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We tested two types of ball bearings with an outer diameter of 750 mm to learn more about the challenges of oscillating motions for pitch bearings. The experimental conditions are derived from aero-elastic simulations, long-term wind speed measurements and a scaling method that considers loads and pitch angles. As a result, the parameters relevant for pitch bearings are represented appropriately, and the findings are transferable to other bearing sizes. For the tested parameter sets, severe wear occurred for over 90% of the exposed contact areas after 12 500 oscillating cycles. Decreasing the number of cycles to 1250 leads to a mix of exposed areas with 13% severe wear, 32% mild wear and 55% no wear, with no apparent pattern. The results demonstrate that a comparatively small amount of consecutive cycles can lead to severe wear. A new type of bearing tested showed less wear for the selected operating conditions.

The friction coefficient of a specific material combination is often assumed to be invariant, even in manufacturing processes, such as during the tightening of threaded fastener joints. This paper considers the impact of storage conditions on threaded fastener friction. Fasteners were stored in hot humid and sub-zero temperature conditions to study friction in the thread and underhead contacts. Four Zn-flake coatings, commonly used in the automotive industry were considered. Consequent tightening of these fasteners at room temperature revealed that storage history had a significant impact on their friction coefficients, halving under-head friction in some cases. This varied behaviour was considered to be a response to coating nano-hardness and structure and differences in adsorption/absorption of water and zinc-oxide formation during storage.

We tested two types of ball bearings with an outer diameter of 750 mm to learn more about the challenges of oscillating motions for pitch bearings. The experimental conditions are derived from aero-elastic simulations, long-term wind speed measurements and a scaling method that considers loads and pitch angles. As a result, the parameters relevant for pitch bearings are represented appropriately, and the findings are transferable to other bearing sizes. For the tested parameter sets, severe wear occurred for over 90% of the exposed contact areas after 12 500 oscillating cycles. Decreasing the number of cycles to 1250 leads to a mix of exposed areas with 13% severe wear, 32% mild wear and 55% no wear, with no apparent pattern. The results demonstrate that a comparatively small amount of consecutive cycles can lead to severe wear. A new type of bearing tested showed less wear for the selected operating conditions. © 2021 The Authors. Wind Energy published by John Wiley & Sons Ltd.

Small oscillating amplitudes (~0. 1°) and larger (> 1°) can both lead to wear, w hich complicates the evaluation of the operating conditions. In this work, a simulation model is used to discuss critical amplitudes. The parametric study, which includes 125 simulations, shows the effect of load and coefficient of friction on the frictional work density for amplitudes ranging from 0.1 to 2.5°. The study concludes that the frictional work density increases with the oscillating amplitude up to a certain point, where it becomes almost constant in relation to the amplitude. This point is reached when the amplitude is so large that a continuous overlapping of the contact zone no longer occurs. It is precisely this point that marks the critical oscillation amplitude.

Non-halogenated boron-based ionic liquids (ILs) composed of phosphonium cations and chelated orthoborate anions have high hydrolytic stability, low melting point and exceptional properties for various applications. This study is focused on ILs with the same type of cation, trihexyltetradecylphosphonium ([P-6,P-6,P-6,P-14](+)), and two orthoborate anions, such as bis(salicylato)borate ([BScB](-)) and bis(oxalato)borate ([BOB](-)). We compare the results of this study with our previous studies on ILs with bis(mandelato)borate ([BMB](-)) and a variety of different cations (tetraalkylphosphonium, dialkylpyrrolidinium and dialkylimidazolium). The ion dynamics and phase behavior of these ILs is studied using H-1 and B-11 pulsed-field-gradient (PFG) NMR. PFG NMR is demonstrated to be a useful tool to elucidate the dynamics of ions in this class of phosphonium orthoborate ILs. In particular, the applicability of B-11 PFG NMR for studying anions without H-1, such as [BOB](-), and the limitations of this technique to measure self-diffusion of ions in ILs are demonstrated and discussed in detail for the first time.

Seminal characteristics such as good corrosion resistance, self-lubrication ability and acceptable wear resistance have made polymer based materials to become popular in a wide and diverse range of tribological applications. Despite numerous applications and decades of research in polymer tribology, a considerable number of questions remain unsolved both regarding fundamental understanding and engineering design issues. One of the reasons is the vast number of different polymers and polymer based composites that are in use, but also the diversity in applications and the difficulties to observe the governing tribomechanisms. Material and component producers are often the only owners of composition and basic material characteristics. Thus, designers and application engineers are obviously forced to rely on catalogue information and scattered literature data. For that reason prior to application of a chosen material/component functional and tribological tests with scale models or laboratory set-ups are performed to obtain better confidence in the proposed design solutions. Each time again the definition of an adequate test program is of major concern. The present paper discusses some challenges related to the use and testing of polymer based tribocomponents such as bearings, sliders, gears, rollers, etc. Attention is not only given to basic influencing parameters such as contact load, sliding/rolling velocity, environmental conditions, mating surface conditions, etc. Also experimental strategies and advanced measuring techniques that allow to follow the dynamic nature of transfer film formation and wear are considered. Finally, actual trends in reinforcements (e.g. natural fibres) and lubricant additives (nanoparticles) are discussed together with opportunities for improved tribobehaviour.

Solid-state NMR spectroscopy is a useful method for elucidating mechanisms of formation of boundary films at solid-liquid interfaces of different metal oxides in contact with different ionic liquids having halogenated anions, such as NTF2- and PF6- [1,2]. However, these halogen-based ionic liquids are susceptible to hydrolysis and generate HF that erode the surface and pollute the environment. In this study, we employed a similar NMR approach to understand the mechanism of film formation by halogen-free orthoborate ionic liquids (hf-BILs) on the metal oxide surfaces.Samples were prepared by grinding the inorganic oxide and 10 wt% of hf-BIL using mortar and pestle. The boundary films on inorganic metal oxides (Al2O3, MgO and SiO2) surfaces in contact with hf-BILs have been characterized using solid-state MAS (11B, 31P and 29Si) NMR spectroscopy. The single pulse 11B NMR data indicate that bis(mandelato)borate anion, [BMB]-, in [P6,6,6,14][BMB] BIL strongly interacts with these metal oxides, in particular, at elevated temperatures (100 °C). In contrast, no products of decomposition were detected for surface of these oxides exposed to [trihexyltetradecylphosphonium][bis(salicylato)borate] ILs at different temperatures. Therefore, it was suggested that the [BScB]- anion is weakly interacting with these oxides. 31P NMR data on the same IL/metal oxide systems revealed strong interactions of the [P6,6,6,14]+ with these oxides. We suggest that [P6,6,6,14]+ cations are also present in immobile surface layers of ILs on particles of these oxides, because 31P resonance lines of ILs were detected using 1H-31P cross polarization MAS NMR giving rise to NMR signals of solid phases with a low molecular mobility only. The existence of strongly adhered surface layers of ILs on particles of metal oxides was further confirmed by 1H-29Si CP/MAS NMR. This study suggests that the boundary film formation between hf-BILs and metal oxide surfaces is a complex process involving various chemical reactions at the interfaces. These findings can be important for understanding of mechanisms of formation and structure of tribofilms in the process of lubrication of nonferrous metal surfaces by hf-BILs. Godkänd; 2013; 20130418 (faisha)

The market for hydropower re-investments in Sweden is approx 2.5 billion SEK/yr the coming decade. Large investments will also be carried out in Swedish tailing dams. This will result in challenging projects and need of experts. A crucial factor for a successful management of these challenges is the supply of engineers and researchers with hydro power and dam skills and knowledge. Swedish Hydro Power Centre (Svenskt vattenkraftcentrum, SVC) is a competence centre for university education and research environments within hydro power and mining dams. SVC comprises of two knowledge areas: Hydraulic Engineering and Hydro Turbines and Generators, respectively. SVC builds high-quality and long term sustainable knowledge at selected universities... Godkänd; 2010; 20110411 (andbra)

Performance of an inlet textured contact is analysed for a temperature dependent lubricant flow. Thermal effects are analysed for different shear rates. Shearing of lubricant and subsequent heating reduce load carrying capacity and frictional losses compared with isothermal conditions. Load carrying capacity of a parallel surface contact can be improved by using texturing at the inlet when thermal effects are considered. It is also shown that for the different convergence ratios considered, the texture enables the sustaining of a load until a certain critical shear rate is reached. This critical shear rate depends on a number of factors such as the convergence ratio and lubricant parameters including the viscosity-temperature coefficient and the dynamic viscosity at reference temperature. Godkänd; 2008; Bibliografisk uppgift: CD-ROM; 20080828 (cervante)

Analysis of a 3D inlet textured slider bearing with a temperature dependent fluid is performed. Numerical simulations are carried out for a laminar and steady flow. Hot and cold lubricant mixing in the groove is modelled and examined for different operating conditions. Thermohydrodynamic performance of the bearing is analysed for different texture lengths. Results show that texture has a stronger and positive influence on load carrying capacity when thermal effects are considered. This beneficial effect is at a maximum for the longest dimples with a length shorter than the pad length. Texture is also beneficial for the load carrying capacity when the sliding speed and inlet flow rate are varied: with an appropriate supply mass flow, load carrying capacity can be increased by 6-7% at low sliding speeds. Godkänd; 2008; Bibliografisk uppgift: 1 CD-ROM; 20080812 (cervante)

An analysis of a lubricated journal bearing is performed with special attention to the influence of textured surfaces which may improve hydrodynamic performance. The bearing is subjected to an external applied load and the force balance is fulfilled with the force of the flow acting on the bearing. The position of the shaft is fixed whereas the bearing, centred at the starting time, moves under the forces until equilibrium is reached. A mesh deformation technique is used with CFD (Computational Fluid Dynamics) in order to perform the simulations. The flow is laminar, isothermal, three-dimensional (3D) and unsteady. Cavitation is taken into account. Results are analysed with smooth and textured surfaces on the bearing. Friction force and eccentricity ratio are compared for different configurations.It is found that shallow grooves under light loading (ε < 0.15) enhance the minimum film thickness while reducing the friction force. Under high loading (ε > 0.5), deep grooves are able to reduce the friction force despite a reduced minimum film thickness. For the second case, the predicted performance is superior to those of a smooth journal bearing with thinner lubricant. Godkänd; 2008; Bibliografisk uppgift: 1 CD-ROM; 20081111 (ysko)

Journal bearings are used in many applications. An increase of their load carrying capacity and/or decrease of their losses may allow for savings of an enormous amount of energy. One way to enhance the characteristics of journal bearings is to modify the surface texture of the stator. The purpose of the present study is to investigate the influence of a textured rotor on journal bearing characteristics. Computational Fluid Dynamics is used to model the flow between the rotor and the journal. The full Navier-Stokes equations are solved under unsteady conditions with the commercial software ANSYS CFX 11. A two-dimensional geometry is used to model the bearing. In order to make a simulation, a separate rotor and stator are made and are attached to each other using a rotor-stator interface. Firstly, a single mesh for the smooth journal bearing is used to evaluate possible numerical artefacts created by the interface. The results illustrate a difference of 2.8 % in the load carrying capacity. Simulation with a dimpled rotor followed. Comparison between a dimpled rotor and smooth rotor shows no significant increase in load carrying capacity of the journal bearing when thermal effects are not taken into account. Godkänd; 2008; Bibliografisk uppgift: CD-ROM; 20080828 (cervante)

Hydropower still faces complex scientific and technical challenges in order to secure the availability and reliability of the power plants despite more than a century of development. The main challenge is due to new market constrains such as electrical market deregulation and introduction of renewable sources of energy. The major problem is related to the dynamic of the rotor involving several fields: hydraulics, power engineering and mechanics. On the other side, the large and growing hydropower world market represents an opportunity for technically advanced companies offering better efficiency. The difficulty to scale rigorously any technical advance makes full-scale experiment a necessity. World unique facilities are available at Porjus, Sweden, for this purpose. The Porjus Hydropower Centre is composed of a Francis (U8) and a Kaplan (U9) turbine of 10 MW, each exclusively dedicated to education, research and development. In order to further investigate specific issues related to availability and reliability, a project was initiated in 2006. The main objective is to make U9 a full-scale hydropower laboratory able firstly to furnish the necessary data for the development of rotor-dynamic models but also turbines and bearings. To this purposes more than 200 sensors have been installed to measure displacements, forces, pressure, film thickness, strains... The work presents an overview of the newly upgrade facility as well as some of the problems faced during the instrumentation of the machine. Godkänd; 2008; Bibliografisk uppgift: CD-ROM; 20081103 (cervante)

Polymer composites are employed as facing materials in hydrodynamic bearings for their low friction and "compliant" properties which play an important role during machinery operation. In journal bearings, this low friction property can be of significant importance during start and stop cycles when insufficient oil is available to fully separate the surfaces in relative motion. Current work is aimed at determining a suitable material for use in hydrodynamic journal bearings. This study investigates friction and wear encountered during the transition from the stationary state to operational speed (acceleration) during initial start-up. This is examined for virgin PTFE together with a series of commercially available PTFE-based composites and a babbitt material in boundary / mixed lubrication conditions. Tests are performed using a standard laboratory block-on-ring test apparatus with a VG32 mineral oil. Godkänd; 2008; Bibliografisk uppgift: Værtspublikationsredaktører: Jaakko Kleemola Værtspublikationsredaktører: Arto Lehtovaara Titel på proceedings: Proceedings of NORDTRIB 2008 Undertitel på proceedings: 13th Nordic Symposium on Tribology; 20080904 (ysko)