The term "sliding bearing" refers to types of bearing where two conformal surfaces (usually the stationary bearing and a moving shaft) slide relative to one another with load distributed directly across the interface. A suitable lubricant may be employed to reduce the friction between these two surfaces. In "fluid film" bearings, this lubricant builds up a layer of sufficient thickness such that the two surfaces are completely separated. Examples include journal and thrust bearings and shaft bushings. Unlike ball or roller bearings which have a limited lifespan, sliding bearings have, at least in theory, an indefinite operational lifespan. As long as an oil film of sufficient thickness is maintained and contamination is avoided, the bearing may continue to do its job indefinitely. However, more and more onerous demands are being placed on such bearings and their associated methods of lubrication in order to maximise performance in terms of efficiency and load carrying capacity, for example in hydroelectricity generators and turbines. Given the sensitivity of operating any form of mechanical equipment in the vicinity of watercourses, often the source of drinking water for major population centres, the hydropower industry has a duty of responsibility in ensuring that as much as possible is done to minimise the risk of contamination of the water or damage to flora and fauna. Two aims - increased output, decreased environmental impact - are currently the major driving forces behind Research and Development in the hydroelectric power generation industry. Looking at these from a tribological (friction and lubrication) point of view, three areas of particular interest can be identified. These are: 1) How can the load carrying capacity of thrust bearings be increased whilst at the same time improving performance within existing dimensional constraints? 2) What is the influence on bearings of transient events (rapid changes in speed or loading) and what impact do they have on the machinery components? 3) How does the use of Environmentally Adapted Lubricants (as opposed to mineral oils) influence friction and wear etc, specifically with reference to shaft bushings, and what is the impact of fluid ageing (oxidation) on their performance? Each of these three points has been studied in the course of the work carried out for this thesis. / Godkänd; 2005; 20061214 (haneit)

This licentiate thesis deals with the influence of transient loading, at high pressures, on the pressure-dilatation relation and frictional properties of lubricants. A Split-Hopkinson pressure bar and a Ball and Bar apparatus have been used for the experiments. Both methods share the same type of evaluation approach: evaluation by analysis of wave propagation in structures. The advantage with this method is that results are presented as function of time, i.e. every experiment yields a history of the studied event, not just a single value. Different theoretical evaluation methods have been used and refinements have been made by introducing compensation terms in order to enhance accuracy. Several lubricants have been studied and an empirical second-degree polynomial has been suggested, for a naphthenic mineral oil and a synthetic 5P4E oil, describing the pressure-dilatation relation over a wide pressure range. It is found that 5P4E exhibits lower compressibility, i.e. higher stiffness than the naphthenic oil. Curves representing friction coefficient as function of time for different lubricants at different pressures are included. It is evident that the Naphthenic- and Paraffinic mineral oils have the highest friction coefficient followed by Polyglycol, Polyalphaolefin and Rape seed oil. The observed distinctions agree well with the expected outcome on basis of molecular structure and pressure variation and correlates well with other density and friction investigations. A general trend of decreasing friction coefficient with increasing pressure is discovered. / Godkänd; 2000; 20070318 (ysko)

Long and frequent train delays, striking many periodically make headlines. The question is raised: what might be done about it? The on-going deregulation of the Swedish railway, with more actors entering the market, contributes to the question's topicality. In this thesis, problems and symptoms concerning punctuality are described and analysed. Herein, punctuality is defined as the extent to which an event takes place when agreed, for example the agreement between passengers and the company selling the ticket, considering the event that the train arrives at a certain time. The terminology in use on punctuality-related entities is floating. Causes for unpunctuality are related to the infrastructure, locomotives, wagons and personnel. Herein, primarily failures related to infrastructure are discussed. Maintenance, i.e. correcting and preventing failures, together with the track, rolling stock, weather, driver, other personnel and the timetable determine how good the punctuality will be. To the ore and steel transports studied it is more important to limit the lengths of the transport times, rather than having high punctuality, i.e. adherence to timetable. Generally, for freight transports it is difficult to give an estimation of the cost for unpunctuality. To find the root cause of a delay is vital, as is identification of symptoms and triggering events, in order to be able to carry out appropriate actions. Often the information needed to do so is lacking in the Ofelia database for infrastructure failures. Comparisons between regions or over time are complexified by the varying policies on how failure coding is to be performed. To improve punctuality by learning from others is made more difficult by e.g. different countries employing different ways of denoting punctuality. In the transport chain of post in Norway, terms related to punctuality varied even more among stakeholders. They considered being informed on estimated time of arrival as important, but getting this information was, despite this, not among the quantified goals. Few requirements were quantified, despite this often being simple to do. The consequences of failure are important to consider, not only e.g. the number of failures. Studying the variation in transport time on different line sections might help in identifying problems, because coding of delays shorter than five minutes is not carried out in the Swedish railway. Such causes of delay include low contact wire voltage, minor problems with locomotives and slippery rails due to leaves on the track. Disadvantageously, this variation is masked in the case of heavy trains or steep and curvy lines. In a studied maintenance organisation, the indicators of maintenance measured the result of the entire maintenance process. In order to manage each sub process better, it is more advantageous to measure the performance of them individually. Considering the specific sub process that decides which maintenance actions are to be carried out, it only uses expenses for the action itself when deciding, not resulting future costs and punctuality. The indicators focus on measuring past performance, not on facilitating planning for the future. A design of information systems facilitating information usage from different functions of the organisation would facilitate informed decisions. Information concerning technology, traffic and economy need to be integrated. / Godkänd; 2005; 20061218 (haneit)

No description available.

The work presented in this thesis concerns computer simulations of the lubrication process. The main subject of interest is elastohydrodynamic lubrication (EHL) and, to some extent, hydrodynamic lubrication (HD). The thesis comprises an introductory section and three papers; referred to as A, B and C. Simulation of EHL is an inter-disciplinary task, incorporating the fields of fluid mechanics, solid mechanics, thermodynamics and rheology. In almost all numerical simulations of lubrication performed today, the hydrodynamics are modelled using the Reynolds equation. This equation is derived from the equations of momentum and continuity and using the thin film approximation. However, the assumptions made when deriving this equation limits the size of the computational/spatial domain and the equation cannot predict pressure variations across the lubricating oil film. The subject of papers A and B are numerical simulations using the full equations of momentum and continuity, (Paper B), and the equation of energy (Paper A). The main aim of the work was to investigate the possibilities of carrying out numerical simulations based on the above equations. The rheology was assumed to be Newtonian; the equations are then commonly referred to as the Navier-Stokes equations (N-S). The second aim of the work was to investigate the possibilities of using a commercial software, CFX 4.3 [1], to carry out the numerical simulations. The results in Paper A show that it is possible to simulate thermal EHL line contacts up to pressures of approximately 1 GPa. The limitations of the approach are due to a singularity that can occur in the equation of momentum when a critical shear stress is reached. With a more complete rheological model (non-Newtonian rheology) it should be possible to perform simulations at even higher contact pressures. Paper B presents the results of isothermal simulations comparing the N-S and Reynolds equation approaches. The result show that there may be some discrepancies between the two approaches; although only small discrepancies have been observed in the smooth line contact simulations made. The characteristics of the EHL-contact with a wide range of scales and large gradients in pressure, viscosity and temperature make developing accurate numerical simulations to a difficult task. The computational cost is high due to the small under-relaxations factors that must be used in order to obtain converged numerical solutions. The work to date has shown that is possible to use the extended approach in conjunction with a commercial software, CFX 4.3 [1]. This approach makes it possible to extend the computational domain in future in EHL-simulations, where the Reynolds approach is not valid. Paper C presents the results of simulations of a lubricated pivoted thrust bearing. The objective of this study was to verify a thermo-hydrodynamic (THD) model for this type of bearing. The model developed handles three-dimensional temperature distribution in the oil film and pad, as well as two-dimensional temperature variation in the runner. The viscosity and density are treated as functions of both temperature and pressure. Experiments have been performed in a test rig consisting of two identical equalising pivoted pad thrust bearings. Experimentally measured power loss, runner temperature and pressure profiles as a function of load and rotational speed were compared with the theoretical investigations. The results showed fairly good agreement when the oil inlet temperature and heat transfer coefficients were modified in order to obtain the same runner temperature in both theory and experiment. / Godkänd; 2001; 20070314 (ysko)

No description available.

Since the usage of pressurized systems, there has been a challenge to prevent and control leakage of different fluids. When a metal-to-metal face seal is designed, different aspects are to be considered. Its ring shaped sealing surface is designed to prevent leakage and also to maintain pressure. In this thesis, the main objective is to study how out-of-flatness affects the leakage. This property of sealing interface can be described by different wave parameters and in this case, by means of modelling and numerical simulations. The best approach is the usage of Heterogeneous Multiscale Method (HMM). The data obtained by means of the two-scale stochastic model showed that the pressure amplitude is the most important parameter of the out-of-flatness. In same level of importance, comes the mean pressure even though it is not considered an out-of-flatness parameter. From the data obtained, a simple mathematical expression for leak rate was constructed that shows the effect of out-of-flatness.

The purpose of this thesis is to summarize the research carried out that led to the development of measurement techniques which measure the water content of lubricating grease. A simple and effective grease mixing method for preparing grease samples was developed and tested for repeatability. Calcium sulphonate complex (CaS-X) grease was used in all experiments. The water content of these samples were also tested with time and temperature as added variables to study if and how much water will evaporate from the samples. Additionally, two measurement techniques were investigated: optical attenuation in the visible and near-infrared (NIR) region and with a dielectric measurement method. The optical attenuation investigation found that the attenuation ratio of two wavelengths of light appear to approximate the water content of grease samples with an acceptable coefficient of determination. Additionally, aged and oxidized grease were measured as well and were not found to affect the measurement results. The dielectric method uses the temperature dependence on the dielectric properties of water-contaminated grease to approximate the water content of the grease samples. An additional parameter of incomplete fill/coverage of the sensor has been investigated as a prestudy. Both methods were found to provide measurements of water content in the prepared grease samples (ranging from 0.22% to 5.5% added water). The dielectric measurement is likely going to be better for applications requiring the possibility of measuring a larger bulk of the grease within the bearing. It shows promise for providing an accurate and robust system for monitoring grease condition as well as the amount of grease contained. The optical measurement will likely provide additional information; however, it will only measure small point samples within the bearing instead of the larger bulk. This could be of use though, because the sensors could be small (in the several millimeter scale) and could measure where water damage is determined to be most important to detect at.

Conformal contacts like those found in journal or inclined slider bearings are widely encountered in various types of machines from small engines to large turbines. These contacts involve convergent gaps that are used to separate the surfaces in relative motion and generate pressure in the lubricant film. The contacts have to carry a load while keeping friction as low as possible. Environmental and economic concerns require the machines to operate with minimal power loss. A number of design modifications have been proposed over the years in order to decrease bearing power consumption. There are indications that surface topography can have a significant and positive influence on hydrodynamic performance. Texturing of a load carrying surface is a process that would be beneficial in lubricated conformal contacts as it would be possible to obtain thicker films and reduced frictional losses. Textured lubricated contacts are analysed with Computational Fluid Dynamics (CFD) code through different geometries. The effects of the texture on hydrodynamic performance of the contact are investigated. For the simulations performed, the full Navier-Stokes equations are solved under steady-state conditions. The flow is taken to be laminar and two- dimensional. A journal bearing with several dimples created on the stationary part is firstly investigated. A realistic multiphase flow cavitation model is introduced and successfully validated. It is shown that the coefficient of friction can be reduced if dimples of suitable depth are introduced. This can be achieved either in the region of maximum hydrodynamic pressure for a bearing with high eccentricity ratio or just downstream of the maximum film for a bearing with low eccentricity ratio. A new effect of pressure build-up, generated by the surface texture, has been identified at low eccentricity ratios. This pressure build-up effect is more extensively investigated through the study of an inclined slider bearing with a texture located at the inlet part of the contact, i.e. just downstream of the maximum film. The governing mechanism at the origin of an optimum in load carrying capacity for a smooth slider bearing is analysed and the effects of the texture on the pressure build-up and load carrying capacity are explained. The energy received by the fluid from the moving wall is converted into pressure in the first part of the converging contact and into losses in the second part. Convergence ratio can be increased until the limit where flow recirculation begins to occur is reached in order to get the greatest pressure gradient. The texture appears to reach its maximum efficiency when its depth is such that the velocity profile is stretched at its maximum without incoming recirculating flow. Thus, the wall profile shape controlling the velocity profile can be optimized for many hydrodynamic contacts. For such contacts, heat is usually produced due to shearing of the flow and the lubricant is subjected to temperature variations. Since the dynamic viscosity of the lubricant is temperature dependent, variation of the viscosity as well as frictional losses and load carrying capacity is expected. Thermal effects are analysed for different shear rates in this inlet textured slider bearing. Shear losses and subsequent heating reduce load carrying capacity compared with isothermal conditions. Texture has a positive effect in a parallel surface contact when thermal effects are considered. It has been found that for the different convergence ratios considered, the texture enables the sustaining of a load only until a certain critical shear rate is reached. This critical shear stress depends on a number of factors such as the convergence ratio and lubricant parameters including the viscosity-temperature coefficient and the reference dynamic viscosity. / <p>Godkänd; 2007; 20070320 (ysko)</p>

Rail grinding has been employed since the 1980s in maintaining optimal rail profile as well as in the elimination of surface defects such as corrugations and head-checks. Likewise, the wheel sets also require re- turning to remove surface defects and restore the desired profile. The influence of surface roughness in the wheel/rail contact has been a concern for railway owners since the introduction of rail grinding as a maintenance strategy. Presently, there are no scientifically derived guidelines regarding the surface topographies of ground rails and re-turned wheels. There is thus a need to establish well defined guidelines regarding the surface topographies for new surfaces on the rails and wheels in order to minimize grinding cost/time and improve wheel/rail performance. This thesis concerns the influence of surface roughness of wheel/rail surfaces on running-in behaviour, wear, friction and resultant surface damage. The results presented in this thesis are based on both field measurements and experimental simulations in the laboratory. A two-disc rolling/sliding test machine has been used in the experimental work to simulate the wheel/rail contact. The test specimens were manufactured from actual wheel/rail parts. The maching/finishing parameters were chosen in such a way as to obtain different surface roughness on the test specimens. A Design of Experiment approach (DOE) has been used to conduct experiments and to analyse the results. Results obtained from the field measurements show that the surface roughness of a newly ground rail changes rapidly during the initial stages following grinding. It was also concluded that there is a considerable variation of the surface roughness of re-turned wheels depending on which workshop performed the turning operation. Experimental results show that the surface roughness of the test specimens in certain material pairs do influence wear, friction and resultant surface damage. There is also a significant difference in the tribological behaviour of tests run in dry conditions and those run with water lubrication. / <p>Godkänd; 2007; 20070820 (pafi)</p>