• 한국연소학회:학술대회논문집
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• 대한연소학회 2003년도 제27회 KOSCO SYMPOSIUM 논문집
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• pp.243-250
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• 2003

The present study discuss about numerical methods to analyze design parameters of pyrolysis-melting incineration system. Various numerical methods of different viewpoint are introduced to simulate the performance of the system. Process analysis of the overall system is the beginning procedure of basic design process. Heat and material flow of each element are connected and are influential to each other, hence, an appropriate process modeling should be executed to prevent from unacceptable process design concepts that may results in system failure. Models to simulate performance of each elementary facility generate valuable informations on design and operation parameters, and, derive the basic design concept to be optimized. A pyrolysis model derived from waste bed combustion model is introduced to simulate the mass conversion and heat transfer in the pyrolysis process. CFD(Computational fluid dynamics) is an effective method to optimize the thermal reacting flow in various reactors such as combustor and heat exchanger. Secondary air jets arrangement and the shape of the combustor could be optimized by CFD technology.

• 한국산업융합학회 논문집
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• 제25권4_2호
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• pp.621-626
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• 2022

Tungsten is a high melting point metal unlike other steel materials, and it is difficult to manufacture because of its high melting temperature. In this study, pressure sintering process method was applied to manufacture the tungsten materials at low temperature. Therefore, it is necessary to densify the sintered material by using a sintering additive. Studies have been conducted on how the amount of titanium for sintering tungsten affects the mechanical properties of tungsten in this study. In order to secure the densification mechanism of tungsten powder during the sintering process, the characteristics of the sintered tungsten material according to the change of titanium content were evaluated. It was investigated the relationship between sintering parameters and mechanical properties for densification of microstructures. The sintered tungsten materials according to sintering additive content showed high sintered density (about 16.31g/cm³) and flexural strength (about 584 MPa) when the content of sintering additive was 3 wt%. However, as the content of the sintering additive increases, mechanical property of flexural strength is decreased, and the porosity is increased due to the heterogeneous sintering around titanium.

• 소성∙가공
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• 제28권1호
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• pp.21-26
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• 2019

Direct Laser Melting (DLM) of $Ti-xTiH_2$ (mixing ratio x = 2, 5, 10 wt.%) blended powder is characterized by producing porous titanium parts. When a high energy laser is irradiated on a $Ti-TiH_2$ blended powder, hydrogen gas ($H_2$) is produced by the accompanying decomposition of the $TiH_2$ powder, and acts as a pore-forming and activator. The hydrogen gas trapped in a rapidly solidified molten pool, which generates porosity in the deposited layer. In this study, the effects of a $TiH_2$ mixing ratio and the associated processing parameters on the development of a porous titanium were investigated. It was determined that as the content of $TiH_2$ increases, the resulting porosity density also increases, due to the increase of $H_2$ produced by $TiH_2$. Also, porosity increases as the scan speed increases. As fast solidified melting pools do not provide enough time for $H_2$ to escape, the faster the scan speed, the more the resulting $H_2$ is captured by the process. The results of this study show that the mixing ratio (x) and laser machining parameters can be adjusted to actively generate and control the porosity of the DLM parts.

• 한국산학기술학회논문지
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• 제19권12호
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• pp.25-31
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• 2018

선택적 레이저 용융 (Selective Laser Melting) 기법은 금속 소재를 다루는 대표적인 3D 프린팅 기법중의 하나이다. SLM 기법으로 제작되는 구조물의 특성을 좌우하는 주요 제작 인자로는 구조물의 적층 제작 방향, 레이저 파워, 레이저 스캔 스피드 및 스캔 간격 등을 고려할 수 있다. 이번 연구에서는 AlSi10Mg 합금을 대상 소재로 하여, 인장 시편의 제작 방향, 레이저 스캔 스피드 및 스캔 간격을 변수로 하여, 인장특성 결과를 비교 분석하였다. 인장특성으로는 항복 응력, 인장강도 및 연신율을 고려하였다. 시험결과로부터, 인장 시편의 제작 방향 기준으로 0도, 45도, 90도 순서로 항복 응력 값이 낮아짐을 확인하였다. 레이저 스캔 스피드 기준으로는 1870mm/min에서 가장 큰 항복 응력값을 보였으며, 스캔 스피드가 낮아질수록 항복 응력 크기도 줄어들었다. 레이저 스캔 간격 기준으로, 그 크기가 증가할수록 항복 응력값은 증가하지만, 다른 시험 기준에 비해 그 변화폭은 가장 적었다. 인장강도 및 연신율은 시험조건에 따른 명확한 경향성을 파악하기 어려웠다.

• 한국방사성폐기물학회:학술대회논문집
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• 한국방사성폐기물학회 2017년도 춘계학술논문요약집
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• pp.259-260
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• 2017

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회B
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• pp.2256-2261
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• 2008

The electric snow melting and deicing system by electric heating cable which is adopted in this study is a part of road facilities to keep surface temperature of the road higher than freezing point of water for melting the snow or ice accumulated on it. The electric heating cables are buried under paved road at a certain depth and a certain pitch and operated automatically and manually. Design theory, amount of heating, and installation standard vary according to economic situation, weather condition, and installation place. A main purpose of this study is figuring out the appropriate range of required heat capacity and installation depth and pitches for solving snowdrifts and freezing problems with minimum electric power consumption. This study was performed under the ambient air temperature($-2^{\circ}C$, $-5^{\circ}C$), the pitches of the electric heating cables (200 mm, 300 mm), heating value ($250\;W/m^2$, $300\;W/m^2$, $350\;W/m^2$).

• Journal of Welding and Joining
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• 제33권5호
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• pp.53-60
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• 2015

Laser surface Melting Process is getting hardening layer that has enough depth of hardening layer as well as no defects by melting surface of substrate. This study used CW(Continuous Wave) Yb:YAG and STD11. Laser beam speed, power and beam interval are fixed at 70mm/sec, 2.8kW and 800um respectively. Hardness in the weld zone are equal to 400Hv regardless of melting zone, remelting zone overlapped by next beam and HAZ. Similarly, microstructures in all weld zone consist of dendrite structure that arm spacing is $3{\sim}4{\mu}m$, matrix is ${\gamma}$(Austenite) and dendrite boundary consists of ${\gamma}$ and $M_7C_3$ of eutectic phase. This microstructure crystallizes from liquid to ${\gamma}$ of primary crystal and residual liquid forms ${\gamma}$ and $M_7C_3$ of eutectic phase by eutectic reaction at $1266^{\circ}C$. After solidification is complete, primary crystal and eutectic phase remain at room temperature without phase transformation by quenching. On the other hand, microstructures of substrate consist of ferrite, fine $M_{23}C_6$ and coarse $M_7C_3$ that have 210Hv. Microstructures in the HAZ consist of fine $M_{23}C_6$ and coarse $M_7C_3$ like substrate. But, $M_{23}C_6$ increases and matrix was changed from ferrite to bainite that has hardness above 400Hv. Partial Melted Zone is formed between melting zone and HAZ. Partial Melted Zone near the melting zone consists of ${\gamma}$, $M_7C_3$ and martensite and Partial Melted Zone near the HAZ consists of eutectic phase around ${\gamma}$ and $M_7C_3$. Hardness is maximum 557Hv in the partial melted zone.

• 콘크리트학회논문집
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• 제24권2호
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• pp.173-183
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• 2012

최근 고강도 콘크리트의 폭렬현상에 관한 메커니즘의 연구와 더불어 폭렬을 방지하는 방법으로써 섬유혼입에 의한 콘크리트의 수증기압을 낮추는 방법이 선호되고 있는 실정이다. 주로 단일 형태의 폴리프로필렌 섬유를 혼입하여 폭렬을 저감하는 방법들이 사용하고 있으나 초고강도 콘크리트 영역에서는 실제로 급격하게 온도가 상승하는 경우에 있어서 폭렬 및 급격한 수증기 팽창압을 고려할 수 없다는 점을 들 수 있다. 따라서 이 연구에서는 콘크리트 내부온도상승조건에 따라 섬유의 용융점에 따른 공극의 형성 및 폭렬의 상관성을 분석하고자 하였으며, W/B 12.5%의 초고강도 콘크리트를 대상으로 용융점이 다른 PE섬유, PP섬유, 나일론섬유를 각각 0.15vol%, 0.25vol% 혼입하여 폭렬 성상, 수증기압, 시차열 중량 분석, 해석적 검토를 행하였다. 실험 결과, 동일 섬유 혼입률 조건에서 섬유의 용융점이 낮더라도 초고강도 콘크리트에서는 섬유의 기화에 의한 섬유의 중량손실이 발생하지 않으면 초기 폭렬의 방지가 어렵고, 가열시간 10분 전후의 빠른 공극을 형성하는 섬유가 폭렬의 방지에 효과적인 것으로 나타났다.

• 한국산학기술학회논문지
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• 제21권12호
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• pp.115-119
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• 2020

선택적 레이저 용융 (SLM, Selective Laser Melting) 기술은 미세한 금속 분말 위에 레이저를 조사하여 특정 영역의 융착을 진행하고 이 과정을 반복적으로 진행함으로써 최종적으로 3차원 형태의 구조물을 제작하는 최신의 적층 공정 기술이다. 적층 공정 기술 특성상 레이저에 의한 금속 소재의 용융 현상은 레이저의 조사 방향과 적층 방향 등 공정 조건에 의해 방향성을 가지게 되며 이로 인해 구조물 내에서 금속 소재 조성은 불균일 특성을 보인다. 본 연구에서는 SLM 기술을 적용하여 알루미늄 (AlSi10Mg) 시편을 제작하고 시편 내부의 소재 조성 특성을 분석하였다. 시편은 적층 제작 방향을 기준으로 0°, 45°, 90°로 구분하여 실린더 형태로 제작하였으며 시편 평면의 표면 형상을 광학적으로 분석하였다. 그리고 레이저 조사로 생성되는 시편 내부의 멜팅풀 형상을 대상으로 하여 멜팅풀 내부와 경계면에 대해 각각 TEM 분석을 수행하였다. 분석 결과로부터 멜팅풀 내부와 경계면의 미세 셀 구조의 차이를 확인하였고, Si 의 조성 비율이 셀의 경계면에서 더 높게 보임을 확인하였다.

• Journal of Welding and Joining
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• 제19권4호
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• pp.379-383
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• 2001

Resistance spot welding has been widely used in the sheet metal joining processes because of low cost, high productivity and convenience. Recently, automobile and aerospace industries are trying to replace partly steel sheets with aluminum alloy sheets. But in the case of dissimilar materials, to apply resistance spot welding has been known to be very difficult owing to the effect of melting temperature. On this study, an effort was made to apply spot welding of dissimilar sheet metals, 2024 aluminum alloy and zinc coated steel sheet, evaluate the spot weld quality with tensile-shear strength test and nondestructive evaluation technique, C-scan image methodology. In this study results, as the current below 11 kA, melting of materials is not achieved well. Also as the current exceeds to 13.5 kA, the more spatters happen at welded zone and tensile-shear strength lowered. So, the feasibility of C-scan image technique proposed in the study is found to be suitable evaluation method for resistance spot weldability.