Wayside TORL basics, benefits

	Figure 1. Forces acting on a wheel set and rails on a curve.

	Figure 2. Typical wear produced on two rails in a curve.

	Figure 3. Type of damage produced on the high rail of a curve.

	Figure 4. Lubrication effects on spike stress.

For nearly a century, it was believed that the top of rail had to be kept clean and dry for optimum train operation. This approach provides good traction and braking ability but simultaneously produces severe rail wear and track damage on curves.

The high rail wears on the gauge corner while the low rail experiences severe flattening and eventual corrugation of the top of the rail. On tangent track, unlubricated rail restricts or reduces the maximum safe speed due to a dynamic lateral instability, called hunting.

Rail lubrication of the gauge corner or gauge face was introduced in the middle of the last century. It helps to reduce high-rail gauge-face wear, but does not reduce the flattening and corrugation wear of the low rail or hunting tendencies on tangent track. Above all, it does not reduce damage to the track produced by large lateral forces that continue to be produced even with this lubrication. Cost of rail replacement and maintenance of way thus continues to be high.

With the significantly increased axle loads and train lengths used today, the rail wear and plastic flow problems become further exacerbated. Top-of-rail lubrication, when implemented with precision and intelligence, optimizes the wheel-rail contacts of the car wheels, reducing the above problems without compromising the performance of the locomotive wheels.

This article discusses the revolutionary new technology called TORL that improves performance, safety and profitability for the railroad industry.

In 1987-88¹, I introduced the concept of TORL when I was professor and director of the Railroad Engineering Laboratory at the Illinois Institute of Technology in Chicago. In the early 1990s, I guided my graduate student, Guowei Yu, to computer model and analyze the energy and wear for a train on tangent track with different ‘what if’ wheel rail top-of-rail and gauge-corner friction scenarios. The results were remarkable and were presented at the 1995 ASME-IEEE Joint Railroad Conference².

Even on tangent track, energy consumed and wear produced for a train with TORL (friction coefficient on top of rail of 0.3 compared with 0.5 dry) were much lower than for dry rail. For curved rail, the differences would be larger.

This required development of a special lubricant or friction modifier, which would lower the friction levels to around 0.3 and be environmentally clean. In 1990, Texaco Research joined in to help develop the lubricant³ and in 1993 Norfolk Southern joined in to test the concept of TORL on its trains⁴. The concept was validated in the first year, but it took several years to develop and improve the control and application systems.

In 1996-97 the U.S. Department of Energy and the Federal Railroad Administration jointly sponsored a project with the Transportation Technology Center⁵ to test the concept under very controlled conditions. The tests confirmed the earlier findings of Norfolk Southern and stated, “The concept of top-of-rail lubrication has demonstrated that it significantly reduces both the energy needed for trains, as well as the lateral wheel/rail loads on curved track.”

DOE and FRA further sponsored a test on CSX Transportation trains in the hills between Corbin, Ken., and Cartersville, Ga., in early 1998⁶. The conclusions were that with the use of TORL, “The average energy savings for a round trip … was determined to be 7.83 percent” and that the TORL “did not...negatively effect either train handling or speed control.... Braking performance was found to be safe.”

In 1997, TTCI tested three top-of-rail-lubrication systems⁷ and concluded, “TOR concept for lubrication can be applied on a continuous basis and not lead to a detrimental build up. Energy savings from a reduction in curve resistance in a closed loop environment were approximately 13 percent. Curving forces (lateral forces on the rails) were reduced five to 45 percent, depending on curvature and car type. … Train braking was not adversely affected. … Noise levels were reduced for trains under TOR lubrication conditions. …”

The TORL concept was further tested by several other railroads, including Union Pacific and CN. It should be pointed out that the above testing was conducted with on-board TOR lubrication systems. However, the TORL concept is valid for both on-board and wayside lubrication systems since the wheel-rail contact performance is improved regardless of the source of the lubricant.

Today, several companies produce TORL products for the benefit of the railroad industry. It is now fully accepted that TORL is the best way to lubricate rails. Over 70 percent of the railroad classification yards already use TORL to improve performance, economy and cleanliness and many railroads are taking advantage of TORL on main line track.

Optimizing lubrication

There are many factors that play a role in optimizing rail wheel lubrication. The first is the wheel set and rail geometry and wheel tread and flange profiles. In principle, the wheel set consists of two conical wheels with flanges mounted on a nearly rigid axle. For U.S. freight trains, the conicity of the wheels is 1 in 20. The wheel flange is designed to reduce the wheel’s tendency to climb over the rail when high lateral forces develop and to contain wheel flange and rail gauge wear.

The rail head profile is a combination of matched circles of different radii, which are selected to satisfy the complex requirements of limiting contact stress, delaying wheel climb over the rail and achieving stable train dynamics. The other factors are the wheel rail friction and creep.

Wheels rolling on rails need a certain friction (adhesion). This friction needs to be optimized with respect to its magnitude and direction. It needs to be large enough for good braking but not excessive to avoid energy wastage, development of large lateral forces (which damage the track) and excessive wear. It depends on the condition of the contacting surfaces of the rail and wheel, the track geometry and the rail wheel profiles.

There is a micro-slip (creep) that develops in all rolling contacts. Its magnitude depends on the geometry of the contacting surfaces, the torque experienced by the wheel such as in braking and the elasticity of the steel used.

There are three types of creep and three types of friction associated with each creep. These are: longitudinal (rolling direction), lateral (perpendicular to the rail) and spin (rotational).

Longitudinal friction is needed for car wheels in braking and for locomotive wheels in traction and braking. This is in fact the most important friction. Only a small amount of lateral friction is needed for curve negotiation. Large magnitudes of lateral friction are damaging for the track and are responsible for excessive rail wear and energy consumption. Spin creep and friction are small and of small consequence.

The magnitude of friction developed depends on the amount of creep and the surface condition (dry or lubricated, roughness, etc.). The geometry of the wheel and rail has been nearly optimized to date. The only aspect that can be altered is the surface lubricity to achieve optimization of the wheel-rail contacts. Well-designed TORL systems achieve this optimization for significant benefits to the m/w department.

The various forces acting on a wheel set on a curve are shown in Figure 1. The lateral creep that is inherently produced on a curve due to the angle of attack of the wheel with the rail⁸ produces the lateral forces C1L1 and C2L2. The result of lateral creep forces produced on the rail is shown on the set of rails in the lower portion of Figure 1. These forces become larger for heavily-loaded cars and as the rail curve becomes sharper.

NS Research and Test engineers have measured lateral forces exerted by a single axle as high as 20,000 pounds and larger on curves. These forces push the two rails outwards. On the high rail the wheel flange pushes the rail and on the low rail the wheel tread friction on top of the rail pushes it like a shear load.

Typical wear produced on the two rails is shown in Figure 2. The flattening of the head of the low rail due to severe wear eventually results in surface corrugation and the rail must be ground to correct its profile. It is easy to see that once TORL is applied, lubricant on top of the low rail will reduce this force dramatically. It reduces from 20,000 pounds to less than 10,000 pounds, thereby greatly reducing track damage and saving energy at the same time.

The large lateral forces also increase the track gauge, particularly when the train is traveling on the rails, sometimes to dangerous levels (>57 3/4-inches FRA limit). Static gauge may look acceptable but the dynamic gauge could be beyond limit.

Conventional gauge-face lubricators do not help much in reducing this lateral force and the damage produced by it. Figure 3 shows the kind of damage that is seen on the high rail. Most track supervisors have seen the rail spikes pulled up and in some extreme cases even sheared and broken off. The tie plates cut into the ties. The incidence of broken spikes was high enough that NS Research and Test engineers conducted a research project on this subject. They instrumented a number of spikes and measured the stresses in the spikes. Results are shown in Figure 4. As can be seen, there was a dramatic reduction in stress in the spikes with the use of TORL.

The damages discussed above are due to the excessive lateral forces on the rail and they can all be reduced significantly by using TORL or, better still, by using TORL plus gauge-face lubrication.

A special lubricant or friction modifier and a precision application method are needed for TORL. The lubricant should reduce the friction coefficient on top of the rail for car wheels to levels of approximately 0.3 with a thin film application. Thicker films of the lubricant should be able to lower the friction coefficient further. It should flow smoothly in controlled quantities in winter or summer (-30 degrees to 165 degrees F). It needs to be environmentally clean. It should not leave a residue on the rail or dry and cake or build up.

The method of application should be such that the lubricant can be applied to the top of the rail and gauge face in different film thickness and not contaminate the track. Only very small quantities of the lubricant should be applied to where they are needed, thereby making it economical for the railroad and producing little wastage.

The lubricant should not be applied to locomotive wheels and the controls should be such that it can be applied at different rates in opposite directions (important for application on long hill grades and entry of curves). Ideally, the method of application should be such that one machine can lubricate both top of rail and gauge corner and be placed in the middle of a curve to maximize the range of coverage.

In summary, TORL systems can achieve many goals and provide benefits for the m/w department and they are now available to railroads to install on their main line tracks. Gauge- face applicators simply do not provide these benefits.

References

1. Witte, Arnold, Manager, Lubricants Research, Texaco Laboratory, Port Arthur, Texas. Dr. Kumar gave a Colloquium Lecture in 1988.

2. Kumar, S.; Yu, Guowei and Witte, Arnold C., “Wheel-Rail Resistance and Energy Consumption Analysis of Cars on Tangent Track with Different Lubrication Strategies,” ASME-IEEE Joint Railroad Conference, Spring Meeting, Baltimore, Md., April 1995.

3. Kumar, S.; Witte, A.; McDuff, P. J.; and McInerney, D. G., “Development of a Laboratory Test for Rail Lubricants,” Annual Meeting, Society of Tribologists and Lubrication Engineers, Philadelphia, May 1992.

4. Blank, R. W., Ward, T.W., Keegan, S., and Alran, M. G., “Field Evaluation of Track Lubricants and Application Theory Developed by Tranergy, Inc., and Texaco.” Test Report of Norfolk Southern Research and Tests Laboratory, Alexandria, Va., December 22, 1993.

5. Reiff, Richard P., Gage, Scott and Kumar, Sudhir, “Top of Rail Lubrication Energy Tests.” DOE/FRA/ORD-98-01, February 1998 Final Report.

6. Davis, Kenneth, Strikland, Wayne, and Sherrock, Eric, “Evaluation of a Top of Rail Lubrication System.” DOT/FRA/ORD-99/13, August 1999 Final Report.

7. Reiff, Richard and Gage, Scott, “Evaluation of Three Top of Rail Lubrication Systems.” Report No. R-936, Transportation Technology Center, Inc., Dec. 1999.

8. Technical Note TC08.1 on Tranergy Website, http://www.tranergy.com.