• Journal of Korea Foundry Society
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• v.25 no.6
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• pp.254-258
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• 2005

Semisolid process is possible in any material system possessing a freezing range where the microstructure should consist of the nondendritic globular solid phase separated and enclosed by the liquid phase, referred to as semisolid slurry. There are two primary semisolid processing routes, thixocasting and rheocasting. Especially, rheocasting process has become a new focus in the field of semisolid process because of its many advantages such as no special billet required and possibility of in-house scrap recycling, compared with the thixocasting process. In-Ladle direct thermal control (DTC) rheocasting has been developed, based on the fact that there is slurry and mush transition in every molten metal and the transition, which normally occurs in the range of liquid traction of 0.1 to 0.6, could be controlled by controlling solid shape and relative solid-liquid interfacial energy. In this study, A356 Al alloy was investigated to verify In-Ladle DTC rheocasting for obtaining semisolid slurry. Modeling of heat transfer was carried out to investigate the effect of pouring temperature and ladle material, geometry and temperature and the simulation results were compared with the actual experiments.

• Journal of Pharmaceutical Investigation
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• v.35 no.3
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• pp.207-224
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• 2005

The objective of this study was to explore the principles of SUPAC-SS and its regulatory application in handling postapproval changes to nonsterile semisolid dosage forms. The types of postapproval changes that SUPAC-SS described were modifications in formulation (components and composition), batch size, manufacturing equipment & process, and the site of manufacturing. SUPAC-SS defined the levels of postapproval changes and what chemistry, manufacturing, and control tests should be conducted for each change level. The guidance also specified several occasions the manufacturers should perform in vitro release test (Franz cell diffusion test) and/or in vivo bioequivalence test. Finally, SUPAC-SS classified appropriate filing forms to be used in supporting postapproval changes. It was crystal clear that SUPAC-SS helped maintain the safety and quality of approved semisolid dosage forms when they were subject to certain postapproval changes. The availability of SUPAC-SS made contributions to reducing regulatory burdens of the industry, as well as expediting the postapproval process of regulatory agencies. This study also shed light on the background of relevant pharmaceutical sciences that the SUPAC-SS guidance adopted. Finally, the KFDA and the industry were strongly urged to implant a similar guidance in handling postapproval changes to semisolid dosage forms available in the Korean marketplace.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.10a
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• pp.148-151
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• 2004

Different kinds of feedstock of semisolid a356 aluminum alloy manufactured by EMS stirring only, inoculation of Al-5Ti-B only and combination of inoculation and EMS stirring were investigated. It is found that the grain size of these feedstock are $350{\mu}m$ for EMS casting only, $320{\mu}m$ for inoculation by Al-5Ti-B, and $100{\mu}m$ for the combination of EMS stirring and inoculation of Al-5Ti-B master alloys. The microstructure of the sample obtain by combination of inoculation and EMS system show the best homogeneousness and finest grains.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.668-671
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• 2004

The mechanics of the dendrite fragmentation is a very important aspect of grain refinement in rheocasting. In this work, the stress field of the dendrite stirred in the semisolid slurry was simulated by Metlab 6.0 software. The result shows that stress concentration at the root of the dendrite arms is great enough to cause plastic deformation though the agitation is moderate. Accordingly, dendrite fragmentation was suggested to be caused by fractured after fatigue erosion.

• Journal of Korea Foundry Society
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• v.27 no.4
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• pp.173-178
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• 2007

The bearing bracket, which has produced by the squeeze casting for the high strength in lightweight part of automobile, was developed by the rheocasting process using the H-NCM slurry. Compared with the squeeze casting, the rheocasting process has some merits such as shortening cycle-time, reducing total weight, and increasing productivity. In this study, partial feeding test was carried out by controlling plunger stroke length and compared with semisolid simulation. Optimal casting parameters such as injection speed and stroke variations were established. Sound products with integral microstructure were obtained by the H-NCM slurry and X-ray analysis also showed the integral condition throughout the entire parts.

• Journal of Korea Foundry Society
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• v.28 no.6
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• pp.256-260
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• 2008

The Hybrid-Lower Arm, which has been developed for reducing cost and weight, was produced by three kinds of casting methods such as the high-pressure diecasting(HPDC), the squeeze casting(SC), and the H-NCM rheocasting process. The important factors for development of the Hybrid-Lower Arm are the integral feeding in Al casting for heat treatment and the high joinning ratio between the steel part and the Al part. In this study, effects of these casting processes on the quality of Hybrid-Lower Arm were investigated. Compared with HPDC and squeeze casting, the rheocasitng process using the H-NCM slurry had some advantages in joinning different materials of Al and steel pipe without deforming the steel pipe. X-ray analysis also showed the poreless microstructure in semisolid Hybrid-Lower Arm. In the torsion stress test, semisolid Hybrid-Lower Arm was satisfied with the requirements of automobile standard.

• Journal of Korea Foundry Society
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• v.23 no.1
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• pp.40-46
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• 2003

Semisolid forming requires alloys with non-dendritic microstructure of the thixotropy. Recently, low pouring temperture method without stirring, i.e. liquidus casting has been found out new fabrication method of the semisolid metals. Effects of melt superheat and mold conditions on the globulization of primary Al of $AlSi_7Mg$ alloy were investigated in gravity casting process without stirring. The microstructures of primary Al as function of melt superheat and mold temperature show globular, rosette and dendritic shapes. The conditions for globular microstructure of primary Al were low melt superheat < 35 K and low mold temperature < 500 K. The thermal conditions for globular microstructure of primary Al were undercooled melt at early solidification stages and slow cooling < 0.6 K/s. It was found that the initial microstructure was maintained throughout the solidification and the globules of primary Al can be obtained by high nucleation of fine and spherical nuclei due to enhanced undercooling of melt.

• Journal of Korea Foundry Society
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• v.25 no.6
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• pp.249-253
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• 2005

The present study focuses on 7075 aluminum wrought alloy to investigate the potential industrial applications of thixoextrusion process. The microstructural evolution of 7075 aluminum wrought alloy for thixoextrusion has been investigated as a function of isothermal holding temperature and time in the partially remelted semisolid state. The results showed that the liquid fraction increased with increasing isothermal holding temperature and time while the average grain size was inversely proportional to isothermal holding temperature and time up to 5min. However, there was no big change of liquid fraction and average grain size with respect to isothermal holding temperature and time. The important fact that the liquid fraction and average grain size were almost uniform after 5 min holding time is considered very useful for thixoextrusion in terms of process control.

• Microbiology and Biotechnology Letters
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• v.17 no.5
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• pp.510-518
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• 1989

Most of orange peels are disposed from orange juice manufacturing process. Thus, our purpose is to utilize these orange peels as fermentation substrate. We have investigated culture conditions and factors influencing citric acid production by an isolated strain, Asp. niger. Citric acid production was much higher in semisolid culture than in submerged culture and the particle size of ground orange peels was favored at 20 mesh in semisolid culture. The optimal pH and temperature were 4.5-5.0 and 3$0^{\circ}C$ respectively and the temperature cycling at 35$^{\circ}C$ for 20 hrs durig exponential phase, 1$0^{\circ}C$ for 4 hrs and 3$0^{\circ}C$ during stationary phase showed higher citric acid production than did at fixed temperature, 3$0^{\circ}C$. The addition of NH$_4$NO$_3$0.2%, MgSO$_4$7$H_2O$ 0.1%, methanol 2.5%, ethanol 1.5%, to culture medium promoted citric acid production but the addition of trace metal ions as nutrients had not effect on the acid production in orange peel medium. Under the optimal culture conditions, maximum yield of citric acid was 80.4% in solid medium. Almost of all original components of citrus peel was consumed by Asp. niger during fermentation.

• Journal of Korea Foundry Society
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• v.24 no.6
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• pp.331-339
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• 2004

Melt-extrusion process, a metallic melt poured and solidified up to semisolid state in the container can be directly extruded through the die exit to form a product of bar shape without other intermediate processes. In this study, the fabrication characteristics of the process were evaluated with various process parameters, such as preheating temperature of extrusion dies, extrusion temperature and extrusion ratio. AI-Cu alloys were successfully extruded after squeezing out of liquid during melt-extrusion with smaller force compared to the solid extrusion. Soundly AI-Cu alloy bar was fabricated at the preheating temperature of $500{\sim}520^{\circ}C$. The range of extrusion temperature for soundly melt-extruded AI-Cu alloy bar was increased with increasing extrusion ratio. Mechanical properties of melt-extruded AI-Cu alloy bars were found change with Cu content of the melt-extruded bars due to the occurrence of segregation. The various extrusion temperature yielded equiaxed structure with a grains size about 200 ${\mu}m$.