Lubricants

329 KiB

Open AccessArticle

Characterization of Thermal Stability of Synthetic and Semi-Synthetic Engine Oils

by Anand Kumar Tripathi and Ravikrishnan Vinu

Lubricants 2015, 3(1), 54-79; https://doi.org/10.3390/lubricants3010054 - 17 Mar 2015

Cited by 58 | Viewed by 15350

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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446 KiB

Open AccessReview

On the Characteristics of Misaligned Journal Bearings

by Joon Young Jang and Michael M. Khonsari

Lubricants 2015, 3(1), 27-53; https://doi.org/10.3390/lubricants3010027 - 16 Mar 2015

Cited by 68 | Viewed by 12976

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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611 KiB

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

by Christian Fabry, Carmen Zietz, Axel Baumann and Rainer Bader

Lubricants 2015, 3(1), 14-26; https://doi.org/10.3390/lubricants3010014 - 16 Feb 2015

Cited by 15 | Viewed by 9209

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)

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780 KiB

Open AccessArticle

Experimental Performance Study of a High Speed Oil Lubricated Polymer Thrust Bearing

by Jie Zhou, Barry Blair, John Argires and Donald Pitsch

Lubricants 2015, 3(1), 3-13; https://doi.org/10.3390/lubricants3010003 - 21 Jan 2015

Cited by 27 | Viewed by 9158 | 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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16 KiB

Open AccessEditorial

Acknowledgement to Reviewers of Lubricants in 2014

by Lubricants Editorial Office

Lubricants 2015, 3(1), 1-2; https://doi.org/10.3390/lubricants3010001 - 09 Jan 2015

Viewed by 3191

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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Lubricants, Volume 3, Issue 1 (March 2015) – 5 articles , Pages 1-79

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