Magnetic fluids are synthetic materials that combine in a single medium the properties of fluids and magnetic materials. The action of a magnetic field on the magnetic fluid allows the design of new types of bearings and also provides conventional ones with new properties. This work presents a contribution to the study of the lubrication of linear isothermal non-conformal contacts with magnetic fluids under the action of a non uniform magnetic field perpendicular to the plane of the contact. The fluid is assumed to present extrinsic superparamagnetism. The regime of lubrication considered is the isoviscous-rigid. The analytical approach adopted considers small perturbations of the classical analytical solution already known for this type of contact. The main objectives of the work are: To establish the equations and assumptions that are necessary to treat the proposed lubrication problem To analyze the impact of the change in the apparent viscosity of the magnetic fluid on the thickness of the lubricating lm due to the presence of the magnetic field ° To develop an experimental technique able to deal with the problems that arise with the use of magnetic fluids in the lubrication of a two-disc machine The mathematical treatment of the proposed problem brings together the analytical methods adopted in fluid lm lubrication to the analysis of long isothermal hydrodynamic bearings and those from the magnetic-liquid fluid dynamics (ferrohydrodynamics) usually adopted to study the flow of magnetic fluids that present extrinsic superparamagnetism. The result is a coherent system of equations supported by a well defined set of assumptions. The solution obtained allows the study of the eventual change of the lm thickness that can be achieved by the application of a magnetic field across the contact. The work also discusses the experimental technique necessary to study the problem in a two-disc machine that runs with minute amounts of lubricant, applies a magnetic field across the contact and measures the lm thickness by a capacitance method. The work concludes by showing theoretically that the lm thickness can be either increased or reduced depending on the magnetic and viscous properties of the fluid and the intensity of the magnetic field. These conclusions are supported by experiments with a magnetic oil in a two-disc machine.

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This thesis describes the development of pre column derivatisation reactions for the selective determination of organic functional groups in oxidised oils by liquid chromatography (LC) with luminescence detection. The testing of oils for oxidative stability and the current methods of oil analysis are reviewed in chapter one. An overview of LC and luminescence spectrometry, with particular regard to chemiluminescence (CL) is also presented. Chapter two is a flow injection investigation of the experimental variables of the peroxyoxalate CL reaction. Two aryl oxalates; bis(2,4-dinitrophenyl)oxalate and bis(2,4,6-tricblorophenyl)oxalate were compared for their suitability to LC detection. A charge coupled device (CCD) was used to obtain the CL spectra of fluorophores and to investigate the CL emission background. Chapter three and four describes procedures for the determination of carboxylic acids in oils by pre column esterification with 9-anthracenemethanol, reversed phase LC and either peroxyoxalate CL or fluorescence detection. The oils were dialysed prior to derivatisation to remove high molecular weight species which were found to interfere with the reaction. Carboxylic acids were present in the oxidised oils and their concentrations reflected the degree of degradation of the oils. The determination of aldehydes in oxidised oils is described in chapter five. The aldehydes in oil dialysates are labelled by reductive amination with 3- aminofluoranthene and the derivatives separated by isocratic reversed-phase LC with peroxyoxalate CL detection using TCPO-hydrogen peroxide. Aldehydes were also found to be produced by the oxidation of oils in car engines.

This research continues the earlier researches on wear friction and lubrication and its application to the powder metallurgy industries. A detailed study of the parameters involved in wear and friction has been made by using the "Pin and Disc" machine with cross cylinders technique. One iron powder was chosen and compacted over a range of densities with a series of metallic stearates as admixed lubricants for the purpose of examinations. These compacts were used as the "pins" for the wear and friction apparatus, the "disc" was made from high carbon high chromium steel which is one of the steels normally used in punches and dies in the powder metallurgy industries. The wear behaviour of these compacts was studied in relation to the following parameters: applied load between compact (or pin) and disc, sliding speed, travelled distance, density and hardness of compact. These were examined for a range of stearate lubricants and the wear rates determined, these data were then related to the possible industrial life for punches and dies in powder metallurgy presses. Besides wear rate, friction forces between the compact (or pin) and disc were measured and these forces of friction were translated into coefficients of friction for each type of lubricant. The thesis presents the results of these investigations with a survey of current theories on wear and friction of metallic systems relevant to powder metallurgy. Conclusions have been drawn and suggestions made on the most useful solid lubricant necessary in the pressing of metallic powders to reduce wear and friction in production presses. Calculations have been carried out using the data collected to estimate the possible press tool wear and accordingly a possible tool life was determined for pressing with each type of ~tearate lubricant. The overall conclusion was that zinc stearate is the best solid lubricant in the five metallic stearates (Al, Na, Mg, Ca and Zn) for use in iron powder compaction.

To modify the rheological behaviour of rubber compounds, in order to improve their processing behaviour, lubricants based on fatty acid derivatives are added at the mixing stage. This research has been directed towards identifying the modes of action of commercially available lubricants in a number of elastomers and elastomer compounds, with the objective of providing a rational basis for the further development of lubricants. The primary tool for rheological measurement was an advanced biconical rotor rheometer (Negretti TMS Rheometer); and a capillary rheometer was used to provide an independent verification of results. Conceptual and mathematical models have been proposed which provide a rational explanation and simulation of lubricant action. The conceptual model takes account of elastomer morphology, relative solubility parameters of elastomer and lubricant and chemical reactions between the lubricant and elastomer in order to explain internal lubrication, chain extension/crosslinking, solvation and external lubrication. The mathematical model simulates the primary lubricant actions of internal lubrication and chain extension/cross-linking.

Blends of lubricant base stocks are commonly employed to produce lubricants with optimised performance. However, the influence of blending on lubricant behaviour within high pressure, mechanical contacts, particularly the film forming capacity and friction, have largely gone unstudied. This thesis examines both of these aspects for a range of base fluids and their blends. Film thickness generation and fluid friction are reviewed in the context of elastohydrodynamic (EHD) lubrication. Various models addressing the origin and mechanism of liquid viscosity are reviewed. The derivation of viscosity as a thermodynamic property is also reviewed and its relevance to the current study is discussed. Consideration is also given to two commonly accepted yet contrasting models of EHD traction, resulting in one being adopted for this research. The relationship of molecular structure to film generation is examined experimentally by studying a number of single component fluids with widely varying chemical structures. It is shown that pressure-viscosity coefficients derived from film thickness are strongly related to the respective chemical “family” of the lubricant. EHD friction (traction) measurements are also made and analysed in order to establish a reliable method for comparing the influence of fluid composition on traction. The method, based on a well regarded fluid model, allows accurate description of full fluid traction by means of the Eyring stress and pressure-viscosity coefficient in the central EHD contact. Binary blends of well-defined base fluids are studied. It is found that the pressure- viscosity coefficient, as derived by the aforementioned methods, varies nonlinearly with the composition and tends toward the lower value of the individual components, at times attaining values lower than either of the individual components.

A high-traction fluid is one of the vital components of a traction drive; a mechanism where input power is transformed into an output force when pressure and shear force are applied to the fluid. In this environment they need to withstand high pressures, temperatures and shear forces, and must be able to lubricate at the same time. So far there has been very little research relating engineering performance to molecular structure. Previous work with model hydrocarbon traction fluids has shown that molecular rigidity about the centre of the molecule appears to be important. This work has now been extended to cyclohexyl esters. A series of cyclohexyl esters was synthesised, and where possible, x-ray structures were obtained. Extensive 13C T1 and NOE relaxation data over a range of radiofrequencies and temperatures were obtained and used to calculate correlation times, for both overall and internal motion, using both the "model-free" and reduced Lorentzian models. This provided information on the rigidity of the molecules studied, In addition molecules have been modelled using molecular dynamics techniques to calculate order parameters and torsion angle distributions. ESR studies have been conducted to measure the viscosity of each fluid. A spin probe, with a similar structure to one of the molecules studied, was synthesised. This allowed complimentary correlation time measurement, and showed that the molecule rotated isotropically. Difficulties were encountered in fitting the NMR data to the motional models and the need for higher radiofrequency data is indicated, to check the validity of the models used. The NMR, ESR and molecular dynamics results did, however, provide a consistent indication of the differing rigidities and motions of these molecules.

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No description available.

The development of more fundamental knowledge of the tribology of the cam and follower mechanism calls for a more comprehensive theoretical analysis and experimental investigation than has been previously reported. A mixed lubrication analysis has been applied to the problem to give an estimation of the nominal minimum film thickness and friction force associated with the contact in such mechanisms. The analysis showed that the roughness height and the distribution of the roughness between the two contacting surfaces had important effects on the lubrication performance of the contact. A full numerical transient EHL analysis was carried out allowing the normal velocity to vary along the conjunction. This revealed that local squeeze film velocity provided an increased damping effect which contributed to the persistence of the minimum film thicknesses in the two zero entraining velocity regions. An approximate technique for determining the minimum film thickness of a transient EHD line contact associated with rough surfaces was developed and applied to the mixed lubrication analysis of a four-power polynomial cam and non-rotating flat faced follower arrangement. The results demonstrated that under certain circumstances mixed lubrication predominated in the conjunction of the cam and follower with the surfaces being separated by an EHL film on the cam flanks. Existing experimental apparatus was improved to test the effects of altering the bulk temperature and camshaft rotational speed by measuring the friction torque and electrical resistivity across the contact. By adopting advanced techniques for data sampling and processing the instantaneous friction torque was successfully obtained with the camshaft rotational speed exceeding (2000 rpm). The wear characteristics were also examined. The bulk temperature showed a mild effect on the wear characteristics of the cam and follower as it was increased from (75° C) to (105° C), whilst, a substantial influence was found as the temperature was further increased to (120°C). Increasing the bulk temperature caused an increase in both the friction torque and power loss o f the valve train, but this increase was not considerable. Based upon the theoretical analyses and experimental observations, a theoretical model for evaluating the tribological performance of the valve train was developed. A multi-aspect comparison between theoretical and experimental results was made. The excellent agreement between theoretical and experimental results showed that the model provided a reliable prediction o f the tribological characteristics of the cam/flat faced follower. Three critical portions of the cycle could be identified — one over the cam nose and two in the vicinity of the zero entraining velocity regions. The minimum separation between the cam and follower occurred near the falling flank of the cam.