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  This is an Open Access Journal Open Access journal
   ISSN (Online) 2075-4442
   Published by MDPI Homepage  [124 journals]
  • Lubricants, Vol. 3, Pages 1-2: Acknowledgement to Reviewers of Lubricants
           in 2014

    • Authors: Lubricants Office
      Pages: 1 - 2
      Abstract: The editors of Lubricants would like to express their sincere gratitude to the following reviewers for assessing manuscripts in 2014:[...]
      PubDate: 2015-01-09
      DOI: 10.3390/lubricants3010001
      Issue No: Vol. 3, No. 1 (2015)
  • Lubricants, Vol. 3, Pages 3-13: Experimental Performance Study of a High
           Speed Oil Lubricated Polymer Thrust Bearing

    • Authors: Jie Zhou, Barry Blair, John Argires, Donald Pitsch
      Pages: 3 - 13
      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 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.
      PubDate: 2015-01-21
      DOI: 10.3390/lubricants3010003
      Issue No: Vol. 3, No. 1 (2015)
  • Lubricants, Vol. 3, Pages 14-26: Wear Performance of Sequentially
           Cross-Linked Polyethylene Inserts against Ion-Treated CoCr, TiNbN-Coated
           CoCr and Al2O3 Ceramic Femoral Heads for Total Hip Replacement

    • Authors: Christian Fabry, Carmen Zietz, Axel Baumann, Rainer Bader
      Pages: 14 - 26
      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 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.
      PubDate: 2015-02-16
      DOI: 10.3390/lubricants3010014
      Issue No: Vol. 3, No. 1 (2015)
  • Lubricants, Vol. 2, Pages 162-176: Windage Power Losses of Ordinary Gears:
           Different CFD Approaches Aimed to the Reduction of the Computational

    • Authors: Franco Concli, Carlo Gorla, Augusto Della Torre, Gianluca Montenegro
      Pages: 162 - 176
      Abstract: Efficiency improvement is one of the main challenges in all fields of design. The reduction of power losses is becoming a great concern also in the design of power transmissions. For this reason it is important to have specific models available in order to quantify the power losses during the design stage. The power losses of a gear transmission can be subdivided into bearing losses, seal losses, meshing losses and hydraulic losses. Although literature provides models for the prediction of losses related to bearings or to gear meshing, for the calculations of the losses generated by the interaction with the lubricant, only few and simplified models are available. For this reason the authors recognize that a general purpose method is required in order to overcome this lack of fit and to improve the capability to predict the efficiency of gearboxes. Being able to compare different design solutions means being able to improve the efficiency, reduce the operating temperature and, consequently, improve the reliability of the system. In this paper, the windage losses generated by a single rotating gear have been studied exploiting different numerical approaches. The results obtained have been compared with measurements showing good agreement.
      PubDate: 2014-10-15
      DOI: 10.3390/lubricants2040162
      Issue No: Vol. 2, No. 4 (2014)
  • Lubricants, Vol. 2, Pages 177-192: Influence of Temperature on the
           Frictional Properties of Water-Lubricated Surfaces

    • Authors: Troels Røn, Seunghwan Lee
      Pages: 177 - 192
      Abstract: The influence of temperature on the lubricating properties of neat water for tribopairs with varying bulk elasticity moduli and surface hydrophilicity, namely hard-hydrophobic interface (h-HB), hard-hydrophilic interface (h-HL), soft-hydrophobic interface (s-HB), and soft-hydrophilic interface (s-HL), has been investigated. With increasing temperature, the coefficients of friction generally increased due to the decreasing viscosity of water. This change was more clearly manifested from soft interfaces for more feasible formation of lubricating films. Nevertheless, dominant lubrication mechanism appears to be boundary and mixed lubrication even for soft interfaces at all speeds (up to 1200 mm/s) and temperatures (1 to 90 °C) investigated. The results from this study are expected to provide a reference to explore the temperature-dependent tribological behavior of more complex aqueous lubricants, e.g., those involving various additives, for a variety of tribosystems.
      PubDate: 2014-10-15
      DOI: 10.3390/lubricants2040177
      Issue No: Vol. 2, No. 4 (2014)
  • Lubricants, Vol. 2, Pages 193-205: Development and Validation of a Wear
           Model to Predict Polyethylene Wear in a Total Knee Arthroplasty: A Finite
           Element Analysis

    • Authors: Bernardo Innocenti, Luc Labey, Amir Kamali, Walter Pascale, Silvia Pianigiani
      Pages: 193 - 205
      Abstract: Ultra-high molecular weight polyethylene (UHMWPE) wear in total knee arthroplasty (TKA) components is one of the main reasons of the failure of implants and the consequent necessity of a revision procedure. Experimental wear tests are commonly used to quantify polyethylene wear in an implant, but these procedures are quite expensive and time consuming. On the other hand, numerical models could be used to predict the results of a wear test in less time with less cost. This requires, however, that such a model is not only available, but also validated. Therefore, the aim of this study is to develop and validate a finite element methodology to be used for predicting polyethylene wear in TKAs. Initially, the wear model was calibrated using the results of an experimental roll-on-plane wear test. Afterwards, the developed wear model was applied to predict patello-femoral wear. Finally, the numerical model was validated by comparing the numerically-predicted wear, with experimental results achieving good agreement.
      PubDate: 2014-11-18
      DOI: 10.3390/lubricants2040193
      Issue No: Vol. 2, No. 4 (2014)
  • Lubricants, Vol. 2, Pages 206-222: Modeling and Forecasting of Depletion
           of Additives in Car Engine Oils Using Attenuated Total Reflectance Fast
           Transform Infrared Spectroscopy

    • Authors: Ronald Nguele, Hikmat Al-Salim, Khalid Mohamad
      Pages: 206 - 222
      Abstract: On average, additives make up to 7% of a typical lubricant base. Commonly, they are blended with lube oils to enhance specific features thereby improving their qualities. Ultimately, additives participate in the performance of car engine oils. Using an analytical tool, attenuated total reflectance fast transform infrared spectroscopy, various grades of car engine oils, at different mileages, were analyzed. Sulfate oxidation and wear were found to trigger chemical processes which, in the long run, cause lubricant degradation while carbonyl oxidation was observed to occur only at a slow rate. Based upon data obtained from infrared spectra and using a curve fitting technique, mathematical equations predicting the theoretical rates of chemical change due to the aforementioned processes were examined. Additive depletions were found to obey exponential regression rather than polynomial. Moreover, breakpoint (breakpoint is used here to denote the initiation of deterioration of additives) and critical mileage (critical mileage defines the distance at which the lubricant is chemically unusable) of both samples were determined.
      PubDate: 2014-11-26
      DOI: 10.3390/lubricants2040206
      Issue No: Vol. 2, No. 4 (2014)
  • Lubricants, Vol. 2, Pages 223-236: Detection of Elemental Composition of
           Lubricating Grease Using Laser Induced Breakdown Spectroscopy

    • Authors: Cherry Dhiman, Martha Reddy, Kamal Gulati, Mohd. Khan
      Pages: 223 - 236
      Abstract: The elemental composition of lubricating soft grease used in rail engines are studied using laser induced breakdown spectroscopy (LIBS) technique. LIBS spectra of fresh, partially used and fully used grease samples are recorded using time-gated ICCD spectrometer for verification of compositional degradation of the used grease. LIBS spectra of grease samples are analyzed by comparing with emission spectra of elements published by NIST standard database. Many spectral lines of impurity elements like Fe, Cu, Ba, Mg, Mn, Ni, S, Zn, Si, Pb, Ti, Ca and Al present in the grease in ppm or ppb level in trace level concentrations are observed in excess in the used grease mainly due to wear and tear. On the other hand in fresh grease, spectral lines of Ca, Al and Na are observed predominantly.
      PubDate: 2014-12-18
      DOI: 10.3390/lubricants2040223
      Issue No: Vol. 2, No. 4 (2014)
  • Lubricants, Vol. 2, Pages 237-248: Recycled and Virgin HDPEs as Bleed
           Inhibitors and Their Rheological Influences on Lubricating Greases
           Thickened with PP and mPP

    • Authors: Ravi Dixena, Eltepu Sayanna, Rajendra Badoni
      Pages: 237 - 248
      Abstract: Polypropylene (PP) thickened lubricating grease exhibits high oil bleed tendency at low temperatures, which makes it a promising candidate for low temperature applications. At elevated temperatures, PP thickened lubricating grease exhibits excessive oil bleeding, which limits its use at high temperatures. Excessive oil bleed adversely affects the lubricating performance of the PP thickened grease. The present work is focused on the study of the oil bleed tendency of PP and Maleated Polypropylene (mPP) thickened greases at various temperatures by incorporating virgin and recycled high density polyethylene (HDPE) into the thickener system. Grease containing various percentages of PP and mPP thickeners were prepared and modified with different percentages of virgin and recycled HDPE. Polymers were characterized through differential scanning calorimetry (DSC) techniques. The oil bleed performance of these greases was evaluated by the conical sieve method (ASTM D 6184) at various temperatures. Storage (G′) and loss modulus (G″) of greases was determined by rheometry at 25 °C. Incorporation of HDPE and recycled HDPE in PP thickened grease decreased oil bleeding compared to the base grease.
      PubDate: 2014-12-18
      DOI: 10.3390/lubricants2040237
      Issue No: Vol. 2, No. 4 (2014)
  • Lubricants, Vol. 2, Pages 113-123: Tribofilm Formation As a Result of
           Complex Interaction at the Tool/Chip Interface during Cutting

    • Authors: German Fox-Rabinovich, Iosif Gershman, Mohamed Hakim, Mohamed Shalaby, James Krzanowski, Stephen Veldhuis
      Pages: 113 - 123
      Abstract: Tribofilms are dynamic structures that form at the interface during frictional sliding. These films play a significant role in friction control, particularly under heavy loaded/high temperature conditions, such as those found at the cutting tool/chip interface. The thermodynamic aspects of tribofilm formation are discussed here. Thermodynamic analysis of entropy production during friction shows that there are two types of tribofilms that affect the wear behavior of a cutting tool: (1) tribofilms forming as a result of the surface modification of the cutting tools with further tribo-oxidation; and (2) tribofilms that form as a result of material transfer from the contacting frictional body (the workpiece) during the tool/chip interaction. Experimental examples are presented, outlining the beneficial role of both types of tribofilms.
      PubDate: 2014-07-21
      DOI: 10.3390/lubricants2030113
      Issue No: Vol. 2, No. 3 (2014)
  • Lubricants, Vol. 2, Pages 124-136: Growth Control of Microbial in Miscible
           Cutting Fluids Using Ultraviolet Radiation

    • Authors: Eduardo Bianchi, Paulo Aguiar, Olavo de Arruda, Francine Piubeli
      Pages: 124 - 136
      Abstract: Considering the issues involved in industrial cutting and machining systems, and, in particular, the problems arising from the use of cutting fluids in these systems, this study presents the results of an analysis that points to a safe and efficient way to reduce contaminated microbial cutting fluids using ultraviolet radiation. The study proposes a transmitter system of simple ultraviolet radiation, safe and easy to obtain. The results of this study showed that the action of ultraviolet radiation on microorganisms in metalworking fluids is very effective and leads to a significant reduction of the load of microorganisms. In addition, no changes were observed during the experimental period that would lead to impairments in the performance of the activities of the cutting fluid used. Given the results, we can conclude that the use of ultraviolet radiation in the prevention and control of contamination is an important contribution to the durability of cutting fluids in machining and grinding operations.
      PubDate: 2014-09-02
      DOI: 10.3390/lubricants2030124
      Issue No: Vol. 2, No. 3 (2014)
  • Lubricants, Vol. 2, Pages 137-161: The Preparation of Graphene Oxide and
           Its Derivatives and Their Application in Bio-Tribological Systems

    • Authors: Jianchang Li, Xiangqiong Zeng, Tianhui Ren, Emile van der Heide
      Pages: 137 - 161
      Abstract: Graphene oxide (GO) can be readily modified for particular applications due to the existence of abundant oxygen-containing functional groups. Graphene oxide-based materials (GOBMs), which are biocompatible and hydrophilic, have wide potential applications in biomedical engineering and biotechnology. In this review, the preparation and characterization of GO and its derivatives are discussed at first. Subsequently, the biocompatibility and tribological behavior of GOBMs are reviewed. Finally, the applications of GOBMs as lubricants in bio-tribological systems are discussed in detail.
      PubDate: 2014-09-24
      DOI: 10.3390/lubricants2030137
      Issue No: Vol. 2, No. 3 (2014)
  • Lubricants, Vol. 2, Pages 44-65: Graphite and Hybrid Nanomaterials as
           Lubricant Additives

    • Authors: Zhenyu Zhang, Dorin Simionesie, Carl Schaschke
      Pages: 44 - 65
      Abstract: Lubricant additives, based on inorganic nanoparticles coated with organic outer layer, can reduce wear and increase load-carrying capacity of base oil remarkably, indicating the great potential of hybrid nanoparticles as anti-wear and extreme-pressure additives with excellent levels of performance. The organic part in the hybrid materials improves their flexibility and stability, while the inorganic part is responsible for hardness. The relationship between the design parameters of the organic coatings, such as molecular architecture and the lubrication performance, however, remains to be fully elucidated. A survey of current understanding of hybrid nanoparticles as lubricant additives is presented in this review.
      PubDate: 2014-04-24
      DOI: 10.3390/lubricants2020044
      Issue No: Vol. 2, No. 2 (2014)
  • Lubricants, Vol. 2, Pages 66-89: Abrasive Resistant Coatings—A

    • Authors: Linmin Wu, Xingye Guo, Jing Zhang
      Pages: 66 - 89
      Abstract: Abrasive resistant coatings have been widely used to reduce or eliminate wear, extending the lifetime of products. Abrasive resistant coatings can also be used in certain environments unsuitable for lubrications. Moreover, abrasive resistant coatings have been employed to strengthen mechanical properties, such as hardness and toughness. Given recently rapid development in abrasive resistant coatings, this paper provides a review of major types of abrasive coatings, their wearing mechanisms, preparation methods, and properties.
      PubDate: 2014-05-21
      DOI: 10.3390/lubricants2020066
      Issue No: Vol. 2, No. 2 (2014)
  • Lubricants, Vol. 2, Pages 90-112: Reducing Friction and Wear of
           Tribological Systems through Hybrid Tribofilm Consisting of Coating and

    • Authors: Shuichiro Yazawa, Ichiro Minami, Braham Prakash
      Pages: 90 - 112
      Abstract: The role of surface protective additives becomes vital when operating conditions become severe and moving components operate in a boundary lubrication regime. After protecting film is slowly removed by rubbing, it can regenerate through the tribochemical reaction of the additives at the contact. However, there are limitations about the regeneration of the protecting film when additives are totally consumed. On the other hand, there are a lot of hard coatings to protect the steel surface from wear. These can enable the functioning of tribological systems, even in adverse lubrication conditions. However, hard coatings usually make the friction coefficient higher, because of their high interfacial shear strength. Amongst hard coatings, diamond-like carbon (DLC) is widely used, because of its relatively low friction and superior wear resistance. In practice, conventional lubricants that are essentially formulated for a steel/steel surface are still used for lubricating machine component surfaces provided with protective coatings, such as DLCs, despite the fact that the surface properties of coatings are quite different from those of steel. It is therefore important that the design of additive molecules and their interaction with coatings should be re-considered. The main aim of this paper is to discuss the DLC and the additive combination that enable tribofilm formation and effective lubrication of tribological systems.
      PubDate: 2014-06-23
      DOI: 10.3390/lubricants2020090
      Issue No: Vol. 2, No. 2 (2014)
  • Lubricants, Vol. 2, Pages 1-10: The Application of Molecular Dynamics in
           Fullerene-Based Journal Bearing Simulation

    • Authors: Alexey Kornaev, Leonid Savin, Mikhail Nozdrichkin
      Pages: 1 - 10
      Abstract: The article is devoted to modeling of the molecular microscopic journal bearing. The walls and the lubricant of the bearing are fullerene-like molecules. On the basis of similarity theory and analysis of the dimensions, the similarity criterion is proposed. This criterion characterizes the convergence of a numerical solution. The test calculation is also made to evaluate the quality of the proposed criterion.
      PubDate: 2014-02-24
      DOI: 10.3390/lubricants2010001
      Issue No: Vol. 2, No. 1 (2014)
  • Lubricants, Vol. 2, Pages 11-20: Lubricants for Metal Belt Continuously
           Variable Transmissions

    • Authors: Keiichi Narita
      Pages: 11 - 20
      Abstract: This paper reviews the effects of lubricant additives and base stock used in metal belt continuously variable transmissions (CVT) fluids on the CVT transmission torque capacity. Additive formulation composed of phosphorus anti-wear agent, calcium detergent, and dispersant improved the friction coefficient between the metals. The analysis on the post-test surface suggests that the friction behavior strongly depends on the local morphology of the tribofilms derived from lubricant additives. Examining the effect of base stock on the torque capacity in actual belt CVTs revealed that SN (synthetic naphthene) exhibited 10% higher torque capacity than that of PAO (polyalphaolefin). It is believed that the difference in the torque capacity is due to the difference in the oil-film shearing force generated by the relative sliding between the belt and pulley.
      PubDate: 2014-02-25
      DOI: 10.3390/lubricants2010011
      Issue No: Vol. 2, No. 1 (2014)
  • Lubricants, Vol. 2, Pages 21-43: Lubricants in Pharmaceutical Solid Dosage

    • Authors: Jinjiang Li, Yongmei Wu
      Pages: 21 - 43
      Abstract: Lubrication plays a key role in successful manufacturing of pharmaceutical solid dosage forms; lubricants are essential ingredients in robust formulations to achieve this. Although many failures in pharmaceutical manufacturing operations are caused by issues related to lubrication, in general, lubricants do not gain adequate attention in the development of pharmaceutical formulations. In this paper, the fundamental background on lubrication is introduced, in which the relationships between lubrication and friction/adhesion forces are discussed. Then, the application of lubrication in the development of pharmaceutical products and manufacturing processes is discussed with an emphasis on magnesium stearate. In particular, the effect of its hydration state (anhydrate, monohydrate, dihydrate, and trihydrate) and its powder characteristics on lubrication efficiency, as well as product and process performance is summarized. In addition, the impact of lubrication on the dynamics of compaction/compression processes and on the mechanical properties of compacts/tablets is presented. Furthermore, the online monitoring of magnesium stearate in a blending process is briefly mentioned. Finally, the chemical compatibility of active pharmaceutical ingredient (API) with magnesium stearate and its reactive impurities is reviewed with examples from the literature illustrating the various reaction mechanisms involved.
      PubDate: 2014-02-25
      DOI: 10.3390/lubricants2010021
      Issue No: Vol. 2, No. 1 (2014)
  • Lubricants, Vol. 1, Pages 75-94: On the Interactions of Additives in
           Metalworking Fluids with Metal Surfaces

    • Authors: Joachim Schulz, Ekkard Brinksmeier, Daniel Meyer
      Pages: 75 - 94
      Abstract: Metalworking fluids (MWF) play a significant role in manufacturing processes, such as machining or forming. Consequently, a high number of MWF with varying chemical composition are commercially available. However, the working mechanisms of the MWF are still object of discussion in science and application. This paper addresses the possible interactions of additives with metal surfaces taking the characteristic conditions in machining and forming processes as well as the chemical properties of the surface and the additives into account. The new model for possible interaction of additives with the metal surface is considered and supported by experimental data. This new model does not imply reaction layers as tribological active layer anymore.
      PubDate: 2013-11-15
      DOI: 10.3390/lubricants1040075
      Issue No: Vol. 1, No. 4 (2013)
  • Lubricants, Vol. 1, Pages 95-101: Nanomaterials in Lubricants: An
           Industrial Perspective on Current Research

    • Authors: Boris Zhmud, Bogdan Pasalskiy
      Pages: 95 - 101
      Abstract: This paper presents an overview on the use of various classes of nanomaterials in lubricant formulations. The following classes of nanomaterials are considered: fullerenes, nanodiamonds, ultradispersed boric acid and polytetrafluoroethylene (PTFE). Current advances in using nanomaterials in engine oils, industrial lubricants and greases are discussed. Results of numerous studies combined with formulation experience of the authors strongly suggest that nanomaterials do indeed have potential for enhancing certain lubricant properties, yet there is a long way to go before balanced formulations are developed.
      PubDate: 2013-11-20
      DOI: 10.3390/lubricants1040095
      Issue No: Vol. 1, No. 4 (2013)
  • Lubricants, Vol. 1, Pages 102-131: Experimental Investigations of
           Biological Lubrication at the Nanoscale: The Cases of Synovial Joints and
           the Oral Cavity

    • Authors: Javier Sotres, Thomas Arnebrant
      Pages: 102 - 131
      Abstract: Interactions between surfaces are ubiquitous phenomena in living organisms. Nature has developed sophisticated strategies for lubricating these systems, increasing their efficiency and life span. This includes the use of water-based lubricants, such as saliva and synovial fluid. These fluids overcome the limitations of water as a lubricant by the presence of molecules such as proteins, lipids, and polysaccharides. Such molecules may alter surface interactions through different mechanisms. They can increase viscosity enabling fluid-film lubrication. Moreover, molecules adsorb on the surfaces providing mechanisms for boundary lubrication and preventing wear. The mentioned molecules have typical sizes in the nanometer range. Their interaction, as well as the interaction with the entrapping surfaces, takes place through forces in the range of nanonewtons. It is therefore not surprising that the investigation of these systems have been boosted by development of techniques such as scanning probe microscopies and the surface force apparatus which allow studying tribological processes at the nanoscale. Indeed, these approaches have generated an enormous amount of studies over the last years. The aim of this review is to perform a critical analysis of the current stage of this research, with a main focus on studies on synovial joints and the oral cavity.
      PubDate: 2013-11-25
      DOI: 10.3390/lubricants1040102
      Issue No: Vol. 1, No. 4 (2013)
  • Lubricants, Vol. 1, Pages 132-148: Phosphate Esters, Thiophosphate Esters
           and Metal Thiophosphates as Lubricant Additives

    • Authors: David Johnson, John Hils
      Pages: 132 - 148
      Abstract: Phosphate esters, thiophosphate esters and metal thiophosphates have been used as lubricant additives for over 50 years. While their use has been extensive, a detailed knowledge of how they work has been a much more recent development. In this paper, the use of phosphate esters and thiophosphate esters as anti-wear or extreme pressure additives is reviewed with an emphasis on their mechanism of action. The review includes the use of alkyl phosphates, triaryl phosphates and metal containing thiophosphate esters. The mechanisms of these materials interacting with a range of iron and steel based bearing material are examined.
      PubDate: 2013-12-18
      DOI: 10.3390/lubricants1040132
      Issue No: Vol. 1, No. 4 (2013)
  • Lubricants, Vol. 1, Pages 61-74: Employing Acoustic Emission for
           Monitoring Oil Film Regimes

    • Authors: Mhmod Hamel, Abdulmajid Addali, David Mba
      Pages: 61 - 74
      Abstract: The major purpose of a gear lubricant is to provide adequate oil film thickness to reduce and prevent gear tooth surface failures. Real time monitoring for gear failures is important in order to predict and prevent unexpected failures which would have a negative impact on the efficiency, performance and safety of the gearbox. This paper presents experimental results on the influence of specific oil film thickness on Acoustic Emission (AE) activity for operational helical gears. Variation in film thickness during operations was achieved by spraying liquid nitrogen onto the rotating gear wheel. The experimental results demonstrated a clear relationship between the root mean square (r.m.s) value of the AE signal and the specific film thickness. The findings demonstrate the potential of Acoustic Emission technology to quantify lubrication regimes on operational gears.
      PubDate: 2013-07-03
      DOI: 10.3390/lubricants1030061
      Issue No: Vol. 1, No. 3 (2013)
  • Lubricants, Vol. 1, Pages 22-47: Nanotribological Behavior of Carbon Based
           Thin Films: Friction and Lubricity Mechanisms at the Nanoscale

    • Authors: Costas Charitidis, Elias Koumoulos, Dimitrios Dragatogiannis
      Pages: 22 - 47
      Abstract: The use of materials with very attractive friction and wear properties has raised much attention in research and industrial sectors. A wide range of tribological applications, including rolling and sliding bearings, machining, mechanical seals, biomedical implants and microelectromechanical systems (MEMS), require thin films with high mechanical strength, chemical inertness, broad optical transparency, high refractive index, wide bandgap excellent thermal conductivity and extremely low thermal expansion. Carbon based thin films like diamond, diamond-like carbon, carbon nitride and cubic boron nitride known as “super-hard” material have been studied thoroughly as the ideal candidate for tribological applications. In this study, the results of experimental and simulation works on the nanotribological behavior of carbon films and fundamental mechanisms of friction and lubricity at the nano-scale are reviewed. The study is focused on the nanomechanical properties and analysis of the nanoscratching processes at low loads to obtain quantitative analysis, the comparison obtain quantitative analysis, the comparison of their elastic/plastic deformation response, and nanotribological behavior of the a-C, ta-C, a-C:H, CNx, and a-C:M films. For ta-C and a-C:M films new data are presented and discussed.
      PubDate: 2013-04-02
      DOI: 10.3390/lubricants1020022
      Issue No: Vol. 1, No. 2 (2013)
  • Lubricants, Vol. 1, Pages 48-60: Interaction between Lubricants Containing
           Phosphate Ester Additives and Stainless Steels

    • Authors: David Johnson, Matthew Bachus, John Hils
      Pages: 48 - 60
      Abstract: One way to improve fuel efficiency in today’s jet aircraft engines is to create an environment for higher operating temperatures and speeds. New and improved lubricants and bearing materials must be developed to remain stable in these elevated operating temperatures. Three lubricants, with varying amounts of tricresyl phosphate added as an anti-wear/extreme pressure additive were tested on two different stainless steels at varying temperatures ranging from 300 °C to 350 °C in vacuum. Significant decomposition of the lubricant base-stocks and the phosphate ester additive did occur in most of the trials resulting in the formation of carboxylic acids and phenols. In these cases a film containing phosphorus was deposited onto the stainless steel substrate.
      PubDate: 2013-05-17
      DOI: 10.3390/lubricants1020048
      Issue No: Vol. 1, No. 2 (2013)
  • Lubricants, Vol. 1, Pages 3-21: A Review of Ionic Liquid Lubricants

    • Authors: Anthony Somers, Patrick Howlett, Douglas MacFarlane, Maria Forsyth
      Pages: 3 - 21
      Abstract: Due to ever increasing demands on lubricants, such as increased service intervals, reduced volumes and reduced emissions, there is a need to develop new lubricants and improved wear additives. Ionic liquids (ILs) are room temperature molten salts that have recently been shown to offer many advantages in this area. The application of ILs as lubricants in a diverse range of systems has found that these materials can show remarkable protection against wear and significantly reduce friction in the neat state. Recently, some researchers have shown that a small family of ILs can also be incorporated into non-polar base oils, replacing traditional anti-wear additives, with excellent performance of the neat IL being maintained. ILs consist of large asymmetrical ions that may readily adsorb onto a metal surface and produce a thin, protective film under boundary lubrication conditions. Under extreme pressure conditions, certain IL compounds can also react to form a protective tribofilm, in particular when fluorine, phosphorus or boron atoms are present in the constituent ions.
      PubDate: 2013-01-21
      DOI: 10.3390/lubricants1010003
      Issue No: Vol. 1, No. 1 (2013)
  • Lubricants, Vol. 1, Pages 1-2: Welcome to Lubricants, a New Open Access
           Journal for Interdisciplinary Research in the Field of Tribology

    • Authors: James E. Krzanowski
      Pages: 1 - 2
      Abstract: Welcome to Lubricants, a new open access journal for researchers and practitioners working in the field of tribology. The journal will publish peer-reviewed research papers, reviews, letters and communications, as well as papers on research ideas and proposals. The concept of open access is exciting because it allows free access of all publications to anyone, resulting in the widest dissemination possible for the authors publishing in the journal. In addition, publication is rapid, and full use can be made of color figures which are published at no additional cost to the authors. The contents of the journal will nonetheless be archival and articles can therefore have a long-term impact. [...]
      PubDate: 2012-07-02
      DOI: 10.3390/lubricants1010001
      Issue No: Vol. 1, No. 1 (2012)
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