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Lubricants, Volume 3, Issue 1 (March 2015) , Pages 1-79

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Open AccessArticle
Characterization of Thermal Stability of Synthetic and Semi-Synthetic Engine Oils
Lubricants 2015, 3(1), 54-79; https://doi.org/10.3390/lubricants3010054 - 17 Mar 2015
Cited by 12 | Viewed by 4339
Abstract
Engine oils undergo oxidative degradation and wears out during service. Hence it is important to characterize ageing of engine oils at different simulated conditions to evaluate the performance of existing oils and also design new formulations. This work focuses on characterizing the thermo-oxidative [...] Read more.
Engine oils undergo oxidative degradation and wears out during service. Hence it is important to characterize ageing of engine oils at different simulated conditions to evaluate the performance of existing oils and also design new formulations. This work focuses on characterizing the thermo-oxidative degradation of synthetic and semi-synthetic engine oils aged at 120, 149 and 200 °C. Apparent activation energy of decomposition of aged oils evaluated using the isoconversional Kissinger-Akahira-Sunose technique was used as a thermal stability marker. The temporal variation of stability at different ageing temperatures was corroborated with kinematic viscosity, oxidation, sulfation and nitration indices, total base number, antiwear additive content and molecular structure of the organic species present in the oils. At the lowest temperature employed, synthetic oil underwent higher rate of oxidation, while semi-synthetic oil was stable for longer time periods. At higher temperatures, the initial rate of change of average apparent activation energy of synthetic oil correlated well with a similar variation in oxidation number. A mixture of long chain linear, branched, and cyclic hydrocarbons were observed when semi-synthetic oil was degraded at higher temperatures. Full article
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Open AccessReview
On the Characteristics of Misaligned Journal Bearings
Lubricants 2015, 3(1), 27-53; https://doi.org/10.3390/lubricants3010027 - 16 Mar 2015
Cited by 11 | Viewed by 2661
Abstract
Journal bearing misalignment arise generally from the shaft deformation under load, deflection of the shaft, manufacturing and assembly errors, improper installation, and asymmetric loading. During operations, misalignment has a considerable effect on the static and dynamic performances. It could cause wear, vibration and [...] Read more.
Journal bearing misalignment arise generally from the shaft deformation under load, deflection of the shaft, manufacturing and assembly errors, improper installation, and asymmetric loading. During operations, misalignment has a considerable effect on the static and dynamic performances. It could cause wear, vibration and even system failure. In this article, a literature review of misalignment of the journal bearings is presented. The basic theory for the misalignment and some results for the circular journal bearing are also presented to show the general trends of the misalignment. Full article
(This article belongs to the Special Issue Friction and Lubrication of Bearings)
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Open AccessArticle
Wear Performance of Sequentially Cross-Linked Polyethylene Inserts against Ion-Treated CoCr, TiNbN-Coated CoCr and Al2O3 Ceramic Femoral Heads for Total Hip Replacement
Lubricants 2015, 3(1), 14-26; https://doi.org/10.3390/lubricants3010014 - 16 Feb 2015
Cited by 6 | Viewed by 2755
Abstract
The aim of the present study was to evaluate the biotribology of current surface modifications on femoral heads in terms of wettability, polyethylene wear and ion-release behavior. Three 36 mm diameter ion-treated CoCr heads and three 36 mm diameter TiNbN-coated CoCr heads were [...] Read more.
The aim of the present study was to evaluate the biotribology of current surface modifications on femoral heads in terms of wettability, polyethylene wear and ion-release behavior. Three 36 mm diameter ion-treated CoCr heads and three 36 mm diameter TiNbN-coated CoCr heads were articulated against sequentially cross-linked polyethylene inserts (X3) in a hip joint simulator, according to ISO 14242. Within the scope of the study, the cobalt ion release in the lubricant, as well as contact angles at the bearing surfaces, were investigated and compared to 36 mm alumina ceramic femoral heads over a period of 5 million cycles. The mean volumetric wear rates were 2.15 ± 0.18 mm3·million cycles−1 in articulation against the ion-treated CoCr head, 2.66 ± 0.40 mm3·million cycles−1 for the coupling with the TiNbN-coated heads and 2.17 ± 0.40 mm3·million cycles−1 for the ceramic heads. The TiNbN-coated femoral heads showed a better wettability and a lower ion level in comparison to the ion-treated CoCr heads. Consequently, the low volumes of wear debris, which is comparable to ceramics, and the low concentration of metal ions in the lubrication justifies the use of coated femoral heads. Full article
(This article belongs to the Special Issue Tribological Performance of Artificial Joints) Printed Edition available
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Open AccessArticle
Experimental Performance Study of a High Speed Oil Lubricated Polymer Thrust Bearing
Lubricants 2015, 3(1), 3-13; https://doi.org/10.3390/lubricants3010003 - 21 Jan 2015
Cited by 7 | Viewed by 3052 | Correction
Abstract
With the demand for turbomachinery to operate at higher speeds, loads, and power, fluid film bearings that support turbomachinery must be capable of operating in these more demanding applications. Thrust bearings operating at high speeds and loads can experience high surface temperatures and [...] Read more.
With the demand for turbomachinery to operate at higher speeds, loads, and power, fluid film bearings that support turbomachinery must be capable of operating in these more demanding applications. Thrust bearings operating at high speeds and loads can experience high surface temperatures and thin fluid film thickness. Typically, babbitt (white metal) is the bearing lining material for most turbomachinery bearings but is limited in operating temperature and allowable film thickness. Polymer based materials are alternative materials that can operate at high temperatures and with thin films and have been in use for many decades in high load applications, such as electric submersible pumps (ESP). Test results of polymer lined thrust bearings subjected to modern turbomachinery speeds and loads are presented and compared to babbitt lined bearings of the same design and under similar conditions. The test results show polymer lined thrust bearings can operate at higher bearing unit loads than babbitt. Full article
(This article belongs to the Special Issue Friction and Lubrication of Bearings)
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Open AccessEditorial
Acknowledgement to Reviewers of Lubricants in 2014
Lubricants 2015, 3(1), 1-2; https://doi.org/10.3390/lubricants3010001 - 09 Jan 2015
Viewed by 1385
Abstract
The editors of Lubricants would like to express their sincere gratitude to the following reviewers for assessing manuscripts in 2014:[...] Full article
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