Wheel/rail adhesion — the overriding influence of water

Water from the atmosphere affects all rails, depositing in quantities far greater than the minute amounts of oily contamination normally present. Laboratory experiments are described which show how water reduces friction between rail and tyre steel surfaces. Depending on the amount of oily contamination the friction coefficient is reduced to a value between 0.3 (no oil present) and the friction which is characteristic of an excess of the oil. Lower friction on oil-free surfaces is observed using laboratory machines which involve continuous rolling; water mixes with wear debris or surface rust to form a lubricating paste and friction coefficients as low as 0.05 result. The lowest friction occurs when the ratio of water to debris is small and a viscous (non-Newtonian) paste is formed which is observed on the laboratory rigs for a few seconds whenever wetted surfaces are on the point of drying completely. Trains similarly encounter low adhesion in slightly wet conditions, most noticeably on little used lines where a substantial coverage of debris particles is present on the wear band.     

起重机轨道闪光焊焊接技术

由于起重机轨道通常采用高碳中锰的U71Mn钢轧制而成,手工焊接性能较差,焊缝接头容易产生裂纹、夹渣等缺陷,故对轨道传统手工焊接工艺改革非常必要.文中引进高铁常用的轨道焊接技术闪光焊,其特点是焊接速度快,接头质量稳定,是一种成熟的轨道焊接形式.研究闪光焊运用于起重机轨道焊接,并通过多条轨道焊接试验,形成详细的闪光焊轨道焊...     

不同介质作用下轮轨粘着特性研究

利用MMS-2A型微机控制摩擦磨损试验机开展介质工况下的轮轨粘着特性试验,研究干态、水、油、砂、树叶等介质对轮轨粘着系数的影响。结果表明:不同介质工况下的轮轨粘着系数明显不同,干态下轮轨粘着系数最大,油水介质下粘着系数最小,加水和油将显著降低轮轨粘着系数,且油介质下的轮轨粘着系数明显小于水介质下的粘着系数;随环境湿度增加轮轨粘着系数明显降低,当湿度从20%增加到100%时,粘着系数将降低约17%;干态和油水介质下,随轴重增加轮轨粘着系数呈明显增加趋势;轮轨接触面间加入新鲜树叶后粘着系数将降低,树叶与水共同作用下的轮轨粘着系数最小;通过撒砂能提高水油介质工况下的轮轨粘着系数,但会加剧轮轨试样表面损伤,导致剥落损伤出现。     

Evaluation of slant crack propagation under RCF in railway rail

Crack propagation due to rolling contact fatigue (RCF) could be a significant potential challenge to the integrity of railway rails because it may lead to a serious disaster. Fatigue cracks subjected to cyclic rolling contact force experience a complex non-proportional mixed loading and complicated boundary condition. In the present research, complex crack opening/closure/sliding/locked behaviors as the cyclic contact loading movement is analyzed considering liquid lubrication action on rail surfaces as well as crack faces. Based on a series of FE analyses, the calculations of the effective SIF ranges for RCF cracks under certain contact loading and boundary conditions are proposed in the form of polynomial functions which will be appropriately used to predict RCF crack growth rate.     

Investigation of the influence of rail pad stiffness on rail corrugation on a transit system

This paper presents a study on the influence of rail pad stiffness on rail corrugation in an underground line. The paper includes a theoretical analysis justifying the rationale behind the modification of the pad stiffness to reduce corrugation levels, as well as a set of corrugation measurement results took on a test curve section during a period 19 months. The aim of the work is to demonstrate clearly that this treatment, studied by other authors like Ilias [H. Ilias, The influence of railpad stiffness on wheelset/track interaction and corrugation growth, J. Sound Vib. 227 (1999) 935-948], works on a metro system. In this study, the conventional rail pads on a test curve were substituted by softer pads. In order to examine the influence of new rail pads on corrugation, the rail profile was measured before and after the track modifications, during the same period of time. For both situations, wavelengths and amplitudes were analyzed and compared. It was found that soft pads reduce corrugation growth and eliminate one of the wavelengths developed when using stiff pads. The theoretical results were obtained from a model developed by Tassilly and Vincent [E. Tassilly, N. Vincent, Rail corrugations: analytical model and field tests, Wear 144 (1991), 153-161; E. Tassilly, N. Vincent, A linear model for corrugation of rails, J. Sound Vib. 150 (1991) 25-45]. This linear model for the corrugation of rails was used to predict the frequency bands in which corrugations are likely to appear. The track and the wheelset dynamics were studied both experimentally and theoretically. Quasi-static wheel/rail forces and creepages have been obtained with a multibody model of a metro unit. The methodology followed to compare the theoretical and experimental results is based on the work carried out by Grassie and Elkins [S.L. Grassie, J.A. Elkins, Rail corrugation on north american transit systems, Vehicle System Dyn. 28 (1998) 5-17]. The correlation between simulated and experimentally measured corrugation wavelengths appearing in the inner rails of curves is analyzed, and the corrugation mechanism is explained.     

Decarburisation and rolling contact fatigue of a rail steel

Decarburisation is present on all new rails and unless ground off, will be on the running surface once installed. This paper presents a detailed investigation into the effect of decarburisation of rolling contact fatigue and wear. Twin disc testing has been used to study the phenomenon under water-lubricated rolling/sliding contact. Rail discs have been cut from grade 220 rail and heat-treated to give samples with varying depths of decarburisation. It was found that as the depth of decarburisation increased the wear rate of the rail disc increased while that of the wheel disc decreased. The effect of decarburisation on rolling contact fatigue was to increase the crack growth rate of samples with increasing depth. Cracks under rolling contact fatigue were propagated by contact stresses via the fluid pressure mechanism and influenced by microstructure. The effect of decarburisation was predicted to have little effect on rail/wheel contact when scaled from the laboratory tests using the depth of maximum shear stress.     

油污染工况下轮轨黏着特性研究

利用JD-1轮轨模拟试验机研究新污油、油水混合物以及油水砂混合物介质对轮轨黏着系数的影响.结果表明:在污油、油水以及油水砂工况下,轮轨黏着系数均远远小于干态工况下的轮轨黏着系数；对比3种介质,油水介质工况下轮轨黏着系数最小,约为0.03,污油介质工况下轮轨黏着系数略大,约为0.05,油水砂介质工况下轮轨黏着系数最大,约为0.08.     

Magnetic tests of hardness and structure of rail steel

The correlation between the coercive force on the one side, and the structure and hardness of the rail steel on the other has been studied. A technique for testing rails quenched in oil based on measurements of the coercive force has been developed. The technique can be used in acceptance tests of rails by stages of main rail-roads.     

Process design for the hot forging of asymmetric rail to symmetric rail

The process design of hot forging, asymmetric to symmetric rib-web shaped steel, which is used for the turnout of express rails has been studied. Owing to the great difference in shape between the initial billet and the final forged product, it is impossible to hot forge the rail in a single stage operation. The numerical simulation for hot forging of asymmetric shape to symmetric shape was carried out by using commercial FEM code, DEFORMTM-2D. For comparison with the simulation results, a experiment of flow analysis using plasticine was also carried out. The results of the flow experiment showed good agreement with those of the simulation.     

磁场作用下轮轨黏着特性研究

利用JD-1轮轨模拟试验机研究水和油介质工况下磁场对轮轨黏着特性的影响。结果表明:在水和油介质工况下,磁场作用下的轮轨黏着力大于无磁场作用的黏着力,其中加磁水介质黏着力相对增幅达20%,加磁油介质黏着力相对增幅达50%;水和油介质工况下,施加磁场时速度对轮轨黏着力影响不大。     

The wear resistance and worn metallography of pearlite,bainite and tempered martensite rail steel microstructures of high hardness

In order to find out whether it is worthwhile to produce premium rail steels harder than 36–39 HRC and to discover the best microstructure for wear-resistant rail an experimental Cr-Mo alloy rail steel was heat treated to pearlite, bainite and tempered martensite. Each microstructure was prepared at hardness levels of 38, 42 and 45 HRC. These were tested in a dual disk-on-disk machine that closely simulates wheel-rail contact in curves at 1/10 scale. Wear rates were established for dry, grease-sand and pure grease environments. Dry wear rates decreased significantly with increasing hardness in high rails with tempered martensite or bainite microstructures but were almost independent of hardness for pearlite in the range tested. Lubrication reduced the wear rates by up to two orders of magnitude for all microstructures. It is concluded that pearlite gives the best dry wear performance, and there is no advantage in increasing the hardness beyond 38–40 HRC. The superior performance of pearlite in dry wear appears to be due to a very pronounced work hardening near the wearing surface. Electron microscopy reveals a marked refinement in the pearlite microstructure near the wearing surface, and this may explain the high work hardening observed.     

Tribological properties of hardened high strength Boron steel at combined rolling and sliding condition

The use of hardened high strength steel is found in applications where high wear resistance is required. The wear properties of high strength Boron steel are well known in applications with abrasive wear from stones, ore and other hard material. A unique concept of wear protection of rails is newly presented, a wear resistant cap made of hardened high strength Boron steel.Reducing the wear of rails and wheels and controlling the frictional behavior in the wheel/rail contact are two key issues for railway owners in order to reduce the increasing costs related to higher axle loads, higher speeds, more frequent traffic, etc. Therefore, the aim of this work has been to investigate and compare the tribological properties of Boron steel and UIC 1100 rail steel in contact with Blue Light wheel steel (AAR Class C (69-JDG-8)) under dry and water lubricated conditions in a two-disc tribometer. Advanced analytical instruments including 3D optical surface profiler, micro-hardness indenter, light microscope and SEM/EDS were used to analyze the results.Results from the experiments show that the friction coefficient in tests with Boron steel is more stable both in dry and water lubricated conditions than tests including UIC 1100 rail steel used in todays application. Surface damages seen from water lubricated tests on UIC 1100 rail steel are not seen on the surface of the Boron steel discs. In all tests, the wear decreased when water was added in the contact and friction was slightly decreased.     

Effect of passenger car curving on rail corrugation at a curved track

The paper presents a corrugation calculation model, which considers Kalker's non-Hertzian rolling contact theory to be modified, a material wear model and a vertical and lateral coupling dynamics of a half passenger car and a curved track. The dynamics characters of the curved track model in frequency domain were investigated by the commercial finite element code ANSYS, and some results concerning rail corrugation are presented in this paper. During a passenger car passing a curved track the dynamical performance of the vehicle and track and the initiation and growth of the curved rail corrugation are analyzed with the present corrugation calculation model. In the numerical calculation, two track states are investigated. One is that the track does not have any congenital defect except for the discrete rail support by sleepers. The other is that the track has a lateral dent on the gauge corner of the high rail. The rail corrugations analyzed are attributed to the material wear mechanism. The numerical results obtained indicate that (1) a high passing frequency corrugation initiates on the smooth running surface of the curved rail during the first passing of the passenger car through the curved track without defects; (2) the initial corrugation develops quickly and its passing frequencies change with an increase of passenger car passage; (3) the interaction of the leading wheelset of the bogie and the curved rails causes more severe corrugation and wear on the rail running surface than that of the trailing wheelset of the same bogie; (4) discrete rail support by sleepers is the congenital defect leading to rail corrugation formation.     

Investigating the Lubricity and Electrical Insulation Caused by Sanding in Dry Wheel–Rail Contacts

The adhesion (or available friction) in the wheel–rail contact is the most important parameter for the braking and traction operation of rail vehicles. Since the beginning of railway transportation, sanding from the locomotive has been a common practice to enhance the wheel–rail adhesion. In recent years, sanding from electrical multiple units (EMUs) and sand-based friction modifiers (FMs) have been adopted in some railway networks to overcome low adhesion incidents caused by leaf contamination in autumn. Although sanding has been proven to improve the adhesion under most of the typical contamination conditions, laboratory and field investigations have shown that sand may act as a solid lubricant in dry wheel–rail contacts. Nevertheless, the influence of the current sanding parameters on the solid lubrication effect has not been entirely investigated. Depending on the resulting adhesion coefficient, the traction and braking operations of rail vehicles could be affected. Furthermore, the influence of those parameters on the electrical insulation is also of special importance because it may affect the train detection. This article presents a laboratory investigation of the influence of three sanding parameters (i.e., feed rate, particle size, and slip) on the adhesion and electrical insulation in dry wheel–rail contacts. The tests have been carried out with a twin-disk roller rig in rolling-sliding motion under closely controlled conditions. Three different slips representative of the actual traction and braking operations have been considered. Sands of four different sizes and up to five feed rates have been used. The results show that using smaller particle sizes and higher feed rates promotes the lubrication and causes more electrical insulation in the wheel–rail contact. Furthermore, the increase in slip is found to reduce the lubrication, leading to a higher adhesion coefficient.     

Study on the manufacturing process of precision linear guide rail through shape rolling and shape drawing

Guide rails are one of the most important components in terms of equipment because the quality of the linear rail in-fluences on the precision linear motion. For long rails used in the guide rail, high dimensional accuracy as well as a cross-sectional shape is required. As a production method of guide rail, drawing process is mainly used. But, the shape rolling process is open used for the pre-process of the other metal forming process such as forging, extrusion, and shape drawing. The shape rolling process is one of the most effective processes which can make long products with constant irregular cross-sectional shape. Therefore, the tool shape is a very important process variable to obtain the required final product. The objective of this paper is the design of roll shape of the rolling process to produce the initial material with irregular cross sectional shape for shape drawing. Also, the die shape of the drawing process is determined to satisfy the dimensional accuracy of the final product. In this study, FE-analysis and artificial neural network (ANN) were applied to achieve the objective. Further, shape rolling and shape drawing experiments were performed to verify the result of FE-analysis. From results, it was possible to design the roll shape of shape rolling process effectively.     

Multi-point contact of the high-speed vehicle-turnout system dynamics

The wheel-rail contact problems, such as the number, location and the track of contact patches, are very important for optimizing the spatial structure of the rails and lowering the vehicle-turnout system dynamics. However, the above problems are not well solved currently because of having the difficulties in how to determine the multi-contact, to preciously present the changeable profiles of the rails and to establish an accurate spatial turnout system dynamics model. Based on a high-speed vehicle-turnout coupled model in which the track is modeled as flexible with rails and sleepers represented by beams, the line tracing extreme point method is introduced to investigate the wheel-rail multiple contact conditions and the key sections of the blade rail, longer nose rail, shorter rail in the switch and nose rail area are discretized to represent the varying profiles of rails in the turnout. The dynamic interaction between the vehicle and turnout is simulated for cases of the vehicle divergently passing the turnout and the multi-point contact is obtained. The tracks of the contact patches on the top of the rails are presented and the wheel-rail impact forces are offered in comparison with the contact patches transference on the rails. The numerical simulation results indicate that the length of two-point contact occurrence of a worn wheel profile and rails is longer than that of the new wheel profile and rails; The two-point contact definitely occurs in the switch and crossing area. Generally, three-point contact doesn’t occur for the new rail profile, which is testified by the wheel-rails interpolation distance and the first order derivative function of the tracing line extreme points. The presented research is not only helpful to optimize the structure of the turnout, but also useful to lower the dynamics of the high speed vehicle-turnout system.     

高速轮轨黏着机制进展及模拟试验研究

列车的运行要借助于轮轨之间的黏着和制动,轮轨之间的最大黏着力受到接触斑上黏着系数的限制,因此轮轨关系中的黏着问题是与高速铁路运营密切关联的带有基础性的研究课题。综述国内外高速轮轨黏着的进展及现状,指出研究面临的主要问题。介绍轮轨模拟试验机开展的轮轨黏着试验,结果表明:油水砂介质下的轮轨黏着系数最大,油水介质下的轮轨黏着系数最小,利用此模拟试验机可开展轮轨黏着特性研究。     

Wheel/rail adhesion—Boundary lubrication by oily fluids

Oils on rails are present in minute quantities and are found to be complex mixtures containing an unusually high proportion of chemically active compounds. Laboratory experiments are described which study how such oils and related compounds affect friction when present in surface concentrations similar to those found on the track. The friction is sensitive to small changes in the quantities present, and this gives an explanation why adhesion varies on dry rails. All types of fluid give similar results. Simple mixtures can be dominated by an active, low-friction component but the friction of oils appears to be an “average” of their many components. High humidity during specimen preparation promotes lower friction. It is suggested this is due to its effect on the physical properties of the oxide formed on the steel surface.     

Review of top of rail friction modifier tribology

The aim of this paper was to review the current state of research for top of rail friction modifiers (TORFM). In the railway industry, friction modifiers is a catch all term for a wide range of products applied for different purposes which has led to confusion. It is hoped that recently published definitions will aid industry to a better understanding of the different products and how they function. The benefits of friction modifiers are well understood with a large body of research supporting the benefits. Comparatively, there is a lot less knowledge of the optimum amount of product to achieve the benefits or how far down the track from an application site the benefit will be seen. Modelling of the products is another area where there is little research, with most of the modelling papers found focussing on dry wheel–rail contact due to the complexity of introducing a third-body layer to a friction force model. Furthermore, only one paper was found which relates how friction modifiers are affected by contaminants or other applied products such as lubricants. With many different products applied to wheels and rail for different purposes, understanding their interaction is key. At the time of this review, there are currently no standards that prescribe how TORFM should behave although the European Committee for Standardisation is currently developing them at the moment. This review has also attempted to appraise the research against a set of criteria. Depending on how many of the criteria the piece of research filled, it was categorised as A, B or C. It was found that most of the research was of category, this was mainly due to only one test method being used or the scale presented. Category A research incorporated modelling or multiple test-scales to support the results presented.     

Analysis and tests of boned insulted rail joints subjected to vertical wheel loads

In traditional railroad tracks, joint bars are being used to connect the ends of adjoining rails. Because the vertical bending stiffness of two bars is generally much lower than of the rails, the passing wheels generate larger deflections in the joint region. This in turn leads to larger wheel forces caused by the dynamics of the passing vehicles and to accelerated track deterioration. In recent decades these expansion joints are being eliminated by the introduction of the continuously welded rails (CWRs). However, the retention of the automatic block signaling system created the need for electrically insulated joints is that the bending stiffness of the insulated joints bars is even smaller than of the non-insulated bars that are being eliminated. There are very few published analyses of joints in track; especilly of insulated joints. The purpose of this paper is to contribute to a better understanding of the mechanics of rail joints. At first an analysis is presented for the joint tests to be conducted. Then a test program is described that utilizes actual bonded joints. The obtained test results are then compared with the corresponding analytical results. The agreement is good. This confirms the validity of the assumed joint model and of the presented analysis. The paper concludes by analyzing the effect of a rail joints in a CWR track caused by a vertical wheel load.