Improved profiles need special grinding: experts in wheel/rail interaction are custom-designing rail profiles for railroads based on the specific complexities of the particular stretch of track

Railway Track and Structures, Dec, 2004 by Peter Sroba, Eric Magel, Fred Prahl

Rail systems ranging from mass transit to high-speed passenger to heavy-haul are grinding to different rail profiles and are using different grinding approaches than they did 10 years ago. This is because they have engaged experts in the wheel/rail interaction to design rail profiles based on their system-specific characteristics. These new designs will usually consider the variety and complexity of different rolling stock, wheel profiles, track curvature, and the extent of gauge-face lubrication and top-of-rail friction management (if any).

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In many cases, however, a railroad may be using profiles that were designed years ago for the conditions that existed at that time. These profiles are unlikely to be applicable to present-day premium rail and their implementation also may not be compatible with today's available track time or the production capability of modern grinding equipment.

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For example, a property may have been previously grinding the rail to profiles that managed surface fatigue on softer rails, while the new profiles have been designed for current premium rail standards. Thousands of dollars may have been wasted in the past on grinding their premium rails to maintain profiles that failed to minimize surface fatigue and promoted hollowing of the wheels.

Rail profiles developed by the National Research Council of Canada's Centre for Surface Transportation Technology have been applied by most North American heavy-haul systems since the late 1980s.

But, over the past 15 years or so, there have been tremendous changes in the railway industry, both on the track side and the vehicle side. These changes include rails with improved hardness and metallurgy, track with better gauge restraint and vehicles with improved suspension and steering capability.

Despite these developments, the profiles developed 15 years ago continue to be used on many railways.

Changes to rail and wheel systems have caused engineers to re-think the criteria for designing and implementing an optimized wheel/rail interface. In recent years, CSTT has been commissioned to analyze a number of rail systems using the older profile designs and has found that outdated profiles and grinding practices are contributing to systemic over-grinding of modern rails.

Also, when CSTT investigated the wheel/rail system on these railroads, it found that the continuous maintenance of narrow and central running bands on the rail with sharp rail head radii (of six to eight inches) is promoting wheel hollowing, and, in some cases, the development of a geometrical stress raiser on the tread of some wheels (Figure 1).

Hollow wheels are associated with hunting, poor curving and excess fuel consumption, while the GSR contributes to wheel shelling. The rail templates designed in the 1980s were conceived to deal with a very-different railway environment; in particular, the softer rail metallurgy in use at that time, which wore and plastically flowed very readily. So, given today's harder rail and wheel steels, how can a railroad's track engineering department eliminate the significant over-grinding, and how do they explain to senior management the wasted metal and the cost of the previous grinding programs?

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Over the past 10 years, CSTT has been designing and implementing new rail profiles that are tailor-made for today's railway environment. These new shapes have been found to provide considerable savings in grinding implementation costs.

A typical example is the CSTT design of rail profiles for a railway that had been using the 1989 designs for several years. (1) An example of the reduced metal removal associated with the new NRC templates is shown in Figure 2. The latest CSTT designs are more conformal, and usually incorporate a 10-inch railhead radius that creates a higher tolerance to plastic flow in the harder steels. Instead of eight profiles, as used in the past, more-recent families of rail profiles often utilize only four to five templates.

Often, the high-rail profiles include separate templates for sharp and mild curves, and sometimes two different tangent rail profiles are applied. These modern high-rail designs generally produce more conformal contact with the wheel flange-root to improve truck curving performance and reduce wheel-flange wear.

The two tangent templates produce either a central or field-biased running band and are applied to approximately even lengths of track. The goal of the two different running bands is to promote uniform wear across the entire running surface of all wheels and reduce wheel hollowing.

Sometimes the field-biased tangent profile is also applied on the low rail of curves, though often a separate profile is required. Recent low-rail designs have been generated that reduce contact stress, spread wheel wear, and take advantage of the increasing hardness of modern rail steels. Improved rail profiles must have, as their goal, the overall health of both wheel and rail.

Once a railroad has the new designs, the implementation of these profiles must be planned carefully or else there will be a significant wastage of grinding and rail life. A railroad and/or a grinding contractor must be able to gradually transition to the new profiles by moving contact bands to the locations specified by the profiles. If the new rail profile is applied immediately, rather than gradually, as intended, the high metal removal often required can result in an inappropriate allocation of the available grinding effort.