Low friction lubricant development provides a worthwhile contribution to vehicle CO₂ emission reduction. Conventional low friction lubricant development focuses on empirical processes using out dated engine technology and old test methods. This strategy is inefficient and restricts the lubricant's potential. A new method proposed in the present research combines tribological simulations with rig, engine and vehicle tests. This approach provides insights undocumented until now. The contribution to CO₂ emission reduction from individual engine components on vehicle drive cycles that include warm-up is predicted using lubricants down to the new SAE 8 viscosity grade. A bearing model is used to design the lubricant's non Newtonian characteristics to achieve friction reduction. An isoviscous lubricant with a viscosity of 4.6 cSt is shown to achieve the minimum friction in the bearing. The research shows that by starting with lubricants having kinematic viscosities higher than this value, it is possible to improve lubricant performance by lowering viscosity index (VI), introducing shear thinning, or reducing the density and pressure viscosity coefficient. Conversely, for lubricants with lower starting viscosities it is shown that higher VI values, more shear-stable lubricants and higher densities and pressure viscosity coefficients are required. The model predicts that high oil film pressures occur in the bearing and cause significant local lubricant viscosity increase (300%), indicating that the lubricant's pressure viscosity behaviour is important here, despite the contact being conformal. Simulation and motored engine testing establishes lubricant behaviour in the piston-to-bore conjunction. This analysis identifies a poor correlation between measured and predicted values at low engine speeds. A rig-on-liner tribometer shows that this error is attributable to a deficiency in the simulation's characterisation of boundary regime friction. An oil pump test determines how a modern variable displacement oil pump (and its control system) responds to lowering viscosity. The hypothesis that low viscosity lubricants cause the parasitic load from this component to increase is disproven using this component-level rig test. Chassis dynamometer testing compares the CO₂ reduction performance of lubricant thermal management systems to the values achieved by reducing the viscosity grade. CO₂ reductions of between 0.4% and 1.0% are identified using a cold-start new European drive cycle (NEDC) with a 5W-30 preheated to 60°C and 90°C respectively. Reductions in CO₂ emissions between 0.4% and 1.2% are found on the NEDC by lowering the oil fill volume from 5.1 L to 2.1 L. For the unmodified case, a 3.7% reduction in CO₂ emissions is reported by reducing the viscosity grade from a 5W 30 to an SAE 8 in the NEDC. The performance of a novel external oil reservoir is simulated to understand its ability to retain oil temperature during the vehicle cool-down procedure. An oil temperature of 65°C at the end of the soak period (following a prior test where the oil was assumed to reach 90°C) is predicted by installing insulation to the reservoir and indicates that a viable method to achieve the CO₂ benefits identified through lubricant preheating tests exists. A full vehicle model combines the outputs from each of these sub-models to predict lubricant performance on the NEDC the new World-wide harmonized light duty test cycle (WLTC). This new approach provides a tool that enables next generation low friction lubricants to be developed. The model predicts that an SAE 8 lubricant can reduce CO2 emissions by 2.8% on the NEDC and 1.9% on the WLTC compared to a 5W-30. A theoretical experiment, where all lubricant related friction was deleted from the simulation, predicts that lubricant-related CO₂ emissions are 8.7% on the NEDC and reduce to 6.3% on the WLTC. These results indicate that the planned adoption of the WLTC in September 2017 reduces the potential contribution to CO₂ emission reduction from lubricants by 28%.

O atual cenário competitivo do mercado siderúrgico exige que os custos industriais sejam minimizados ao máximo a fim de garantir o retorno aos acionistas e, em última análise, até mesmo a sobrevivência das companhias em certos mercados. Neste contexto, o homem de manutenção passa a exercer papel fundamental no sentido de trabalhar para evitar perdas, sejam por paradas inesperadas de produção ou por estratégias incorretas de manutenção, buscando conhecer melhor seus equipamentos e introduzir melhorias no projeto de forma a reduzir custos de manutenção e aumentar sua confiabilidade. Este trabalho tem o objetivo de fazer um estudo teórico-prático com a finalidade de conhecer os mecanismos de desgaste envolvidos na interface roda-trilho de pontes rolantes utilizadas em siderurgia a fim de se implementar melhorias no projeto destas rodas e estender a sua vida útil, reduzindo assim custos de manutenção e os prejuízos causado por interrupções não programadas de produção. Inicialmente, é feita uma revisão bibliográfica sobre o tema, sobretudo quanto ao desgaste mecânico e a interface roda-trilho. Como um típico sistema de desgaste mecânico, a abordagem foi feita analisando a influência das condições de superfície, de material e geometria. Com a condição de material fixada (roda e trilho), definiu-se analisar experimentalmente a influência da condição de lubrificação e da geometria das rodas, produzindo ao todo quatro experimentos. As rodas foram dimensionadas e colocadas em operação sob as mesmas condições e o seu desgaste foi monitorado na mesma base de tempo. Os resultados apontaram que a lubrificação exerce influência predominante na vida da roda, estendendo consistentemente sua vida útil, enquanto que a alteração de geometria exerce influência secundária, porém ainda com alguma contribuição. / The current competitive steel market requires that manufacturing costs are minimized to the maximum to ensure the return to shareholders and, ultimately, even the survival of companies in certain markets. In this context, the maintenance man begins to exercise its role in order to work to avoid losses, whether by unexpected production stoppages or incorrect maintenance strategies, seeking to better understand their equipment and make improvements in design to reduce maintenance costs and increase its reliability. This work aims to make a theoretical study and a practical evaluation in order to understand the wear mechanisms involved in the wheel-rail interface of overhead cranes used in the steel making industry in order to implement improvements in the design of these wheels with a view of extending life and reduce maintenance costs as well as losses due to unscheduled production interruptions. We begin with a literature review on the subject, focusing on the mechanical wear and wheel-rail interface. As a typical system of mechanical wear, the approach was made by analyzing the influence of surface conditions, material and geometry. With the condition of fixed material (wheel and rail), it was decided to analyze experimentally the influence of the lubrication condition and geometry of the wheels, producing a total of four experiments. The wheels were measured and made to operate under the same conditions and wear was monitored at the same time base. The results indicated that lubrication has a predominant influence in the life of the wheels, consistently extending its useful life, while the change in geometry influences secondary, but still with some contribution.

Health condition monitoring, commonly referred as Integrated Vehicle Health Management (IVHM) for fleets or vehicles, studies the current and future health state of a system. Health monitoring techniques based on data driven approaches have proven successful in several areas and are easily scalable; however they do not rely on the understating of the physics of failure; whereas Physics-based Model (PbM) approaches require expert knowledge of the failure modes and are based on the understanding of the component behaviour and degradation mechanisms. The development of IVHM is particularly challenging for legacy aircraft due to the restrictive regulations of the aerospace industry. This thesis proposes a novel PbM technique to detect metal-metal contact in hydrodynamic bearings. The planetary transmission of an aircraft’s Integrated Drive Generator (IDG) is used as a case study. Research on the detection of metal-metal contact in hydrodynamic bearings has focused on data driven approaches using vibration or acoustic emissions rather than on PbMs. The proposed technique estimates metal-metal contact by modelling the physical phenomena involved in the failure mechanism and only the speed, load and temperature are required as inputs, all of them available in the IDG and not requiring any additional sensors. The study of metal-metal in hydrodynamic bearings in the field of tribology has focused on mixed lubrication models of the whole bearing, or computational models accounting for local effect under the hydrodynamic lubrication region. In addition to the IVHM technique, this thesis contributes to the field of tribology by proposing a computational mixed lubrication model capable of studying metal-metal contact locally along the lubricated surface of the bearing. Experimental results of a plain journal bearing have been used to validate the PbM and a replica of the transmission of the IDG has been tested to evaluate the effectiveness of the proposed technique at detecting metal-metal contact.

O atual cenário competitivo do mercado siderúrgico exige que os custos industriais sejam minimizados ao máximo a fim de garantir o retorno aos acionistas e, em última análise, até mesmo a sobrevivência das companhias em certos mercados. Neste contexto, o homem de manutenção passa a exercer papel fundamental no sentido de trabalhar para evitar perdas, sejam por paradas inesperadas de produção ou por estratégias incorretas de manutenção, buscando conhecer melhor seus equipamentos e introduzir melhorias no projeto de forma a reduzir custos de manutenção e aumentar sua confiabilidade. Este trabalho tem o objetivo de fazer um estudo teórico-prático com a finalidade de conhecer os mecanismos de desgaste envolvidos na interface roda-trilho de pontes rolantes utilizadas em siderurgia a fim de se implementar melhorias no projeto destas rodas e estender a sua vida útil, reduzindo assim custos de manutenção e os prejuízos causado por interrupções não programadas de produção. Inicialmente, é feita uma revisão bibliográfica sobre o tema, sobretudo quanto ao desgaste mecânico e a interface roda-trilho. Como um típico sistema de desgaste mecânico, a abordagem foi feita analisando a influência das condições de superfície, de material e geometria. Com a condição de material fixada (roda e trilho), definiu-se analisar experimentalmente a influência da condição de lubrificação e da geometria das rodas, produzindo ao todo quatro experimentos. As rodas foram dimensionadas e colocadas em operação sob as mesmas condições e o seu desgaste foi monitorado na mesma base de tempo. Os resultados apontaram que a lubrificação exerce influência predominante na vida da roda, estendendo consistentemente sua vida útil, enquanto que a alteração de geometria exerce influência secundária, porém ainda com alguma contribuição. / The current competitive steel market requires that manufacturing costs are minimized to the maximum to ensure the return to shareholders and, ultimately, even the survival of companies in certain markets. In this context, the maintenance man begins to exercise its role in order to work to avoid losses, whether by unexpected production stoppages or incorrect maintenance strategies, seeking to better understand their equipment and make improvements in design to reduce maintenance costs and increase its reliability. This work aims to make a theoretical study and a practical evaluation in order to understand the wear mechanisms involved in the wheel-rail interface of overhead cranes used in the steel making industry in order to implement improvements in the design of these wheels with a view of extending life and reduce maintenance costs as well as losses due to unscheduled production interruptions. We begin with a literature review on the subject, focusing on the mechanical wear and wheel-rail interface. As a typical system of mechanical wear, the approach was made by analyzing the influence of surface conditions, material and geometry. With the condition of fixed material (wheel and rail), it was decided to analyze experimentally the influence of the lubrication condition and geometry of the wheels, producing a total of four experiments. The wheels were measured and made to operate under the same conditions and wear was monitored at the same time base. The results indicated that lubrication has a predominant influence in the life of the wheels, consistently extending its useful life, while the change in geometry influences secondary, but still with some contribution.

Axial piston machines are operating at high pressure and varying speeds, which requires high reliability of the components. The machine components are separated by a fluid film, but sometimes this film gets penetrated by the surface asperities causing the machine to operate with metal-to-metal contact. In order to improve the design and predict the operating conditions might numerical tools be used. The goal with this thesis was to describe how the tribological contacts in Parkers machines can be modelled, considering oil and surface roughness. The so called Luleå Mixed Lubrication Model have therefore been investigated and it has been described how the model can be used in Parkers machines. The model uses a two-scale method to include the influence of real surface topographies of the components, it gives information about how the surface roughness affect the lubrication conditions. Different options of softwares have been investigated and compared to get an understanding of what possibilities and shortcomings they might have when it comes to this kind of simulations. Results show that all interesting contacts can't be treated the same, therefore must each contact be investigated separetly even though the Luleå Mixed Lubrication Model is used in all cases.

Neste trabalho foram conduzidos experimentos de laboratório no intuito de avaliar o efeito da textura superficial no desempenho de óleos lubrificantes aditivados e não aditivados. Os materiais envolvidos nos ensaios são referentes a materiais de anel e camisa de motores de combustão interna e as condições de superfície envolveram processamentos de lixamento e retífica, bem como texturização de microcavidades a laser. Os ensaios foram do tipo alternado, com regime limítrofe de lubrificação. Inicialmente foram feitas análises sobre a metodologia utilizada para o cálculo do coeficiente de atrito em ensaios alternados, mostrando que os valores fornecidos diretamente pelo equipamento (aqui chamados de coeficiente de atrito pico a pico) não foram efetivos para este estudo, pois apresentam alta dispersão entre as réplicas dos ensaios e não é representativo em termos de eficiência do tribossistema. Foram geradas microcavidades nas superfícies de alguns blocos de ferro-fundido mediante texturização a laser. Esta texturização gerou rebarbas que foram retiradas por um processo de lixamento. Com isso, uma parte dos resultados avaliou o efeito do lixamento nos parâmetros de rugosidade, no entanto que o processo acaba por aumentar os valores de raio de aspereza e reduzir a altura média dos picos. Por fim, ensaios com óleo sem aditivo tiveram formação de óxido em todas as condições de superfície, com pouca variação do coeficiente de atrito. Já nos ensaios com óleo aditivado, os resultados mostraram pouca influência das microcavidades e maior contribuição das características de picos (raio e altura) na formação de tribofilmes redutores de atrito (neste caso MoS2). / This work was conducted by experimental tests in order to evaluate the effect of surface texture on fully formulated oil and base-oil performance. In these tests, the materials were related to the piston ring and cylinder, in which surfaces were sanded, grounded and textured by laser. In addition, the tests were carried out by reciprocating movement and boundary conditions. A coefficient of friction study in reciprocating tests was performed, showing that peak-to-peak methodology does not represent properly the tribosystem efficiency. Burr was generated around the dimples (made by laser surface texturing), in which were removed by sanded process. The results showed that sanded process increased the peak radius and decreased the peak height. The results considering the base oil showed oxide formation on the surface in all the cases, occurring low variation of friction coefficient in the system. On the other hand, in the fully formulated oil results, the dimples had no influence on MoS2 formation; however, it was possible to see a strong relation with the radius and average height of the asperities.

O atual cenário competitivo do mercado siderúrgico exige que os custos industriais sejam minimizados ao máximo a fim de garantir o retorno aos acionistas e, em última análise, até mesmo a sobrevivência das companhias em certos mercados. Neste contexto, o homem de manutenção passa a exercer papel fundamental no sentido de trabalhar para evitar perdas, sejam por paradas inesperadas de produção ou por estratégias incorretas de manutenção, buscando conhecer melhor seus equipamentos e introduzir melhorias no projeto de forma a reduzir custos de manutenção e aumentar sua confiabilidade. Este trabalho tem o objetivo de fazer um estudo teórico-prático com a finalidade de conhecer os mecanismos de desgaste envolvidos na interface roda-trilho de pontes rolantes utilizadas em siderurgia a fim de se implementar melhorias no projeto destas rodas e estender a sua vida útil, reduzindo assim custos de manutenção e os prejuízos causado por interrupções não programadas de produção. Inicialmente, é feita uma revisão bibliográfica sobre o tema, sobretudo quanto ao desgaste mecânico e a interface roda-trilho. Como um típico sistema de desgaste mecânico, a abordagem foi feita analisando a influência das condições de superfície, de material e geometria. Com a condição de material fixada (roda e trilho), definiu-se analisar experimentalmente a influência da condição de lubrificação e da geometria das rodas, produzindo ao todo quatro experimentos. As rodas foram dimensionadas e colocadas em operação sob as mesmas condições e o seu desgaste foi monitorado na mesma base de tempo. Os resultados apontaram que a lubrificação exerce influência predominante na vida da roda, estendendo consistentemente sua vida útil, enquanto que a alteração de geometria exerce influência secundária, porém ainda com alguma contribuição. / The current competitive steel market requires that manufacturing costs are minimized to the maximum to ensure the return to shareholders and, ultimately, even the survival of companies in certain markets. In this context, the maintenance man begins to exercise its role in order to work to avoid losses, whether by unexpected production stoppages or incorrect maintenance strategies, seeking to better understand their equipment and make improvements in design to reduce maintenance costs and increase its reliability. This work aims to make a theoretical study and a practical evaluation in order to understand the wear mechanisms involved in the wheel-rail interface of overhead cranes used in the steel making industry in order to implement improvements in the design of these wheels with a view of extending life and reduce maintenance costs as well as losses due to unscheduled production interruptions. We begin with a literature review on the subject, focusing on the mechanical wear and wheel-rail interface. As a typical system of mechanical wear, the approach was made by analyzing the influence of surface conditions, material and geometry. With the condition of fixed material (wheel and rail), it was decided to analyze experimentally the influence of the lubrication condition and geometry of the wheels, producing a total of four experiments. The wheels were measured and made to operate under the same conditions and wear was monitored at the same time base. The results indicated that lubrication has a predominant influence in the life of the wheels, consistently extending its useful life, while the change in geometry influences secondary, but still with some contribution.

Orientador: Kátia Lucchesi Cavalca Dedini / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-17T14:50:07Z (GMT). No. of bitstreams: 1 Alves_DiogoStuani_M.pdf: 4752857 bytes, checksum: 6027628d11d6b6a8db09521349fd47b8 (MD5) Previous issue date: 2011 / Resumo: Os mancais lubrificados hidrodinamicamente estão presentes em muitas aplicações modernas, especialmente em maquinas rotativas que necessitam de operações mais precisas. Nestes casos, a lubrificação é essencial para a máquina, pois, diminui o atrito entre as peças internas e previne o contato metal-metal, além de agir como elemento de vinculo dinâmico para as pistas do mancal. Devido ao cisalhamento do lubrificante durante a operação, tem-se o aquecimento do fluido e com isso uma modificação nas condições de lubrificação, já que a viscosidade, parâmetro que caracteriza as particularidades do escoamento, diminui com o aumento da temperatura. A diminuição da viscosidade causa diminuição do atrito viscoso, o que acarreta em diminuição da capacidade de carga, gerando efeitos negativos nos coeficientes equivalentes e sendo possível, em alguns casos, a observação de contato direto entre as partes metálicas. Sendo assim, o estudo do atrito e das condições de lubrificação durante a operação de máquinas é de extrema importância em problemas como manutenção, durabilidade e confiabilidade de máquinas. Utilizando o método das diferenças finitas, é possível resolver simultaneamente as equações de Reynolds e da energia, que são responsáveis pelas distribuições de pressão e temperatura, respectivamente. Com isso, é possível analisar as diferenças de pressão, disposição do eixo no interior do mancal e coeficientes equivalentes de rigidez e amortecimento, de um modelo em que se usa viscosidade variante com a temperatura (termohidrodinâmico) e de um modelo que não apresenta esse fenômeno (isotérmico). Finalmente, utilizando um software de dinâmica de rotores, foi obtida a resposta dinâmica de um sistema mancal-rotor para turbocompressores / Abstract: The hydrodynamic lubricated bearings are present in modern applications, especially in rotational machines that need precisely operations. In those cases, the lubrication is essential for the machine, because it reduces the wear between the internal parts and prevents the metallic contact, and also, acts like an element of dynamic link for the bearing. Due to the lubricant shear, the fluid heats up and modifications on the lubrication conditions occurs, since the viscosity, parameter that characterize the flow, decreases with the increase of the temperature. The decrease of visco ity causes a decrease in the viscous friction, which entails in a decrease of the load sustaining capacity, negative effects in the equivalent coefficients and possible observation of metallic contact. So, the study of friction and lubrication conditions during the machine operation is extremely important on maintenance, durability and reliability of machines. Using the finite difference method it is possible to solve, simultaneously, the Reynolds and the energy equations that are responsible for the pressure and temperature distribution, respectively. Therewith, it is possible to analyze the differences in pressure, shaft position in the bearing and equivalent stiffness and damping coefficients, for a model that uses changes in viscosity with the temperature (thermohydrodynamic) and for a model that does not take it in account (isothermal). Finally, using a rotordynamic software (ROTORTEST), the dynamic response of a turbocharger bearing-rotor system was obtained and analyzed / Mestrado / Mecanica dos Sólidos e Projeto Mecanico / Mestre em Engenharia Mecânica

Nous avons étudié la dynamique de particules rigides et sphériques immergées dans un écoulement de cisaillement simple et oscillant à bas nombre de Reynolds. Les particules, au delà d’une déformation critique, se comportent de façon irréversible. La particules suivent alors un processus diffusif appelé: diffusion induite par cisaillement. Dans cette thèse, nous avons montré, par une approche numérique et expérimentale, que les collisions solides entre particules sont à l’origine de ce phénomène. Des simulations numériques ont été effectués afin d’évaluer l’importance relative des forces hydrodynamiques longues portées, des forces de lubrifications et des forces de contact. Deux expériences ont été effectuées afin de mettre en évidence l’influence des contacts solides entre particules. Nous avons étudié la dynamique de 3 particules soumises à un écoulement de cisaillement périodique. Les trajectoires des particules sont irréversibles durant le premier cycle et réversible pour les cycles suivants. En montrant que l’amplitude de l’irréversibilité est corrélée à la rugosité des particules, nous fournissons une preuve évidente que des collisions solides entre particules ont bien lieu et que ces collisions influencent la dynamique des particules. Effectuée dans une suspension homogène, le rôle des contacts a aussi été mis en évidence en montrant que l’amplitude critique de déformation dépend de la rugosité des particules. Un modèle géométrique simple qui considère des `particules effectives’ ayant un volume dépendant de l’amplitude de déformation et de la rugosité des particules, nous a permis de quantitativement reproduire les mesures expérimentales. / Even at low Reynolds number, particles within a shear flow exhibit irreversible dynamics. Many theories have been put forth to explain this phenomenon, the origin of irreversibility remains unclear. An integrated program of experimental and computational studies has been performed to assess the origin of the irreversible behavior of particles. Numerical simulations were used to evaluated the relative importance of long-range hydrodynamic interactions, lubrication, and contact forces. By isolating contribution of these interactions, we have shown that neither the long-range hydrodynamic interactions nor the lubrication are responsible for irreversibility. Solid contacts between particles largely dominate this phenomenon. However, producing realistic results requires both contact interactions and lubrication. Two different experiments were performed to address the role of contacts between particles in sheared suspensions. In the first experiment, the particle trajectories are irreversible during the first cycle but reversible for the next cycles. By showing that the magnitude of irreversibility increases with the particle roughness, we provide direct evidence that contacts occur in viscous flow. Experimental particle trajectories are well captured by the numerical model. In the second experiment, performed in a homogeneous suspension, the role of solid collisions was also revealed by showing that the critical strain amplitude depends on the particle roughness. A geometrical model based on the assumption that colliding particles produce irreversibility was derived. The model successfully reproduces the measured values of the critical strain amplitude.

The aim of this study was to determine the influence of alumina increase on the functioning of casting powder during continuous casting. Two aspects of the powder's performance were experimentally measured, namely the influence of alumina on the viscosity and the crystallisation behaviour. These two aspects were then related to the in-mould functioning of the casting powder with the aid of literature references. Casting slag must provide lubrication between the mould surface and the thin steel shell. Alumina increase will cause viscosity increase in casting slags and will hinder lubrication when the inflow of casting slag into the mould/strand gap deteriorates. Heat transfer across the gap is determined by the amount of solid casting slag and the form (glass or crystalline) thereof. Heat transfer across a crystalline material may be up to seven times lower than that across a glass phase. The increased alumina will serve to increase the ratio of glassy phase to crystalline phase in the gap, so increasing the heat transfer. To determine the true extent of alumina increase with modern clean steel practice, samples were taken from the moulds of both the VI and V2 continuous casters at ISCOR Vanderbijlpark. The influence of this alumina increase on the viscosity and the crystallisation behaviour of the casting slag were experimentally measured. Viscosity measurements were done with a rotating bob viscometer (in a vertical tube furnace) on two commercial casting powders (with increasing AI2O3 content). Viscosity prediction models were evaluated with the data from the measured viscosity values. Crystallisation measurements were done by quench experiments with the aid of the hot thermocouple technique. Crystallisation behaviour after a specified heat cycle was presented as the percentage opaque material (crystalline) to vitreous material (glassy) measured with an optical microscope. For the seven sequence casts during which samples were collected from the mould, it was found that the alumina content of the casting slag reached a steady-state value within the first ladle (first 40 minutes) with an increase of 3 to 4 mass %. The influence of a 4 mass % alumina increase on the measured viscosity is small enough that proper lubrication function of the slag will not be negatively affected. Viscosity prediction models vary in their accuracy and are limited with respect to the composition range of the casting powder and the temperature range for which they are valid. The increased alumina content was found to have a strong influence on the percentage crystalline material present. After the sample was heated to 1300°C, kept there for 10s, and then quenched, the crystalline material will decrease from 60 % to 30 % for 5 mass % alumina added. This decreased crystalline material present may notably increase heat transfer. Full crystallisation does not occur at a single temperature, and crystallisation occurs over a temperature interval (of up to 200°C). This means that crystallisation temperature values quoted by casting powder manufacturers depend on the heat cycle and the technique used during crystallisation measurements. Several crystalline phases are usually present in solidified casting slag and these crystalline phases are strongly influenced by the alumina content: the stable crystalline phases may change as alumina content increases. For the current alumina increase in casting powders the effect on viscosity is small, while crystallisation behaviour may be influenced to a greater extent. / Dissertation (M Eng (Metallurgical Engineering))--University of Pretoria, 2006. / Materials Science and Metallurgical Engineering / unrestricted