effective conicity can lead
patterns may be predicted to further determine the vehicle to hunting at lower speeds for lightweight vehicles. Hence,
performance under worn wheel/rail shapes. one goal of profile design should be that a general low effec-
A new wheel profile may also be requested for an existing tive conicity trend is maintained for a large population of
rail system with worn wheels and rails. Under this condition, passing wheels that may have varying tread slopes due to dif-
the existing worn wheel/rail shapes should be taken into con- ferent levels of wear.
sideration when designing the new wheel profile, for exam- One way to lower conicity (actually, to lower the RRD of
ple when adopting a new wheel profile with a higher flange two wheels) from the ground rail is to reduce the contact at
angle to replace the existing low-flange-angle wheel. If the the wheel flange throat by producing a strong, two-point con-
profile change is significant compared to the existing design, dition when the wheel flanges, as illustrated in Figure 3.23.
it is likely that an interim profile (more than one, when nec- Then, the rail has no chance to contact the flange throat, thus
essary) will be needed to gradually approach the desired pro- reducing the variation of rolling radius.
file. Further, a transition program should be carefully Care needs to be taken when grinding the rails in straight
planned by considering the capacity of both wheel truing and track to avoid concentrating contact in just one portion of the
rail grinding on the system. An example is discussed in Sec- wheel tread. Concentrated contact can lead to excessive
tion 4.2.3 of Appendix A.
wheel hollowing.
3.7 GROUND RAIL PROFILE 3.7.2 Ground High Rail Profile
In general, North American transit operations use Ameri- The ground high rail shapes generally should be close
can Railway Engineering and Maintenance of Way Associa- to the stable, worn high rail shapes at the rail gage shoul-
tion (AREMA) standard rails (13). The AREMA 115-pound der and corner. Severe two-point contact should be
(115RE) and the 132-pound rail (132RE) are two types of rail
avoided because it produces poor steering.
that are commonly used on transit lines, especially for newer
systems. Some old systems have lighter weight rails (90- to
110-pound rail) still in use on their lines.
Rail profiles are generally not ground back to the new rail
shapes. The ground rail shapes determine the contact condi-
tion after rail grinding or determine the variations of contact
condition compared to the situation prior to grinding. There-
fore, properly designed ground rail profiles are critical for
producing minimum disturbances to a profile-compatible
system. This would result in a short wear-in period to reach
the equilibrium stage.
Sometimes, rail grinding is conducted for a major cor- Figure 3.23. Example of reducing effective conicity by
rection of rail shapes, such as increasing contact angle or controlling contact position.
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If grinding were only conducted on the stable, worn rail
shapes to remove corrugations or surface defects, maintain-
ing these stable shapes would lead to a minimum disturbance
to the existing conformal contact. Such grinding requires the
removal of only a thin layer of metal--not more than the
depth of corrugation and surface defects.
3.7.3 Ground Low Rail Profile
Figure 3.24. Example of grinding tolerance for a high
The ground low rail profiles should be designed to avoid rail.
contact positions that significantly face toward the field side.
This is especially important for the low rails in curves, where
hollow-worn wheels can give very high contact stresses on
to a point with an angle of 10 degrees on the field side and to
the field side. Fieldside contact can also increase the risk of
a point with an angle of 40 to 60 degrees on the gage side.
rail rollover or gage spreading.
The angle on the gage side is based on the capacity of the
Varying low rail shape by grinding can alter the RRD by
grinders (the maximum angle that can be reached by the
intentionally moving the contact positions on wheels to a
grinder).
desirable area, such as from the gage shoulder to the crown
Much work has been done in recent years to set tolerances
area by lowering the gage shoulder. Because the contact
on profiles given by rail grinding. Based on a survey of these
radius in the rail crown area is larger than on the rail shoul-
references (14, 15, 16), the recommended tolerance for the
der, this adjustment reduces contact stress.
ground rail transverse profile should be from -0.4 mm to
In designing ground rail profiles for curves, the contact
+0.3 mm. Negative tolerances mean that the ground rail
conditions of both leading and trailing wheels should be con-
sidered. The leading wheels on the high rail are generally shape is below the design rail shape. Positive tolerances
flanging for curves above 3 degrees. Vehicles that are mean that the ground rail shape is above the design rail
designed with soft yaw suspension that allow the axles to shape. The example in Figure 3.24 shows negative toler-
steer may flange at higher degree curves. Therefore, it is rec- ances, that is, the measured rail profile is inside the template.
ommended that the assessment of vehicle curving perfor- Some grinders can reach even better accuracy with careful
mance be conducted for the ground rail design. The trailing control of the grinding stone patterns.
wheels are generally not flanging. They usually have a small Positive tolerances in the gage corner can be much more
lateral shift relative to the track center, depending on vehicle detrimental than negative tolerances. A large positive toler-
and track conditions. ance in the gage corner can lead to high contact stress and
consequent high wheel- and rail-wear rates and the potential
for crack formation. With good grinding accuracy, the
3.7.4 Grinding Tolerance ground rail shape will quickly wear to a profile that is con-
formal with the wheels passing over it.
During rail grinding, the transverse rail profile is produced Rail template gages are also commonly used to inspect the
by a series of straight facets from the individual grinding rail shapes during routine checks or after rail grinding. Expe-
units. Thus, the grinding process unavoidably produces a rienced inspectors can estimate differences by looking at the
polygon-curve approximation to the desired profile, and this gaps between the template and the actual rail shape (Figure
causes variance between the actual ground rail profile and the 3.25). Note that in order to allow the gage to slide over the
target design rail profile. The stone pattern selections and set- head of the two rails (even under the wide gage condition),
tings can also cause deviations of ground rail shape from the the template gages usually do not have the whole shape of the
target shape. rails.
Thus, a grinding tolerance needs to be specified to limit the
variation from the target shape. The tolerance is defined as
the radial distance between the measurements of the ground 3.7.5 Rail Lubrication after Grinding
rail profile and the target design profile. To check whether
grinding has produced the design ground rail profile within Slight lubrication immediately after rail grinding can
the specified tolerance, the ground rail profile should be over- reduce the wheel flange climbing potential, just as lubri-
laid on the target rail profile. cation after wheel truing can. The rough rail surface after
Tolerances should be assessed as shown in Figure 3.24. grinding can reduce the limiting L/V ratio for flange
Tolerance is evaluated from the highest point on the rail top climb.
