• Journal of Korea Foundry Society
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• v.15 no.2
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• pp.184-193
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• 1995

Effects of process parameters during thixocasting, such as solid volume fraction, mold temperature and extrusion ratio, on the mold filling behaviour and fluidity of Mg alloy(AZ91D) have been investigated. The semi-solid ingot held for 60 minutes at the semi-solid temperature range did not contain the equilibrium volume fraction of solid as expected from the phase diagram. Therefore, in order to obtain the desired solid fractions, and to suppress the exaggerated grain growth during heating, it was required to heat the ingot rapidly up to the temperature $10^{\circ}C$ higher than the semi-solid temperature suggested from the phase diagram for a specific volume fraction of solid. The experimental results show that mold filling behaviour and fluidity can be improved with the use of the higher mold temperature and the lower volume fraction of solid, but remain nearly unaffected by the change of extrusion ratio.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.10a
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• pp.865-869
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• 1997

In recent years, there has been increasing demand of ultra-fine grain graded cemented tungsten carbide material with high hardness and toughness which is used as high speed cutting tool for development in semiconductor, electronics and die/mold industry, which bring into limelight high-precision, high-efficient machining of sculptured surfaces. This paper deals with the performance of variation in the ultra-fine grain graded cemented tungsten carbide material such as grain size, hardness and density varied according to the volume of added elements, Co or TaC, and he changing of mixing, sintering process. Also, the performance of developing material with uniformed grain size of 0.5${\mu}{\textrm}{m}$ is compared with other domestics' & foreign companies' with analyzing and cutting performance testing.

• Korean Journal of Materials Research
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• v.32 no.3
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• pp.139-145
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• 2022

Reheat treatment process of mold is necessary when partial machining of the mold is required, such as shape correction for an existing mold. If defects such as cracks or significant deterioration of mechanical properties of the mold occur during reheat treatment, it is impossible to reuse the mold. In this study, reheat treatment was performed up to two times for STD11 tool steel, and microstructure and mechanical properties according to the reheat treatment were evaluated. Carbide fraction and grain size of prior austenite were almost unchanged after the reheat treatment. Hardness and impact toughness increased significantly after QT treatment, and these properties were maintained without significant change even after the reheat treatment. It is concluded that up to two iterations of reheat treatment does not cause deterioration of properties of STD11 tool steel. Based on these results, a mold for a face-lifted front bumper was manufactured through machining and reheat-treating of an existing mold.

• Design & Manufacturing
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• v.10 no.2
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• pp.34-38
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• 2016

In this paper, a transversely isotropic behavior of AZ31 Mg alloy produced by equal-channel angular pressing (ECAP) process was investigated through tensile test and microstructure observation. The effects of initial ECAP pass number on the anisotropic behavior and mechanical properties of the Mg alloy are evaluated after conventional direct extrusion test, which are carried out at a temperature of $200^{\circ}C$. As a result of the tensile test in three directions ($0^{\circ}$, $45^{\circ}$, and $90^{\circ}$ to the extrusion direction of the sheet) at room temperature, elongation of as-extruded AZ31 alloy(ECAP for 0 pass) showed an unusual anisotropic behavior depending on the extrusion direction although the yield strength and tensile strength are similar to the ECAPed AZ31 alloy. After ECAP for 4 passes at $200^{\circ}C$, microstructural observations of ECAPed magnesium alloy showed a significant grain refinement, which is leading to an equiaxed grain structure with average size of $2.5{\mu}m$. The microstructures of the extruded billet are observed by the use of an electron back-scattering diffraction (EBSD) technique to evaluate of the influence on the grain refinement during extrusion process and re-crystallization mechanism of AZ31 Mg alloy.

• Journal of Korea Foundry Society
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• v.17 no.3
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• pp.237-244
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• 1997

This study has been carried out to investigate into the influence of solidification conditions mold on the structure and mechanical properties of Al-5wt%Mg alloy by metallic mold casting. The percentage of equiaxed grain of Al-5wt%Mg alloy castings increased both when pouring temperature decreased and when the low part or bottom of metallic mold was cooled. The hardness was checked and showed that hardness of outside in the castings was higher than that inside, and that it is the highest at the pouring temperature of $680^{\circ}C$. The castings had the highest U.T.S. and elongation when the bottom of metallic mold was cooled. At the same pouring temperature, the structure of castings was changed as the position of cooling parts of metallic mold was varied. When the castings were solidified through cooling of the bottom of the metallic mold, the morphology of Fe intermetallic compound has tendency to change to a Chinese script and the U.T.S. and elongation of Al-5wt.%Mg alloy castings was increased.

• Journal of Korea Foundry Society
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• v.36 no.5
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• pp.153-158
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• 2016

The lost foam casting process was used to fabricate Al-Si-Mg cast specimens, and the effects of the chemical composition and process variables on the tensile properties and the mold filling ability were investigated. Some porosity formation was observed in thick sections of the casting and better tensile properties were obtained for thin sections, presumably because of their lower porosity and the higher cooling rate. Tensile properties were not clearly enhanced by grain refining treatment with Ti; however, the elongation was significantly improved by Sr modification of the Al-Si-Mg alloy. The mold filling distance was generally proportional to the pouring temperature of the melt, and the distance was also increased by the addition of Ti.

• Mycobiology
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• v.44 no.2
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• pp.67-78
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• 2016

Rice contaminated with fungal species during storage is not only of poor quality and low economic value, but may also have harmful effects on human and animal health. The predominant fungal species isolated from rice grains during storage belong to the genera Aspergillus and Penicillium. Some of these fungal species produce mycotoxins; they are responsible for adverse health effects in humans and animals, particularly Aspergillus flavus, which produces the extremely carcinogenic aflatoxins. Not surprisingly, there have been numerous attempts to devise safety procedure for the control of such harmful fungi and production of mycotoxins, including aflatoxins. This review provides information about fungal and mycotoxin contamination of stored rice grains, and microbe-based (biological) strategies to control grain fungi and mycotoxins. The latter will include information regarding attempts undertaken for mycotoxin (especially aflatoxin) bio-detoxification and microbial interference with the aflatoxin-biosynthetic pathway in the toxin-producing fungi.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2007.11a
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• pp.79-82
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• 2007

Recently, the use of ALC has became increasingly popular. ALC is a unique building material. Because of its cellular nature, it is lightweight, self-insulating, sound and fireproof, as well as insect and mold resistant. Furthermore, ALC is free of VOCs and various fibers associated with wood and glass wool construction. However, ALC have high water absorption, low compressive strength and popout the origin of the low surface strength in its properties. These properties make troubles under construction such as cracking and popout. Thus, this study is to improve the fundamental strength by controls of increasing of admixtures, and grain size. Admixtures make use of metakaolin, silica fume, sodium silicate and sodium hydroxide. From the test result, the ALC using admixture have a good fundamental properties compared with plain specimen. Compressive strength, specific strength and abrasion's ratio were improved depending on increasing admixtures ratio's, and grain size.

• Korean journal of food and cookery science
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• v.31 no.3
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• pp.264-279
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• 2015

The principal objective of this study was to evaluate the effects of the addition of sourdough to various grain flours in bread, specifically, in regards to the physicochemical characteristics of bread dough, sensory evaluation, and bread storage. As the incubation time of sourdough increased, the total titratable acidity increased. Viable yeast counts of sourdough increased consistently until the third day, while lactic acid bacteria counts increased until the second day. The weight of breads containing sourdough made with rye flour, strong flour, and Korean wheat flour were higher than that of the control. However, the height, volume, and specific volume of control were higher than those of the groups with sourdough made with various grain flours. The pH of breads containing sourdough was lower than that of the control, while the total titratable acidity and moisture content were higher than those of the control. In analyzing the visible mold colony during the five days of storage at $30^{\circ}C$, mold growth in breads containing sourdough made of Korean wheat flour, barely flour, and rye flour was retarded. In the color measurement, the L values of the control and bread containing sourdough made with barley flour were higher than that of the other groups after five days. The a value of bread containing sourdough made of rye flour was higher, and the b values of breads containing sourdough made of Korean wheat flour, barley flour and rye flour were higher than those of the other groups after five days. The hardness of breads containing sourdough increased as storage time increased, where as breads containing sourdough made of Korean wheat flour, Korean whole wheat flour, and rye flour revealed no significant differences with control group. Sensory evaluation scores in terms of after swallowing, taste, and overall preference of bread containing sourdough made of Korean wheat flour was higher than those of the control group.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.12 no.3
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• pp.120-125
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• 2002

Si-wafers for solar cells were cast in a size of $50{\times}46{\times}0.5{\textrm}{mm}^3$ by vacuum casting method. The graphite mold coated by BN powder, which was to prevent the reaction of carbon with the molten silicon, was used. Without coating, the wetting and reaction of Si melt to graphite mold was very severe. In the case of BN coating, SiC was formed in the shape of tiny islands at the surface of Si wafer by the reaction between Si-melt and carbon of the graphite mold on the high temperature. The grain size was about 1 mm. The efficiency of Si solar cell was lower than that of Si solar cell fabricated on commercial single and poly crystalline Si wafer. The reason of low efficiency was discussed.