4-06 T R I B O L O G I A Henryk BĄKOWSKI * THE INFLUENCE OF SOLID LUBRICANTS USED FOR THE LUBRICATION OF WHEEL FLANGES ON RAILWAYS TO REDUCE THE CORROSION OF RAILS WPŁYW WYBRANYCH SMARÓW STAŁYCH STOSOWANYCH DO SMAROWANIE OBRZEŻY KÓŁ KOLEJOWYCH NA POWSTAWANIE ZJAWISKA KOROZJI W SZYNACH KOLEJOWYCH Key words: wear, solid lubricant, corrosion, rail steel Słowa kluczowe: zużycie, smar stały, korozja, stal szynowa Abstract The paper presents the influence of selected solid lubricants used for the lubrication of wheel flanges of railways on the formation and development of corrosion. Tested solid lubricants consisted primarily of graphite, molybdenum disulphide, and soybean oil additives. Moreover, grease sticks were selected to make it possible to compare and evaluate their suitability in applying the * Silesian University of Technology, Faculty of Transport, ul. Krasińskiego 8, 40-09 Katowice, Poland, e-mail: henryk.bakowski@polsl.pl.
T R I B O L O G I A 4-06 lubrication of railway wheels. The study is based on the European standard that allows the determination of wear in the test samples to determine the advantages in relation to the processes of corrosion. INTRODUCTION Lubrication of wheel flanges and rails greatly reduces operating costs associated with the wear of rails. The contact surface has a permanent change depending on many factors, either structural or operational. As a result of the overlapping of these factors, the problem of the stability of the surface layer, particularly the running surface of rails, remains a major problem. To improve the conditions for cooperation with the rail and wheels, especially when driving rolling stock in curves with a small radius (cross slides), lubrication is used in places most exposed to abrasive wear. Lubrication is used only at the lateral contact of the wheel flanges of the inner surface of the railhead (Fig. ), which is a way of using lubricant to prevent the penetration of the surfaces of rolling wheels and rails. This is important in order not to reduce the adhesion of wheels and rails on the surfaces that develop a tractive force and a friction force during braking. Depending on the profile of the railway, the intensity wheel flange wear on the locomotive varies. Research conducted by various railway managements have shown that locomotives without lubricating devices that support lines with a difficult profile have less mileage between repairs of the railway rim of 8000 to 35000 km. After the introduction of these devices to lubricate locomotive wheels under the same operating conditions, there is a 3 fold increase in the course of repairing between the sets of wheels. Thus, the durability of the railway rim is improved up to a factor of three. An additional profit from the use of lubrication is to reduce the wear of rails. On lines rich in curves with small radii the durability can be improved by a factor of two [L. ]. Fig.. Areas of lubrication and the acceptable wear limit of the railway wheel Rys.. Obszary smarowania i dopuszczalnego zużycia koła kolejowego The advantages of equipment for railway flange lubrication on locomotives are as follows [L. ]: Saving high-alloy steels (up to 80%) and the rails,
4-06 T R I B O L O G I A 3 Reducing the labour intensity while maintaining wheel sets (rarer repairing), Reducing downtime of traction vehicles in repair sheds and repair shops for replacement and rolling the railway rim, Energy savings from 5% to 5%, Reducing the resistance to motion from which flows saving electricity or fuel, Taking care of the environment by reducing noise, The application of biodegradable measures, Low self-weight equipment, Intelligent electronic control for easy adaptation to different requirements, Reducing the cost of maintaining railroads (replacement of rails), Limiting the time of track closures for the replacement of rails, and Improving safety against derailment. The European Standard 608 gives requirements for the lubricants for the lubrication of cooperating contact surfaces between the wheel rim and the edge of the rail (active surfaces) used both directly and indirectly on the rim of the wheel or rail in order not to exceed the permissible levels of friction and wear. PN-EN 608 provides a comparison of the operation of stick greases and determines which one has better lubricity, corrosion resistance, and can maintain a low coefficient of friction for a longer period. MATERIAL, EQUIPMENT AND TEST CONDITIONS Corrosion testing was carried out in accordance with Polish and European standards [L. 3 6]. They use a special container made of stainless steel, into which is inserted a sample made of steel with a pearlitic structure. Samples were prepared in accordance with PN-84/H-0433 (Fig. 3). On the rolling surface of the samples, a layer of grease was applied in accordance with PN-EN 608 (Fig. ). Fig.. The method of mounting the applicator for solid lubricants used in the real object, i.e. in a wheel-rail system Rys.. Sposób zamocowania aplikatora dla smarów stałych wykorzystywanego w obiekcie rzeczywistym, tj. w układzie koło-szyna
4 T R I B O L O G I A 4-06 An applicator used a grease tray on a real wheel-rail system that pushes the grease onto the wheel flanges of the railway (Fig. ). This was to reflect the actual conditions of contact during testing. The force that the applicator with lubricant is pressed against to roller made of steel with a pearlitic structure was 7 N. a) b) Fig. 3. A view of the roller surface before applying the lubricant (a) and after the application of lubricant (b) Rys. 3. Widok powierzchni rolki: przed naniesieniem smaru (a) i po naniesieniu smaru (b) In studies of corrosion resistance, a special container with heating chamber and the mixer was used (Fig. 4). Duration was 4 hours at 60 ± C. Studies were carried out in the presence of distilled water and in synthetic seawater with double repetition, according to the standard ISO 70: 0. a) b) c) Fig. 4. Elements of the test system: a) heating the container, b) a container for the test, c) a mixer Rys. 4. Elementy układu badawczego: a) pojemnik grzewczy, b) pojemnik do badań, c) mieszadło
4-06 T R I B O L O G I A 5 For the solid lubricants, the addition of soy, graphite, and molybdenum disulphide were used (Fig. 5). a) b) c) Fig. 5. Sticks of solid lubricants used in the study: a) with the addition of soy, b) a graphite additive, c) containing molybdenum disulphide Rys. 5. Sztyfty smarów stałych wykorzystywanych w badaniach: a) z dodatkiem soi, b) z dodatkiem grafitu, c) z dodatkiem dwusiarczku molibdenu To determine the corrosion resistance, a metallographic examination was performed. The surface condition was evaluated after the tribological tests using quantitative image analysis (Fig. 6). Fig. 6. A sample image of the analysed surface after the anti-corrosion studies using a Met-Ilo program for quantitative metallographic analysis. Rys. 6. Przykładowy obraz analizowanej powierzchni po badaniach przeciwkorozyjnych z wykorzystaniem programu Met-Ilo stosowanego do ilościowej analizy metalograficznej
6 T R I B O L O G I A 4-06 A solution was prepared of synthetic seawater with the chemical composition presented in Table. Table. The chemical composition of the synthetic seawater [L. 3] Tabela. Skład chemiczny syntetycznej wody morskiej [L. 3] Salt NaCl MgCl 6H O NaSo 4 CaCl KCl NaHCO 3 KBr H 3 BO 3 SrCl 6H O NaF Concentration, g/l 4.54.0 4.09.6 0.69 0.0 0.0 0.03 0.04 0.003 RESULTS The test results of anticorrosion properties are presented in Figure 7. a) Tests in the distilled water Test in the synthetic sea water b)
4-06 T R I B O L O G I A 7 c) Fig. 7. The surface of samples of steel with a pearlitic structure after the anticorrosion test: corrosion layer, metallic surface Rys. 7. Powierzchnia próbek ze stali o strukturze perlitycznej po badaniach przeciwkorozyjnych: warstwa korozji, powierzchnia metaliczna The results of the participation of the individual components (a/b metal/corrosion) are presented in Table. Table. Anticorrosion test results of metallic surfaces with selected solid lubricants in a different environment. Tabela. Wyniki badań antykorozyjnych powiezrchni metalicznej z naniesionym smarem stałym w różnym środowisku Grease with the addition of Water Environment Synthetic sea water soybean oils 73.86/6.4 4.40/58.60 graphite 38.85/6.5 0.93/89.07 molybdenum disulphide 7.40/9.60.98/98.0 a/b the percentage of metallic/percentage of the surface covered with corrosion. CONCLUSIONS Comparative studies on the anticorrosive properties of solid lubricants with the addition of soybean oils, graphite, and molybdenum disulphide were carried out in a neutral environment (in distilled water) and corrosive environments (in synthetic seawater). Based on quantitative metallographic analysis, it was found that steel with a pearlitic structure coated solid lubricant with the addition of soybean oil (just over 6% of the surface corrosion in an aqueous medium, and approx. 58% corrosion in aggressive environments) had greater corrosion resistance. In addition, a metal surface coated with a solid lubricant containing molybdenum disulphide (more than 90% coverage of oxides of corrosion in both environments) was the most vulnerable to corrosion. This is due to
8 T R I B O L O G I A 4-06 electrochemical activity in contact with the steel surface, which accelerates the development of corrosion. REFERENCES. Reddy V., and others: Modelling and analysis of rail maintenance cost Int. J. Production Economics 05 (007), 475 48.. Wójtowicz A., Bąkowski H.: Oszczędności wynikające ze smarowania obrzeży kół w łukach o różnym promieniu. TTS Tech. Transp. Szyn. nr /3, 03, 58 6. 3. PN-ISO 70:0. Przetwory naftowe i środki smarowe Oleje naftowe i inne płyny Oznaczanie właściwości przeciwkorozyjnych w obecności wody. 4. PN-ISO 007:00. Przetwory naftowe i środki smarowe Badanie właściwości przeciwrdzewnych smarów plastycznych. 5. PN-C-0443:956. Przetwory naftowe Smary stałe Badanie odporności na utlenianie. 6. PN-55/C-04079. Przetwory naftowe. Smary stałe. Badanie zdolności chronienia metali przed korozją. Acknowledgements Special thanks I would like to express the company PROMOTION Andrzej Wojtowicz, Rajec Poduchowny 5 C, 6-63 Radom for providing research materials (sticks of solid lubricants) and financial support. Streszczenie W pracy przedstawiono wpływ wybranych smarów stałych stosowanych do smarowania obrzeży kół kolejowych na powstawanie i rozwój zjawiska korozji. Badane smary stałe składały się z przeważającej części z grafitu, dwusiarczku molibdenu i soi. Dobór sztyftów smarów stałych podyktowany był względami ekonomicznymi i tribologicznymi, bowiem tylko takie są obecnie stosowane na smarowanie obrzeży kół kolejowych przez sekcje eksploatacji poszczególnych przewoźników na PKP. Sztyfty ponadto zostały tak dobrane, aby umożliwiły porównanie i ocenę ich przydatności w stosowaniu do smarowania kół kolejowych. Badania przeprowadzono w oparciu o normę europejską pozwalającą na określeniu zużycia badanych próbek w atmosferze sprzyjającej procesom korozji.