The highest costs due to premature failures in wind turbine drivetrains are related to defects in the gearbox, with bearing failures being overrepresented. Vibration monitoring has been identified as ...the primary tool to detect and diagnose these types of failures. However, late or no signs of the failures are still being reported. Artificial neural networks (ANNs) has been shown to favourably be used as a classifier of bearing failures to increase the detection and diagnosis performance, which requires labelled data when training for all types of considered failures. However, less work has been done with an ANN used to create descriptive functions of the vibration and turbine operation data relationship and thereby negating inherent variance in the vibration data and increasing the detectability when a defect appears. Therefore, this study utilizes the relationship between the rotational speed recorded during a vibration measurement and the calculated condition indicator values of specific bearing failures in three wind turbine gearbox failures. An ANN establishes a function between the rotational speed and condition indicator values with healthy training data collected before the failure occurred. Thereafter, whole datasets leading up to the changing of the gearboxes is used to predict the condition indicator values without the failure influence. The difference between the predicted and true values show an increased sensitivity of the detection in two cases of gearbox output shaft bearing failures as well as indicating a planet bearing failure which with the previous data had gone undetected.
There are many moving machine assemblies with conformal tribological contacts at very high contact pressures, e.g., sliding bearings, propeller shaft bearings and machine guideways. Furthermore, ...applications such as trunnion and guide vane bearing in Kaplan turbines have very low sliding speeds and oscillatory types of motion. Although there is a vast selection of tribology test rigs available, there is still a lack of test equipment to perform friction and wear tests under high contact pressure, reciprocatory sliding and large area contact. The aim of this work is thus to develop a novel reciprocating tribometer and test method that enables friction and wear tests under low-speed reciprocatory sliding with contact pressures up to 90 MPa in a flat-on-flat contact configuration. First, a thorough description of the test rig design is given. Secondly, the influence of contact pressure and stroke length on the tribological properties of a stainless steel and polymer composite material combination is studied. The significance of considering creep, friction during the stroke and contact temperature is specifically highlighted. The novel tribometer can be used to screen different bearing and shaft material combinations and to evaluate the friction and wear performance of self-lubricating bearings for the specific operating conditions found in Kaplan turbines.
Self-lubricating bearings in hydropower applications are often lubricated with water under boundary lubricating conditions. Polyhydric alcohols replacing water have shown the potential to reduce both ...friction and wear. The objective of this work is, therefore, to evaluate the effect of a polyhydric alcohol-based environmentally-acceptable lubricant (EAL) on the friction and wear of self-lubricating materials for conformal contacts under boundary lubricating conditions. The lubricating properties of four commercially-available self-lubricating bearing materials were investigated under three different lubricating conditions: dry, water and a new polyhydric alcohol-based EAL. Bearing materials include one metallic composite and three polymer composites. A reciprocating motion test rig was used to evaluate the wear and friction properties. Surface analysis was performed by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and optical profilometry. Results show that the wear rate for the polymer composites is increased when water is present compared to dry operating conditions. The new polyhydric alcohol-based EAL substantially improves both friction and anti-wear performance of all four self-lubricating bearing materials compared to both dry and water conditions. Surface analysis indicates that the material transfer to the counter-surface is limited when the polyhydric alcohol-based EAL is used.
In Kaplan turbines, the most critical components are the self-lubricating polymer composite bearings used to control the guide vanes and the turbine blades. Reducing the sliding wear and friction of ...these bearings can benefit both the economy and the environment, including longer useful life, lower operational costs, and higher efficiency. In this study, the influence of stainless-steel counter surface roughness and lay on the tribological behaviour of three bearing materials used in hydropower applications were investigated using a linear reciprocating flat-on-flat configuration under high contact pressure and low sliding speed. The surface roughness was measured using white light interferometry. SEM and EDS analysis were used to investigate the worn surfaces. Results from this study show that overly smooth surfaces result in higher friction and wear of the counter surface, while rougher surfaces have a negative effect on the wear of the polymers. Highest surface coverage using protective transfer layers is found on the steel surfaces with the perpendicular lay and is accompanied with a lower coefficient of friction compared to the parallel lay. The dominant wear mechanism of the bearing materials changes from delamination wear to abrasive wear between the lowest and the intermediate roughness for steel surfaces with the parallel lay. It can be concluded that counter surface topography has a significant influence on the tribological behaviour of these bearing materials and that the effect differs between the self-lubricating polymer composites.
Grinding processes’ stochastic nature poses a challenge in predicting the quality of the resulting surfaces. Post-production measurements for form, surface roughness, and circumferential waviness are ...commonly performed due to infeasibility in measuring all quality parameters during the grinding operation. Therefore, it is challenging to diagnose the root cause of quality deviations in real-time resulting from variations in the machine’s operating condition. This paper introduces a novel approach to predict the overall quality of the individual parts. The grinder is equipped with sensors to implement condition-based maintenance and is induced with five frequently occurring failure conditions for the experimental test runs. The crucial quality parameters are measured for the produced parts. Fuzzy c-means (FCM) and Hotelling’s T-squared (T2) have been evaluated to generate quality labels from the multi-variate quality data. Benchmarked random forest regression models are trained using fault diagnosis feature set and quality labels. Quality labels from the T2 statistic of quality parameters are preferred over FCM approach for their repeatability. The model, trained from T2 labels achieves more than 94% accuracy when compared to the measured ring disposition. The predicted overall quality using the sensors’ feature set is compared against the threshold to reach a trustworthy maintenance decision.
Nowadays, hydropower plants are forced to have more frequent power control and the self-lubricated bearings used in the applications are one of the most critical components affected by the ...continuously changing operating conditions. In this study, microstructure and composition of two commercially available bearing materials (Orkot TXM Marine and Thordon ThorPlas) used in hydropower turbines were studied. In addition, the influence of sliding speed and applied pressure on the friction and wear behavior of the materials was investigated systematically for dry sliding conditions. The bearing materials were characterized using X-ray microtomography, Nuclear Magnetic Resonance (NMR) spectroscopy and Inductively Coupled Plasma–Sector Field Mass Spectrometry (ICP-SFMS) techniques. Friction and wear tests were carried out with a polymer pin sliding against a stainless steel (SS2333) plate with a linear reciprocating motion. Test conditions were: room temperature, 9–28 MPa pressure and 10–40 mm/s sliding speed ranges. Surface analysis of the polymer pins and the wear tracks were performed by optical profilometry, Scanning Electron Microscope (SEM) and Energy Dispersive Spectroscopy (EDS) techniques. Test results show that, for both materials, the coefficient of friction (COF) is decreasing at higher pressures. Surface analysis reveals higher concentrations of solid lubricants in the transfer layers formed at higher pressures, explaining the decrease in COF. Furthermore, the specific wear rate coefficients are increasing at higher sliding speeds, especially at lower pressures. Results of this study demonstrate that, under dry sliding conditions, changes in sliding speed and pressure have a significant influence on the tribological behavior of these bearing materials.
The increased control of hydropower plants (i.e. shift from water level to primary control) leads to an increased number of load cycles on critical components such as bearings in hydropower turbines. ...Despite having shorter sliding amplitudes, this may result in a longer accumulated sliding distance that reduce the useful life of the bearings.
In this study, the effect of stroke length on the tribological performance of two self-lubricating polymer composites, commonly used for bearings in hydropower turbines, during dry sliding against stainless steel is investigated. The reciprocating tests are carried out under relevant conditions, i.e. high pressures and long sliding distance, corresponding to years of operation of a hydropower turbine. The worn polymer and stainless-steel surfaces are examined using 3D optical surface profilometer and SEM/EDS to study the wear and friction mechanisms.
The results show an increasing wear rate with increased stroke length for both bearing materials, especially when the stroke length is longer than the length of the polymer pin. The thermoset show the same trend for the frictional behaviour and it is attributed to decrease in coverage by transfer layers and solid lubricants at the sliding interface as well as increase in abrasive wear of the stainless steel. Meanwhile, the highest friction is observed at the shortest stroke length for the thermoplastic and the lowest at the intermediate stroke. Surface analysis reveals higher abrasive wear of the stainless-steel counter surface at the longest stroke length for both bearing materials due to lower wear particle entrapment. It can be concluded that changes in sliding amplitude have a significant influence on the tribological performance of the two polymer composites sliding against stainless steel.
•The stroke length has a significant influence on both wear and friction of self-lubricating polymer composites.•Increased wear rates with increased stroke length, especially when the stroke is longer than the contact length of the pin.•Longer stroke lengths promotes abrasive wear of the steel counter surface due to reduced protection by transfer layers.•Lowest friction at shorter stroke lengths due to thicker transfer layers with higher concentration of PTFE.•The thermoplastic has a much higher long-term (168 h) creep resistance compared to the thermoset.
Fibre-reinforced thermosets and thermoplastics containing PTFE are commonly used in marine and hydropower applications due to their self-lubricating ability in both dry and water lubricated contacts. ...The constant development of such composite bearings over the last decades make them even more attractive in these fields of application, due to their low maintenance cost and long service life. Their tribological performance is usually estimated by extrapolation of short, accelerated tests, which may induce risks of inaccurate or even incorrect interpretation.
In this work, reciprocating dry sliding behaviour of these materials against stainless steel is investigated under typical hydropower conditions. The aim is to study the wear and friction behaviour and the development of transfer layers during long sliding tests, corresponding to years of operation. In order to mimic operational shutdowns, the tests are stopped every 20 h and the counter surfaces are examined using 3D optical interferometry and SEM to study development of surface topography and transfer layers.
Test results show that the wear rates of both materials decrease significantly with time. For the thermoplastic, COF decreases with time due to accelerated material transfer observed after 80 h. In contrast, much less material transfer is observed for the fibre-reinforced thermoset, which shows its highest transfer amount after 20 h. Surface analysis indicates severe abrasive wear of the counter surface caused by the wear debris from steel and reinforcements in the material and is accompanied by simultaneous COF increase for the thermoset. Cross-sectional analysis reveals thinner transfer layers and higher wear of the steel in the middle of the wear tracks, where the sliding speed and number of load cycles are highest. These findings contribute to a more accurate interpretation of results obtained than that of short time tests regarding the tribological performance of these materials. As a direct conclusion, the selection of counter surface material can be crucial.
•Friction and wear results from long duration (160 h) tribological tests involving self-lubricating polymer composites.•The friction and wear mechanisms for the tested polymer bearing materials are transient processes over long durations.•Transfer layer formation involves wear debris accumulation in counter surface valleys and consolidation in to layers.•Abrasive wear is the dominant wear mechanism of the bearing materials as well as the stainless steel counter surface.
In the present work, graphene oxide is used as template to produce CuO nanosheets, which solves aggregation and dispersion problems of CuO nanosheets resulting in improved lubricating performance. ...SEM and AFM studies show that CuO nanosheets are present in fusiform flake shape with a thickness, width and length of around 13, 400 and 1000 nm, respectively. CuO nanosheets were added to the carbon fibers reinforced Polytetrafluoroethylene (CF/PTFE) to study their lubricating performance. It is interesting, from fractured surfaces of composites, to find that CuO nanosheets enhance the interface properties between carbon fibers and PTFE. The wear resistance property of CF/PTFE is remarkably improved after filling CuO nanosheets. For example, the wear rate is reduced by 51% after filling 1.5 wt % CuO nanosheets. The wear resistance improvement effect of CuO nanosheets is much better than that of commercial CuO nanogranules and CuO nanorods. Worn surfaces and counter-surfaces studying indicates that CuO nanosheets can not only prevent the rubbed-off of PTFE or the detachment of CF, but also improve the properties of transfer films, which greatly reduce the adhesive wear and abrasive wear.
To mitigate the effects of downstream lubricant spillage from hydroelectric power plants, environmentally friendly lubricants are required. For the sustainable operation of oil-free bearings, the ...development of high performance bearing materials is crucial. In this study, the tribological performance of PPS and UHMWPE-based composites, incorporating various reinforcements, such as graphene oxide, is evaluated and compared with five commercial materials. Experiments were performed under different lubricating conditions; Dry, water, and using a glycerol-based environmentally adaptive lubricant (EAL). The use of water inhibited an adequate transfer film, which increased wear for most materials. EAL lubrication showed a significant reduction in friction (up to 98%) when compared to dry conditions. The experimentally developed PPS composite provided superior tribological properties, especially under water-lubricated conditions.
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•Two graphene oxide-based self-lubricating polymer composites were developed.•The tribological performance of the developed composites and five commercial materials in different lubrication conditions was evaluated.•The developed composites provided a superior friction and wear performance, especially under water lubricated conditions.•The used environmentally adaptive lubricant was effective in significantly reducing both friction and wear for all materials.
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