the influence of solid lubricants used for the

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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, 40-019 Katowice,
Poland, e-mail: [email protected].
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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. 1), 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 2–3 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. 1].
Fig. 1. Areas of lubrication and the acceptable wear limit of the railway wheel
Rys. 1. Obszary smarowania i dopuszczalnego zużycia koła kolejowego
The advantages of equipment for railway flange lubrication on locomotives
are as follows [L. 2]:
– Saving high-alloy steels (up to 80%) and the rails,
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– 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 15%,
– 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 16028 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 16028 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-04332 (Fig. 3). On the rolling surface of
the samples, a layer of grease was applied in accordance with
PN-EN 16028 (Fig. 2).
Fig. 2. The method of mounting the applicator for solid lubricants used in the real object,
i.e. in a wheel-rail system
Rys. 2. Sposób zamocowania aplikatora dla smarów stałych wykorzystywanego w obiekcie
rzeczywistym, tj. w układzie koło-szyna
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An applicator used a grease tray on a real wheel-rail system that pushes the
grease onto the wheel flanges of the railway (Fig. 2). 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
17 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 24 hours at 60 ± 1°C. Studies
were carried out in the presence of distilled water and in synthetic seawater with
double repetition, according to the standard ISO 7120: 2011.
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
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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
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A solution was prepared of synthetic seawater with the chemical
composition presented in Table 1.
Table 1. The chemical composition of the synthetic seawater [L. 3]
Tabela 1. Skład chemiczny syntetycznej wody morskiej [L. 3]
Salt
NaCl
MgCl2·6H2O
Na2So4
CaCl2
KCl
NaHCO3
KBr
H3BO3
SrCl2·6H2O
NaF
Concentration, g/l
24.54
11.10
4.09
1.16
0.69
0.20
0.10
0.03
0.04
0.003
RESULTS
The test results of anticorrosion properties are presented in Figure 7.
Tests in the distilled water
Test in the synthetic sea water
a)
1
1
2
2
b)
2
1
1
2
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c)
1
2
2
1
Fig. 7. The surface of samples of steel with a pearlitic structure after the anticorrosion test:
1 – corrosion layer, 2 – metallic surface
Rys. 7. Powierzchnia próbek ze stali o strukturze perlitycznej po badaniach przeciwkorozyjnych:
1 – warstwa korozji, 2 – powierzchnia metaliczna
The results of the participation of the individual components (a/b –
metal/corrosion) are presented in Table 2.
Table 2.
Anticorrosion test results of metallic surfaces with selected solid lubricants in
a different environment.
Tabela 2. Wyniki badań antykorozyjnych powiezrchni metalicznej z naniesionym smarem
stałym w różnym środowisku
Grease with the addition of
soybean oils
graphite
molybdenum disulphide
Environment
Water
73.86/26.14
38.85/61.15
7.40/92.60
Synthetic sea water
41.40/58.60
10.93/89.07
1.98/98.02
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 26% 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
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electrochemical activity in contact with the steel surface, which accelerates the
development of corrosion.
REFERENCES
1.
2.
3.
4.
5.
6.
Reddy V., and others: Modelling and analysis of rail maintenance cost Int. J. Production Economics 105 (2007), 475–482.
Wójtowicz A., Bąkowski H.: Oszczędności wynikające ze smarowania obrzeży
kół w łukach o różnym promieniu. TTS Tech. Transp. Szyn. nr 2/3, 2013, 58–61.
PN-ISO 7120:2011. Przetwory naftowe i środki smarowe – Oleje naftowe i inne
płyny – Oznaczanie właściwości przeciwkorozyjnych w obecności wody.
PN-ISO 11007:2010. Przetwory naftowe i środki smarowe – Badanie właściwości
przeciwrdzewnych smarów plastycznych.
PN-C-04143:1956. Przetwory naftowe – Smary stałe – Badanie odporności na
utlenianie.
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 152 C, 26-613 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.