• 환경위생공학
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• 제19권3호
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• pp.58-64
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• 2004

Biological treatment of wastewater was studied with a purpose to remove TOC by the reduction of water hardness. The optimal conditions of coagulant were determined by reaction time and amount of coagulant. Experimental results indicate that the biological treatment after physico-chemical treatment was found to provide very efficient removal efficiency in the process to treat the textile wastewater, including the carbon dioxide treatment. The combined process of carbonization in the physico-chemical treatment respectively was increased the removal efficiencies of $30.0\%$ in biological treatment in comparison with exclusive biological treatment. As a result, the treatment of hardness after carbonization had the best removal efficiency of approximately $60.0\%$. The removal efficiencies in the exclusive biological treatment using Bacillus subtilis and after carbonization were increased by $38.9\%\;and\;69.0\%$ respectively. The combined Bacillus subtilis-assisted biological treatment was determined to be the most effective method to treat the textile wastewater in an economic point of view, the water quality in the wastewater treatment plays an important role.

• 한국인쇄학회지
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• 제20권2호
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• pp.7-18
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• 2002

The emulsification of lithographic printing inks are very important to determine printing quality. In this study, we measured the variation of water pickup according to the hardness of water in dampening solution. In order to observe the rheorogical properties of the emulsified inks, we measured the viscosity, the elastic return, the thixotropy area and yield stress value of the emulsified inks. In this paper, we found that the water pickup of the ink increase the hardness of water with the amount of dampening solution. Also, The viscosity, the yield stress value and the thixotropy area were increase by the water pickup of the ink.

• 한국가정과학회지
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• 제5권2호
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• pp.33-43
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• 2002

This study was investigated textural properties of Injulmi affected by milling methods, varieties and added water volume. Sinsunchalbyeo and Hwasunchalbyeo flours were made using Rin-dry milling(PDM) and roll-wet milling(RWM) methods. The proximate composition of waxy rice starches and waxy rice flours were similar. Water binding capacity, soluble carbohydrate and damaged starch of waxy rice flour by RWM: were higher than those of waxy rice flours by PDM. By increasing added water volume, hardness and adhesiveness of Injulmi were decreased. By increasing storage time, hardness of Injulmi was increased, but adhesiveness was decreased. The hardness of Injulmi made from waxy rice flours by PDM was higher than by RDW.

• 한국재료학회지
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• 제30권12호
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• pp.693-700
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• 2020

Direct water quenching technique can be used in hot stamping process to obtain higher cooling rate compared to that of the normal die cooling method. In the direct water quenching process, setting proper water flow rate in consideration of material thickness and the size of the area directly cooled in the component is important to ensure uniform microstructure and mechanical properties. In this study, to derive proper water flow rate conditions that can achieve uniform microstructure and mechanical properties, microstructure and hardness distribution in various water flow rate conditions are measured for 3.2 mm thick boron steel sheet. Hardness distribution is uniform under the flow condition of 1.5 L/min or higher. However, due to the lower cooling rate in that area, the lower flow conditions result in a drastic decrease in hardness in some areas in the hot-stamped part, resulting in low martensite fraction. From these results, it is found that the selection of proper water flow rate is an important factor in hot stamping with direct water quenching process to ensure uniform mechanical properties.

• 대한환경공학회지
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• 제33권4호
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• pp.258-266
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• 2011

수중 경도물질에 의해 유발된 스케일은 수질 저해는 물론 배관의 기능에 막대한 손실을 초래할 수 있어 관리가 필요하다. 특히 온수시스템의 경우, 온도에 의해 스케일화작용이 가속화되므로 관리가 필요한 시설 중 하나이다. 현재까지는 화학약품이나 에너지가 소모되는 화학적, 물리적, 전자기적 방법과는 다른 무전원방식의 Frequency Driver (FD)를 이용하여 스케일 생성 방지 효과를 확인하고자 하였다. 500 mg/L의 경수에 33일간 3종류의 관 시편을 침지시켜 관 재질별 스케일 형성도를 비교하기 위해 XRD와 SEM을 이용하여 표면을 분석하였다. 주철관에서는 경도에서 유발된 스케일인 calcite ($CaCO_3$)가 형성되었고, 구리나 스테인리스관에 비해 부식율이 높았다. 온수순환장치를 제작하여 경도 300 mg/L로 $50^{\circ}C$의 조건에서 FD 설치 유무에 따른 주철관의 스케일 형성도와 수질 변화를 비교하였다. XRD 결과에서 FD를 설치하였을 경우 calcite의 생성은 비교적 적은 반면, 좋은 부식생성물인 magnetite ($Fe_3O_4$)의 생성을 확인할 수 있었으며, SEM 사진에서도 FD의 스케일 저감 효과를 확인할 수 있었다. 관 내부의 스케일 양의 경우, FD를 설치하지 않은 경우에 비해 FD를 설치하였을 경우 관 연결부분에서는 16%, 관 전체길이에서는 14%, 열교환기에서는 42%의 적은 스케일이 형성되어 FD의 스케일 저감효과를 확인할 수 있었다. 또한 FD 설치 유무에 따른 수질분석 결과를 토대로 FD가 수질의 화학적 변화 없이 경도물질의 결정화를 방지하는 것으로 나타나 환경적으로도 안전함을 확인하였다.

• 열처리공학회지
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• 제31권3호
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• pp.104-110
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• 2018

The effects of heat treatment time and cooling method on microstructure and mechanical property of Cu-22wt%Sn alloy were discussed. ${\alpha}+{\delta}$ mixed phase structure was obtained in air-cooled specimens after heat treatment at 775, 750, and $700^{\circ}C$ for 1 hour. On the other hand, in water-cooled specimens, ${\alpha}+{\beta}^{\prime}$ martensite mixed phase was obtained. In the case of water-cooled specimens, the hardness value decreased with decreasing heat treatment temperature because the volume fraction of ${\alpha}$ phase with low hardness value increased as the heat treatment temperature decreased. In water-cooled specimen after heat treatment at $600^{\circ}C$, ${\gamma}^{\prime}$ martensite was formed instead of ${\beta}^{\prime}$ martensite. The hardness value of ${\gamma}^{\prime}$ martensite was lower than those of ${\beta}^{\prime}$ and ${\delta}$ phases.

• 구강회복응용과학지
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• 제30권2호
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• pp.138-144
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• 2014

목적: 이 연구의 목적은 다양한 이원 중합 레진 시멘트의 수분 흡착도를 조사하고, 수분 흡착에 따른 미세 경도 변화를 비교해보는 것이다. 연구 재료 및 방법: 다섯 가지의 이원중합 레진시멘트를 선정하였다(Maxcem, Duo-link, Panavia F, Variolink II, Rely X Unicem). 각 그룹 당 10개씩, 총 50개의 시편을 제작하였다.각 그룹 당 5개의 시편들을 증류수에 7일 동안 보관 후 수분 흡착도를 평가하였다. 증류수에 보관한 시편과 보관하지 않은 시편들을 비교하여 결과를 얻었다. 결과: 1. 수분 흡착도에 있어서 Maxcem이 유의성 있게 가장 높았다. 2. 증류수에 보관하지 않았던 시편의 미세 경도는 Rely X Unicem의 유의성 있게 가장 높았다. 3. 증류수에 보관하였던 시편의 미세 경도는 Rely X Unicem이 유의성 있게 가장 높았다. 4. 수분 흡수에 따른 미세 경도의 변화에 있어서 Variolink II는차이가없는것으로나타났으나, Duo-link, Panavia F, 그리고 Rely X Unicem은 감소되었으며, Maxcem은 증가되었다. 결론: 임상적으로 레진시멘트 선택시 수분 흡착도가 작고, 미세 경도가 높은 재료를 선택하는 것이 추천된다.

• International Journal of Precision Engineering and Manufacturing
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• 제8권1호
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• pp.46-51
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• 2007

Environmental contamination creates shortages of potable water. In such situations, the leakage of water due to breakage or aging of rubber valve seats is a serious problem. Rubber is apt to break when it is placed between two materials that contact each other. One way to avoid water leakage due to rubber damage and breakdown is to replace the rubber with metal, which is currently taking place in water distribution systems. In tribology, a severe form of wear is characterized by local macroscopic material transfer or removal, or by problems with sliding protrusions when two solid surfaces experience relative sliding under load. One of the major problems when metal slides is the occurrence of galling. Experimentally, various conditions influence incipient galling, such as hardness, surface roughness, temperature, load, velocity, and the external environment. This study sought to verify the galling tendencies of metal according to its hardness, surface roughness, load, and sliding velocity, and determine the quantitative effect of each factor on the galling tendencies.

• Journal of the Korean Wood Science and Technology
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• 제31권3호
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• pp.17-23
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• 2003

As a fundamental study of developing sawdust board from thinning softwood logs from three species (Pinus densiflora S. et Z., Larix leptolepis G. and Pinus koraiensis S. et Z.), this study examined the effect of board density and resin content on physical and mechanical properties of sawdust board. As the board density increase, thickness swelling, bending strength, and Brinell hardness increased while water absorption decreased. With increasing the resin content, the bending strength and hardness increased while water absorption and thickness swelling decreased. The board made of L. leptolepis was slightly low in its water absorption, and the one made of P. koraiensis was a little high in its bending strength, while there was no definite difference between each kind of trees in their hardness values.

• 펄프종이기술
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• 제31권2호
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• pp.15-24
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• 1999

A new technique for recycling of white water was developed in order to reduce the calcium hardness in a closed OCC recycling system. Calcium ions present in the white water were precipitated as calcium carbonate by reacting with sodium carbonate, and the precipitated $CaCO_3$ was removed from the system using a flotation fractionation method, which has been commonly used in deinking process. In the flotation stage, a mixed gas of $CO_2$-air was purged into the flotation cell because the pH of $Na_2CO_3$-treated white water was reduced to neutral by $CO_2$ gas. Since $CaCO_3$ precipitate tends to stick onto fine fiber surface and then selectively removed from the white water, a proper amount of suspended solid in white water acts as an important factor for deciding the removal efficiency. By the application of $Na_2CO_3$ addition-$CO_2$ flotation to the short circulated white water, the calcium hardness was significantly reduced by 87% and more. Removal of calcium ions with fine fibers led to a drainage improvement, reduction of fresh water consumption, and enhanced efficiency of wet-end chemicals.