bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurement of friction during the metalforming process
Authors: Wang S. L. , Ramaekers J. A. H. , Smeets M. J. H.
Published: July 2006

With the development of numerical simulation of forming processes, there is an increasing need to develop a more suitable friction description for use in the numerical simulation codes. In this paper, a plane‐strain compression tribometer is described which can measure vertical force, friction force, and vertical displacement simultaneously and accurately. Three different friction models are evaluated with the experimental results. A modified friction model is proposed and some directions are given for future research on friction in metalforming processes.
Development of the PSA TU‐3 test for valve train scuffing wear
Authors: Bovington C. , Arnould H. , Mace J.‐Y. , Brégent R. , Durrant R.
Published: July 2006

The development of the valve train scuffing wear test by the CEC PL‐35 group is described. This test is run on the PSA TU‐3 engine, comprises a cold/low speed and a hot/high speed phase and is of 100 h duration. Oil performance is evaluated in terms of camshaft wear and follower contact pad scuffing merit rating.

Studies undertaken by the group to identify those factors essential to the control of test development are described. The evolution of the test, with the introduction of a single point fuel‐injected engine, is detailed and the consequences of this on severity and repeatability and reproducibility are discussed.
Simulation of the tribological behaviour of components and cutting tools by means of model wear testing
Authors: zu Köcker G. Meier , Habig K.‐H. , Woydt M.
Published: July 2006

Modelling the wear test process can initiate real‐life friction and wear of components and cutting tools. In this paper we describe model wear tests that were developed to discover (a) whether or not simulation of the wear processes that occur during cutting is possible, and (b) how the wear of indexable inserts can be reduced by using thin hard coatings, e.g. TiN, (Ti,Al)N, Ti(C,N) when milling metallic materials. The real‐life wear of the track groups of various tracked vehicles was also investigated, in order to evaluate the wear resistance of certain materials.
A simplified wet friction clutch test apparatus
Authors: Scott W. , Suntiwattana P.
Published: July 2006

A small, economic, test rig to evaluate friction materials and fluids for wet clutch applications has been designed, built and commissioned. In this paper, the construction, operation and performance of the machine are described, and results are presented, for two sets of typical tests. The system is capable of recording data, and torque test track, coefficients of friction, and oil temperature rise, are given.
Model and computer simulation of friction
Authors: Rakowski W. A.
Published: July 2006

A model, consisting of the stochastic formulae which describe the relationship between the friction coefficient and the parameters known to be significant in dry friction, is proposed for dry sliding friction between two randomly rough surfaces. The model considers the frictional phenomena which dominate in energy dissipation and which may occur simultaneously between contacting elements. The kind of interaction in a given spot of asperity contact depends on the local energy flux density. The effect of several parameters on the friction coefficient, the real area of contact, and the number of contact spots can be calculated with the FRI‐SIM program. A comparison of the simulation and experimental data shows a convergence of results.
Characterisation of soot‐laden oils by quantitative voluminosity measurements
Authors: Ryason P. R. , Hansen T. P.
Published: July 2006

Soot‐related viscosity increase has long been recognised as a potential problem in diesel engine operation. Proposed emissions regulations have led to investigations of changes in combustion to reduce soot emissions. Some of these changes, though effective in reducing exhaust soot emissions, result in increased amounts of soot in the crankcase. With a potential for a renewed emphasis on control of soot‐related crankcase oil viscosity increase, methods of characterising soot‐laden oils have become desirable. In this paper, a method is described to compare viscosity increases in different oils produced by soot in a given engine. Precision controlled shear rate rheometry can be used to determine the voluminosity of an engine soot in an oil. Comparison of voluminosities ranks oils quantitatively.
The effect of surface roughness on contact and stress states of spur gears
Authors: Väradi K. , Kozma M. , Poller R.
Published: July 2006

The contact characteristics of spur gears are analysed, taking into consideration real surface micro‐geometry, and using numerical algorithms. The contact pressure distribution, contact area, and rigid body rotation of the gears have been calculated for different types of gear surface according to machining: shaping, grinding, or milling. Finally, the sub‐surface stress state is evaluated for different pressure distributions, by finite element method.
Tribological problems of mineral comminution
Authors: Scieszka S. F.
Published: July 2006

A laboratory method has been developed which involves the use of three new rigs simulating the grinding action in the majority of existing types of mills. All three rigs combine abrasion and erosion with comminution processes. The object of this investigation was to develop a test procedure that would be suitable for general use in estimating the abrasiveness of particular minerals, and to study abrasive wear in various grinding systems. Three separate industrial problems involving coal grinding have been investigated by means of the novel apparatus.

The results from the relatively simple laboratory procedures, designed and operated according to the principles of similarity, may be used to predict the service life of grinding machine elements.

The tribo‐testing procedure and apparatus can be used to evaluate the abrasiveness of any granular mineral, and for testing the wear resistance of any material in abrasive or erosive action. A second paper (see p. 257) publishes results obtained using the apparatus.
Laboratory evaluation of the dispersancy power of a gasoline engine oil and its relationship with sequence VE test results
Authors: Hipeaux J. C. , Durand J. P. , Prigent M. , Binet D. , Rossi A. , Vallez D.
Published: July 2006

The evaluation of the dispersancy power of a gasoline engine oil is included among such international specifications as those of the Committee of Common Market Automobile Constructors (CCMC) and the American Petroleum Institute (API). Such an evaluation is carried out by means of long, severe, and expensive engine bench tests, the engines used being Mercedes M102E (CCMC G4 and G5 levels) or the Ford Pinto 2.3 (API SG and SH levels). The cost of these tests necessitates pre‐selection of oils by laboratory tests and these need to be a reliable indicator of bench test performance. The present study proposes two new laboratory methods, the OXYDISP and the POTDISP tests, which associate artificial ageing of the lubricants with modified blotter spots tests. These tests showed excellent correlation with Sequence VE engine test results. They were also capable of distinguishing oils of different API standards. They therefore provide an effective tool for preselection of lubricants, without pretending to be a replacement of or substitute for Sequence VE or other engine bench tests.
Stress and fatigue analysis of fretting on a stressed specimen under partial slip conditions
Authors: Fouvry Siegfried , Ruiz Franscisco , Kapsa Philippe , Vincent Léo
Published: July 2006

A new Fretting on a Stressed Specimen (FSS) device has been conceived to help evaluate the influence of static stress on cracking during fretting wear in a sphere‐on‐plane contact. The mechanical analysis of the stressing state induced by such a loading has been performed for elastic conditions. It is completed by the analytical determination of multiaxial Dang Van's fatigue crack nucleation criterion. The theoretical developments are confirmed by tests on a well‐known low alloy steel. Analysing the stressing state of the maximum loading condition at the critical surface contact borders, it is shown that a simple uniaxial approach can be used to define the crack nucleation risk in fretting wear and FSS. Comparing the classic fatigue descriptions that define the admitted alternated stress amplitude as a function of the mean stress value, the VDI approach is found to be the most relevant. Satisfying the linear relationships between stress components, specific FSS relationships are introduced to fit the experiments better. Because of this analytical description, all materials, surface, geometry, and contact parameters can be connected.
Measurement of wear in radial journal bearings
Authors: Ligterink D. J. , De Gee A. W. J.
Published: July 2006

In this article, the measurement of wear in radial journal bearings is discussed, where a distinction is made between stationary and non‐stationary contact conditions. Starting with Holm/Archard's wear law, equations are derived for the calculation of the specific wear rate k of the bearing material as a function of the wear depth d, measured after an experiment or a period of use in practice. It is also possible to calculate a value for the maximum allowable apparent pressure pa at given values of k, required lifetime and maximum allowable wear depth d, or a value of d at a given value of pa. In order to facilitate the use of the equations mentioned above, non‐dimensional diagrams are presented. Two examples are given to explain the use of these diagrams.
FT‐NMR and FTIR applications in lubricant distillates and base stocks characterisation
Authors: Adhvaryu Attanu , Sing I. D.
Published: July 2006

Lubricant distillates undergo different stages of refining in order to produce the quality required of base stock for lubricating oil formulations, incorporating different additives in various doses. It is essential to monitor the degree of refining at different stages and additive response in base stocks, using fast and accurate techniques. FT‐NMR and FTIR techniques offer a new dimension to the monitoring and characterisation of lubricant distillates and base stocks.

In the present paper, an attempt is made to demonstrate the application of these techniques to deriving some average structural parameters and to correlate them with various physico‐chemical characteristics of lubricant distillates and base stocks. These correlations could be used to optimise various process parameters during the refining of lubricant distillates. If the process parameters are constant, such correlations could be used to predict the quality of the base stocks obtained from any change in the composition of the lubricant distillates. Various applications of FTIR in base oil characterisation and its processing are also reviewed.
Structures of adsorbed zinc dithiophosphates and their relationship to engine wear
Authors: Yamaguchi E. S. , Ryason P. R.
Published: July 2006

Zinc dithiophosphates (ZnDTPs) have been used extensively as anti‐wear agents for over 30 years. The mechanism of action of these remarkable materials is not fully understood. In particular, the molecular composition of the antiwear film produced by the ZnDTPs remains an area requiring investigation.

In this paper, the molecular composition of adsorbed ZnDTPs on aluminium oxide (Al2O3) surfaces has been studied using Inelastic Electron Tunnelling Spectroscopy (IETS), a highly sensitive molecular spectroscopy specifically applicable to surface species at low coverages. As such, it complements other surface science techniques for determining surface compositions. A vibrational spectroscopy, IETS utilises the literature on group characteristic frequencies available from the very extensive correlations developed for infrared and Raman spectra. Thus, functional groups may be identified that are formed by the reaction of a lubricating oil additive with a metal surface covered by a native oxide.

Using IETS, we show that ZnDTP aryl esters are dissociatively chemisorbed, and do not appear to form P=S groups bonded to the surface. By contrast, primary and secondary ZnDTPs retain the phosphate ester groups and bond to the surface by the P=S bond to different degrees. These spectral differences are qualitatively correlated with the observed antiwear performance of these materials.
Analysis of three‐body abrasive wear with fatigue theory
Authors: Xiaopeng Xie , Xie Y. B.
Published: July 2006

The effect of various parameters in the process of three‐body abrasive wear is analysed by fatigue theory. A formula for the wear volume in three‐body wear is derived. Results indicate that this formula can basically reflect behaviour in three‐body wear experiments.
Condition monitoring of aircraft by quantitative filter debris analysis
Authors: Bennett L. G. I. , Swanson Sarah , Koza F. D. , Poland J. S.
Published: July 2006

Various condition monitoring techniques are used collectively to monitor the health of aircraft engines and transmission, a concept known as Integrated Health Monitoring (IHM). A well‐established quantitative technique is Aircraft Oil Analysis (AOA), in which spectroscopic techniques such as Rotating Disk Electrode Atomic Emission Spectroscopy (RDE‐AES) are employed to analyse periodic oil samples for wear debris. Usually, no sample preparation is undertaken, as the oil sample containing both dissolved and suspended metallic wear debris is analysed directly. AOA works well for oil‐lubricated systems with relatively coarse filtration that allow circulation of the debris and its subsequent abrasive contact with moving components. To avoid this secondary wear, finer filtration is employed on both new and older aircraft. Less wear debris, and thus information, is available in the oil. A technique that quantitatively analyses the wear debris caught on the filter has been developed and is termed Quantitative Filter Debris Analysis (QFDA).

Actual oil filters from CF88 Challenger ALF 502L‐2C and Hornet F404 engines were obtained in sequence, when possible, prepared by the developed procedure, and analysed with AOA instrumentation. With sufficient results, both normal and abnormal levels of wear rates emerged, as has been recorded and used for AOA. Moreover, trending of the data for sequential samples has demonstrated the capability of GFDA for condition monitoring.
Estimation of lubricant interlayer shear strength under conditions of imperfect boundary lubrication
Authors: Konchits V. V. , Markova L. V.
Published: July 2006

This paper considers the use of contact electrical conductivity for investigations into molecular tribology. The shear strength of thin lubricant films has been studied at nominal point contact between two crossed cylindrical steel probes. The interface was simultaneously monitored using electrical contact resistance. It is shown that the binomial law of friction holds for the sliding path portions where electrical measurements point to a continuous lubricant film. The experimental data can be used to evaluate the molecular friction parameters. An algorithm and software with which to evaluate shear strength and its components under conditions of imperfect boundary lubrication have been formulated.
A new tribometer for measuring friction data at high temperature in a continuous operation
Authors: Dalverny Olivier , Denape Jean
Published: July 2006

This paper describes a rotary tribometer that can function at high temperature in a pin‐on‐disc or ring‐on‐disc configuration. With this tribometer the tribological properties of ceramics (structural ceramics or coatings) and metallic alloys can be studied from room temperature to 900 °C. The sliding velocity can be varied from 0.1 to 1.5 m/s, and the normal load from 10 to 2000 N. The test apparatus is unique in terms of the wide range of loads which can be tested, and in its sensor and computer data acquisition system, which allows different test parameters, such as friction coefficient, vertical displacement of samples, and temperature near the interface, to be measured in one continuous operation.
Modelling lubricated friction for dynamic contact systems
Authors: Hess Daniel P.
Published: July 2006

Multi‐valued friction is often observed in lubricated contact systems operating under unsteady sliding conditions. In the past, this behaviour has been modelled using a measured time delay between changes in sliding velocity and resulting changes in friction. More recent work has revealed that fluctuations in normal separation are the principal cause of this deviation from steady friction behaviour. This paper demonstrates that tangential contact dynamics can result in apparent deviations from steady friction that can resemble true deviations found from fluctuations in normal separation. Two different dynamic models are considered. One model accommodates the tangential rider dynamics of a friction test apparatus. The other model considers the possibility of tangential dynamics associated with asperity contacts.
Performance of a microgrooved journal bearing under steady and dynamic loading
Authors: Hargreaves D. J. , Armatys D.
Published: July 2006

This paper looks at the performance of plain, longitudinally and transversely grooved journal bearings. An experimental apparatus was created to test the performance, in terms of frictional torque under static and dynamic loading, of each of the three bearing types, to try and understand whether grooving created a different film thickness. The tests were carried out for various combinations of load and speed. The results showed an agreement between theoretical and experimental values that gave some confidence in the experimental methods, and showed the frictional torques between the plain and longitudinally grooved bearings to be similar at all loads, and at lower rather than higher speeds, while those of the transversely grooved bearing differed from the others.
Comparison of oil analysis and filter content analysis: A case study
Authors: Toersen H. , Slob P. A. A.
Published: July 2006

Oil filters contain useful information on wear that has occurred in the oil‐wetted mechanical system. However, filter analysis for wear detection is seldom performed, because the method is fairly cumbersome. On the other hand spectral oil‐analysis can be economically done in highly automated laboratories and is therefore widely accepted.

This paper describes the case involving a small passenger car diesel engine, where the results of the filter analysis were compared with the results of simultaneously performed oil analysis using X‐ray fluorescence. Oil and filter samples were analysed after each 10,000 km, when oil and filter changes took place, over the life of the engine to 165,000 km.

The results, as derived from the filter samples, showed a roughly shaped bath‐tub curve development of the wear rate before the final stage of serious deterioration. However, the oil analysis did not confirm this trend. It is believed that the different in characteristics between a filter sample and an oil sample, and the effects of particle size and of oil filtration on the oil sample, may cause this discrepancy. If the latter is the case, care has to be taken in oil sampling for wear analysis, particularly in systems with fine full‐flow filtration.

Suggestions are made at the end of the paper for the design of dedicated diagnostic filters for wear debris detection.
A laboratory study of friction in hip implants
Authors: Levitin Michael , Shamshidov Boris
Published: July 2006

One of the most promising methods of reducing wear and extending the useful life of artificial joints is by regular microrelief treatment, a novel finishing technology based on the formation of a system of fine grooves by means of plastic deformation of surfaces with a ball‐tipped diamond. Laboratory friction testing of treated joint prostheses is an essential component in the developmental process of this application. In order to evaluate the friction characteristics of hip prostheses made up of metal ball heads treated with regular microrelief, a computer‐monitored friction tester was developed. The ball head was pressed against the cup by a load. The friction torque was measured by means of a load cell. Distilled water was used as the lubricant. Before the friction test, all balls were tested in a specially developed wetting ability tester, to evaluate the effect of regular microrelief treatment on the wetting behaviour of the head surface in water. The results obtained showed that the wetting ability of balls treated with regular microrelief was higher by 30% as compared with non‐treated hip heads. The articulating pairs with heads treated with regular microrelief showed a 25–35% reduction in the friction torque, when compared with conventional, non‐treated joints.
Experimental evaluation of the influence of macro circumferential residual stress on the wear resistance of some metals
Authors: Özmen Yilmaz
Published: July 2006

To investigate the effect of residual stress on the wear resistance of metals, macro circumferential residual stresses σI were modelled as externally applied stress, below the yield stress of the material because residual stress cannot exceed yield stress, with a special apparatus. In order to compare the effect of residual stress on wear resistance, three different stress levels were applied to each specimen, 0 Re, 0.5 Re, and 0.8 Re. A full programme of testing under all combinations of factors would be very expensive and time consuming, so, in the present case, all the other factors were fixed at constant values, while the chosen factor was varied in a controlled way in a series of tests. There has been no universally accepted theory or law on the effect of residual stress on wear resistance. In this study, the wear results for dry wear tests in terms of residual stress applied mechanically to specimens were very difficult to interpret.
A test method to investigate the tribological behaviour of friction materials under ultrasonic fretting conditions
Authors: Rehbein Peter , Wallaschek Jörg , Löhe Detlef
Published: July 2006

To investigate and understand the tribological behaviour of high‐frequency tribosystems such as ultrasonic motors, a specific test method is necessary. This work reports on the construction of a test machine to evaluate the friction and wear behaviour of friction materials under ultrasonic fretting conditions, as well as giving some representative experimental results. Hard/soft (steel/polymer) and hard/hard (steel/alumina, alumina/alumina) couples were studied with respect to their application as contact materials in ultrasonic motors. Investigation of friction behaviour at high frequencies showed that friction‐induced vibrations lead to friction forces of much lower magnitude than predicted by quasistationary friction coefficients obtained for sliding friction. The wear behaviour is characterised by abrasive, adhesive, fatigue and oxidative mechanisms, depending on the mating materials. For polymeric friction materials, the influence of fibre reinforcement and the incorporation of PTFE as a solid lubricant were evaluated. The presence of PTFE resulted in a strong improvement of both friction and wear behaviour.
Evaluation of the low‐temperature performance of engine lubricants using the scanning brookfield viscometer
Authors: Kinker B. G. , Souchik J. M. , Neveu C. D.
Published: July 2006

When subject to low‐temperature conditions, the paraffins in a lubricant come out of solution to form structures that can impair oil flow. The size of the paraffinic crystals, and the strength of the three‐dimensional network they form, depend on physical parameters, such as temperature, cooling rate and soaking time, as well as on the chemical nature of the wax and of other components in the oil.

To evaluate the ability of lubricants to flow under low‐temperature conditions, a number of test methods have been developed, from the simple pour‐point test (ASTM D‐97), to very sophisticated tests such as the MRV TP‐1 (ASTM D‐4864). In the early 1980s, a new technique, using the scanning Brookfield viscometer (ASTM D‐5133), was developed. This method has progressively gained acceptance by industry and is now part of the ILSAC GF‐2 specification. The scanning Brookfield technique provides a new approach to continuous measurement of the viscosity of engine lubricants at very low shear rates, with decreasing temperature. It is said to be unique in its ability to identify oils which develop gel structures at low temperature.

After presenting background information on the scanning Brookfield viscometer, this paper examines its use with modern engine lubricants, and its ability to evaluate the effect of pour‐point depressants on the low‐temperature performance of engine lubricants.
Diffraction methods in tribosystem diagnostics
Authors: Garbar I. I. , Sher E.
Published: July 2006

In this paper, two structural analysis methods, X‐ray diffraction and electron diffraction, are considered for their use in tribosystem diagnosis. It is shown that, for certain applied tribological problems, such as determination of friction conditions and type of wear regime, estimation of running‐in period, selection of optimum wear‐resistant materials, and of suitable conditions of friction and wear, these methods can be used in addition to more conventional tribotesting and tribodiagnostic methods.

A study of the structure of certain friction pair materials and wear particles was conducted. X‐ray investigations of the surface layers of the friction pair materials showed that structural characteristics, such as broadening and intensity of diffraction lines, can be used in the estimation of friction conditions. Examples of the choice of structurally wear‐resistant engineering materials, and of suitable friction conditions, are given. The study of wear particles produced under different friction conditions shows that these particles vary not only in form and dimensions, but also in phase composition. This provides important additional information for friction and wear process diagnostics. The method involves electron diffraction analysis of isolated wear particles, which allows us to characterise the wear processes under friction conditions. It is shown that a definite phase composition, the fineness of wear particles, and the quantitative ratio of each of the wear product phases, can be characterised for different wear types. Some useful applications of these investigative methods for analysis of the wear nature of friction pairs are described.
Development of a high‐vacuum wear test apparatus mounted in a scanning electron microscope
Authors: Lacey P. I. , Naegeli D. W.
Published: July 2006

The lubrication of sliding components in vacuum conditions offers unique challenges. High vacuum precludes the use of many conventional liquid lubricants because of vaporisation, while the lack of a naturally‐occurring oxide film on metal surfaces may cause instant seizure following the failure of a lubricant. Solid lubricants, such as molybdenum disulphide and tungsten disulphide, are also used, but are less effective than more complex liquid lubrication mechanisms. New surface treatment processes, such as diamond‐like carbon (DLC), are becoming available and may further reduce wear. The purpose of the present paper is to describe an apparatus that can evaluate solid lubricants under a wide range of contact conditions at vacua down to 3 × 10−7 Torr. The wear test stage is mounted in the chamber of a Scanning Electron Microscope (SEM), which allows real‐time high magnification photography of the contact area. The complete stage may be moved in three planes to facilitate observation of the complete contact area. Realtime measurement of applied load and friction coefficient is also provided.
Development of dispersivity tests for gasoline and diesel engine lubricants
Authors: Diraison C. , Bourgognon H. , Abellaneda G.
Published: July 2006

One of the aims of the Groupement Français de Coordination (GFC, branch of CEC), and their working group LM2, is to develop laboratory tests to forecast dispersivity problems for new lubricants, both gasoline and diesel. This paper looks at the development of a spot test for forecasting dispersivity, allowing correlations to be made with reference oils used in the M102E test (gasoline), and the XUD 11 ATE test (diesel). Various round robins were undertaken to establish the relative importance in terms of influence of various factors, including spot storage temperature, paper batch, and quantity of deposited oil. The work has resulted in recommendations as to method and materials.
CVT lubrication: The effect of lubricants on the frictional characteristics of the belt‐pulley interface
Authors: Watts Raymond F. , Richard Katherine M.
Published: July 2006

Two tests for evaluating continuously variable transmission (CVT) lubricants have been developed using readily available test equipment and test parts. These tests have been designed to rank lubricants using a number of criteria relevant to the performance of the lubricant in a push‐belt variator. These include overall level of friction, friction stability, temperature dependence of friction, and load dependence of friction. Testing lubricants of different types has shown the effect of lubricant chemistry on the parameters measured and indicates that some existing fluids, a CVT fluid and passenger car motor oil, as well as an experimental fluid, should give good performance in a continuously variable transmission using a push‐belt variator.
Friction and wear behaviour of hard coatings in vibrating contacts
Authors: Skopp A. , Klaffke D.
Published: July 2006

The friction and wear behaviour of thin hard coatings, such as TiN and the promising class of C‐based coatings (a‐C, a‐C:H, and diamond for example), are compared under oscillating and reciprocating sliding conditions. The typical effects of test parameters, such as stroke, frequency, normal force, relative humidity and test duration, are described as a basis for the proper selection of test conditions or, conversely, for the selection of suitable coatings for particular practical applications.

Friction and wear data from over 1000 vibrating tests using thin hard coatings against 100Cr6 and against Al2O3 have been compiled in a database. This allows easy manipulation and comparison of test results. Using selection criteria and filter procedures (e. g., lifetime of coatings, friction limits, and critical wear rate), suitable coating systems for different test conditions can be chosen from the database. The effects of test parameters on friction and wear behaviour and changes have anyway to be known for meaningful tribotesting, as well as for the selection of coatings.
Measurement of the temporary shear stability of lubricants in a gear pump
Authors: Bielmeier E. , Bartholomae I. , Neveu C. D.
Published: July 2006

In specially designed test equipment, consisting of a hydraulic pump loop capable of measuring oil flow rate for given output pressures, the authors have shown that increased output pressure results in an actual decrease in flow rate, this decrease being linear. It is concluded that some ‘leakage’ takes place between the gears and the pump housing, which increases when decreasing the oil velocity, for a given output pressure and temperature. Models are presented which provide a good representation of internal leakage observed in practical tests of various fluids.
DSC as a valuable tool for the grease laboratory
Authors: Josef Pohlen Martin
Published: July 2006

There is a need to reduce both the time and cost involved in research and development for lubricating greases. Most of the normal test methods used to characterise a grease are long‐term tests, but it is important to develop screening tests that also give reliable information. Thermal analysis is one such way to fulfil these requirements. In the present work, a differential scanning calorimeter (DSC) with a normal pressure cell was used in a grease laboratory. By varying the atmosphere and the heating rate, different tests were worked out. The effects of changing physical parameters, such as viscosity and thickener structure, or chemical parameters, such as additives and thickener types, were examined. These methods can be used for controlling raw materials, improvement of grease formulations and production processes, development of new products, as a replacement for the oxidation bomb (ASTM D‐942, DIN 51 808), and as a screening test for the FE9 life (DIN 51 821) test rig.
The influence of contact geometry on friction and wear characteristics
Authors: Michalczewski R. , Piekoszewski W. , Szczerek M. , Wiśniewski M.
Published: July 2006

This paper describes some results of evaluating the influence of contact geometry on tribological characteristics. Friction characteristics obtained for a distributed contact (pin‐on‐disc and block‐on‐ring), a linear concentrated contact (pin and vee‐block and block‐on‐ring) and a point concentrated contact (ball‐on‐disc and three cylinder‐cone) are presented. The wear scars were analysed using scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). The results show different values of friction and wear coefficients for the different types of contact geometry. The paper also assesses the effect of non‐test characteristics, e. g., vibration.
An investigation into the surface fatigue of materials and thin layers using a sliding diamond spherical segment
Authors: Iliuc Ivan , Jumolea Alina
Published: July 2006

Methods for testing the surface fatigue of materials or thin layers normally involve configurations with two or more rolling balls or discs. Such equipment and test specimens are quite complicated, and for a large number of experiments, costly. Testing could be considerably simplified if the stressing of the material surface were performed with a sliding natural diamond spherical segment. A diamond on steel (or any different material) friction pair has the particular attribute that sliding wear is absent. Under these circumstances, after a certain number of strain cycles, fatigue failure of the investigated surface or layers appears. A particularly relevant application is investigation of the adhesion of a DLC layer.
Major pathways for used oil disposal and recycling. Part 2
Authors: Kajdas Czeslaw
Published: July 2006

One of the main concerns with lubricating oil relates to used oil management for both industrial and engine oils, although the environmental impact of gasoline and diesel engine oils is the most critical. Provided that efficient management systems are in place, most used oil should not reach the environment, so, the major question is ‘how should we dispose of collected used oil?’ The first option lies in burning it as a fuel, the second in recycling (re‐claiming, reprocessing, re‐refining). The latter allows recovery of mineral base oils, which are valuable constituents of crude oil.

In the first part of this paper, the author looked at the problems associated with used oil, its use as a fuel, and simple recycling. He went on to look at major re‐refining processes, starting with hydrogenation (KTI, Mohawk, BERC/NIPER, and PROP technologies). In Part 2 he covers other processes, including Safety Kleen, IFP/Snamprogetti, UOP Hylube, and vacuum distillation and clay treatment technologies.
Developments in tribological materials in the next millennium
Authors: Santner E.
Published: July 2006

The materials needed for tribological contact systems in the next millennium will depend on the trend and pace of technological development, and environmental policy. The latter will certainly demand lower pollution and energy consumption, so materials should preferably be light, and work in most friction systems without lubrication, but with low friction, and no wear. The following properties, or requirements, of future tribomaterials can be conceived of in such a scenario: it seems likely that micro‐mechanical systems will achieve great importance, but silicon must be either surface protected or replaced by an optimised material; light metal alloys must be conditioned by surface treatment or coating; coatings must be improved, e.g., by nanomaterials; ceramic materials sintered at low temperatures from nano‐powders will be ductile and machinable, but retain the other beneficial properties of ceramics; and ultra‐precise surface finishing of materials may lead to nearly friction‐free and wearproof tribocontacts.
Macro‐ and microtribology — similar results, different origins?
Authors: Scherge M. , Schaefer J. A.
Published: July 2006

Many friction effects are investigated extensively on both the macro‐ and the nanoscale. However, the range between these limits — the range of micrometres and micronewtons — has scarcely been probed. Using new test equipment, this particular range has been analysed. The example of the stick—slip phenomenon was chosen for discussion of the internal physical properties at different length scales. Results are presented for the entire range, from newtons to nanonewtons. Reality was simulated by friction testers operating at various length and force scales. The data were acquired with the help of a pin‐on‐disc tester for the macroscale, a novel micro‐friction tester for the microscale, and an atomic force microscope for the nanoscale.
The repeatability of friction and wear results obtained from unlubricated reciprocating sliding tests
Authors: Klaffke D. , Hartelt M. , Koesling F.‐P.
Published: July 2006

Laboratory tests can help in the analysis of tribological failures of elements, and improve tribo‐systems by choosing appropriate materials. In order to characterise the friction and wear behaviour of candidate materials, various different test methods have been developed in the past and are still in use. One such method is the reciprocating sliding of a ball against a disc.

In the work reported here, the repeatability of friction and wear results was evaluated with ten tests under identical conditions with a steel (100Cr6) or alumina (Al2O3) ball against a steel (100Cr6) disc under unlubricated conditions at room temperature. The influence of ambient humidity on friction and wear behaviour was determined in three additional tests in dry and in moist air, respectively. The repeatability of friction coefficient in normal air was better than 5% for alumina/100Cr6 and 12% for 100Cr6/100Cr6, while the repeatability of volumetric wear was slightly better than 10% for alumina/steel, and slightly worse than 10% for steel/steel.

For both couples the coefficient of friction is lowest in moist air and about 50% higher in dry air. The coefficient of wear is also least in moist air and higher by a factor of 3(5) in dry air for tests with a 100Cr6 (alumina) ball.
An ESCA study of the effectiveness of antiwear and extreme‐pressure additives based on substituted phosphorodithioate derivatives, and a comparison with ZDDP
Authors: Jain M. C. , Unnikrishnan R. , Martin V. , Mehta A. K. , Bhatnagar A. K.
Published: July 2006

Ashless substituted dithiophosphoric acid derivatives (ADPs) are a new generation of multifunctional additives with promising antiwear (AW) and extreme‐pressure (EP) characteristics. Three such additives synthesised in the authors' laboratory have been evaluated for their AW and EP properties by standard four‐ball friction and wear tests. The friction‐reducing properties of these additives were compared with those of a commercial zinc dialkyldithiophosphate (ZDDP). It was found that the phosphorodithioate compounds studied here possessed excellent AW/EP properties. Their AW characteristics were found to be comparable to those of ZDDP at low loads. However, at higher loads they show inferior AW characteristics in comparison to ZDDP. Nevertheless, ADP derived from cashew nut shell oil had a higher load‐carrying capacity than ZDDP.

The mechanism of the AW and EP behaviour exhibited by the different additives was investigated using X‐ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and scanning electron microscopy (SEM) of the worn surfaces formed during friction. XPS and AES analyses of the worn surfaces reveal that the tribochemical film formed on the ADP‐tested surfaces consisted mainly of metal phosphates and only a small amount of metal sulphides, even though the ADPs contained twice the number of sulphur atoms than phosphorus atoms. The ZDDP‐tested surface showed a mixture of metal sulphides and metal phosphates. Alkylamino substitution appeared to have no significant effect on the AW/EP properties of the additive.

XPS and AES analyses also revealed that the tribochemical film formed on an ADP‐tested surface was thicker than that present on the ZDDP‐tested surface at low loads, whereas at higher loads the reverse was true. The higher weld load obtained for the blend containing cashew nut shell oil‐derived ADP is attributed to the thicker adsorbed reaction film formed on the surface due to the long alkyl groups present in the original additive structure. Short‐chain alkyl groups, however, form only a thin adsorbed layer, which may get rubbed off during the friction at high load. The low sulphide formation on ADP‐tested surfaces was attributed to the absence of any metal atom in the additive, which would help in the formation of metal sulphides during tribofragmentation and further tribochemical reactions.
Comparison of water measurement results in polyol ester‐based lubricating fluids determined by the coulometric karl fischer method and a thin‐film polymer capacitive water sensor
Authors: Farooq Kal , Fowler Rob
Published: July 2006

Field samples of MIL‐PRF‐23699 and DOD‐L‐85734, both polyol ester‐based fluids, were evaluated for water concentration by the coulometric Karl Fischer (KF) method according to ASTM D 6304 and with a prototype thin‐film polymer capacitance‐based sensor at Naval Air Systems Command (NAVAIR). The NAVAIR KF results showed a consistent negative bias, 190 ppm on average, compared to the results obtained with the water sensor. Since the calibration of the water sensor was performed by the sensor manufacturer using a different KF instrument and reagent/co‐solvent system, the ∼190 ppm negative bias probably reflects the difference in KF results between sensor manufacturer and NAVAIR. A limited round robin test, involving several laboratories using different instruments, reagents, solvents, and techniques, showed that water concentrations determined by the KF method can vary significantly from laboratory to laboratory. A larger round robin test was conducted to assess more accurately the variability in water measurement results. The results of the two round robin tests show that the particular KF instrument, reagents/solvents, and procedures being utilised by the various participating laboratories lead to a KF measurement variability of 20–30% for polyol ester‐based lubricating fluids. The results show that it is possible to obtain ∼190 ppm difference, observed between the water sensor and KF measurements at NAVAIR, between two laboratories. The results of the round robin tests showed a maximum repeatability of 9%. The significant difference between the repeatability and reproducibility indicates that there is potential for improved reproducibility of KF measurements through standardisation of, for example, instrument type, reagent/solvent system, test method, and laboratory procedure. Further work is required to determine the optimum KF test parameters for polyol.
Scratch properties of poly(methyl methacrylate) surfaces: The time‐temperature dependence of friction and hardness
Authors: Gauthier C. , Schirrer R.
Published: July 2006

Viscoelastic‐viscoplastic behaviour is usually not taken into account in models describing the scratch properties of polymeric surfaces. In the case of a standard indentation test with stationary tip, the elastic‐plastic boundary and the boundary of the region being subjected to hydrostatic pressure beneath the tip are understood. Such well‐known models have been used in this study to understand the geometry of the groove left on the surface of a viscoelastic‐viscoplastic body by a moving diamond tip. A new apparatus was built that can control the velocity of the tip over the range 1 μm/s to 15 mm/s, at several different temperatures from −10 to +100°C. The material used was a commercial grade of cast poly(methyl methacrylate) (PMMA). The normal and tangential loads and groove size were used to evaluate the dynamic hardness, which behaved like a stress‐ and temperature‐activated process. The values for the activation energy and volumes of the dynamic hardness and of the interfacial shear stress were in good agreement with the mechanical properties usually attributed to PMMA.
Analysis of microstructure and wear of ZnA112Pb alloy used in low‐speed bushing applications
Authors: Jingpei Xie , Wenyan Wang , Yinmin Tu , Aiqin Wang
Published: July 2006

Wear experiments on ZnAl12Pb alloy and Pb‐based Babbitt alloy (Zch PB16‐16‐2) have been carried out under identical conditions. The wear behaviour of the alloys has been investigated using scanning electron microscopy and surface profile analysis. The results show that ZnAl12Pb alloy is a good material for bushing or bearing applications, and the wear resistance of ZnAl12Pb alloy is better than that of Pb‐based Babbitt alloy.
Improving the wear life of a cocoa spray‐drying unit
Authors: Arda T. , Salman S. , Yukler I. , Unal H.
Published: July 2006

In the chocolate production process, the moisture content of ground cocoa is removed in a spray‐drying unit, in which wet cocoa is pumped through a high‐pressure pump. Wear occurs in this high‐pressure pump, which can cause problems in the system. Originally, valves and beds were made of AISI 316 Ti austenitic stainless steel, and their average wear life was less than 280 h, obviously too short for use in industrial production. The aim of the research reported in this paper was to investigate ways to increase the wear life of these parts. In this respect six different materials were tested. Valves and beds were produced from four different steels and two powder metals. The steel parts were hardened by heat treatment. All the parts were electroplated with CrN or TiN. Wear life tests were carried out, and it was shown that AISI M2 high‐speed steel valves and beds gave the longest wear lives.
Comparison of vickers V‐104C and 20VQ5 vane pump wear rates for various water‐glycol hydraulic fluids
Authors: Totten George E. , Webster G. M. , Bishop Roland J.
Published: July 2006

Work is currently under way within the ASTM D.02 N.07 ‘Hydraulic Fluid Testing’ Committee to evaluate the potential of replacing the Vickers V‐104C vane pump with a newer, more current model 20VQ5 vane pump for use in an updated ASTM D 2882 standard and other national standards. All the round robin work conducted within the Committee thus far has involved the use of non‐aqueous hydraulic oils. Although there are some significant inter‐laboratory reproducibility problems, it appears that the overall ranking of these hydraulic oils by most laboratories appears to be consistent. To further evaluate the potential utility of replacing the Vickers V‐104C pump with the 20VQ5 pump, a series of different water‐glycol hydraulic fluid formulations with significantly different wear rates were evaluated using a ‘modified’ ASTM D 2882 testing procedure. The results showed that expected catastrophic pump failures, which occurred with the V‐104C pump, not only did not occur with the 20VQ5 pump, but the relative orders of wear rates for some of the fluids were also different.
Lubrication in helical gears
Authors: Mordukhovich G. , Anderson N.
Published: July 2006

In this paper, a method to determine elastohydrodynamic film thickness in helical gears is developed by combining the Dowson‐Higginson elastohydrodynamic lubrication (EHL) formulation with helical gear geometry and kinematics. Comparisons are made with traditional gear film thickness models. This analysis is then used to characterise the film thickness and lambda ratio in an automotive planetary gearset. Methods to measure surface roughness in fine‐pitch gears are described.