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Lubricants
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Lubricating Greases 2017
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Lubricating Greases 2017

A special issue of Lubricants (ISSN 2075-4442).

Deadline for manuscript submissions: closed (30 June 2017) | Viewed by 42392

Special Issue Editors

Prof. Dr. José M. Franco

E-Mail Website1 Website2 Website3
Guest Editor
Chemical Product and Process Technology Research Center (Pro2TecS), Department of Chemical Engineering and Materials Science, ETSI, University of Huelva, 21071 Huelva, Spain
Interests: rheology; bio-sourced materials; bio-lubricants; lubricating greases; colloids; biopolymers; tribology; gels with emphasis on oleogels and organogels
Special Issues, Collections and Topics in MDPI journals
Prof. Dr. Erik Kuhn

E-Mail Website
Guest Editor
TREC, Institute of Engineering Design and Product Development, Hamburg University of Applied Sciences, Berliner Tor 21, 20099 Hamburg, Germany
Interests: tribology; lubricating grease; energetic approach
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

This Special Issue came as the natural consequence of the great success of the previous Special Issue “Lubricating Greases”.

Although lubricating greases are widely used in many specific applications, their market only constitutes a very low percent of the total amount of lubricants processed in the world. This may be one of the reasons why, up to now, not much attention has been paid to innovation and research on lubricating grease formulations and related functional properties. On the other hand, it is worth mentioning that the mechanical response of greases in a lubricated contact is not yet fully understood. This is due to its complex rheological behavior in comparison with other liquid lubricants. Since lubrication is mainly a deformation and flow problem, the knowledge of the rheological properties of lubricating greases may contribute to elucidate one of the unresolved problems in tribology: the effect of viscoelasticity on lubrication characteristics and, consequently, the way in which a lubricating grease behaves under operating conditions. Suitable structural and physical characteristics may be reached from a proper selection of the ingredients but, also, from a process optimization.

The relationship among composition, microstructure and functional properties is another important issue which deserves more investigation as well as the development of new formulations with improved characteristics. In this sense, mostly in the last two decades, lubricant customers are aware of the negative effects that traditional lubricants exert on the environment and, therefore, are demanding new green products able to reduce this impact.

This special issue aims to collect and disseminate the latest developments and trends in the field of lubricating greases including physical, chemical, microstructural and rheological characterization, tribological response and associated mechanisms, technical information and modeling on grease behavior in lubricated contacts (bearings, seals, etc.), processing of greases and pumpability, development of new formulations including bio-greases and new thickeners agents, etc.

Prof. Dr. José M. Franco
Prof. Dr. Erik Kuhn
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Lubricants is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

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Published Papers (7 papers)

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Research

11 pages, 2679 KiB  
Article
Tribological and Rheological Characterization of New Completely Biogenic Lubricating Greases: A Comparative Experimental Investigation
by Nazli Acar, Erik Kuhn and José M. Franco
Lubricants 2018, 6(2), 45; https://doi.org/10.3390/lubricants6020045 - 5 May 2018
Cited by 16 | Viewed by 4136
Abstract
Against the background of raw material shortage and the ever-expanding environmental consciousness, the use of biodegradable greases becomes more and more important. The aim of this experimental work is to investigate the tribological response of completely biodegradable greases. Complete biodegradable lubricating greases were [...] Read more.
Against the background of raw material shortage and the ever-expanding environmental consciousness, the use of biodegradable greases becomes more and more important. The aim of this experimental work is to investigate the tribological response of completely biodegradable greases. Complete biodegradable lubricating greases were formulated with high-oleic sunflower oil (HOSO) and/or castor oil, and different biodegradable thickener agents such as natural cellulose fibers of different lengths and some derivatives, as well as glyceryl and sorbitan stearates. To investigate the friction process, the model greases were tribologically examined with a nanotribometer at a normal force of 200 mN using a material combination of a steel ball on a steel disc. All frictional results, along with the volumes of wear tracks and micrographs of the main contacting area on the steel plate, are presented and discussed. In addition to this, rotational transient flow measurements were carried out on a rheometer at different temperatures to monitor the evolution of the shear stress with time at a constant shear rate, and to characterize the internal friction behavior by quantifying the energy density. All results were also analyzed from an energetic point of view. Full article
(This article belongs to the Special Issue Lubricating Greases 2017)
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13 pages, 10822 KiB  
Article
Effect of Base Oil Type in Grease Composition on the Lubricating Film Formation in EHD Contacts
by Dennis Fischer, Georg Jacobs, Andreas Stratmann and Gero Burghardt
Lubricants 2018, 6(2), 32; https://doi.org/10.3390/lubricants6020032 - 9 Apr 2018
Cited by 20 | Viewed by 8542
Abstract
The service life of rolling bearings is significantly affected by the film formation in elastohydrodynamic (EHD) contacts, which depends on the operating conditions, like rotational speed or temperature. In grease lubricated EHD contacts, the film formation is determined by the grease consistency and [...] Read more.
The service life of rolling bearings is significantly affected by the film formation in elastohydrodynamic (EHD) contacts, which depends on the operating conditions, like rotational speed or temperature. In grease lubricated EHD contacts, the film formation is determined by the grease consistency and composition, i.e., thickener and base oil type as well as properties of the bleed oil, which is released from the grease during operation. Thus, the film formation of grease lubricated contacts as compared to base oil lubricated contacts can be different. With increasing rolling speed, the film thickness of oil lubricated contacts usually grows. However, in case of grease lubricated contacts, which are not fully flooded, the film thickness remains constant or even decreases with further increasing rotational speed. This effect is referred to as starvation. Since the onset of starvation depends on the grease composition, the film formation of two different grease compositions is investigated in this study. The film thickness measurements are performed on a ball-on-disc tribometer for each grease, as well as the corresponding bleed and pure base oils. Thereby, the characteristic rotational speed leading to the onset of starvation has been identified in dependence of the grease composition and the differences in the lubricating film formation of base oil, bleed oil, and grease lubricated EHD contacts have been discussed. The investigations should help to establish an advanced understanding of the physical mechanisms leading to the onset of starvation to encourage future work with focus on a method to predict the film formation in grease lubricated EHD contacts. Full article
(This article belongs to the Special Issue Lubricating Greases 2017)
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13 pages, 2725 KiB  
Article
Contaminant Particle Motion in Lubricating Grease Flow: A Computational Fluid Dynamics Approach
by Lars-Göran Westerberg, Josep Farré-Lladós, Chiranjit Sarkar and Jasmina Casals-Terré
Lubricants 2018, 6(1), 10; https://doi.org/10.3390/lubricants6010010 - 17 Jan 2018
Cited by 6 | Viewed by 4310
Abstract
In this paper, numerical simulations of particle migration in lubricating grease flow are presented. The rheology of three lithium greases with NLGI (National Lubricating Grease Institute) grades 00, 1 and 2 respectively are considered. The grease is modeled as a single-phase Herschel–Bulkley fluid, [...] Read more.
In this paper, numerical simulations of particle migration in lubricating grease flow are presented. The rheology of three lithium greases with NLGI (National Lubricating Grease Institute) grades 00, 1 and 2 respectively are considered. The grease is modeled as a single-phase Herschel–Bulkley fluid, and the particle migration has been considered in two different grease pockets formed between two concentric cylinders where the inner cylinder is rotating and driving the flow. In the wide grease pocket, the width of the gap is much smaller compared to the axial length scale, enabling a one-dimensional flow. In the narrow pocket, the axial and radial length is of the same order, yielding a three-dimensional flow. It was found that the change in flow characteristics due to the influence of the pocket lateral boundaries when going from the wide to the narrow pocket leads to a significantly shorter migration time. Comparing the results with an existing migration model treating the radial component contribution, it was concluded that a solution to the flow in the whole domain is needed together with a higher order numerical scheme to obtain a full solution to the particle migration. This result is more pronounced in the narrow pocket due to gradients in the flow induced by the lateral boundaries. Full article
(This article belongs to the Special Issue Lubricating Greases 2017)
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8 pages, 14263 KiB  
Article
Application of a Thermodynamic Concept for the Analysis of Structural Degradation of Soap Thickened Lubricating Greases
by Erik Kuhn
Lubricants 2018, 6(1), 7; https://doi.org/10.3390/lubricants6010007 - 11 Jan 2018
Cited by 9 | Viewed by 4276
Abstract
Lubricating greases are special lubricants with a wide range of application. The tribologically stressed grease is used as tribological system and finally modeled as an open thermodynamic system. This study investigated the phenomenon of self-optimization and applied to the process of shearing a [...] Read more.
Lubricating greases are special lubricants with a wide range of application. The tribologically stressed grease is used as tribological system and finally modeled as an open thermodynamic system. This study investigated the phenomenon of self-optimization and applied to the process of shearing a grease. The conditions for self-optimization and the consequences of created dissipative structures are investigated according to the interpreted literature. Full article
(This article belongs to the Special Issue Lubricating Greases 2017)
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7222 KiB  
Article
Sealing of Dry Particles with Grease-Filled Non-Contacting Sealing Systems
by Florian Bosch and Werner Haas
Lubricants 2017, 5(4), 38; https://doi.org/10.3390/lubricants5040038 - 11 Oct 2017
Cited by 3 | Viewed by 5878
Abstract
There is no wear and no friction with non-contacting sealing systems. Because of this, there is in principle no lifetime-limit. However, this does not apply for grease-filled labyrinth seals. To seal against particles, the grease inside the gaps of the seal has to [...] Read more.
There is no wear and no friction with non-contacting sealing systems. Because of this, there is in principle no lifetime-limit. However, this does not apply for grease-filled labyrinth seals. To seal against particles, the grease inside the gaps of the seal has to bind pollution particles and the grease-filled gap must be opened. If the surfaces of the grease layers in the gaps are saturated with particles, further particles penetrating the sealing system can no longer be bound. The seal must then be relubricated. Based on the actual state of the art, this work shows the latest results of experiments to enable designers to unerringly develop non-contacting sealing systems with grease-filled gaps to seal dry particles with reliable function. To that end, a lot of experiments were done to expand existing design guidelines. Additionally, new operating instruction were found to ensure permanent operation. A possibility to reduce the complexity of the sealing system is presented at the end of the present work. Full article
(This article belongs to the Special Issue Lubricating Greases 2017)
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3846 KiB  
Article
Film Thickness and Friction Relationship in Grease Lubricated Rough Contacts
by David Gonçalves, António Vieira, António Carneiro, Armando V. Campos and Jorge H. O. Seabra
Lubricants 2017, 5(3), 34; https://doi.org/10.3390/lubricants5030034 - 17 Aug 2017
Cited by 31 | Viewed by 9762
Abstract
The relationship between the film generation and the coefficient of friction in grease lubricated contacts was investigated. Ball-on-disc tests were performed under different operating conditions: entrainment speed, lubricant temperature and surface roughness. The tests were performed with fully formulated greases and their base [...] Read more.
The relationship between the film generation and the coefficient of friction in grease lubricated contacts was investigated. Ball-on-disc tests were performed under different operating conditions: entrainment speed, lubricant temperature and surface roughness. The tests were performed with fully formulated greases and their base oils. The greases were formulated with different thickener types and also different base oils natures and viscosities. Film thickness measurements were performed in ball-on-glass disc tests, and Stribeck curves were measured in ball-on-steel disc tests with discs of different roughness. The role of the thickener and the base oil nature/viscosity on the film thickness and coefficient of friction was addressed and the greases’ performance was compared based on their formulation. Full article
(This article belongs to the Special Issue Lubricating Greases 2017)
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4222 KiB  
Article
Tribological Investigation of Layered Zirconium Phosphate in Anhydrous Calcium Grease
by Yingjing Dai, Wenxing Niu, Xiaosheng Zhang, Hong Xu and Jinxiang Dong
Lubricants 2017, 5(3), 22; https://doi.org/10.3390/lubricants5030022 - 30 Jun 2017
Cited by 8 | Viewed by 4546
Abstract
The tribological properties of α-zirconium phosphate particles as an additive in anhydrous calcium grease were studied by using an Optimol SRV-V oscillating reciprocating tester and a four-ball tester. Fortunately, α-Zr(HPO4)·H2O (α-ZrP) grease exhibits excellent properties in anti-friction and wear-resistant, [...] Read more.
The tribological properties of α-zirconium phosphate particles as an additive in anhydrous calcium grease were studied by using an Optimol SRV-V oscillating reciprocating tester and a four-ball tester. Fortunately, α-Zr(HPO4)·H2O (α-ZrP) grease exhibits excellent properties in anti-friction and wear-resistant, load-carrying capacity, and extreme pressure properties. Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS) and 3D analysis show that α-ZrP particles appear to form a protective film allowing increased load capacity and operating frequency of the rubbed pairs. Meanwhile, α-ZrP particles can provide low friction coefficient and wear loss during a long-term test. Full article
(This article belongs to the Special Issue Lubricating Greases 2017)
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