bluuebunny/crossref_metadata_2025 huggingface dataset:
Modelling the effect of lubrication on friction behaviour
Authors: Avitzur Betzalel
Published: July 2006

Models of typical characteristics of the surfaces of two solids interfacing one another under pressure and sliding with respect to each other are described in Models 1 (Figure 1) and 2 (Figure 2). In Model 1 (Figure 1) the asperities, wedges of the harder surface indent into the softer surface due to the applied pressure, thus producing opposing ridges on the surface of the softer component. The gap between the opposing asperities is filled with liquid, establishing boundary lubrication. As sliding is maintained, the ridges are mobilized and an eddy flow is established in the trapped lubricant. The power required to mobilize the ridges and to establish eddy flow in the lubricant is calculated and thus the friction resistance to sliding is determined. Simultaneously, the pressure generated in the liquid due to shear is also evaluated. It becomes clear that the height of the ridge due to indentation is inversely proportional to the speed of sliding. The higher the sliding speed, the higher is the liquid pressure that is countering the loading pressure and the smaller is the indentation. At a high enough speed (to be replaced in due course by the Sommerfeld Number) the entire load is supported by the pressure generated in the liquid, indentation is eliminated and hydrodynamic lubrication commences. The classic model for hydrodynamic lubrication where two inclined surfaces glide atop each other is described in figure 2. Here the gap between the two surfaces (q.J a t their closest point is a monotonically increasing function of Sommerfeld Number (S). The resistance to sliding as established through the shear in the liquid determines thefriction value. This model leads directly to the characteristic of Coulomb or Emontons where for diminishing values of Sommerfeld Number the resistance to sliding is proportional to the pressure (τ = μp) and the proportionality factor is equal to the tangent of the angle of inclination (μ = tana). In the present work, the increase infnction with increasing values of the Sommerfeld Number is also determined. Combining the two models one notices that, a t low speed and Somrfeld Number values, the liquid pressure is not sufftcient tofloat the two surfaces and indentation prevails together with boundary lubrication. With increasing speed (Sommerfeld Number) the height of the ridge (by Model 1) decreases, and when it diminishes to values lower than those predicted for the gap between the surfaces in the second model for the same speed, the boundary lubrication ceases and hydrodynamic lubrication commences.
Stabilization of white solid lubricant suspensions by additives
Authors: Zakar A. , Vámos E.
Published: July 2006

This paper reports work on stability in suspension of white solid lubricants in a number of media. Lubricants included calcium carbonate, calcium hydroxide, and calcium acetate. Additives were used to increase suspension stability, and centrifugation to obtain sedimentation.
Studies on the interrelationships between the character of metals and antiwear additives
Authors: Huang Y. W. , Cheng G. X. , Dong J. X.
Published: July 2006

In machines which operate under conditions of potential boundary lubrication, all the lubricants used normally contain antiwear agents. When the antiwear properties of the lubricants are evaluated on a frictional wear tester, because the test peice is made of a single material, it is not certain that the antiwear properties of the lubricants tested are the same as those on real machines. Zhao et al. observed a correlation between the chromium content of steels and antiwear load of an antiwear agent containing sulphur or phosphorus.1 Zang studied the friction decreasing effect of an oiliness agent with different metals.2 In this report, the authors changed the test piece of a four‐ball machine for a plane ring in order to look at the test piece with different metal materials, with the aim of examining the mutual relation between the different materials and antiwear agents. This paper presents the results.
The role of sulphur in ZDDP‐induced reaction films formed in the presence of ZDDP: Contribution of electron spectroscopic imaging technique
Authors: Hallouis M. , Belin M. , Martin J. M.
Published: July 2006

The anti‐wear action of zinc dithiophosphate (ZDDP), extensively used in engine oils, is here studied by analysis of wear particles generated during a friction test between two ferrous substrates. It is known in this case that the interfacial film is complex, and contains elements from surfaces, environment and degradation products of the additive. This paper deals with the presence and the form of sulphur species in the constitution of this film. Analytical Transmission Electron Microscopy (TEM, STEM, EDS and EELS filtered images) of particles shows that sulphur is in the form of small crystallites of iron sulphide Fe7S8, embedded in an amorphous phosphate matrix. Wear tests performed at different normal loads show the variation of the P/S ratio in the particles. The results are discussed.
Industrial oil performance in terms of base oil chemical structure
Authors: Abou Naga H. H. El , Bendary S. A. , Salem A. E. M.
Published: July 2006

Some performance properties for turbine, hydraulic and gear oils were correlated with changes in chemical structure for incorporated base oils. Blends with different viscosity grades were formulated from different neutral oils, brightstocks and additives.

Different statistical approaches were used to evaluate the degree of fit for these correlations. The derived models were considered at a minimum of 99% confidence. Results clarified the role of non‐hydrocarbons and aromatic compounds, either by type or by content, in changing the performance behaviour for tested industrial oils.
Prediction of lubrication regimes of concentrated contacts
Authors: Schipper D. J. , Vroegop P. M. , De Gee A. W. J.
Published: July 2006

Friction experiments are performed on lubricated concentrated contacts (LCCs) to obtain the transitions EHL‐ML and ML‐BL as a function of the operational conditions under which these contacts operate. A transition diagram is developed to determine the lubrication mode of an LCC as a function of the operational conditions. In this investigation the LCCs operated macroscopically in the lubricants' liquid state regime.
The influence of rheological properties of mineral oil in the stick‐slip phenomenon
Authors: Tudor Andrei
Published: July 2006

Within the range of small and very small sliding velocities that are typical of applications such as clutch mechanisms, guideways of machine‐tools, hydraulic or electric drives for robots, and continuous‐indexing mechanisms, the phenomenon of ‘stick‐slip’ occurs. By taking into consideration the dependence of kinetic friction force on sliding velocity during the slip period, three critical velocities of movement stability are revealed. One of the important ways for reducing the amplitude of the phenomenon is by designing lubricating grooves of optimum geometry brought about by oil viscosity and surface tension.
Lubrication of forging under thick film conditions with thermal effects
Authors: Montmitonnet P.
Published: July 2006

In cold upsetting with a liquid lubricant, a film is trapped at the beginning of the process. Then, as plastic deformation proceeds, a non‐lubricated external zone appears, while the film thins out in the central part.1,2 This behaviour is influenced by thermal effects, namely, self‐heating of the viscous fluid4 and heating of the workpiece surface by plastic deformation.3 To improve local computation of friction, these thermal effects are here accounted for; a semi‐analytical Reynolds equation is proposed; and its solution by a finite difference scheme gives the film thickness everywhere in the film, and the extent of the non‐lubricated zone. Inclusion of the rheology of the fluid can then permit computation of the local friction stress, which can be coupled as a boundary condition in a model of workpiece plastic deformation.
Measurement of oil film thickness in big‐end bearings and its relevance to engine oil viscosity classifications
Authors: Bates T. W. , Vickars M. A.
Published: July 2006

Minimum oil film thickness MOFT measurements have been carried out in big‐end bearings of V6 and in‐line four‐cylinder gasoline engines during engine operation. MOFT decreases with increasing crankshaft speed above 2000 r/min. The most severe practical steady‐state operation is high‐speed cruising. Maximum shear rates are in the region of 107s−1 at 4000 r/min. the dynamic viscosities at a shear rate of 106s−1 correlate significantly better with monograde MOFT data than with multigrade data; the correlation parameters for mono‐ and multigrade data are also significantly different. Although the dynamic viscosity measurement correlates with multigrade data better than the low‐shear rate kinematic viscosity, the differences are not always significant at the 95% confidence level. Some other rheological parameter or combination of parameters may be better than either kinematic or dynamic viscosities.
Does the automotive industry need a standard engine test to measure journal bearing oil film thickness?
Authors: Spearot James A.
Published: July 2006

Automotive manufacturers are dissatisfied with the high‐temperature portion of the SAE Viscosity Classification, J300. This dissatisfaction occurs because the low‐shear, 100°C conditions at which viscosities are specified are not representative of the conditions to which oils are subjected at operating temperatures in an engine. Recent efforts to modify the high‐temperature viscosity specifications have dealt primarily with developing correlations between oil film thickness measured in the journal bearings of operating engines and viscosity values measured at different high‐temperature, high‐shear rate conditions in laboratory viscometers. However, it has also been suggested that the industry develop a standard engine test for measuring journal bearing oil film thickness, and that oils be ‘classified’ on the basis of film thickness rather than viscosity. This paper reviews the methods which have been developed to measure bearing film thickness, the correlations which have been calculated between film thickness and viscosity, and the conclusions drawn from such efforts. Reasons for relying on high‐temperature, high‐shear viscosity specifications rather than a standard industry bearing film thickness test are offered. In addition, the merits and drawbacks of developing an industry bearing distress test are also discussed.
Can engine effects be separated from lubricant effects?
Authors: Hoult David P.
Published: July 2006

In this paper, it is argued that, at high precision, it is impossible to separate the effects of lubricant rheology from engine geometry. Correlations based upon such a separation have little intrinsic value.
Effects of directional properties of roughness and tangential force on pressure flow between contacting surfaces
Authors: Nakamura T. , Funabashi K.
Published: July 2006

The fluid flow phenomena between contacting surfaces which exhibit roughness are interesting for the lubrication mechanisms and the sealing problems. The effects of the directional properties of roughness and tangential forces on the pressure flow are examined in this paper. Annular sealing surfaces ground in a radial direction and in a peripheral direction were prepared, and the leakage rates were measured. The experimental results showed that directional properties and tangential forces affected the leakage rates. In the last part of this paper, the directional properties of roughness are discussed, based on two‐dimensional Fourier analysis.
Evaluation of the antiwear performance of aged oils through tribological and physicochemical tests
Authors: Monteil G. , Mérillon A. M. , Lonchampt J. , Roques‐Carmes C.
Published: July 2006

Extending automotive engine drain intervals requires a good knowledge of the antiwear aspect of lubricant performance, which is often closely linked to the oxidative degradation of the oils. In this paper, we report the physicochemical analyses and tribological tests carried out on several oils oxidised by laboratory oxidation tests at different stages. An interesting correlation was found between the antiwear efficiency and some characteristics of the eletrochemical impedance spectra of such oxidised lubricants. A promising way of understanding the mechanisms of wear mitigation by aged engine oils is proposed.
A liquid crystal lubricant with partial polymerisation
Authors: Gunsel Selda , Yu Bing , Friberg Stig E.
Published: July 2006

Lamellar lyotropic liquid crystals were evaluated as lubricants in a slow sliding ball‐on‐disk friction rig. The liquid crystalline structure was modified by addition of a monomer and the influence of polymerisation on lubrication properties was studied. The results showed that partial polymerisation of a monomer located close to the polar group layer in the liquid crystal, followed by addition of a small amount of long‐chain aliphatic hydrocarbon, gives low friction coefficient and enhances load‐carrying capacity.
EP‐efficient 1,2,4‐dithiazolines and their tribological effect on steel bearing balls of different composition
Authors: Bhattacharya A. , Verma V. K.
Published: July 2006

This paper deals primarily with the potential extreme‐pressure (EP) activity of certain cyclic disulphide additives in paraffin oil. The antiwear and antifriction properties of 1,2,4‐dithiazo‐line additives have been evaluated on a four‐ball machine by using 12.7 mm diameter steel ball bearing specimen‐I. The paper also includes a discussion on the effectiveness of 3‐p‐Cl‐phe‐nylimino‐5‐(N‐methylphenyl)amino‐1,2,4‐dithiazoline on steel bearing balls of different compositions. The topography and the surface chemistry of the bearing ball wear scar were studied by Scanning Electron Microscopy (SEM) and Auger Electron Spec‐troscopy (AES).
Laser microprecision treatment to raise EHD lubrication effects
Authors: Guang Lin Zi , Bin Gao Zuo
Published: July 2006

Laser microprecision treatment of the surfaces of mechanical parts takes place after machining, where the surfaces of mechanical parts, especially highly‐loaded (counterformal) parts (e.g. gears, rolling bearing and cams with point or line contact) are re‐treated microprecisely by laser to produce an asperity texture with transverse orientation. This man‐made surface topography is favourable to EHD lubrication of parts in relative motion and greatly increases the load capacity of such parts. Timken tests of rings whose surfaces were treated microprecisely by laser demonstrate its ability to raise the Timken OK loads (or anti‐scuffing capacity).
A mixed model to predict friction forces in lubricated contact with non‐newtonian fluids
Authors: Najji B. , Bou‐Said B.
Published: July 2006

A mixed model to predict friction forces in thermohydrodynamic lubricated contacts with non‐Newtonian fluids is proposed, with an integral formulation and a finite element method resolution. The mixed model is used here for the first time in lubrication. It takes into account the implicit rheological laws. The shear stress field appears in this formulation as a nodal unknown and eases the use of rheological laws with yield criteria.
Tribochemical behaviour and lubrication characteristics of aromatic compounds
Authors: Nakayama Keiji
Published: July 2006

Radical scavenger, radical anion scavenger, and peroxide decomposer were added to aromatic hydrocarbons and phosphates in aromatic rings with and without side chain, and the effect of these inhibitors on tribopolymerisation and the lubrication characteristics of the aromatic compounds were investigated, in various atmospheres, in order to clarify the reaction mechanism. The aromatics of both hydrocarbons and phosphates with a methyl group in aromatic rings react readily at the rubbing surfaces to form polymer or polymer‐like products, improving the lubricating characteristics. The tribochemical reactions of alkylaromatic compounds is shown to differ from those of trialkyl or triarylphosphates. It was concluded that the reaction proceeds through the radical or radicalanion and via peroxide to cause polymerisation.
Adsorption of ZDDP on iron surfaces and its relation with surface tension
Authors: Huang Xin , Ying Yi‐Nan , Zhang Yna‐Hao
Published: July 2006

This paper reports work on the relationship of surface tension of ZDDP solutions to adsorption isotherms. The surface tension of the solutions varies with their composition, and information about adsorption, decomposition or other chemical changes of ZDDP in solution can be obtained from the correlation of solution concentration and surface tension. From this work, the authors conclude that adsorption of ZDDP on iron can occur at even low concentrations, increasing with temperature, and that decomposition, association and interaction between components may occur in solution at high temperatures.
Physical and chemical mechanisms of influence of Cu‐containing additives on grease properties
Authors: Ischuk Y. , Karaulov A. , Lukiniuk M. , Melnik Z. , Nosovsky O.
Published: July 2006

The mechanisms governing the influence of copper additives (powders, oxides, organic and inorganic salts, complex compounds) on tribological, rheological and basic physical properties of greases with various thickeners (lithium, complex lithium, complex aluminium and polyurea) are discussed. The copper plating effect was found to occur only under EP conditions. The physical and chemical patterns of copper‐containing grease additives under antiwear and extreme pressure conditions are discussed together with rational application alternatives in friction couples of equipment and machinery.
Drilling models for a synthetic cutting fluid
Authors: Leep Herman R. , Peak Marie A.
Published: July 2006

The primary objective of this research was to develop relationships which predict tool wear from measured cutting forces. Different cutting speeds and feed rates were examined. The workpiece materials used were a medium‐carbon steel and a titanium alloy. A synthetic cutting fluid was used with a 9.525 mm drill and a 6.350 mm drill, for drilling the medium‐carbon steel and the titanium alloy, respectively.

Preliminary testing was conducted to find the optimal values for cutting speeds and feed rates. The main drilling tests were performed using the cutting conditions resulting from the preliminary tests. Statistical analysis of the results of the main drilling tests showed that the axial force was significant at the 5 per cent level in models for both materials. It also showed that the moment about the vertical axis was significant at the 5 percent and the 15 per cent levels in the models for the titanium alloy and the medium‐carbon steel, respectively. The model for the smaller holes drilled into the more homogeneous material, the titanium alloy, was more accurate in predicting tool wear.
An approach to the study of plasto‐elastohydrodynamic lubrication in the wire drawing process part 1: Experimental
Authors: Ei‐Butsh A. M. A. , Ei‐Badrawy R. S. , Mokhtar M. O. A.
Published: July 2006

This paper describes an experimental study of hydrodynamic lubrication in wire drawing in which different types of lubricants (straight oils, emulsions and grease) are used. The experiments were conducted on a specially designed laboratory wiredrawing test rig, to assess the frictional force and film thickness, while drawing an aluminium wire at different speeds. Hydro‐dynamic performance, including frictional force and film thickness, were measured and plotted graphically, showing lubricant and drawing speed as the main influences.

Results indicate that the frictional force decreased and the oil film thickness increased using straight oils with high viscosity at high drawing speed.
Spectroscopic studies and electronic properties of heat treated calcium sulphonate
Authors: Bertheville B. , Deroide B. , Zanchetta J. V. , Palermo T.
Published: July 2006

Overbased calcium sulphonate and its derivatives have been characterised by means of thermogravimetric analysis, X‐ray and IR spectroscopy. The study was carried out after thermal treatment up to 900°C. Different phases appeared, showing a transition from an amorphous system to a crystallised medium. Electrical measurements showed electron behaviour for compounds obtained at low temperatures. ESR experiments produced classical results connected with the decomposition of organic chains.
Overbased lubricant detergents – a comparative study
Authors: O'Connor S. P. , Crawford J. , Cane C.
Published: July 2006

Overbased detergents are commonly used in automotive and marine lubricants. Their main functions are to neutralise potentially corrosive acids and to contribute to engine cleanliness. The major types of overbased detergents that are produced commercially are phenates, sulphonates and salicylates. This paper describes the chemistry of these additive classes and reviews their properties and performance in bench and engine tests. The paper also describes a new class of overbased detergents, where novel chemistry has been used to produce new types of highly overbased phenate, sulphonate, and salicylate. These new products exhibit significant improvements in properties and performance over conventional detergents. Evidence from bench and engine tests is presented to demonstrate the benefits of the new detergent types. An appendix gives more detail on the results of tribological tests on these new detergents.
Experiment and computer simulation of particulate suspensions under shear flow
Authors: Heyes D. M.
Published: July 2006

In this paper is described the role of molecular simulation as a useful quasi‐‘experimental’ tool to help in understanding the interplay between molecular structure under shear flow and the manifested tribology/rheology. The development of non‐equilibrium molecular simulation techniques are discussed, from the molecular dynamics approach through to the modelling of dispersions by brownian dynamics. Recent advances and extensions of the technique to weakly flocculated systems, such as electro‐rheological fluids, are described.
Action mechanism of 35S‐containing antiwear and EP additives
Authors: Herdan J. M. , Negoita N.
Published: July 2006

Antiwear and extreme‐pressure additives labelled with 35S were synthesised by reacting 35S2Cl2 with isobutylene and treating the adduct with potassium xanthate, or by labelling the unlabelled compound with elemental 35S in boiling carbon di‐sulphide. Static adsorption tests of the labelled additives on iron or copper specimens show an adsorption increase with temperature. The data are in good agreement with the results of thermal analysis of the additive as such or mixed with iron or copper powder. The behaviour of the oil solutions containing labelled additives on a friction machine emphasised the formation of superficial layers on a metallic surface containing the reaction products of the additive decomposition compounds with the metal. The thickness of these layers remains nearly constant during the test but increases with normal load. Pyridine washing of the specimens removes adsorbed layers whereas chemisorbed layers remain on the metallic surface.
A hydrodynamic lubrication model for the deep‐drawing process
Authors: Mahdavian S. M. , He D.
Published: July 2006

A steady hydrodynamic lubrication model that includes the pressure viscosity factor has been developed for the deep‐drawing process. Equations for lubricant film thickness, radial and drawing stresses are presented. Analysis reveals that the pressure viscosity factor has a significant influence on estimating lubricant film thickness and radial and drawing stresses.
Computer simulation of turbine oil oxidation. 1: Consumption of a hindered phenol antioxidant in model hydrocarbon systems at 115°C
Authors: Igarashi Jinichi , Yoshida Toshio
Published: July 2006

Computer simulation of the inhibited oxidation of model hydrocarbon systems representing turbine oils of different composition, hexadecane/tetralin mixtures containing di‐tert‐butyl pcresol (DBPC), has been achieved using the kinetic and mechanistic information obtained from fundamental hydrocarbon autoxidation and inhibition studies. The oxidation life, the time to complete consumption of DBPC and its reactive intermediates, was calculated using previously reported and newly measured absolute rate constants for reaction involved. The results of this calculation of oxidation life were in good agreement with values experimentally determined. The oxidation life has been found to decrease with increasing amount of tetralin in the mixtures. This can be explained by the increased rate of consumption of antioxidants, caused by an increase in the rate of free radical formation, via the direct reaction of hydrocarbons with oxygen, and via the homolytic decomposition of hydroperoxides. The observed decrease in oxidation life, however, is not significant, despite the fact that the addition of tetralin considerably increases the rate of free‐radical formation. The relatively low sensitivity of oxidation life to the rate of free‐radical formation caused by the addition of an easily oxidisable substrate can be attributed to the occurrence of a direct oxidation of antioxidants. That is, kinetic analysis for the consumption of antioxidants disclosed that antioxidant consumption mostly occurred not through the inhibition of oxidation, but through direct oxidation. The direct oxidation of antioxidants obeys the rate equation ‐d[AH]/dt = k6[AH]1.0[O2]1.5 where k6 can be calculated, at various temperatures, from Arrhenius parameters obtained in this study (log (A/M−1s−1) = 9.6 and Ea = 22.6 kcall mol).
Tribological studies of some N, S, and Cl containing extreme pressure additives
Authors: Bhattacharya A. , Singh T. , Singh A. P. , Singh R. , Verma V. K.
Published: July 2006

The antiwear and EP properties of certain p‐chlorophenyl groups containing nitrogen and sulphur open‐chain and cyclic compounds, in paraffin oil, were evaluated in a four‐ball test. The performance of the additives were compared with a commercially available sulphur‐phosphorus reference additive. All the additives, in general, exhibited good EP activity at different loads as compared to paraffin oil and the reference additive. However, the cyclic additives, e.g., 2‐phenyl‐3‐phenylimino‐5‐p‐Cl‐phenylamino‐1,2,4‐thiadiazolidine, and 2‐amino‐5‐p‐Cl‐phenylamino‐1,3,4‐thiadiazole, were found to possess good antiwear and EP properties in comparison to the plain paraffin oil, reference additive, and open chain additives. The wear surface tribochemistry and topography were studied using Scanning Auger Electron Spectroscopy (AES) and Scanning Electron Microscopy (SEM) techniques, respectively.

A comparative EP activity evaluation of 1‐p‐Cl‐phenyl‐2,5‐dithiohydrazodicarbonamide and 3‐p‐Cl‐phenylimino‐5‐(N‐methylphenyl)amino‐1,2,4‐dithiazoline on steel bearing balls of different composition was undertaken to assess the suitability of replacing chromium alloy steel balls with cheaper carbon steel balls. The additive, 3‐p‐Cl‐phenylimino‐5‐(N‐methylphenyl)amino‐1,2,4‐dithiazoline exhibited its effectiveness on the alloy steel as well as low carbon steel bearing balls.

A plausible explanation for the enhanced activity of additives is suggested and efforts made to correlate the effect of substituents and structure on the efficiency.
New data on the mechanism of antiwear action of zinc dithiophosphates in lubricating oils
Authors: Vipper A. B. , Karaulov A. K. , Mischuk O. A.
Published: July 2006

ZDDP reacts with oil‐soluble copper salts to form complex compounds and these compounds can substantially surpass the initial additive in the effectiveness of antiwear and antioxidant action. Application of AES allows us to establish the influence of ZDDP and complex compounds formed by it on the structural state of the friction surfaces. The specific nature of action of these complex compounds lies in minimisation of the oxidation processes in the surface microvolumes of the lubricating medium, the consequence of which is the localisation of tribo‐chemical processes of secondary structure‐film formation in the thinner layers. On the whole, the results obtained offer evidence of the existence of certain interrelations and generality of the processes producing antiwear and antioxidant action by zinc dithiophosphate additives in lubricating layers.
The mechanism of synergism between ZDDP and CeF3 additives
Authors: Lian Yafeng , Xue Qunji , Zhang Xuxhou , Wang Hanqing
Published: July 2006

The interaction of zinc dialkyldithiophosphate (ZDDP) with cerium fluoride and cerium dioxide in lithium grease has been studied for friction, wear, and EP characteristics on a four‐ball and SRV tester. The combination of ZDDP and cerium trifluo‐ride has been shown to be beneficial in reducing wear, especially over a long period of friction and with increasing EP load. The test results show that adding cerium dioxide to lithium grease does not improve the antiwear and friction performance of the paste. The analytical results of X‐ray photoelectron spectrum (ESCA, XPS) reveal that ZDDP inhibits the decomposition of cerium fluoride and improves its film‐forming property. The wear scar reaches a minimum at an atomic concentration ratio of 3P:2Zn:1S:25F, and an atomic concentration ratio of 2S:2P:1Zn:4F gives the highest EP load. The scratch test results show that combining ZDDP with cerium trifluoride improves the tenacity of the surface film. The stabilisation of cerium trifluoride by ZDDP is proposed.
Friction and wear characteristics of organic thiophosphoro derivatives — a critical appraisal
Authors: Anand O. N. , Singh A. K. , Kumar Vijay , Bisht R. P. S.
Published: July 2006

The friction‐ and wear‐reducing characteristics of a number of oil soluble sulphurised and phosphosulphurised derivatives for automotive and industrial applications have been reviewed. A critical appraisal of the suggested causes and mechanism of friction reduction and antiwear characteristics has been made. A review of the investigations carried out so far indicates that the creation of in situ films of simple inorganic salts, such as molybdenum disulphide, iron sulphide or phosphates of low shear strength and lamellar structures, does not appear to be the primary cause of low friction and wear.

The authors have, therefore, undertaken a programme to synthesise and study the chemistry and tribochemical reactions in relation to friction and wear characteristics of hydrocarbon‐soluble thiophosphoro derivatives of alkyl phenol, alcohols and fatty esters, in order to establish relationships between the reactivity, chemical nature and crystal structure of films formed on rubbing surfaces, and antifriction and antiwear characteristics. Molybdenum salts of various phosphorothio derivatives of pentadecylphenol and lauryl oleate of specific structures have been synthesised, and the friction and wear properties of their blends in mineral oil base stock have been studied. It can be clearly inferred from the results that type of bonding between sulphur, phosphorus and molybdenum, and reactivity of these derivatives with rubbing surfaces, determine their friction‐reducing and antiwear characteristics. Their reactivity with iron and the nature of films formed are under investigation.
Effect of coatings on thermal conditions of EHL
Authors: Bogdański Stanisław
Published: July 2006

The thermal EHD model of rectangular contact has been applied to analysing the effect of coatings on thermal conditions in EHL. The model takes into account variation of oil viscosity along and across the oil film according to the Barus formula. The solution has been obtained by means of the Newton‐Raphson method. The effect of the coating has been examined by comparison of the temperature distributions in the oil film and on the surfaces of rollers for the cases with and without coating. In addition, the oil film shapes and minimum values, the pressure distributions and traction coefficients, have also been compared.
Influence of oil‐soluble copper salts on catalytic oxidation of lubricating oil in laboratory conditions and in a single‐cylinder engine
Authors: Vipper A. B.
Published: July 2006

During oxidation of an engine oil under laboratory conditions, and testing in a single‐cylinder gasoline engine, it has been found that oil ageing depends on the copper content, in particular the oil‐soluble copper salt content. The latter considerably intensifies engine oil oxidation, loss in bearing weight, and piston deposit formation. Several regularities in the oil ageing process were found. It was noted that interaction of copper naphthenate with zinc dithiophosphate essentially influences this process.
Colloidal thiophosphorus calcium salt as antiwear additive
Authors: Delfort Bruno , Born Maurice , Daoudal Bertrand , Chivé Agnes
Published: July 2006

This paper describes the synthesis of an oil‐soluble colloidal calcium thiophosphate by a direct route. It consists of the reaction of calcium oxide or hydroxide with tetraphosphorus decasulphide and water in the presence of a surfactant such as a calcium alkylaryl sulphonate in an organic medium. Reaction and micellisation occurred simultaneously according to a one‐step process. The product is characterised by a high calcium, phosphorus and sulphur content. The colloidal nature of the product has been confirmed by dialysis. The 31P‐NMR spectrum showed signals characteristic of a blend of different calcium thiophosphates, plus calcium phosphate. The product could be defined as a core of different calcium (thio)phosphates surrounded by a calcium alkylaryl sulphonate shell, according to a reverse micelle type association in oil. This compound was evaluated as an antiwear additive in a 130 Neutral Solvent mineral oil by anti‐wear and extreme‐pressure four‐ball tests. The extreme‐pressure characteristics depend on the concentration of mineral colloidal core in oil. The antiwear properties are a function not only of the concentration, but also of the colloidal core/surfactant shell ratio. Thermogravimetric analysis of these colloidal species shows a weight loss in the 350°C to 450°C range, due to surfactant degradation. The further evolution of weight loss up to 900°C demonstrates the high thermal stability of the colloidal calcium (thio)phosphate core.
Reducing the effect of three‐body abrasive wear by adding polymeric powder to lubricating grease
Authors: Ali W. Y. , Mousa M. O. , Khashaba M. I.
Published: July 2006

The present paper reports on work aimed at improving the abrasive wear resistance of surfaces lubricated with contaminated greases. The intended improvement can be achieved by reducing the effect of wear occurring between the abrasive particles and the rubbing surfaces. Different polymeric thickeners in powder form, such as high‐density polyethylene (HDPE), low‐density polyethylene (LDPE), polyvinylchloride (PVC), polyamide (PA6) and polymethylmethacrylate (PMMA), were added to lithiumbased grease.

The wear resistance and the coefficient of friction of cylindrical steel specimens were examined using a cross‐pin test machine. The test machine provides concentrated contact under mixed lubrication conditions. Wear was measured on the stationary test specimen by the wear scar diameter, using an optical microscope, with an accuracy of ±1 μm. The frictional torque generated between the rubbing surfaces was measured using a full bridge strain gauge measuring cell attached to the stationary test specimen holder. The experiments were performed using clean and contaminated lubricating greases to which Air Cleaner Fine Test Dust (SCFTD) was added to the greases at a concentration of 10 wt.%.

The results show that the effect of the abrasive contaminants can be reduced by the addition of polymeric powders. However, the addition of polymer to lubricating grease at relatively high concentration (more than 35 wt.%) has no effect on the antiwear action of the lithium grease. Further, the addition of polymeric powder with a particle size relatively greater than that of the contaminant can be considered as a useful method of eliminating the cutting process of the three‐body abrasive mechanism introduced by the presence of the hard contaminant particles.
Creep transport of grease subjected to low frequency vibrations
Authors: Lundberg Jan , McFadden Terry
Published: July 2006

Creep transport is defined as the velocity of a mass of grease when it is subjected to vibrational and gravitational forces. The method developed to assess this, measured the time taken for the grease submitted to low frequency vibrations to creep, under the influence of gravity, a specified distance down a cylindrical tube. The vibrations were characteristic in frequency and amplitude to those commonly experienced by commercial rotating machinery. Vibrational excitation was found to have a widely varying effect on creep transport of grease, suggesting that this parameter may be important in the selection of greases for specific applications where vibration is present; in contrast, the NLGI number gave almost no indication as to the effect of vibration on a particular grease. A vibration number related to the creep rate is suggested for grease selection. The vibration number correlates to the yield stress of the grease, with higher yield stress correlating to higher creep rate. However, no correlations between creep rate and base oil viscosity or bleed rate were found.
Development of engine crank‐case oil formulations for oxidation stability using indigenously blended lubricant base‐stocks
Authors: Sharma R. K.
Published: July 2006

With changing engine design putting more emphasis on fuel economy, emissions control and low engine oil consumption, the quality levels of engine crank‐case oils are changing fast. With this in view, experimental work has been carried out towards the development of engine crankcase‐oil formulations meeting the required levels of oxidation stability.

Three lubricant base‐stocks meeting the physico‐chemical characteristics of engine oils, prepared from lubricant streams obtained from different refined crude oils and one re‐refined engine oil base‐stock were used. The viscosity index of these base‐stocks ranged from 84 to 98, and carbon residue from 0.06 to 2.2. The antioxidant used in the formulation was of ZDDP type, and the detergents were calcium and barium sulphonates.

The base‐stocks were evaluated using the IIP oxidation stability test, to determine their suitability in the formulation of engine crankcase oils. The base‐stocks were then dosed with additives, and tested again by the IIP Oxidation Stability Bench Test, for their additive response.

The final formulations were then tested on a CRC‐L‐38 standard engine test prescribed in Indian Standard 13656:1993 for IC Engine Crankcase Oils with respect to bearing corrosion and piston deposit tendencies. It was observed that higher VI lubricant base‐stocks and the re‐refined engine oil base‐stock gave better test performance in both bench and standard engine tests.
Trends in gear oil additives
Authors: Herdan J. M.
Published: July 2006

Of the total amount of additives produced and sold in the world, gear oil additives are the second largest group, after the engine oil additives. According to the purpose of the finished lubricant, these additives can be classed as either additives for automotive gear lubricants or additives for industrial gear lubricants. Although the main function of such additives is the same for both types of lubricants, namely to reduce friction and wear and avoid surface fatigue, permanent deformation of the tooth, and excessive wear, the requirements that these lubricants have to meet are different. The most important specifications for automotive gear lubricants are, in the USA, API GL‐1—GL‐6, and MIL L 2105 A—2105 D, respectively, whereas in Europe manufacturers tend to have taken GL‐4 or GL‐5 as a basis, and added their own supplementary requirements. Industrial gear lubricants are manufactured according to US Steel 224 specification, DIN 51517/3, and AGMA 250.04. The gear oil additives themselves are based on sulphur and phosphorus chemistry, but other chemicals are introduced into the additive packages to ensure oxidation stability, anti‐corrosion protection, copper compatibility and better seal compatibility. Boron compounds are shown to improve the antiwear and extreme‐pressure properties of the lubricants, as well as oxidation stability, thermal stability and detergency. Rig and bench tests demonstrate the benefits of adding boron compounds to fully formulated GL 5 oils and to classic sulphur‐phosphorus additive packages for automotive and industrial gear oils.
Exploring possible connections between tribology and osteoarthritis
Authors: Furey Michael J.
Published: July 2006

This paper is part of a continuing study aimed at exploring possible connections between tribology and mechanisms of synovial joint lubrication and degeneration. In a separate paper, the focus was on the tribological behaviour of natural and ‘normal’ synovial joints. The central thrust or purpose of the present paper is to stimulate discussion of ‘abnormal’ joint behaviour, in particular, degenerative joint disease or osteoarthritis, from the point of view of a tribologist, and in the light of our findings on cartilage wear. Some provocative questions are raised. For example, can a lack of ‘proper’ synovial joint lubrication or a specific biochemical ‘anti‐wear’ agent lead to degeneration of the joint or more rapid removal of articular cartilage? Does osteoarthritic articular cartilage have poorer resistance to wear than ‘normal’ cartilage? It is not argued that arthritis is a tribological problem. However, it would seem that tribological connections with degenerative joint disease — and possibly other forms of arthritis — are indeed possible, but complex.
The tribological behaviour and tribochemical mechanism of action of oxovanadium (IV)‐dithiophosphate
Authors: Guo‐Xu Chen , Ren‐Gen Xiong , Jun‐Xiu Dong
Published: July 2006

Vanadium (IV)‐oxo‐dicyclodithiophosphate (VDTP) was prepared and its additive properties evaluated using a four‐ball machine. The results show that VDTP exhibits better extremepressure performance, but lower antiwear activity, when compared with ZDTP. The reaction film composition, characterised by scanning Auger microscopy (SAM), X‐ray photoelectron spectroscopy (XPS) and diffractometer surface techniques, reveals that the antiwear and friction layer containing vanadium oxide, phosphate/phosphide, and sulphide, prevent the rubbing pairs from contacting directly, resulting in better extreme‐pressure and antiwear behaviour.
Formation, structure, and properties of lubricant‐derived antiwear films
Authors: Willermet P. A. , Carter R. O. , Schmitz P. J. , Everson M. , Scholl D. J. , Weber W. H.
Published: July 2006

In recent years, surface analytical methods that determine structure have been combined with methods that measure elemental composition and oxidation states, to yield an improved understanding of lubricant‐derived tribofilms. Methods assessing the mechanical properties of thin films have also been applied to tribofilms with thicknesses of the order of nanometres. These methods, in combination with chemical and physical studies of bulk lubricant systems and assessments of lubricant behaviour in tribological environments, have made it possible to describe comprehensively film forming mechanisms, structures and tribological properties. This paper outlines the initial results of such an attempt, focusing on zinc dialkyl dithiophosphates and overbased detergents in model systems and engine oils.
Comparison of the fretting wear of 100Cr6/100Cr6, Si3N4/Si3N4 and Si3N4/100Cr6 contacts in lubricated and dry conditions
Authors: Vižintin J. , Kalin M. , Podgornik B. , Novak S.
Published: July 2006

The fretting wear behaviour of bearing steel against bearing steel, silicon nitride against silicon nitride, and silicon nitride against bearing steel, was investigated under lubricated and dry conditions. Amplitudes in the intermediate 5 to 50 μm range, and test durations from 10 to 360 min, were studied. Light microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive X‐ray spectroscopy (EDS) were employed to determine the detailed nature of the friction and wear processes.

In the silicon nitride against silicon nitride contact, brittle fracture of Si3N4 grains, and tribochemical reaction creating an amorphous layer on the mechanically damaged surface, were found. The main mechanism of fretting wear in the case of bearing steel against bearing steel contact was delamination. In the silicon nitride against bearing steel contact, chemical reactions predominated.
Sleeve dampers for externally pressurised gas journal bearings
Authors: Uneeb M. , Gohar R.
Published: July 2006

An approximate small eccentricity analysis is presented, for finding the threshold of fractional speed whirl instability of an unloaded double plane admission hybrid gas journal bearing supported by a non‐rotating externally pressurised gas journal bearing sleeve damper. A line source is assumed at the feeding planes to the gas film with flow and load correction factors to account for the discreteness of the feed holes (details of these factors are presented in a related publication). The results show that, by careful selection of the design parameters, it is possible almost to remove fractional speed whirl instability from the bearing arrangement. Some practical designs of sleeve dampers are also presented.
Development of a high performance railroad diesel engine oil for improved oil consumption control
Authors: Mazumdar S. K. , Tiwari O. P. , Chaubey D. M. , Rao A. M. , Srivastava S. P. , Bhatnagar A. K.
Published: July 2006

High output railroad diesel engines today require high‐performance crankcase lubricants, not only for extending drain intervals, but also for economising by lowering oil consumption. Although the importance of engine design in controlling oil consumption has been recognised for quite some time by the oil and railroad industries, another approach has been to reduce oil consumption by effective design of crankcase lubricants. This paper reports the development of a high‐performance railroad diesel engine oil with superior detergency, dispersancy, oxidation and thermal stability characteristics vis‐à‐vis oils formulated with the latest generation packages. The same oil has also given reduced oil consumption in the Petter AV‐1 performance engine test. Multigrading this formulation has resulted in further reduction in oil consumption.
Extreme‐pressure behaviour of lubricated ceramic/steel couples
Authors: Bartelt G. , Becker R. , Zimmermann B.
Published: July 2006

The friction and wear behaviour of lubricated ceramic/steel couples was studied, for increasing loads, with a four‐ball tester. For the steel spheres of ceramic/steel couples, a transition point to severe wear was observed, which occurred at loads four to five times higher than the transition for the corresponding steel/steel couple. The extreme‐pressure behaviour for conditions of lubrication with pure hexadecane is compared with the results for lubrication with solutions containing zinc di‐n‐butyl dithiophosphate or zinc di‐sec‐butyl dithiophosphate.
A study of the rheological behaviour of multigrade oils
Authors: Hassanean M. H. M. , Bartz W. J. , Abou Naga H. H. El
Published: July 2006

The rheological behaviour of four blends of multigrade oils containing different commercial viscosity index improvers has been studied for increasing shear rate and temperature.

Polyalkylmethacrylate has been found to demonstrate different behaviour to styrene‐isoprene, styrene‐butadiene and ethylene‐propylene copolymers. Oil blends for all these hydrocarbon copolymers have shown non‐Newtonian behaviour with increasing shear rate (0 to 35,000 s−1) at low and moderate temperatures (−15 to 40°C), i.e. their viscosities were subject to a significant decrease, while the viscosity of the polyalkyl‐methacrylate blend showed a limited decrease. With increasing shear rate at high temperature (100°C), all the formulated blends behaved as Newtonian fluids, i.e. with nearly constant viscosities.

Increasing shear rate can also change the behaviour of some hydrocarbon copolymers from thickeners to viscosity index improvers.