• 열처리공학회지
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• 제22권4호
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• pp.228-233
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• 2009

In order to predict the temperature distribution of stainless steel strip in Bright Annealing (BA) furnace, we performed the analysis of heat transfer and fluid flow using STAR-CCM+. The analysis model included unsteady fluid flow, heat transfer with radiation and moving grid. Two kinds of radiative properties, emissivity and reflectivity, were applied to the stainless steel strip, one is constant and the other is variable with time. As we call, the BA furnaces of stainless steel strip have two different types, muffle and no-muffle. The using of muffle type has been faced with some problems such as rising in material price and shortening of life cycle, etc. So the development of no-muffle type BA furnace is very important in order to save energy cost, lower environmental load and increase the productivity. The designed (or expected) temperature of stainless steel strip coming out of BA furnace was about $1065^{\circ}C$ while the environment temperature maintains around $1100^{\circ}C$. The result of our calculation was very close (or similar) to design temperature, and the application of radiative properties variable with time produced more accurate result than applying constant ones.

• 방사성폐기물학회지
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• 제3권3호
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• pp.249-256
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• 2005

우라늄 변환시설의 라군 슬러지에 함유된 질산염의 안정적 처리를 위해 물 첨가 용해를 실시한 뒤, 여과 케이크의 안정화 특성에 대하여 알아보았다. 물 용해에 의해 대부분의 질산염은 고농도 질산염 용액으로 제거되었으므로, 여과 케이크의 열분해는 $900^{\circ}C$에서 하나의 단계로 수행하였다. Muffle furnace를 이용하여 $900^{\circ}C$에서 5시간동안 여과 케이크의 열분해를 실시한 결과 라군 1 슬러지에 포함된 U은 $NaNO_3$의 열분해와 함께 $Na_{2}O{\cdot}2UO_3$의 형태로 안정화 되었다. 라군 2 열분해 잔류물의 경우에는 열분해 시 생성된 CaO가 냉각과정에서 수분과 반응하여 $Ca(OH)_2$로 전환되는 것을 TG/DTA 분석과 XRD 분석을 통해 확인할 수 있었지만, 처분장에서 대기중 노출이나 지하수의 침출 등에는 안정한 화합물로 알려져 있으므로, 특별한 첨가제의 첨가 없이 단순 열분해 후 처분이 가능할 것으로 판단된다.

• Restorative Dentistry and Endodontics
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• 제27권6호
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• pp.612-621
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• 2002

The purpose of this study was to compare the histomorphological change of curved root canal preparation using GT rotary File, Profile .04 taper and stainless steel K-file. 45 mesial canals(over 20 degree) of extracted human mandibular first molars were mounted in resin using a modified Bramante muffle system and divided into three groups. The roots were cross-sectioned at 2.5mm 5mm and 8mm levels from apical foramen. Tracings of the canals were made from preinstrumentation pictures of the cross section. The canals were prepared using a step-back technique with stainless steel K file(group 1), Profile .04 taper rotary file(group 2) and GT rotary file(group 3). Tracings of the prepared canals were made from postinstrumentation picture. Canal centring ratio. amount of transportation, area of dentin removed and shape of canal were measured and statistically were evaluated with Student-Newman-Keuls test using Sigma Stat(Jandel Scientific Software, USA). The results were as followings : 1 Amount of transportation of group 2 was the lowest at apical part, but there was no statistical difference. The direction of transportation was the outside of curvature at apical part. 2. Centering ratio at the apical part of group 1 was the highest, and there was statistical differences between apical and middle part, apical and coronal part(p＜0.05). Centering ratio at the middle part of group 3 was the lowest, and there was statistical difference between apical and middle part(p＜0.05). Centering ratio of group 2 was the lowest at apical part, but there was no statistical difference. 3. Amount of dentin removed of group 1 was the highest at coronal, middle and apical part among three groups, and there was statistical difference(p＜0.05). 4. The majority of the cross-sectioned canal shape after instrumentation were irregular at coronal, middle and apical part. But there are more number of round shaped canals at group 3 than other group.

• Restorative Dentistry and Endodontics
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• 제29권5호
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• pp.446-453
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• 2004

하악 대구치 근심치근의 danger zone에서 수종의 전동 니켈-티타늄 파일의 근관성형력을 근관성형 전후 치질 두께의 변화를 측정하여 평가하고자 하였다. 기구에 따라 총 40개의 하악 대구치를 10개씩 $Profile^{\circledR}$, GT Rotary file, Quantec 및 ProTaper 4개 군으로 나누고 각 치아당 2개의 근관을 straight up-and-down과 anticurvature 군으로 나누어 근단부 근관을 모두 30번 크기로 일정하게 확대하였다. 수정된 Bramante법을 사용하였으며 술전 및 술후의 근관 상아질 두께를 치수저 하방 1, 3 및 5 mm지점에서 측정, 이원변량분석법으로 통계분석하였다. 모든 군의 danger zone과 safe zone에서의 straight up-and-down 동작과 anticurvature 동작 사이에는 치근상아질 두께변화에 현저한 차이를 나타내지 않았다 (p > 0.05). ProTaper는 danger zone과 safe zone 모두에서 다른 기구에 비해 많은 량의 근관상아질 삭제를 보였으며 특히 분지부 3 mm 수준에서 현저하였다(p < 0.05).

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2001년도 추계학술강연 및 발표대회
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• pp.7-7
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• 2001

The increasing interest in light weight materials coupled to the need for cost -effective processing have combined to create a significant opportunity for aluminum P/M. particularly in the automotive industry in order to reduce fuel emissions and improve fuel economy at affordable prices. Additional potential markets for Al PIM parts include hand tools. Where moving parts against gravity represents a challenge; and office machinery, where reciprocating forces are important. Aluminum PIM adds light weight, high compressibility. low sintering temperatures. easy machinability and good corrosion resistance to all advantages of conventional iron bm;ed P/rv1. Current commercial alloys are pre-mixed of either the AI-Si-Mg or AL-Cu-Mg-Si type and contain 1.5% ethylene bis-stearamide as an internal lubricant. The powder is compacted in closed dies at pressure of 200-500Mpa and sintered in nitrogen at temperatures between $580~630^{\circ}C$ in continuous muffle furnace. For some applications no further processing is required. although most applications require one or more secondary operations such as sizing and finishing. These sccondary operations improve the dimension. properties or appearance of the finished part. Aluminum is often considered difficult to sinter because of the presence of a stable surface oxide film. Removal of the oxide in iron and copper based is usually achieved through the use of reducing atmospheres. such as hydrogen or dissociated ammonia. In aluminum. this occurs in the solid st,lte through the partial reduction of the aluminum by magncsium to form spinel. This exposcs the underlying metal and facilitates sintering. It has recently been shown that < 0.2% Mg is all that is required. It is noteworthy that most aluminum pre-mixes contain at least 0.5% Mg. The sintering of aluminum alloys can be further enhanced by selective microalloying. Just 100ppm pf tin chnnges the liquid phase sintering kinetics of the 2xxx alloys to produce a tensile strength of 375Mpa. an increilse of nearly 20% over the unmodified alloy. The ductility is unnffected. A similar but different effect occurs by the addition of 100 ppm of Pb to 7xxx alloys. The lend changes the wetting characteristics of the sintering liquid which serves to increase the tensile strength to 440 Mpa. a 40% increase over unmodified aIloys. Current research is predominantly aimed at the development of metal matrix composites. which have a high specific modulus. good wear resistance and a tailorable coefficient of thermal expnnsion. By controlling particle clustering and by engineering the ceramic/matrix interface in order to enhance sintering. very attractive properties can be achicved in the ns-sintered state. I\t an ils-sintered density ilpproaching 99%. these new experimental alloys hnve a modulus of 130 Gpa and an ultimate tensile strength of 212 Mpa in the T4 temper. In contest. unreinforcecl aluminum has a modulus of just 70 Gpa.

• 청정기술
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• 제30권2호
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• pp.134-144
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• 2024

본 연구는 7대 온실가스 중 하나인 HFC-134a를 효과적으로 분해하기 위한 촉매로써 산업 부산물인 red mud를 상업적으로 사용하기 위한 기계적 안정성 향상에 관한 것이다. 알루미늄 공정에서 배출한 산업용 폐기물인 red mud는 분쇄-분취-압축-성형-소성 공정으로 HFC-134a 분해가 가능한 촉매 제조가 가능하였는데, 소성을 통해 촉매 성능 향상 및 기계적 안정성을 확보할 수 있었다. 최적의 열처리 조건을 확인하기 위하여, 펠렛형태로 압축성형한 red mud는 머플퍼니스를 이용하여 300, 600, 800 ℃에서 5시간 소성하여 촉매성능 및 기계적 안정성을 확인하였는데, 기계적 안정성은 증류수에 촉매를 담근 후 초음파 처리 전후 무게 손실률로 확인하였다. 열처리에 따른 촉매성능 및 기계적 안정성을 확인한 결과 800 ℃에서 소성한 촉매(RM 800)가 기계적 안정성은 물론 촉매활성 또한 가장 우수하였다. RM 800 촉매를 사용한 촉매 성능 및 100시간 동안 수행한 내구성 측정 결과 650 ℃에서 1 mol% HFC-134a를 99% 이상 분해하였고, 내구성 측정 기간동안 촉매성능 저하는 관찰할 수 없었다. XRD 분석 결과 800도 소성 후 Ca, Si, 및 Al의 상호작용으로 인해 기계적 강도와 활성 향상에 영향을 미치는 트라이 칼슘알루미네이트와 게레나이트 결정상이 나타났다. 내구성을 측정한 촉매 SEM/EDS 분석 결과 RM 800 촉매는 HFC-134a 분해로 인한 활성물질 저감 및 형상변화가 나타나지 않았다. 본 연구를 통해 산업폐기물인 red mud는 경제성이 매우 높고 분해효율 및 기계적 안정성 또한 매우 높아 폐냉매 처리를 위한 촉매로써 상용화가 가능할 것으로 기대한다.