Interface - The Journal of Wheel/Rail Interaction

WRI '08 SEMINAR OVERVIEW

Wheel/Rail Interaction ’08: Data to Information
Part 1 of 2 (continued)

Wheel Shelling and Spalling
Wheel maintenance is another primary area of concern relating to vehicle/track interaction.

“Wheel tread damage, primarily in the form of shelling or spalling, costs the railroad industry $350 million annually,” said Scott Cummings, Senior Engineer at the Transportation Technology Center, Inc.

The Wheel Defect Prevention Research Consortium (WDPRC), which includes Class I railways, the FRA, private car owners and industry suppliers, was formed to determine the actions, events, and mechanisms that initiate wheel damage, and to identify remedies. The WDPRC’s findings are based on a range of activities, including inspections, controlled condition tests, data recorded during revenue service operations, and computer modeling results. The primary defects are:

• Slid flats and spalling: A wheel sliding on the rail creates enough heat to produce a metallurgical transformation and eventually to produce a spall.

• Fatigue and shelling: Repeated cycling of stresses causes cracks to form and eventually produce a shell.

The WDPRC determined that nearly half of the 700,000 wheelsets changed out in 2006 were due to tread damage-related causes (Why Made Codes 61, 65, 67, 75, and 78).

The WDPRC used data from various sources to determine root causes. Sources included inspections of damaged and undamaged wheelsets from good and bad actor cars; controlled condition testing of air brake valves, brake shoe forces and drag brake thermal testing; analysis of data from Wheel Impact Load Detectors (WILD) and wayside wheel temperature detectors; and computer simulation of wheel sliding and wheel fatigue.

Analysis of 163 wheelsets (with Why Made Codes 11, 61, 64, and 65) were inspected. Etchant was applied, radial runout was recorded, and the type of damage was tied to the type of car and service. Analysis indicated that shelling was the primary defect on coal cars, a mix of spalling and shelling (primarily spalling) on non-coal cars, and thermal mechanical shelling on intermodal cars.

Movement of cars with handbrakes applied was shown to be the primary cause of wheel spalling. Previous analyses have shown that cars with truck mounted brakes have more tread damage to the wheels on the “B” end. The WDPRC analysis further reinforced this, finding a 95% to 5% split for a group of 294 tank cars.

NUCARS® simulations of cars traversing rough track that excited suspension bounce resonance determined that empty cars (especially those with malfunctioning E/L devices) can slide wheels under heavy braking in low wheel/rail COF conditions, regardless of track geometry, and may be a minor source of spalling.

The WDPRC analysis found that most Rolling Contact Fatigue (RCF) damage occurs on the low rail wheel of the wheelset in the lead position of the truck on loaded cars during curving. These findings were further supported by wheelset inspections, revenue service instrumented wheelset data, WILD data and NUCARS modeling. Analysis of data from instrumented wheelsets on a loaded coal car through 1,500 miles in revenue service indicated some level of RCF was likely to occur on curves of 4 degrees or greater, and in instances when the trains were operated below the curve balance speed.

Data from a wheel temperature detector installed near the bottom of a hill, which analyzed more than 600,000 wheelsets on 1,575 trains, indicated that 76% of the descending cars with a wheel temperature greater than 500 degrees F had only a single wheel above this level. While the wheels in these cars were generally at higher temperatures than the wheels of other cars in the train, there were large temperature differences between individual wheel locations. Repeated hot wheel behavior was found on 37% of the descending cars with hot wheels, and at 20% of individual hot wheel locations.

The cause of hot wheel behavior within cars and between cars is difficult to identify, Cummings said. One car was found with a handbrake applied; no cause was found for 14 other cars that were inspected. A detailed inspection/teardown and brake tests indicated that the selection of bad and good actor cars based on wheel temperatures correlated well with wheelset replacements. “Bad actors had twice as many replacements,” Cummings said.

The WDPRC recommends increased adherence to handbrake release policies to reduce wheel spalling. Operators should minimize the use of train brakes and maximize the use of dynamic braking, especially in regions with heavy grades, to reduce average wheel temperatures. The WDPRC also recommends examining the effects of rail profiles, superelevation and the coefficient of friction on the development of RCF. It recommends the use of trucks with high warp resistance and low axle steering resistance to reduce wheel/rail tangential forces during curving.

Bob Tuzik is Publisher and Editor-in-Chief of Interface Journal.

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