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Lubricants
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Grease II
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Grease II

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

Deadline for manuscript submissions: closed (1 January 2024) | Viewed by 11909

Special Issue Editors

Dr. Raj Shah

E-Mail Website
Guest Editor
1. Director, Koehler Instrument Company, Holtsville, NY 11742, USA
2. Industrial Advisory Board Chair for the Deptartment of Chemical Engineering, State University of NY, Stony Brook, NY, USA
3. Adjunct Professor, Deptartment of Material Science and Chemical Engineering, State University of New York, Stony Brook, NY, USA
4. Industrial and Professional Advisory Committee, SEDTAPP, The Pennsylvania State University, State College, PA, USA
5. External Board of Advisors (Co-chair) at Tribology Minor Program in Deptartment of Mechanical Engineering, Auburn University, Auburn, AL, USA
Interests: friction; wear; oxidation; analytical instrumentation; tribology; bench testing techniques; greases
Special Issues, Collections and Topics in MDPI journals
Dr. Mathias Woydt

E-Mail Website
Guest Editor
MATRILUB, Materials Tribology Lubrication, Limonenstr. 16, D-12203 Berlin-Dahlem, Germany
Interests: ceramic composites; thin film coatings and thermally sprayed coatings; abrasive wear; lubricant formulations and tribo-testing including their dissemination into industrial applications
Special Issues, Collections and Topics in MDPI journals
Prof. Dr. Andreas Rosenkranz

E-Mail Website
Guest Editor
Department of Chemical Engineering, Biotechnology and Materials, Universidad de Chile, Santiago de Chile, Chile
Interests: MXenes; nanocomposites; tribology
Special Issues, Collections and Topics in MDPI journals
Dr. Simon C. Tung

E-Mail Website
Guest Editor
Innovation Technology Consulting Inc., Glenview, IL 60026, USA
Interests: automotive lubricants; driveline lubrication; industrial lubricants; EV/hybrid components; thermal management coolants; tribological performance testing; nanofluids; energy storage materials; fuel cell applications
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Grease is commonly used in our daily lives. Therefore, greases or consistent lubricants have become important functional carriers that keep our systems in motion, invisible in the background and hardly noticed. The proper application of greases is essential for maintaining lubricating films on industrial components and allowing machinery to operate under extreme conditions, such as high temperatures, high pressures, and heavy loads. Greases can function as sealants to prevent lubricant leakage and to keep out corrosive contaminants and foreign materials.

Although being of the utmost importance, lubricating greases are often underrepresented in the technical literature. In the last few years, significant research progress has been made on greases, ranging from specific chemical formulation of greases for special applications to how grease interacts with various surfaces, tribological advances in grease properties, new techniques for grease property measurements, electrical and thermal cooling properties, sustainability, and eco-toxicological properties, and making the development work more complex and demanding. In addition, the future development of electric vehicles will globally influence the selection and development of greases as they will be in contact with electric modules, sensors, and electronics and will be affected by electrical current and electromagnetic fields. The increasing presence of electrical parts in EVs/HVs will demand the corrosion protection of bearings and other remaining mechanical components. Thus, it is imperative that specialized greases should be explored for specific applications in EVs/HVs to ensure maximum protection from friction, wear, thermal cooling, and corrosion protection to guarantee the longevity of the operating conditions for advanced powertrain and EVs/HEVs.

We anticipate that greases are capable to meet all these requirements and attributes in the future. We aim to select the top research avenues and papers worldwide related to lubricating greases in this compilation. Our Special Issue, “Grease II”, is a continuation of our first successful Special Issue, “Grease I”, with the aim to discuss the latest developments worldwide encompassing all areas related to greases.

Dr. Raj Shah
Dr. Mathias Woydt
Prof. Dr. Andreas Rosenkranz
Dr. Simon C. Tung
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.

Related Special Issue

Published Papers (8 papers)

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Research

17 pages, 5303 KiB  
Article
Development of a Space Grease Lubricant with Long-Term-Storage Properties
by Fabian Schüler, Malgorzata Holynska, Théo Henry, Michael Buttery, Katrin Meier-Kirchner and Christian Göhringer
Lubricants 2024, 12(3), 72; https://doi.org/10.3390/lubricants12030072 - 24 Feb 2024
Viewed by 1080
Abstract
Controlled vacuum environments as in space applications represent a challenge for the lubrication of tribological components. In addition to common space lubricant requirements like, e.g., low evaporation, a broad operational temperature range and a high stability during operation, long-term-storage (LTS) properties have gained [...] Read more.
Controlled vacuum environments as in space applications represent a challenge for the lubrication of tribological components. In addition to common space lubricant requirements like, e.g., low evaporation, a broad operational temperature range and a high stability during operation, long-term-storage (LTS) properties have gained increasing attention recently. The term addresses the time-dependent stability of a lubricant under static conditions, which can mean chemical degradation processes such as oxidation on the one hand, but also the physical separation of oil and thickener in heterogeneous lubricants like greases. Due to the extended storage periods of lubricated components on-ground but also during a space mission for several years, it has to be ensured that a lubricant is still functional after LTS. This article depicts the development of a space lubricant grease with LTS properties. Firstly, LTS requirements and methods for their assessment are discussed. In the following, a systematic approach towards the design of a grease formulation compatible with LTS is described. Finally, the manufacturing of prototype formulations and their broad characterization by means of LTS behaviour, outgassing, and tribological performance is presented. Full article
(This article belongs to the Special Issue Grease II)
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18 pages, 3265 KiB  
Article
Comparison of Rheological Methods to Measure Grease Degradation
by Alan Gurt and Michael Khonsari
Lubricants 2023, 11(11), 468; https://doi.org/10.3390/lubricants11110468 - 31 Oct 2023
Viewed by 1332
Abstract
In a previous paper, methods that have been used to quantify grease mechanical degradation were compared, finding that crossover stress is a practical method for estimating the cone penetration value of a grease using a small sample. This paper covers techniques that have [...] Read more.
In a previous paper, methods that have been used to quantify grease mechanical degradation were compared, finding that crossover stress is a practical method for estimating the cone penetration value of a grease using a small sample. This paper covers techniques that have not generally been applied to modeling grease degradation and indicates their usefulness in characterizing the state of a grease. Three methods are examined, each using a different flow profile: rotation, oscillation, and normal force/extension. It is found that crossover stress is likely still the best choice for estimating cone penetration, and a fast, practical method is introduced here. In addition, a procedure for evaluating pull-off force is provided that describes some of the stretching behavior experienced by grease in a rolling contact; this method can also be used as an estimate of cone penetration. Finally, the applications of a “start-up yield” measurement are covered, providing details about the significance of wall slip as well as an independent way of estimating cone penetration. Full article
(This article belongs to the Special Issue Grease II)
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18 pages, 9382 KiB  
Article
Tribology and Rheology of Polypropylene Grease with MoS2 and ZDDP Additives at Low Temperatures
by Xinrui Zhao, Chengguang Tian, Lei Hao, Hong Xu and Jinxiang Dong
Lubricants 2023, 11(11), 464; https://doi.org/10.3390/lubricants11110464 - 30 Oct 2023
Cited by 2 | Viewed by 1404
Abstract
Polypropylene (PP) grease is a type of lubricating grease with excellent low-temperature performance. The wear and friction performance of steel/steel couples lubricated with PP grease containing molybdenum disulfide (MoS2), zinc dialkyldithophosphate (ZDDP) and MoS2/ZDDP as additives at low temperatures [...] Read more.
Polypropylene (PP) grease is a type of lubricating grease with excellent low-temperature performance. The wear and friction performance of steel/steel couples lubricated with PP grease containing molybdenum disulfide (MoS2), zinc dialkyldithophosphate (ZDDP) and MoS2/ZDDP as additives at low temperatures was investigated using an Optimol SRV reciprocating tester. Compared with MoS2 or ZDDP as single additives, the combination of MoS2 and ZDDP resulted in outstanding tribological properties, especially for higher-load, longer-duration and low-temperature working conditions. The analysis of the wear surface indicated that MoS2 not only adhered to the steel surfaces to form a solid film, but also combined with ZDDP to form a tribofilm. The active components of the additives reached the metal surfaces effectively, indicating that the polymer system did not interfere with the function of the additives. The rheological experiment results also showed that PP grease with additives can maintain stable viscoelasticity, viscosity recovery rates and ductility at low temperatures. Full article
(This article belongs to the Special Issue Grease II)
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12 pages, 2781 KiB  
Article
The Standard for Assessing Water Resistance Properties of Lubricating Grease Using Contact Angle Measurements
by Koottaparambil Lijesh, Roger A. Miller, Raj Shah, Khosro Shirvani and Michael M. Khonsari
Lubricants 2023, 11(10), 440; https://doi.org/10.3390/lubricants11100440 - 12 Oct 2023
Cited by 1 | Viewed by 1659
Abstract
Many grease-lubricated machines operate in wet environments, and are vulnerable to contamination because of water exposure. Reports suggest that even the presence of 1% water in grease reduces the life of a bearing by 90%. Nevertheless, only a few qualitative tests and standards [...] Read more.
Many grease-lubricated machines operate in wet environments, and are vulnerable to contamination because of water exposure. Reports suggest that even the presence of 1% water in grease reduces the life of a bearing by 90%. Nevertheless, only a few qualitative tests and standards are available to characterize the water resistance properties of greases. In this paper, we propose a standard for evaluating the water resistance properties of greases by studying their hydrophobic and hydrophilic nature via a custom-designed apparatus for measuring the grease contact angle. In this approach, a water droplet is dispensed onto the surface of the grease and the contact angle of the droplet is studied. For this purpose, an apparatus was designed, built, and tested with twelve different greases. To validate the efficacy of the test method and setup, tests were performed at two different locations by independent operators. From the obtained contact angle values, the authors propose categorizing a grease’s water-resistance properties into five different grades that can be set as guidelines for the industrial user when selecting a grease for machinery operation in a wet environment. The classification of the water-repellent properties of greases, using the proposed standard is compared with existing ASTM standards used for evaluation of grease properties in the presence of water. Full article
(This article belongs to the Special Issue Grease II)
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17 pages, 9193 KiB  
Article
Optimization of the Tribological Performance and Service Life of Calcium Sulfonate Complex—Polyurea Grease Based on Unreplicated Saturated Factorial Design
by Hong Zhang, Yimin Mo, Qingchun Liu, Jun Wang and Qian Li
Lubricants 2023, 11(9), 377; https://doi.org/10.3390/lubricants11090377 - 05 Sep 2023
Viewed by 630
Abstract
In order to further extend the service life of calcium sulfonate complex–polyurea grease (CSCPG) while ensuring its tribological performance, this article starts with the production of raw materials and the preparation process of the grease and explores the factors that significantly affect the [...] Read more.
In order to further extend the service life of calcium sulfonate complex–polyurea grease (CSCPG) while ensuring its tribological performance, this article starts with the production of raw materials and the preparation process of the grease and explores the factors that significantly affect the tribological performance and service life of CSCPG based on unreplicated saturated factorial design (USFD). The Kriging prediction model is used along with the optimization objectives of friction coefficient and service life, and nondominated sorting genetic algorithm II (NSGA-II) was used for a multi-objective optimization solution. The tribological and service life tests were conducted before and after optimization. The results show that the viscosity of the base oil and the content of the nano-solid friction reducers have a significant impact on the tribological properties of CSCPG. The content of polyurea thickeners and antioxidants, as well as the thickening reaction temperature, have a significant impact on the service life of CSCPG. When the friction coefficient and service life are optimized as objectives and are compared to the initial group, the friction coefficient of CSCPG could be reduced by 5.3%, and the service life could be extended by 3.8%. The Kriging prediction model based on USFD has high accuracy and can be used to guide the preparation and performance optimization of CSCPG. Full article
(This article belongs to the Special Issue Grease II)
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16 pages, 3340 KiB  
Article
Research on the Rheological Characteristics of Wind Power Grease Based on Rheological Parameters
by Han Peng, Songyin Li, Linjian Shangguan, Hai Zhang and Defang Zhao
Lubricants 2023, 11(7), 299; https://doi.org/10.3390/lubricants11070299 - 19 Jul 2023
Cited by 3 | Viewed by 1147
Abstract
Our research scrutinizes the impact of grease rheological properties on the lubrication performance of wind turbine spindle bearings. The rheological behavior of three distinct commercial wind turbine greases was examined with a rotational rheometer. Investigations into the viscoelastic, flow, and viscosity–temperature attributes of [...] Read more.
Our research scrutinizes the impact of grease rheological properties on the lubrication performance of wind turbine spindle bearings. The rheological behavior of three distinct commercial wind turbine greases was examined with a rotational rheometer. Investigations into the viscoelastic, flow, and viscosity–temperature attributes of the grease under varying temperatures were conducted, and the rheological parameters were fitted utilizing the Herschel–Bulkley (H–B) model. Constitutive equations of the grease derived from fitting the H–B model can efficaciously predict its rheological properties and viscosity–temperature behavior for wind power spindle bearings at disparate temperatures. Full article
(This article belongs to the Special Issue Grease II)
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11 pages, 3035 KiB  
Article
Effect of Contact Conformity on Grease Lubrication
by Michal Okal, David Kostal, Petr Sperka, Ivan Krupka and Martin Hartl
Lubricants 2022, 10(11), 289; https://doi.org/10.3390/lubricants10110289 - 01 Nov 2022
Viewed by 1851
Abstract
This work focused on the experimental study of grease lubrication mechanisms around contacts in radial ball bearing 6314. The main objective of this work was to show the influence of conformities and their impact on grease lubrication in ball bearings. For the experiments, [...] Read more.
This work focused on the experimental study of grease lubrication mechanisms around contacts in radial ball bearing 6314. The main objective of this work was to show the influence of conformities and their impact on grease lubrication in ball bearings. For the experiments, a tribometer of ball-on-ring configuration was used and fluorescence microscopy was chosen as the observation method. The results showed that, under starvation conditions, a conformity of 0.52 at velocities around 2 m/s produces a 50% thicker lubricating film than a conformity of 0.58. The available amount of lubricant around the contact area for conformity 0.52 was approximately three times less than that for conformity 0.58, and the same ratio was observed for the amount of lubricant on the rolling track. Experiments show that a realistic tribometer geometry allows a more accurate experimental study of the lubrication mechanisms of greases in ball bearings. Full article
(This article belongs to the Special Issue Grease II)
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15 pages, 4208 KiB  
Article
The Impact of Water on the Tribological Behavior of Lubricating Grease Based on Calcium Carbonate Polymorphs
by Longqi Sun, Rui Ma, Qin Zhao, Gaiqing Zhao and Xiaobo Wang
Lubricants 2022, 10(8), 188; https://doi.org/10.3390/lubricants10080188 - 19 Aug 2022
Cited by 6 | Viewed by 1945
Abstract
In this article, calcium sulfonate complex grease with different polymorphs was acquired. With reference to the improved rolling stability test method, 5% and 10% water were added to the calcium sulfonate composite grease respectively. The influence of water on the flow and deformation [...] Read more.
In this article, calcium sulfonate complex grease with different polymorphs was acquired. With reference to the improved rolling stability test method, 5% and 10% water were added to the calcium sulfonate composite grease respectively. The influence of water on the flow and deformation characteristics of grease under external force was characterized by rheological analysis. Moreover, the influence of water on the tribological behaviors of grease was evaluated at 30 and 80 °C. The results indicate that water could affect the flow and deformation characteristics of calcium sulfonate complex grease in vaterite polymorph (CSCG-V) more than calcium sulfonate complex grease in calcite polymorph (CSCG-C), and CSCG-V could combine with water to form a more stable grease under external force. Tribological results also clearly show that CSCG-C with water shows better tribological properties than CSCG-V with water under harsh conditions. There was no significant difference in the components of the films that consisted of CaCO3 and CaO regardless of grease within or without water. The improvement of tribological properties of CSCG-C with 5% and 10% water benefited from the influence of water on the film forming capacity of calcium carbonate on the steel surface. Full article
(This article belongs to the Special Issue Grease II)
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