This article discusses that freight carriers have their own sets of issues. Faced with the same economic pressures as long-haul trucks on the nation’s highways, freight trains are getting heavier and heavier, increasing axle loads and the forces that bear on the tracks. The challenges of minimizing wear and energy consumption are becoming more demanding for railroads. Managing friction between the wheel and the rail is an increasingly tough job, but a critical one for avoiding a host of performance problems and high costs. Friction modifiers are coatings that provide a controlled coefficient of friction at the contact point between the wheel tread and the top of the rail. The key point is control, which makes it possible to achieve a specific friction range. This is the main difference between friction modifiers and ordinary grease. CSX Corp. has begun tests of the two systems in cooperation with the Transportation Technology Center. The center has installed instrumentation in a section of track, and CSX has bought five TracGlide systems and five locomotive-mounted Lubriquip systems that will apply Kelsan’s friction modifier.
Anyone who has ridden a transit system knows the ear-splitting screech of trains as they follow tight curves in tunnels or in the residential neighborhoods that they serve. Freight carriers have their own sets of issues. Faced with the same economic pressures as long-haul trucks on the nation’s highways, freight trains are getting heavier and heavier, increasing axle loads and the forces that bear on the tracks.
The challenges of minimizing wear and energy consumption are becoming more demanding for railroads. Managing friction between the wheel and the rail is an increasingly tough job, but a critical one for avoiding a host of performance problems and high costs.
A major source of friction lies in the way trains handle curves.
A front-wheel-drive car has a constant-velocity joint; a rear-drive car has a differential. In either case, the mechanism allows the outer wheel to travel farther than the inner wheel so the car doesn’t skid when it rounds a curve.
Trains have nothing like that. Their wheels are slightly tapered so locomotives and cars bank on curves. That way, inner wheels will ride on a smaller diameter than the outer ones. Although this helps, friction still presents considerable problems of noise and wear.
One long-standing solution to controlling friction is to lubricate the interface between the flange—the protruding edge of the wheel—and the inside face of the rail. Suppliers of lubricant systems claim that application to the side of the track helps to increase the life of the flange and the rail, reduce noise, and increase fuel economy. These systems are designed to apply lubricants to the side of the rail only, in a precise manner—and away from the top of the rail, where they could introduce traction and braking problems.
Over the last several years, some railroads have begun to focus on the top of the rail, where a relatively new family of materials known as friction modifiers can be applied. Suppliers of friction modifiers take pains to stress that these materials are not lubricants. They differ from traditional lubricants primarily in the controlled coefficient of friction that they provide on the railhead or top surface of the rail.
Friction modifiers have been around in the railroad industry for about a decade. Originally attracting the attention of transit systems trying to reduce noise, friction modifiers have been implemented commercially by some passenger carriers, and are also being evaluated by some freight railroads for reduction in lateral loads and energy consumption.
Research groups, including the Transportation Technology Center Inc., a unit of the Association of American Railroads in Pueblo, Colo., and the Federal Railroad Administration, have also evaluated friction modifiers.
Friction modifiers are coatings that provide a controlled coefficient of friction at the contact point between the wheel tread and the top of the rail. The key point is control, which makes it possible to achieve a specific friction range. This is the main difference between friction modifiers and ordinary grease.
Friction modifiers are designed to reach a plateau of friction. Grease doesn’t hit a plateau.
According to Richard Reiff, principal investigator of the Transportation Technology Center, “There is a breakaway point that, as long as the thickness of the friction modifier is at a certain range, it will maintain the target range of friction.”
Reiff said that the railroad industry is still working out its definition of friction modifiers as distinct from conventional lubricants. Right now, he said, the consensus is that friction modifiers result in a target friction level.
Kelsan Technologies Corp., a supplier of friction modifiers in North Vancouver, British Columbia, aims for a coefficient of friction for the top of the rail in a range between 0.3 and 0.35.
Another supplier of a friction modifier, Friction Management Services LLC of West Chicago, 111., says that its friction modifier acts like a lubricant under rolling conditions and like a friction agent during braking. Eric Wolf, president of Friction Management and chairman of the ASME Rail Division, said the company’s TracGlide product has a coefficient of friction of 0.15 under normal rolling conditions and 0.5 under braking conditions or under traction from a locomotive.
Don Eadie, vice president of research and development at Kelsan Technologies, defines a lubricant as a material that makes the coefficient of friction as low as possible. Friction modifiers, by contrast, have two attributes, he said. One is an “intermediate” coefficient of friction. For application on the top of the rail, it's important that friction is not too low, because a slippery surface will interfere with traction and braking, he said.
The second attribute is something Eadie calls positive friction. Most materials in nature have negative friction, in which the coefficient of friction is reduced with increasing sliding velocity, or creep. On the railroad, steel creeps on steel, especially when a train follows a curve.
“Negative friction is the underlying cause of a number of problems—particularly wheel squeal, the screeching noise as the train rounds a corner,” Eadie said.
Eadie said that most people assume that wheel squeal originates from contact between the wheel flange and the side of the rail. In fact, most of the noise results from oscillation between the tread of the wheel and the top of the rail, which is initiated because of the negative friction, together with lateral creep forces. The web of the wheel amplifies the noise arising from the frictional vibration.
Negative friction also causes a phenomenon called short pitch corrugation—little areas of wear on the track that appear in short intervals. This type of wear is common in transit systems and requires railroads to periodically grind rails to reduce noise and prevent further deterioration, he said.
According to Eadie, friction modifiers change the frictional characteristics of the thin layer between the wheel and rail from negative to positive, and it is this change that allows the elimination of wheel squeal.
The Transportation Technology Center evaluated liquid friction modifiers and conventional lubricants in various combinations of top-of-rail and side-of-rail applications. A report, issued in July 2000, found that friction modifiers applied to the top of rail did indeed reduce lateral loads and energy consumption. The report also noted that the best results came from a combination of top-of-rail and gauge-face applications.
In its trials, the center looked at top-of-rail friction modifiers from Kelsan Technologies and Friction Management. The next step will be to monitor the systems in service.
Reiff said the tests also showed that a friction modifier applied too liberally to the rail acts more like a conventional lubricant. He expressed concern that buildup from succeeding trains could result in slippage.
Eadie of Kelsan Technologies said that the observed increase in lubrication was likely due to the moisture content in the spray. The more heavily the friction modifier is applied, the longer it will take to dry, and the water base of the spray will act as a lubricant, he explained. Once it is dry, the modifier will not drop below a coefficient of friction of 0.3, even with buildup on the rail, he said.
Freight railroads are hauling heavier burdens, and as trains get heavier, they have more propensity to derail.
Eadie said Kelsan Technologies’ friction control system intends to have the material build up over time.
Friction Management, which has developed an onboard application system described in an article last February, uses a modifier designed to dissipate as the train passes.
Kelsan Technologies originally developed its friction modifier as a solid stick in the early 1990s. One of its first customers was the Vancouver Sky Train, a light-rail transit system. In the solid version, the friction modifier is in a polymer matrix that is applied mechanically to the wheel. Eadie said that stick friction modifiers are used in a half-dozen transit systems today.
In 1996, the company formulated a water-based liquid version and since then has teamed with outside equipment vendors to develop application systems. To date, four types of systems have been developed or are under development—two are mounted on the train itself and two are applied at the rail.
The company is working with Lubriquip, based in Cleveland, to develop an on-board application system for locomotives.
Sumitomo of Japan has developed an on-board system for transits, in partnership with Eidan, the main Tokyo subway operator. That system is in operation on a limited basis on the Tokyo subway, where it is undergoing evaluation.
Portée Rail Products, based in Pittsburgh, has developed and patented a stationary trackside application system, and is completing the design for a second system, which can be mounted on a hi-rail vehicle, a pickup truck equipped to ride on tracks. The Portée Rail track-side applicator for the top of the rail evolved from conventional grease wayside systems.
The trackside unit applies the friction modifier as a liquid bead, whereas the on-board systems and hi-rail system will use an atomizing spray of the liquid.
Portée Rail’s stationary system is placed alongside the track ahead of the curve. The system deposits a bead of friction modifier, which product manager Ward Powell described as having the consistency of paint. The bead gets carried into a thin film along the top of the rail by the passing train, drying through the body of the curve almost immediately, he said.
Kelsan and Portée Rail recommend that the patented friction modifier be deposited on both rails in a curve.
The trackside system is equipped with controls that time and regulate the quantity of friction modifier dispensed. “We look at a particular site, how sharp the curve is, how long, how worn the railhead is, and dial it up or down to accomplish what we want to do,” Powell said.
Powell said that Portée Rail has sold somewhere between 25 and 35 units, primarily to transit systems to solve noise problems. “Noise is easy to demonstrate,” he said. “If you can go out there and put something on the rails and quiet the curve, the difference is immediate.”
Richard Jarosinski, division president and general manager of Portée Rail Products, said the hi-rail application system will be “another arrow in the quiver” available to railroads for depositing friction modifier on the top of the rail. To date, the company has sold one system to a freight rail operator in Canada. A Class 1 railroad in North America is also testing a unit, he said.
The reasons for investigating friction modifiers vary with the operational circumstances of the railroad. Freight railroads are concerned with lateral loads, particularly as trains haul increasingly heavier burdens, Powell said. Lateral loads cause wear on the top and side of the rail, and on the wheels, treads, and flanges, he said.
There is another issue, too: As trains get heavier, they have an increased propensity to derail, Powell said. Railroads “are interested in what they can do with friction management and lubrication to limit those situations,” he added. Portée is entering into a project with its railroad customers to put instruments at curves to measure lateral force reductions, he said. Not least, there is also the issue of fuel savings.
For transit systems, the main attraction may be in noise abatement. James Dwyer, director of technical support for the Port Authority of Allegheny County in Pittsburgh, was faced with a severe noise problem with the opening of its light-rail system in the mid-1980s, which he described in a presentation at the 2000 American Public Transit Association Conference in St. Louis.
One of the problem areas in the line was the Gateway Loop, which consisted of two curves making a complete 180-degree turn. The curves have a radius of 82 feet on a 2 percent grade; the total length of the loop is 390 feet. The stick and slip of the wheels as they rounded the sharp curve there and at other problem spots resulted in significant frictional noise.
Reducing Neighborhood Noise
Faced with complaints from surrounding residential neighborhoods, the Port Authority tried various solutions—traditional wayside lubricators, sound-absorbing blankets, and spraying with water—but met with only limited success, Dwyer said. Then he heard about a friction modifier used by Southern Pacific Railroad to solve a noise problem on a curve in California, and decided to give it a try.
The Port Authority first applied Kelsan Technologies’ friction modifier with a hand applicator each day, after the last train passed, to give the spray time to dry. That took care of the noise, but applying the material was labor-intensive, Dwyer wrote. It was later that the agency contacted Portée for an automated trackside system, which was installed first at the Gateway curve.
The trackside system can be powered by a variety of sources. The Port Authority opted for a solar panel. The installation cost about $7,500 and the cost of operation averaged $36.46 a day.
Friction Management, a joint venture of Timken Co. and Tranergy Corp., markets a competing system that uses a glycol-based material originally developed by Texaco Lubricants. An on-board, computer-controlled system sprays it onto the track from nozzles located behind the last locomotive axle.
According to Wolf, the company’s president, under normal rolling conditions, the coefficient of friction is low, about 0.15. As shear forces increase during braking or traction, the molecules of the polymer stretch and the coefficient of friction can triple in value.
According to Friction Management’s Web site, several years of tests indicate that the TracGlide system can offer trains fuel savings of as much as 42 percent. The company says the system lets trains add two or three miles an hour to their speed, even on hills.
Wolf estimated that almost two dozen TracGlide systems have been sold to railroads.
The company is marketing them as productivity enhancers for the freight haulers. It says that railroads using the friction modifier have the option of running faster, carrying more weight, or extending the length of their trains.
Kelsan Technologies is also marketing to freight railroads, but has less penetration in that market than it does among transit system operators.
CSX Corp. has begun tests of the two systems in cooperation with the Transportation Technology Center. The center has installed instrumentation in a section of track, and CSX has bought five TracGlide systems and five locomotive-mounted Lubriquip systems that will apply Kelsan’s friction modifier.
According to Ken Davis, manager of test and lab services at CSX’s research laboratory in Waycross, Ga., tests will run in stages. The first will collect benchmark data on untreated track. The next will monitor the performance, particularly the effect on lateral forces, of the Lubriquip/Kelsan system mounted on five engines.
A separate series of trials will gather similar data for the TracGlide system on five other engines. Davis said that CSX also plans to collect information on the effects of applying grease to the top of the rails.
Reiff said the Transportation Technology Center has received funding for the tests from the Federal Railroad Administration.
CSX and other freight carriers will want to know if they can optimize their rails and if doing so will pay off in cash.
The primary value for the transit companies is not always as easily measured. As Dwyer at the Allegheny County Port Authority wrote: “It is difficult to value the reduction of noise in dollar terms.”
But then, the agency wasn’t trying to improve its bottom line. The authority was looking for something else, and Dwyer said he may have found it. He read it as a sign of rising good will when complaints dropped off.