Janusz JANECKI, Jolanta DRABIK, Marek WOLSZCZAK, Zbigniew PAWELEC – Institute for Sustainable
Technologies, National Research Institute, Radom, Poland
Please cite as: CHEMIK 2013, 67, 4, 309-316
Introduction
The studies on the application of regenerating materials and / or
structural polymer composites as an alternative to metal engineering
materials have been conducted for many years. The results of
such studies were published in many papers, of which the most
important are, among other things, the papers written by: J. Broś [1],
J. Janecki [2], R. Marczak and S. Zawalski [3], J.M. Warda [4] and
J. Sikora [5]. Attempts to employ adequate composites based on
polymers in the regeneration processes of worn machine parts
have produced good results, whereas the fact those mechanical
properties of polymer composites are worse than the properties
of metals used to produce the regenerating part somehow limit
a wider range of their application. S. Banaszkiewicz [6], J. Szumniak
[7, 8] and S. Zawalski [9] were involved in works on the effect
of fillers on tribological properties of composite friction materials.
An important issue that requires a particular consideration is a fact
that the loads of friction nodes favour an increase in temperature,
which then requires the maintenance of lubrication stability at
higher temperatures, e.g. by introducing proper additives resulting
in reduced friction and thus, temperature drop [10]. The papers
on modifying tribological properties of composites indicated, inter
alia, that a composite with solid lubricant additives had better
tribological properties than the composites without such additives
[11 ÷ 13]. The changes in tribological properties and the degree
of wear of a composite produced from phenol formaldehyde
resin by adding TiO2 nanopowder were described in the paper of
F.-H. Su et al [14]. On the other hand S. S. Kim et al. used additives
demonstrating self-lubricating properties in composites based on such
a type of resin which additionally was characterized by the increased
thermal resistance. The used additives counteracted seizing of
co-operating mechanical elements [15].
The surface layer of co-operating elements is destroyed as
a result of a series of complex phenomena leading to the lack of its
cohesion, scaling or mass decrements. The destruction of surface
layers in slide bearing depends mainly on the mutual velocity of
rotating parts and the load value. For such machine parts, the
degree of their wear depends on the temperature which adversely
influences the non-homogeneous, previously regenerated, surfaces
by reducing their operation period [2, 4, 13]. Regardless of the
fact whether the durability of the surface layer was reduced as
a result of the process of their natural wear, the faults in design
or operational forces, it resulted in the damaged surface. Such
changes are irreversible. However, their scope and occurrence
intensity can be reduced as well as an attempt can be made
to define a set of factors that decide on their significance, and
to determine the area enclosed within boundary values describing
operational strength of surfaces prone to abrasion. The above issue
is connected with establishing criteria that are used to perform such
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assessments following the determination of significant operational
features. The faced difficulty lies in ambiguous indicators for
assessing operational systems, for which the wear of machine
parts is observed and which require the renovation by replacing
or regenerating [4].
As part of the performed research [17, 21, 22], the authors
assumed that functional properties determined on the basis of
tribological tests, were reliable indicators to assess the operational
suitability of friction elements made of composite materials.
Such test conditions as slide velocity of co-operating surfaces,
loading and a temperature reached in the friction process,
a type of lubrication considerably affect the condition of the surface
layer of co-operating parts. For slide bearings with parts made of
polymer materials, an adequate selection of a lubricant, inter alia,
to avoid the impact of operational pollution which, with respect
to composite materials, clearly affects the wear of a machine part and
often results in the catastrophic degree of wear. Taking into account
the above, while developing the composition of composite materials
intended for parts of a sliding pair operating under the conditions of
technical dry friction, plastic grease [16, 19, 20] was used as one of
the components of metal-polymer composite [17].
This solved the problem of lubricating a sliding pair of composite
material – steel, while only plastic grease contained in the composite
material was used for lubrication. The tribological tests confirmed
the positive impact of plastic grease in the composite on the wear,
in comparison to the specimen of analogical composite without
such grease [17].
This paper presents the results from experimental tests related
to the analysis of the surface layer of metal-polymer composites
with plastic grease additive and without it, after performing
tribological tests under the conditions of technical dry friction. In
these tests, the wear of tested composites was determined on the
basis of friction – wear characteristics, and the surfaces after their
testing were assessed regarding element composition employing the
method of scanning electron microscope SEM and energy dispersive
spectrometry EDS.
Experimental part
Methodology
The tribological tests were conducted on a stand type T-05
[18] in a roller–block friction pair representing the real pin-bearing
system in the slide bearing (Fig. 1). A distributed contact created
by a rotating roller and a block pressed against the roller was
a parameter characteristic for the friction node. The experiments
were performed under the conditions of variable sliding velocity
within the range of 0.1 m/s – 0.4 m/s under the constant unit
pressure of 6 MPa. A block made of the tested composite material
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Tribological tests in the system of steel-composite
made of phenol formaldehyde resin and the analysis
of the effect of plastic grease in resin on the state
of surface layer
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was the specimen, and a roller made of bearing steel 100Cr6 (ŁH15)
of the hardness of 56-60 HRC was the counter specimen. For each
pair, three research courses were performed.
Table 1
Physical, chemical and lubricating properties of FS 1265 oil
and F plastic grease [20]
a)
Properties
Method
Result
Properties of fluorosilicone oil
Molecular formula of FS oil 1265 (C4H7F3OSi)n
poly [methyl (3,3,3-trifluoropropyl) siloxane
Kinematic viscosity at 100°C, cST
PN-EN ISO 3104:2004
74
PN-ISO 2909:2009
>220
PN-EN ISO 1516:2003
304
Flow temperature, °C
PN-ISO 3016:2005
-40
Welding load, kG
PN-C-04147:1976
160
Flaw diameter d, mm
PN-C-04147:1976
0.63
Viscosity factor, VF
Ignition temperature in a closed pot, °C
b)
Properties of F plastic grease
a block made of a composite material
a roller made of bearing steel
Fig. 1. Photo of a) a stand type T-05 and friction node – association
of a friction pair of roller-block type and b) a shape and dimensions
of the specimen (composite block) and the counter specimen (a roller
made of steel 100Cr6)
The composite materials were prepared on the matrix
of a thermosetting moulding compound FSzG-2 s– a mixture of
phenol formaldehyde resin of novolac type, and fillers, which is
usually used in the production of technical products of low friction
coefficient (Fig. 2).
Dropping point, °C
PN-ISO2176:2011
230
Penetration, 10-1 mm
PN-ISO 2137:2011
245
Consistency class acc. to NLGI
PN-ISO 2137:2011
3
Flaw diameter d, mm
PN-C-04147:1976
0.98
Welding load, kG
PN-C-04147:1976
500
The tests on friction and wear of the prepared composite
materials were carried out on a tribological stand type T-05 under
the conditions of technical dry friction. During the test, the specimen
temperature and friction force were recorded, and after completing
the test, the worn mass was determined and the friction coefficient
was calculated (Tab. 2).
Table 2
Conditions for tribological tests [17]
Test conditions
Pin-bearing sliding pair
Velocity, m/s
Fig. 2. General formula of novolac resin
Metallic filler – Fe metal powder of type NC 100 24 of Höganas
company (FN specimen) and 1% m/m of plastic grease (FN 1S
specimen) were added to the powdered moulding compound
to obtain the specimens of composite materials. As part of research
works performed in the Institute for Sustainable Technologies
– National Research Institute , a high-temperature plastic grease
was developed using DOW CORNING® fluorosilicone oil
FS 1265 and Aerosil® type silica thickener [20]. It was characterized
by very developed specific surface and high thermal stability. Some
of the properties of base oil and the produced plastic grease are
presented in Table 1.
For the purpose of obtaining the composite material, after
thorough mixing of the components, pressing process using
a hydraulic press PHM-100 was conducted according to the
developed procedure at a temperature of 160oC and at a pressure
of 10 MPa [17]. Using mechanical working, blocks intended for
frictional co-operation with the roller made of bearing steel were
cut out from the obtained moulded pieces (Fig. 1 b).
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Determined parameters
Distributed contact
0.1
0.2
0.3
Friction distance, m
2400
Unit pressure, MPa
6
Type of lubrication
during tests:
0.4
• Friction force, N
• temperature of friction node, oC
after tests:
• worn mass of the specimen, g
without external
• friction coefficient
lubricant (technical dry)
The surface layer of the composite specimen was subjected to the
analysis of X-ray radiography using the SEM/EDS technique before
and after the tribological tests. The measurements were performed
to test the changes in the content of carbon, oxygen, iron and silicon
in the friction traces of the composite surface layer depending on the
conditions of the tribological test [17].
The Noran energy dispersive X-ray (EDS) microanalyser with
Norvar window, SiLi crystal and the resolution of 133eV, electronically
coupled to the Hitachi scanning electron microscope (SEM) S 2460N
with the option of conducting tests in rough vacuum range, was
employed to identify elements present in the area of friction trace. Linear
scanning of friction traces was performed at a 40-fold enlargement, at
an accelerating voltage of 15 kV and a detection angle of 25o under the
conditions of high vacuum.
Discussion on results
The tribological tests showed that adding plastic grease to the
metal-polymer composite affected the stabilisation of the tribosystem
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Fig. 3. Effect of sliding velocity on the change in friction coefficient in
tests performed under constant pressure of 6 MPa (FN – specimen
of phenol formaldehyde resin composite with lubricant,
FN 1S – specimen of phenol formaldehyde resin composite
containing 1% by weight of plastic grease)
On the basis of the obtained results, it was found that the
dependence of friction coefficient in the function of sliding velocity
was non-linear. For FN specimens at the velocities of 0.2 and 0.3 m/s,
the friction coefficient was created at a lower level when compared
to its values obtained at the velocities of 0.1 and 0.4 m/s. However,
adding 1% of plastic grease to that composite caused that the friction
coefficient was stabilised within the range of tested velocities.
After completing the tribological tests conducted at a variable
velocity within the range from 0.1 to 0.4 m/s and under the constant
unit pressure of 6 MPa, the worn mass of the specimens were
assessed (Fig. 5).
An increase in sliding velocity under the constant unit pressure,
under the conditions of technical dry friction deteriorated the
wear resistance of the FN metal-polymer composite. At increased
velocities, the clear increase in worn mass of the FN specimen
was observed. Adding the plastic grease to the composite (FN 1S
specimen) resulted in reduced worn mass of the specimen, and
this reduction was distinct. The greatest difference in worn mass
for the assessed composites was found at the sliding velocity of
0.3 m/s. Under such conditions, worn mass of the FN 1S specimen
was considerably reduced by ca. 40% when compared to the FN
specimen (Fig. 5). The determined characteristics of friction and
wear confirmed the positive impact of the plastic grease contained in
the metal-polymer composite on the conditions of the co-operation
of composite-steel pair.
After performing the tribological tests, the surface layer of
the composite was assessed to observe any impact of the test
conditions on changes in the material structure. The tests consisted
in analysing element composition of the composite surface layer in
the area of visible friction traces. Fig. 6 illustrates the exemplary test
results for deposits formed on the composite surface following the
friction process taking place under the pressure p = 6 MPa and the
velocity v = 0.3 m/s.
a)
c)
e)
b)
d)
f)
Fig. 4. Effect of sliding velocities on the change in temperature
recorded during tribological tests performed under the constant
pressure of 6 MPa
The temperature in the friction node recorded during the
tribological tests was increasing as the velocity, both for FN and FN
1S composites, was increasing. It was observed that the presence
of lubricant in the composite provided better conditions for the cooperation of the FN 1S composite – steel pair, which reduced the
temperature in the friction node.
Fig. 5. Effect of sliding velocities on the change in the specimen wear
after performing tribological tests under the constant pressure of 6 MPa
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Fig. 6. Surfaces of composite wear scars subjected to energy
dispersive X-ray (EDS) analysis following the friction process: a,
b) SEM images of FN and FN 1S specimens respectively; c, d)
images of oxygen atoms distribution in FN and FN 1S specimens
respectively; e, f) images of silicon atoms distribution in FN
and FN 1S specimens respectively
Depending on the test conditions, the intensity of signals and the
percentage content of tested elements were changing in the surface
layers of the tested composites FN and FN 1S (Fig. 7). The conducted
SEM/EDS analysis of the surface layer of FN 1S composite following
the friction under the conditions of various sliding velocities confirmed
that signals indicating the presence of such elements as oxygen and
silicon in the surface layer probably came from the components of the
plastic grease used as the composite modifier. The obtained results
indicated that lubricants were absorbed in friction traces, which directly
influenced the reduction in friction coefficient and in the temperature of
the sliding pair of steel–FN 1S composite and thus, its wear resistance
increased under the test conditions (Figs 3÷5).
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operation within the whole range of the conducted tests; both the
temperature and friction force was created at a lower level than for the
composite (FN) without the lubricant additive (Figs 3, 4).
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Fig. 7. Results from the energy dispersive X-ray analysis of surface
layers of FN and FN 1S composites after conducting tribological
tests at various velocities (0.1–0.4 m/s) and under the constant unit
pressure of 6 MPa
The obtained results were used to identify the content of carbon,
iron, oxygen and silicon in the surface layer. Carbon, iron and oxygen
could originate from the components of FN composite, whereas
the increased content of silicon and oxygen could only come from
the plastic grease contained in the FN 1S specimen. During the tests
carried out under the conditions of technical dry friction, it was also
found that the surface layer of the composite containing lubricant was
changing the co-operation conditions of the composite-steel pair. On
the basis of the X-ray analysis of friction traces,improved conditions for
the co-operation and the smaller worn mass of the tested specimen
were observed as the content of elements present in the surface layer
and originating from the plastic grease was increasing (Fig. 7).
Under the experimental conditions, adding the plastic grease to the
friction surface was likely to release grease dispergated in the composite,
which effectively protected the surface layer against wearing.
Summary
By conducting the tribological tests at the constant load and at
various sliding velocities, it was found that the co-operation conditions
of friction elements in polymer composite – steel system were improved
by adding the plastic grease to the polymer – steel composite. The
performed tests demonstrated that the increase in sliding velocity
considerably influenced the change in the friction coefficient and the
temperature in the friction node, and at the same time it influenced the
degree of wear of the tested composite materials.
The analysis of the surface layer of the specimen, after performing
the tribological tests, showed that the increase in wear resistance of
the composite containing the plastic grease can be assessed on the
basis of the quantity and intensity of signals characteristic for silicon
and oxygen, originating from the oxosilane group of the plastic grease
present in the phenol formaldehyde resin, which were identified in
the energy dispersive X-ray spectrum. An increase in the content of
these groups in the surface layer of the FN 1S composite indicated that
the self-lubricating layer resistant to the wear process was properly
shaped and thus, this layer had a positive impact on the co-operation
conditions of the sliding pair of polymer composite – steel.
This research work has been financed from the Polish science budget for years 2010‒2012
– Project No. N N508 481138.
Literature
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Programu Strategicznego pn. „Innowacyjne systemy wspomagania technicznego zrównoważonego rozwoju gospodarki” w Programie Operacyjnym Innowacyjna Gospodarka”. ITE-PIB Radom, 2010-2014.
Janusz Tytus JANECKI – (Sc.D., Eng), Full Professor obtained a university
degree in 1954. He obtained an academic degree of doctor in 1961, and
habilitated doctor of technical sciences in the field of tribology in 1969. He was
awarded the title of the Associate Professor in 1972, and the title of the Full
Professor in 1984. Professor J.T. Janecki is a member of the Polish Tribology
Society, a full member of the Academy of Engineering in Poland, a member
of the European Materials Research Society in Strasbourg, an honorary
member of the Russian National Committee of Tribology, the laureate of
many departmental and university distinctions, including the distinctions of
the Poznań University of Technology and Military University of Technology
(WAT). Professor J. T. Janecki is a researcher at the Institute for Sustainable
Technologies – National Research Institute in Radom. He is the author and
co-author of over 250 Polish and foreign publications, a co-author of many
papers and announcements presented at the conferences, a co-author of
monographs, patents and patent applications.
Jolanta DRABIK - Ph.D., (Eng)g., graduated from the Faculty of Chemistry
and Chemical Technology at the University of Technology and Agriculture
in Bydgoszcz in 1981. She has been working in the Institute for Sustainable
Technologies – National Research Institute in Radom since 1990, currently as
an assistant professor. She was granted the degree of Doctor at the Air Force
Institute of Technology in Warsaw in 1995. She is the author and co-author
of 127 Polish and foreign publications, 45 papers and announcements and
10 posters presented at the national and international conferences, a coauthor 9 of patents and 8 patent applications.
email: Jolanta.Drabik@itee.radom.pl
Marek WOLSZCZAK – Eng., graduated from the School of Engineering
in Radom in 1981. He has been working in the Institute for Sustainable
Development – National Research Institute in Radom since 1986. He is
co-author of 12 papers, 2 patents and studies elaborated on the basis of
scientific and research works. Research interests: materials for the recovery
of machines and equipment, pro-ecological technologies and equipment for
the production, operation and utilisation of operational fluids.
Zbigniew PAWELEC – Ph.D,. (Eng), graduated from the Faculty of
Materials Science at the Radom University of Technology. In 1998, he was
granted the degree of Doctor in the field of construction and operation
of machines, specialisation in tribology, at the Military Institute of Armour
and Car Technology (WITPiS). He works at the Institute for Sustainable
Technologies – National Research Institute in Radom, currently as an assistant
professor. He is the author and co-author of 60 papers on the composition
and operational properties of materials containing a polymer matrix, and a
co-author of 4 patents and 2 patent claims.
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