The DC casting process used for the production of cast aluminium alloy products intended for processing by rolling, extrusion or forging is an economically important process with approximately 10 million tonnes of DC cast product being produced annually world wide [1]. Process productivity, particularly with respect to elimination of casting defects and hence process scrap is an important factor to DC cast product producers. The literature reporting the DC casting process, particularly with respect to the formation of defects on the cast surface, is reviewed and the mechanisms for the formation of such defects examined. A universally understood and accepted explanation was found for only one of the normal surface defects encountered in practice. A number of samples of commercially cast DC products were subject to detailed cast surface examination, particularly surface microstructures. The results of this examination and the literature survey identified molten metal surface tension as a possible contributing factor affecting the molten metal meniscus stability within the DC casting mould. Meniscus instability is linked with the formation of surface defects. The literature on surface tension of aluminium alloys provided only limited information hence the surface tension of a range of binary and ternary alloys, including commercial alloys was determined, producing data hitherto not available. Of the common alloying elements used in commercial aluminium alloys, iron and magnesium were found to significantly reduce the surface tension. Surface fracture also resulted in a reduction in surface tension for the majority of alloys tested. The surface tension data is combined with mould thermal and physical model calculations to propose a mechanism for the formation of the cast surface defects. The model proposes a maximum stable size for the meniscus according to the alloy and mould conditions. Conditions outside these limits result in meniscus instability and the formation of cast surface defects. The model suggests possible operating changes that may reduce the incidence of surface defect formation. The work also identifies a number of areas requiring further investigation before major practical process changes aimed at cast surface defect elimination, may be formulated.

Thesis (M.S.)--Ohio University, August, 1980. / Title from PDF t.p.

Diss. (sammanfattning) Uppsala : Univ., 2003. / Härtill 7 uppsatser.

Thesis (MS)-Montana State University--Bozeman, 2008. / Typescript. Chairperson, Graduate Committee: Stephen W. Sofie Includes bibliographical references (leaves 77-78).

Thesis (M.S.)--Ohio University, November, 1990. / Title from PDF t.p.

Thesis (Ph. D.)--Ohio State University, 2004. / Title from first page of PDF file. Document formatted into pages; contains xx, 199 p.; also includes graphics. Includes bibliographical references (p. 196-199).

Thesis (Ph.D.)--Tennessee Technological University, 2009. / Title from title page screen (viewed on Aug. 20, 2009). Includes bibliographical references.

Thesis (M.S.)--Montana State University--Bozeman, 2006. / Typescript. Chairperson, Graduate Committee: Michael E. Hahn. Includes bibliographical references (leaves 57-59).

MENDES, Francisco Rogênio da Silva. Blendas e filmes de galactomanana e xiloglucana: caracterização físico-química. 2015. 92 f. Dissertação (Mestrado em Bioquímica)-Universidade Federal do Ceará, Fortaleza, 2015. / Submitted by Anderson Silva Pereira (anderson.pereiraaa@gmail.com) on 2017-01-04T20:47:58Z No. of bitstreams: 1 2015_dis_frsmendes.pdf: 4536625 bytes, checksum: 0bccbc297a617df8cede4d29292c8d24 (MD5) / Approved for entry into archive by Jairo Viana (jairo@ufc.br) on 2017-01-04T22:33:25Z (GMT) No. of bitstreams: 1 2015_dis_frsmendes.pdf: 4536625 bytes, checksum: 0bccbc297a617df8cede4d29292c8d24 (MD5) / Made available in DSpace on 2017-01-04T22:33:25Z (GMT). No. of bitstreams: 1 2015_dis_frsmendes.pdf: 4536625 bytes, checksum: 0bccbc297a617df8cede4d29292c8d24 (MD5) Previous issue date: 2015 / Plant hemicelluloses have been widely used in the industry due to their ability to form edible and biodegradable films with glycerol as plasticiser. This work aimed to obtain hemicellulose-based films using Caesalpina pulcherrima and Tamarindus indica seeds as sources, also to evaluate the physicochemical properties of these blends. Both hemicelluloses were obtained by aqueous extraction followed by ethanol precipitation. T. indica and C. pulcherrima seeds showed yields of 25% and 20% galactomannan (GalCp) and xyloglucan (XilTi), respectively. The XilTi showed the lowest content of nitrogen related to proteins, as those are the most contaminant in these extractions. On the other hand, xyloglucans showed the highest ash content when compared to galactomannans. Through GPC the estimated molecular weight was 4.35 x 106 g / mol and 2.03 x 106 g / mol for GalCp and XilTi, respectively. The mannose / galactose ratio for GalCp was determined by 1H NMR 2.52: 1. Glucose / xylose / galactose ratio for XilTi was obtained by 13C NMR (2.6: 2.4: 1). All blends solutions showed a nonlinear relationship between the shear stress and the strain rate at 25 °C, presenting a non-Newtonian behaviour. FTIR revealed absorptions in the range 3000-3500 cm-1 typical for carbohydrates, concerning to the vibrational stretch (OH) bands in the range of 2926-2899 cm-1 attributed to symmetric and asymmetric vibrations of the grouping CH. Also, the bands at 815 cm-1 and 872 cm-1 were detected which refer to the stretch of the anomeric conformations of polysaccharides, α-D-galactopironose and β-D-mannopyranose, respectively. The FTIR spectrum for xyloglucan apart from the bands at 3000-3500 cm-1 and 2926-2899 cm-1, showed bands at 820 cm-1 and 870 cm-1 which are attributed to stretching of the links in α-D-xylose and β-D-galactose monosaccharides. Moreover, it was detected absorptions around 800-1200 cm-1 which are specific for xyloglucan polysaccharides. The obtained films by casting method showed no significant difference between their thicknesses and showed water vapour permeability ranging from 1,604 to 2,474 (g.mm/h.KPa.m). Through atomic force microscopy over the surface of the films, parameters such as texture, waviness and roughness were estimated. All blend-based films presented low irregular surfaces. In sum, the films and blends based on plant cell wall polysaccharides reserve is promising due to its biodegradability and come from renewable sources. / As hemiceluloses têm sido bastante utilizadas na indústria por, possuirem a capacidade de formar filmes comestíveis e biodegradáveis juntamente com plastificante geralmente glicerol. O objetivo desta pesquisa foi formular blendas e filmes à base de hemiceluloses de Caesalpina pulcherrima (Cp) e Tamarindus indica (Ti) e avaliar suas propriedades físico-químicas. As hemiceluloses foram obtidas por extração aquosa seguida de precipitação com etanol 96 %. As blendas e filmes foram preparados pelo método de casting. As sementes apresentaram rendimentos de 25% e 20% de galactomanana (GalCp) e xiloglucana (XilTi) respectivamente. Na composição centesimal, a XilTi apresentou menor teor de proteínas como contaminante, quando comparado com a GalCp. No entanto, a xiloglucana mostrou maior teor de cinza em relação à galactomanana. A massa molar aparente foi obtida por GPC foi de 4,35 x 106 g/mol e 2,03 x 106 g/mol para GalCp e XilTi, respectivamente. A razão de manose/galactose da GalCp determinada por RMN 1H foi de (2,52:1). Enquanto que a razão de glucose/xilose/galactose para a XilTi obtida por RMN 13C foi de (2,6:2,4:1). As soluções filmogênicas apresentaram uma relação não linear entre a tensão de cisalhamento e a taxa de deformação a 25°C, caracterizando-se como fluídos não newtonianos. A espectroscopia na região do infravermelho revelou absorções na região 3000-3500 cm-1 característica de carboidratos cíclicos, atribuída ao estiramento vibracional (O-H) e bandas de absorção entre 2926-2899 cm-1 atribuída às vibrações simétricas e assimétricas do grupamento C-H e as bandas em 815 cm-1 e 872 cm-1 referem-se ao estiramento das conformações anoméricas das unidades α-D-galactopironose e β-D-manopiranose, respectivamente. O espectro de FTIR para a xiloglucana foi identificado além das bandas em 3000-3500 cm-1 e 2926-2899 cm-1, mostrou absorções em 820 cm-1 e 870 cm-1 que é atribuída ao estiramento das ligações das unidades α-D-xilose e β-D-galactose, revelou também absorções entre 800-1200 cm-1 que representa a região de identidade para xiloglucana. As blendas e filmes não apresentaram permeabilidade ao vapor de água variando entre 1,604 e 2,474 (g.mm/h. kPa.m). A microscopia de força atômica permitiu determinar os parâmetros de superfície, onde se verificou pequenas irregularidades de superfícies. Em suma, filmes e blendas a base de polissacarídeos de reserva de parede celular de plantas é promissor devido a sua biodegradabilidade e por serem provenientes de fontes renováveis.

Mold behavior, mold-related quality and the columnar-to-equiaxed transition influenced by in-mold EMS were examined by performing trials at two steel companies, metallurgical examination of the billet samples and mathematical modelling. The thermal fields in the walls of billet molds (102 X 102mm and 127 X 178mm) and in the cooling water were monitored by a system of thermocouples as the EMS was switched on and off during the continuous casting of several heats. The effect of electro-magnetic stirring on mold heat extraction was found to be negligible. The mold temperatures and cooling water temperatures are strongly dependent on the mold/billet gap which is affected by dynamic distortion of the mold tube. In the case of the square mold, the time-dependent mold distortion resulted from boiling adjacent to the cold face due to low water velocity and poor water quality. In the rectangular mold, differential expansion of the wide and narrow faces of the mold led to periodic wall movement at the midface causing cycling in the mold and water temperature. Both effects completely dominated any potential influence of EMS on mold heat extraction. Cooling water velocities measured in separate experiments and the mold temperature profiles were input to a two-dimensional heat-flow model to establish mold heat-flux profiles. A steep taper of 2.6 %/m in the upper regions of the mold increased heat extraction compared to previously published heat-flux data in 0.8 %/m tapered-molds. However, due to the periodic wall movement in the rectangular mold, the heat flux declines to lower values periodically. The calculated heat flux profiles were employed in a one-dimensional transient heat flow model to predict superheat removal from the liquid pool under a variety of assumed fluid flow conditions. The major heat flow effect of EMS was inferred to be one of increasing the convective heat flow at the solidification front leading to earlier superheat extraction from the liquid steel. Solidification structures in billet samples collected during the trials were examined. The columnar-to-equiaxed transition in continuous casting takes place provided all the superheat is removed from the melt and there is a sufficient density of nuclei present in the pool. At superheats of <20° C in the tundish, high heat extraction in the mold and remelting of the mold generated nuclei facilitate the removal of the superheat well within the mold and the columnar-equiaxed transition is triggered after 10-15 mm of shell growth on both the inside and outside radius faces. At higher superheat in the tundish, the liquid pool leaves the mold with residual superheat which takes longer to remove because of the declining fluid flow. Even though all the superheat is removed lower in the machine, the columnar-equiaxed transition occurs only if dendrite debris generated in the vicinity of the mold has survived in their descent through the superheated liquid. The effect of carbon on the columnar-to-equiaxed transition appears to stem from its influence on facilitating dendrite arm remelting and the survival of the dendrite fragments till the pool reaches sub-liquidus temperature. EMS extracts more superheat by maintaining a steep temperature gradient in the thermal boundary ahead of the solidification front and achieves an earlier columnar-equiaxed transition. Electro-magnetic stirring appears not to affect either the average depth or the variation of depth of oscillation marks across a given face. However, the electro-magnetically driven flow dominates the turbulance at the meniscus due to the input stream and stabilizes a meniscus shape with the result that the oscillation marks are also of a well-defined shape unlike the unstirred billets. No influence of EMS was found on the formation of "hooks" or the fine equiaxed crystal zone near the surface. The influence of EMS on inclining the growing dendrites appears to not come into effect until about 1 mm of shell has formed. It appears that the existence of the momentum boundary layer where the velocity of the rotating steel falls to zero at the surface is the reason for the absence of the influence of EMS on the subsurface solidification. Rhomboidity and off-corner crack formation were found to depend, as reported by previous researchers, on mold distortion and its dynamic nature. The absence of any effect of EMS on these defects is due to its lack of effect on mold heat transfer and thus mold distortion. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate