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19 pages, 9358 KiB

Open AccessArticle

Lifting Lightweight Metals to a New Level—Tribological Improvement by Hybrid Surface Solutions on Aluminium and Magnesium

by Anna Buling and Joerg Zerrer

Lubricants 2020, 8(6), 65; https://doi.org/10.3390/lubricants8060065 - 13 Jun 2020

Cited by 3 | Viewed by 3611

Abstract

Nanocrystalline PEO (plasma electrolytical oxidation) coatings were performed on Al 6082 and Mg AZ31 alloys, resulting in hard, dense and wear-resistant surfaces to increase the wear resistance of those alloys. To soften the wear influence on the counter body side and to reduce [...] Read more.

Nanocrystalline PEO (plasma electrolytical oxidation) coatings were performed on Al 6082 and Mg AZ31 alloys, resulting in hard, dense and wear-resistant surfaces to increase the wear resistance of those alloys. To soften the wear influence on the counter body side and to reduce friction in a tribological application, the high-performance polymer PEEK (poly-ether-ether-ketone) was added to the load-supporting PEO surface by a laser melting technique to avoid heat influence on the lightweight substrate. The usage of additives in the PEEK dispersion led to stable conditions in the tribological system by decreasing the wear on the coated substrate as well as the counter body to a minimum accompanied by a low coefficient of friction during the whole life-time. The adopted hybrid coating systems were characterized using laser scanning microscopy (LSM), secondary and back scattered electron microscopy (SEM) and energy dispersive spectroscopy (EDS). A pin-on-disc test was employed to analyze the wear behavior of the different PEO and hybrid coatings and the influences of these surfaces on the coefficient of friction. Full article

(This article belongs to the Special Issue Selected Papers from the 7th European Conference on Tribology (ECOTRIB2019))

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19 pages, 3043 KiB

Open AccessArticle

Triboemission of FINE and Ultrafine Aerosol Particles: A New Approach for Measurement and Accurate Quantification

by Roman Nevshupa, Marta Castellote, Jesus Antonio Carlos Cornelio and Alejandro Toro

Lubricants 2020, 8(2), 21; https://doi.org/10.3390/lubricants8020021 - 17 Feb 2020

Cited by 5 | Viewed by 3061

Abstract

A dynamic model based on mass balance of fine aerosol particles was developed in order to tackle the problem of accurate quantification of mechanically stimulated particle emission (MSPE) from nanofunctionalized and solid lubricating materials. In contrast to the conventional approach, the model accounts [...] Read more.

A dynamic model based on mass balance of fine aerosol particles was developed in order to tackle the problem of accurate quantification of mechanically stimulated particle emission (MSPE) from nanofunctionalized and solid lubricating materials. In contrast to the conventional approach, the model accounts for the effect of air turbulization caused by moving parts of the experimental tribological setup on the enhancement of particle deposition velocity. The increase of the velocity of the moving parts results in an increase of the deposition velocity that leads to a significant underestimation of experimentally measured particle emission rates. The developed model was experimentally verified using natural and artificial nanoparticle aerosols. Finally, the new methodology of particle emission rate quantification was employed for the analysis of fine particle emission produced when the solid lubricating materials were tested against a sliding steel surface. The developed method paves the way for defining a standard method of experimental assessment of nanoparticle triboemission enabling the experimental results obtained in various laboratories to be compared. It also bridges the gap between the phenomenological models and experimental measurements. Full article

(This article belongs to the Special Issue Selected Papers from the 7th European Conference on Tribology (ECOTRIB2019))

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14 pages, 9484 KiB

Open AccessArticle

Friction and Wear Performance of Various Polymer Coatings for Journal Bearings under Stop Start Sliding

by Florian Summer, Florian Grün and Emma R Ravenhill

Lubricants 2020, 8(1), 1; https://doi.org/10.3390/lubricants8010001 - 18 Dec 2019

Cited by 15 | Viewed by 4565

Abstract

Increasing environmental legislation and demands for improved fuel economy performance have resulted in the introduction of various measures to optimize the internal combustion engine. Many of these actions significantly change the operating conditions of the engines and bring with them new challenges that [...] Read more.

Increasing environmental legislation and demands for improved fuel economy performance have resulted in the introduction of various measures to optimize the internal combustion engine. Many of these actions significantly change the operating conditions of the engines and bring with them new challenges that original engine manufacturers (OEMs) have to solve. One example is stop start technology, which changes the operation of many core parts of engines such as journal bearings. Hence, the current paper deals with this topic. In particular, different polymer coated bearings have been studied regarding their friction and wear performance under stop start sliding. Detailed material characterization of the materials was carried out using light microscopy and scanning electron microscopy. Furthermore, tribometric tests were conducted under controlled and similar conditions on a TE92 tribometer using a bearing segment test set up. The results show that the various polymer coated bearings tested provide enhanced friction and wear performance in comparison to other bearing types (e.g., lead-based electroplated) and that friction and wear performance differs also among them. In this regard, a higher amount of solid lubricant fillers and a dense filler structure appears to be beneficial under the given test conditions. Full article

(This article belongs to the Special Issue Selected Papers from the 7th European Conference on Tribology (ECOTRIB2019))

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13 pages, 10164 KiB

Open AccessArticle

Tribological Properties of Alkyldiphenylethers in Boundary Lubrication

by Renguo Lu, Masaya Morimoto, Hiroshi Tani, Norio Tagawa and Shinji Koganezawa

Lubricants 2019, 7(12), 112; https://doi.org/10.3390/lubricants7120112 - 10 Dec 2019

Cited by 4 | Viewed by 3261

Abstract

Lubricants that are used in miniaturized moving mechanical components generally serve under severe conditions, such as high temperature, high speed, and high load. Although alkyldiphenylethers (ADEs) are used as base oils for high-temperature greases, their tribological properties remain unclear. This study investigated the [...] Read more.

Lubricants that are used in miniaturized moving mechanical components generally serve under severe conditions, such as high temperature, high speed, and high load. Although alkyldiphenylethers (ADEs) are used as base oils for high-temperature greases, their tribological properties remain unclear. This study investigated the influence of the alkyl chains on the tribological properties of ADEs. Longer and more attached alkyl chains decreased the friction coefficient of ADEs under both reciprocating and continuous sliding conditions. Wear was found to be independent of the alkyl chain under reciprocating sliding conditions due to abrasion being caused by debris that was not readily removed. ADEs showed good anti-wear properties when used as either a lubricant or an additive under continuous sliding conditions. Much smoother surfaces in the friction track were observed in comparison to poly-α-olefin. Fourier-Transform infrared spectroscopy analysis suggested that the ether groups were attracted to the worn steel surface, phenyl groups became consequently perpendicular, and the attached alkyl chains repelled other substances and prevented further wear of the surface. Moreover, ADEs showed a high adaptability with traditional additives. Full article

(This article belongs to the Special Issue Selected Papers from the 7th European Conference on Tribology (ECOTRIB2019))

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12 pages, 22111 KiB

Open AccessArticle

Development of a Model Test System for a Piston Ring/Cylinder Liner-Contact with Focus on Near-to-Application Seizure Behaviour

by Michael Pusterhofer, Florian Summer, Daniel Wuketich and Florian Grün

Lubricants 2019, 7(12), 104; https://doi.org/10.3390/lubricants7120104 - 22 Nov 2019

Cited by 12 | Viewed by 5571

Abstract

Physical simulations of tribo contacts in internal combustion engines can act as a supporting tool to match upcoming guidelines and emission restrictions. In particular, the scuffing resistance of the contact between the piston ring and cylinder liner suffers under decreasing oil viscosity and [...] Read more.

Physical simulations of tribo contacts in internal combustion engines can act as a supporting tool to match upcoming guidelines and emission restrictions. In particular, the scuffing resistance of the contact between the piston ring and cylinder liner suffers under decreasing oil viscosity and limitation of antiwear additives. This paper aims to provide an experimental method to simulate the scuffing of the piston ring/cylinder liner-contact and to validate this method with real engine parts and the literature from engine tests. The experimental methodology uses a linear tribometer TE77 to test specimens from original piston rings and liners under reciprocating motion. Additionally, the ring specimen is given the opportunity to perform secondary movements (ring twisting, ring turning) and to run under deficient lubrication conditions similar to the engine. A specially designed test strategy enables the reproducible creation of seizure of the tribosystem. The seizure resistance of two engine oils, tested for validation, correlates with the known engine performance. Therefore, the model test system can be seen as a reproducible tool for simulating seizure of a ring/liner-system, showing similar trends and wear mechanisms as in an engine. Surface analysis depicts similarities between the scuffed surfaces of an engine and the model and discusses the origin of seizure based on the model specimens together with the relevant literature. Full article

(This article belongs to the Special Issue Selected Papers from the 7th European Conference on Tribology (ECOTRIB2019))

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17 pages, 5157 KiB

Open AccessArticle

Interactions of Ethanol with Friction Modifiers in Model Engine Lubricants

by Henara L. Costa and Hugh Spikes

Lubricants 2019, 7(11), 101; https://doi.org/10.3390/lubricants7110101 - 15 Nov 2019

Cited by 7 | Viewed by 5467

Abstract

When employed as an engine fuel, ethanol can accumulate in the lubricant during use. Previous work has shown that ethanol contamination affects friction and elastohydrodynamic lubrication (EHL) film formation, and also the growth and stability of anti-wear tribofilms. The present work uses spacer-layer [...] Read more.

When employed as an engine fuel, ethanol can accumulate in the lubricant during use. Previous work has shown that ethanol contamination affects friction and elastohydrodynamic lubrication (EHL) film formation, and also the growth and stability of anti-wear tribofilms. The present work uses spacer-layer ultrathin interferometry and MTM tests to investigate how ethanol (both hydrated and anhydrous) interacts with friction modifiers in model lubricants. Small proportions (5 wt %) of ethanol were added to solutions of friction modifiers (one MoDTC and three organic friction modifiers) in a Group I base oil. For the three organic friction modifiers, the presence of ethanol promoted the formation of thick viscous boundary films so that very low friction coefficients were measured at low entrainment speeds. For the MoDTC additive, the presence of ethanol prevented the formation of a low friction film at low speeds at 70 °C, but this effect disappeared at 100 °C, probably due to ethanol evaporation. Full article

(This article belongs to the Special Issue Selected Papers from the 7th European Conference on Tribology (ECOTRIB2019))

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28 pages, 13687 KiB

Open AccessArticle

Cooled Pads for Tilting-Pad Journal Bearings

by Steven Chatterton, Paolo Pennacchi, Andrea Vania and Phuoc Vinh Dang

Lubricants 2019, 7(10), 92; https://doi.org/10.3390/lubricants7100092 - 17 Oct 2019

Cited by 24 | Viewed by 4875

Abstract

Tilting-pad journal bearings (TPJBs) are widely installed in rotating machines owing to their high stability, but some drawbacks can be noted, such as higher cost with respect to cylindrical journal bearings and thermal issues. High temperatures in the pads correspond to low oil-film [...] Read more.

Tilting-pad journal bearings (TPJBs) are widely installed in rotating machines owing to their high stability, but some drawbacks can be noted, such as higher cost with respect to cylindrical journal bearings and thermal issues. High temperatures in the pads correspond to low oil-film thicknesses and large thermal deformations in the pads. Therefore, the restriction of the maximum temperature of the bearing is a key aspect for oil-film bearings. The temperature reduction is generally obtained by adopting higher oil inlet flowrates or suitable oil nozzles. In this paper, the idea of using cooled pads with internal channels in which an external cooling fluid is circulated will be applied to a TPJB for the first time. The three-dimensional TEHD model of the TPJB, equipped with a cooled pad, will be introduced, and the results of the numerical simulations will be discussed. Several analyses have been performed in order to investigate the influence of cooling conditions, such as the type, flowrate, inlet temperature and number of cooled pads. Two types of pad geometry with different cross-sections of the cooling circuit, namely, circular and six-square multi-channel sections, have been compared to the reference bearing with solid pads. Simple experimental tests were performed by means of a test rig equipped with a cooled pad bearing obtained with the additive manufacturing process, thus showing the effectiveness of the solution and the agreement with the predictions. Full article

(This article belongs to the Special Issue Selected Papers from the 7th European Conference on Tribology (ECOTRIB2019))

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11 pages, 943 KiB

Open AccessReview

Rethinking Tribology–Tracking Trends, Their Presence at the ECOTRIB 2019 Conference, and Their Impact on Tribology Research in Austria

by Friedrich Franek, Nicole Dörr, Ewald Badisch and Andreas Pauschitz

Lubricants 2020, 8(8), 80; https://doi.org/10.3390/lubricants8080080 - 31 Jul 2020

Cited by 2 | Viewed by 4024

Abstract

Economic and societal changes and technological development guide the focus of tribology research. “Classical” tasks, such as the improvement of materials or the tuning of a lubricant, have long been replaced by a function-oriented aggregate design, including specifications defined by needs arising from [...] Read more.

Economic and societal changes and technological development guide the focus of tribology research. “Classical” tasks, such as the improvement of materials or the tuning of a lubricant, have long been replaced by a function-oriented aggregate design, including specifications defined by needs arising from production and the environment. Tribology faces, among other remarkable changes, a paradigm shift according to the tendency to replace classic internal combustion engine (ICE) drivetrains with electric drives. How tribology will develop, and which research topics will prevail in the future, are being explored by several studies based on the experience of experts. The variety of contributions to journals and conferences provide an indicator of the importance of such tasks or topics. Here, a report on the ECOTRIB 2019—7th European Conference on Tribology held in Vienna, Austria, is presented. From the available information, an even stronger integration of other disciplines into tribology is noticeable, with certain hype in the fields of advanced material technology, sensor integration and the implementation of data science. Measures to rethink tribology from both an organizational and scientific point of view to cope with future tasks are being targeted and comprehensively implemented in the current research program “InTribology”, operated by the Austrian Center of Competence for Tribology (AC²T) in Wiener Neustadt, Austria. Full article

(This article belongs to the Special Issue Selected Papers from the 7th European Conference on Tribology (ECOTRIB2019))

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20 pages, 1783 KiB

Open AccessReview

Tribochemistry: A Review of Reactive Molecular Dynamics Simulations

by Ashlie Martini, Stefan J. Eder and Nicole Dörr

Lubricants 2020, 8(4), 44; https://doi.org/10.3390/lubricants8040044 - 6 Apr 2020

Cited by 63 | Viewed by 8393

Abstract

Tribochemistry, the study of chemical reactions in tribological interfaces, plays a critical role in determining friction and wear behavior. One method researchers have used to explore tribochemistry is “reactive” molecular dynamics simulation based on empirical models that capture the formation and breaking of [...] Read more.

Tribochemistry, the study of chemical reactions in tribological interfaces, plays a critical role in determining friction and wear behavior. One method researchers have used to explore tribochemistry is “reactive” molecular dynamics simulation based on empirical models that capture the formation and breaking of chemical bonds. This review summarizes studies that have been performed using reactive molecular dynamics simulations of chemical reactions in sliding contacts. Topics include shear-driven reactions between and within solid surfaces, between solid surfaces and lubricating fluids, and within lubricating fluids. The review concludes with a perspective on the contributions of reactive molecular dynamics simulations to the current understanding of tribochemistry, as well as opportunities for this approach going forward. Full article

(This article belongs to the Special Issue Selected Papers from the 7th European Conference on Tribology (ECOTRIB2019))

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