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《International Journal of Cast Metals Research》2013,26(6):328-334
AbstractIn this work the authors show how to build a semi-industrial scale macrothermal analysis experimental apparatus for low pressure aluminium casting AA 354 with quasi-unidirectional solidification. Several thermocouples were connected to a multichannel electronic device allowing a sampling rate up to 10 Hz; the thermocouples were installed in the mould at different locations to acquire the discontinuous cooling curves at those same locations.With this type of experiment and appropriate mathematical procedures it was possible to build a reasonable response surface T?=?f(x, t) and the respective derivatives: ?T/?t and ?T/?x. Exponential polynomials were applied for modelling the curves and linear interpolation to relate the several cooling curves. Mathematical tools applied to the modelled curves allowed the authors to identify different solidification events and correlate them with the specific thermal gradient, cooling conditions and solidification fronts phenomena such as columnar to equiaxed transition of α aluminium grains. Growth velocity of proeutectic aluminium α and eutectic fronts were also determined. 相似文献
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Robert Kabbert Karsten Kotte Birgit Cech und Herbert Kunzek 《Zeitschrift für Lebensmitteluntersuchung und -Forschung A》1996,203(6):512-516
Ethanol pre-treated apple parenchyma cells are dried in a laboratory vacuum dryer. Various ethanol contents (75 to 95% m/m) and moisture contents (2 to 15 g ethanol-water-mixture per g dry mass) of the cells were adjusted before drying and the influence of these factors on drying behaviour as well as the related structural changes are studied. The initial ethanol content was found to have a significant influence on both, drying behaviour and macrostructure of the dried material. In the case of a low initial value, the ethanol content during drying already drops at moisture contents of about 0.5–1.5 g/g. As a consequence the residual particle moisture consists mainly of water at the end of drying. In contrast to high initial ethanol contents, cells at a low initial ethanol content become strongly deformed on drying. The porosity of the dried material also decreases in the latter case, relatively large and stable aggregates are formed and the water binding capacity of the dried product has diminished on a large scale. The initial moisture content influences the drying behaviour especially on applying low initial ethanol contents. If the initial moisture content is reduced the drop of the ethanol content is shifted towards the end of the drying process. The influence of initial moisture content on macrostructure, however, was found to be small compared with the effect of the initial ethanol content. 相似文献
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The objective of this work is to present the relationship between macro- and microstructure of the rheocast alloy A356 obtained by electromagnetic stirring. There is a direct relationship between grain size (macrostructure) and globule size/shape factor (microstructure): the smaller the grain size, the smaller are the globule size and shape factor. The A356 alloy was processed in a simple device, which constitutes a semi-continuous casting system, coupled with a power source. The A356 (Al–7.0 wt.%Si) alloy was electromagnetically stirred under different cooling rates (controlled by the casting speed of 1 and 3 cm/s) and different power levels (600–1200 W). Ingots with 45 mm of diameter and 3 kg with very refined and homogeneous rheocast structures were obtained. The direct relationship between macro- and microstructures of the ingots were exploited. A quality index is proposed to better characterise the rheocast structure. 相似文献
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T. A. Costa A. L. Moreira D. J. Moutinho M. Dias I. L. Ferreira J. E. Spinelli 《Materials Science & Technology》2015,31(9):1103-1112
The roles of growth direction and Si content on the columnar/equiaxed transition and on dendritic spacings of Al–Cu–Si alloys still remain as an open field to be studied. In the present investigation, Al–6 wt-%Cu–4 wt-%Si and Al–6 wt-%Cu alloys were directionally solidified upwards and horizontally under transient heat flow conditions. The experimental results include tip growth rate and cooling rates, optical microscopy, scanning electron microscopy energy dispersive spectrometry and dendrite arm spacings. It was found that silicon alloying contributes to significant refinement of primary/secondary dendritic spacings for the upward configuration as compared with corresponding results of the horizontal growth. Experimental growth laws are proposed, and the effects of the presence/absence of solutal convection in both growth directions are discussed. 相似文献
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The macroscopic grain structure of a 234 t steel ingot was simulated by using cellular automaton and finite element method provided by ProCAST. The growing speed coefficient of Kurz–Giovanola–Trivedi model was modified to reflect the growing process of grains. Chilled fine grains, columnar grains and coarse equiaxed grains were obtained from surface to core of the ingot, which were roughly in agreement with the measured ones. The influences of the nucleation and growth parameters were investigated. It was found that the relationship between nucleation and growth determines the macrostructure profile. An index, the ratio of growing speed over the nucleated sites at certain undercooling was proposed to estimate the macrostructure tendency. 相似文献