• Composites Research
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• v.13 no.4
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• pp.19-32
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• 2000

The fabrication process of particulate metal matrix composites(PMMCs) with homogeneous distribution of reinforcement and reheating for thixoforming has been studied. Both of eletro-magnetic stirring and mechanical stirring were used to fabricate particulate metal matrix composites(PMMCs) for variation of particle size. The electrical and mechanical processing conditions for fabricating PMMCs are also suggested. For thixoforming of PMMCs, fabricated bi1lets are reheated by using the designed optimal coil with as function of length between PMMC billet and coil surface, and coil diameter and billet. The effect of reinforcement distribution according to variation of billet temperature were investigated with solid fraction theory with a function of matrix alloy and volume fraction of reinforcement.

• Journal of the Korean Society of Food Science and Nutrition
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• v.37 no.8
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• pp.1049-1057
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• 2008

The purpose of this study was to microbiologically evaluate common foods and preparation processes in three large (over 100 pyeong) western-style restaurants in Daegu. Microbiological testing was conducted for pathogens including E. coli, Salmonella spp., Listeria monocytogenes, Staphylococcus aureus, E. coli O157:H7, Vibrio parahaemolyticus, and Bacillus cereus, as well as total plate count and coliforms. Food samples selected for testing represent common menu items and preparation processes. These samples included: 1) hamburger steak (cooking process), 2) mashed potatoes (reheating process), and 3) salad (non-heating process). The results showed that E. coli and S. aureus were detected in the raw ground beef used to prepare hamburger steak, but they were not detected after cooking at $82{\sim}86^{\circ}C$, 10 min. Microbiological quality of the mashed potatoes was better after reheating than during storage in a refrigerator after cooking. Total plate count and coliforms increased, and E. coli was detected in the salad ingredients stored in the refrigerator before serving. In order to serve foods of good microbiological safety and quality in western-style restaurants, standard cooking and reheating temperatures must be maintained during the cooking and reheating processes, and sanitation standard operating procedures must be followed for washing and storage of non-heated and refrigerated menu items.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.10a
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• pp.180-183
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• 1997

The forming process of metal matrix composites by the die casting and squeeze casting process are limited in size and dimension in term of final parts without machining. The thixoforming process for metal matrix composites has numerous advantages compared to die casting, squeeze casting and compocasting. The characteristics of thixoforming process can decrease the liquid segregation because of he improvement in fluidity in a globular microstructure state and utilizes flow without air entrapment. Therefore, in order to obtain the sound parts of metal matrix composites by using thixoforming process which as co-existing solidus-liquidus pahse, it si very important to obtain reheating condition. However, for he thixoforming process, the billet with the desired volume fraction must be heated to obtain a uniform temperature distribution over the entire cross-sectional areas. To obtain the reheating conditions of composites, the particulate reinforced metal matrix composites for thixoforming were fabricated by combined stirring process which is simultaneously performed with electro-magnetic stirring process which is simultaneously performed with electro-magnetic stirring and mechanical stirring process.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1999.03b
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• pp.195-198
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• 1999

For the thixoforming process beside an existing solidus-liquidus interval, the reheating conditions to obtain the globular microstructure are very important. It relies on the control of globular microstructure of semi-solid alloys that contain non-dendritic particles. To obtain the globular microstructure in cross section of billet, the optimal design of the induction coil is necessary. Therefore, in this paper the optimal coil design to minimize electromagnetic end effect will be proposed. The results of coil design were also applied to the reheating process to obtain a fine globular microstructure. Finally, reheating data base of aluminum alloys for thixoforming and FEM model for induction heating based on the optimal coil design have been proposed.

• Journal of Korea Foundry Society
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• v.27 no.6
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• pp.263-265
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• 2007

틱소오 다이캐스팅을 위하여는 재가열 시 고상율을 제어할 때 구상화 조직을 가진 소재가 필요하다. 현재까지 전자교반법에 의하여 제조한 빌렛을 이용하여 틱소오 다이캐스팅에 이용하였다. 그러나 제품의 원가절감과 소재개발 측면에서 틱소오 다이캐스팅을 위한 압출소재의 개발 공정을 설명하고자 한다. 재가열시 압출비가 구상화 조직에 미치는 영향과 기계적 성질 사이의 관계를 규명하였다.

• 축산식품과학과 산업
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• v.8 no.1
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• pp.58-59
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• 2019

• 기계와재료
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• v.23 no.3
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• pp.16-29
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• 2011

결정 합금 대비 비정질 합금은 높은 경도를 갖기 때문에 마모 저항성도 좋고 내부 식성 등 환경에 대한 저항성도 월등하며, 또한 과냉된 액상 상태까지 재가열하게 되면 낮은 점성도를 갖게 되므로 복잡한 3차원적인 형상을 가지는 부품을 환경에 대한 저항성, 피로 저항성, 강도 및 경도 등을 모두 고려하여 높은 정밀도를 가지고 제조하는 것이 가능하므로 우수한 물성을 갖는 구조 및 기능성 재료로의 다양한 응용이 타진되고 있다. 이러한 비정질 합금의 변형 거동에 대한 연구는 대부분 유리 천이 온도 이하에서의 전단 및 파단에 이르는 이른바 불균일 변형(Inhomogeneous Deformation) 거동에 대한 이해를 위한 실험 및 해석적 연구에 집중되어 왔다. 반면 상업화의 기반이 되는 고상 기반 2차 정형 성형은 과냉 액상 영역에서의 구조 완화 및 결정화롤 대표되는 미세 구조 제어 균일 변형(Homogeneous Deformation)에 대한 이해 없이는 불가능하므로, 이러한 관점에서 비정질 합금 특유의 점성 유동 특성을 이용한 균일 변형 응용 예시 및 미세구조 변화 연계 해석 기술의 현황을 소개하고자 한다.

• Transactions of Materials Processing
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• v.7 no.3
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• pp.215-224
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• 1998

A semi-solid forming has a lot of advantages compared to the die casting. squeeze casting and conventional forging. therefore, semi-solid forming process is now becoming industrial interest for the production of metal components and metal matrix composites. However the material behaviour in the semi-solid temperature range is not sufficiently known although it controls the whole process through forces and geometry evolutions because the behaviour of metal slurries is complex. The semi-solid materials(SSMs) fabricated under electric-magnetic stirring condition is necessary to be applicated in forming process. A reheating conditions were studied with the reheating time holding time and reheating temperatures. The microstructure of SSM(specimen size : d39${\times}$h85) at the condition of heating time 10min and heating temperature 590${\circ}C$ is the most globular and finest one. The microstructure of SSM(specimen size : d76${\times}$h60) reheated under the three step reheating conditions is most globular and finest.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2001.10a
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• pp.236-239
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• 2001

In thixoforming, the globule size is determined by the hoding time of last reheating stage. In this study, some experiments to investigate the relationship between the mechanical properties and the holding time were performed A357, A390 and A3l9 alloys are used in this study. This paper shows the evolution of the microstructure according to the holding time of last reheating stage. Tensile test was performed for each reheating condition to examine the effect of globule size.

• Transactions of Materials Processing
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• v.11 no.2
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• pp.155-164
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• 2002

One of the important steps on semi-solid forming Is the reheating process of raw materials to the semi-solid state. This Process is not only necessary to achieve the required SSM billet state, but also to contro1 the microstructure of the billet. In reheating process, the globule size is determined by the holding time of last heating stage. Therefore, some experiments to investigate the relationship between the mechanical properties and the holding time in the last heating stage was performed. The alloys used in this experiment were 357, 319 and A390 alloys. The experiments of reheating were performed by using an Induction heating system with the capacity of 50kw. This paper shows the evolution of the microstructure according to the holding time of last reheating stage. Furthermore, to evaluate the effect of globule size controlled by holding time in last heating stage uniaxial tension test was performed. The strain-stress curves were plotted according to the holding time.