• 한국정밀공학회지
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• 제22권11호
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• pp.45-50
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• 2005

In this study, the casting/forging process was applied in manufacturing a low control arm, in order to prove that application of casting/forging process to Al6061 is likely to get the effect of light weight compared with existing steel products and to reduce the cost of materials. Firstly, In order to set up the optimum casting condition of the forging material, Al6061, casting experiments were carried out by controlling pouring temperature of the aluminum for casting, mold temperature, and pouring time. $700^{\circ}C$ pouring temperature, $300^{\circ}C$ mold temperature and 10-second pouring time were taken into account as the optimum casting conditions. With respect to a hot forging test, it is practiced on the basis of a temperature of materials, strain rate, and reduction rate so as to observe each microstructure and examine strain-stress curve simultaneously; examine tensile test and hardness test; eventually set up the optimum hot forging condition. A hot forging test, tensile test, hardness experiment, and microstructure observation were carried out on condition of $70\%$ reduction rate, $500^{\circ}C$ temperature of materials, and 1 strain rate. As a result of those experiments, 330MPa tensile strength, $16.4\%$ elongation, and 122.8Hv hardness were recorded. In oder to get a sound preform which has no unfitting cavity and less flash, two preforms were proposed on the basis of volume rate of the final product; the optimum volume rate of preform for the low control arm was $115\%$. In conclusion, it is confirmed that using the forging material rather than casting materials in casting/forging process is likely to get more superior mechanical properties. Compared with Al6061, performed by means of general forging, moreover, cast/forged Al6061 can not only stimulate productivity by reducing production processes, but cut down the cost of materials by reusing forging scraps.

• Korean Chemical Engineering Research
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• 제51권3호
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• pp.313-318
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• 2013

$V_2O_5-WO_3/TiO_2$ 촉매의 질소산화물 환원반응에 있어서 $V_2O_5$ 함량이 NO 환원 및 $N_2O$ 생성에 미치는 영향을 조사하기 위하여 분말촉매를 사용한 미분반응기에서 실험 연구를 수행하였다. 고정된 비율의 $WO_3$와 $TiO_2$에 $V_2O_5$ 함량을 1에서 8 wt%까지 변화시킨 촉매에서 NO 환원반응과 암모니아 산화반응 특성이 조사되었다. $V_2O_5-WO_3/TiO_2$ 촉매에서 NO 환원 반응은 $200^{\circ}C$ 이하에서도 상당량 진행되지만, $V_2O_5$ 함량을 1 wt% 촉매의 경우 700 ppm의 NO를 99.9%이상 전환시키는 최저 반응온도가 $340^{\circ}C$에서 아주 좁은 활성 온도창으로 일어났다. 그리고 이 활성온도는 촉매의 $V_2O_5$ 함량이 증가됨에 따라 점점 저온 쪽으로 이동하여, 6 wt% 촉매의 경우 $220{\sim}340^{\circ}C$에서 높은 활성을 보였다. $V_2O_5$ 함량이 8 wt% 촉매의 경우 전 온도 구간에서 6 wt% 촉매보다 낮은 NO 환원율을 보였다. 그러나 반응온도 $340^{\circ}C$ 이상에서는 촉매의 $V_2O_5$ 함량이 증가함에 따라 NO 전환율이 감소하였다. 이는 $V_2O_5-WO_3/TiO_2$ 촉매의 NO 환원을 위한 촉매 활성점 상당 크기 이상의 $V_2O_5$ 입자와 관계되는 것으로 판단되며 촉매 입자가 클수록 $320^{\circ}C$ 이상에서 암모니아 산화에 의해 발생되는 $N_2O$ 생성을 고려하여야 한다. $V_2O_5-WO_3/TiO_2$ 촉매는 배기가스 중의 질소산화물 제거를 위하여 현재 통상적으로 $350{\sim}450^{\circ}C$의 영역에서 운전되고 있으나, 고온 영역에선 2차 오염물인 $N_2O$의 발생을 피할 수 없고 에너지 소비량이 많으므로, $250{\sim}320^{\circ}C$의 저온 영역에서 적합한 촉매로써 $V_2O_5$ 함량이 높은 $V_2O_5-WO_3/TiO_2$ 촉매의 사용이 권장되었다.

• 열처리공학회지
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• 제18권4호
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• pp.242-246
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• 2005

Silver nanoparticles were synthesized by liquid phase reduction method from aqueous silver nitrate solution and borohybride as a reduction agent. The morphology, particle size and shape were influenced by the reaction conditions such as the concentration of $AgNO_3$, a reduction agent and addition of surfactant. The particle size decreased with decreasing the concentration of silver nitrate and using a borohydride. The obtained Ag particles showed the spherical shape with the range of 10-20 nm.

• Tribology and Lubricants
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• 제21권6호
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• pp.249-255
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• 2005

In this paper, the friction characteristic of engine bearings has been analyzed in terms of a friction loss power, a minimum film thickness and an oil film pressure. This analysis has been focused on the fuel economy improvement with a low viscosity engine oil such as SAE 0W-40, which is used for a friction loss reduction and increased for a Diesel fuel economy. The friction loss power, the minimum oil film thickness and oil film pressure distribution for plain bearings of a Diesel engine are analyzed using an AVL's EXCITE program with a conventional engine oils of SAE 5W-40 and 10W-40, and a low viscosity engine oil of SAE 0W-40. The computed results indicate that a viscosity of engine oils is closely related to the friction loss power and the decreased minimum film thickness in which is a key parameter of a load carrying capacity of an oil film pressure distribution. When the low viscosity engine oil is supplied to engine bearings, it does not affect to the formation of a minimum oil film thickness. But the friction loss power has been significantly affected by low viscosity engine oil at a low operating temperature of 0. Based on the FEM computed results, the low viscosity engine oil at a low temperature range will be an important factor for an improvement of the fuel economy improvement.

• 에너지공학
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• 제7권2호
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• pp.163-171
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• 1998

고분자 첨가물의 퇴화는 시험용액의 고온상태에서 증가된다. 합성고분자용액의 퇴화에 대해 시간에 따른 온도와 고분자 농도의 영향을 알아보기 위해 6$0^{\circ}C$, 8$0^{\circ}C$의 온도와 100, 200, 400, 600 ppm의 다양한 고분자 농도에 따라 폐회로방식으로 실험적인 연구를 하였다. 퇴화효과는 기계적 퇴화보다 온도에 더 의존적임이 밝혀졌다. 마찰계수와 레이놀즈 수의 관계는 레이놀즈 수가 5만부터 15만까지의 범위에서 레이놀즈 수가 증가함에 따라 마찰계수가 감소하고, 저온에서 마찰은 Vi가의 최대마찰저항감소 점근선에 접근한다는 것을 보인다. 일정한 유량과 온도에 대해, 높은 고분자 농도에서 퇴화효과가 더 작게 밝혀졌다. 일정한 유량과 고분자 농도에 대해서는 퇴화율이 주로 온도에 영향받는 것으로 밝혀졌다. 8$0^{\circ}C$의 온도, 100 ppm의 고분자 농도에서 4시간후에 마찰저항 감소효과가 없어졌다. 그러나, 열적퇴화는 고분자 분자들간의 결합력을 증가시켜 주는 것으로 생각되는 계면활성제 같은 추가적인 물질을 이용하여 극복할 수 있을 것이다.

• 대한기계학회논문집A
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• 제30권8호
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• pp.965-975
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• 2006

High pressure turbine blades are one of the key components in fossil power plants operated at high temperature. The blade is usually made of 12Cr steel and its operating temperature is above $500^{\circ}C$. Long term service at this temperature causes material degradation accompanied by changes in microstructures and mechanical properties such as strength and toughness. Quantitative assessment of reduction of strength and toughness due to high temperature material degradation is required for residual life assessment of the blade components. Nondestructive technique is preferred. So far most of the research of this kind was conducted with low alloy steels such as carbon steel, 1.25Cr0.5Mo steel or 2.25Cr1Mo steel. High alloy steel was not investigated. In this study one of the high Cr steel, 12Cr steel, was selected for high temperature material degradation. Electrochemical polarization method was employed to measure degradation. Strength reduction of the 12Cr steel was represented by hardness and toughness reduction was represented by change of transition temperature, FATT. Empirical relationships between the electrochemical polarization parameter and significance of material degradation were established. These relationship can be used for assessing the strength and toughness on the aged high pressure blade components indirectly by using the electrochemical method.

• 한국식품과학회지
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• 제31권5호
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• pp.1216-1220
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• 1999

팽윤도와 용해도는 blanching time이 길어질수록 증가했으며 blanching 온도 $55^{\circ}C$가 $45^{\circ}C$ 보다 낮은 경향을 보였으며 blanching온도 $45^{\circ}C$/15분을 유지시킨 것이 가장 높은 팽윤도와 용해도를 보였고, 수분흡수지수와 수분용해지수는 각 온도에서 holding time이 길어질수록 상대적으로 증가하는 경향을 나타냈으며 수분흡수지수는 blanching 온도 $55^{\circ}C$/15분 유지한 것이, 수분용해지수는 blanching 온도 $45^{\circ}C$/30분 유지한 것이 가장 높은 경향을 나타내었다. Visco/amylograph 측정에서 최대점도는 온도와 시간에 많은 영향을 받는 것으로 나타났으며 blanching 온도 $55^{\circ}C$/60분 유지시킨 것이 가장 높은 점도를 나타내었다. 이와 같은 실험결과로 보아 blanching 온도와 시간이 밤에 존재하는 가용성성분의 변화와 함께 밤가루 내의 전분사슬과 밤가루 표면구조의 변화에 영향을 미쳐 호화 특성에 변화를 준 것으로 보인다. 따라서, blanching처리한 밤가루가 밤가공품의 중간소재로 사용함으로서 다양한 성질을 나타내는 과정으로 생각된다.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2008년도 춘계 학술논문 발표대회
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• pp.57-60
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• 2008

This study investigated the results of insulation heat curing method using double layer bubble sheet in slab concrete and mass concrete in cold weather environment. First of all, when double bubble sheets are applied, it was shown that slab concrete was protected from early freezing by remaining between 6 and 15℃ even in case outside temperature drops -9℃ below zero until the 2nd day from piling, and in the case of mass concrete, with the maximum temperature difference between the center and surface less than 4℃, crack occurrence index was close to 2 and no hydration heat crack occurred by internal constraint. The insulation heat preservation curing method using the double bubble sheet applied in this field prevented early freezing owing to stable curing temperature management, deterring concrete strength development delay at low temperature, and obtained the needed strength. Also, it was proven that the method is highly effective and economic for cold weather concrete quality maintenance through curing cost reduction like construction period shortening and labor cost reduction, etc by reducing the process of temporary equipment installation and disassembling.

• 공업화학
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• 제18권3호
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• pp.255-261
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• 2007

망간계 금속산화물을 이용한 저온 선택적 촉매 환원 반응에 대하여 연구하였다. 망간계 금속산화물은 $200^{\circ}C$ 이하의 저온에서 우수한 탈질 특성을 보인다. 온도에 따른 $NH_3/NOx$ 몰비 변화 실험을 통하여 미반응 암모니아의 배출은 몰비가 증가하고 온도가 감소할수록 증가하였으며, $NO_2$의 발생은 반대의 현상을 보였다. $NO_2$는 NO가 촉매 표면에 흡착된 후 nitrate종으로 산화되어 생성되는 것으로 보인다. 촉매 표면에 생성된 nitrate종과 흡착된 암모니아가 반응하기 때문에 $NH_3/NOx$ 몰비 1.0 이상에서도 미반응 암모니아의 배출이 없었다. 담지된 금속산화물의 영향은 Zr은 산화상태를 증가시켜 $NO_2$의 배출이 증가하였으며, Ce를 첨가시킨 경우 $NO_2$ 발생량이 감소하였다. 그러나 금속산화물의 첨가는 전체적으로 NOx 전환율을 감소시켰다

• 대한치과보철학회지
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• 제45권1호
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• pp.60-70
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• 2007

Statement of problem: The cement-type abutment would be needed for the reduction of its body in order to correct the axis and to assure occlusal clearance. In the case of intraoral preparation, there is a potential risk that generated heat could be transmitted into the bone-implant interface, where it can cause deterioration of tissues around the implant and failed osseointegration. Purpose: The purpose of this study was to assess the difference of the heat transmitting effect on external and internal connection implant types under various conditions. Material and method: For evaluating the effects of alternating temperature, the thermocoupling wires were attached on 3 areas of the implant fixture surface corresponding to the cervical, middle, and apex. The abutments were removed 1mm in depth horizontally with diamond burs and were polished for 30 seconds at low speed with silicone points using pressure as applied in routine clinical practice. Obtained data were analyzed using Mann-Whitney rank-sum test and Wilcoxon / Kruskal-Wallis Tests. Result: Increased temperature on bone-implant interface was evident without air-water spray coolant both at high speed reduction and low speed polishing (p<.05). But, the difference between connection types was not shown. Conclusion: The reduction procedure of abutment without using proper coolant leads to serious damage of oral tissues around the implant irrespective of external and internal connection type.