Dissertations / Theses on the topic 'EXTRUSÃO DE TUBOS'

O polietileno de média densidade (PEMD) é um polímero termoplástico parcialmente cristalino, cujo uso tem crescido bastante em aplicações de engenharia, como em tubos plásticos para sistemas de distribuição de água e de gás. Sob carga constante, entretanto, este material pode eventualmente apresentar fratura por fluência, por meio de um mecanismo de crescimento lento de trincas, provocando acentuadas perdas por vazamento nos sistemas. Os métodos atuais empregados pela indústria para estimar a durabilidade dos tubos são caros, demorados, pouco práticos e imprecisos. Busca-se o desenvolvimento de técnicas mais eficientes, sendo que os métodos da mecânica da fratura são promissores no sentido de descrever a etapa de propagação da trinca. Ensaios de mecânica da fratura, entretanto, requerem a introdução de pré-trincas nos corpos de prova. Sabe-se que as técnicas artificiais de introdução de pré-trincas causam algum tipo de dano na matriz polimérica, que pode ou não afetar os resultados dos ensaios, dependendo dos eventos que ocorrerem após o carregamento inicial. A principal propriedade requerida de um método de introdução de pré-trinca, portanto, é reprodutibilidade. Neste estudo foram aplicados três importantes métodos de mecânica da fratura ao PEMD e investigados os efeitos de diferentes técnicas de introdução de pré-trincas sobre os resultados dos ensaios e sobre as estruturas de deformação na matriz do material na ponta da trinca. Os ensaios de tenacidade à fratura no estado plano de deformação - KIc - foram realizados em condições criogênicas, em vista do comportamento dúctil do material à temperatura ambiente, sendo que a estratégia mostrou-se satisfatória. Os resultados dos ensaios de Integral-J sugerem que o método pode não ser aplicável ao PEMD, devido ao peculiar mecanismo de fratura do material. O método do trabalho essencial de fratura - EWF - se aplica bem ao PEMD. Os resultados dos ensaios de KIc e EWF demonstraram que diferentes técnicas de introdução de pré-trincas provocam diferentes estruturas de deformação no material na ponta da trinca e afetam os resultados de ensaios de fratura no PEMD. Os resultados de EWF demonstraram ainda que o processamento também afeta as propriedades de fratura do material. É proposta uma nova técnica para a introdução de pré-trincas, com características mais naturais, a qual requer estudos complementares para seu aperfeiçoamento.
Medium density polyethylene (MDPE) is a semicrystalline thermoplastic polymer that has been increasingly used in engineering applications, as plastic pipes for water and gas distribution systems. Under constant load, however, this material may occasionally present creep failure, by means of a mechanism of slow crack growth, leading to leakage losses in the systems. Current methods used by industry to estimate durability of pipes are expensive, time consuming, non practical and inaccurate. The development of more efficient methods is a common target and fracture mechanics methods are promising in describing the crack propagation stage. Fracture mechanics testing methods, however, require the introduction of pre-cracks into the specimens. It is known that artificial methods of introducing pre-cracks produce some damage on the polymeric matrix, which may or not affect the results of tests, depending on the events that occur after the initial loading. Main propriety required of a pre-crack introducing method, therefore, is reproducibility. In this study three important fracture mechanics methods were applied to MDPE and the effects of different methods of pre-cracking over test results and over deformation structures of material matrix at the crack tip were investigated. Plane-strain fracture toughness - KIc tests were performed under cryogenic conditions, in view of the ductile behavior of material at room temperature and this strategy was well succeed. Results of Integral-J tests suggest that this method may not be applicable to MDPE, due to the peculiar fracture mechanism of the material. The essential work of fracture method EWF is well suited to study MDPE. The results of KIc and EWF tests showed that different pre-cracking methods cause different deformation structures in the material at the crack tip and affect the fracture tests with MDPE. EWF results showed also that the processing affect the fracture properties of materials too. It is proposed a new method for introducing pre-cracks, with more natural characteristics that requires complementary studies for its improving.

O látex de borracha natural foi formulado, radiovulcanizado e, em seguida, estabilizado radioliticamente (GAMATEX), para ser empregado na fabricação de artefatos de borracha utilizados na área médica. A eficiência de reticulação do látex, quando radiovulcanizado com raios gama, correlacionou-se matematicamente com a razão de concentração do sistema de radiosensibilizador (x1 = [An-B] / [KOH]) e com a dose de vulcanização (x2), apresentando alto grau de interação, segundo o seguinte modelo matemático: , onde representa a resistência à tração na ruptura. O processo RVNRL foi otimizado para baixas doses de vulcanização e altas concentrações de An-B. A resistência radioxidativa da borracha, obtida a partir do GAMATEX, foi atingida adicionando-se uma mistura de antioxidantes (45% BANOX S + 55% TNPP). Esta mistura apresentou um efeito sinérgico. O látex apresentou comportamento pseudoplástico com a ocorrência de tensão de escoamento. A taxa de desestabilização irreversível do látex foi diretamente proporcional à [An-B] e inversamente proporcional à [KOH]. O efeito pós-irradiação do látex ou a desestabilização reversível, ocorreu devido à presença de uma concentração residual de An-B que não reagiu. A irradiação melhorou a estabilidade coloidal do GAMATEX, devido ao aumento da tixotropia e da tendência newtoniana além da correlação entre o grau de consistência (k) e o índice pseudoplástico (n), de acordo com o modelo matemático . Este fato permite um tempo maior de estocagem do GAMATEX. A viscosidade relativa do látex correlaciona-se com a temperatura e com o teor da borracha seca conforme o modelo matemático: , onde rw é a razão (BS/100-BS). O látex radiovulcanizado coagulou à temperatura de –10ºC no sistema de refrigeração projetado.
The natural rubber latex was formulated, irradiation vulcanized and stabilized (GAMATEX) to make rubber goods for medical purpose. When the latex was vulcanized by gamma rays the effectiveness crosslinking of GAMATEX relationship between the concentration ratio of sensitizer system (x1=[n-BA]/[KOH]) and the vulcanization dose (x2), showing high interaction grade according to the following the mathematical equation: , where is the tensile strength. The RVNRL process was optimized for low vulcanization doses and high concentrations of n-BA. The resistance to radiolitic oxidation of rubber obtained from GAMATEX was attained when one antioxidants mixture (45% BANOX S + 55% TNPP) was added. This mixture exhibited synergetic effect. The latex showed pseudoplastic rheological behavior and the yield stress occurrence. The irreversible destabilization rate of latex was direct proportional to [n-BA] and indirect proportional to [KOH]. The post-irradiation effects or reversible destabilization of latex occurred because there is a residual concentration of [n-BA] that it was not reacted. The colloidal stability of GAMATEX improved with irradiation, showing showing the increase of thixotropic behavior and the tendency to newtonian behavior flow besides the relationship between the viscosity index (k) and the pseudoplastic index (n) according to the mathematical model: . This fact allows the higher storage time of GAMATEX. The relative viscosity of latex was relationship between the temperature and the total dry rubber content according to the mathematical model: , where rw is the ratio (BS/100-BS). The radiation vulcanized latex coagulated at –10ºC into the projected freezing system.

O polietileno tem sido muito empregado em transmissão de água potável, particularmente em ramais prediais. Este polímero apresenta vantagens em relação a seus concorrentes, como flexibilidade, baixo preço, facilidade de instalação e resistência à corrosão. Os tubos fabricados com polietileno de alta densidade –PEAD, como o material é genericamente conhecido na indústria de saneamento básico no Brasil - são suscetíveis de apresentar falhas em serviço por fratura em fluência, as quais provocam vazamentos e perdas de água e incorrem em maiores custos de manutenção. Os principais fatores que influenciam a vida dos tubos de polietileno são: material, meio, condições de carga e técnicas de instalação. A busca de melhores materiais tem levado a indústria petroquímica ao contínuo desenvolvimento de novas resinas, com maior resistência às falhas, que ocorrem através do crescimento lento de trincas. Essa resistência à falha em serviço dos tubos geralmente é avaliada através de ensaios de resistência à pressão hidrostática interna de longa duração, realizados em diferentes temperaturas. Nestes ensaios observa-se que o PEAD apresenta comportamento dúctil (acompanhado de significativa deformação plástica) e falha em menor período de tempo a níveis elevados de tensão, enquanto que em níveis mais baixos de tensão o material apresenta falhas com aparência frágil - sem deformação plástica visível apreciável - após longos períodos de tempo. As falhas em serviço são predominantemente deste último tipo. Esta transição 'dúctil-frágil' no comportamento do material, pelo menos ao nível da falha macroscópica, é muito importante e precisa ser bem compreendida pois pode abreviar a vida útil do tubo através de falhas precoces. Dados de tensão circunferencial versus tempo de ruptura dos tubos podem ser plotados em escala bi-logarítmica, formando o que se conhece na prática industrial por 'curva de regressão', a qual é linear, com inclinação negativa e com maior inclinação (em módulo) na região correspondente às falhas do modo frágil. Dessa forma, a transição 'dúctil-frágil' apresenta-se na 'curva de regressão' como um ponto de inflexão. A tensão de transição dúctil-frágil é característica de uma dada formulação (composto) e não é facilmente determinada em ensaios conduzidos à temperatura ambiente. Apesar de sua ampla aceitação na indústria os testes de resistência à pressão hidrostática interna de longa duração devem ser criticados pois são muito longos, caros e pouco práticos para efeito de controle de qualidade dos tubos de polietileno. Além disso, a maioria dos dados são coletados a altas pressões internas (ou seja, na região 'dúctil') para economizar tempo, enquanto que os tubos operam na região 'frágil'. A filosofia desses testes, como empregados na indústria, também implica que o tempo de falha é uma propriedade do material, enquanto que fatores extrínsecos, como defeitos introduzidos durante a instalação, podem reduzir o tempo de nucleação da fratura, levando à falha precoce. O crescente emprego de tubos de polietileno em sistemas de distribuição de água, além de outras aplicações, como em sistemas de gás, requer o desenvolvimento de novos métodos de avaliação de desempenho, que levem em conta não apenas o tempo de falha como também os mecanismos de fratura. Busca-se desenvolver métodos de laboratório, de curta duração, para se estabelecer o comportamento dos tubos a longo prazo, principalmente para prevenir falhas precoces, do tipo frágil, dentro do período de vida útil esperado. A mecânica da fratura é justamente a disciplina que estuda o comportamento dos materiais na presença de trincas. Neste sentido duas abordagens são propostas no presente trabalho: 'Ramp Test' e o método do Trabalho Essencial de Fratura. O método do 'ramp test' permite estimar a tensão crítica correspondente à transição dúctil-frágil da 'curva de regressão' a partir de ensaios simples de tração. Por outro lado, o método do Trabalho Essencial de Fratura permite estimar diretamente as partes essencial e não essencial do trabalho específico de fratura. São analisadas cinco resinas provenientes de fornecedores tradicionais de matérias-primas para a produção de tubos de polietileno e duas outras resinas, desenvolvidas para outros fins. Os resultados permitem concluir que os ensaios propostos são viáveis como substitutos ou complementares ao ensaios de resistência à pressão hidrostática na avaliação da tendência de tubos de polietileno apresentarem falhas em serviço.
Polyethylene has been largely used in potable water distribution systems, mainly in service lines. This polymer offers many advantages over its competitors: flexibility, low cost, ease installation and corrosion resistance. Pipes made with high density polyethylene – HDPE, the generic designation of the material in the sanitation industry in Brazil – fail in service by fracture due creep, giving rise to leakage and water losses, resulting in higher maintenance costs. Main factors that affect the service life of polyethylene pipes are: material, environment, load and settlement. The search for improved materials leads the petrochemical industry to the continuous development of new resins, with increased resistance to failure, which occurs via slow crack growth. This resistance to in-service failure is usually measured in long-term hydrostatic strength tests, at different temperatures. In these tests HDPE behaves like ductile material (followed by significant plastic deformation) and fails in lower period of time under high stress levels, whereas under lower stress levels it fails in a brittle-like mode - with no visible permanent plastic deformation - after longer times. Failures in service are mainly brittle-like. This ductile-fragile transition in the behavior of the material at least at macroscopic scale, is very important and must be well understood, because it can abbreviate the service life of the tube, through early failure. Time-stress failure data can be ploted in bi-log scale to form what is known in the industrial praxis as regression curve, which is linear, with negative slopes, and a larger slope in modulus for the brittle-like fracture mode. In this way, the ductile-fragile transition appears as a point of inflection. The 'ductile-to-brittle' transition stress is claracteristic of a given formulation and is not easily determined in tests conducted at room temperatures. In spite of its widespread acceptance in the industry, the long-term hydrostatic strength test must be criticized because it has long duration, is expensive and not practical for pipes’ quality control. Beside that, most of the data are collected at high inner pressures to save time, while the tube is expected to operate in the 'brittle-like' region. The philosophy of these tests, as used in the industry, also implies that the time-to-failure is a material property, while extrinsic factors may shorten the fracture nucleation time, leading to a premature failure. The rising use of polyethylene pipes in water distribution systems, beside other applications as in gas systems, requires the development of new performance evaluation methods, that take into account not the time to failure but also the fracture mechanisms. It is desirable for developing short-term laboratory tests to establish the long-term behavior of pipes, to prevent premature brittle-like failures in the desired service life. Fracture mechanics is just the subject which studies the behavior of materials in the presence of cracks. In this way, two approaches are suggested for the present work : 'ramp test' and the Essential Work of Fracture method. The 'ramp test' method allows to estimate the critical stress that corresponds to the ductile-brittle transition in the regression curve using standard tensile test samples. On the other hand, the Essential Work of Fracture allows a direct estimation of the essential and the non-essential parts of the specific work of fracture. Five different resins for production of polyethylene pipes obtained from traditional raw material suppliers and two other resins designed for other purposes are analysed. The results allow to conclude that the suggested tests are feasible as substitutes or complementaries to the long-term hydrostatic stress tests to evaluate the tendency of the polyethylene pipes to present service failures.

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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Ciência e Engenharia de Materiais, Florianópolis, 2011
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Materiais com poros interconectados são comumente usados em diversas aplicações de filtragem, como, por exemplo, purificação de água, filtração de metais fundidos e filtração de gases quentes. Se por um lado, os filtros devem conter uma estrutura de elevada porosidade aberta; em contrapartida, esses materiais devem apresentar resistência mecânica suficiente para suportar a queda de pressão durante o processo de filtração. O objetivo deste trabalho foi estudar a viabilidade de produção de tubos porosos, em compósitos de matriz cerâmica e metálica reforçados por fibras, via extrusão termoplástica de pós, para aplicação em processos de filtração. A extrusão termoplástica é um processo contínuo, capaz de promover um alto nível de alinhamento de fibras na direção de extrusão, sem que haja excessiva fratura de fibras durante o processamento. Pós de alumina e superliga de níquel foram selecionados para formar a matriz dos compósitos de matriz cerâmica e metálica, respectivamente. Fibras curtas de alumina foram utilizadas como reforço. Como componentes do sistema ligante foram utilizados polietileno de baixa densidade (LDPE), parafina (PW) e ácido esteárico (SA). Diferentes proporções entre LDPE-PW-SA foram estudadas a fim de desenvolver um sistema ligante apropriado ao processo. A evolução da viscosidade da mistura em função do teor de sólidos foi estudada e comparada a diversos modelos de viscosidade. Após o desenvolvimento do feedstock de extrusão, 30 % em volume de fibras foram adicionadas a mistura. Tubos com 4,5 a 10,0 mm de diâmetro, com 0,6 e 1,0 mm de espessura foram então extrudados com sucesso, após sucessivas etapas de ajuste dos parâmetros de extrusão. Análises microscópicas confirmaram o alinhamento satisfatório das fibras. Finalmente, após a sinterização dos tubos a 1300 ºC durante 60 minutos, meso e macroporosidades foram identificadas através de análises porosimétricas por intrusão de mercúrio, totalizando um volume de poros de, aproximadamente, 41 e 36 % nos tubos de matriz cerâmica e metálica, respectivamente. O nível de porosidade, bem como o tamanho médio de poros, foi considerado adequado à aplicação em certos processos de filtração, em especial a filtração de gases quentes.

Actuellement, les tubes PVC multi-couches dédiés aux systèmes d'assainissement ne garantissent pas une résistance aux chocs suffisante. Une étude a donc été menée pour améliorer la ténacité des tubes. L'analyse du procédé de fabrication, l'extrusion, montre que ce processus est complexe. Les propriétés attendues des tubes dépendent de paramètres liés au procédé de fabrication ainsi qu'à ceux liés produit. Il existe une réelle difficulté à déterminer les paramètres cruciaux sur lesquels agir pour améliorer la ténacité. Afin de les identifier, des tests de chocs instrumentés ont été réalisés. Ces tests montrent que la ténacité n'est pas homogène autour du tube. Il existe des zones de plus faible résistance au niveau des surfaces de recollement créées lors de la fabrication. Pour limiter l'impact de ces surfaces sur la ténacité des tubes, un modèle numérique en 3D de l'écoulement de la matière dans la tête d'extrusion a été mis en place. Une modification de l'outillage a été proposée
Currently, the multi-layer PVC pipes, used for sewage systems does not guarantee an enough impact resistance. A study was thus undertaken to improve the toughness of pipes. The analyse of the manufacturing process, the extrusion, shows that this process is complex. The awaited properties of the pipes depend on parameters related to the manufacturing process like to the product. It exists a real difficulty to find the crucial parameters on which to act to improve the toughness. To identify them, instrumented impact tests were realized. These tests show that thoughness is not homogeneous aroud the pipe. There are zones of weakest strength to the level of the welding surfaces, created during the manufacturing. To reduce the impact of these surfaces on the pipe toughness, a 3D numerical model of the melt flow was set up. A modification of the dies was proposed

Notre objectif dans cette étude aura été de se rapprocher progressivement du comportement et des caractéristiques des polyéthylènes afin de décrire les mécanismes de formation des contraintes résiduelles lors du calibrage des tubes.
Le modèle le plus simple, basé sur une loi de comportement liquide - solide élastique, a mis en évidence deux mécanismes de formation des contraintes résiduelles. Le premier est relié aux différences de température lors du refroidissement qui provoquent des différences de retrait dans l'épaisseur. Ceci met les couches extérieures du tube en compression et les couches intérieures en traction. Ce profil de contrainte fait se refermer le tube lorsqu'on le découpe suivant la génératrice
Le second mécanisme est relié aux efforts extérieurs qui s'appliquent sur le tube. La dépression dans le calibreur maintient le tube contre la chambre de calibrage et l'empêche de se rétracter lors du refroidissement ce qui induit des contraintes de traction dans les couches solidifiées. En fait la dépression bloque le retrait thermique qui était à l'origine du premier mécanisme. Si la dépression est suffisante pour maintenir le tube jusqu'à la fin de la solidification le profil de contraintes résiduelles est nul. Les profils de contraintes intermédiaires sont obtenus par une évolution des conditions aux limites lors de la solidification, la dépression n'étant en faite pas suffisante pour maintenir le contact pendant toute la solidification.
Le modèle élastique a également mis en avant l'influence des forces axiales et en particulier les forces de frottement entre le tube et la chambre de calibrage. En étirant le tube, elles tendent à diminuer son diamètre. La dépression bloque cette rétraction en plus du retrait thermique. Ceci accentue les contraintes de traction dans les couches extérieures jusqu'à inverser le profil des contraintes résiduelles. Le tube peut alors s'ouvrir lorsqu'on le découpe suivant la génératrice.
Le modèle élastique est suffisant pour expliquer l'influence de la dépression sur le profil des contraintes résiduelles. Cependant les propriétés des matériaux que ce modèle peut prendre en compte restent assez éloignées de celui des polyéthylènes pendant le refroidissement.
Le modèle viscoélastique que nous avons développé est original par rapport à la bibliographie dans le sens où la variation du volume spécifique et les propriétés mécanique lors de la transition fluide -- solide sont directement basés sur l'évolution du taux de cristallinité, paramètre du premier ordre sur le comportement physique du matériau.
Le taux de cristallinité peut être obtenu dans le modèle soit par le modèle de cristallisation d'Ozawa soit en reprenant directement les résultats obtenus par DSC. Celui-ci est alors utilisé pour déterminer l'évolution du volume spécifique et permet de tenir de l'importante rétraction du matériau qui se produit lors de la cristallisation. L'influence du retrait du à la cristallisation doit cependant être nuancé car il se produit à des températures pour lesquelles la relaxation des contraintes n'est pas négligeable. Pour des matériaux semi-cristallins tel que les polyéthylènes, il est donc nécessaire d'utiliser un modèle viscoélastique pour pouvoir prendre en compte le retrait lors de la cristallisation.
Afin de pouvoir appliquer les forces d'étirage et de frottement dès le début de la solidification, nous avons montré qu'il était nécessaire de tenir compte des contraintes dans les couches non solidifiées afin de charger progressivement les couches solidifiées. Le comportement viscoélastique des matériaux est pris en compte dans les états fluides et solide par des lois de Maxwell multimode. La répartition des contraintes prédit dans les couches fluides et solides par le modèle viscoélastique permet d'avoir une première information sur l'importance des propriétés mécaniques du matériau à l'état fluide. Les calculs permettent d'expliquer en partie l'orientation mesurée dans les couches extérieures lors de l'étude des polyéthylènes basse densité linéaire.
Le modèle viscoélastique apporte peu de renseignements supplémentaires sur les mécanismes de formation des contraintes résiduelles finales mais il permet de les quantifier en utilisant des caractéristiques matériaux proches de celles des polyéthylènes lors du refroidissement.
Une étude numérique confirme que le procédé de calibrage est relativement sensible à tous les paramètres du procédé et caractéristiques du matériau même si la dépression reste le paramètre de premier ordre.
Finalement, les comparaisons entre les calculs et l'expérience montrent que nous sommes parvenus à borner la réalité en expliquant l'origine des contraintes résiduelles qui se forment lors du calibrage des tubes.

Dans le procédé d’extrusion de tubes en polyamide 12, l’étape de calibration a une influence prépondérante sur les propriétés mécaniques résultantes. La calibration combine une trempe et un étirage des couches extérieures du tube, ce qui conduit à une orientation moléculaire importante dans cette zone. Nous avons montré qu’augmenter la lubrification dans le calibre amène à une diminution du taux d’étirage dans le calibre, DrCAL (rapport entre la vitesse de ligne et la vitesse en entrée de calibre). Une corrélation nette a été montrée entre la biréfringence en peau (DnPEAU) et DrCAL: réduire DrCAL conduit à une orientation plus faible en surface. Une modélisation thermomécanique a permis de déterminer la carte de température au cours du refroidissement, et de montrer de quelle manière les forces d’étirage se concentrent en peau. DnPEAU a été relié aux propriétés mécaniques : l’allongement à la rupture augmente lorsque l’orientation diminue
In polyamide 12 tube extrusion, calibration - or sizing - is the key step that affects subsequent mechanical properties. Influence of calibration is twofold. Since it combines a quenching and a mechanical drawing of the tube external surface, high molecular orientation is generated in this zone. We have shown quantitatively that increasing the lubrication level leads to a diminution of the draw ratio in calibrator, DrCAL (ratio between line velocity and velocity at the calibrator entrance). Excellent correlation has been found between tube superficial orientation (Dn) and DrCAL: a reduced elongation of the polymer in the calibrator leads to less superficial orientation. A thermomechanical model was used to predict temperatures in the tube thickness and to show how drawing forces, concentrated at the external skin during the crystallization, lead to orientation. Besides, elongation at break has been found to strongly depend on Dn and on the surface defects resulting from calibration

Zeolites are highly porous materials that are most commonly used in granular or beaded forms. In general, zeolite granules, beads or monoliths are manufactured by using an inorganic binder which helps to cement zeolite crystals together. However, this inorganic binder decreases the purity of the zeolite structures and accessibility to the zeolite pores. A new and relatively easy method was offered for the production of binderless zeolite A tubes and bars from amorphous alumina silicate extrudates in this study. Amorphous alumina silicate powder, which is obtained by filtering the homogenous hydrogel with a composition of 2.5Na2O:1Al2O3:1.7SiO2:150H2O, is mixed with an organic binder (HEC-Hydroxyethyl Cellulose) to obtain the paste. The paste is then extruded through a die of a home-made extruder into bars and tubes. These extrudates were dried at room temperature for 24 hours, then calcined at 600oC for 2 hours and finally synthesized at 80oC for 72 hours in hydrothermal conditions to convert amorphous alumina silicate to zeolite. The most appropriate amorphous alumina silicate powder (A) / 4wt% HEC solution (H) ratio to prepare paste, hence to prepare bars and tubes was found as 0.82. The crystallinity of bars and tubes was 91% and 97%, respectively, and zeolite A was the only crystalline material. The bars and tubes were composed of highly intergrown zeolite A crystals with high porosity. Porosity of the bars is approximately 39% and porosity of the tubes is 29%, with a narrow pore size distribution. Bars have macropores of 2 &
#956
m, while the macropores of the tubes are 3-4 &
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m. The BET surface area of the bars was 411 m2/g and of tubes was 439 m2/g, which are comparable with the commercial zeolite A beads. Bars had a crushing strength of 0.42 MPa, which is sufficiently high to handle. In conclusion, zeolite A bars and tubes, with their high purity, macroporous structure and high mechanical strength, can be used in adsorption and ion exchange processes. The developed synthesis method can be scaled up to prepare honeycomb monoliths that provide higher surface are per unit volume with an appropriate extruder die.

Dans le procédé d'extrusion de tubes en polyamide 12, l'étape de calibration a une influence prépondérante sur les propriétés mécaniques résultantes. Lors de la calibration, le polymère fondu est tiré à travers un manchon cylindrique (calibre) situé dans un bac à eau sous vide. Le niveau de vide (dépression DP) est ajustable. Un débit d'eau (débit de suintement DSU) est appliqué à l'entrée du calibre et permet la formation d'un film d'eau qui lubrifie le contact tube/calibre. La calibration combine une trempe et un étirage des couches extérieures du tube, ce qui conduit à une orientation moléculaire importante dans cette zone (zone de peau). Par ailleurs, l'état de surface du tube est défini par les conditions de contact entre tube et calibre. La vitesse du polymère en entrée de calibre et l'épaisseur du film d'eau entre tube et calibre ont été mesurées. Nous avons ainsi montré qu'augmenter la lubrification dans le calibre amène à une diminution du taux d'étirage dans le calibre, taux noté DrCAL (rapport entre la vitesse de ligne et la vitesse en entrée de calibre). Niveau de lubrification et état de surface ont été corrélés par rugosimétrie. Par ailleurs, l'orientation des couches externes a été évaluée par des mesures de biréfringence. Une corrélation nette a été montrée entre la biréfringence en peau (DnPEAU) et DrCAL: réduire DrCAL conduit à une orientation plus faible en surface. Une modélisation thermomécanique a permis de déterminer la carte de température au cours du refroidissement, et de montrer de quelle manière les forces d'étirage se concentrent en peau lors de la cristallisation et génèrent des contraintes à l'origine de l'orientation dans le produit final. Enfin, DnPEAU et l'état de surface ont été reliés aux propriétés mécaniques: l'allongement à la rupture augmente lorsque l'orientation diminue et que le nombre de défauts de surface est limité. Connaissant les relations entre les paramètres du procédé, la structure des tubes, et les propriétés mécaniques, il est à présent possible d'adapter les paramètres de calibration de façon à augmenter le niveau de lubrification au sein du calibre et à réduire le taux d'étirage dans le calibre pour améliorer systématiquement les propriétés mécaniques résultantes.

碩士
國立臺灣科技大學
機械工程研究所
83
In this study, a numerical simulation model for forward hot extrusion process of tube has been developed. This numerical si- mulation model combines the upper bound method with the finite difference method, and it is proposed to predict the deformation behaviors and forming load during the extrusion process. Besi- des, in order to investigate the influence of process variables to extrusion process, mechanical property tests of the extruded tube are performed. The Kinematically admissible velocity field of tube is de- rived , the energy consumption can be calculated, and metal fl- ow pattern can be obtained.Then, the finite difference method is applied to predict the temperature distribution in the billet ,and in the interface of billet and die during the extrusion process. For the purpose of examining the availability of this numerical simulation model, A6061 tubes are extruded at various temperatures. The metal flow is observed on macro etched section of the discard remained in the container, and the charge welding seams in the cross-section of the extruded tubes are observed by macro etching. The strength of welded portions of extruded tube is evalua- ted by the expanding and flattening tests. The expanding ratios of extruded tubes are compared with those of seamless tubes pro- duced by machining the same materials. It is found that the st- rength of the extruded tubes is comparable to the tear streng- th of billets. From the experimental and analytical results, the optimal tube extrusion conditions can be found.

碩士
國立中山大學
機械與機電工程學系研究所
100
This study investigates analytically and experimentally extrusion processes of magnesium hollow tubes by a single-cylinder extrusion machine and double-cylinder extrusion machine. The first part of this study is to conduct analysis and experiment of hollow helical tube extrusion by single-cylinder extrusion machine. Firstly, a design criterion is proposed to determine the forming parameters and discuss the effects of product size, extrusion ratio, billet length, etc. on the mandrel surface stress. The effects of the die bearing part length, angle of rotation, extrusion speed, initial temperature, petal number, etc. on the radial filling ratio are also investigated. Better parameters are chosen from analytical results to conduct hot extrusion experiments for obtaining sound products. Microstructure observation and hardness test are conducted at the cross-section of the product. The experimental values of extrusion load and product’s dimensions are compared with the analytical values to verify the validity of the analytical models. The second part of this study is to conduct analysis and experiment of hollow tubes extrusion by a double-cylinder extrusion machine. The effects of extrusion ratio, billet length, mandrel diameter, etc. on the drawing force on the mandrel and critical conditions without mandrel fracture are discussed.

碩士
國立中山大學
機械與機電工程學系研究所
102
This study is focused on the analysis and experiment of hot extrusion of magnesium alloy. Porthole dies with an inclination angle leads to non-uniform velocity distributions. This kind of design can make a gradient hardness tube that grain sizes at the material surface are smaller and harder than those at the center zone. Then it can have superior hardness on surface and good toughness in internal structure. This study aims to design porthole dies and mandrel with different inclination angles and use magnesium alloy AZ31 to conduct hot extrusion. Mainly in analyze extrusion load, normal plane and bonding plane’s effective strain distributions and material flow by the finite element method. Choose best parameter to manufacture a porthole die to conduct magnesium hot extrusion experiments. Microstructures of the materials are observed to understand the effects of the die inclination angles.

We present a platform that allows homogeneous and heterogeneous 3-D soft materials to be continuously defined in a single step. Biopolymer solutions are introduced to a microfluidic device and radially distributed to feed to a common outlet at the device center. This forms concentric sheaths of complex fluids and upon crosslinking, a hydrogel tube at the exit. This approach allows for the controlled and continuous extrusion of tubes with tailored diameters of 500 μm to 1500 μm, wall thicknesses of 20 μm to 120 μm, and compositions, as well as predictable mechanical and chemical properties. Using the same platform, single and multi-walled hydrogel tubes with defined heterogeneities and patterns of discrete spots of secondary biopolymer materials can be continuously extruded. A tube-hosting device is presented which can independently perfuse and superfuse isolated tube segments, allowing precise microenvironmental control without cannulation for up to an hour.

A presente dissertação descreve o trabalho realizado na empresa Heliflex Tubos e Mangueiras, S.A. no qual o principal objetivo foi o desenvolvimento da ferramenta de extrusão necessária para a produção de uma nova gama de tubos flexíveis reforçados com espira em PVC rígido para contacto alimentar. Para ser possível realizar tal tarefa foi essencial uma compreensão do processo de extrusão de polímeros e conhecer os diferentes métodos de extrusão utilizados para o fabrico dos produtos Heliflex, bem como as ferramentas de extrusão usadas nestes diferentes métodos. Após a compreensão dos métodos de extrusão utilizados pela empresa e observação pormenorizada das ferramentas usadas para a produção de produtos idênticos ao produto final pretendido deu-se início ao projeto da nova ferramenta, que foi posteriormente submetida a simulação do escoamento no seu interior para análise da necessidade de possíveis melhorias na sua configuração. As peças foram depois mandadas maquinar, montadas na linha de extrusão e efetuados os ensaios em linha de produção. Destes ensaios resultaram as amostras que foram sujeitas a ensaios de desempenho para aferir se o produto está conforme os valores mínimos da norma aplicada ao respetivo teste e os valores estabelecidos pela própria Heliflex. No final foi feita uma comparação com o tubo usado originalmente para a mesma função. Foi observada uma redução do atrito com a superfície, que era o principal objetivo a alcançar. Em contrapartida, o tubo desenvolvido não cumpriu os requisitos mínimos nos ensaio da pressão hidrostática interior a 20ºC e à tração. Apesar do resultado do ensaio de pressão não ser relevante para este tipo de tubo, uma vez que a sua utilização apenas o sujeita a vácuo, o facto de não cumprir os requisitos do ensaio de tração pode vir a ser um problema na sua utilização, podendo a espira rígida deixar de aderir ao material flexível quando sujeito a deformações mecânicas elevadas. Como tal, são indicadas hipóteses de como resolver este problema no futuro.
This dissertation describes the work carried out in the company Heliflex Tubos e Mangueiras, S.A. in which the main objective of this work was the development of the extrusion tool necessary to produce a new range of flexible tubes reinforced with rigid PVC for food contact. To be able to accomplish such a task it was essential to understand the polymer extrusion process and to know the different extrusion methods used to manufacture Heliflex’s products, as well as the extrusion tools used in these different methods. After understanding the extrusion methods used by the company and detailed observation of the tools used to produce products identical to the intended final product, the design of the new tool began, which was later submitted to flow simulations inside it to analyze the need for possible improvements in its configuration. The parts were then machined, assembled on the extrusion line and tested on the production line. From these tests resulted the samples that were subjected to performance tests to assess whether the product complies with the minimum values of the standard applied to the respective test and the values established by Heliflex itself. At the end, a comparison was made with the tube originally used for the same function. A reduction in surface friction was observed, which was the main objective to be achieved. On the other hand, the developed tube did not meet the minimum requirements of the inner hydrostatic pressure test at 20ºC and the tension test. Although the result of the pressure test is not relevant for this type of pipe since its type of use only subjects it to vacuum, the fact that it does not meet the requirements of the tensile test may become a problem in its use, as the rigid coil may no longer adhere to the flexible material when subjected to high mechanical deformation. As such, hypotheses on how to solve this problem in the future are indicated.
Mestrado em Engenharia Mecânica

碩士
國立臺灣大學
機械工程學研究所
93
The superior properties of aluminum-alloy attracted attentions from the light-trend industry recently. Although the principal manufacturing process of the aluminum-alloy hollow products has been extruded by using porthole dies, the seamless extrusion with a mandrel has considerable potential because of its competitive productivity and performance. So the seamless extrusion process of aluminum-alloy tubes at elevated temperatures was studied in the present study by the finite element analysis and experiments. The trend of processing load and temperature on single-hole die extrusion was studied at first, the finite element software DEFORM was employed to simulate the hollow tubes processes. The experiment of single-hole die extrusion was practiced to verify the analyzed results. The experimental results obtained in the present study show good agreement with simulations. It shows the finite element software DEFORM is suitable to process of seamless tube extrusion. In order to increase the productivity, multi-hole die with several mandrels is applied. But the defects, which are the bias of mandrel and the unbalanced thickness of production caused by material flow are critical issues. The influence of important process parameters such as the temperature, extrusion speed, production dimension, billet size, number and position of holes on die are analyzed by simulations. According to the results of analysis, it shows the serious effect could be caused by the number and position of holes on die. Besides, the material flow is better when the hole is near the focus of action area. The bias phenomenon of mandrel could be improved after die stress analysis by the software DEFORM. The results of this study can be reference resources for related academic research and can also be used to develop related products for industry production.

碩士
國立中山大學
機械與機電工程學系研究所
97
This study involves analyses and experiments of magnesium’s hot extrusion of thin sheets and tubes. At first, hot compression tests are conducted to obtain the magnesium’s plastic flow stresses in high tempearatures, which will be used in the finite element analysis. In the FE simulations of thin sheet extrusion, the flow pattern of the magnesium billet within the die, the temperature history at die exit and the elastic deformation of the die is analyzed. Sound and good thin sheets are obtained by appropriate die design, initial billet temperature and extrusion velocity’s control. The goal of constant temperature extrusion is expected to achieved by controlling the extrusion velocity which will influences the billet temperature at die exit. In FE simulations of thin tube extrusion, the flow pattern of the magnesium billet within the port-holes, welding chamber and die bearing is analyzed. The elastic deformation of the die is dicussed. Extrusion of sound thin tubes is achieved by appropriate extrusion conditions. Finally, hot extrusion experiments are conducted and the experimental values of the extrusion load and dimensions of the products are compared with the analytical values to verify the validity of the analytical models.

碩士
國立臺灣大學
機械工程學研究所
96
The superior properties of magnesium-alloy draw attention from the light-trend industry recently. In this thesis, the finite element code, DEFORM, is employed to simulate the extrusion processes of L-shape solid profile and hollow tubes of AZ31 magnesium-alloy. The extrusion of L-shape solid profiles was examined first and the pocket die design was applied to the extrusion study. In the extrusion of the L-shape solid profiles, the unbalanced material flow that causes the extruded part being curved usually occurs. The finite element simulation results show that the unbalanced material flow is affected by the process parameters such as the location of L-shape profile, initial temperature, extrusion speed, friction factor (m), and pocket angle. And the pocket angle is found to be the major process parameter that causes the unbalanced material flow. The finite element analysis was performed to examine the effect of pocket angle on the material flow in details and an optimum pocket die design that renders a straight extruded part was determined. The actual extrusion experiments were conducted to validate the finite element analysis and the good agreement between the experimental data and the simulation results confirm the validity of the finite element analysis on the pocket die design. The extrusion of seamless AZ31 magnesium-alloy circular tubes was also studied in the present study with the use of the finite element analysis. The effects of the process parameters such as initial extrusion temperature, extrusion speed, and m value on the formability of the extruded circular tube were examined. The limited values of the process parameters that yield a temperature at the exit far below the ignition point of the magnesium-alloy were determined. The proposed design values for the process parameters could be used as design guidelines for the extrusion of AZ31 magnesium-alloy circular tubes.

碩士
國立中央大學
機械工程研究所
93
The purpose of this investigation is to discuss bi-material tubes extrusion using Hwang[22] proposed stream fuction. Building a model of bi-material upper bound method for extrsion problem. First, using incompressible plastic method to obtain sleeve layer and core layer of rigid/plastic interface fuction, by using upper bound method obtain extrusion of the total power. This investigation is number solution analyse utilize IMSL optimization procedure NCONF to request upper-bound solutin, The solution with Chitkarara[6] proposed theory and experiment prove. Discuss line die and curve die is reduction of area ,the friction factor, the semi-die angle and ect. to counter to with the effect of extrusion pressure and final radius ratio.