Thesis (Ph. D.)--University of Texas at Austin, 2001. / Vita. Includes bibliographical references (leaves 224-227). Available also in a digital version from Dissertation Abstracts.

Abstract not available

Forward slip (FS), the percent difference between the roll velocity and the strip exit velocity, was achieved by altering four variables: reduction, rolling speed, lubricant viscosity, and roll roughness. A two-high laboratory mill was used to roll strips of unalloyed, H-18 temper aluminum. An SEM and a Leitze Orthoplane microscope were used to examine the strip surface. A grainy pattern, which varied with the rolling condition, was observed on the sample surface. The grainy pattern resulted from three effects: grooves imprinted by the rolls, black spots identified as hydropitting (HP), and horseshoe shaped marks which were attributed to FS. These effects were studied and the following conclusions drawn. Higher viscosity, high speed, and rough rolls produced more HP. Increasing reduction produced HP with the viscous lubricant, oil, but less HP with kerosene. No HP was observed at 59 percent reduction but FS marks occurred and were more prevalent with oil than kerosene. The smooth rolls produced more FS marks than the rough rolls. Two postulates were presented to explain the pattern of these effects. First, the FS mark lengths were of the same order of magnitude as one set of theoretically calculated relative slip lengths; indicating that FS was responsible for the marks. Second, the absence of HP and presence of FS marks, in particular cases, indicated that a hydraulic effect was responsible for the FS marks. The FS marks would have been created as localized high pressure lubricant flowed across the surface to equalize the film pressure. / Master of Science

Orientador: Maria Helena Robert / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-11-08T18:37:47Z (GMT). No. of bitstreams: 1 Delbin_Daniel_M.pdf: 8551361 bytes, checksum: 770e9d00eeb959cc6e40cf3f314faa4e (MD5) Previous issue date: 2006 / Resumo: Neste trabalho é estudada a viabilidade de produção de esponjas metálicas pela conformação de pasta tixotrópica da liga A2011, sobre camada de agente bloqueador (NaCl) posteriormente removido para formação da porosidade. Investiga-se a influência da temperatura de tratamento térmico, para obtenção da pasta semi-sólida, e da granulometria do agente bloqueador, na estrutura formada do material celular (aspecto geral, caracterização qualitativa e quantitativa dos poros, microestrutura da parede celular e densidade) e nas características de processo (forças de tixoforjamento e capacidade de penetração da pasta). São produzidos cilindros de material poroso metálico tipo sanduíche, compostos de camada porosa entre camadas maciças da liga, com três diferentes classes de porosidade: fina, média e grosseira. As esponjas foram submetidas à tomografia computadorizada e à análise metalográfica para sua caracterização estrutural. Os resultados obtidos mostram a viabilidade de obtenção de esponjas metálicas utilizando a tecnologia de semi-sólidos e o tipo de bloqueador utilizado. O sucesso do processo depende da fração líquida presente na pasta metálica tixotrópica, reduzida fração líquida pode resultar em incompleta infiltração e compressão das partículas do agente bloqueador. Nas condições analisadas a granulometria do agente bloqueador não teve influência sensível na qualidade do produto. A densidade do material poroso aumenta com o aumento da temperatura de processo, devido ao aumento da espessura de paredes metálicas na estrutura porosa / Abstract: The work analyses the possibility of the production of cellular material by pressing the A2011 alloy in the thixotropic semi-solid state, into a space holder pre-form. Space holder particles used are NaCl, which are removed from the product after the forming operation, resulting the porous material. It is investigated the influence of the thixoforming temperature and the size of space holder particles, in the structure of the obtained porous material (general aspect, quantitative and qualitative characterization of porosity, microstructure of cell walls and density of the product), as well as in the processing characteristics (required forces for infiltration, penetration ability of the slurry in the salt pre-form). Cylindrical samples, sandwich type, with a porous layer inserted between layers of compact alloy are produced, presenting three different ranges of porosity. The cellular material obtained contains opened porosity, being characterized as sponge. Products were analyzed by tomography and metallographic techniques. Results show that the proposed process is able to produce acceptable porous material, with a simple and low cost technique. The quality of the product depends rather on the processing temperature than on the size of space holder particles. Low liquid fraction in the thixotropic slurry can lead to incomplete infiltration and deformation of the pre-form. In the analyzed conditions, influence of the size of space holder particles could be observed neither in the processing ability nor in the quality of the product. Density of produced porous material increases as processing temperature increases, due to the increase of thickness of cell walls / Mestrado / Materiais e Processos de Fabricação / Mestre em Engenharia Mecânica