• 대한금속재료학회지
• /
• 제49권4호
• /
• pp.298-303
• /
• 2011

Mg-23.5 wt%Ni-xwt%Cu (x = 2.5, 5 and 7.5) samples for hydrogen storage were prepared by melt spinning and crystallization heat treatment from a Mg-23.5 wt%Ni-5 wt%Cu alloy synthesized by the gravity casting method. They were then ground under $H_2$ to obtain a fine powder. Among these samples the Mg-23.5Ni-2.5Cu sample had the highest hydriding and dehydriding rates after activation. The Mg-23.5Ni-2.5Cu sample absorbed 3.59 and 4.01 wt%H for 10 and 60 min, respectively, at 573K under 12 bar $H_{2}$. The activated 88(87.5Mg-10Ni-2.5Cu)-$5Nb_{2}O_{5}-7NbF_{5}$ sample absorbed 2.93 wt%H for 10 min, and 3.14 wt%H for 60 min at 573K under 12 bar $H_{2}$.

• 한국주조공학회지
• /
• 제41권6호
• /
• pp.528-534
• /
• 2021

본 연구는 Al-Mg-Si 합금에서 Cu가 첨가 후 자연시효와 인공시효에 따른 제2상 석출 반응이 합금의 열확산도 및 경도에 미치는 영향을 연구하였다. 연구에 사용된 Al-0.4Mg-0.2Si 합금과 Cu를 0.6 wt%, 1.0wt% 추가한 Al-Mg-Si-Cu 합금을 각각 중력 주조로 제작하고 열확산도 경도를 측정하고 석출 반응을 확인하기 위해 열량 분석을 실시 하였다. Al-Mg-Si 합금에 첨가된 Cu는 Q'상 및 θ'상과 같은 강화상 형성에 참여하여 합금의 경도와 고온 열확산도를 향상시켰다. 한편, 자연시효 시간 증가는 Al-Mg-Si-Cu 합금의 열확산도에는 큰 영향을 미치지 않았으나, 경도를 하락시키는 것으로 확인되었다.

• 한국산학기술학회논문지
• /
• 제22권2호
• /
• pp.593-601
• /
• 2021

축류팬은 여러 산업분야에서 사용되며, 환기 및 제연을 목적으로 사용하는 송풍기의 핵심 요소이다. 유체 운동을 이용하는 축류팬의 연구는 공력성능에 대한 연구가 많이 진행되어 왔다. 본 연구 대상은 100마력의 송풍기에 사용되는 축류팬이며, 직경 1800 mm의 대형 송풍기이다. 송풍기의 축류팬은 블레이드, 허브, 허브 캡, 보스로 구성되어 있으며, 블레이드와 허브는 중요한 구성부품이다. 공력성능에 많은 영향을 미치는 블레이드에 대한 설계는 공력성능 예측 프로그램을 이용해 3차원 점 데이터를 추출하여 이를 3D 모델링 형상을 생성하게 된다. 중요 구성부품이 절삭가공을 이용해 가공하게 되면 제품의 수정이 용이하다. 하지만, 블레이드와 허브는 다이캐스팅이나 중력주조를 통해 제작하는 환경으로 인해 금형 제작 전에 구조안전에 대한 연구가 필요하게 되었다. 본 연구에서는 축류팬 정격운전속도와 그 이상의 운전속도에서 주요 구성부품에 대한 구조안전성에 대한 특성과 취약부위에 대한 해석결과는 최대응력과 안전계수를 통해 검증하고 설계시 반영된 여유간극은 블레이드의 회전과 다른 부품과의 간섭 여부를 확인하기 위해 변위 결과를 도출하여 축류팬의 구조안전성에 대해 검증하고자 한다.

• 한국의상디자인학회지
• /
• 제14권1호
• /
• pp.81-96
• /
• 2012

The purpose of this study is to provide fundamental information for standardization of 3D body measurement. This research analyzes errors occurring in the process of extracting body size from 3D body scan data. First, as a result of analyzing basic state of the 3D body scanner's calibration, the point number of each section was almost the same, while the right and left as well as the front and back coordinates of the center of gravity are not, showing unstable data. Nevertheless, the latter does not influence on the size of cylinder such as width and circumference. Next, we analyzed point coordinates variations of scan data on a mannequin nude by life casting. The result was great deflection in case of complicated or horizontal sections including the reference point beyond proper distance from centers of four cameras. In case of the mannequin's size, accuracy proves comparatively high in that measurement errors in height, width, depth, and length dimension occurred all within allowable errors, only except chest depth, while there were a lot of measurement errors in a circumference dimension. Secondly, analysis of accuracy of automatic extraction identification program algorithm presented that a semi-automatic measurement program is better than an automatic measurement program. While both of them ate very acute in parts related to crotch, they are not in armpit related parts. Therefore, in extracting of human body size from 3D scan data, what really matters seems to parts related to armpits.

• 한국정밀공학회지
• /
• 제19권2호
• /
• pp.114-125
• /
• 2002

As semi-solid forging (SSF) is compared with conventional easting such as gravity die-easting and squeeze casting, the product without inner defects can be obtained from semi-solid forming and globular microstructure as well. Generally speaking. SSF consists of reheating, forging, ejecting precesses. In the reheating process, the materials are heated up to the temperature between the solidus and liquidus line at which the materials exists in the form of liquid-solid mixture. The process variables such as reheating time, reheating temperature, reheating holding time, and induction heating power have much effect on the quality of the reheated billets. It is difficult to consider all the variables at the same time when predicting the quality. In this paper, Taguchi method, regression analysis and neural network were applied to analyze the relationship between processing conditions and solid fraction. A356 alloy was used for the present study, and the learning data were extracted by the reheating experiments. Results by neural network were on good agreement with those by experiment. Polynominal regression analysis was formulated by using the test data from neural network. Optimum processing condition was calculated to minimize the grain size, solid fraction standard deviation, otherwise, to maximize the specimen temperature average. In this time, discussion is liven about reheating process of row material and results are presented with regard to accurate process variables for proper solid fraction, specimen temperature and grain size.

• 한국주조공학회지
• /
• 제35권4호
• /
• pp.67-74
• /
• 2015

In this study, Mg-Zn alloys are investigated in terms of their thermal properties after an addition of Cu. Al element is added to improve the mechanical properties and castability in general case. However, it was excluded here because it significantly decreases the thermal conductivity. On the other hand, Zn was added as a major element, which had less influence on reducing the conductivity and can complement the mechanical properties as well. Cu was also added, and it improved the heat transfer characteristics as the amount was increased. The composition ranges of Zn and Cu are 6 wt.% and 0~1.5 wt.%, respectively. Mg-6Zn-xCu alloy was prepared by a gravity casting method using a steel mold and then the thermal conductivity and the microstructure of the as-cast material were investigated. By measuring the density_(${\rho}$), specific heat_(Cp) and thermal diffusivity_(${\alpha}$), the thermal conductivity_(${\lambda}$) was calculated by the equation ${\lambda}={\rho}{\cdot}Cp{\cdot}{\alpha}$. As the amount of Cu increased in the Mg-6Zn-xCu alloy, the heat transfer characteristics were improved, resulting in a synergistic effect which is slow when the added Cu exceeds 1 wt.%. In order to investigate the relative thermal conductivity/emission of the Mg-6Zn-xCu alloy, AZ91 and AZ31 were experimentally evaluated and compared using a separate test equipment. As a result, the Mg-6Zn-1.5Cu alloy when compared to AZ91 showed improvements in the thermal conductivity ranging from 30 to 60% with a nearly 20% improvement in the thermal emission.

• Applied Microscopy
• /
• 제25권3호
• /
• pp.99-107
• /
• 1995

The morphological changes of primary solid particles as a function of process time on hypereutectic Al-15.5wt%Si alloy during semi-solid state processing with a shear rate of $200s^{-1}$ are studied. In this alloy, it was observed that primary Si crystals are fragmented at the early stage of stirring and morphologies of primary Si crystals change from faceted to spherical during isothermal shearing for 60 minutes. To understand the role of Al dissolved in the primary Si crystal by shear stress at high temperature, lattice parameters of the primary Si crystals are determined as a variation of high order Laue zone(HOLZ) line positions measured from convergent beam electron diffraction(CBED) pattern. The lattice parameter of the primary Si crystal in the rheocast Al-15.5wt%Si alloy shows tensile strain of about 5 times greater than that of the gravity casting. Increase of the lattice parameter by rheocasting is due to the increased amount of Al dissolved in the primary Si crystal accelerated by shear stress at high temperature. The amounts of solute Al in the primary Si crystal are measured quantitatively by EPMA method to confirm the CBED analysis.

• 한국주조공학회지
• /
• 제42권1호
• /
• pp.3-11
• /
• 2022

본 연구에서는 전산모사를 활용하여 오스테나이트계 내열강인 HR3C 합금의 수축 결함 파라미터를 확보하고, 건전부 85% 이상의 잉곳 몰드 설계 및 제작을 진행하였다. 잉곳 몰드 설계 단계에서 전산모사를 활용하여 최적의 잉곳 몰드를 설계 및 제작하였으며, 제작한 잉곳 몰드를 통해 시험조업을 수행하였다. 시험조업 후, 절단 및 비파괴 검사를 통해 결함 양상을 분석하여 수축 결함 파라미터와 잉곳 몰드 설계를 검증하였다. 검증 결과를 기반으로 HR3C 합금의 수축 결함 파라미터 (Niyama 인자, 급탕효율인자, 열간 균열 인자 등)를 확보하였으며, 확보한 파라미터를 통해 건전부 85% 이상의 잉곳 몰드 설계 방안을 확보하였다.