Top Of Rail Friction Modifiers Research Articles

Studying the transfer mechanisms of water based top-of-rail products in a wheel/rail interaction

The railway industry uses top-of-rail products to control and manage the friction in the wheel/rail interface to help ensure efficient train operations and reduce wheel and rail damage. A product is typically applied from a wayside applicator that pumps a puddle onto the rail head where a passing wheel will pick it up and then transfer it down the track. The aim of this study was to study the transfer mechanisms of water-based top-of-rail friction modifiers (TOR-FMs) and how they are linked to the friction conditions in the wheel/rail interface. The transfer mechanisms were split into three parts: pick-up, carry-on and consumption. Pick-up looks at how the product transfers from the puddle on the rail to a wheel tread, whereas the carry-on mechanism relates to the product transfer back to the wheel. Consumption focuses on the removal rate of the product layer from the wheel or rail. A full-scale rig and twin disc machine were chosen to perform the tests because each rig could give different insights into understanding the product transfer mechanisms. Two products were tested of similar formulation. Results show that there are differences in the transfer and friction between the two products despite them being relatively similar. The test methods developed can clearly resolve differences between varying product types, which could be useful for product development studies or approvals work. The outcomes could also be used to develop a model of transfer/consumption.

Experimental evaluation of amount and repeated applications of top of rail friction modifiers on wear and adhesion

ABSTRACT A laboratory evaluation of top-of-rail friction modifiers (TORFM) is conducted to evaluate their effect on wear and adhesion, in settings that are closer to field conditions. The study, which uses the Virginia Tech-Federal Railroad Administration (VT-FRA) roller rig, extends past tribological studies with twin disks. Separate tests are performed in two phases. In Phase 1, the effect of TORFM volume, ranging from light to heavy applications (about 1 to 25 μm layer thickness), is evaluated on wheel wear. The normalized results indicate that light applications of TORFM yield the most favourable wear-to-cost ratio. In Phase 2, TORFM effectiveness duration is evaluated by applying the material in multiple cycles and monitoring the time-lapse for adhesion to recover to the unlubricated condition. Repeated applications of TORFM in moderate amounts (5 μm layer thickness) could lead to a stick-slip phenomenon that could not only diminish adhesion but also lead to surface markings on the rail.

The effect of third bodies on wear and friction at the wheel-rail interface

The friction forces between the wheel and rail depend on a number of variables including the third body layer at the wheel–rail interface, the wheel and rail profiles, and the train dynamics. The third body layer significantly influences the damage mechanisms at the wheel-rail interface, especially wear, rolling contact fatigue (RCF), corrugations and other surface defects that then require maintenance. The introduction of additional constituents at the wheel–rail interface in the form of an additive with anti-wear and anti-crack properties can reduce the wear and RCF. In general, such an additive also reduces the friction. However, it is important to avoid the friction coefficient between the wheel tread and the top of the rail falling below 0.3 because the result would be wheel slip and long braking distances. Measuring friction coefficients accurately is still a challenge, as most existing tribometers are unable to replicate the wheel-rail contact conditions, specifically the contact pressure and sliding speed. The present study used a newly designed handheld tribometer that is able to match the typical contact pressure. Results obtained with the handheld tribometer have been compared with values extracted from the traction-force measurement system of a locomotive. The tribometer field measurements have shown that by using a top-of-rail friction modifier (TOR-FM), both the wear and the friction coefficients can be reduced, but also that heavy TOR-FM films may cause unacceptably low friction. Comparing the results of field and laboratory tests confirms that weather and realistic third bodies present on the track have a significant effect on friction and wear.

New laboratory methodologies to analyse the top of rail friction modifier performance across different test scales

Test methodologies originally developed for greases have been adapted to be used for top of rail friction modifiers (TORFMs). This has included: a small-scale benchtop tribometer to measure the tackiness of different TORFMs, attaching an applicator bar to a section of rail and rolling a scaled-wheel through the TORFM applied to the rail head to analyse the effect of different variables on pick-up, and applying TORFM to a full-scale test facility to analyse the scaling effects and the effect of slip, load and speed on pick-up. These methods can be used to measure the relative performance of different TORFMs with respect to how much product is picked up by the wheel. The results have shown that the relative ranking of different TORFMs is the same across the three test scales. This shows that these small-scale test methods that are more suitable for inclusion in test standards could be used to reduce the need for the more time-consuming and expensive larger scale tests, as the relative performance is the same.

Life cycle cost analysis for the top-of-rail friction-modifier application: A case study from the Swedish iron ore line

The application of top-of-rail friction modifiers (TOR-FMs) is claimed by their manufacturers as a well-established technique for minimising the damages in the wheel–rail interface. There are various methods for applying friction modifiers at the wheel–rail interface, among which stationary wayside systems are recommended by TOR-FM manufacturers when a distance of a few kilometres is to be covered. An on-board system is recommended when an area of many kilometres has to be covered and focus is more on particular trains. Trafikverket in Sweden is considering the implementation of the TOR-FM technology on the iron ore line. Directly implementing such technology can be inappropriate and expensive, because the life cycle cost of a TOR-FM system has never been assessed for the conditions of the iron ore line. In the present study, the life cycle cost is calculated for wayside and on-board application systems, by taking inputs from the research performed on iron ore line. The present research has taken the iron ore line as a case study, but the results will be applicable to other infrastructure with similar conditions. The results have shown that the wayside equipment is economically unfeasible for the iron ore line. In this case, the life cycle cost increases by 4% when the friction modifier is applied on all curves with a radius smaller than 550 m and by 19% when the friction modifier is applied on all curves with a radius smaller than 850 m. The on-board system used in this study is shown to be economically feasible, as it has a significantly lower operation and maintenance cost than the wayside equipment. The reduction in the maintenance (grinding and rail replacement) cost when the cost of the friction modifier application is added is 27% when the friction modifier is applied on curves with a radius smaller than 550 m and 23% when the friction modifier is applied on curves with a radius smaller than 850 m.

Carry distance of top-of-rail friction modifiers

Rail issues such as corrugation, rolling contact fatigue, noise and wear have been increasing with the increase in railway traffic. The application of top-of-rail friction modifiers (TOR-FMs) is claimed by their manufacturers in the railway industry to be a well-established technique for resolving the above-mentioned issues. There are various methods for applying friction modifiers at the wheel–rail interface, among which stationary wayside systems are recommended by TOR-FM manufacturers when a distance of a few kilometres is to be covered. TOR-FM manufacturers also claim that by using wayside equipment, the TOR-FM can be spread over a minimum distance of 3 km, over which it maintains a coefficient of friction of µ = 0.35 ± 0.05. To determine the carry distance of TOR-FMs, some researchers use tribometers to measure the coefficients of friction. However, moisture and deposits from the environment and trains can alter the top-of-rail friction and give a misleading indication of the presence of a friction modifier. Therefore, the coefficient of friction itself is not a clear indicator of the presence of TOR-FMs. In the present study, cotton swabs dipped in a mixture of alcohol and ester were used to collect surface deposits (a third body) from both the wheel and rail at various distances from the point of application. Subsequently, the third body collected on the cotton swab was analysed using an energy dispersive X-ray analysis. The results have shown that the maximum carry distance of TOR-FMs on the top of the rail is limited to 70 m when using a TOR-FM from one manufacturer and to 450 m when using a TOR-FM from another manufacturer. The carry distance on the contact band of the wheel is limited to 100 m and 340 m. The friction modifier on the edges of the contact band was detected over a distance of up to 3 km; however, this will not minimise the damage or friction at the wheel–rail interface.

The effects of friction management materials on rail with pre existing rcf surface damage

Management of rolling contact fatigue (RCF) risk is a critical maintenance activity in railway operations. Practical means of RCF mitigation involve: 1) preventative and corrective grinding to remove RCF cracks; 2) management of wheel and rail profiles to minimize peak contact pressures; and 3) selection of appropriate rail metallurgy. In addition, reduction of traction forces by application of dry film Top of Rail friction modifiers (FM) has recently been shown to reduce crack growth and extend grinding intervals.Hydro-pressurisation and crack face lubrication are processes by which liquid materials (e.g., water), enter pre-existing RCF cracks and under wheel/rail contact pressure and cause accelerated crack growth, leading to spalling and shelling on rail and wheels. Thus, any liquid material added deliberately to the wheel/rail interface should be considered carefully in terms of the potential for aggravating RCF damage. This study compares the impact on hydro-pressurization and crack face lubrication of different types of materials designed for application to the top of rail using twin disc testing. One type of FM material is water-based, drying providing solid particles to the rail-wheel contact. Two other types are oil or oil-plus-water-based (hybrid material) that do not naturally dry and have been introduced more recently to the market. In addition, a commonly used gauge face lubricant (grease) was evaluated.

Effects of curve radius and rail profile on energy saving in heavy haul achieved by application of top of rail friction modifier

Energy saving achieved by application of top of rail (TOR) friction modifier (FM) in heavy haul are modeled, and the effects of curve radius and rail profile on the energy saving are discussed. A vehicle model for a C70 freight car running on the track of a heavy haul line was established. The coefficient of friction and Kalker coefficient were adjusted to simulate the creepage/force relationship when the TOR FM is applied to the wheel/rail interface. Friction work is used to represent the energy dissipation due to wheel/rail creepage. Energy saving achieved by applying TOR FM was calculated. The energy saving was studied under different operating conditions, and the effects of track curve radius and rail profile were studied. It is found that the curve radius of the track has significant influence on the energy saving. The energy saving was also found to behave differently on new and worn rails. The dramatic increase of lateral creepage on new rail when FM is applied and the decrease of the difference of wheel rolling radius when the rail profile changes from new to worn were found to be the main reasons that cause the difference.

Measurements of friction coefficients between rails lubricated with a friction modifier and the wheels of an IORE locomotive during real working conditions

The real friction coefficients between the rails and the wheels on a 360t and 10,800kW IORE locomotive were measured using the locomotive׳s in-built traction force measurement system. The locomotive consisted of two pair-connected locomotives had a CoCo+CoCo bogie configuration, and hauled a fully loaded set of 68 ore wagons (120t/wagon). The measurements were performed both on rails in a dry condition and on rails lubricated with a water-based top-of-rail (ToR) friction modifier on the Iron Ore Line between the cities of Kiruna and Narvik in Northern Sweden and Norway, respectively. Since full-scale measurements like these are costly, the friction coefficients were also measured at the same time and place using a conventional hand-operated tribometer, with and without the ToR friction modifier. The most important results are that the real friction coefficient is definitely not constant and is surprisingly low (0.10–0.25) when the ToR friction modifier is used, and that it is also significantly dependent on the amount of ToR friction modifier. A large amount will reduce the friction coefficient. Furthermore, it is concluded that the real friction coefficients are in general lower than the friction coefficients measured with the hand-operated tribometer. A final remark is thus that the use of a water-based ToR friction modifier can give excessively low friction, which can result in unacceptably long braking distances.

A predictive model of energy savings from top of rail friction control

In this paper the authors present a predictive model of train energy requirements due to the application of a top of rail friction modifier (TOR-FM) versus dry wheel/rail conditions. Using the VAMPIRE® Pro simulation package, train energy requirements are modeled for two sets of TOR-FM frictional conditions, one using full Kalker coefficients and the other by using a Kalker coefficient of 18%. Both scenarios use a top of rail saturated coefficient of friction of 0.35. Under both TOR-FM frictional conditions, train energy savings are shown for complete laps of the Transportation Technology Center Inc.’s (TTCI) Transit Test Track (TTT) loop, and also when isolating only the tangent section of the loop. However, the magnitude of energy savings varies greatly depending on the Kalker coefficient factor used, highlighting the need to model this relationship as accurately as possible. These simulation results are compared with data obtained from a field study, in which train energy savings of 5.3% (lap) and 7.8% (tangent) are shown due to the application of TOR-FM.

Managing rail profile

Managing the contact conditions between train wheels and the running rail is key to controlling the dynamic behaviour of railway rolling stock and preventing rail defect initiation and growth. This paper describes the rail profile management strategies deployed by Network Rail. The development of policies and standards is discussed, highlighting the reasons behind the selection of target rail profiles and friction management techniques. Practical implementation of the strategies is described, with consideration given to the challenges faced delivering rail profile management on the operational railway. Recent developments in rail friction management and reprofiling technology are presented, e.g. top of rail friction modifiers, rail milling and high productivity grinding. The costs and benefits of the new technologies are examined. The impact of these developments on the Network Rail’s approach to managing rail profile is discussed. Drawing conclusions from this analysis, a future vision of rail profile management on Network Rail infrastructure is presented.

The influence of precipitation and friction control agents on forces at the wheel/rail interface in heavy haul railways

This paper presents an analysis of the influence of materials that can be present in the so-called “third-body layer” at the wheel/rail interface on curving forces generated in heavy haul operating conditions. The third-body layer is the interfacial layer whose shear properties determine the bulk frictional characteristics that emerge in wheel/rail contact. It is often postulated that precipitation (rain) provides an effective form of lubrication at the wheel tread/rail head interface, reducing curving forces and corresponding wear. The postulate is explored through the analysis of lateral and vertical force data collected under a wide range of environmental conditions in full-scale revenue service. The effects of precipitation are rigorously explored and compared with the effects of top of rail friction modifiers, which are intentionally introduced into the third-body layer. This paper originated from the 2011 IHHA Conference.

Friction management on a Chinese heavy haul coal line

Shuohuang Railway (SHR) is one of the major coal carriers in China, with a total network length of 590 km running from Shenchi to Huanghua. Significant increases in annual operating tonnage have generated accelerated rail wear and rolling contact fatigue (RCF) growth problems for many sharper/lower radius curves. In order to address these rail problems, SHR is interested in the state-of-the-art total friction management (TFM) technology currently deployed by some North American heavy haul freight railroads and is evaluating the impact of TFM via a field trial at SHR’s Yuanping subdivision. This paper presents an evaluation of the effect of TFM, which includes both wayside gauge face lubrication and wayside application of a thin film top of rail friction modifier on control of lateral forces, rail wear and RCF.

The effects of top of rail friction modifier on wear and rolling contact fatigue: Full-scale rail–wheel test rig evaluation, analysis and modelling

The effect of thin film friction modifier (FM) technology on the development of rolling contact fatigue (RCF) and wear are evaluated on a full scale wheel–rail rig, and compared with modelling results of the contact conditions. Under dry conditions (no FM), test stand conditions are identified which reproducibly generate head checks as well as significant wear. With FM application head check development and surface cracks were eliminated. Wear was also greatly reduced by FM. Surface and subsurface plastic flow were about a factor of two lower with FM. Modelling of dynamic conditions confirm the peak pressures and creepages under test conditions. On a shakedown diagram the dry conditions are seen as providing normal pressures/tangential tractions in the ratcheting zone, whereas with FM peak pressures/tractions remain in the “safe” zone for RCF development.

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The real friction coefficients between the rails and the wheels on a 360 t and 10,800 kW IORE locomotive were measured using the locomotive׳s in-built traction force measurement system. The locomotive consisted of two pair-connected locomotives had a CoCo+CoCo bogie configuration, and hauled a fully loaded set of 68 ore wagons (120 t/wagon). The measurements were performed both on rails in a dry condition and on rails lubricated with a water-based top-of-rail (ToR) friction modifier on the Iron Ore Line between the cities of Kiruna and Narvik in Northern Sweden and Norway, respectively. Since full-scale measurements like these are costly, the friction coefficients were also measured at the same time and place using a conventional hand-operated tribometer, with and without the ToR friction modifier. The most important results are that the real friction coefficient is definitely not constant and is surprisingly low (0.10–0.25) when the ToR friction modifier is used, and that it is also significantly dependent on the amount of ToR friction modifier. A large amount will reduce the friction coefficient. Furthermore, it is concluded that the real friction coefficients are in general lower than the friction coefficients measured with the hand-operated tribometer. A final remark is thus that the use of a water-based ToR friction modifier can give excessively low friction, which can result in unacceptably long braking distances.