Interaction Conditions of Improvement in the System wheel rail

Transcription

1 Interaction Conditions of Improvement in the System wheel rail Petr N. Scherbak Rostov State Transport University, Construction Department, Chair Railway Track and Infrastructure Vladimir V. Shapovalov Rostov State Transport University, Railroad Construction Machines Department, Chair Transport Machines and Tribotechnics Nickolay I. Boiko Rostov State Transport University, Railroad Construction Machines Department, Chair Machinery Maintenance and Repair Akhmat Ch. Erkenov Rostov State Transport University, Railroad Construction Machines Department, Chair Transport Machines and Tribotechnics Alexander L. Bykadorov Rostov State Transport University, Power Engineering Department, Chair Automated Systems of Electric Power Supply Abstract The actuality of wheels and rails flange wear reduction targets is described. The use of up-to-date technical lubrication aids of the system wheel rail allows to affect the consumed power resources, to increase the life of wheels and rails, to form safe train movement conditions on crooked sections of a track and to reduce noise level on the environment. Among lubrication systems the application of firm lubricants in board flange rail lubricants of bar type is particularly distinguished. Possible mechanisms of linking adhesion forming reasons between friction surface and antifriction film have been considered. The developed technology of bar flange rails lubricating using contact rotaprint firm antifriction additive bars scheme has been presented. On the basis of these researches the scientifically proved version of plating anti friction lubricating material which includes three thermoplastic adhesive with different melting temperatures has been worked out. Keywords: wheel rail system, friction unit, lubrication technology, firm lubricating materials, adhesion, thermoplastic adhesive. INTRODUCTION The most effective method of friction system wheel rail efficiency raising, life increase, traction power loses reduction is the flange or rail surface lubrication technology. The contact of wheel flanges with rail head side surface refers to open friction units. When choosing a technology, technological equipment and dispensable materials for lubrication contact of a wheel with rails it is necessary to take into account peculiarities and operational conditions of a particular friction unit, determining the corresponding life specifications. In the basis of the most effective lubrication technology the scientifically proved optimal versions of lubricating material and way of its friction surface application are laid. All operational board lubrication systems may be divided into two types: spray type and bar type. In the open friction units the conditions of oil wedge forming are lacked that abruptly reduces effect while using liquid and consistent lubricating materials. At the same time board flange lubricators of bar type possess the decisive advantages if compared with board flange lubricators of spray type: 1. Lubricating material supply on wheel flange is strictly 11442

2 oriented and its operation doesn t depend on locomotive crew activity. 2. They have simple structure providing their reliable operation, maintenance and repair work does not require specialized technological equipment and refilling devices. 3. Operating capacity of bar flange lubricators doesn t depend on locomotive movement speed, strength and direction of wind, environment temperature. 4. Lubricating materials being applied in bar flange lubricators doesn t pollute rail head and locomotive crew. 5. They have a lower cost for a single locomotive equipment and allow to decrease lubrication costs two or four times, while possessing high ecological rates. METHODS The analysis of outbound tribo specifications of lubricating materials and their application conditions reveals that in order to protect rails and wheels the special lubricating materials of firm lubricating covering type are required, which are like those being used in forging and moreover, the corresponding supply systems are necessary. That is why the worldwide trend of lubrication development system aims to use firm plastic lubricators made in forms of bars, ingots, etc. and which in contact of wheel flange or side rail surface produce friction rubbing of the lubricant on their surface. These lubricating materials are firm dry coverings, possessing high bearing capacity and withstanding contact load up to 2 3 hpa and for the last time with the booming of nanotechnologies nanocoverings. The experience of bar type lubricators, for example in Paris metro revealed that bar flange lubricators besides characteristics having been noted, reduce the risk of wheel pair derailment at low running speeds, don t pollute air, don t affect traction and braking, provide accurate dosed required material supply of essential quality lubricating material in contact of wheel flange with rails. At present time the prominent foreign and Russian companies conduct active work on invention of high resource firm lubricating materials, capable to resist intensive dynamic forces and possessing steady tribo characteristics in a wide temperature range (from +50 to 50 ). The specialists of RSTU have developed firm lubricating material plating anti friction material (PAM). According to complex index price-resource it corresponds the best domestic and foreign analogs of firm lubricating materials. The technology of contact rotaprint bar rail flange lubrication «ГРС-РАПС» meeting optimal lubrication scheme requirements is worked out (fig. 1). According to the technology lubricating material is applied by the contact rotaprint way on the wheel flange with the following active transfer on rail head side edges. In this case wheel rail system lubrication may be conducted by any type of rolling stock at any speeds [3]. The use of firm plastic material covering contact scheme in different forms of geometrical performance allows to exclude wheel and rail tractive surfaces oiling, permanent way elements and locomotive running gears. It can optimize lubrication technological process realizing geometrically accurate place of lubricator covering with dosed quantity of additives which creates protective anti friction films on contacting surfaces of wheels and rails. Figure 1: Scheme of contact rotaprint friction surface modification: a driving gear on the serve effect basis; b conservative driving gear This optimizes lubricant consumption, which price has been risen because of up-to-date multifunctional additive usage, particularly nano particles. For the firm plastic lubricants solution one of the main technological equipment problems for lubrication is to provide achieving accuracy of positioning regarding wheel flange or rail head side surface and to exclude air speed flow affect. Wear and undercut of wheel flange, pointed rolling occurrence are the main reasons of tractive rolling stock wheel pairs rejection. Surface wear rate in contact wheel rail zone depends on a number of external factors: contact zone loading, speed regarding wheel sliding, operational temperature conditions, mode of locomotive operation, aggressive environmental impact, physics mathematics surface modifications in friction process and others. In conditions of external friction in the wheel rail system under normal and tangent loading, surface metal layers undergo resilient plastic deformation. Load and deformation fields application in the form of waves from external forces affect as well as friction forces results in metal array fracture following mechanical strength reduction, especially in surface layers: grade, cut load, shift module, resilience module and other mechanical specifications. With cycles number load increase the steel micro grade decreases abruptly, up to 20 % after 5 million cycles. In a number of cases external friction turns into internal. The depth of deformed layer depends on friction mode, i.e. load, its specifications, speed regarding to sliding, temperature and temperature gradients as well as wear modes caused by friction conditions. Under external forces affect strips sliding development occurs in the form of extrusion and intrusion that results in wheel and rail materials micro volume loosening, mechanical properties and wearproof decline. Surface active substances in lubricating material raise dislocation density. Rails defects analysis reveals that 82 % of wrecks appear on the surface, 58 % of them being on friction surfaces. Among majority of internal factors physical and mechanical wheel and rail material specifications including near-surface layers, rheological and physical chemical lubricator s properties, lubricating method are determining, 11443

3 the most effective. One more quickly realized method of intensive wear control is the technology of wheel pairs flanges rail head side surface. One of the promising lubricating materials in the form of cladding anti friction material bars are used to create protective anti friction films on operational surfaces of open friction units. Atmospheric precipitation does not have essential effect on cladding anti friction nano films as adhesives thermos plastics are not diluted in water. In working ranges of track rolling stock system operation loading speedy rates, after the so called non-forced away volume formation, generated film is hardly to be forced out from the surface. The presence of nano particles in it results in micro spaces relief filling that plays an especially important part in the aging and curing micro defects process of mating surfaces during their braking. By means of active strongest environmental nano particles lubricating material polarization on friction surfaces the film of a definite width and optimal geometry is formed that increases trimming bearing capacity. In this way reliable share friction surface occurs, parts wear is partially compensated and kinematic pairs accuracy is risen. DISCUSSION At present there is no full interpretation of adhesive link forming nature between friction surface and anti-friction film. Thus there is no conventional theory and being considered ones below have real grounds and theoretical explanation. Adsorptive molecular adhesion theory considers link formation between adhesive presenting in lubricating material and friction surface to be a result of inter-molecular forces activity. This theory is like Debroyn and Mac-Laren developed one. [1, 2] Adsorptive adhesion theory divides the adhesive link forming process into two stages. On the first stage resulted in Brownian movement adhesive molecules transfer to the surface occurs and adhesive molecules polar groups are approaching to metal surface polar groups. On the second stage absorption occurs. The second stage begins from the moment when the distance between molecules will become smaller micron. Adsorptive theory considers adhesion from the following point of view: it is a result of forces emergence of contacting bodies inter-molecular interaction. Link occurrence between adhesive and metal is determined by their chemical structure and contact conditions (temperature, time, oxidation process presence. \ \ Me-OH+CH2-CH- Me-O-CH2-CH- / / OH Probability of chemical links formation between adhesive polymer and metal surface is relatively low, because of little chemical activity of most polymers interacted with metals. But in case of such relationships formation high adhesive strength will be achieved. For example, in interaction of polyurethane with silica gel or aeroxyl (amorphous SiO 2) which have a large number of hydroxyl groups on the surface, there exist a great probability of chemical links formation: R-N=C=O + HO-Si R-N-C-O-Si HO A lot of polymers and fillers have groups capable to form in chemical links in definite situations: hydroxyl (-ОН), acid (- СООН), amine (-NН 2), epoxy and others. If the probability of chemical and hydrogen links emergence is high, the high adhesive strength is expected. Mechanical, electric and adsorptive factors make their contribution in adhesive interaction value. From the adhesion mechanical theory point of view formation process occurs only by means of polymer mechanical coupling on friction rough surface. The significance of mechanical adhesion is great irrespective of chemical or other links existence. The mechanical theory explains adhesion as a result of mechanical coupling of adhesives with rough part surface. (fig. 2) Figure 2: Model of adhesive mechanical theory The mechanical model underlines the significance of rough surface. It clearly explains definite adhesive cases, particularly well coupling of adhesive with rough surface, however, as any other models it has some restrictions. In the solidification process, i.e. transformation of adhesive from liquid state to solid (either chemical or physical way) entropy loosing takes place that is expressed in occupied volume reduction. This phenomenon is known as shrinkage and comes out from lack of full contact, adhesion reduction if it is connected only with mechanical coupling. Adhesive chemical theory gives an idea of adhesive metal surface link origin. Therefore adhesive link formation caused by chemical interaction is considered as one of the possible adhesive cases. The cause of adhesive interaction is due to the resistance of cohesive (chemical and physical connections) and adhesive bonds (atoms and/or groups of atoms). During this interaction chemisorption takes place (ionic or covalent, or metallic connections generate). The result of this interaction is adhesion. A metallic connection occurs when valence electrons leave 11444

4 their atoms and form an electronic gas inside the solid body. It should be mentioned that this type of relations is not typical for the interaction of polymer macromolecules with each other. Ionic and covalent bonds refer to chemical connections. They are the main connections in the process of creation of molecules. This type of relations occurs as a result of the exchange or distribution of electrons between two adjacent atoms. The ionic bond occurs when the electron moves from the orbit of one atom to the orbit of another. If the atom loses an electron, it becomes positively charged (by cation) if, on the contrary, it acquires an electron, it becomes negatively charged (anion). Figure 4: Structure of the lubricating rod Figure 3: The model of origination of interatomic and intermolecular connections In covalent connection some electrons are equally distributed between the adjacent atoms, i.e. they are socialized. For simplicity it is supposed that only valence electrons are socialized. In the covalent connection valence electrons are socialized by certain atoms in such a way that each partner obtains a stable electron configuration. A covalent connection is rarely symmetrical and usually polarized, i.e. it is asymmetric. Covalent connections are rather solid (more than 400 kj/mol), due to the very small distance between neighboring atoms, which is usually amounts to 0,15 nm. Covalent connections are typical for the elements occupying an intermediate position between metals and nonmetals (boron, carbon, silicon, arsenic, etc.). A covalent connection is a common feature of all polymers. Thus, the analysis of theoretical studies of the adhesion process of antifrictional film on the metal surface shows that none of the existing theories can fully explain all processes of formation. We can assume that each of these theories describes a certain stage of the process, which, depending on conditions, manifests itself in one of them. RESULTS Considering the operating conditions of the open friction system wheel flange - side surface of the rail head, the most effective system of lubrication is the application of contact-rotaprint scheme of lubrication. And as the lubricant material, solid lubricant rods with antifriction additives should be used. An example of such material is PAM (plate antifriction lubricating material), which at least, allows to organize adhesion connection due to the cold surface of friction. Three thermoplastic adhesives with different melting points, being in the composition, allow to form anti-friction film on the surface of friction in the following way. The first thermoplastic adhesive is an elastic mass. When heated above 80ᵒC it transfers to the molten state and it is the launch mechanism of the formation of low friction film. The second thermoplastic adhesive, that is included in a lubricating composition at the working temperature of ᵒC, is melted and transfers into viscous-flow state. Due to external forces irreversible deformation arises, i.e. genuine flow of polymers. Flow of polymers is possible owing to the flexibility of their macromolecules and is carried out by diffusion mechanism. The flow is realized by moving of separate parts of the macromolecules. The movement of the whole chain occurs as a result of multiple shifting of all sections. The fluidity of polymers is higher, the lesser the role of the energy interaction, i.e. the lower is the viscosity. The viscosity of the polymers decreases with the lowering of the degree of polymerization, increasing of the temperature and dilution of large chain macromolecules by small molecules. The processes of the flow play a very important role, as they penetrate and fill the irregularities on the surface of friction. Currently for open friction units there are no standard evaluation methods of tribotechnical and tribospectral characteristics of solid lubricant coatings. Therefore, when solving practical problems, the method of dynamic monitoring of friction system wheel flange rail was used [7]. It allows to perform a comparative analysis of tribotechnical and tribospectral characteristics of the given tribological system with the introduction by technical means of the lubrication in contact with lubricating materials of the type of solid lubricants. Analysis of amplitude-phase-frequency characteristics of the tribosystem wheel rail allowed to establish, that the change in the average value or the peak factor of the integral estimates on the characteristic frequency range (fig.5) characterizes the presence or absence of the lubricating material on the lateral surface of the rail head, residual life of its one-time application, type and quality, as well as possible cases of thermal destruction of the friction contact

5 Figure 5: Diagrams of traction coefficient change and characteristics of degree of instability of the system wheel-rail at onetime application of the lubricating material PAM The time of the appearance of the unstable state of the friction links of the wheel with the side surface of the rail with the existence of the lubricant in their contact is indicated by figure 1, the moment of the stability loss in an amplitude or a phase - by figure 2, and the area of the frictional interaction of wheel with the rail at the absence of a lubricant - by number 3. Lubricant PAM according to its tribological properties has four phases of operation (Fig.5): a formation of frictional connections with the surfaces of the wheel and the rail (exploding and pasting of the bituminous base, filling the microcracks of the surfaces; the formation of strong adhesion connections); b a mode of the stable operation of the lubricant with graphite inclusions; c the area of formation of silicate oxides of the lubricant and reducing of the amount of bituminous base; d the area of micro-cracks healing of surfaces in contact due to silicate inclusions in the lubrication of PAM. At tearing of silicate inclusions the coefficient of friction increases to the conditions of dry contact, and its mean-square deviation increases (3 in Fig.5) [4]. Evaluation of the dissipative component of friction of the tribological system when using PAM has shown, that external friction is spent 1,5...2 times less than the dissipative energy, i.e. resistance to motion forces. This is due to the lack of immediate friction contact of the wheel flange with the side surface of the rail, good adhesion between the lubricant PAM with a metal, because of the lack of local bridges setting, reduction of the inertial oscillations and the lack of points of loss of stability of tribological system. The given condition of tribological system is shown in figure 5, where one can see only few moments of stability loss [4]. The test results showed [4, 5, 6, 7], that depending on the state of the antifriction contact of wheel with the rail over time the friction factor f increases, the stability margin on the amplitude of L decreases and the integral estimates of the dissipative component of the friction IQ and the degree of dissipation I increase (table). This corresponds to the transition of the given coordinates of the state of the wheel-rail system from one stationary condition to another. Table 1: Comparative characteristics of the tribosystem wheel-rail Time, s Friction coefficient f Integral estimates Reserve of resistance of stability in an amplitude L, db Dissipative component of friction IQ Degrees of dissipation Iγ Energy losses If Coherence coefficient IC 1 3,45 0,104 37,3 3,02 0,79 0,78 0, ,6 0,163 24,7 4,72 0,57 1,41 0, ,45 0,301 12,5 6,83 0,70 53,39 0,

6 CONCLUSION Analyzing the wear mechanism of the given couple, we can say that the main type of deterioration of the friction pair wheelrail, especially during driving in curves, is the wearing out at the binding as a result of seizure, deep smoothing of materials, moving it from one surface to another and the impact of emerging irregularities on the conjugate surface in the form of wide and deep furrows in the direction of sliding. Related types of wear are contact fatigue due to repeated deformation of microand macrovolumes of materials of the friction surfaces as during rolling and sliding, abrasive and plastic deformation, amounting up to 20% of the volume of the metal. Ensuring of interaction throughout the life cycle between rolling stock and railway track of optimal tribological characteristics in the wheel-rail system is possible by the formation in the zone of friction contact wheel-rail of the multiphase lubricant layer, resistant to external influence in a wide range of operational factors. The application of multiphase solid lubricant materials like PAM, for work in the open, heavily charged (up to 3.5 GPa) friction units, ensures the efficiency of the wheel-rail pair in wide temperature ranges (from - 50ᵒC up to + 130ᵒC). It has a high resource of one-time application, eliminating the buildup on the lubricated surface of the abrasive particles (sand) in the working phase. Lubricant PAM has no harmful effect on the environment. REFERENCES [1] Kutkov, A. A., 1976, Wear-Resistant and Antifriction Materials, M., Engineering, p. 152 [2] Komarov, G. V., 2006, Compounds from Polymeric Materials, Teaching aid.- SPb.: Profession, 592p. [3] Shapovalov, V. V., Mogilevsky, V.A., Lubyagov, A. M., etc., 2006, Friction Modifiers, monograph, Rostov State Transport University, Rostov on Don, 236 p. [4] Shapovalov, V.V., Chelokhyan, A.V., Ozyabkin, A.L., and others, 2010, Amplitude-Phase-Frequency analysis of the Critical State Friction Systems : monograph, M., Educational and Methodical Centre on Education on Railway Transport, 383 p [5] Ozyabkin, A.L., Lubyagov, A.M., Wishepan, A.L., and others, 2012, Amplitude-Phase-frequency Analysis of Friction Processes and Wear, Coll. scientific. Works, XII International Conf. Tribology and Reliability, SPb., Baltic State Technical University by D. F. Ustinov, pp [6] Shapovalov, V.V., Shcherbak, P.N., Ozyabkin, A.L, and others, 2011, The Development of Innovative Technology Lubrication in the System "Wheel Rail" on the Basis of Nanomaterials, Friction and Lubrication in Machines and Mechanisms. No. 10., pp [7] Shapovalov, V., 2006, Tribospectral Identification of the Friction Processes and Wearing", Intern. Conf. Eurotrib-5 (AD-AIT-2006), Italy: Panama