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Lubricants, Volume 2, Issue 4 (December 2014) – 6 articles , Pages 162-248

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528 KiB

Open AccessArticle

Recycled and Virgin HDPEs as Bleed Inhibitors and Their Rheological Influences on Lubricating Greases Thickened with PP and mPP

by Ravi Dixena, Eltepu Sayanna and Rajendra Badoni

Lubricants 2014, 2(4), 237-248; https://doi.org/10.3390/lubricants2040237 - 18 Dec 2014

Cited by 10 | Viewed by 6937

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. Full article

(This article belongs to the Special Issue Lubricating Greases)

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566 KiB

Open AccessCommunication

Detection of Elemental Composition of Lubricating Grease Using Laser Induced Breakdown Spectroscopy

by Cherry Dhiman, Martha N. Reddy, Kamal Gulati and Mohd. Shahid Khan

Lubricants 2014, 2(4), 223-236; https://doi.org/10.3390/lubricants2040223 - 18 Dec 2014

Cited by 5 | Viewed by 6790

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. Full article

(This article belongs to the Special Issue Lubricating Greases)

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914 KiB

Open AccessArticle

Modeling and Forecasting of Depletion of Additives in Car Engine Oils Using Attenuated Total Reflectance Fast Transform Infrared Spectroscopy

by Ronald Nguele, Hikmat Said Al-Salim and Khalid Mohammad

Lubricants 2014, 2(4), 206-222; https://doi.org/10.3390/lubricants2040206 - 26 Nov 2014

Cited by 9 | Viewed by 9709

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. Full article

(This article belongs to the Special Issue Lubricity in Fuel)

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418 KiB

Open AccessArticle

Development and Validation of a Wear Model to Predict Polyethylene Wear in a Total Knee Arthroplasty: A Finite Element Analysis

by Bernardo Innocenti, Luc Labey, Amir Kamali, Walter Pascale and Silvia Pianigiani

Lubricants 2014, 2(4), 193-205; https://doi.org/10.3390/lubricants2040193 - 18 Nov 2014

Cited by 24 | Viewed by 7257

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. Full article

(This article belongs to the Special Issue Tribological Performance of Artificial Joints)

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993 KiB

Open AccessArticle

Influence of Temperature on the Frictional Properties of Water-Lubricated Surfaces

by Troels Røn and Seunghwan Lee

Lubricants 2014, 2(4), 177-192; https://doi.org/10.3390/lubricants2040177 - 15 Oct 2014

Cited by 10 | Viewed by 6504

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. Full article

(This article belongs to the Special Issue Bio and Bio-Inspired Lubricants)

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2639 KiB

Open AccessArticle

Windage Power Losses of Ordinary Gears: Different CFD Approaches Aimed to the Reduction of the Computational Effort

by Franco Concli, Carlo Gorla, Augusto Della Torre and Gianluca Montenegro

Lubricants 2014, 2(4), 162-176; https://doi.org/10.3390/lubricants2040162 - 15 Oct 2014

Cited by 50 | Viewed by 7748

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. Full article

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