Vol. 24 No. 3 2022 3 EDITORIAL COUNCIL EDITORIAL BOARD EDITOR-IN-CHIEF: Anatoliy A. Bataev, D.Sc. (Engineering), Professor, Rector, Novosibirsk State Technical University, Novosibirsk, Russian Federation DEPUTIES EDITOR-IN-CHIEF: Vladimir V. Ivancivsky, D.Sc. (Engineering), Associate Professor, Department of Industrial Machinery Design, Novosibirsk State Technical University, Novosibirsk, Russian Federation Vadim Y. Skeeba, Ph.D. (Engineering), Associate Professor, Department of Industrial Machinery Design, Novosibirsk State Technical University, Novosibirsk, Russian Federation Editor of the English translation: Elena A. Lozhkina, Ph.D. (Engineering), Department of Material Science in Mechanical Engineering, Novosibirsk State Technical University, Novosibirsk, Russian Federation The journal is issued since 1999 Publication frequency – 4 numbers a year Data on the journal are published in «Ulrich's Periodical Directory» Journal “Obrabotka Metallov” (“Metal Working and Material Science”) has been Indexed in Clarivate Analytics Services. We sincerely happy to announce that Journal “Obrabotka Metallov” (“Metal Working and Material Science”), ISSN 1994-6309 / E-ISSN 2541-819X is selected for coverage in Clarivate Analytics (formerly Thomson Reuters) products and services started from July 10, 2017. Beginning with No. 1 (74) 2017, this publication will be indexed and abstracted in: Emerging Sources Citation Index. Journal “Obrabotka Metallov” (“Metal Working & Material Science”) has entered into an electronic licensing relationship with EBSCO Publishing, the world's leading aggregator of full text journals, magazines and eBooks. The full text of JOURNAL can be found in the EBSCOhost™ databases. Novosibirsk State Technical University, Prospekt K. Marksa, 20, Novosibirsk, 630073, Russia Tel.: +7 (383) 346-17-75 http://journals.nstu.ru/obrabotka_metallov E-mail: metal_working@mail.ru; metal_working@corp.nstu.ru
OBRABOTKAMETALLOV Vol. 24 No. 3 2022 4 EDITORIAL COUNCIL EDITORIAL COUNCIL CHAIRMAN: Nikolai V. Pustovoy, D.Sc. (Engineering), Professor, President, Novosibirsk State Technical University, Novosibirsk, Russian Federation MEMBERS: The Federative Republic of Brazil: Alberto Moreira Jorge Junior, Dr.-Ing., Full Professor; Federal University of São Carlos, São Carlos The Federal Republic of Germany: Moniko Greif, Dr.-Ing., Professor, Hochschule RheinMain University of Applied Sciences, Russelsheim Florian Nürnberger, Dr.-Ing., Chief Engineer and Head of the Department “Technology of Materials”, Leibniz Universität Hannover, Garbsen; Thomas Hassel, Dr.-Ing., Head of Underwater Technology Center Hanover, Leibniz Universität Hannover, Garbsen The Spain: Andrey L. Chuvilin, Ph.D. (Physics and Mathematics), Ikerbasque Research Professor, Head of Electron Microscopy Laboratory “CIC nanoGUNE”, San Sebastian The Republic of Belarus: Fyodor I. Panteleenko, D.Sc. (Engineering), Professor, First Vice-Rector, Corresponding Member of National Academy of Sciences of Belarus, Belarusian National Technical University, Minsk The Ukraine: Sergiy V. Kovalevskyy, D.Sc. (Engineering), Professor, Vice Rector for Research and Academic Affairs, Donbass State Engineering Academy, Kramatorsk The Russian Federation: Vladimir G. Atapin, D.Sc. (Engineering), Professor, Novosibirsk State Technical University, Novosibirsk; Victor P. Balkov, Deputy general director, Research and Development Tooling Institute “VNIIINSTRUMENT”, Moscow; Vladimir A. Bataev, D.Sc. (Engineering), Professor, Novosibirsk State Technical University, Novosibirsk; Vladimir G. Burov, D.Sc. (Engineering), Professor, Novosibirsk State Technical University, Novosibirsk; Aleksandr N. Gerasenko, Director, Scientifi c and Production company “Mashservispribor”, Novosibirsk; Sergey V. Kirsanov, D.Sc. (Engineering), Professor, National Research Tomsk Polytechnic University, Tomsk; Aleksandr N. Korotkov, D.Sc. (Engineering), Professor, Kuzbass State Technical University, Kemerovo; Evgeniy A. Kudryashov, D.Sc. (Engineering), Professor, Southwest State University, Kursk; Dmitry V. Lobanov, D.Sc. (Engineering), Associate Professor, I.N. Ulianov Chuvash State University, Cheboksary; Aleksey V. Makarov, D.Sc. (Engineering), Corresponding Member of RAS, Head of division, Head of laboratory (Laboratory of Mechanical Properties) M.N. Miheev Institute of Metal Physics, Russian Academy of Sciences (Ural Branch), Yekaterinburg; Aleksandr G. Ovcharenko, D.Sc. (Engineering), Professor, Biysk Technological Institute, Biysk; Yuriy N. Saraev, D.Sc. (Engineering), Professor, Institute of Strength Physics and Materials Science, Russian Academy of Sciences (Siberian Branch), Tomsk; Alexander S. Yanyushkin, D.Sc. (Engineering), Professor, I.N. Ulianov Chuvash State University, Cheboksary
Vol. 24 No. 3 2022 5 CONTENTS OBRABOTKAMETALLOV TECHNOLOGY Permyakov G.L., Davlyatshin R.P., Belenkiy V.Y., Trushnikov D.N., Varushkin S.V., Pang S. Numerical analysis of the process of electron beam additive deposition with vertical feed of wire material...................... 6 Ilinykh A.S., Banul V.V., Vorontsov D.S. Theoretical analysis of passive rail grinding.................................. 22 Chinchanikar S. Modeling of sliding wear characteristics of Polytetrafl uoroethylene (PTFE) composite reinforced with carbon fi ber against SS304........................................................................................................ 40 EQUIPMENT. INSTRUMENTS Abbasov V.A., Bashirov R.J. Features of ultrasound application in plasma-mechanical processing of parts made of hard-to-process materials...................................................................................................................... 53 MATERIAL SCIENCE Stolyarov V.V., Andreev V.A., Karelin R.D., Ugurchiev U.Kh., Cherkasov V.V., Komarov V.S., Yusupov V.S. Deformability of TiNiHf shape memory alloy under rolling with pulsed current....................... 66 Vorontsov A.V., Filippov A.V., Shamarin N.N., Moskvichev E.N., Novitskaya O.S., Knyazhev E.O., Denisova Yu.A., Leonov A.A., Denisov V.V. Microstructure and residual stresses of ZrN/CrN multilayer coatings formed by the plasma-assisted vacuum-arc method........................................................................... 76 Ivanov I.V., Safarova D.E., Bataeva Z.B., Bataev I.A. Comparison of approaches based on the WilliamsonHall method for analyzing the structure of an Al0.3CoCrFeNi high-entropy alloy after cold deformation....... 90 Kryukov D.B. Structural features and technology of light armor composite materials with mechanism of brittle cracks localization.......................................................................................................................... 103 EDITORIALMATERIALS 112 FOUNDERS MATERIALS 123 CONTENTS
OBRABOTKAMETALLOV Vol. 24 No. 3 2022 TECHNOLOGY Theoretical analysis of passive rail grinding Andrey Ilinykh a,*, Viktor Banul b, Denis Vorontsov c Siberian Transport University, 191 Dusy Kovalchuk st., Novosibirsk, 630049, Russian Federation a https://orcid.org/0000-0002-4234-6216, asi@stu.ru, b https://orcid.org/0000-0002-4257-2686, banul@ngs.ru, c https://orcid.org/0000-0002-3819-781X, voroncovds@stu.ru Obrabotka metallov - Metal Working and Material Science Journal homepage: http://journals.nstu.ru/obrabotka_metallov Obrabotka metallov (tekhnologiya, oborudovanie, instrumenty) = Metal Working and Material Science. 2022 vol. 24 no. 3 pp. 22–39 ISSN: 1994-6309 (print) / 2541-819X (online) DOI: 10.17212/1994-6309-2022-24.3-22-39 ART I CLE I NFO Article history: Received: 15 June 2022 Revised: 29 June 2022 Accepted: 05 July 2022 Available online: 15 September 2022 Keywords: Rail grinding Passive grinding Machining effi ciency Grinding performance Funding The research was carried out with the fi nancial support of subsidies from the Federal Budget for the development of cooperation between Russian educational institutions of higher education, state scientifi c institutions and organizations of the real sector of the economy in order to implement complex projects to create high-tech industries. Acknowledgements Research were partially conducted at core facility “Structure, mechanical and physical properties of materials”. ABSTRACT Introduction. There are different rail machining technologies designed to eliminate defects on the tread surface and extend the life cycle of rails. The most used is the technology of grinding rails with rotating grinding wheels using rail-grinding trains. Its main disadvantage is the low working speed of the grinding train that requires the organization of track possessions with stopping the movement of trains along the haul. To perform preventive rail grinding with minimal metal removal from the rail head, passive grinding technologies using grinding wheels have become widespread in last years. Passive grinding is when there is no power on the grinding wheel to rotate it actively. Such methods make it possible to achieve high speeds of the grinding train, and the work can be carried out in the train schedule without closing the stage. Currently, passive grinding technologies are relatively new and do not have the necessary scientifi c basis for optimizing the machining process. The aim of the work is to perform theoretical studies of kinematic and force analyzes of two methods of rail passive grinding: the periphery and the end face of the grinding wheel. Methodology of the work is kinematic and power calculations of rail grinding schemes. Results and discussion. Within the framework of theoretical studies, a kinematic and force analysis of two methods of passive grinding are carried out, on the basis of which the optimal conditions for its implementation are determined. It is established that the method of passive grinding by the periphery of the wheel has a 20 % higher productivity and energy effi ciency of the process before end passive grinding due to the higher rotation speed of the grinding wheel with equal forces of pressing it to the rail. At the same time, passive grinding with the end of the wheel is distinguished by a twice greater range of change in both the speed of the grinding wheel rotation and the force of its pressing that makes it possible to achieve greater metal removal at equal speeds of the grinding trains. In conclusion, promising tasks for further research in the fi eld of passive rail grinding are formulated. For citation: Ilinykh A.S., Banul V.V., Vorontsov D.S. Theoretical analysis of passive rail grinding. Obrabotka metallov (tekhnologiya, oborudovanie, instrumenty) =Metal Working andMaterial Science, 2022, vol. 24, no. 3, pp. 22–39. DOI: 10.17212/1994-6309-2022-24.3-22-39. (In Russian). ______ * Corresponding author Ilinykh Andrey S, D.Sc. (Engineering), Professor Siberian Transport University, 191 Dusy Kovalchuk st., 630049, Novosibirsk, Russian Federation Tel.: 8 (383) 328-03-92, e-mail: asi@stu.ru Introduction Nowadays, due to the intense use of railways, the maintenance of the railway tracks and rails in particular are drawing a lot of attention. One of the priority areas, which allows extending the life cycle of rails, is the technology of their grinding in the conditions of a railway track [1–3]. The tasks assigned to this type of technological impact are extensive and can consist both in the preventing the formation of contact wear defects, and in removing existing defects and forming the required rail profi le [4]. In this regard, depending
OBRABOTKAMETALLOV TECHNOLOGY Vol. 24 No. 3 2022 on the assigned objectives there are the following types of grinding: preventive (prophylactic), maintaining (corrective) and reconstructive (profi ling) grinding. Each of these approaches determines the technology of its implementation [5]. Thus, reconstructive grinding is characterized by the need for a large metal removal from the rail using rail grinding trains (RGT) operating at relatively low speeds, and in turn, preventive grinding should be performed with the RGT running at maximum speed but with a relatively small removal of metal from the rail (Table). It is impossible to effectively implement such a range of operating modes on one type of process equipment [6–8]. Rail grinding trains, such as RR-48, RShP-48 and RShP-48K models are limited to the following grinding modes: RGTs with an operating speed of 4 to 8 km/h; average metal removal speeds from 0.05 to 0.3 mm per pass. During each pass, the “active” grinding process, which consists in fl at face grinding with rotating abrasive wheels running with a rotation speed of 3600 rpm with wheels being rotated using electric motors. With grinding work being carried out at speeds not exceeding 8 km/h and with only minimal metal removal, the use of these types of rail grinding trains for preventive purposes is extremely ineffi cient. Technological impacts of rail grinding Technological impact The purpose of the impact Machining technology Preventive (prophylactic) Preventing the formation of surface defects in rails Insignifi cant metal removal ( up to 0.1 mm) at high speeds (up to 90 km/h) Repair (corrective) Removal of surface defects of rails, elimination of wave-like wear, correction of the cross profi le of the rail Heavy metal removal (up to 1.5 mm) in certain sections of the rail head at medium speeds (up to 15 km/h) Restorative (profi ling) Restoration of the transverse (repair) profi le of rails, reprofi ling of old-year rails and when relaying rails in curved track sections Heavy metal removal (up to 3.5 mm) along the entire transverse profi le of the rail at low speeds (up to 6 km/h) Another factor that has a signifi cant impact on the effi ciency of the rail grinding process is the necessity to organize periods when sections of track are “temporarily closed for maintenance” while the work is carried out. The existing speeds of the RGT (up to 8 km/h) do not allow it to be used within the schedule of passenger and freight trains. This leads to the need to close entire hauls for traffi c – the organization of technological windows, – and as a result, to the occurrence of large fi nancial costs caused by a decrease in the capacity of sections of the railway track [9]. In view of the above limitations, the current problem facing the maintenance of railway tracks is the need for the expansion of the rail grinding trains technological capacities. The key task in solving this problem is to increase the operating speed of rail grinding trains everywhere in order to eliminate or at least reduce the duration of closures for maintenance. The most promising solution lies in increasing the operating speeds of the RGT when performing work on preventive and corrective grinding with insignifi cant removals of the rail metal [10, 11]. Since its inception, rail grinding technology has been focused primarily on preventing the formation of wave-like rail wear, wheelspin and surface defects in the most loaded sections of the track, i.e. it was of a preventive nature. For this purpose, the technology of rails passive grinding has been used since 1960s [12]. The term “passive”, in this case, characterizes the absence of additional movements in an abrasive tool (usually rotating or reciprocating) due to special drive mechanisms. Grinding occurs only as a result of the pressing and longitudinal movement of the tool. This technology on local railways was implemented with the help of the so-called rail-grinding carriages (RGC), which also lubricate the rails. These carriages were driven by a locomotive. During this process (Fig. 1, a) abrasive bars were pressed against the rail with a constant force. These bars were located on the
OBRABOTKAMETALLOV Vol. 24 No. 3 2022 TECHNOLOGY running bogies of the carriages between the wheelsets (Fig. 1, b). Thus, when the carriages were moving, the rolling surface of the rail head was polished. This grinding technology assumed the working movement of the RGC at suffi ciently high speeds – up to 60 km/h and did not require closing tracks for maintenance. At the same time, there were a number of signifi cant drawbacks, such as the rapid salting loading of abrasive bars and the need to break-in it to a specifi c transverse profi le of the rail. In addition, during the grinding process, only longitudinal risks were formed on the processed surface of the rail, which reduced the effi ciency of metal removal. а b Fig. 1. Railgrinder RShV: a – grinding schematic diagram; b – general view of the grinding equipment Due to the above-mentioned drawbacks and the low effi ciency of the process of bar passive grinding, by the mid 90s this was almost completely replaced by the technology of grinding using “active” working bodies – rotating grinding wheels. But, as it was noted earlier, the RGTs implementing the active grinding technology are signifi cantly limited by the maximum speed of the working movement and require tracks to be closed for the maintenance. As a rule, these trains are used for maintenance and reconstruction grinding. Thus, achieving the preventive grinding of rails was complicated by the lack of appropriate equipment capable of grinding rails at high speeds. With the growing density and speed of freight and passenger transportation, and the development of high-speed transportation, the need for preventive grinding without disrupting train movements has only increased. In this regard, in the early 2000s the German company Stahlberg-Rönsch (SRL) proposed a method of high-speed passive grinding of rails with the periphery of the grinding wheel – High Speed Grinding (HSG). This method to some extent eliminated the disadvantages of the known bar passive grinding [13–14] (hereinafter referred to as the HSG method). Using the HSG method, the upper and lateral working surfaces of the rail head are simultaneously ground using cylindrical grinding wheels. These wheels have the ability to freely rotate around its axis and, using the appropriate corresponding mechanism, are pressed against the rail head at a given angle to the direction of movement. The grinding wheels rotate due to the frictional forces between the surfaces of the rail and the wheel that occur during the longitudinal movement of the abrasive tool (Fig. 2, a). Thus, in the course of spontaneous turning of the grinding wheel, continuous renewal of the working surface of the abrasive tool is ensured and, as a result, its salting loading is excluded [14, 15]. In 2007, SRL built a machine that uses the HSG method. The new RC-01 rail grinding train included 96 grinding wheels (Fig. 2, b) and could grind at speeds up to 80 km/h, while removing a layer of metal with a thickness of about 0.05 mm per pass. At that time, the RC-01 was the fi rst and the only rail grinding train in the world that was used to grind rails without the need to stop train movements on the section of rail and without any disruption to freight and passenger trains schedules. The RC-01 operated on the main lines and high-speed lines of Deutsche Bahn Netz AG [14, 15].
OBRABOTKAMETALLOV TECHNOLOGY Vol. 24 No. 3 2022 Later SRL became a part of the Vossloh group and today the HSG method is its unique technology. Using this technology and the accumulated experience of operating the RC-01 grinding train, Vossloh continued to develop this method and in 2010 manufactured a new rail grinding train – the HSG-2 (Fig. 3). The new machine uses the same HSG method (Fig. 2, a), while the maximum operating speed of the train is increased to 100 km/h [15]. Fig. 2. Railway grinding train RC-01: a – grinding schematic diagram; b – general view of the grinding equipment а b a b Fig. 3. Railway grinding train HSG-2: a – general view of HSG-2; b – general view of grinding equipment HSG-2 Invention of the new grinder made Vossloh the fi rst private company to provide preventive maintenance services for high-speed railway sections in Europe and China. With all these positive aspects, however, the HSG method does have a disadvantage. The main negative side of the passive grinding method with the periphery of the grinding wheel is the need of breaking-in the abrasive tool to the worked transverse profi le of the rail. When the grinding process begins, the grinding wheel has a cylindrical shape and is only in contact with the rail along the rolling surface (Fig. 4,a). As grinding proceeds, the abrasive wheel begins to wear out and takes on the shape of the rail profi le, while the contact of the wheel with the rail increases (Fig. 4,b). With further processing, the abrasive wheel starts to grind both the upper and lateral working surfaces of the rail (Fig. 4, c). Thus, a certain amount of time must pass from the moment the grinding starts to the full breaking-in of the abrasive tool. Considering that the operating speed of the rail grinding train is about 100 km/h, the train passes a signifi cant part of the track on which the rail profi le remains incompletely processed. In addition, it should be noted that the geometry of the transverse profi le of the rail on different sections of the railway track may not be the same, i.e. it can be assumed that under certain conditions, the abrasive wheels may
OBRABOTKAMETALLOV Vol. 24 No. 3 2022 TECHNOLOGY а b c be partially in a state of breaking-in until it is completely worn out. This is especially true for the sections of track of different curvature, descents or ascents, braking or acceleration sections on the processed run. To eliminate this disadvantage of the HSG method, the Siberian Transport University (STU) put forward a method of passive grinding using the end of an abrasive wheel [16]. In the proposed method, the position of grinding wheels in relation to the rail is similar to the method of active processing with rotating grinding wheels used on rail grinding trains of the RGT type (Fig. 5), while the abrasive tool is not driven by an electric engine and is freely fi xed on the axis of rotation. Fig. 4. The scheme of breaking-in of an abrasive wheel by HSG technology: a – process beginning; b – breaking-in process; c – broken-in tool a b Fig. 5. Grinding equipment of RShP rail grinding trains: a – general view of the grinding equipment RShP; b – scheme of the grinding wheels arrangement along the rail transverse profi le In this case grinding occurs by pressing the end of the abrasive wheel against the surface of the rail being processed and simultaneously installing it with an eccentricity e relative to the corresponding grinding track (Fig. 6), thereby providing passive rotation of the grinding wheel, due to the action of friction forces as the rail grinding train moves linearly [16] (hereinafter referred to as the STU method). An additional advantage of the STU method is the possibility of its implementation on the basis of the existing design of rail grinding trains of the RCP type, as well as the possibility of combining passive and active grinding technologies in one track machine. Assessment of the possibility of applying certain methods of rail processing for given operating conditions should use the existing scientifi c basis of passive grinding, which is currently absent due to its limited
OBRABOTKAMETALLOV TECHNOLOGY Vol. 24 No. 3 2022 applicability. Also the technology of passive grinding of rails is relatively new and is characterized by a small amount of research in this area, and as a result, a limited number of publications, which is confi rmed in the works. Thus, purpose of the studies presented in this paper was to conduct a comparative theoretical analysis of the two methods passive grinding of rails using the HSG and STU methods from the standpoint of the effectiveness of its application in the machining of rails. Theoretical research The effi ciency of the rail grinding process is determined, fi rst of all, by the productivity of the machining process, which in turn is determined by the speed of linear motion of the abrasive tool (the speed of the rail grinding train) and the removal of metal from the surface of the rail. In order to compare the two grinding methods, it is assumed that two grinding trains travel at the same speed. Then the key parameter for assessing effectiveness will be the removal of metal during processing. Here metal removal implies an analogue of the processing allowance, which differs in that, due to the lack of rigidity of the technological system, the amount of metal layer to be removed is determined not by the adjusting size of the technological equipment but by the force of pressing the grinding wheel to the rail [17]. Based on the theory of single grit cutting [18–20], the metal layer to be removed during grinding is determined by the depth of the scratch marks formed by the abrasive grit and by its quantity. In turn, the depth of the scratch marks is determined by the pressing force of the grinding wheel to the surface being processed, and its number is determined by the speed of rotation of the grinding wheel. Thus, the potential productivity of the “passive” grinding methods will be determined by the increasing speed of rotation of a grinding wheel and its torque. Together, these two parameters determine the possible cutting power. In view of the foregoing, in order to determine productivity, a kinematic and force analysis of the two grinding methods was carried out. The following assumptions were made: 1. During the analysis, idealized conditions for the interaction of the grinding wheel with the rail were taken. 2. The movement of the grinding train transmits a force to the grinding wheel through the rail. That is, the impact of the rail on the grinding wheel is considered. 3. The interaction of the grinding wheel with the rail at the point of contact on its periphery is analyzed. At this point, there is a force effect from the movement of the grinding train. 4. The metal cutting coeffi cient is taken as the coeffi cient of friction. The analysis does not take into account the area of interaction of the grinding wheel with the rail. a b Fig. 6. Passive grinding method by STU: a – grinding schematic diagram of; b – formation of eccentricity diagram
OBRABOTKAMETALLOV Vol. 24 No. 3 2022 TECHNOLOGY 5. In the analysis, identical conditions for the implementation of grinding are applied. In comparative calculations, the same values of friction coeffi cients, pressing forces, grinding wheel diameters and grinding train speeds were taken. Taking into account the task, the main focus during the kinematic analysis of the grinding methods is to determine the possible speed of the grinding wheel relative to the speed of movement of the grinding train. To determine the possible range of speeds of the grinding wheels, we shall consider the models of the interaction of the grinding wheel with the rail in the different grinding modes. The models are shown in Fig. 7 (top view). a b Fig. 7. Kinematic interaction schemes of grinding wheels: a – HSG method; b – STU method For the given models, the rotation speed of the grinding wheel will be determined by the following ratios: for the HSG method: cos , c t V V (1) where Vc is the grinding wheel rotation speed, m/s; Vt is the grinding train speed, m/s; α is the angle of rotation of the grinding wheel in relation to the direction of movement (in degrees). for the STU method: cos (2) where φ is the angle that determines the point of contact of the grinding wheel with the rail (in degrees), depending on its shifting in relation to the axis of the rail. cos , e R (3) where e – eccentricity, m (shifting of the grinding wheel axis of rotation in relation to the grinding track (Fig. 6)); R is the radius of the grinding wheel, m (in further calculations, R = 125 mm). Taking into account formula (3), equation (2) will take the following form: . t c V R V e (4)
OBRABOTKAMETALLOV TECHNOLOGY Vol. 24 No. 3 2022 The dependencies (1) and (4) are shown on the diagram in Fig. 8. As it can be seen from the diagrams, in both grinding modes the increase in the grinding wheel speed occurs in proportion to the increase in the grinding train speed. In this case, the rate of change in the speed of the grinding wheel is signifi cantly affected by the angle α for the HSG method and the eccentricity e for the STU method. a b Fig. 8. Dependence of a grinding wheel rotation speed on grinding train speed: a – HSG method; b – STU method The area shaded in gray highlights the possible values of the grinding wheel speed depending on the initial conditions. The graph (Fig. 8, a) shows that in the HSG grinding method, the grinding wheel speed can reach a maximum value of 27.7 m/s at a train speed of 100 km/h and α = 0°. This indicates the rotationrolling of the grinding wheel without slipping. In other words, the chip cutting process will not occur when α = 0° regardless of the speed of the train. Looking at the graph of the STU grinding method (Fig. 8, b) it can be seen that unlike the HSG scheme, a wheel speed of 27.7 m/s is the minimum possible value for the speed of the train moving at 100 km/h and this speed is realized at the maximum eccentricity e, which is equal to the radius of the grinding wheel (e = 125 mm). With a decrease in eccentricity e, the speed of the grinding wheel increases signifi cantly, and at values e close to zero, it can theoretically reach value of 3,500 m/s (beyond the scope of the diagram). Thus, all other things being equal, the STU grinding method initially has a higher grinding wheel speed, which indicates greater possible potential effi ciency of the grinding process. However, a separate kinematic analysis does not give a full picture of the machining process effectiveness. Let’s analyse the force effect on the grinding wheel which occurs during the implementation of the grinding methods under consideration. The diagrams are shown in Fig. 9. The movement of the grinding train transmits the force effect Ft through the rail on the grinding wheel, which in turn consists of the force that drives the grinding wheel into rotation Fr and the force Fg preventing rotation which can be conditionally taken as the force of direct grinding (cutting force). It should be noted that in both cases, the force effect from the grinding train Ft is the same and is determined by the equation: , t F Q (5) where Q is the pressing force of the grinding wheel to the machined surface of the rail head, N; λ is the coeffi cient of interaction of the grinding wheel with the surface of the rail. This coeffi cient is an analogue of the coeffi cient of friction, depending on the properties of the abrasive tool (abrasive grit, material of the abrasive grain, etc.) and the machined surface of the rail. This coeffi cient is determined empirically based on the ratio of the friction force to the reaction of the force when perpendicular to the surface that occurs when the grinding wheel is pressed against the rail. Since we are comparing two grinding methods, the
OBRABOTKAMETALLOV Vol. 24 No. 3 2022 TECHNOLOGY a b Fig. 9. Force interaction of grinding wheels schemes: a – HSG method; b – STU method value of λ is the same for both methods. To simplify further comparative calculations for both grinding graphs it is assumed that λ = 1. Using the graphs shown in Fig. 9a, the constituent forces generated between the grinding wheel and the rail can be determined. For the HSG grinding method, the constituent forces are determined by the following equations: cos cos , r t F F Q (6) sin sin . g t F F Q (7) For the STU method: cos , t r t F e Q e F F R R (8) 2 2 2 2 sin . t g t F R e Q R e F F R R (9) From the above equations (6)–(9), it can be seen that an increase in one of the components of the force leads to a decrease in the second. The ratios of the constituent forces are determined by the angle of α for the HSG method and for the STU method, the angle of φ is determined by the eccentricity e. As an example, let’s calculate all possible ranges of the angle α and eccentricity e using equations (6)– (9). The following values will be used: Q = 500 N and λ = 1, R = 125 mm. The results of the calculations are displayed in the diagrams shown in Fig. 10. Both graphs (Fig. 10) show that there is a point of intersection of the dependences of the force action components Fr and Fg. Those areas of the graphs, where the force Fr, which causes the grinding wheel to rotate, is less than the cutting force Fg, are characterized by the fact that the grinding wheel has less ability to turn. At the same time, the greater the difference in the values of these components of the force, the less
OBRABOTKAMETALLOV TECHNOLOGY Vol. 24 No. 3 2022 the probability of the grinding wheel turning. So, when the angle α is close to 90°, and the eccentricity e is close to zero, the rotation of the grinding wheels is practically eliminated and the process of machining the rail, according to its principle, passes into the usual bar grinding described earlier (Fig. 1). The reverse situation occurs when the value of the force Fr exceeds the value of the force Fg. In this case, the free rotation of the grinding wheel begins to dominate over the process of cutting the metal, and at the minimum values of the angle α and the maximum values of the eccentricity e, the movement of the abrasive tool actually turns into rotation-rolling without turning, in which the machining process does not occur. The point of intersection on the diagrams can be considered as a condition for optimizing the values of the angle α or eccentricity e for the relevant grinding methods, in which the most effi cient machining of the rail surface will be carried out with uniform rotation of the grinding wheel, excluding its salting loading and loss of effi ciency. Based on the condition Fr = Fg, the simultaneous solution of equations (6) and (7) for the HSG method shows that cosα = sinα, which corresponds to α = 45°, which can be considered the best value of the angle of rotation of the grinding wheel. A similar solution of equations (8) and (9) for the STU method shows that the best value of eccentricity e is determined by the dependence: a b Fig. 10. Graphs of variance in components of force action on a grinding wheel at Q = 500 N, λ = 1 and R = 125 mm: a – HSG method; b – STU method
OBRABOTKAMETALLOV Vol. 24 No. 3 2022 TECHNOLOGY 2 , R e (10) with an assumed grinding wheel radius R = 125 mm and e = 88.4 mm. The obtained optimal values of α and e are constant and unalterable, regardless of the values of Q and λ. Looking at the kinematic analysis, we can compare the rotation speed of the grinding wheels for the obtained optimal values α and e (Fig. 8). For example, at a value of α = 45° and a rail grinding train speed of 100 km/h, the grinding wheel speed for the HSG method will be 19.6 m/s. For the STU method, conditions being equal, at a value of e = 88.4 mm the speed of the grinding wheel will be 39.3 m/s, which indicates the potential of the STU method in terms of greater effi ciency of machining. The kinematic and force analyzes of the considered grinding methods performed separately does not allow to fully evaluate the effi ciency of machining processes. In order to compare the results obtained, it is needed to determine the rotation speed of the grinding wheel as a function of the force effect on the abrasive tool. To do this, the law of variation of kinetic energy is used. If the limit is set so that the initial kinetic energy is equal to zero, in other words, the motion begins from a state of rest, then the equation will be as follows: 0 1 , k n k T T A (11) where T is the kinetic energy of the considered system, J; T0 is the initial kinetic energy of the considered system, J; Ak is the work of the k-th force affecting the grinding wheel, J. In general, the kinetic energy for the cases under consideration will be calculated using the formula: 2 2 2 2 , c c mV J T (12) where ωc is the angular velocity the grinding wheel rotation, rad/s; J is the grinding wheel moment of inertia, kg·m2. Omitting the determination of the moments of inertia and angular velocity of grinding wheels, formula (12) will take the following form for the grinding methods under consideration: for the HSG method: 2, c T mV (13) for the STU method: 2 5 4 , c T mV (14) where m is the mass of the grinding wheel in kilograms. From the diagrams (Fig. 9) it can be seen that the work is performed only by the torque of the grinding wheels, which is determined by the following equations: for the HSG method: cos , r M F R Q R (15) for the STU method: . r M F R Q e (16) Thus, the work of the torque of the grinding wheel for both methods will be determined by the equation: , c A M (17)
OBRABOTKAMETALLOV TECHNOLOGY Vol. 24 No. 3 2022 where M is the torque generated by the force Fr when the grinding wheel contacts the surface of the rail, Н·m; φc is the angle of rotation of the grinding wheel in relation to the calculated axis of rotation per time unit t, determined by the angular velocity ωc by the equation: . ñ ñt (18) Taking into account equations (15), (16) and (18), the dependence for determining the work of grinding wheels (17) will take the following form: for the HSG method: cos , A Q V t (19) for the STU method: . c Q eV A t R (20) Substituting equations (13), (14) and (19), (20) for the respective processing methods into equation (11) and solving it with respect to the grinding wheel speed Vc, we obtain: for the HSG method: cos , c Q V t m (21) for the STU method: 4 5 . c Q e V t mR (22) The obtained dependencies make it possible to take into account the force and kinematic components of the considered processes of passive rail grinding and to assess its effectiveness for a fi rst approximation. Results and its discussion The obtained dependencies (21) and (22) for the previously determined optimal values of α = 45° and e = 88.4 mm are calculated taking all other conditions remaining equal: the range of variation of pressing force Q from 100 to 1,000 N, m = 10 kg, λ = 1. The results of the calculations are shown in diagram in Fig. 11. The diagram (Fig. 11) shows that with the same pressing force of the grinding wheel to the rail Q, the effective operation speed according to the HSG method is 20 % higher than the speed that occurs with the STU method. For example, at Q = 450 N, the effective operation of the grinding wheel with the HSG method will be achieved at Vc = 31.8 m/s, and with the STU method at Vc = 25.5 m/s. Thus, it can be concluded that at equal values of Q, the performance of the HSG method is 20 % higher than that when using the STU method. It should be noted that in accordance with the kinematics of the processing process, at the same speed of the grinding train, the possible speed of the grinding wheel according to the STU method is almost 2 times higher than the speed of the wheel according to the HSG method. Thus, at a train speed of Vt = 100 km/h, the maximum possible grinding wheel speed for the HSG method is Vc = 19.6 m/s, and Vc = 36.3 m/s (Fig. 8) for the STU method. Therefore, the passive grinding technology implemented by the HSG method will initially be limited by the maximum achievable grinding wheel speed and the corresponding pressing force. In the graph (Fig. 11), the area of possible values of Vc and Q for the HSG method are shown in dark gray. In this case, using the STU method, both the rotating speed of the grinding wheel and the pressing force it exerts have a wider range of variation and, as a consequence, there is a greater possibility of increasing the removal of metal. The light gray area, shown on the diagram, is the range of possible values of Vc and Q for t he STU method. These areas are an example of a grinding train moving at a speed of 100 km/h. In general, the results of theoretical studies correlate with the obtained experimental data presented in [21, 22].
OBRABOTKAMETALLOV Vol. 24 No. 3 2022 TECHNOLOGY Fig. 11. The dependence of a grinding wheel rotation speed on the force of its pressing against rail at optimal values α = 45° and e = 88.4 mm: 1 – STU method; 2 – HSG method Conclusion The theoretical analysis of two methods of passive grinding of rails using grinding trains allows drawing the following conclusions: 1. The technology of passive grinding, implemented by the HSG method, has a higher productivity and energy effi ciency of the machining process in comparison with the STU method due to the higher rotation speed of the grinding wheel with equal forces of pressing it to the rail. 2. The STU passive grinding method is distinguished by a wide range of changes in both the rotation speed of the grinding wheel and its pressing force. This makes it possible, at the same speeds as the HSG method, to achieve a higher speed of grinding the rail surface and to achieve greater metal removal due to a stronger pressing of the grinding wheel to the rail. 3. The presented approach makes it possible to form a database of optimal modes for passive grinding of rails, on the basis of which it is possible to carry out a well-reasoned choice of pressing forces of the grinding wheel to the rail based on the required metal removal and the specifi ed speed of the grinding train. 4. The analysis carried out is of an idealized nature, which does not take into account a number of signifi cant parameters that have a signifi cant impact on both the physical processes of interaction between the grinding wheels and the rail, and the machining process itself. At the same time, it gives a general comparative idea of the effi ciency and possible productivity of the passive grinding methods under consideration. 5. A promising direction for further research in the fi eld of passive grinding of rails is to expand the theory of interaction of grinding wheels with a rail by including in the mathematical model such parameters as the contact area of the grinding wheel with the rail, the structure and grain size of the abrasive tool, and metal removal. The experimental and theoretical determination of the numerical values of the coeffi cient of interaction of the grinding wheel with the rail λ can also be considered a key task. References 1. Jeong W., Hong J., Kho H., Lee H. Rail surface quality analysis according to rail grinding on operational railway track. Journal of the Korean Society for Railway, 2021, vol. 24, iss. 10, pp. 852–860. DOI: 10.7782/ JKSR.2021.24.10.852. 2. Lundmark J. Rail grinding and its impact on the wear of wheels and rails. Licentiate Thesis, 2007. Available at: https://www.diva-portal.org/smash/get/diva2:990239/FULLTEXT01.pdf (accessed 03.08.2022).
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