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Coatings are added to components to provide enhanced protection from the surroundings or to recondition them after the surfaces have been damaged. But the change in conditions at the surface will often lead to a change in the resistance to fatigue loading. This investigation is focused on the behaviour of shouldered shafts electroplated with nickel, chromium and a cobalt/chromium carbide composite. Changes, in fatigue strength are demonstrated. Each of the materials has a unique effect on the behaviour of a shaft, although there is a similarity which can be utilised in design. Each can reduce the fatigue strength by a substantial amount, but it is possible to optimize the design of a new shaft so that its strength is not significantly different to that of an uncoated version. The composite coating has the least effect. Explanations for these effects are given, based on differences in the mechanical properties of the substrate and coating materials, the distribution of residual stresses within the materials, and the interaction of these factors with the applied stress profile. Recommendations and methods of analysis which can be used in the design of coated components are presented. The contribution of the manufacturing processes is discussed, and grinding is highlighted as a dominant factor. Gentle grinding procedures are shown to produce ideal conditions by inducing large compressive residual stresses in the surfaces. Radial plots of the residual stresses have been produced. These were obtained by techniques based on Sachs' method, using electrochemical machining and an extended analysis developed for use with coated parts. The stress distributions were not affected by fatigue limit loading, indicating that stress relief methods using amplitudes of this order are ineffective and unsafe.

Intumescent coatings are used in the field of fire protection to prevent certain construction elements reaching the critical temperatures at which excessive damage would. occur, thus avoiding premature structural collapse. The studies presented in this thesis have been directed towards an understanding of intumeseent coatings and the process of intumescence. The kinetics and mechanism of intumeseence are discussed. The behaviour of the raw materials used in the preparation of intumeseent coatings, was studied at elevated temperatures using thermal analytical techniques, and new formulations were developed. These formulations were examined In the laboratory using various screening tests and were also subjected to a large scale hydrocarbon fire test alongside other commercially-avallable coatings. A simplified coating formulation with the minimum of ingredients required to produce good intumescent properties was developed. This formulation was subjected to various heat-radiation intensities using an ISO ignitablilty apparatus. The behaviour of the intumescence, process observed was explained by a simple theoretical model. The model of Buckmasterv Anderson and Nachman was used and several new results were derived. In particular a relationship was derived giving the time taken for the temperature at the inner surface of the coating to reach a given value. The durability of the newly-developed intumescent coatings, and methods of improving it, were also investigated.

Please read the abstract in the section 00front of this document / Dissertation (M Inst Agrar ( Food Processing))--University of Pretoria, 2006. / Food Science / unrestricted

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Investigation of flame retardant materials (FRM) identified materials as effective substitutes for halogenated FRM. Many promising materials were tested such as hydrotalcite-type Al–Mg–Zr complex hydroxide, huntite, aluminum hydroxide, hydrotalcite, magnesium carbonate hydroxide pentahydrate, magnesium sulfate heptahydrate, magnesium phosphate hydrate, magnesium chloride hexahydrate, sodium metasilicate pentahydrate, XZO 2022 (Mg3Al) and halloysite. Electrophoretic deposition (EPD) manufacturing technique has been developed for the fabrication of coatings containing the most promising FRM candidates. Identifying charging and dispersion agents, such as poly(4-vinylpyridine-co-butyl methacrylate), humic acid, 2,2′- biquinoline-4,4′-dicarboxylic acid, quaternized hydroxyethylcellulose ethoxylate, 3- phosphonopropionic acid, 16-phosphonohexadecanoic acid, octadecylphosphonic acid, celestine blue, chitosan, to facilitate EPD was of great importance for successful deposition of composite FRM films. The films were investigated using scanning electron microscopy, transmission electron microscopy, X-ray diffraction analysis, thermogravimetric and differential thermal analysis, as well as Fourier Transform Infrared and Ultraviolet-Visible spectroscopy. / Thesis / Master of Science (MSc) / Technology is expanding, as is our understanding of the environmental and health impacts of chemicals. New flame retardant materials (FRM) must be developed to help protect against fire hazards in increasingly complex products, but care must be taken to avoid implementing dangerous chemicals. This work identifies new FRM which can be efficient replacements for widely used, but toxic FRM. FRM can be applied as a coating cheaply, quickly, and evenly onto substrates of even a complex shape. Techniques and additive chemicals are suggested to create advanced FRM coatings

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