| 1. |
- Del Din, Massimo, et al.
(författare)
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Wear characteristics with mixed lubrication conditions in a full scale journal bearing
- 1999
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Ingår i: Wear. - 0043-1648 .- 1873-2577. ; 232:2, s. 192-198
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Tidskriftsartikel (refereegranskat)abstract
- Increased awareness of environmental problems has stressed the importance of switching from traditional lubricants to more environmentally friendly alternatives. Different investigations with standard test methods indicate that such a switch is possible without loss of lubricating power. The question arises if the statement above is true for industrial lubricating conditions, without laboratory cleanliness. This paper presents a study of friction and wear in a two grooved journal bearing at different shaft speeds, oil temperatures and contamination levels. A number of tests have been conducted combined with a theoretical analysis of film thickness and lubricating regime. The aim was to investigate whether an environmentally adapted rape seed-synthetic ester oil could replace a traditional mineral oil in a full scale application. The results show that the rape seed-synthetic ester oil gives significantly lower values of wear regardless of the operating conditions and there is also a tendency of lower values of frictional torque compared with the mineral oil. Mainly operating in the mixed lubrication regime, no signs of impending bearing failure have been registered, even though a large amount of silica particles added to the oil gave higher wear values than with uncontaminated oil.
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| 2. |
- Gåhlin, Rickard, et al.
(författare)
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Wear volume and wear distribution of hydraulic motor cam rollers studied by a novel atomic force microscope technique
- 1998
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Ingår i: Wear. - 0043-1648 .- 1873-2577. ; 220:1, s. 1-8
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Tidskriftsartikel (refereegranskat)abstract
- The wear volume and wear distribution of chromium steel cam rollers in a high-torque hydraulic motor has been investigated. The cam roller is a part of a novel silicon nitride/chromium steel journal bearing system. An atomic force microscope (AFM) was used to obtain topographical images of the cam roller surfaces before and after use in a full-scale test of the hydraulic motor. The surfaces were marked with small Vickers indentations to make it possible to reposition the AFM to the same locations. To measure the microscopical wear and produce high resolution maps of the local distribution of wear, a recently developed method was utilised. The method is based on two techniques to treat digital topographical images. To map the distribution of wear, the image of the unworn surface is substracted by the image of the worn surface. To measure the wear volume, the bearing histogram is used to calculate a volume relative to a fixed depth. The calculated volume of the unworn surface is then subtracted by the volume of the worn surface. The ceramic/metal system displayed an extremely low wear rate. corresponding to a typical total mean wear depth of about 30 nm. The surface topography showed very limited changes with the minute wear mainly localised to the uppermost part of the surface ridges. The adopted method thus allowed a unique high resolution mapping and volumetric measurement of the initial stages of wear (1 mg lost out of 600 g) on a real machine element. This high resolution analysis is promising for improving tribological testing of real machine elements with long expected wear lives, by reducing the need for excessively accelerated tests or extremely long and costly test durations.
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| 3. |
- Holgerson, Mikael
(författare)
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Apparatus for measurement of engagement characteristics of a wet clutch
- 1997
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Ingår i: Wear. - 0043-1648 .- 1873-2577. ; 213:1-2, s. 140-147
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Tidskriftsartikel (refereegranskat)abstract
- The problem of obtaining smooth gear changing whilst maintaining long life of wet clutches in automatic transmissions demands more knowledge about their behaviour. Experimental and theoretical studies on the engagement of a wet clutch have been carried out. A wet clutch test rig which can apply a drive torque during engagement was developed. The apparatus could also vary the sliding velocity, inertia, force rate, and lubrication. Measured output data included normal force, brake torque, sliding velocity and temperature over time. The input parameters and output characteristics obtained were similar to those in automatic transmissions used in cars. The friction characteristics as well as power and temperature were investigated. A simple model was developed to estimate the engagement performance which gave a good approximation of the performance measured in the tests. The friction is high in the beginning and end of the engagement cycle and lower inbetween. There is a torque peak just before the clutch stops owing to friction characteristics. The maximum developed power occurs at about half of the engagement time, while the maximum temperature is just before clutch stop
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| 4. |
- Höglund, Erik, et al.
(författare)
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Effect of pressurised gases on the viscosity of polyalkylene glycols
- 1997
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Ingår i: Wear. - 0043-1648 .- 1873-2577. ; 207:1-2, s. 24-28
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Tidskriftsartikel (refereegranskat)abstract
- Experiments have been conducted into the effect of pressurised hydrocarbons on the viscosity of a polyalkylene glycol. This lubricant is intended to be used in a sub-sea compressor/pump unit and the risk of diluting the lubricant by the surrounding natural gas, thus reducing the lubricant's viscosity, was to be investigated. Dilution can cause insufficient lubrication of the compressor's moving parts. A pressurised Höppler type viscometer was used for the tests which were conducted at 50 °C with a methane based hydrocarbon mixture and with pure nitrogen. The viscosity of the lubricant was reduced to 24% after 24 h exposure at 100 bar with the hydrocarbon mixture. A gas analysis was performed which indicates that the heavier hydrocarbons used are relatively soluble in the lubricant even at relatively low pressures. Nitrogen was found to have a very limited effect on the viscosity even if some was dissolved in the oil. A long duration test of 11 days was also made with nitrogen. This test did not show any significant reduction of the viscosity.
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| 5. |
- Höglund, Erik
(författare)
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Influence of lubricant properties on elastohydrodynamic lubrication
- 1999
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Ingår i: Wear. - 0043-1648 .- 1873-2577. ; 232:2, s. 176-184
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Tidskriftsartikel (refereegranskat)abstract
- In hard EHL, encountered in, e.g., gears, rolling element bearings etc. the properties of the lubricant play a significant role in the forming of a lubricating film and reducing friction between the contacting surfaces. The influence of pressure and temperature on viscosity, limiting shear stress and density, has to be taken into account when creating lubricant models to be used in numerical calculations of film thickness and friction. This paper describes some experimental methods to determine these properties of a number of different lubricating oils, both from mineral, vegetable and synthetic origin. The results show that, apart from 5P4E, naphthenic mineral oil has the highest values of pressure-viscosity as well as limiting shear stress-pressure coefficients. It also exhibits the highest density increase with pressure. Rapeseed oil has a rather high pressure-viscosity coefficient but a low limiting shear stress-pressure coefficient as well as a low density increase with pressure. Thus, rapeseed oil is a strong alternative to naphthenic (and also paraffinic) oil since it has the ability to form a relatively thick oil film and at the same time give a low coefficient of friction. Ester, polyglycol and polyalphaolefin oils also exhibit low values of friction but are not equally good as rapeseed oil to form a lubricant film as a result of their lower pressure-viscosity coefficients
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| 6. |
- Jonsson, Ulf J.
(författare)
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Lubrication of rolling element bearings with HFC-polyolester mixtures
- 1999
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Ingår i: Wear. - 0043-1648 .- 1873-2577. ; 232:2, s. 185-191
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Tidskriftsartikel (refereegranskat)abstract
- Manufacturers of refrigeration and air-conditioning compressors have had to re-evaluate their knowledge of compressor bearing lubrication following the introduction of hydrofluorocarbon (HFC) refrigerants and polyolester lubricants. The lack of anti wear protection in comparison to traditionally used refrigerants/lubricants makes the lubrication of bearings using these modern systems a much more difficult task than before. This paper presents results from ongoing research activities to develop methods and generate data that can be used to support engineers and chemists designing compressors and lubricants. Viscosity and pressure-viscosity data for three ISO VG 32 polyolester lubricants and also a film forming comparison between two ISO VG 68 polyolester lubricants are presented. This data shows that a high degree of branching has a negative effect on the performance of the lubricant in certain applications. Whilst a branched lubricant offers the benefit of a higher-pressure-viscosity coefficient under normal conditions, the reduction in viscosity and pressure-viscosity coefficient when diluted by refrigerant is far greater than for normal/linear lubricants. This characteristic results in a poorer film forming ability in applications where the lubricant is subjected to refrigerant gas with a low superheat
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| 7. |
- Kassfeldt, Elisabet, et al.
(författare)
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Environmentally adapted hydraulic oils
- 1997
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Ingår i: Wear. - 0043-1648 .- 1873-2577. ; 207:1-2, s. 41-45
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Tidskriftsartikel (refereegranskat)abstract
- A comparison has been carried out between one mineral based hydraulic oil and three environmentally adapted hydraulic oils. Two of these are semi-synthetic oils, i.e. mixtures of vegetable base oil and synthetic esters, and the last is based on synthetic esters only. Technical properties such as viscosity, pour point etc., and chemical properties such as phosphorus and sulphur content etc. were documented using standard test methods. The lubricant capability properties were determined through measurements of the capability of each oil to build a film in an elastohydrodynamic contact. The oil film thickness is important to avoid wear and failure and to guarantee separation of surfaces. The results show that at 40°C the environmentally adapted oils give a thicker film than the mineral oil. At 80°C there is no significant difference between the different types of oil in their capability to build a lubricating film. The maximum shear strength was measured and these results are presented with the constant of proportionality γ, from the theoretical model τ approximately equals γp, which is valid at very high pressures. The measurements were carried out at contact pressures in the range 5-7 GPa. The results show that all environmentally adapted oils give a lower γ value than the mineral oil, which is an advantage since a low shear strength results in lower friction in highly loaded contacts. Measurements of toxicity to aquatic organisms (Daphnia magna) show very large differences between the tested oils, and this implies that a change from a mineral oil to an environmentally adapted oil can give important environmental advantages.
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| 8. |
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| 9. |
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| 10. |
- Larsson, Roland, et al.
(författare)
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Study of lubricated impact using optical interferometry
- 1995
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Ingår i: Wear. - : Elsevier BV. - 0043-1648 .- 1873-2577. ; 190:2, s. 184-189
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Tidskriftsartikel (refereegranskat)abstract
- An experimental study of lubricated impacts between a steel ball and a flat glass surface has been performed. The experimental set-up consists of a Ø70 mm ball mounted on a pendulum which impacts onto a lubricated glass disc. The contact region is studied by means of optical interferometry using a monochromatic light source, a microscope and a high-speed video recording equipment. The lubricants are of PAO type and the viscosity ranges from 27 to 2600 mm2 s-1 at the test temperature. The impact velocity is varied between 0.08 and 0.29 m s-1. A dimple occurs at the centre of the contact where the lubricant is trapped. The influence of viscosity and impact velocity on the dimple's depth and diameter is studied.
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