• Journal of Welding and Joining
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• 제28권1호
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• pp.60-65
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• 2010

This paper is concerned with effects of Al, Mn and Si contents on spatter, fume, microstructure and mechanical property with 490MPa Grade Flux Core Wire(FCW). Ten kinds of FCW were fabricated by varying Mn, Si and Al contents and each FCW was weld for check the amount of spatter and fume generations, microstructures and mechanical property. Amount of spatter and fume generations was decreased with the increasing Si contents and decreasing by Al contents in FCW. And, their microstructure of weld metal were changed by Mn, Al and Si contents in FCW. With increasing of Al and Si, acicular ferrite was fine and volume fraction of acicula ferrite was increased. Thereby leading to improvement of Charpy impact property and strength.

• 한국농공학회지
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• 제38권3호
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• pp.58-69
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• 1996

In recent years, the research and development about the new material proceeds rapidly and actively. In building industry, high strength concrete is of interest as a new material. Since the building structure becomes bigger, higher and more specialized, the demand of material and member with high strength expands greatly. Therefore in this experiment, cement complex with high strength was made using the condensed silica fume, a basic experiment was performed on strength property, and optimum-mixture-state was determined for manufacturing a high-strength concrete. Shear behaviour and fracture property of concrete beams with high strength were evaluated. On the whole, in spite of many researches, it is one of the difficult problems that shear fracture of concrete beams has not yet been clearly understood theoretically, and now the shear-design-standard forms in many countries are a formula based on experiment. In this study, the variable of shear behavior experiment was shear-reinforcement-ratio. By analyzing test results and comparing with computation value by ACI code, the basic data was offered on shear design of reinforced concrete beams with high strength. The effect of epoxy repair was also investigated for the beams with cracks due to flexural and shear loading.

• Elastomers and Composites
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• 제41권3호
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• pp.157-163
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• 2006

침전실리카와 친수성 및 소수성 흄실리카를 사용하여 첨가량에 따른 실리콘 고무인상재의 젖음성과 기계적 물성 향상 연구를 수행하였다. 고무인상재의 경화시간에는 흄실리카 종류보다는 입자크기가 영향을 미쳤으며, 입자크기가 가장 작은 A300을 사용할 경우 약 9분 정도의 경화시간 지연을 초래하였다. 소수성 흄실리카인 R972를 대체 사용할 경우 고무인상재의 젖음성 특성이 가장 우수하였다. 침전실리카와 A300 흄실리카를 85:15로 혼합하여 사용할 경우 인열강도가 약 1.5N/mm 정도 증가하지만 경화시간의 과도한 지연과 더불어 점도가 상승하기 때문에, 흐름성 및 기계적물성 측면에서 침전실리카와 흄실리가(A300)를 90:10으로 혼합하여 사용하는 것이 최적이었다.

• 한국안전학회지
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• 제34권4호
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• pp.32-40
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• 2019

During the manufacturing process of a printed circuit board(PCB), fumes and mists are generated as the ink dries on the PCB surface. The generated fumes and mists are deposited in the dryer wall and the exhaust duct. Deposited fumes and mists may present a fire hazard if the dryer temperature control system fails. In this study, the thermal stability of the fumes and mists deposited in the dryer and ducts has been analyzed by experimental methods such as thermo gravimetric analysis (TGA), differential scanning calorimetry (DSC), auto ignition temperature (AIT), and multiple mode calorimetry(MMC). According to the experimental analyses, experimental samples are likely to generate gas at the temperature ($180{\sim}240^{\circ}C$) that deviates from the normal operating temperature ($150{\sim}156^{\circ}C$). It has been shown that the thermal stability is degraded when the temperature is deviated from the normal operating temperature. In the end, engineering and management safety measures of accidental prevention have been suggested.

• 산업기술연구
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• 제41권1호
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• pp.1-6
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• 2021

Fly ash and silica fume belong to industry by-products that can be used to produce concrete. This study shows the model of a neural network to evaluate the strength development of blended concrete containing fly ash and silica fume. The neural network model has four input parameters, such as fly ash replacement content, silica fume replacement content, water/binder ratio, and ages. Strength is the output variable of neural network. Based on the backpropagation algorithm, the values of elements in the hidden layer of neural network are determined. The number of neurons in the hidden layer is confirmed based on trial calculations. We find (1) neural network can give a reasonable evaluation of the strength development of composite concrete. Neural network can reflect the improvement of strength due to silica fume additions and can consider the reductions of strength as water/binder increases. (2) When the number of neurons in the hidden layer is five, the prediction results show more accuracy than four neurons in the hidden layer. Moreover, five neurons in the hidden layer can reproduce the strength crossover between fly ash concrete and plain concrete. Summarily, the neural network-based model is valuable for design sustainable composite concrete containing silica fume and fly ash.

• 철학연구
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• 제143권
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• pp.165-188
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• 2017

브레이부르크(1976)와 소벨(1976)에 따르면, 전통적인 사회계약론의 두 전제, 즉 투쟁적 자연상태라는 '상황'과 타인의 복지에 대해 무관심하고 자기 이익을 추구하는 합리적 개인이라는 '동기'의 두 가정 하에서는 계약의 성립과 준수는 불가능하다. 소위 '사회계약론의 문제'로 불리는 이 문제는 현대 사회계약론에도 유전된다. 그렇다면 현대 사회계약론은 이 문제를 해결하고 있는가? 이 논문은 전통적 사회계약론의 문제에 대한 현대 사회계약론의 해법에 '상황'과 '동기'가 어떻게 순환함으로서 선결문제를 요구하는지 분석한다. 그리고 현대 계약론에서 나타나는 순환을 벗어나기 위해서 사회계약론이 자연화 될 필요성을 관습주의를 참고하여 논변한다.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2021년도 가을 학술논문 발표대회
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• pp.176-177
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• 2021

In order to compensate for the defects of concrete made using only Portland cement, three-component powder mixed with blast slag and fly ash, and four-component powder concrete mixed with silica fume are being produced. When each of the admixtures is used alone, the above-described excellent performance is expressed and up to 70% of the powder is used. These technologies are also contributing to the reduction of greenhouse gases under Act on Low Carbon. Green Growth. However, calcium hydroxide is consumed as a stimulator or reaction in the case of silica fume, which causes latent hydroponicity of slag, pozzolane reaction, and silica mixtures represented by fly ash. It is known that the consumption of calcium hydroxide affects the alkalinity of concrete. As a result, the carbonation resistance is significantly lower among the durability of concrete. Research on quantification of such effects is insufficient. In this study, an experiment was conducted to quantify calcium hydroxide of the three-component and four-component powder paste using thermal analysis equipment (DTG), and the effect of the mixing amount was discussed.

• 대한토목학회논문집
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• 제14권4호
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• pp.783-794
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• 1994

근래에 들어 대형 구조물의 시공실패사례가 보고되고 있어 이에 대한 개선이 시급하게 요청되고 있다. 이러한 실패사례의 주요원인은 콘크리트의 품질문제이며 따라서 고품질 콘크리트의 개발과 사용이 절실히 필요하다. 콘크리트의 품질향상을 위한 방안으로 현재 주목받고 있는 것은 유동성의 확보와 함께 각기 다른 독특한 특성을 보이는, 플라이 애쉬, 고로 슬래그, 실리카 흄 등 혼화재의 혼입이다. 따라서, 본 연구에서는 슬럼프를 $17{\pm}1cm$로 제어하여 기본적인 유동성을 확보한 콘크리트 배합에 대하여, 위의 혼화재들의 혼입률에 따른 역학적 특성과 내구적 특성을 고찰하여 보았다. 본 연구에서 고려한 주요 실험변수들로는 혼화재의 종류와 혼입률, 두 종류의 단위시멘트량과 물/시멘트비의 조합 등이다. 이들 실험변수들을 고려하여 14개 시리즈에 대한 포괄적인 실험을 수행하였으며, 각 혼화재 혼입량에 따른 재령별 압축강도 증진양상과 콘크리트내에 매립된 철근씩 부삭특성을 분석, 고찰하였다. 본 실험연구로부터 각 경우별 최적의 혼화재 혼입량과 성능을 도출하였으며 이것은 앞으로 고성능 콘크리트의 활용에 토대가 될 것으로 사료된다.

• 한국산업보건학회지
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• 제5권2호
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• pp.172-183
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• 1995

The airborne concentrations of the welding fumes produced during $CO_2$ arcwelding process at shipbuilding, shiprepairing, container manufacturing and car accessary manufacturing industry were investigated. The effects how much reduced the welding fume were checked when the portable fan was used. The results were as follows; 1.The geometric mean of welding fume concentration in shipbuilding factory was $10.05mg/m^3$. This exposure concentration was higher than other 3 manufacturing industries at 95% confidence level. 2. The sampling filters for welding fume could be digested with acid within 1 hour by microwave oven. The recoveries for investigated metal elements were all over 95%. 3. The optimal wavelength could be selected for the simultaneous analysis of 8 metal elements by ICP(Inductively Coupled Plasma). 4. Noxious gases($O_1,NO_2$) produced during $CO_1$ gas arc welding process were detected that the concentration of ozone($O_1$) was less than 0.01 ppm and that of nitrogen dioxide($NO_2$) was 0.01-0.03 ppm. 5. The geometric mean of welding fume particle diameter was $1.26{\mu}m$ and geometric standard deviation was 1.51 for the counts when particle an analyzer(ELZONE) had been used. 6. When the portable fan had been used,the reduced percent of total welding fume for workers was about 47.8% when portable fan was applied to blow and 71.7% when to exhaust.

• Journal of Preventive Medicine and Public Health
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• 제31권3호
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• pp.414-423
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• 1998

Metal fume fever has been known as an occupational disease is induced by intense inhalation of fresh metal fume with a particle size smaller than $0.5{\mu}m\;to\;1{\mu}m$. The fumes originate from heating metals beyond their boiling point, as happens, for example, in welding operations. Oxidation usually accompanies this process. In most cases, this syndrome is due to exposure to zinc oxide fumes; however, other metals like copper, magnesium, cadmium, manganese, and antimony are also reported to produce such reactions. Authors report a case of metal fume fever suspected to be associated with copper fume inhalation. The patient was a 42-year-old male and was a smoker. He conducted inert gas tungsten arc welding on copper-coated materials without safety precautions such as a protective mask and adequate ventilation. Immediately after work, he felt metallic taste in his mouth. A few hours after welding, he developed headache, chilling sensation, and chest discomfort. He also complained of myalgia, arthralgia, feverish sensation, thirst, and general weakness. Symptoms worsened after repeated copper welding on the next day and subsided gradually following two weeks. Laboratory examination showed a transient increase of neutrophil count, eosinophilia, elevated erythrocyte sedimentation rate, and positive C-reactive proteinemia. Blood and urine copper level was also increased compared to his wife. Before this episode, he experienced above complaints several times after welding with copper materials but welding of other metals did not produce any symptoms. It was suggested that copper fume would have induced metal fume fever in this case. Further investigations are needed to clarify their pathogenic mechanisms.