• Journal of Korea Foundry Society
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• v.30 no.6
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• pp.210-216
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• 2010

The aim of this study is to characterize a thixoextruded 7075 Al wrought alloy bar in terms of its isotropic behavior through the optical microscope, mechanical test and electron back scattered diffraction. It is also discussed of the extrudability improvement for 7075 Al wrought alloy by thixoextrusion, with emphasis on controlling thixoextrusion parameters. Hot extrusion shows that the maximum extrusion pressure depends on their characteristics in terms of flow stress and hot workability. In the contrary, thixoextrusion demonstrates that the maximum extrusion pressure is almost uniform regardless of the experimental parameters, such as initial ram speed, die bearing length and thixoextrusion temperature. The hot extruded microstructures become elongated to extrusion direction, while the thixoextruded microstructures are isotropic and homogeneously distributed due to the existence of liquid phase between solid grains during the process. The grain refinement due to dynamic recrystallization during thixoextrusion has been also occurred. Subsequent recrystallization would lead to the strengthening of mechanical properties, as observed in the study. The important point is that the values of tensile, yield strength and elongation of the thixoextruded bar without plastic deformation are similar to those of the hot extruded bar with severe plastic deformation.

• Journal of Korea Foundry Society
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• v.19 no.5
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• pp.393-402
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• 1999

The reheating of the billet in the semi-solid state as quickly and homogeneously as possible is one of the most important aspects. From this point of view, an optimal design of the induction coil is necessary. The objective of inductive coil designsi a uniform induction heating over the length of the billet. The effect of coil length, diameter, the gap between coil surface and billet and axial position of the billet on temperature distribution of billet has been investigated. These design parameters have an important effectiveness on the electro-magnetic field. Therefore, in this study an optimal coil design to minimize electromagnetic ed effect will be proposed by defining the relationship between billet length and coil length. In particular, key point in induction heating process is focussed on optimizing the coil design with regard to the size of the heating billet and the frequency of induction heating system. After demonstrating the suitability of an optimal coil design through the FEM simulation of the induction heating process, the results of the coil design are also applied to the reheating process to obtain a fine globular microstructure. Its considered that the reheating conditions of aluminum alloys for thixoforging and a new CAE model of the induction heating process are very useful for thixoforging practitioners including induction heating ones.

• Journal of Korea Foundry Society
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• v.17 no.5
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• pp.472-479
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• 1997

The effect of size and mass fraction of SiC particulate on the fatigue and wear have been investigated for semi-liquid formed SiCp/AZ91HP Mg composites. In the study, different particulate sizes of 7, 20, $50 {\mu}m$ were prepared with various mass fraction for sample preparation. By tension-tension fatigue tests, whose procedures are standardized in ASTM standard 647E-93, the da/dN vs. ${\Delta}K$ curves were obtained. Also, the crack propagation paths were observed by optical microscope. As a result of wear test, specific wear loss is decreased with increasing mass fraction and particulate size. Specific wear loss of 30 mass% $50 {\mu}m$ SiC reinforced Mg composite is compared to SKD11.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1999.06a
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• pp.15-32
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• 1999

A relationship between stress and stain is very important to design a die to avoid defects of products during semi-solid forming process. Since the liquid will be of eutectic composition in alloys liquid segregation will result in significant or undesirable situation. The materials used in this experiment are A 357. A390, Al2024 alloys that is fabricated by the electro-magnetic stirring process from Pechiney in France. The compression test was performed by induction heating equipment and MTS. In order to prevent the liquid segregation these measured temperature would be useful to control of strain rate during compression test. The liquid segregation is controlled as change of the strain rate and solid fraction during the compression process, The characteristics of flow between solid and liquid phase considering liquid segregation is examined through the above experiments. In the case of medium and high volume fractions of solid the distribution of strain rate is calculated by using compression test data of semi-solid materials (SSM). The thixoforming experiments with the designed die are carried out successfully. The die filling patterns of SSM for variation of die temperature and pressing force have been investigated. The hardness of the thixoformed scroll products is evaluated in terms of the microstructure for each position.

• Journal of the Korean Society for Precision Engineering
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• v.16 no.9
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• pp.123-134
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• 1999

A new forming technology has been developed to fabricate near-net shape components by using aluminum alloys with globular microstructure. The estimations of filling characteristic in the forging simulation with arbitrarily shaped dies of SSM are calculated by finite element method with proposed algorithm. The proposed model and various boundary conditions for arbitrarily shaped die are investigated with the coupling calculation between the liquid phase flow and the solid phase deformation. The simulation processes with arbitrarily shaped dies are performed on the isothermal conditions and axisymmetric problems. To analyze the forging process simulation with SSM, new stress-strain relationship for semi-solid behaviour is described, and forging the liquid flow. Furthermore, For the purpose of getting net shape of SSM, it is important to be obtain a solid fraction in forging process with arbitrarily shaped dies. To produce a automotive part which have good mechanical properties, the filling pattern in accordance with die velocity and solid fraction distribution has to be estimated for arbitrarily shaped die.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.1
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• pp.44-55
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• 2001

The flow behavior of semi-solid materials (SSM) is required to assist the industrial application of thixoforming technology. Particularly, to reduce many lead times, many numerical analysis packages have been developed to simulate required metal forming processes. The objectives of the development of SEMI-FORM for thixoforming process design are to predict the effect of various process variables such as pressing force, die temperature, and die velocity. However, there have not been any reports which adapt these packages to the specific characteristics of SSM. SO, this paper presents an overview of the development of thixoforming simulator of SEMI-FORM. The solver and post-processor of SEMI-FORM S/W for an automated thixoforming process design with arbitrarily shaped die are composed of FORTRAN Power Station 4.0 and Visual Basic 5.0, respectively. This developing SEMI-FORM S/W would be very useful for thixoforming practitioners and engineers to select the optimal process conditions to produce automotive parts with high quality.

• 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 Radioactive Waste Society Conference
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• 2004.06a
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• pp.304-304
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• 2004

차세대관리 종합공정은 사용후핵연료를 안전하고 효율적인 관리를 위하여 제시된 공정으로 이 공정을 이용하여 사용후핵연료를 금속으로 전환하고 고발열성 핵종(CS, Sr)을 효율적으로 제거할 경우 사용후핵연료의 부피, 발열량 및 방사선의 세기를 최대 1/4까지 감소시키고, 처분용기의 소요량과 처분장의 소요면적을 1/2 이상으로 축소함으로서 처분 안정성과 경제성을 높일 수 있다. 차세대관리 종합공정은 용융염 매질에서 사용후핵연료를 처리하는 건식핵연료주기 기술로서 중심적으로 연구개발을 추진하고 있는 공정기술의 일부이다.(중략)

• 한국신재생에너지학회:학술대회논문집
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• 2008.10a
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• pp.142-144
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• 2008

본 논문은 정부의 연구 지원에 의해 참여기업인 (주)동명알피에프에 설치되고 있는 상용인 반연속식 로터리 킬른형 유화 장치 개발 현황에 대해 논하고자 한다. 본 공정의 특징은 지자체에서 수거된 EPR 종말품을 대상 원료로 하였고, 2기의 병렬로 설치된 킬른형 반응기를 사용하여 주기적 처리에 의해 효율적인 동시에,처리량을 크게 향상시켰다.이 반응 시스템은 용융 및 열분해가 동시에 이루어짐에 따라 공정은 단순하지만 생성 오일의 질이 저하되어 후단에 오일 고급화 공정과 정제 공정이 설치되어 최종 제품의 질을 향상시켰다.이에 대한 전반적인 현황과 공정 기술에 대해 언급되었다.

• Fire Science and Engineering
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• v.23 no.5
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• pp.196-205
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• 2009

Electric mosquito repellent mats can be ignited by damage of cables, partial disconnection, overload. tracking and so on. In this study, we examined the structure of mosquito repellent mat, positive temperature coefficient(PTC) thermistor, used for heating element and phenomenological characteristics of remains, obtained on the scene of fires. After reappearance ignition test of PTC thermistors, we did comparison analysis them. And we could confine that the feature of heating plate and the shape of bursting were same.