Interface - The Journal of Wheel/Rail Interaction

TRACK BUCKLE

Preventing Track Buckle (continued)

During VERSE testing, it is not unusual to find RNT 20 to 30 degrees below the desired RNT. If the RNT falls to the range of 70 degrees (F), a rail temperature of only 120 degrees (F) could put significant compressive stress in the track, and increase the probability of sun kink. Therefore, track maintenance personnel should be alert for possible heat stress every spring. Signs of heat stress include "nervous" or "kinky" rail (see Figure 3) that tends to crowd the shoulders of the tie plate, first to the field side, then to the gauge side. Also, formation of voids or pockets off the ends of ties (see Figure 4) may indicate that the track is moving to one side or other under the influence of buckling forces.

Another factor that can lower the effective RNT is the insertion of rail during cold weather months. Internal rail defects often grow and propagate in the cold winter months when the rail is in tension. Ultrasonic testing can find these defects, necessitating rail replacement. When a "plug" rail is installed, it will be at lower neutral temperature than the adjoining rail strands. When warm weather arrives, the plug rail will tend to expand more than the adjoining rails, thus placing excessive compressive forces into the track, resulting in a buckle. Careful notes and documentation should be made of any replacement rails installed during the cold months, so that proper adjustment can be made in the spring.

RNT constantly changes from season to season. More importantly, RNT rarely increases, but generally decreases. A decrease in RNT increases the likelihood that even a moderate increase in rail temperature can generate dangerous compressive forces in the rail, with an attendant risk of sun kink. Thus, no matter how carefully RNT is controlled during rail installation, every spring brings the chance of track buckle.

Steps to Prevent Track Buckles
There are a number of ways to increase the resistance of rail to buckling. The first and most common is the use of rail anchors to limit the longitudinal expansion of the rail. Anchors come in a variety of designs, but they all apply several thousand pounds of clamping force on the base of the rail. When applied properly against each side of the crossties, the anchors prevent expansion of the rail in the longitudinal direction. In most territories, box anchoring every other tie is generally sufficient to prevent expansion. Some railroads box anchor every tie in severe curve territory. Where bolted joints exist in CWR territory, most railroads box anchor every tie for a distance of five rail lengths, or 200 feet, on each side of the joint.

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