Interface - The Journal of Wheel/Rail Interaction

MAINTENANCE RULES

New AAR Maintenance Rules for Freight Car Trucks
(continued)

Rule 46: Section 2
Section 2 of Rule 46 provides for truck inspection criteria and condemning limits when a car is on a repair track for any reason. The primary features of Section 2 include:

— The truck side frame casting wear plate is worn to a thickness of less than 1/4 inch in any area. When the column wear plates begin to wear, or become dished and hollowed, they will allow greater wedge rise. In extreme cases, this could cause toe-in on the plates, increasing the possibility of bolster lock up.

— The bolster wear plate is worn 50% or more from its new condition, as observed when the truck is dismantled for other cause. (Note that the truck must be dismantled for these measurements to be done and for this criteria to take effect).

— The friction casting wedge rise height (measured by an approved method) exceeds the limits indicated in Figures A-1, A-2, A-3, B-1, C-1, D-1 (of the Rule), or if wedge rise exceeds the manufacturer's recommendations. Figure 5 shows the correct method to check wedge rise for a Ride Control truck; Figure 6 shows the correct method for a Barber style truck.

— More than 25% of the material (or as recommended by the manufacturer) is missing on an individual friction shoe (casting) equipped with friction or composition materials.

— Column guides and gib clearance are at or exceed the wear limits in Table 2 (see Figure 7). Worn gibs are primarily an indicator of truck instability — particularly with regard to truck hunting at high speeds. When gib wear becomes excessive, it can lead to greater warp angles, and the potential for the truck bolster to become off-center, resulting in jackknifing tendencies under extreme buff loads.

— Mismatched side frames: Mate side frame mismatch is not greater that one button; with mate side frame wheel base nominal dimensions to match. Buttons are used on side frames to indicate slight tolerances in the desired axle center length of the side frame. Each button represents approximately 3/64 inches of tolerance. A truck frame that is measured to be precisely 70 inches for a 100-ton truck would have three buttons. If the truck frame was 3/16 inches too short, it would have two buttons; if it was 3/64 inches too long, it would have four buttons. Testing and research have shown that trucks with even one button mismatch do not perform as well in curving and stability as trucks with a precise button match. However, the AAR has determined that a one-button mismatch is sufficient to provide for acceptable performance.

— Vertical clearance between the truck bolster center bowl rim and the body plate is less than 1/8 inches at any location. When a car is on the repair track, any clearance between the bowl rim and the body center plate that is less than 1/8 inches is condemnable, whereas, in the train yard the clearance must be less than 1/16 inches to be condemnable. Inadequate clearance between the bowl rim and the bolster results in fouling between the surfaces, and changes the center of rotation of the centerplate from the center of the bowl to the outer edge of the bowl rim. This greatly increases truck turning resistance, resulting in the possibility of warped trucks.

Additional provisions of Rule 46 deal with correct repair procedures, centerbowl lubrication and billing repair card requirements. There are many more details, measurements and specifications in the complete Rule 46. This article, which is not meant to supplant or interpret the meaning of the rule, provides only a summary of the major provisions. In total, Rule 46 should go a long way toward improving the performance of freight car trucks, which should reduce fuel consumption, wheel and rail wear rates, tie degradation and the risk of derailment.

Gary P. Wolf is President of Rail Sciences Inc.

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