Showing papers in "Tribotest in 2000"

A review of condition monitoring and fault diagnosis for diesel engines

Abstract: Technical advances and environmental legislation in recent years have stimulated the development of a number of techniques for condition monitoring and fault diagnosis (CMFD) in diesel engines. This paper firstly summarises common faults, fault mechanisms and their effect on diesel engine performance. Corresponding measurands are presented. Standard CMFD methods for parameters and CMFD systems for diesel engines are reviewed. Finally, some advanced CMFD techniques, including neural networks and fuzzy logic, which may be more powerful, are discussed.

Major pathways for used oil disposal and recycling. Part 1

Abstract: 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 to dispose of collected used oil. The first option lies in burning it as a fuel, the second in recycling (reclaiming, reprocessing, re-refining). The latter allows recovery of mineral base oils, which are valuable constituents of crude oil. Mobile (on site) and fixed plants for industrial oil recycling will first be discussed, and the paper will look at the most modern re-refining processes that produce base oils of as high quality as virgin base oils. Based on current re-refining experience, the quality of finished lubricants blended from re-refined base stocks is also noted. Re-refining today may be of significant benefit to the economy and can, of course, protect the environment. All modern re-refining technologies produce small amounts of by-products in which toxic materials may have been concentrated. A final aspect of reprocessing used oil is to integrate it, after hydrogen treatment, into existing refineries. This valuable raw material can then be directly routed to a lube oil unit or even to a cracking unit for conversion to gasoline. The integration of used oil treatment processes into selected refineries may be the most effective pathway to used oil disposal. In this first part, the author looks at the nature of the problems associated with used oil, its use as a fuel, and simple recycling. He then goes on to look at major re-refining processes, starting with hydrogenation (KTI, Mohawk, BERC/NIPER, and PROP technologies). Part 2 will describe other processes, including a range of vacuum distillation/clay treatment technologies.

Wear investigation of spur gear teeth

Abstract: An FZG back-to-back gear test machine has been used to investigate the initial wear of spur gears. By making plastic replicas of the tooth surfaces, and measurements of the same using a 3D stylus instrument, the wear pattern has been analysed. The wear tests were run on the machine according to a predefined schedule. During planned stops, negative surface replicas were made. The replicas were measured, and the amount and distribution of wear analysed. SEM pictures were also taken of the tooth surfaces, and several different types of damage were identified. The results were compared with simulated results using identical loading and geometry. It was found that the wear was quite severe at the root of the wheels and also significant at the tip. The wear was also found to form an overloaded wave pattern on the original involute form of the tooth.

Engine friction lubricant sensitivities: A comparison of modern diesel and gasoline engines

Abstract: Engine friction models have been developed that take account of the variations in lubricants with temperature, shear rate, and pressure. These models have been used to study the lubricant sensitivities of modern diesel and gasoline engines. Total engine friction losses for a Perkins Phaser four-cylinder, 4.0 l, turbocharged, inter-cooled diesel engine, operating at 1300 rpm, with an SAE 15W-40 lubricant, were estimated at approximately 2 kW, with the piston assembly contributing 46%, the bearings 49%, and the valve train 5%. Total engine friction losses for a Mercedes Benz M111 2.0 l gasoline engine (used in CEC sludge and fuel economy engine tests) operating at 2500 rpm, and medium load, for an SAE 15W-40 lubricant, were estimated at 1.5 kW, with the piston assembly contributing 42%, the bearings 39%, and the valve train 19%.

Influence of operating conditions on friction and temperature characteristics of a wet clutch engagement

Abstract: To optimise the gear change in automatic transmissions, more knowledge is needed of the engagement behaviour of wet clutches. A factorial design investigation of the engagement of a wet clutch has been carried out. The friction and temperature characteristics have been studied. The experiments were carried out in an apparatus that can vary sliding velocity, drive torque, inertia, force rate, and lubricant flow. The results show how these parameters affect the response data: engagement time, developed energy, temperature rise, maximum torque, maximum power, static friction, dynamic friction, and initial friction. There are interaction effects between some of the input parameters, but they are relatively small. The friction coefficient varies over time but is independent of the input parameters, except for dynamic friction, which decreases with increasing sliding velocity, drive torque, and inertia. The temperature rise was found to be proportional to developed energy and both these were most affected by sliding velocity. The drive torque and force rate have the greatest effect on the engagement time.

The impact of detergent chemistry on TBN retention

Abstract: Historically, the characterisation of fresh and used diesel engine lubricants has been based on a limited number of analytical techniques. One of the most important methods of analysis has been total base number (TBN) measurement. Although TBN measurements are informative, easy, and quick, it can be misleading to base the judgement of an oil's performance solely on one criterion. This paper offers some observations from a field test, showing that some detergent types gave unacceptable performance even though the TBNs were at an acceptable level. It is hypothesised that some detergents do not effectively neutralise all acidic species present in the lubricant, thereby reserving their own base, while in fact the oil may no longer provide sufficient protection against bearing corrosion. This hypothesis is supported by bench and engine test data. It is recommended that, at a minimum, total acid number (TAN) measurements be included in any analysis, and where time and cost permit, wear metals content, oxidation, soot content, and viscosity should also be evaluated.

Fundamentals of tribotesting

Abstract: Tribology is an experiment-oriented branch of a complex, interdisciplinary science, in which testing plays a major role in the solution of technical problems, in the field as well as in the development of tribomaterials. Various test methods are used for this purpose, and the results are sensitive to the choice of test method and test conditions. In this paper, the effects of test parameters on friction and wear results are considered, some selected results of model tests with different types of materials are presented, and guidelines are derived, that help improve the reliability and level of confidence of tribological tests performed in laboratories.

Major pathways for used oil disposal and recycling. Part 2

Abstract: 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.

Pulsed field gradient (PFG) NMR spectroscopy: An effective tool for the analysis of mixtures of lubricating oil components

Abstract: In the presently reported work, the multinuclear two-dimensional (2D) diffusionordered nuclear magnetic resonance (NMR) spectroscopy (DOSY) technique based on the pulsed field gradient (PFG) has been used in experiments to analyse mixtures of lubricating oil components. One-dimensional (1D) PFG experiments have also been used to simplify and edit the NMR spectra of the mixtures. Such experiments provide a clean spectrum of the highest molecular weight (slower diffusing) component by eliminating the signals of lower molecular weight (faster diffusing) components, without any prior physical separation. These pulsed field gradient experiments not only facilitate the separation of resonance signals of different components, but also lead to their subsequent identification, and provide information about the number and structure of components in a mixture. Some examples of our initial efforts to establish 1D and 2D PFG-based NMR experiments for the analysis of mixtures of lubricating oil components are given and assessed to illustrate the potential applications of such techniques in the field of lubricating oils.

A method of measuring oil consumption by labelling with radioactive bromine

Abstract: A method of determining the oil consumption rate of combustion engines is presented. It is based on labelling the individual oil fractions of engine oil with radioactive bromine isotope82 Br and on the quantitative absorption of radioactive bromine compounds in the exhaust gas in an aqueous solution of nitric acid and silver nitrate. The advantages of this method are that the oil that is consumed in the exhaust gas can be directly measured, without the fluctuating amounts of oil in the sump influencing the result, and the behaviour of the individual components of the oil in the consumption process can be determined. The test is quick, only twenty minutes being required to detect oil consumption at one operating point; and with a single labelling, the oil consumption at a great number of working engine points can be measured 82 Br has a short half-life of only 36 h, so that compliance with radiation protection measures is inexpensive and investigations can be carried out using a conventional testing device. As part of the research project, a study was made of the influence of different base oil types, with and without polymer additives, on consumption. Results showed that Noack evaporation loss correlated with oil consumption only with boiling fractions of exactly the same base oil, and not with different, in particular synthetic, base oils; that polymer additives (VI improvers) significantly reduced the rate of oil consumption; and that the polymer additive and the type of base oil both had more influence on oil consumption than viscosity.

A study of electrical pitting of journal bearings with water‐contaminated lubricant

Abstract: The investigations reported in this paper concern the effect of the use of a degraded lubricant on bearing life. A diagnosis of the premature failure of the hydrodynamic journal bearings of a synchronous condenser has been carried out. The surface of the failed bearings has been examined and the cause of the failure investigated. A theoretical analysis has also been undertaken to calculate the number of cycles that take place before failure occurs. The number of cycles thus established matched that of the cycles/duration of operation before the premature failure of the bearings. The process leading to the premature failure and the role of the degraded lubricant have been identified. Remedial measures have been successfully implemented to reuse the existing bearings. Measures have been suggested to avoid repeated failures. The theoretical analysis has the potential to ascertain the shaft voltage once the severity of the physical damage on the liner surface of the bearing and the duration of its operation have been established.

An investigation into the surface fatigue of materials and thin layers using a sliding diamond spherical segment

Abstract: 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.

The use of topography‐based parameters for the assessment and prediction of surface wear

Abstract: This paper examines the use of surface parameters as ‘tools’ for assessing and predicting surface wear. It begins by briefly reviewing other work published on wear assessment based on entirely topography-based parameters, and concludes that other elements of surface condition are needed, in addition to topography, to assess and characterise the contact if topography-based parameters are to be employed to predict wear. This paper discusses why areal measurements of bearing area and plasticity index are suitable candidates as a basis for assessing and predicting surface wear, and outlines the potential value of using these parameters in conjunction with a wear equation. The validity of this suggestion is illustrated by some preliminary data from a series of pin-on-disc wear experiments involving areal assessments of the bearing area and plasticity index of the rough tip of a brass pin. Predictions of the first stage of a wear simulation are compared to experimental data, and the paper concludes by presenting some general conclusions and suggestions about how the work could be developed.

The influence of contact geometry on friction and wear characteristics

Abstract: 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.

Tribological properties of plasma nitrided AISI 4140 steel under dry and lubricated sliding conditions

Abstract: In this investigation, the microstructural, mechanical and tribological properties of plasma and pulse plasma nitrided AISI 4140 steel have been investigated in comparison to hardened steel. The influence of nitriding case depth, as well as the presence of a compound layer, have been tribologically examined for both dry and lubricated sliding. Testing was carried out on a pin-on-disc machine in which surface-treated pins were mated to hardened ball bearing steel discs. The surface treated samples were characterised using metallographic, SEM, microhardness and profilometric techniques, before and after wear testing. The resulting wear loss and coefficient of friction were monitored as a function of load and of test time. The results showed improved tribological properties of the AISI 4140 steel after plasma and pulse plasma nitriding as compared to the hardened steel, in both dry and lubricated sliding. However, the compound layer should be removed from the surface, either by mechanical means or by decreasing the amount of nitrogen in the nitriding atmosphere, in order to avoid impairment of the tribological properties by fracture of the hard and brittle compound layer, followed by formation of hard abrasive particles.

Analysis of engine oil and phosphorus volatility

Abstract: An apparatus has been designed that allows the measurement of phosphorus volatility, which is important in, among other things, controlling the degradation of exhaust catalysers in automobiles. Following on from the original Noack volatility test, the Selby—Noack apparatus can measure up to 99.9% of volatiles. The apparatus has been used in the present work to assess the relationship between engine oil volatility and engine oil phosphorus volatility (from additives), some reflections on which are presented.

Mechanical testing of hydraulic fluids

Abstract: The antiwear properties of hydraulic fluids are important because hydraulic pump and motor wear is costly. While international hydraulic fluid performance standards continue to be developed, e. g., the ISO/TC28/SC4 committee's draft ISO DIS 11158 ‘Specifications for mineral oil hydraulic fluids’, the normal hydraulic fluid performance specifications represent minimum requirements. Performance specifications for nonmineral oil hydraulic fluids are also being developed. Typically, both the user and the fluid manufacturer possess insufficient objective information about the antiwear properties of special fluids, e. g., environmentally acceptable hydraulic fluids (EAHF) or fire-resistant hydraulic fluids (FRHF) for use in hydraulic equipment such as axial-piston pumps, vane pumps or radial-piston motors. Manufacturer's specifications must therefore be determined. The required lubrication properties can be determined by either laboratory pump tests or a field trial, often at the customer's expense. The lubrication properties of a hydraulic fluid should ideally be determined under conditions that are equivalent to field practice. This paper will discuss the use of the vane pump test and the FZG gear test to gauge ‘recommended’ hydraulic fluid performance; many non-mineral hydraulic fluids, such as environmentally acceptable hydraulic fluids, fire-resistant fluids or synthetic hydraulic fluids, cannot be used in axial-piston systems based only on results obtained with these tests, and additional testing is always required. Proposals are made for testing of such fluids on a variable-load test rig. These tests are done with axial-piston pumps, or other similar displacement systems, and are intended to determine the industrial suitability of non-mineral hydraulic fluids.

Stick‐slip with the slip phase as the starting point

Abstract: In the literature, the stick-slip phenomenon is always explained and modelled as starting from an initial stick phase. However, stick-slip can also occur after a decrease in the imposed velocity, commencing above the critical (stick-slip-free) velocity. In this paper, it will be shown how stick-slip can originate from a situation of pure sliding (without stick phases), if the slope of the friction force-relative sliding velocity relation (F-vrel gradient) is negative. The F-vrel gradient used to study stick-slip must, because of the interaction between the friction force and the dynamic behaviour of the mechanical system, be derived from velocity changes with the same time-constant as the mechanical system of which the friction interface is part. It will also be shown that steady-state friction data, and dynamic (non-stationary) friction results obtained for relatively large (but fast) velocity variations, can lead to completely false conclusions related to stick-slip.

Developments in tribological materials in the next millennium

Abstract: 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.

DSC as a valuable tool for the grease laboratory

Abstract: 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.

Modifications to improve the accuracy of a four-ball test apparatus

Abstract: The four-ball wear test machine is one of the most widely used tribological tools in both research and industry. In general, the test geometry is self-aligning and minimises the opportunity for random variation. Nonetheless, accurate control of the test parameters remains vital to repeatability and reproducibility. The present paper details a number of modifications to a commercially available test apparatus that have been found to improve accuracy. The applied load on some apparatus was found to vary from the correct value, probably due to frictional drag in the loading system. A feedback control loop was designed and fitted to the applied load mechanism, which resulted in significantly improved accuracy. Finally, the apparatus was fully automated, with complete computer control of all test parameters. Under this, following cleaning and assembly of the test specimens, the required test procedure could be selected from a menu of standard methods, and the computer program then adjusted the test parameters according to the method selected, greatly reducing the possibility of operator error.