Interface - The Journal of Wheel/Rail Interaction

EFFECTS OF WIDE GAUGE

Effects of Wide Gauge on Derailment Potential
(part 2 of 2) (continued)

Stiff or Warped Truck Conditions
"Truck Warp: Causes and Cures" (Part 1 of 2) showed how warped trucks caused poor steering and excessive gauge spreading forces. Trucks warp, or parallelogram, for a variety of reasons. Conditions in the centerbowl or bolster can cause an increase in truck turning moment. These include:
• Interference at the centerbowl rim with the body centerplate.
• Fastener contact anywhere around the centerbowl rim.
• Incorrect repairs or rough centerplate surface.
• Insufficient, or tight, side bearing clearance (one or both sides).
• Excessive wear in the bowl or centerplate causing an egg-shaped condition.
• Incorrectly or overloaded car on one side.

Other factors can lead to poor truck steering. These include:
• Mismatched side frames (button mismatch).
• Mismatched wheel diameters (wheel tape sizes).
• Hollow worn wheels.
• Wedge rise or lack of damping.

If a detailed mechanical inspection of the first derailed vehicle reveals that one, several or many of these mechanical conditions are present, the primary cause of the "wide gauge" derailment may be of mechanical origin. In other words, the track structure was able to restrain normal gauge spreading forces, but not the excessive lateral forces that a particular car was generating. In a case like this, it is more appropriate to assign a mechanical code such as E46C: "Truck Bolster Stiff, Improper Swiveling." It's important to recognize that yard and industry tracks are built to standards designed to accommodate lower speed, and lower wheelset force environments. If excessive forces are placed on these tracks due to a poor mechanical curving condition, the appropriate cause code should begin with a "E" not a "T."

Human Error during Switching
Spread gauge derailments also occur on good track with no obvious mechanical problem. In cases like these, human error may be the cause of a derailment. Poor train handling, even during switching, can cause excessive slack action, which leads to excessive drawbar forces. The forces imparted into the drawbars of freight cars are eventually transferred to the centerbowl, through the bolster, into the side frames, and eventually into the wheels. Thus, these drawbar forces are additives to all the other normal curving forces, and can overwhelm the track structure. When engineers use too much independent braking effort or excessive dynamic braking, excessive buff forces can be developed. Also, shoving against a heavy air brake reduction can likewise create heavy buff forces in the train. Simulations show that when buff forces exceed about 250 kips, the potential exists for compromising the gauge of nominal track. Bypassed couplers in switching operations can also exert tremendous lateral gauge-spreading pressure against the rails. Investigators should look for evidence of coupler impact or coupler shank contact against the side of the striker casting.

All of this is to say that the T110 "wide gauge" cause code should be assigned to a derailment in which the gauge measures in excess of FRA requirements. But before routinely assigning the T110 code, the role of human error and mechanical causes should also be examined.

Gary P. Wolf is President of Rail Sciences Inc.

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