Tribological Properties Of Lubricants Research Articles

Position of Carbonyl Group Affects Tribological Performance of Ester Friction Modifiers.

The tribological properties of lubricants can be effectively improved by the introduction of amphiphilic molecules, whose performance is largely affected by their polar head groups. In this work, the tribological performance in steel-steel contacts of two isomers, glycerol monostearate (GMS) and stearyl glycerate (SG), a glyceride and a glycerate, were investigated as organic friction modifiers (OFM) in hexadecane. SG exhibits a much lower friction coefficient and wear than GMS despite their similar structures. The same applies when comparing the performance of oleyl glycerate (OG) and its isomer, glycerol monooleate (GMO). Surface chemical analysis shows that SG forms a polar, carbon-based, tribofilm of around tens of nanometers thick, while GMS does not. This tribofilm shows low friction and robustness under nanotribology test, which may contribute to its superior performance at the macro-scale. The reason for this tribofilm formation can be due to the stronger adsorption of SG on the steel surface than that of GMS. The tribofilm formation can be stress-activated since lower friction and higher tribofilm coverage can be obtained under high load. This work offers insights into the lubrication mechanism of a novel OFM and provides strategies for OFM design.

A Methodological Approach to Assessing the Tribological Properties of Lubricants Using a Four-Ball Tribometer

Based on the analysis of standards for the testing of lubricants, both liquid and plastic, on a four-ball tribometer, and the analysis of the parameters by which lubricants are evaluated, this paper proposes a methodology and an integral parameter for the estimation of tribological properties. The methodological approach proposed in this paper allows for the integration of a variety of parameters provided in the standards for the testing of lubricants into one indicator. Herein, we show that the developed technique is based on the energy approach and takes into account the specific wear work of the test material (steel balls) in the lubricating medium to be investigated. The results of laboratory tests of a wide range of lubricants are presented: hydraulic fluids, motor and transmission oils of various purposes and classifications. It is shown that the magnitude of the integral parameter can be used to assess the effectiveness of anti-wear and anti-scuff additives in base lubricants, as well as the ranges of their applications. This allows for differentiation and quantitative evaluation of the effectiveness of such additives. The obtained results allow us to state that all tests according to the developed method are reproducible and homogeneous, which is confirmed using the Cochran criterion. The coefficient of variation during testing does not exceed 18%. We show that the presented methodology and the integral parameter can be used in the first stage of the laboratory selection tests of new lubricants and additives of various origins, reducing the costs of their development and implementation.

Effects of TiO2 nano-particles on wear-resistance and vibration-reduction properties of a polymer for water-lubricated bearing

Water-lubricated bearings play a vital role in improving the energy efficiency and environmental friendliness of ships. However, under the operating conditions such as start-stop and steering, the ship's stern bearing is often in boundary-lubricated or even dry friction condition due to the weak load-bearing capacity of the water film between the ship's drive shaft and the stern bearing. Therefore, the design of a polymer material with a low coefficient of friction and low vibration amplitude in both water-lubricated and dry friction conditions can greatly improve the stability and safety of the ship's operation. As a common reinforcing filler, TiO2 nanoparticles have a notable enhancement effect on the tribological properties of lubricants. Therefore, in this paper, the tribological behaviors between UHMWPE matrix reinforced with TiO2 nanoparticles and zirconia ceramic ball were investigated and the frictional vibrations during the friction process were analyzed. The results showed that TiO2 generated a ball-bearing effect on the surfaces of the friction pair, which led to a smooth and flat wear surface and reduced the friction and vibration behaviors. The modified composite with 0.9 wt% TiO2 exhibited the best tribological and vibration-absorbing properties in both water-lubricated and dry friction conditions. This study helps to provide a theoretical foundation for the design of marine water-lubricated bearing materials with excellent wear-resistance and vibration-reduction properties.

Effect of functional groups on tribological properties of lubricants and mechanism investigation

Nine organic compounds were utilized as model lubricants to investigate the impact of functional groups on tribological performances. Nonanoic Acid with carboxyl showed the best lubrication properties, and fluid film and tribofilm were coexistent in its friction test, bringing a low friction coefficient and wear rate. In addition, the lubricant with low friction coefficient corresponded to high adsorption energy in density functional theory (DFT) calculations. And the lubricant forming adsorption film with large surface energy displayed small wear rate in friction test. Moreover, adsorption energies positively correlated surface energies. Based on the experimental results, the action mechanism of functional groups on tribological properties of lubricants was proposed. Various functional groups make lubricant molecules show different adsorption energies and surface energies. Lubricant molecules with high adsorption energy are more likely to adsorb on substrates and form a vertical monolayer, which can maintain a regular molecular brush structure during friction and bring a low friction coefficient. And lubricant molecules with high surface energy may be more prone having tribochemical reactions during friction and forming protective tribofilm, which leads to a low wear rate.

Determination of the dynamic hardness of greases as a characteristic of deformation properties in a tribocontact

The efficiency of plastic oil is determined by the duration of its retention on the surface. Evaluation of the effectiveness of plastic lubricants depends on their mechanical properties. It is proposed to use the dependence of hardness on time when pressing a spherical indenter as one of the basic characteristics of the mechanical properties of plastic oils. The method of determining the function of oil hardness is based on the mechanics of contact interaction of a solid ball and a plane presented in this work, which has the property of creep according to the flow theory. One of the main methods of testing the deformation properties of plastic lubricants is to determine the number of penetrations. The number of oil penetrations is determined by the depth of indentation of the indenter; more informative for such a process is the ultimate pressure (hardness), which actually reflects the phenomenon of resistance to indenter indentation in the material. For uniform distribution of pressure under a spherical indenter the technique of construction of function of dynamic hardness of plastic materials is defined and on the basis of tests results of construction of dynamic hardness are received. Tests on contact creep of plastic lubricants are carried out, functions of dynamic hardness are received and the analysis of influence of character of change of dynamic hardness on wear processes in the presence of lubricants is carried out. To analyze the influence of deformation properties on the tribological properties of lubricants, comparative tests of the two above-mentioned types of lubricants on a four-ball friction device were performed. It was found that Litol-24 oil has the best wear resistance. The nonlinear period of running-in for this oil is practically absent that, obviously, under the given conditions of tests is connected with more stable in time deformation properties.

Influence of Nano-Materials in Enhancing the Tribological Properties of Lubricants – Review

Influence of Nano-Materials in Enhancing the Tribological Properties of Lubricants – Review

Effect of Alkyl Chains on Tribological Properties of Lubricants

Effect of Alkyl Chains on Tribological Properties of Lubricants

Performance enhancement in tribological properties of lubricants by dispersing TiO2 nanoparticles

Nano-lubricants have attracted many investigators since past decade due to their better anti-wear and friction reducing abilities. Still a major challenge lies in preparation of stable nano-lubricants with uniform nanoparticles suspension. In research studies synthesis of nanoparticle, preparation of nano-lubricants, characterization, and their performance are generally reported. Every single study has reported the enhancement in tribological capabilities of the nano-lubricants. TiO2 nanoparticle based nano-lubricants are specially focused which are either used after surface modification with acids or directly dispersed in base oil. Nano-lubricants with water and paraffin oil as base lubricant is rarest and common respectively. Several hybrid combination of nano-particles with TiO2 have also proved to be efficient. What further challenges is the optimization of the nano-lubricants performances with better stability and less preparation cost. No mathematical model yet exists to predict the properties and tribological behavior of the nano-lubricants.

Evaluation of tribological characteristics of technical oils with fullerene compositions

The paper presents experimental studies of the tribological characteristics of liquid lubricants of various viscosity classes and various groups of operation when using fullerene compositions. Tribological characteristics were evaluated on a four-ball friction machine according to GOST 9490. The use of fullerene compositions in the form of a finely dispersed fullerene powder, pre-dispersed (dissolved) in vegetable high oleic oils, for example, rapeseed, with the subsequent addition of the resulting composition to technical oils of various viscosity classes and various groups of operation, leads to the following positive effect. The anti-wear properties of oils, which are assessed by the wear indicator, increase by 20,0…30,7 %, and the critical load on 18,8…25,0%. These indicators significantly exceed similar indicators when using fullerene fine powders without preliminary dispersion in vegetable oils, where the effect is on the border 11,1…15 %. Fullerene additives do not affect the extreme pressure properties of base oils, which are assessed by the scuffing load. This result makes it possible to state that the way to improve the tribological properties of lubricants by introducing a fine powder of fullerenes into base technical oils is ineffective. The experimental results obtained confirm the hypothesis about the possibility of the micelle formation mechanism in the lubricant under the action of the electrostatic field of the friction surface. The presence of a surfactant solvent (vegetable oil) allows you to "start" the micelle formation process at lower fullerene concentrations and to obtain the effect of increasing anti-wear properties.

Evaluation of tribological characteristics of liquid lubricants with fullerene additives

The paper presents experimental studies of the tribological characteristics of liquid lubricants of various viscosity classes and various groups of operation when using fullerene additives. Tribological characteristics were evaluated on a four-ball friction machine according to GOST 9490. Assessment was subject to: wear rate and critical load, which characterize the anti-wear properties of the lubricant, as well as welding load and bully index, which characterize an anti-bully properties of the material. It is shown that the improvement of the wear index for all oils begins with the concentration 0,2 % masses, fullerenes in the lubricant and does not exceed the values 11,1 … 15 %. At a fullerene concentration less than 0,2 % masses, no positive effect is observed. Positive effect 11,8 … 17,4 % characteristic of the indicator – critical load that characterizes the range of performance of anti-wear additives. At the same time, an increase in the critical load begins with concentration 0,1 % masses, fullerenes in a lubricant and manifests itself most effectively at a concentration 0,2 % masses. Changes in the magnitude of the welding load during the experiments were not recorded, this allows us to conclude, that the addition of a finely dispersed fullerene powder in a liquid lubricant does not improve anti-bully properties, but is only an anti-wear additive. It is shown that the way to improve the tribological properties of lubricants by introducing a finely dispersed powder of fullerenes in base technical oils is ineffective. It is necessary to develop other, more technological methods and methods for introducing fullerene additives into technical lubricants.

Effect of Electric Field on the Tribological Properties of Lubricants

Effect of Electric Field on the Tribological Properties of Lubricants

Influence of alumina/MWCNT hybrid nanoparticle additives on tribological properties of lubricants in turning operations

A hybrid lubricant with improved thermal and tribological properties was developed by blending multiwalled carbon nanotubes (MWCNTs) with alumina-based nanoparticles into cutting fluid at fixed volumetric proportions (10:90). The hybrid cutting fluid was prepared in different volumetric concentrations (0.25, 0.75, and 1.25 vol%), and the tribological properties and contact angles were measured using pin-on-disc tribometry and goniometry, respectively. The study showed a reduction in wear and friction coefficient with increasing nanoparticle concentration. The cutting fluid performance was investigated using minimum quantity lubrication (MQL) in the turning of AISI 304 stainless steel. Regression models were developed for measuring the temperature and tool flank wear in terms of cutting speed, feed, depth of the cut, and nanoparticle concentration using response surface methodology. The developed hybrid nanolubricants significantly reduced the tool flank wear and nodal temperature by 11% and 27.36%, respectively, as compared to alumina-based lubricants.

Study on tribological properties of zinc perrhenate in oil‐based hybrid lubrication system over a broad temperature range

AbstractThe zinc perrhenate used as oil additive was synthesised via aqua‐solution method and was dispersed into pentaerythritol ester with the surface‐active agents. The tribological properties of lubricants were examined by 4‐ball tester and ball‐on‐disc testing machine. Additional investigations were performed using XRD, XPS, SEM‐EDS, and DTA/TG to probe the possible lubricating mechanism. Four‐ball test results showed compared to base oil, the friction coefficient and wear scar diameter of oil with zinc perrhenate additive were reduced by 14.9% and 16.6%, suggesting that zinc perrhenate additive could improve the lubricating property of base oil under 4‐ball test condition. Frictional tests under a wide temperature range indicated that oil with zinc perrhenate additive exhibited friction‐reducing performance during elevated temperature process because of its intrinsic shear susceptible property and could form a protective layer with native oxides of the disc sample at the interface, thus significantly minimised friction.

Experimental Investigation on Usage of Cotton Seed Oil as a Lubricant to Substitute Mineral Oil

Lubricants and lubrication were inherent in a machine ever since man invented machines. The continued increasing environmental concerns force to increase the usage of vegetable oil utilization in lubricants for many applications. The vegetable oil is one of the alternative lubricant base stocks as it has environmental friendly and non-toxic characteristic. India has great potential in growing vegetable oil plants. Even though vegetable oil is one of the best alternatives for lubricant, the tribological properties of vegetable oil are slightly less than mineral oil. This research work is carried out to check the tribological properties of refined cottonseed oil, as a lubricant and compared to 20W50 lubrication oil. To improve the lubrication properties of cottonseed oil, chemical modification like transesterification is carried out. A common solution to improve the properties is to add effective additives into the base stock of vegetable oil which gives significant improvement in thermal as well as tribological properties of lubricant. The properties like viscosity, viscosity index, pour point of refined CSO and chemically modified CSO were tested and compared with 20W50 oil. The additives like MoS2, hBN and ZDDP are used by varying concentrations to enhance anti-wear properties and thermal stability. Four Ball Tester is used for tribological testing according to ASTM standard D 4172 procedures.

Anti-Scoring Additives for Transmission Oils Based on C10 α−Olefin Fraction

Sulfur- and chlorine-containing products are obtained by reacting C10 α -olefins with sulfur monochloride. By sulfidation of the resulting reaction mixture with saturated aqueous sodium sulfide solution sulfur-containing products are synthesized. The optimum conditions are determined for synthesis of these products, which can be recommended as additives that improve tribological properties of lubricants. It is shown that specimens of mineral oils prepared by using the synthesized additives correspond in key performance properties to transmission oils TM-4, SAE, 80W-90, and API-type oil GL-4 with improved anti-scoring properties.

Catalytic Sulfidation of C12 – C14 α-Olefin Fractions

The process of sulfidation of C12 C14 α -olefin fractions in the presence of various dialkyl dithiophosphoric acid derivatives is studied. The optimal catalyst concentrations and process duration that help get a high-sulfur product containing 24.8 wt. % of chemically bound sulfur are determined. The product can be recommended as an additive for improving tribological properties of lubricants.

Tribological properties of lubricants modified by complexes of hard micro- and nanoparticles

The results of study of the effect of multicomponent micro- and nanomodifiers for lubricants on the tribological performance of friction units are presented. It is shown that the presence of a complex of nanoadditives of β-sialon and carbon nanotubes is effective for the considerable diminishing of the friction coefficient and the growth of the loading capacity.

Synergistic Tribological Performances of Borate Additive in Lubricants

Abstract A four-ball tester was used to evaluate the tribological behaviors of nitrogen-containing borate (BNO) combined with zinc dialkyldithiophosphate (ZDDP) and tin dialkyldithiocarbamates (SnDDC) in liquid paraffin or mineral oil, even respectively. The surface analytical tools such as X-ray photoelectron spectrometer (XPS), X-ray diffractometer (XRD), and energy dispersive X-ray (EDX) were used to investigate the chemical states of some typical elements and composition on the rubbing surface of the wear scar. The tribological results show that BNO exhibits better antiwear properties in base oils, and can exhibit good antiwear synergism when it was combined with additives ZDDP and SnDDC, respectively, while the antiwear properties of oil-containing additive packages are optimal under certain concentration ranges. The results of XPS and XRD analyses indicated that BNO can form tribochemical mixed protective films consisting of BN or B2O3 compounds on the rubbing surface, and the combination of BNO with SnDDC may form tin, oxides, sulfide, and N-containing compounds on the rubbing surfaces, which contribute to improving the tribological properties of lubricants. A considerable amount of ZDDP can be partially replaced by BNO in synergistic mixtures, or replaced completely by the combination of BNO with SnDDC, which is especially important for ZDDP used in ecologically sensitive applications.

The influence of lubricants on cam failure

This paper studies the effects of lubricants on the failure and reliability of cams. Experimental investigations of the influence of lubricants on cam failure have been carried out at a metalworking factory. This paper presents following: – A classification of industrial oils for cams. To establish this classification, two essentials of parameters have been taken into account: the environment (ambient temperature) and the cam operating conditions (load and sliding velocity). – A flowchart of lubricating oil selection procedure for cams as a function of all relevant influencing factors. – An analysis of the symptoms and the causes of failure of machine tool cams. – An analysis of the average life and curves of cam reliability of machine tools as a function of tribological properties of some industrial oils. The obtained results have proved that the tribological properties of lubricants has a great influence on: – reduction of failures, – extension of the life and – increase of the reliability of cams.

Influence of test parameters on tribological measurements ‐ results from international round robin tests

AbstractA series of cooperative interlaboratory tests (‘round robins’) was conducted in 1997, 1998, 1999, 2000, and 2001 by the DIN 51834 Working Group on Tribological Tests in Translatory Oscillation Apparatus. Statistical analysis of these results showed the influence of cleaning solvent, machine model, and evaluation criteria on the tribological properties of the lubricants tested. Coefficients of friction and wear results were ranked according to the effects of ten different cleaning solvents, where isopropanol gave the lowest values and isoparaffin solvents the highest. The effect of machine model on coefficients of friction varied from about 0.2 to 0.9% of the average. Wear results were not affected. The tests also showed that the seizure criteria and methods of measuring wear required in the test procedure do not provide a suitable measure of the tribological properties of certain lubricants.