Publication: Diseño y desarrollo de sistemas ligantes ecológicos para moldeo por inyección de polvos como una nueva ruta de procesamiento del circón
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2016-04
Defense date
2016-04-15
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Abstract
El silicato de circonio o circón (ZrSiO₄) es un material cerámico que presenta unas buenas propiedades termo-físicas que permanecen estables en un amplio rango de temperaturas. Sin embargo, a partir de los métodos de procesamiento tradicionales sus aplicaciones están limitadas. Las principales industrias de aplicación de circón son la industria de refractarios, la industria de fundición y la industria cerámica. En esta última, principalmente se emplea como aditivo, uso en el que no se aprovecha el potencial de sus propiedades. Este trabajo de investigación propone el estudio de la viabilidad de una nueva ruta de procesamiento de circón mediante el moldeo por inyección de polvos (PIM powder injection moulding), en el que se mezclan dichos polvos con un sistema ligante polimérico para moldearlos sin limitación de forma. Esta técnica avanzada de procesamiento permite la obtención de piezas pequeñas, con alta precisión geométrica y con forma muy cercana a la deseada. Y todo ello a bajo coste para grandes volúmenes de producción. Con la combinación de las ventajas que ofrece esta tecnología junto con las propiedades que presenta el circón, se puede ampliar el uso de este material en nuevos sectores industriales y otorgarle un alto valor añadido. La amplia disponibilidad y el coste asequible que presenta el circón obtenido de arenas minerales hacen atractivo el empleo de polvos de este material, a pesar de que dichos polvos presentan una morfología irregular, desfavorable para esta tecnología por sus limitaciones de flujo. Salvar esta dificultad constituye el uno de los objetivos del presente trabajo. Para alcanzarlo, se diseña y desarrolla el sistema ligante de una manera exhaustiva y satisfactoria. Actualmente, los sistemas ligantes multicomponentes que se emplean en la industria para ser eliminados en dos etapas se basan, generalmente, en derivados del petróleo, lo que implica el uso de disolventes orgánicos. Estos disolventes son tóxicos, inflamables e incluso cancerígenos. Por ello, se está haciendo un gran esfuerzo en la investigación de sistemas ligantes que tienen una parte soluble en agua. En este trabajo se propone el uso de Polietilenglicol (PEG) soluble en agua y Acetato Butirato de Celulosa (CAB) como componentes principales del sistema ligante en desarrollo. Del mismo modo, proponemos también el uso de antioxidantes. La optimización del proceso PIM se lleva a cabo por etapas. Con el fin de evitar la aparición de defectos en la etapa de eliminación con disolventes, se empieza por el estudio de la influencia de los pesos moleculares de los polímeros en dicha etapa. Se caracterizan los feedstocks (mezcla de polvo y ligante) mediante las técnicas de reología de torque y capilar entre otras. Después se estudia la etapa de eliminación por disolución. Una vez optimizada la composición del ligante se lleva a cabo el ajuste de la carga óptima de polvo. Para determinar el valor de carga óptima se contrastan diferentes métodos. Para completar el estudio del sistema en desarrollo (PEG–CAB-ZrSiO₄), se compara el proceso PIM completo empleando materiales comerciales. Se combina el sistema ligante desarrollado y el polvo de circón con un sistema ligante comercial soluble en agua y polvos de alúmina como se indica a continuación. - PEG-CAB-Nabalox®Al₂O₃ - Licomont®-ZrSiO₄. Por último, optimizando cada etapa del proceso a partir del feedstock desarrollado, se obtienen piezas sinterizadas de circón con un excelente acabado superficial. Tras la caracterización de las piezas sinterizadas, se alcanzan propiedades comparables a las logradas con otras tecnologías avanzadas de procesamiento, con la ventaja que presenta el PIM en cuanto a los costes y la complejidad de formas. Además se ha probado su comportamiento en condiciones industriales y se han obtenido con éxito piezas industriales reales.
Zirconium Silicate, commonly known as zircon is a ceramic material (ZrSiO₄) with excellent and stable thermo-physical properties in a wide range of temperatures. Zircon is generally used in refractory field, although the main application for the raw zircon powder used in this work is as an opacifier in the ceramic industry, without taking advantage of some of its remarkable properties. This material could be considered as a potential structural ceramic material, especially, in those fields where an abrupt change of temperature can happen. The processing of structural ceramic is the main limitation in many applications due to its high cost and the difficulty of the technology. The present research work aims to develop a new processing route for zircon by powder injection moulding (PIM). This technology combines the traditional shape-making capability of the plastic injection moulding and the material flexibility of the powder technology. PIM is a cost effective and competitive manufacturing technology for high volume production of small, complex-shaped and high-performance parts. The combinaison of zircon powder properties with the advantages of PIM processing is an innovative an interesting way to be able to obtain zircon parts to use them in new industries. The wide availability and the moderate cost of raw zircon powders obtained from mineral sands are a great advantage to use these powders despite its irregular morphology. This morphology implies a huge effort in feedstock optimization due to the flow behaviour limitation. Among debinding methods, two-step debinding (solvent followed by termal degradation of polymers) brings about shorter debinding times and defect free parts. However, normally binder system are composed by waxes and polyolefins that implie the use the flammable, toxic and not environmentally acceptable solvents. Development of new binders has always been at the most interest of researchers. The use of new eco-friendly binder system composition mainly based on polyethylene glycol (PEG), as a water soluble polymer, and cellulose acetate butyrate (CAB) is deeply studied. The use of some additives is also considered. The whole PIM process has been optimized for new feedstock compositions. In order to obtain free defects parts after water immersion, the initial study analyses the influence of molecular weights of both polymers during solvent debinding stage. Exhaustive feedstocks characterization has been carried out by torque and capillary rheology among other techniques. After the study of binder system composition, the solid loading is optimized through different methods. In order to compare the behaviour of these feedstocks along the PIM process with the behaviour of the developed feedstock (PEG–CAB-ZrSiO₄), commercial alumina powders and binder system (Nabalox® and Licomont®) have been combined with PEG-CAB binder system composition and ZrSiO₄ respectively. Finally, surface free defects samples have been obtained by powder injection moulding using the eco-friendly developed feedstock composition of PEG–CAB-ZrSiO₄. Achieved properties are in the same range of the obtained ones by others advanced processing routes for zircon. Furthermore, a small and complex real industrial sample has been successfully processed.
Zirconium Silicate, commonly known as zircon is a ceramic material (ZrSiO₄) with excellent and stable thermo-physical properties in a wide range of temperatures. Zircon is generally used in refractory field, although the main application for the raw zircon powder used in this work is as an opacifier in the ceramic industry, without taking advantage of some of its remarkable properties. This material could be considered as a potential structural ceramic material, especially, in those fields where an abrupt change of temperature can happen. The processing of structural ceramic is the main limitation in many applications due to its high cost and the difficulty of the technology. The present research work aims to develop a new processing route for zircon by powder injection moulding (PIM). This technology combines the traditional shape-making capability of the plastic injection moulding and the material flexibility of the powder technology. PIM is a cost effective and competitive manufacturing technology for high volume production of small, complex-shaped and high-performance parts. The combinaison of zircon powder properties with the advantages of PIM processing is an innovative an interesting way to be able to obtain zircon parts to use them in new industries. The wide availability and the moderate cost of raw zircon powders obtained from mineral sands are a great advantage to use these powders despite its irregular morphology. This morphology implies a huge effort in feedstock optimization due to the flow behaviour limitation. Among debinding methods, two-step debinding (solvent followed by termal degradation of polymers) brings about shorter debinding times and defect free parts. However, normally binder system are composed by waxes and polyolefins that implie the use the flammable, toxic and not environmentally acceptable solvents. Development of new binders has always been at the most interest of researchers. The use of new eco-friendly binder system composition mainly based on polyethylene glycol (PEG), as a water soluble polymer, and cellulose acetate butyrate (CAB) is deeply studied. The use of some additives is also considered. The whole PIM process has been optimized for new feedstock compositions. In order to obtain free defects parts after water immersion, the initial study analyses the influence of molecular weights of both polymers during solvent debinding stage. Exhaustive feedstocks characterization has been carried out by torque and capillary rheology among other techniques. After the study of binder system composition, the solid loading is optimized through different methods. In order to compare the behaviour of these feedstocks along the PIM process with the behaviour of the developed feedstock (PEG–CAB-ZrSiO₄), commercial alumina powders and binder system (Nabalox® and Licomont®) have been combined with PEG-CAB binder system composition and ZrSiO₄ respectively. Finally, surface free defects samples have been obtained by powder injection moulding using the eco-friendly developed feedstock composition of PEG–CAB-ZrSiO₄. Achieved properties are in the same range of the obtained ones by others advanced processing routes for zircon. Furthermore, a small and complex real industrial sample has been successfully processed.
Description
Mención Internacional en el título de doctor
Keywords
Materiales cerámicos, Circón, Moldeo por inyección de polvos