Interface - The Journal of Wheel/Rail Interaction

FRICTION MODIFICATION

Top of Rail Friction Modification in Tough Terrain
By Kevin Conn and Kevin Oldknow • April, 2008

Implementation of wayside Top of Rail (TOR) friction control on Norfolk Southern’s mainline coal route has provided the means to reduce damaging lateral forces and wear rates in a high-stress environment. It is critical, however, to examine the interaction between train speeds, track geometry, train handling and friction control in order to understand, quantify and maximize the benefits. This article presents the results from an extensive study of the effectiveness of a TOR friction modifier under a range of heavy ascending and descending grade conditions. The study included a detailed look at the interaction between speed, superelevation and lateral forces.

Norfolk Southern operates a mainline coal route in the southern coal fields of West Virginia, moving 40 million gross tons (MGT) of heavy axle load traffic per year between Williamson and Bluefield. The mountainous terrain presents a challenging environment that includes several 3- to 12-degree curves, short spirals and very little tangent track between the curves. The track follows creeks and rivers, and many tunnels and bridges are required to minimize the steepness and number of ascending and descending grades. Many tunnel approaches are configured with curves on bridges, with no easy way to optimize the track alignment (see Figure 1).

Typical train lengths are 100 to 170 cars, depending on the grade. In ascending grade operations, trains are typically powered with three head-end locomotives and three rear-end pushers. Heavy sanding is used to maintain adhesion. Trains typically operate below balance speed. In descending grades, trains are powered by two head-end locomotives. They typically operate at or slightly above balance speed. Extensive use of air and dynamic braking is required to maintain train speed, resulting in elevated wheel temperatures. These conditions combine to produce a very high-stress operating environment, which is evidenced by a number of undesirable rail and track conditions. Figure 2 shows an example of head-checking at the high rail gauge corner/gauge face of the rail. Scuff marks on the low rail running surface are often present, due to the wheel/rail stick-slip phenomenon.

The high-stress environment also produces wide-gauge problems. Figure 3 shows an example of the rail base shifting inside the tie plate due to the high lateral forces. These lateral forces are not only transmitted from the rail to the tie plate, but also to the fasteners. As a result, breakage of large numbers of cut spikes and screw spikes occurs, especially where curves are located on bridges (see Figure 4).

In addition to gauge-face wear on the high rail, low rail running surface wear, as evidenced by metal shavings on the rail base, is a significant issue. In severe cases, gauge corner cutting on the low rail is indicative of negative steering moments. Locomotive sanding and underbalance speeds promote high rates of wear that flatten the low rail profile shortly after grinding. Finally, the repetitive high lateral forces result in accelerated tie plate cutting and cant issues, which require frequent adzing and tie replacement (see Figure 5).

TOR Friction Modifiers
NS utilizes KELTRACK® Trackside Freight, a water-based TOR friction modifier that dries rapidly upon application to establish a dry, thin film that controls friction at the wheel/rail interface. The material controls friction by providing an intermediate coefficient of friction (target ~0.35 at saturated creepage) and positive friction, which refers to a monotonically increasing traction force with increasing creepage. These attributes enable the TOR friction modifier to mitigate the wheel/rail interaction conditions that cause high lateral forces, rail roll-over derailment potential, track structure degradation (including gauge widening and fastener breakage), rail and wheel wear, rolling contact fatigue, corrugation and noise — all without negative effects on braking, adhesion or the track signaling system.

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