Interface - The Journal of Wheel/Rail Interaction

DERAILMENT PREVENTION

Inspection and Analysis of Switch Derailments
(Part 2 of 2) continued

Chipped or Broken Switch Points
Many wheels climb switch points because the switch point itself is blunted or cracked from repeated wheel impacts. One of the more ambiguous clauses in the FRA Track Safety Standards is 213.135 (h) which states: “Unusually chipped or worn switch points shall be repaired or replaced.”

Exactly what constitutes an “unusual” condition, as referred to in this phrase, is the subject of debate. The standard allows for some chipping of the point, but it does not allow an excessive amount of chipping. Where, then, do we draw the line? Some railroads have written internal standards that quantify the amount of chipping allowable on the tip of the switch point. As a rule of thumb, if the point is chipped at a depth of 3/4 inches or more, over a distance of 12 inches from the tip of the point, you may be dealing with a defective point that could cause a flanging wheel to climb up and over the point. Other railroads specify that the point must be repaired if it presents a blunt face that is more than 3/16 inches wide at all points closing along the straight stock rail. Thin flange wheels (but not condemnable) that flange hard against the stock rail are likely to find the chipped and broken switch point and create a climbing action. To ensure a low risk of derailment, switch points exhibiting signs of chipping and breaking should be built up and ground smooth. Figure 3 shows examples of switch points exhibiting “unusual” wear that requires repair.

Switch point protectors (see Figure 4) are used by many railroads to prevent wheel flanges from striking the points. In order to be effective, they must be properly adjusted, as the face of the protector wears due to wheel rim contact.

Derailments in the Frog Area
Wheels can “pick” frog points, just as they can pick switch points. If the tip of the frog has become chipped and broken, a marginally steering wheel can be diverted from its intended path and proceed through the wrong side of the frog. The FRA Track Safety Standards are more specific when it comes to defining a chipped and broken frog point. Section 213.137 (b) states: “If a frog point is chipped, broken, or worn more than 5/8 inches down and six inches back, operating speed over the frog shall not be more than 10 mph.”

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