• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 추계학술대회 논문집
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• pp.111-114
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• 2005

Experimental and numerical studies were carried out in order to investigate the processability and the transcriptability of the injection molding of micro structures. For this purpose, we designed a mold insert having micro rib patterns on a relatively thick base part. Mold insert has a base of 2mm thickness, and has nine micro ribs on that base plate. Width and height of the rib are $300{\mu}m\;and\;1200{\mu}m$, respectively. We found a phenomenon similar to 'race tracking', due to 'hesitation' in the micro ribs. As the melt flows, it starts to cool down and melt front located in the ribs near the gate cannot penetrate further because the flow resistance is large in that almost frozen portion. When the base is totally filled, the melt front away from the gate is not frozen yet. Therefore, it flows back to the gate direction through the ribs. Consequently, transcriptability of the rib far from the gate is better. We also verified this phenomenon via numerical simulation. We further investigated the effects of processing conditions, such as flow rate, packing time, packing pressure, wall temperature and melt temperature, on the transcriptability. The most dominant factor that affects the flow pattern and the transcriptability of the micro rib is flow rate. High flow rate and high melt temperature enhance the transcriptability of micro rib structure. High packing time and high packing pressure result in insignificant dimensional variations of the rib. Numerical simulation also confirms that low flow rate causes a short shot of micro ribs and high wall temperature helps the filling of the micro ribs.

• 공업화학
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• 제19권4호
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• pp.397-401
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• 2008

본 연구에서는 용암석상의 무기물인 퍼라이트의 팽창에 관한 비등온 상태 전산 모사를 수행하여 실험 결과와 비교하여 모델의 유효성을 검증하고자 하였다. 기존의 연구를 기반으로 에너지 수지식을 적용하였고 이에 따른 물성값의 온도에 따른 변화를 적용하였다. 비등온 팽창에서 버블 부피의 변화, 수분 증발에 의한 변화 그리고 열 플럭스의 버블내로의 유입에 따라 버블의 온도 변화를 고려하였으며 이에 따른 용융 퍼라이트의 온도 분포 형성 또한 고려되었다. 이의 결과로 1100 K 이하에서 5% 이내의 정확성을 가지는 예측 모델 및 동특성 해석 코드를 개발하였고 1100~1400 K 범위에서도 7% 이내의 오차를 가지고 팽창도를 예측할 수 있었다.

• 한국염색가공학회지
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• 제34권3호
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• pp.197-206
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• 2022

The purpose of this study was to confirm the optimal spinning conditions for PLA (Polylactic acid) as a fiber forming polymer. According to the melt spinning test results of PLA, the optimal spinning temperature was 258℃. However, it needs to note that relatively high pack pressure was required for spinning at 258℃. At an elevated temperature, 262℃, mono filament was broken easily due to hydrolysis of PLA at a higher temperature. In case of fiber strength, it was confirmed that the draw ratios of 2.7 to 3.3 were optimal for maximum strength of melt spun PLA. Above the draw ratio, 3.3, the strength of the PLA fibers was lowered. It was presumed that cleavage of the PLA polymer chain over maximum elongation. The heat setting temperature of GR (Godet roller) showed that the maximum strength of the PLA fibers was revealed around 100℃. The degree of crystallinity and the strength of the PLA fibers were decreased above 100℃. The optimal take-up speed (Spinning speed) was around 4,000m/min. Thermal analysis of PLA showed 170℃ and 57℃ as Tm (melting temperature) and Tg (glass transition temperature), respectively.

• 한국결정성장학회지
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• 제24권4호
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• pp.158-163
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• 2014

Mineral fiber, or be called mineral wool when it assembles in large amounts, is a kind of wide applied man-made material with excellent thermal and acoustic insulation properties. In this work, mineral fiber was produced via melt spinning method by using iron blast furnace slag as raw material. Two critical experimental parameters for fabrication were investigated: melt pouring temperature and rotating speed of spinning wheels. The mineral fiber produced under the condition of melt pouring temperature $1500^{\circ}C$ and spinning speed 4000 rpm, showed the smoother surface and most quality, while the others had rough surfaces or with heavy shots. In general, mineral fibers with the size in the range of $12{\sim}49{\mu}m$ in diameter and 8~130 mm in length can be fabricated by this method, and the production rate is more than 34 wt.%, which could be up to 57 wt.% at maximum.

• 한국주조공학회지
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• 제23권1호
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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.

• 한국초전도ㆍ저온공학회논문지
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• 제24권3호
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• pp.35-40
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• 2022

To fabricate large grain YBCO bulk superconductors by melt process, Sm123 single crystal with a high melting point are mostly used as seeds. However, it also uses Y123 film deposited on MgO single crystal substrate. This study investigated the growth behavior of the Y123 grain during a melt process when single grain YBCO bulk was used as a seed. Single grain Y123 bulk was grown when the seed size was small. When the seed size was relatively large, multiple grains were grown but the grains were still large. Y123 seed crystal was completely decomposed during high temperature anneal at 1040℃ and new Y123 crystals were nucleated during a slow cooling stage below a peritectic temperature. Thereafter, newly formed Y123 crystals from the seed area are thought to grow into the Y1.8 powder compact. The crystallographic orientations of newly nucleated Y123 grains are independent of the crystallographic orientation of Y123 seed. It is thought that the crystallographic orientation of newly nucleated Y123 crystal can be controlled by using Y211-free Y123 single crystal as a seed of homo-seeding melt growth.

• 접착 및 계면
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• 제7권3호
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• pp.16-25
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• 2006

내열성 및 투습방수기능을 가진 신발용 직물 및 부직포를 제조하기 위하여 스크린 방식으로 공정조건을 검토하고 투습방수 필름을 라미네이팅 한 후, 최종제품의 물성을 평가하였다. 결과는 다음과 같다. 열가소성 핫 멜트와는 달리 반응형 폴리우레탄 핫 멜트는 작업 이후에 적정한 내열성을 보유하는 것으로 나타났다. 최적의 용융접착 공정조건은 다음과 같다 ; 드럼 온도 $95^{\circ}C$, 호스 온도 $97^{\circ}C$, 공급파이프 온도 $100^{\circ}C$, 스크린 온도 $105^{\circ}C$이고, opposite roller의 압력은 $1kgf/cm^2$, laminating roller의 압력은 $3kgf/cm^2$이며, 가공속도는 15 m/min이다. 투습도는 필름의 두께가 증가함에 따라 투습도는 감소하였으나, 내수도는 증가하였고, 공기투과도는 필름의 영향이 지배적이었다.

• 열처리공학회지
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• 제27권4호
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• pp.180-184
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• 2014

In order to make clear relationship between high temperature tensile properties and fine microstructure of rapidly solidified cast-type Ni-base superalloys without heat treatment required for consolidation process, tensile test was carried out by changing strain rate from $5{\times}10^{-5}s^{-1}$ to $2{\times}10^{-2}s^{-1}$ and test temperature from $900^{\circ}C$ to $1050^{\circ}C$ using IN738LC and Rene'80 melt-spinning ribbons by twin roll process which were superior to ribbons by single roll process from the viewpoint of structure homogeneity. The dependence of tensile strength on strain rate and test temperature was studied and strain rate sensitivity, m, were estimated from tensile test results. From this study, it was found that tensile strength was influenced by ${\gamma}^{\prime}$ particle diameter, test temperature and strain rate, and m of ribbons exhibited above 0.3 over $950^{\circ}C$.

• Nuclear Engineering and Technology
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• 제45권1호
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• pp.21-28
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• 2013

The flow and heat transfer characteristics of the ex-vessel core melt (corium) were investigated using a commercial CFD code along with the experimental data on the spreading of corium available in the literature (VULCANO VE-U7 test). In the numerical simulation of the unsteady two-phase flow, the volume-of-fluid model was applied for the spreading and interfacial surface formation of corium with the surrounding air. The effects of the key parameters were evaluated for the corium spreading, including the radiation, decay heat, temperature-dependent viscosity and initial temperature of corium. The results showed a reasonable trend of corium progression influenced by the changes in the radiation, decay heat, temperature-dependent viscosity and initial temperature of corium. The modeling of the viscosity appropriate for corium and the radiative heat transfer was critical, since the front progression and temperature profiles were strongly dependent on the models. Further development is required for the code to consider the formation of crust on the surfaces of corium and the interaction with the substrate.

• 폴리머
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• 제29권6호
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• pp.565-570
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• 2005

용융 점도 조절에 의한 나일론6(N6)의 melt impregnation공정에서의 용융가공 특성에 대하여 고찰하여 보았다. N6의 용융 점도를 조절하기 위하여 calcium stearate(CaST)를 윤활제로 사용한 결과, 1 wt$\%$의 윤활제의 첨가에 의하여 용융 점도가 감소함을 알 수 있었다. 아울러 폴리카프로락톤(PCL)을 N6에 반응 용융 블렌딩하여 N6의 용융 점도를 낮출 수 있었으며 phenyl phosphite(PP)와 diphenyl phosphite(DPP)를 첨가하여 블렌딩 시 상호에스테르 교환반응을 증가시켜 추가적인 용융 점도 감소를 확인하였다. 이러한 방법들은 N6의 고온 가공의 문제점으로 지적되는 열안정성 저하를 최소화하면서 melt impregnation 공정에서 필수적인 저점도 가공을 가능하게 할 수 있을 것으로 사료된다.