Interface - The Journal of Wheel/Rail Interaction

WHEEL SHELLING

Implementing an Anti-Shelling Wheel Profile
By Rob Caldwell • October, 2005

Wheel Shelling has presented serious problems on Canadian railroads in recent years, particularly in winter months. Tread shelling on wheels on Quebec Cartier Mining (QCM) railway's heavy-haul fleet, for example, reached condemnable limits within one year of use, during the early 1990s. In some cases, this “infant mortality” occurred within as little as 25,000 miles. Once they reached the condemning limit, the wheels had to be removed from service and re-trued to correct the tread damage. The depth of cut required to correct this damage was often large (typically 6/16-inch), which further reduced wheel life.

QCM contracted the Centre for Surface Transportation Technology (CSTT), a technology center of the National Research Council of Canada (NRC), to design a custom wheel profile to combat this problem. The design, known as the QCM-Heumann profile, was implemented during 1995. During the 1995-96 winter season, QCM found that incidences of wheel shelling were reduced by 60% in head-to-head testing with their standard profile, the AAR1B.

Compared to the AAR1B, the QCM-Heumann profile provides more metal in the flange root, which leads to greater rolling radius difference (ΔR) for any given lateral offset (see Figure 1). This in turn generates a stronger steering moment on the lead axle of the trucks. A stronger steering moment can reduce the angle of attack on the lead axle in mild curves, which reduces the lateral creep forces acting between the wheel and rail. Reducing these creep forces is one way to reduce shelling.

As Figure 1 also indicates, the tread is rolled off with a reversed radius on the field side of the wheel. This feature lengthens the time for the occurrence of tread hollowing and the development of a false flange. A false flange can cause tread shelling through the very high contact stresses that occur when it contacts the low rail. False flange contact can also significantly reduce ΔR for the wheelset, resulting in elevated lateral creep forces acting at the treads of both wheels.

The 1:20 tread slope was maintained on the QCM-Heumann wheel to minimize the risk of hunting. QCM also installed rubberized bearing adapter pads on their ore cars to take advantage of the stronger steering moments, but did not install frame-bracing. This meant that the trucks would be more flexible in yaw and shear than a standard three-piece truck, with higher potential for empty cars to hunt. Hunting ultimately did not occur, however, due in part to the maximum operating speed of 40 mph.

While QCM reaped the benefits of its new wheel profile, wheel shelling had become an epidemic on other Canadian railroads. The seasonal wheel shelling problem, at its worst during the winter months, forced one railroad to raise its Wheel Impact Load Detector thresholds so that its wheel shops were not flooded with shelled wheels that were removed from service because they had exceeded WILD limits. In very cold weather, train speeds were reduced to lower the risk of rail breaks due to high impact forces from shelled wheels.

PAGE 1 OF 4 | NEXT PAGE >