Showing papers in "Lubrication Science in 2006"
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TL;DR: In this article, the authors describe the rheological properties of lubricants under the very severe conditions present in thin-film elastohydrodynamic lubrication contacts, where the fluid film can break down at asperity conjunctions.
Abstract: It is now 60 years since Ertel produced the first solution to the elastohydrodynamic lubrication (EHL) problem. There has been enormous progress since then, both in numerical modelling and in experimental research on EHL. The moving, rough surface EHL problem can now be solved on laptop-level computers, while maps of film thickness, pressure and temperature can be obtained experimentally from within rolling/sliding contacts. However, there remain some important questions that have not been fully resolved. One of the most contentious is how to describe the rheological properties of lubricants under the very severe conditions present in thin film EHL contacts. A second is how to model mixed lubricated contact, where the fluid film can break down at asperity conjunctions. But perhaps the greatest challenge to researchers in EHL is to produce useful design equations for predicting the performance of machine components operating in EHL and thereby ensure that EHL theory becomes an integral part of the design process. Copyright © 2006 John Wiley & Sons, Ltd.
117 citations
TL;DR: In this article, the results of investigations on the amount of gaseous emissions of phosphorus released from engine oils formulated with a range of phosphorus-containing anti-wear additives were reported.
Abstract: Replacing zinc dithiophosphate (ZnDTP) with ashless anti-wear alternatives will lead to a significant reduction of ash and give more flexibility in the use of metallic detergents. The question of the contamination of exhaust gas after treatment devices by volatile phosphorus-containing compounds has recently been raised. We report the results of investigations on the amount of gaseous emissions of phosphorus released from engine oils formulated with a range of phosphorus-containing anti-wear additives. To relate the structure of additives to the observed phosphorus emissions, we have investigated a variety of phosphorus-containing anti-wear agents, metal-containing as well as ashless. We have used established and new laboratory tests in addition to measurements on fired engines to assess the phosphorus emissions. We discuss the anti-wear capability and friction control of these phosphorus-containing additives. We conclude that it is possible to formulate zinc-free, low-ash engine oils which will control wear and corrosion and not release more phosphorus into the exhaust gas after treatment systems than the traditional ZnDTP based oils. Copyright © 2006 John Wiley & Sons, Ltd.
20 citations
TL;DR: In this paper, a new focus on the Walther equation is presented to determine the viscosity of commercial lubricants at different temperatures, which provides very good correlation with experimental measurements.
Abstract: Lubricants are widely used in industrial machinery in order to separate solid tribological surfaces and support high loads under severe conditions. In tribological contacts, viscosity plays an important role in the film-forming abilities of the lubricant, but this property is strongly dependent on temperature. Consequently, small variations in temperature cause appreciable variations in the viscosity of lubricating oils. For this reason it is of practical value to be able to predict viscosity changes with temperature. This paper presents a new focus on the Walther equation to determine the viscosity of commercial lubricants at different temperatures. This new approach provides very good correlation with experimental measurements. Copyright © 2006 John Wiley & Sons, Ltd.
19 citations
TL;DR: In this paper, experimental techniques have been developed to measure the friction, antiwear film-forming and wear properties of lubricants in rolling-sliding contact, showing that zinc dialkyldithiophosphates (ZDDPs) and also some other phosphorus-based additives increase friction in mixed lubrication.
Abstract: Experimental techniques have been developed to measure the friction, antiwear film-forming and wear properties of lubricants in rolling–sliding contact. Friction measurements show that zinc dialkyldithiophosphates (ZDDPs) and also some other phosphorus-based additives increase friction in mixed lubrication. Film thickness measurements show that this increase in friction correlates with the thickness of antiwear film. They also reveal some of the drivers of antiwear film formation and removal. A novel wear tester is described which enables the mild wear resulting from ZDDP-containing oils to be monitored. Copyright © 2006 John Wiley & Sons, Ltd.
13 citations
TL;DR: In this paper, the authors used a scanning electron microscope and energy dispersive spectrometer for analysis of the worn surface, mechanisms of action of various lubricating additives under different friction conditions were identified.
Abstract: Tests were performed on two different four-ball testers. The first was used to determine antiwear (AW) and extreme pressure (EP) properties at sliding friction. The second was used to assess the surface fatigue (pitting) life at rolling movement. Lubricating oils of various chemical compositions were tested. A base mineral oil was blended with two different commercial packages of lubricating additives of AW and EP types. The AW additives contained ZDDP and were blended with the base oil at 0.2 and 3wt %. The EP additives were organic compounds of sulphur and phosphorus, blended with the base oil at 1 and 10wt %. It is shown that AW additives not only improve AW and EP properties but also — at 0.2% — are beneficial for the fatigue life. An increase in the concentration of AW additives leads to an improvement of AW and EP properties but — for one of the packages — reduces the fatigue life. EP additives — at 1% concentration — significantly improve EP properties, and to a lesser extent AW properties. Such a concentration of EP additives has no influence on the fatigue life. An increase in the concentration of EP additives leads to a further improvement of EP and AW properties. However, this is accompanied by a considerable decrease in the fatigue life. By using a scanning electron microscope and energy dispersive spectrometer for analysis of the worn surface, mechanisms of action of various lubricating additives under different friction conditions were identified. Copyright © 2006 John Wiley & Sons, Ltd.
12 citations
TL;DR: In this paper, the impact of different additive chemistries on the friction of carbon fiber clutch plates has been investigated and it was shown that with the appropriate choice of additive system, carbon fiber-based friction plates can offer a number of performance improvements over more conventional materials.
Abstract: Since their introduction over ten years ago, carbon fiber based friction materials have been employed by transmission builders in a wide variety of applications, including torque converter clutches, synchronizers, limited slip devices and shifting clutches This new generation of materials gives improved durability relative to cellulose; carbon fiber materials offer inherently greater wear resistance and improved resistance to thermal degradation However, carbon fiber based materials also bring inherently different friction characteristics than their cellulose based counterparts As a result, a different approach to lubricant formulation is required to provide optimized friction control in applications where they are used It is well known that in order to achieve and maintain the required friction in a clutch, the correct combination of surface properties and additive chemistry is required In this paper the impact of different additive chemistries on the friction of carbon fiber clutch plates has been investigated It will be shown that with the appropriate choice of additive system, carbon fiber based friction plates can offer a number of performance improvements over more conventional materials Copyright © 2006 John Wiley & Sons, Ltd
11 citations
TL;DR: In this paper, a number of benzotriazole derivatives as antioxidants for turbine oils were evaluated by formulating different blends of turbine oil with viscosity grade ISO 46 with different dosages of the synthesized compounds.
Abstract: Evaluation of a number of benzotriazole derivatives as antioxidants for turbine oils was carried out by formulating different blends of turbine oil with viscosity grade ISO 46 with different dosages of the synthesized compounds. Oxidation tests were carried out according to IP 229 on each blend and the optimum dosages of these compounds were determined. Copyright © 2006 John Wiley & Sons, Ltd.
11 citations
TL;DR: In this article, Fourier transform infrared (FTIR) microspectrophotometry and techniques involving a scanning electron microscope equipped with an energy-dispersive spectrometer were used to analyse tribochemical reaction products formed on different substrates.
Abstract: Hexadecane is widely used as the model base oil to investigate both tribological effectiveness and tribochemical reaction mechanisms of various antiwear and extreme pressure additives. On the other hand, it is well known from existing references that hexadecane, similarly to hydrocarbon oils, oxidizes during the lubrication process of tribological systems. It has frequently been pointed out that carboxylic acids are formed which — reacting with rubbing surfaces — generate soaps. Most recent studies, however, demonstrate that the oxidation process under friction conditions is very complex and the major oxidation compounds from hexadecane under boundary friction conditions relate to other oxygenates than carboxylic acids.
This paper aims to examine what types of surface compound are generated from the hexadecane lubricant in the friction contact zone. Tribological tests were performed on a ball-on-disc tribometer. The discs used were made from several materials (steel, aluminium, brass, bronze). Fourier transform infrared (FTIR) microspectrophotometry and techniques involving a scanning electron microscope equipped with an energy-dispersive spectrometer were used to analyse tribochemical reaction products formed on different substrates. Analytical results obtained clearly demonstrate a similar tribochemical reaction process operating on all the metals tested. The FTIR results obtained allowed new absorption bands to be discovered and accounted for. These absorption bands have been assigned to specific complex compounds. Copyright © 2006 John Wiley & Sons, Ltd.
10 citations
TL;DR: In this paper, the UHV friction tests were performed on a tribofilm previously formed on selected diamond-like carbon (DLC) material with molybdenum dithiocarbamate (MoDTC) and ZDDP, and the wear scars of both sliding surfaces were characterized by in-situ analytical tools such as Auger electron spectroscopy, scanning Auger microscopy and micro-spot XPS.
Abstract: The fuel economy and reduction of harmful elements of lubricants are becoming important issues in the automotive industry. One approach to these requirements is the potential use of low-friction coatings in engine components exposed to boundary lubrication conditions. Diamond-like carbon (DLC) coatings, extensively studied as ultra-low friction films to protect ductile metals surfaces for space applications, are expected to fit the bill. The main purpose of this work is to investigate the friction and wear properties of DLC coatings lubricated with molybdenum dithiocarbamate (MoDTC) and zinc dithiophosphate (ZDDP) under boundary lubrication conditions. The mechanisms by which MoDTC reduces the friction in the centirange were studied using ultra-high vacuum (UHV) analytical tribometer. The UHV friction tests were performed on a tribofilm previously formed on selected DLC material with MoDTC and ZDDP containing oil. Ex-situ characterizations show that the composition of this tribofilm is similar to that of a tribofilm obtained on steel surfaces in the same lubrication conditions with MoS2 single sheets dispersed inside zinc phosphate zones. However, analyses by X-ray photoelectron spectroscopy (XPS) indicate that MoDTC and ZDDP additives seem to be more active on steel surfaces than carbonaceous ones. After UHV friction with the tribofilm formed on selected DLC and steel pin counterpart, the wear scars of both sliding surfaces were characterized by in-situ analytical tools such as Auger electron spectroscopy, scanning Auger microscopy and micro-spot XPS. Low friction is associated with the transfer of a thin MoS2 film to the steel pin counterpart. Copyright © 2006 John Wiley & Sons, Ltd.
10 citations
TL;DR: In this paper, the generalized Reynolds equation governing the flow field of lubricant, having variable viscosity, was considered for the performance analysis of capillary compensated hole-entry hybrid journal bearing systems and the results obtained from the study suggest that bearing static performance characteristics can be optimized for the particular bearing operating conditions by proper selection of parameters such as bearing land width ratios, the restrictor design parameter, and the nonlinearity factor.
Abstract: The performance characteristics of capillary compensated hole-entry hybrid journal bearing systems have been studied theoretically. The analysis considers the generalized Reynolds equation governing the flow field of lubricant, having variable viscosity, taking the equation of lubricant flow through a capillary restrictor as constraint. The non-Newtonian lubricant is assumed to follow the cubic shear stress law. The results obtained from the study suggest that bearing static performance characteristics can be optimized for the particular bearing operating conditions by proper selection of parameters such as bearing land width ratios (āb), the restrictor design parameter (Cs2), and the non-linearity factor (K). Copyright © 2006 John Wiley & Sons, Ltd.
9 citations
TL;DR: In this article, the effect of rheology on film thickness and elastohydrodynamic (EHD) friction has been examined and two approaches to maintaining high torque transfer efficiencies (TE) while reducing axle oil operating temperatures (OT) were examined.
Abstract: Effective axle oils must efficiently transfer torque from the drive-train to the wheels, while maintaining low axle oil operating temperatures. Previous studies have shown that fluids, which form thicker elastohydrodynamic (EHD) films and have lower EHD friction, have higher torque transfer efficiencies (TE) and lower axle oil operating temperatures (OT). In general, oils with higher viscosities form thicker films and those with lower viscosities have lower EHD friction. Therefore, optimizing oil's rheological properties to maximize TE and minimize OT is difficult. In this paper, we examine two approaches to maintaining high TE while reducing OT. One approach is to minimize boundary friction since previous studies have shown that the boundary frictional properties of oils influence OT and not TE. A second approach is to more thoroughly examine the effect of rheology on film thickness and EHD friction. Film thickness and EHD friction are related to the high temperature high shear viscosity and pressure-viscosity coefficient of oils. We have found that oils with high pressureviscosity coefficients and low high temperature high shear viscosities will form thick films and have low EHD friction. This optimized combination of physical parameters, along with lowering the boundary friction coefficient of axle oils, results in oils with high TE and low OT. Copyright © 2006 John Wiley & Sons, Ltd.
TL;DR: In this article, a steel ball-bearing was dropped against a flat anvil made of mild steel and the effect of the pressure-viscosity coefficient and of the viscosity was investigated for plastic impact.
Abstract: The squeeze film formation ability of traction fluids is studied under impact load by dropping a steel ball-bearing against a flat anvil made of mild steel. The effect of the pressure–viscosity coefficient and of the viscosity is investigated for plastic impact. The depth difference between the lubricated surface dent and the dry dent increases linearly with the product αη of the pressure–viscosity coefficient α and the viscosity η. The importance of the lubricant parameter αη is observed under the squeeze film formation ability from contact voltage or elastohydrodynamic lubrication central film thickness measurement at rolling condition. The intensity of each impact collision is measured by means of an acoustic emission (AE) sensor. The high-pressure short-time solidification of traction fluids was confirmed by dent analysis after the impact tests and AE analysis under impact loads. Copyright © 2006 John Wiley & Sons, Ltd.
TL;DR: In this article, the effect of surface roughness on the performance of curved pivoted slider bearings is studied, where a more general type of roughness is mathematically modelled by a stochastic random variable with nonzero mean, variance and skewness.
Abstract: In this paper the effect of surface roughness on the performance of curved pivoted slider bearings is studied. A more general type of surface roughness is mathematically modelled by a stochastic random variable with nonzero mean, variance and skewness. The averaged modified Reynolds type equation is derived on the basis of Stokes microcontinuum theory for couple stress fluids. The closed-form expressions for the mean pressure, load-carrying capacity, frictional force and the centre of pressure are obtained. Numerical computations show that the performance of the slider bearing is improved by the use of lubricants with additives (couple stress fluid) as compared to Newtonian lubricants. Further, it is observed that the negatively skewed surface roughness increases the load-carrying capacity and frictional force and reduces the coefficient of friction, whereas the positively skewed surface roughness on the bearing surface adversely affects the performance of the pivoted slider bearings. Copyright © 2006 John Wiley & Sons, Ltd.
TL;DR: In this paper, a four-ball machine was used to evaluate the antiwear performance of three kinds of organomolybdenum compounds and their antiwear synergistic effect with a zinc dialkyldithiophosphate (ZnDDP).
Abstract: A four-ball machine was used to evaluate the antiwear performance of three kinds of organomolybdenum compounds — molybdenum dialkyldithiophosphate (MoDDP), molybdenum dialkyldithiocarbamate (MoDTC), and sulphur- and phosphorus-free organomolybdenum — and their antiwear synergistic effect with a zinc dialkyldithiophosphate (ZnDDP). The results indicate that the three organomolybdenum compounds have good antiwear properties, especially MoDDP, and the organomolybdenum compound — especially MoDTC and sulphur- and phosphorus-free organomolybdenum compound — exhibit good antiwear synergisms with ZnDDP in a paraffin base oil. Copyright © 2006 John Wiley & Sons, Ltd.
TL;DR: In this paper, the combined effect of surface roughness and bubbles content on the hydrodynamic performance of journal bearings is studied, and it is assumed that the bearing and shaft surfaces are covered with homogeneous isotropic roughness, the air bubbles are evenly distributed through the lubricant and the bubble size is very small.
Abstract: In this paper, the combined effect of surface roughness and bubbles content on the hydrodynamic performance of journal bearings is studied. In the analysis, it is assumed that the bearing and shaft surfaces are covered with homogeneous isotropic roughness, the air bubbles are evenly distributed through the lubricant and the bubble size is very small. The modified Reynolds equation governing the pressure generation in the bearing gap for compressible fluid is solved simultaneously with the energy equation. Temperature and pressure distributions, coefficient of friction, bearing load capacity and attitude angle as affected by surface roughness, bubble content and some bearing parameters are presented. Results showed that the bearing load carrying capacity is higher at higher values of average roughness and higher bubble content as a direct consequence of the higher pressure values attained, and the average roughness and the bubbles content had no significant effect on the attitude angle. Copyright © 2006 John Wiley & Sons, Ltd.
TL;DR: In this paper, the axial deflection of double-decker high-precision bearings (DDHPBs) under the influence of axial loads has been theoretically analyzed and has been compared with conventional angular contact and deep-groove ball bearings of the same bore and outer diameter.
Abstract: Axial deflection of double-decker high-precision bearings (DDHPBs) under the influence of axial loads has been theoretically analyzed and has been compared with conventional angular contact and deep-groove ball bearings of the same bore and outer diameter. The analysis, in general, indicates that the ratio of the axial deflection of DDHPBs to that of the conventional angular contact and deep-groove ball bearings under the influence of identical axial loads is less than unity.
The analysis also indicates that angular contact ball bearings mounted back to back for taking the axial load from both directions can be replaced by DDHPBs, which have less axial deflection and longer life under identical applied loads than angular contact and deep-groove ball bearings.
The better dynamic response characteristics, energy efficiency, uniform stress distribution, lower indentation and deflection on the elements of DDHPBs indicate that DDHPBs have relatively better performance characteristics, higher fatigue life and may have higher potential in various industrial applications as compared to that of the conventional bearings under identical operating conditions. Copyright © 2006 John Wiley & Sons, Ltd.
TL;DR: In this paper, the wear, friction and film forming characteristic of ethyl octadecenoate and methyl 12-hydroxy ocatadecenates, their thio and thiopyrophosphoro derivatives have been studied on HFRR friction and wear machine.
Abstract: The wear, friction and film forming characteristic of ethyl octadecenoate and methyl 12-hydroxy ocatadecenoates, their thio and thiopyrophosphoro derivatives have been studied on HFRR friction and wear machine. The structural characteristics of chemisorbed films formed on the iron surfaces by these derivatives have been investigated using various analytical techniques such FT-IR, Microreflectance Absorption and Proton Magnetic Resonance. It has been inferred that these films are primarily organic in nature. The constituents of these films are hydroxy alkyl and aryl ethers, unsaturated and condensed ring hydroxy ketones, aromatic hydroxy quinones and highly condensed aromatic structures chemically linked to iron sufaces through hydroxy, oxy, thia, oxyphosphoro and thiophosphoro moieties forming chelated and coordinated complexes.
The antiwear and antifriction characteristic of alkyl octadecenoates increase with increasing polar linkages in the alkyl ocatadecenoate backbone. This is primarily due to the increase in number of sites amenable to chemisorption on the surfaces and consequently their reactivity. The antiwear and antifriction characteristic of derivatives of ethyl octadecenoates are inferior to the corresponding 12-hydroxy methyl octadecenoates derivatives. This can be attributed to increased reactivity of 12-hydroxy methyl octadecenoates derivatives at the surfaces due to an additional hydroxyl moiety. The films formed are highly condensed ring aromatic layered structures coordinating to iron atoms of the surface particularly in case of thiopyrophosphoro derivatives of methyl 12-hydroxy octadecenoates. These films, as a consequence, provide lower wear and friction characteristics as compared to other types of organic films. These studies have led to much clear evidence of the intimate relationship between the chemical structure of the additives and their film forming characteristics. Copyright © 2006 John Wiley & Sons, Ltd.
TL;DR: In this article, nuclear magnetic resonance (NMR) spectroscopy and electrospray ionization mass spectrometry are used to analyze the molecular structure of three alkyl-benzene sulfonic acids in detail.
Abstract: Overbased calcium sulfonates are used in many modern oil formulations to provide cleaning action and to neutralize the organic acids formed during combustion, preventing corrosion. The performance of detergents is related to their molecular structure, which is generally known only as a chemical category. In the present work, nuclear magnetic resonance (NMR) spectroscopy and electrospray ionization mass spectrometry are used to analyze the molecular structure of three alkyl-benzene sulfonic acids in detail. Some important molecular features were obtained by elaborating the NMR signal intensities, such as the number and positions of alkyl substituents on the benzene ring, the distribution of alkyl chain lengths and the mole fraction of 1-phenyl isomers (synthesized by alkylation of benzene with α-olefin). Ion-trap mass spectrometry is used to obtain the mass spectrometry/mass spectrometry (MS2) spectra of the principal molecular ions. By choosing suitable molecular ions, MS2 spectra can ascertain the presence of different substituted benzene isomers within a mixture because the MS2 spectra show specific fragments due to the number of alkyl substituents on the aromatic ring. Copyright © 2006 John Wiley & Sons, Ltd.
TL;DR: In this article, thin film colorimetric interferometry was used in combination with phase shifting interference for the detailed experimental investigation of changes in real surface microgeometry within the elastohydrodynamic conjunction formed between a real, random, rough surface, a steel ball and a smooth glass disc.
Abstract: Thin film colorimetric interferometry was used in combination with phase shifting interferometry for the detailed experimental investigation of changes in real surface microgeometry within the elastohydrodynamic conjunction formed between a real, random, rough surface, a steel ball and a smooth glass disc. Three real roughness features were studied in detail — the transverse ridge, transverse groove and longitudinal groove. The ridge was found to be heavily deformed within lubricated contact and its height increased with increasing rolling speed. For the transverse groove, a local reduction in film thickness at the leading edge was observed, while the longitudinal groove maintained its undeformed shape. Copyright © 2006 John Wiley & Sons, Ltd.
TL;DR: In this paper, the friction reduction and antiwear properties of a range of nitrogen and sulfur-containing organic borates as oil additives in mineral oil were assessed using a Timken tester with a bearing steel ring against an AZ91D magnesium alloy block.
Abstract: The friction reduction and antiwear properties of a range of nitrogen- and sulfur-containing organic borates as oil additives in mineral oil were assessed using a Timken tester with a bearing steel ring against an AZ91D magnesium alloy block. X-ray photoelectron spectrometry and scanning electron microscopy were employed to examine the boundary film formed on the surface of the magnesium alloy block. The results show that the borate additives were effective at reducing the wear of magnesium. The acting mechanism of borate, which acted as additive in the magnesium-on-steel tribological system, was proposed. Copyright © 2006 John Wiley & Sons, Ltd.
TL;DR: Differential scanning calorimetry experiments with an unsaturated polyolester oil at 190˚C showed that an organotellurium compound in combination with a thiol or a sterically hindered phenol (BHT)...
Abstract: Differential scanning calorimetry experiments with an unsaturated polyolester oil at 190˚C showed that an organotellurium compound in combination with a thiol or a sterically hindered phenol (BHT) ...
TL;DR: In this paper, the impact print and the indentation profiles of the contacting surfaces for different conditions of thermal treatment, roughness, and lubrication were revealed by a ballistic pendulum with a steel ball as contacting part frontally impacts the steel sample.
Abstract: The transient contact between a steel ball and a metal plate is studied experimentally. The main aim of this research is to reveal the impact prints and the indentation profiles of the contacting surfaces for different conditions of thermal treatment, roughness and lubrication. The impact test rig and the measuring devices that have been used to carry out the study are presented. A ballistic pendulum with a steel ball as contacting part frontally impacts the steel sample. Using auxiliary devices, the force, acceleration and total impact duration are simultaneously recorded. When the impact velocity is increased, the force, acceleration and impression diameter increase in all cases. The recorded values of force, acceleration and contact pressure are higher in the lubricated condition than for dry impact for the annealed steel samples used, while the impression diameter is smaller. Copyright © 2006 John Wiley & Sons, Ltd.
TL;DR: In this article, a numerical solution to the elastohydrodynamic lubrication (EHL) problem of two coated elastic bodies in line contact is introduced, where the non-Newtonian behavior of the lubricant is incorporated into EHL analysis using Eyring's nonlinear viscous model.
Abstract: A numerical solution to the elastohydrodynamic lubrication (EHL) problem of two coated elastic bodies in line contact is introduced. The non-Newtonian behavior of the lubricant is incorporated into EHL analysis using Eyring's nonlinear viscous model. The surface elastic deformations are computed from full elasticity analysis of layered elastic half-space. The iterative Newton–Raphson technique is used in the numerical solution. Subsurface stresses are calculated using two different techniques, the numerical integral scheme based on Fourier transformation and the finite element method. The effects of surface coating (material and thickness) on the pressure profile and subsurface stresses are presented and discussed. Copyright © 2006 John Wiley & Sons, Ltd.
TL;DR: Several organic compounds of zinc synthesized, blended in oil, and evaluated in laboratory bench test for antiwear/extreme pressure friction are presented in this article, where the influence of the nature of the structure on the antiwear and extreme pressure properties at wt. 1.5% concentration in a paraffinic oil is studied.
Abstract: Several organic compounds of zinc synthesized, blended in oil, and evaluated in laboratory bench test for antiwear/extreme pressure friction are presented. The influence of the nature of the structure on the antiwear/extreme pressure properties at wt. 1.5% concentration in a paraffinic oil is studied. Copyright © 2006 John Wiley & Sons, Ltd.