Ian Sherrington

Analysis of lubrication and friction for a complete piston-ring pack with an improved oil availability model: Part 1: Circumferentially uniform film

Abstract The study of the tribological performance of piston rings plays an important role in piston assembly design. In this study, a comprehensive analysis of piston-ring pack lubrication has been developed. The model employs a flow-continuity algorithm and considers relative ring locations in the piston-ring pack as well as oil accumulation in front of the ring in determining the oil availability. The computer model is able to predict the effect that bore distortion and ring conformability have on piston-ring performance. (This influence is discussed in Part 2 of the paper). In this part of the paper (Part 1), the theoretical formulation of the model is briefly described. The model is verified through comparison of the calculated ring-liner film thicknesses with those measured experimentally by Hamilton and Moore on a diesel engine. Then some results, obtained under situations where film thicknesses are circumferentially uniform, are presented to simulate a piston-ring pack in a modern petrol engine as an example to demonstrate the capabilities of the model and to show the effects of some important factors on the performance characteristics of the ring pack. The authors have found that the model developed is a robust one which can be used to analyse the tribological performance of ring packs effectively in both circular and distorted cylinder bores of internal combustion (IC) engines.

Experimental methods for measuring the oil-film thickness between the piston-rings and cylinder-wall of internal combustion engines

Abstract Computer models of the lubrication of piston-rings in internal combustion engines normally present an estimate of the minimum oil-film thickness between ring and cylinder wall as a function of crank angle. As a consequence, experimental measurements of film thickness play a critical role in the verification of theoretical models of piston-ring lubrication. A review is presented of the wide range of techniques that have been used to measure this important variable. The strengths and weaknesses of particular techniques are identified and a number of ways in which the techniques could be developed further are proposed

Simultaneous observation of the evolution of debris density and friction coefficient in dry sliding steel contacts

Wear debris can have a significant effect on the coefficient of friction between two components in dry sliding conditions. This paper describes simultaneous measurements of wear particle debris density and friction coefficients made in dry sliding pin-on-disc tests with steel specimens having a range of hardness values. This data is discussed along with a summary of a theoretical analysis conducted by other authors in which friction coefficients were predicted for dry sliding with and without wear debris.

A Three-Dimensional Analysis of Piston Ring Lubrication Part 1: Modelling

The study of piston ring lubrication in internal combustion engines has remained a very active area in tribology. Theoretical analyses have been developed by many researchers to predict the performance characteristics of piston rings, but almost all previous models established were based upon the assumption that ring/cylinder geometry was axisymmetric. This may not be adequate for modern-day engine design since it is well known that cylinder bores are not perfectly circular. They suffer radial distortions which arise for various reasons. In the current work, a three-dimensional model has been developed to account for the effects of bore out-of-roundness. In order to do this, the three-dimensional Reynolds equation was solved cyclically using the finite difference method in fully flooded lubrication conditions. In this part of the paper, the theoretical model is presented and the effect of bore shape on piston ring performance is examined with three proposed types of bore (circular, elliptical and four-lobe). The results have shown that piston ring performance is significantly dependent on the bore shape or bore out-of-roundness.

Towards an understanding of the loosening characteristics of prevailing torque nuts

Abstract Prevailing torque nuts are an extremely popular method of providing resistance to vibration-induced self-loosening of fasteners. Such nuts have a self-contained prevailing torque feature that provides a degree of resistance to rotation. Although such nuts are frequently used, it is not widely realized that they can occasionally come completely detached from bolts. The mechanism by which this can occur has hitherto been unidentified since it has not been possible to replicate detachment under laboratory testing. This article identifies a general condition that can result in the complete loosening and detachment of prevailing torque type nuts. This mechanism involves the application of an axial load when transverse joint slip is occurring. This article describes a modified Junker test machine that allows the application of axial loading to a joint while experiencing transverse displacement. Tests have been completed using an intermittent as well as a constant axial load. Loading in both modes has been demonstrated to result in the complete detachment of this nut type. Based on this investigation, if the magnitude of the axial loading exceeds the residual preload in the bolt retained from sustaining transverse movement alone, the all-metal type of prevailing torque nut can completely detach. Applications that involve shear and axial loading being simultaneously applied to a joint are numerous in engineering.

Mechanical and corrosion resistance properties of TiO2 nanoparticles reinforced Ni coating by electrodeposition

Coatings have been widely used in engineering and decoration to protect components and products and enhance their life span. Nickel (Ni) is one of the most important hard coatings. Improvement in its tribological and mechanical properties would greatly enhance its use in industry. Nanocomposite coatings of metals with various reinforced nanoparticles have been developed in last few decades. Titania (TiO2) exhibit excellent mechanical properties. It is believed that TiO2 incorporation in Ni matrix will improve the properties of Ni coatings significantly. The main purpose of the current work is to investigate the mechanical and anti-corrosion properties of the electroplated nickel nanocomposite with a small percentage of TiO2. The surface morphology of nanocomposite coating was characterized by scanning electron microscopy (SEM). The hardness of the nanocoating was carried out using micromaterials nanoplatform. The sliding wear rate of the coating at room temperature in dry condition was assessed by a reciprocating ball-on-disk computer-controlled oscillating tribotester. The results showed the nanocomposite coatings have a smoother and more compact surface than the pure Ni layer and have higher hardness and lower wear rate than the pure Ni coating. The anti-corrosion property of nanocomposite coating was carried out in 3.5% NaCl and high concentrated 35% NaCl solution, respectively. The results also showed that the nanocomposite coating improves the corrosion resistance significantly. This present work reveals that incorporation of TiO2 in nickel nanocomposite coating can achieve improved corrosion resistance and mechanical properties of both hardness and wear resistance performances, and the improvement becomes stronger as the content of TiO2 is increased.

Laboratory and field studies on thin paint films

An account is presented of some aspects and results of a collaborative project currently being undertaken as part of the European Collaborative Action COST 520 programme in Working Group 3. The project involves the response of biocide- and non-biocide-containing thin paint films to microbial colonisation under laboratory and field conditions. From the results of exposure studies at four sites, two in the UK and two in Norway, it was found that some microorganisms were common to both locations. Matrix-assisted laser desorption ionisation time-of-flight mass spectrometry (MALDI TOF MS) was used in a novel way to establish characteristic mass spectral fingerprints of different fungal genera and different species of the same fungal genus. The results show that databases can be produced which provide convincing evidence for the application of this technique in taxonomy. Scanning electron microscopy was used to visualise Aureobasidium pullulans colonising the paint film. Evidence of hyphal penetration and disruption of the paint binder is suggested. Surface roughness measurement was used to investigate the effect of exposure on the surface topography of the paint. It was found that changes in the surface roughness increased over the duration of the experiment. Fourier transform infrared spectroscopy was used in the reflectance mode to detect chemical changes in the surface of the paint film. It was found that no positional or absorbance changes in the spectrum of the paint film were detected as a result of inoculating the film in a vermiculite bed system. However, some spectra did suggest that surface changes had occurred as a result of a reduction in diffuse scattering from the surface.

Design and performance assessment of a Kelvin clamp for use in relocation analysis of surface topography

Abstract This article describes the design and fabrication of a low-cost relocation device. The device is suitable for relocating small specimens on a stylus roughness measuring instrument to allow observation of the changes in topography of specific surface features arising from processes such as contact, wear, or corrosion. A principal feature of the article is that it describes an indirect method of assessing the accuracy of relocation using positioning tables driven by stepper motors. The method is applied to the authors design.

Application of Taguchi Methods and ANOVA in Optimization of Process Parameters for Surface Roughness of Fused Silica in the Magnetorheological Finishing Processes

Surface roughness plays an important role on optical performances for optics in high-energy laser systems. In this study, optical surface of fused silica were polished by the Magnetorheological Finishing (MRF) processes. The polishing factors in term of Magnetorheological fluid (MR fluid) flow rate, polishing wheel rotational speed, electromagnet current, and polishing ribbon penetration depth, were carried out using an self-developed MRF machine to determine optimum conditions for surface roughness. The settings of the MRF processing parameters were determined by using Taguchi’s experimental design method. Taguchi’s orthogonal array, signal-to-noise (S/N) ratio and analysis of variance (ANOVA) were employed to investigate the optimal processing parameters. The experimental results indicate that surface with smaller roughness could be machined under the conditions with slower rotating speed and higher flow rate and current, and nearly independent of penetration depth.

Preparation of Electrodeposited Ni-CNTs Nanocomposite Coatings with Highly Wear and Corrosion Resistance Properties

Ni-carbon nanotubes nanocomposite coatings were obtained from a Watts bath containing uniformly dispersed carbon nanotubes (CNTs). The surface morphology was investigated by the SEM images of coatings. The mechanical property and corrosion resistance of the nanocomposite coatings were investigated. This study revealed these CNTs reinforced Ni nanocoatings have improved mechanical and corrosion property.