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Proceedings of the 6th International Conference on Mechanics and Materials in Design,
Editors: J.F. Silva Gomes & S.A. Meguid, P.Delgada/Azores, 26-30 July 2015
-1961-
PAPER REF: 5746
ROLLING BEARING WEAR IN WIND TURBINES
Beatriz Graça1(*)
, Ramiro Martins1, Jorge Seabra
2
1Institute of Science and Innovation in Mechanical and Industrial Engineering (INEGI),
University of Porto, Porto, Portugal 2Faculdade de Engenharia (FEUP), University of Porto, Portugal (*)Email: [email protected]
ABSTRACT
This work focus the important information carried out by the wear particles that are present in
a lubricant sample. This information reveal the wear condition of the rolling bearings
providing effective means to increase reliability and availability of wind turbines, minimizing
maintenance costs and increasing the reliability of the machine. Wear particles from rolling
bearings in wind turbine are presented, particularly particles resulting from abrasion, fatigue
and corrosion mechanism. Root cause investigation is made, supported by microscopic
analysis.
Keywords: rolling bearing, wear particles, wind turbines, lubricant analysis.
INTRODUCTION
Wind turbine failure statistics show that most of the operating downtime is bearing related. A
recent National Renewable Energy Laboratory (NREL) study concluded that the majority of
wind turbine gearbox failures start in the bearings (Musial, 2007). High-speed bearings and
planet bearings exhibit a high failure rate and are identified as two of the most critical
components.
So, the bearings are a vital part of wind turbines. They have to operate continuously under
variable load and frequently intermittent lubrication. All of the forces generated by the wind
directly affect the bearings. Highly dynamic forces with extreme peak and minimum loads,
sudden load changes and strongly varying operating temperatures place high demands on the
bearing lubricant. The long-term exposure to high vibrational stresses has an especially
negative effect on rolling bearing cages presenting great challenges for bearing tribology in
wind turbines. The bearings are also exposed to high speeds and temperatures as well as the
risk of current passing through them.
Most bearings fail within 10% of their lifetimes predicted by current standards (Evans, 2012).
Many factors influence bearing life but load and cycles are required for failure. After a
sufficient number of rotations, the bearing will fail from fatigue. And the higher the load, the
sooner it fails. Other factors that accelerate the process include poor row-to-row load sharing,
poor oil condition (such as high water content, debris, additive depletion) and skidding. If damaged bearings are not replaced promptly, significant harm to other mechanical components
may result. High-speed bearings, planet bearings and intermediate-shaft bearings exhibit a
high rate of premature failure and are considered to be some of the most critical components
in wind turbines.
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Tribology Trends for Higher Efficiency and Reliability
-1962-
PITCH ROLLING BEARING WEAR
It is well known that at least 60% of premature bearing failures are due to incorrect
lubrication (Tudose, 2013). So, the lubricant plays a vital role in the performance and life of
rolling element bearings. A lubricant that is designed for specific operating conditions will
provide a load bearing wear protective film by separating the friction surfaces. In addition,
bearing lubricant has to ensure dissipation of heat, elimination of contaminants, flushing away
wear debris, lubricate the seal lips and fill the labyrinth seal gaps. When they fail, it is usually
a critical event, resulting in costly repair and downtime in a wind turbine. There are numerous
causes for lubricant failure, including:
• Insufficient lubricant quantity or viscosity;
• Deterioration due to prolonged service without replenishment;
• Excessive temperatures;
• Contamination with foreign matter;
• Use of grease when conditions dictate the use of static or circulating oil;
• Incorrect grease base for a particular application;
• Over lubricating.
Excessive wear on rolling elements, rings and cages follows, resulting in overheating and
subsequent catastrophic failure. In addition, if a bearing has insufficient lubrication, or if the
lubricant has lost its lubricating properties, an oil film with sufficient load carrying capacity
cannot be generated. The result is metal-to-metal contact between rolling elements and
raceways, leading to surface damage.
There are five dominant surface damage modes in wind turbine rolling bearings (Errichello et
al, 2011):
• Fretting corrosion and false brinelling - as it was pointed out by some authors
(Kotzalas and Doll, 2010), is a common issue in pitch systems when the bearings and
gears are not rotating and are subjected to structure-borne vibrations caused by wind
loads and/or small motions from the control system, termed dither. Under these
conditions, lubricant is squeezed from between the contacts and the relative motion of
the surfaces is too small for the lubricant to be replenished. Natural oxide films that
normally protect steel surfaces are removed, permitting metal-to-metal contact and
causing adhesion of surface asperities. Fretting begins with an incubation period during
which the wear mechanism is mild adhesion and the wear debris is magnetite (Fe3O4).
Damage during this incubation period is referred to as false brinelling. If wear debris
accumulates in amounts sufficient to inhibit lubricant from reaching the contact, then
the wear mechanism becomes severe adhesion that breaks through the natural oxide
layer and forms strong welds with the steel. In this situation, the wear rate increases
dramatically and damage escalates to fretting corrosion.
• Micropitting - in bearings, it is typically caused by sliding or skidding during unsteady
operation. Micropitting is commonly a precursor to larger surface failures. In general,
the major factors influencing micropitting include inadequate EHL film thickness,
surface roughness, unsteady operating conditions and anti-wear lubricant additives;
• Scuffing and smearing - this is surface damage caused by sliding contact friction
caused by inadequate lubrication. In lightly loaded roller bearings, pure sliding between
rolling elements and inner ring can occur when there is a large mismatch between the
inner ring and roller set rotational speed. For demanding applications such as wind
gearbox high-speed shafts, idling conditions and changing of load zones can sometimes
Proceedings of the 6th International Conference on Mechanics and Materials in Design,
Editors: J.F. Silva Gomes & S.A. Meguid, P.Delgada/Azores, 26-30 July 2015
-1963-
lead to high sliding risk. In radially loaded roller bearings, the most critical zone where
sliding can occur is the entrance of the rollers into the load zone. While rotating, the
rollers slowdown in the unload zone of the bearing because of friction and subsequently
have to be suddenly accelerated as they re-enter the load zone.
• Electric discharge - this occurs when factors such as faulty insulation or improper
grounding allow electric current to pass through the bearing and damage the surface.
Wind turbine bearings might be damaged by lightning strikes. When an electrical arc
occurs, it produces temperatures high enough to melt bearing surfaces. Microscopically,
the damage appears as small, hemispherical craters. Edges of the craters are smooth and
they might be surrounded by burned or fused metal in the form of rounded particles that
were once molten. Overall, damage to bearings is proportional to the number and size of
the arcing points. Depending on its extent, electric discharge damage might be
destructive to bearings. Associated microcracking might lead to subsequent Hertzian
fatigue or bending fatigue. If arc burns are found on bearings, all associated gears
should be examined for similar damage;
• Microstructural alteration - this includes white etching area (WEA) cracks and can
lead to axial cracking and macropitting early in relatively new bearings. This is one of
the more critical and least understood wind turbine failure modes. While not unique to
the wind industry, it is found to be much more prevalent than in other applications.
There are several theories about the cause of WEA cracks, including hydrogen induced
embrittlement from lubricant decomposition (Uyama, 2014), mechanically induced,
from high stress and slip conditions (Evans, 2012), mechanical impact loading (Luyckx,
2012), or multiple influencing factors, without one root cause (Holweger et al, 2015).
Another concern related with bearing surface damage is the fatigue failure caused by
lubricant debris (Dwyer-Joyce, 2005). The wear particles suspended in the lubricant passing
through the contact will cause some damage to the bearing surfaces. Debris particles from
steel bearing components are highly cold-worked, and can be produced as spalls or
delaminate flakes from cold-worked surface layers. Since the hardness of debris particles is
equal to or greater than the surfaces that they come into contact with, they can cause abrasion,
denting, and sometimes embedment – especially in softer metals like the bronze roller
separators. The presence of debris particles, either loose, or embedded, leads to a localized
disruption in the function of the inter-element lubricating film. Depending on when the debris
indenting occurred, etches of shallow pits can be sharp or rounded from subsequent plastic
deformation. Raised lips around pits can penetrate into the oil film and lead to localized solid
contact or disruption in smooth flow between surfaces. Ductile particles causes smooth
rounded, relatively shallow indents, whilst brittle particles cause deep steep sided dents (Blau
et al, 2010).
WEAR PARTICLE ANALYSIS
Wear particle analysis is a powerful technique for non-intrusive examination of lubricated
components in machinery. The particles contained in a lubricant carry always a great deal of
information about the operating condition of the equipment as well as provide a leading
indicator of what could be the condition if no corrective action is taken. This information may
be deduced from particle shape, composition, size distribution, and concentration. The
particle characteristics are sufficiently specific so that the operating wear modes within the
machine may be determined, allowing prediction of the imminent behavior of the machine.
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Tribology Trends for Higher Efficiency and Reliability
-1964-
Proactive actions can securely be implemented and/or the corrective work can be well planned
and scheduled.
Some of the more common failure modes that oil analysis can detect include:
• Accelerated oil degradation;
• External contamination (water, dust particles, etc.);
• Component fatigue and wear (sliding, abrasive, corrosive, etc.);
• Incorrect lubricant use and management;
• Inadequate contamination control measures (filtration, leakage, etc.).
To understand the contents enclosed in the combined information obtained through several
lubricant analysis techniques, a certain expertise is required in either, tribological
fundamentals and in maintenance engineering. Lubricant failure causes equipment failure and
vice-versa. The lubricant analysis program should be designed to recognize both modes of
failure.
Some parts of wind power equipment often produce abnormal wear because of assembly,
severe operating conditions and poor oil quality. Thus, analyzing and identify the causes of
abnormal wear is very important for the operation and management staff.
In terms of a wind turbine gearbox, the vast majority of the particulates suspended are wear
debris which have become detached from different gearbox surface components. So, wear
failure condition diagnosis can be effectively made by the quantitative and qualitative analysis
of wear metal particles in the oil, which can guide the maintenance personal to take timely
measures to carry out condition maintenance, and to avoid further deterioration of the
accident to ensure the safe operation of the wind turbine.
Another important issue is to inspect the bearings because they often provide clues about the
causes of gear failure, such as:
• bearing wear can cause excessive radial clearance or end play that misaligns the gears;
• bearing damage may indicate corrosion, contamination, electrical discharge or lack of
lubrication;
• plastic deformation between rollers and raceways may indicate gear overloads.
FERROGRAPHY ANALYSIS
Ferrography is one of the most reliable techniques in providing valuable information about
the wear evolution in mechanical components.
The potentialities of Ferrography are not only limited to predictive maintenance strategies. Its
important contribution to tribology studies, by assisting in a better understanding of the wear
mechanisms and of the lubricant effects on the contact surfaces, turns this versatile
technology into one of the most powerful diagnostic tools to assess the machine health,
providing valuable information about the past, the current and the future condition of the
machine’s lubricated components (Graça, 2007).
Ferrographic analysis compromises two sets of instrumentation:
• Direct Reading Ferrography is the instrument that quantitatively measures the
concentration of wear particles in lubricating oil using a magnetic method. The index
readings are indicated as density small (DS) and density large (DL). DS represents all
particles measuring up to 5µm in size whereas DL indicates all particles greater than
Proceedings of the 6th International Conference on Mechanics and Materials in Design,
Editors: J.F. Silva Gomes & S.A. Meguid, P.Delgada/Azores, 26-30 July 2015
-1965-
5µm in size. When there is a sharp increase of the DL index, it is indicative that
abnormal wear is in progress and an Analytical Ferrography is needed.
• Analytical Ferrography is often referred to as the oil analysis equivalent of criminal
forensic science (Huysman, 2011). Analytical Ferrography utilizes microscopic
analysis to identify the composition of the material present. This technology will
differentiate the type of material contained within the sample and determine the
wearing component from which it was generated. Debris wear can indicate the degree
and type of damage that is being experienced by different machine components. The
size and shape of particles are dependent on the type of wear they have experienced
whilst the number can signify the degree of damage that has occurred (Maslach,
1996). In a windmill gearbox several wear mechanism may occur simultaneously (see
Table 1). A trained ferrographic analyst is able to use the size, shape, concentration
and composition to identify the wear mode and status of the equipment. This allows a
skilled diagnostician to determine the root cause of a specific tribological problem.
Not only the overall equipment condition can be determined, but the lubricant
condition can also be analysed by looking for particles such as those listed in Table 2
(Maslach, 1996).
Table 1 - Wear types and particles which identify abnormal wear
Wear type Particle characteristics Size
(µµµµm) Possible cause
Rubbing Wear Platelets < 15 Sliding of components
Cutting Wear Fine chunks/spirals like machining
swarf
> 5 Misaligned components, abrasive
contamination, cracks in the wear
surfaces
Severe Sliding Wear Deep grooves within irregular-shaped
particles, chunks
> 15 Poor lubrication, severe operating
conditions (speed/load)
Bearing Wear Fatigue spalls
Laminar particles
> 15 Abnormal rolling wear in rolling
bearings or between gear teeth
Gear Wear Fatigue chips from gear teeth
Scuffing/Scoring particles
> 15 Scuffing and scoring of the gear
teeth around the pich line
Spherical Wear Smooth and rough spheres < 5 Early indication of an abnormal
rolling contact
Table 2 - Particles which identify lubricant condition
Particle type Characteristics Possible causes
Black Oxides
(Fe3O4)
Black and irregular in shape High operating temperatures due to
inadequate lubrication
Red Oxides
(Fe2O3)
Red and irregular in shape Rust (water presence) or dirt contamination
Corrosive Wear
(FeO)
< 1 micron in size Acidic lubricant due to additive depletion
Lubricant
Degradation
Irregular shape amorphous matrix
containing ferrous particles
Overstress causing breakdown of the
lubricant structure
Dirt Sand, dirt, fibers, etc. Filter or breather leak
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Tribology Trends for Higher Efficiency and Reliability
-1966-
The advantage of Analytical Ferrography is that the source, cause and scope of equipment
wear can be determined with an overall view of the problem. The analysis determines both the
type and metallurgy of the wear particle, allowing to ‘see’ inside the operating equipment.
However, the lubricant sample has to be taken correctly and in a location strategically
selected. Additional information concerning the lubricant and equipment/component is always
a valuable means to achieve a successful diagnostic of the Ferrography results.
CASE STUDIES
Rolling Bearing Wear Particle Analysis
A grease sample obtained from the pitch thrust bearing of a blade wind turbine has been
analysed through Ferrography. Since this technique is designed to analyse lubricating oils, the
grease sample was submitted to a dissolution procedure using an appropriated solvent
mixture.
The wear indexes obtained by Direct Reading Ferrography were extremely high (DL=100,1
and DS=35,7) showing the presence of an abnormal wear condition. To identify the cause of
the high wear indexes obtained, Analytical Ferrography was performed. The wear particles
observed under microscopic analysis are presented in Figure 1 (Photos 1 to 6). The wear
particles were submitted to heat treatment (325°C during 90sec.) to identify their metallurgy.
The blue and straw color transitions show that they are from AISI 52100 steel and medium
alloy steel, respectively (Photo 4 and Photo 6).
Fig. 1 - Wear Particle analysis from a wind blade thrust bearing grease lubricated
Photo 1
Photo 3 Photo 4
Photo 5
Photo 2
Photo 6
(a)
(b)
Proceedings of the 6th International Conference on Mechanics and Materials in Design,
Editors: J.F. Silva Gomes & S.A. Meguid, P.Delgada/Azores, 26-30 July 2015
-1967-
All the microphotography’s shows a very high concentration of ferrous particles, with a
predominance of small size oxidized wear particles.
Photo 2, which is a 1000x magnification of the Photo 1, makes clear that most of the particles
are black ferrous oxides. These particles are typical from a fretting wear process that occurs as
the result of a low amplitude oscillatory relative motion of the contacting bearing surfaces
under load. Small wear particles are formed through the mechanism of adhesive wear.
Because of the small amplitude of motion and the bearing is grease lubricated, the wear
particles are not carried out of the contact area and removed from the system. So, the particles
produced contribute also to the wear through abrasive action and corrosion.
Besides fretting wear debris, it can be observed in Photo 3 and Photo 5, other ferrous particles
typically from:
• fretting fatigue (a) - which resulted from the friction and a high local temperature in
the fretted area and, as a result, decreases fatigue strength of the material operating
under cycling stress. Cracks are initiated and propagated to the surface very rapidly
with continued fretting, leading to a fatigue spall;
• fatigue cracks (b) – which are the source of small spherical particles (from 1 to 10
microns), generated from tongues of metal removed by a cavitation erosion process
due to the application and release of extreme pressure in the lubricant entrapped in the
propagating crack by rolling contact (Scott, 1973). A marked increase in spherical
particles indicates possible surface distress.
This case study identifies an advanced fretting corrosion wear process promoting a
premature fatigue failure in the bearing elements.
Gearbox Bearings Wear Particle Analysis
The lubricant of a wind turbine gearbox has been evaluated through various analyse
techniques, including Ferrography. The wear indexes obtained by Direct Reading Ferrography
were very high (DL=80,3 and DS=31,6) showing the presence of an abnormal wear condition.
To identify the cause of the high wear indexes obtained, Analytical Ferrography was
performed. The wear particles observed under microscopic analysis are presented in Figure 2.
The microphotography’s presented shows that the wear debris deposited on this ferrogram
were generated by a very severe wear.
Under low magnification (Photo 1 at 200x), it can be observed that the size, the shape and the
concentration of particles (ferrous and non-ferrous) are typical from:
• (c) severe fatigue wear;
• (d) gear scuffing;
• (e) severe sliding wear (chunk).
These particles were submitted to heat treatment (325°C during 90sec.) to identify their
metallurgy. As can be observed in Photo 2, the fatigue and scuffing wear particles are from a
low alloy steel material (gear teeth) and the large sliding particle is a copper alloy, resulted
from a severe surface damage in the rolling bearing, through abrasion action.
Symposium_21
Tribology Trends for Higher Efficiency and Reliability
-1968-
Fig. 2 - Wear Particle analysis from a wind turbine gearbox
Additional information about the wear mechanisms present can be reached using higher
magnification (1000x) and analyzing different areas of the ferrogram (entry, middle and end
region):
• Photo 3: high magnification view (1000x) of the ferrogram entry, shows the oxidized
surface of a severe fatigue particle (c), evidencing high temperatures in the contact;
• Photo 4: high magnification view (1000x) of the mid-section of the ferrogram, shows
a large sliding chunk from copper alloy and small ferrous wear particles;
• Photo 5: low magnification view (200x) of the ferrogram end, shows the presence of
very small ferrous debris. These particles are typical from a corrosive wear;
• Photo 6: high magnification of Photo 5 (1000x) shows a long copper alloy debris over
the corrosive wear particles.
This case study identifies an abnormal wear condition in the rolling bearing elements of
the gearbox.
As already evidenced by the National Renewable Energy Laboratory (NREL) in USA, the
majority of the wind turbine gearbox failures appear to initiate in the bearings. A corrosion
process is taking place in the bearing elements. This will cause an increased bearing clearance
which could be sufficient to result in an unacceptable misalignment in the bearing behavior.
The ferrous wear particles analyzed shown an advanced fatigue wear process in the gear teeth,
inducing that the gearbox operation entered in an abnormal wear condition which could be
related with a main shaft misalignment. A strong presence of wear debris in the lubricant,
promotes an increase of the gearbox wear severity and fatigue. If this problem is not been
Photo 1 Photo 2
Photo 3 Photo 4
Photo 6 Photo 5
(c)
(e) (d)
Proceedings of the 6th International Conference on Mechanics and Materials in Design,
Editors: J.F. Silva Gomes & S.A. Meguid, P.Delgada/Azores, 26-30 July 2015
-1969-
detected and located early on, further damage can occur. A strategic and corrective action
should be implemented to avoid a potential gear failure and/or additional damages in the wind
turbine mechanical components.
Rolling Bearings Failure Diagnostic
The main purpose in this case study was to investigate the nature of element bearing surfaces
damage and to determine possible root cause(s).
The bearing elements analysed were: the inner ring of a tapered roller bearing (HR 30326J)
and the copper cage of the cylindrical roller bearing (NU 2324) from the high speed shaft of a
wind turbine (GE Wind Energy 1.5s). Additivated synthetic gear lubricants were been used to
lubricate this gearbox, containing sulphur (S), phosphor (P), calcium (Ca), molybdenum (Mo)
and boron (B).
The following figures show the damaged areas of the bearing elements submitted to analysis. Detailed studies including visual inspection, Scanning Electron Microscope (SEM) and Energy
Dispersive Spectrum (EDS) analysis were performed on the damaged bearing surfaces.
In the surface of inner ring of the tapered roller bearing (see Figure 3) are observed flaking
relatively deep at the edge of the raceway. This contact fatigue mechanism resulted from
geometric stress concentration (GSC) (Bruce, 2012), and it is often associated with overload
in a misaligned tapered bearing.
Fig. 3 - Inner ring of the tapered roller bearing - HR 30326J: dashed line signifies the axial plane from which the
cross-sectional (a) analysis was conducted
Fig. 4 - Cage of the cylindrical roller bearing (NU 2324) showing intensive chemical corrosion in its surface
(magnified 200x)
(a)
Symposium_21
Tribology Trends for Higher Efficiency and Reliability
Polished cross-sections (a) of the inner ring observed under Scanning Electron Microscope
(SEM) revealed the fine network of subsurface micro
optical microscope photomicrography,
(WEC). This type of microstructural changes of st
wind turbines, and is not associated with the classical mechanism for rolling contact fatigue
(RCF).
Energy Dispersive Spectral analysis (EDS) in the interior of a micro crack (Z1 in
shows the presence of sulphur (S), phosphor (P)
(Cu) is an element compound of the cage material which was also diluted into the lubricant.
According to recent studies published by SKF
hydrogen induced microstructure transformation by means of hydrogen release from the
composition products of the penetrating oil. Premature failure of bearings in gearboxes for
wind turbines is associated with rapid crack p
propagation and branching, according to several authors
be explained by the presence and influence of certain chemicals in the lubricant, such as
oxygen (O2), hydrogen (H2) and its degradation resulting compounds (hydrogen sulfide
among others). Hydraulic effects will additionally drive the crack propagation quickly in
different directions, which depends on the surface crack orientation.
Fig. 5 - SEM view (left) and optical view (right)
Fig. 6 - EDS analysis inside the micro crack (Z1)
Higher Efficiency and Reliability
-1970-
of the inner ring observed under Scanning Electron Microscope
(SEM) revealed the fine network of subsurface micro-cracks propagation (see Figure 5
ptical microscope photomicrography, shows some evidences of "White Etching Cracks"
f microstructural changes of steel bearings often occurs in
wind turbines, and is not associated with the classical mechanism for rolling contact fatigue
ral analysis (EDS) in the interior of a micro crack (Z1 in
shows the presence of sulphur (S), phosphor (P) and copper (Cu). Should be noted that copper
(Cu) is an element compound of the cage material which was also diluted into the lubricant.
According to recent studies published by SKF (Stadler et al, 2013), WEC can be related with
hydrogen induced microstructure transformation by means of hydrogen release from the
composition products of the penetrating oil. Premature failure of bearings in gearboxes for
wind turbines is associated with rapid crack propagation inside the material. This rapid crack
propagation and branching, according to several authors (Gegner, 2011, Uyama
be explained by the presence and influence of certain chemicals in the lubricant, such as
and its degradation resulting compounds (hydrogen sulfide
among others). Hydraulic effects will additionally drive the crack propagation quickly in
different directions, which depends on the surface crack orientation.
and optical view (right) of the cross-sectional surface (a)
EDS analysis inside the micro crack (Z1) of the inner ring.
of the inner ring observed under Scanning Electron Microscope
cracks propagation (see Figure 5). The
some evidences of "White Etching Cracks"
eel bearings often occurs in gearboxes of
wind turbines, and is not associated with the classical mechanism for rolling contact fatigue
ral analysis (EDS) in the interior of a micro crack (Z1 in Figure 6),
. Should be noted that copper
(Cu) is an element compound of the cage material which was also diluted into the lubricant.
, WEC can be related with
hydrogen induced microstructure transformation by means of hydrogen release from the
composition products of the penetrating oil. Premature failure of bearings in gearboxes for
ropagation inside the material. This rapid crack
2011, Uyama, 2013), can
be explained by the presence and influence of certain chemicals in the lubricant, such as
and its degradation resulting compounds (hydrogen sulfide - H2S,
among others). Hydraulic effects will additionally drive the crack propagation quickly in
(a) of inner ring.
Proceedings of the 6th International Conference on Mechanics and Materials in Design,
Editors: J.F. Silva Gomes & S.A. Meguid, P.Delgada/Azores, 26-30 July 2015
-1971-
The cage surface shows a large extension of wear caused by chemical action, with the generation of a
large number of craters. Those craters are covered by a residue mainly composed by sulfur (S),
phosphorous (P) and calcium (Ca) (Z1 and Z2 in Figure 7).
Fig. 7 - SEM/EDS analysis in the cage surface of the cylindrical roller bearing.
CONCLUSION
The following important deductions were obtained from the results of these case studies:
• the results from both wear particle analysis cases shown a corrosion process taking
place in the rolling bearing elements, causing an increase of the bearing clearance
which could be sufficient to result in an unacceptable misalignment in the bearing
behaviour;
• lubricant formulation and decomposition should be considered either regarding to
corrosion wear processes and hydrogen generation and penetration into the bearing
materials;
• micrographic surface analysis show a wear mechanism that is typical of incorrect
alignment of gears causing load distribution unevenly across the face width promoting
overload in a small area (GSC) and lead to premature failure.
Considering the limited accessibility of wind turbines and the costly interventions that rolling
bearing failures can cause, wear particle analysis offers an attractive, proactive way of
maintaining and servicing wind turbine units, leading to improve their reliability. The
combination of wear particles analysis with failure diagnosis is a powerful tool to identify
problems in wind turbine and to understand the lubricant chemistry alterations that could be
related with the problem origin.
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Tribology Trends for Higher Efficiency and Reliability
-1972-
ACKNOWLEDGMENTS
The authors gratefully acknowledge the funding by Fundação para a Ciência, Tecnologia,
FCT, Portugal, within the project EXCL/EMS-PRO/0103/2012. This work was co-funded by:
COMPETE, QREN, EU.
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