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The use of environmentally adapted lubricants (EALs) is a subject of growing interest to industry as legislation increasingly demands the replacement of mineral oil lubricants. Vegetable-based fluids are widely seen as providing lubricants from a renewable source, as well as meeting demands for improved biodegradability. However, at present, utilization of such fluids is limited due to their rapid oxidation. EALs produced from other base stocks (i.e. synthetic esters) have been shown to provide performance benefi ts in hydrodynamic thrust bearings. In the present study, a hydrodynamic journal bearing test rig has been employed to compare the performance of three EALs (a VG32 saturated ester, rapeseed base fluid and a propylene glycoldioleate) relative to three mineral turbine oils (ISOVG32, ISOVG46 and ISOVG68) in the hydrodynamic regime. Results are given in terms of temperature, power loss and minimum fi lm thickness. The impact of oil viscosity index is also discussed., QC 20120309

The effect of ester-based turbine oil on the performance characteristics of a tilting pad journal bearing was studied. Mineral oils with viscosity grade of 32 and 46 and synthetic oil with viscosity similar to that of the mineral oil VG32 were used. Both mineral and synthetic oils provided similar temperatures. Pad temperature was strongly affected by rotational speed. A slower increase in temperature at higher speeds was caused by the shift in the maximum temperature zone due to the pad thermal crowning. Synthetic oil ran slightly hotter than VG32 mineral oil at lower speeds. At higher speed these oils had almost the same temperatures. This is an abstract of a paper presented at the World Tribology Congress, QC 20120217

The effect of compliant PTFE lining on hydrodynamics was studied. Results for the white metal and PTFE lined bearings were compared in terms of the maximum temperature, oil film thickness, and power loss. The oil film thickness in the PTFE bearing was shown. A favorable oil pocket was formed in the loaded zone. Temperature in the PTFE bearing was slightly higher., QC 20120214

While hydropower plant efficiency is exceptional, very little has been done to further improve its already high level of efficiency. In this regard, the bearings stand out as one of the major sources of losses in the plant that has potential for significant improvements with relatively little investment. One way to reduce losses while maintaining operating characteristics is to change lubricating oil to a higher viscosity index (VI) lubricant with a lower viscosity base oil. Studies showed that the thermal performance of mineral-based oils could be improved through the use of VI improvers to match that of synthetic lubricants. Another study investigated the case of polyalphaolefin-based lubricants, which found that lubricant with high VI provides performance equivalent to higher viscosity lubricants with lower VI ratings. Environmentally adapted lubricants, because of their inherent higher VI, provided higher viscosity in the region of lowest film thickness and lower viscosity in the rest of the bearing than standard mineral oil-based lubricants. This reduction in viscosity throughout the bearing led to a measurable reduction in power losses in the bearing system while maintaining desirable film thickness. Lubricants studied in this testing include industry standard VG32 mineral based turbine oil as a reference and synthetic ester and mineral based lubricants enhanced with polymer based VI improver additives., QC 20120210

Environmentally adapted lubricants (EALs) are becoming of increasing interest to the industry as legislation demands the replacement of mineral oil lubricants. However, little or nothing is known about the infl uence of ageing on the performance of these fluids in mixed and boundary lubricated tribological contacts. In this study, samples of three fully formulated lubricating oils, both in their 'unaged' form and 'aged' by means of an oxidation process in the laboratory, were utilized in a detailed study whereby variations in relative lubrication performance were examined. Standard laboratory pin-on-disc equipment was utilized in order to allow comparisons to be made and the definition of conclusions for a sliding tin bronze on steel contact. This simulated the interaction between an oil-lubricated bronze bushing and steel shaft as found in the vane adjustment mechanism of a Kaplan turbine. X-ray photoelectron spectroscopy analysis was employed to assess the effect on surface layer structural chemistry. Results showed, for the specific application being investigated, that EALs continue to function well in terms of their friction and wear performance even at high acid numbers., QC 20120229

The paper presents a thermoelastohydrodynamic (TEHD) analysis of thrust bearings with polytetrafluoroethylene (PTFE) faced pads. The influence of pad active surface geometry on main characteristics such as temperature profile, film thickness and pressure field are investigated. Due to the high compliance of the PTFE layer, deformations of the active surface due to pressure are quite large and have to be taken into account. The initial geometry of the pad is also of great importance; a parametric study on the pad geometry permits clarification of both geometry and deformation effects. The geometry of the pad, particularly for centrally pivoted pads, has to be considered in order to accurately predict performance of PTFE-faced tilting-pad thrust bearings., QC 20120214

The use of Environmentally Adapted Lubricants (EALs) is a subject of growing interest to industry as legislation increasingly demands the replacement of mineral oil lubricants. Vegetable based fluids are widely seen as providing lubricants from a renewable source as well as meeting demands for improved biodegradability. However, at present, utilisation of such fluids is limited due to their rapid oxidation. EALs produced from other base stocks (i.e. synthetic esters) have been shown to provide performance benefits in hydrodynamic thrust bearings. In the present study, a hydrodynamic journal bearing test rig has been employed to compare the performance of three EALs (a VG32 saturated ester, rapeseed base fluid and a Propylene Glycol Dioleate) relative to three mineral turbine oils (ISOVG32, ISOVG46 and ISOVG68) in the hydrodynamic regime. Results are given in terms of temperature, power loss and minimum film thickness. The impact of oil VI is also discussed., QC 20120508

QC 20120214

An analysis of a lubricated conformal contact is carried out to study the effect of surface texture on bearing friction and load carrying capacity using computational fluid dynamics. The work focuses on a journal bearing with several dimples. Two- and three-dimensional bearing geometries are considered. The full Navier-Stokes equations are solved under steady-state conditions with a multi-phase flow cavitation model. The coefficient of friction can be reduced if a texture of suitable geometry is 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. An additional pressure build-up produced as a result of the surface texture has been shown at low eccentricity ratios., QC 20120215

This paper reports results from the field tests of PTFE (polytetrafluoroethylene) faced thrust bearings operating at heavy loads. The PTFE composite bearing technology allows significant improvements in sliding bearing performance. Traditional white metal coating is substituted by a layer of PTFE composite. There are several advantages of using PTFE composites as a pad facing material, especially for hydroelectric equipment subjected to severe operating conditions. PTFE has a thermal conductivity about 170 times lower than that of white metal. Introduction of a thermal barrier, a layer of PTFE, between the oil film and pad backing reduces pad thermal deflection and, consequently, increases bearing load carrying capacity. Elasticity of the PTFE layer helps in adjusting the oil film shape in such a way that the bearings can carry higher loads. This paper also presents some temperature and oil film data for a bearing operating at a specific load of 11 MPa. The bearing was in operation 20 years. No significant signs of damage were observed when the bearing was dismantled in 2006., QC 20120217

The use of Environmentally Adapted Lubricants (EAL) is a subject of growing interest as public environmental awareness and new legislation increasingly demands the replacement of mineral oil lubricants. Vegetable-based fluids are widely seen as providing lubricants from a renewable source as well as meeting demands for improved biodegradability. A study was carried out to extend the available knowledge in respect to the use of vegetable base fluids in hydrodynamic lubrication. The influence of viscosity index (VI) on bearing performance was also examined. Three mineral turbine oils were used. Good comparability between the rapeseed fluid and the two thinner mineral oils was observed. This is an abstract of a paper presented at the 16th International Colloquium Tribology Lubricants Materials and Lubrication Engineering (Stuttgart/Ostfildern, Germany 1/15-17/2008)., QC 20120309

Dynamic coefficients for a lemon bore journal bearing with a compliant PTFE surface are computed. An efficient method for the calculation of bearing dynamic coefficients proposed by Lund [4] has been extended to compliant bearings. Comparison with a rigid babbitted lemon bore journal bearing in terms of dynamic coefficients and stability is given and discussed. It is shown that it is important to consider perturbations of both the oil film and the compliant lining to obtain realistic results. It is also shown that stability of compliant bearings is improved at some eccentricities compared with conventional babbitted bearings., QC 20120214

The use of polymer composites as facing materials in hydrodynamic thrust bearings gives performance benefits in terms of temperature distribution and friction losses. A study was carried out to investigate the break-away friction encountered during the transition phase (acceleration) under initial start-up from stationary state to full operational speed. This was examined for a series of commercially available PTFE-based composites. The lubricant used was a mineral oil. Best performance in terms of relative friction and wear was found for a carbon filled PTFE composite material. This is an abstract of a paper presented at the 16th International Colloquium Tribology Lubricants Materials and Lubrication Engineering (Stuttgart/Ostfildern, Germany 1/15-17/2008)., QC 20120229

A general cavitation algorithm that accommodates for an arbitrary density-pressure relation is presented. It is now possible to model the compressibility of the lubricant in such a way that the density-pressure relation is realistic throughout the contact. The algorithm preserves mass continuity for cavitation caused by bearing geometry and surface topography. It is a commonly accepted physical assumption that the contribution of the pressure driven flow is negligible in the cavitated region. This phenomenon is adopted in the present algorithm, which is similar to that of Elrod, and is modeled by a switch function that terminates the pressure gradient at the cavitation regions. Results with this algorithm for different density-pressure relations are presented and discussed. The effects of inlet conditions, such as surface roughness and starvation, on the load carrying capacity of the contact are analyzed., QC 20120227

This paper describes a method to compute the flow factors that compensate for an arbitrary surface roughness in a compressible hydrodynamic lubrication based on a homogenization technique. The Reynolds equation is used as the governing equation and the two-scale expansion involved in the homogenization process enables the local roughness scale to be treated separately from the global geometry scale. With this method, it is possible to compute the flow factors for any deterministic roughness. Measured two-dimensional surface profiles are used as examples. Profiles having the same Abbot curve are also shown to have the same flow factors, providing an efficient classification of surfaces in hydrodynamic two-dimensional contacts. Flow factors are computed for the rough surface profiles, and solutions for global bearing geometry are obtained and compared with the corresponding solutions from a smooth geometry., QC 20120221

A computational fluid dynamics (CFD) analysisis performed on a lubricated textured contactin order to study performance of texturedsurfaces. The work encompasses simulations of aslider bearing with dimples. The bearing is modelledwith a two-dimensional geometry. The fullNavier-Stokes equations are solved under steadystate conditions for a laminar and isothermalflow. The results are presented and the surfacetexture effects are analysed., QC 20120516

QC 20120215. QC 20130806

Results of a combined theoretical and experimental investigation into the operation of thrust bearings with polytetrafluoroethylene (PTFE)-faced pads are reported. Bearing performance is analyzed in terms of temperature, power loss, oil film thickness and pressure. These parameters are first calculated using a THD model. The effect of PTFE facing on bearing thermal performance is then presented and discussed. A TEHD model is subsequently employed. Obtained TEHD results show that oil film thickness and temperature art strongly, affected by the PTFE layer. Theoretical results are compared with measured temperature, oil film thickness, and pressure., QC 20120229

Experiments are conducted to compare the performance of fresh and aged samples of three oils in a boundary lubricated contact. These oils are Oil A (a commercially available unsaturated synthetic ester based hydraulic fluid (ISOVG32)), Oil B (a mineral based turbine oil (ISOVG68), and Oil C (a saturated synthetic ester based lubricating fluid (ISOVG46)). Tests are performed using a tin-bronze on steel contact in a pin-on-disc apparatus. Results from these tests provide data relating to friction and wear and their coupling to the aging of the fluids. No evidence of any significant deterioration of lubricant performance is observed for any of the fluids tested., QC 20120525

Laboratory experiments and full scale tests are conducted to verify and to quantify the advantages of the environmentally adapted oils in hydrodynamic lubrication in terms of operating film thickness, bearing power loss, and operating temperature. Four different oils were studied. Environmentally adapted PAO and ester base ISO VG46 oils were selected from Group IV and V stocks, respectively. Mineral ISO VG68 oil was selected as the reference oil. Mineral ISO VG46 oil was chosen for comparison. Ester base oil provided the best bearing operating characteristics in terms of the developed oil film, pad temperature, and power loss. Thus, it was chosen for the further tests in large full scale bearings. Environmentally adapted ester base oil ISO VG46 provided much better performance than traditionally used mineral oil ISO VG68. Compared to the mineral oil power loss and bearing temperatures are reduced while minimum oil film remains the same., QC 20120229

QC 20120528

Research regarding environmentally adapted lubricants results of the research performed at Luleå University of Technology were positive. Thus, the formulation work of an environmentally adapted lubricant for hydropower applications started. A change to a synthetic ester based lubricant would give technical advantages as well as environmental benefits. The initial tests were conducted on the base fluid. Two turbine oils were developed, Turb Way SE and TurbWay SE LV, for hydropower applications. Oxidation tests were performed in both the RPVOT (ASTM D 2272) and in TOST (ASTM D 943). The stability of the turbine oil was > 20 times better than tested environmentally adapted hydraulic fluids. Field tests were conducted in a full scale turbine at Porjus hydropower plant to confirm the promising results obtained from the research in the tilting thrust bearing rig., QC 20120307

The aging behavior of synthetic lubricants, in particular environmentally adapted lubricants esters, in comparison to mineral base oils, is studied. V Three fully commercially formulated lubricants were subjected to an oxidation process using a modified dry-Waterless Turbine Oil Oxidation Stability Test. The oils were: Oil A (hydraulic unsaturated ester with antioxidants and corrosion inhibitors), Oil B (turbine mineral oil with antioxidants and corrosion inhibitors), and Oil C (turbine saturated ester oil with antioxidants and corrosion inhibitors)., QC 20120528

The influence of pad facing material on hydrodynamic lubrication in tilting-pad thrust bearings is investigated in terms of pad and oil-film temperatures and thicknesses. Two tilting-pad thrust bearings are examined: one with babbitt pad facing, the other with a layer of PTFE-based composite material. Frictional torque, pad, collar, and oil-film temperatures and thicknesses are all monitored by means of a comprehensive array of sensors mounted in the bearing and shaft. A considerably smaller range of temperature is seen in the steel backing immediately below the surface material for the PTFE faced pads. Oil-film temperatures measured at the mid-point on the pad trailing edge show no significant difference between the two bearings. Oil-film thicknesses in the two bearings are seen to differ. At the leading edge, oil-film thickness is thinner for the PTFE pad than for babbitt. However, at the trailing edge the PTFE pad has the thicker film., QC 20120525

QC 20120529

QC 20120229

QC 20120229

Results of a numerical study of the influence of micro-patterned surfaces in hydrodynamic lubrication of two parallel walls are reported. Two types of parameterized grooves with the same order of depth as the film thickness are used on one stationary wall. The other wall is smooth and is sliding with a specified tangential velocity Isothermal incompressible two dimensional full film fluid flow mechanics is solved using a Computational Fluid Dynamics method. It is shown that, by introducing a micro-pattern on one of two parallel walls, a net pressure rise in the fluid domain is achieved. This produces a load carrying capacity on the walls which is mainly contributed by fluid inertia. The load carrying capacity increases with Reynolds number The load carrying capacity is reported to increase with groove width and depth. However at a certain depth a vortex appears in the groove and near this value the maximum load carrying capacity is achieved. It is shown that the friction force decreases with deeper and wider grooves. Among all geometries studied, optimum geometry shapes in terms of hydrodynamic performance are reported., QC 20120227

The primary objective of this study was to investigate the influence of surface texturing on hydrodynamic lubrication of tilting-pad thrust bearings in terms of bearing power loss, operating temperature, and oil-film thickness. For this purpose, the working faces of six thrust pads from a 228.6-mm-outer-diameter bearing were textured. The textured surface consisted of a system of crossing channels of less than 10 Όm in depth. Tests were conducted with a VG68 mineral turbine oil supplied to the bearings at a constant temperature of 50°C and flow rate of 15 L/min. The following parameters were measured: frictional torque, pad and collar temperatures, oil-film thickness, and pressure profiles along two circumferential lines. No significant change in collar and pad temperature could be observed when the patterned bearing was used. However, the textured bearing showed a tendency to exhibit lower power loss especially when an optimum oil flow supply rate was used. At the same time, inlet and outlet film thicknessesfor the patterned bearing showed larger values than those obtained during tests on the plain babbitt pads., QC 20120229

The influence of pad facing material on hydrodynamic lubrication in tilting-pad thrust bearings is investigated in terms of pad and oil-film temperatures and thicknesses. Two tilting-pad thrust bearings are examined: one with babbitt pad facing, the other with a layer of PTFE-based composite material. Frictional torque, pad, collar, and oil-film temperatures and thicknesses are all monitored by means of a comprehensive array of sensors mounted in the bearing and shaft.A considerably smaller range of temperature is seen in the steel backing immediately below the surface material for the PTFE faced pads. Oil-film temperatures measured at the mid-point on the pad trailing edge show no significant difference between the two bearings. Oil-film thicknesses in the two bearings are seen to differ. At the leading edge, oil-film thickness is thinner for the PTFE pad than for babbitt. However, at the trailing edge the PTFE pad has the thicker film., QC 20120229

A general cavitation algorithm is presented that accommodates for an arbitrary density-pressure relation. Here it is possible to model the compressibility of the lubricant in such way the density-pressure relation is realistic from sub-cavity to high pressure regions respectively. The algorithm preserves mass continuity which is of importance when inter-asperity cavitation of rough surfaces is considered. Results with this algorithm for different density-pressure relations are presented and discussed., QC 20120227

QC 20120229

QC 20120306

An interdisciplinary research group was created at the Lulea University of Technology in Sweden to help develop world leading competencies and knowledge for cutting-edge technologies in hydro power generation. Based on the studies of this Swedish research group, this paper provides a description of the power system from a dynamic point of view to obtain an overall picture, and is completed with a detailed description of the bearings and turbines. The state-of-the-art in each field is presented, together with suggestions for further development, QC 20120306

The effect of oil viscosity grade on the performance of tilting pad thrust bearings is examined in a wide range of shaft speeds and specific bearing loads. Data being discussed were obtained in tests carried out with 228 mm outer diameter (o.d.) and 267 mm o.d. bearings lubricated with ISO VG32 and ISO VG68 mineral oils in a fully flooded mode. In a low-speed range (below 40 m/s), the performance of the 228 mm bearing is analysed in terms of pad and collar temperatures, power loss and oil film thickness. Pad temperature and power loss are employed in the analyses of the 267 mm o. d. bearing operated at high sliding speeds of up to 115 m/s. The results show that there is a significant effect of oil viscosity grade on bearing main operating parameters. The substitution of ISO VG32 oil for ISO VG68 oil results in considerably reduced pad temperatures, lower power loss and thinner oil film thickness. However, no measurable difference in power loss was observed after the onset of turbulence. The influence of oil viscosity grade on pad temperature pattern is analysed. The thermal effect of oil viscosity grade on pad temperature pattern and power loss is also compared with the effect of offset pivot., QC 20120229

Evolution of friction torque in a pivoted-pad thrust pad bearing, as well as collar and shaft temperatures and pressure profiles in transient conditions, have been investigated in [1]. The present paper reports further transient test results for the same thrust bearing with an outer diameter of 228.6mm and 60% offset pivoted pads, operated in fully flooded mode. In this study, a complete set of bearing main performance parameters, including bearing pad and collar temperatures, oil film thickness and friction torque are obtained by means of a high-speed data acquisition system. Evolution of these parameters as a result of sudden variations in rotational speed and load are presented and analysed. Results are generalised in terms of Fourier number and compared with published numerical data., QC 20120229

QC 20120229

In bearings a hydrodynamic oil film separates stationary and moving surfaces reducing friction and eliminating wear. This separation is achieved due to the pressure generation in the converging wedge formed by the surfaces. Thickness of the oil film between the surfaces is an important parameter that affects bearing load carrying capacity and its margin of safety. There are indications that texturing of the load carrying surfaces can provide an additional pressure generation in the oil film and better oil circulation in the loaded zone. Introduction of micro indentations or grooves on the bearing surface can thus contribute to higher load carrying capacity and lower coefficient of friction. Latest experimental data and theoretical findings as well as those available in the scientific literature will be discussed in this paper., QC 20120229

This report is a continuation of the work reported earlier that was aimed to assess the feasibility of replacing the mineral oil in hydro power plants with a more environmentally acceptable fluid. Those studies examined the differences between mineral and synthetic oils in terms of maximum operating temperature, minimum oil film thickness and power loss in a tilting-pad thrust bearing with an outer diameter of 228.6 mm operating in a fully flooded mode. Test data and theoretical results showed that the ester base oil performed better than the traditionally used VG68 mineral oil. In the present paper further performance comparisons between this environmentally adapted ester base oil and VG68 mineral oil, this time in a full scale thrust bearing of a hydro power plant, are reported. Again, a complete set of bearing performance parameters is recorded. Recorded data that include temperature, oil-film thickness and power loss are presented and analysed. It is shown that the environmentally adapted ester base oil significantly improves bearing operating characteristics., QC 20120229