• 한국의류산업학회지
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• 제7권2호
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• pp.247-251
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• 2005

In this the study, the effects of the manufacturing process conditions on the properties Thick and Thin Diameter yarns(TTD yarns) prepared with hot plate device in the draw winder were determined. Physical properties including wet shrinkage, tenacity and elongation of the samples were measured and thick and thin effect was analysed with the evenness tester. The results were as the follows: There was little change the wet shrinkage of the TTD yarns in the range of $70^{\circ}C{\sim}80^{\circ}C$ of $R_1$ temperature(lower hot cylinder) with the same Hot Plate(H/P) temperature, but the wet shrinkage of the TTD yarns decreased 5-10% when $R_1$ temperature was $90^{\circ}C$. The wet shrinkage of the TTD yarns decreased with the H/P temperature at the same temperature of $R_1$. There was little effect of $R_1$ and H/P temperature on the tenacity of TTD yarns. The elongation of TTD yarns increased with $R_1$ temperature at the same H/P temperature. The elongation of TTD yarns increased little bit for the first time and then decreased above that temperature with increasing H/P temperature at the same $R_1$ temperature. The thick and thin effect on the TTD yarns was obvious in $110^{\circ}C$ of H/P temperature regardless of $R_1$ temperature, while there was no thick and thin effect on the TTD yarns in $140^{\circ}C$ of H/P temperature.

• 한국도로학회논문집
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• 제11권2호
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• pp.111-120
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• 2009

본 연구는 배수성 아스팔트 포장의 표면을 아크릴 수지로 코팅 처리할 경우 내구성 측면 및 기능적 측면에서 어떠한 효과가 있는가를 실내시험을 통해 평가하는 기초적인 연구이다. 포장의 내구성 측면에서는 칸타브로 및 휠트래킹, 수분손상 간접 인장 피로 시험 등을 실시하였다. 시험결과 시편을 수지로 코팅을 한 경우 칸타브로 손실률이 3배 정도 감소되었고 균열에 대한 저항성도 대폭 향상되었으나 수분손상 및 소성변형의 저항성은 큰 차이가 없는 것으로 나타났다. 기능적인 측면에서는 코팅 전 후의 투수계수 및 공극률 BPT(British Pendulum Tester)를 사용한 미끄럼 저항성의 변화를 측정하였다. 시험결과 공극률 및 투수계수는 약간 저하되나 기능상의 문제는 없을 것으로 판단되며, 미끄럼 저항성은 규사를 살포하지 않을 경우 미끄럼 저항성이 감소되나 규사를 살포할 경우 코팅 전 수준 이상의 미끄럼 저항성을 확보하는 것으로 나타났다.

• 한국세라믹학회지
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• 제39권1호
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• pp.79-85
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• 2002

플라즈마 용사코팅법을 이용하여 산화몰리브덴이 첨가된 크로미아 용사코팅층을 제조하여 MoO$_3$첨가에 따른 마찰, 마멸특성을 조사하였다. 상온 마찰, 마멸특성에 대한 실험을 위하여 왕복동 마멸시험장치를 사용하였다. 마멸시험후 마멸면의 물리적 변화와 화학적 조성의 변화를 SEM와 XPS를 통하여 살펴보았다. 산화몰리브덴이 첨가된 코팅층에서 마찰계수의 감소를 관찰할 수 있었다. 그러나 마멸량의 경우 산화몰리브덴이 첨가되지않은 크로미아 코팅층에서 가장 낮은 값을 나타내었다. 산화몰리브덴이 첨가된 코팅의 마멸된 표면에 마탈, 마멸에 유리한 보호막의 형성이 광범위하게 일어남을 알 수 있었다. 이러한 보호막에 산화몰리브덴이 MoO$_3$의 형태로 존재하는 것을 XPS분석을 통하여 알 수 있었다. 보호막에 산화몰리브덴의 존재가 마찰계수를 감소시키는 것으로 생각된다.

• Journal of Periodontal and Implant Science
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• 제32권2호
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• pp.315-324
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• 2002

The purpose of this in vitro study was to evaluate the efficiency of Er:YAG laser on calculus removal and the morphologic changes and hardness of the irradiated surface at different power settings. This experiment used human teeth which were extracted due to periodontal disease and had a band of calculus. Forty root slabs ($5{\times}5mm$) were made and divided into control group and irradiated groups. Experimental groups were as follows; Control group (root planing), Group1 (irradiated with laser at 30mJ), Group2 (irradiated with laser at 60mJ), Group3 (irradiated with laser at 100mJ). Twelve root slab embedded in resin block were used in each group. Er:YAG laser was applied under water irrigation with the tip held perpendicular to the root surface in contact mode. The treatment time was measured until the calculus was removed completely under naked eyes. The efficiency of calculus removal was evaluated by the time for removal. Morphological changes of laser irradiated site were observed under SEM and the surface hardness was measured using a VH tester. The results were as follows; 1. The efficiency of laser scaling was increased with increasing the energy level of irradiation(p<0.05). 2. The morphological changes such as carbonization, crater and scale-like defects in the irradiated root surface were frequently observed with increasing the energy level. 3. The surface hardness tended to increase at 60mJ and 100mJ irradiated groups than that of control group. From the results evaluting on the efficiency, morphological change and surface hardness, lower energy level was suggested for the clinical application of the Er:YAG laser in scaling.

• Tribology and Lubricants
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• 제31권1호
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• pp.1-5
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• 2015

In this study, we apply an ultrasonic nanocrystal surface modification (UNSM) technique to radial journal bearings (JBs) and disks made of SUJ2 and SCM440, respectively. We investigate frictional properties of untreated and UNSM-treated specimens using a ball-on-disk tester. We construct the Stribeck curve at the boundary, under mixed and full hydrodynamic lubrication conditions for the specimens using friction data obtained from JB tests. The friction at the boundary lubrication condition and the transition period to mixed lubrication condition on the UNSM-treated specimens is reduced, which improves the service life of JBs. The major effects of this reduction in the three lubrication regimes can be explained in the terms of improved mechanical properties and the presence of micro dimples. Moreover, we estimate the friction and fatigue properties of SCM440 specimens using a ball-on-disk specimen under dry and oil-lubricated conditions. Friction test results reveal that the UNSM-treated specimens show lower friction coefficient than the untreated specimens under both dry and oil-lubricated conditions. We evaluate the fatigue properties of SCM440 specimens by calculating the Hertzian stress with respect to the failure cycles. Fatigue tests results also reveal that the UNSM-treated specimens possess a longer fatigue life than the untreated specimens. The improved properties are effective in increasing the energy efficiency of bearings.

• 한국안전학회지
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• 제22권5호
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• pp.77-83
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• 2007

식물류에 다량으로 함유되어 있는 Cellulose는 인체에 무해할 뿐 아니라 연소시에 발생하는 유해가스가 적어서 친환경적인 에너지 자원으로 대두되고 있다. 특히 Cellulose의 유도체 중 하나인 Hydroxypropyl Methyl Cellulose(HMC)는 의약품의 코팅재료를 비롯하여, 고급용 건축자재, 염료, 화장품 등의 첨가제로 사용되면서, 사용량이 계속해서 증가하고 있다. 따라서 여러 가지 위험에 노출될 수 있으며, 열적 위험특성을 알기 위한 방법으로 일본에서 많이 사용되고 있는 단열자기발열실험장치(SIT-II)를 이용하여 HMC의 한계발화온도와 겉보기활성화에너지를 구하였다. 또한 국제적으로 널리 알려진 Frank-Kamenetskii의 무한평판을 기준으로 한 자연발화실험(IF-SIT)자료를 이용하여 자연발화온도와 활성화 에너지 값을 비교하였다. HMC의 자연발화온도와 겉보기 활성화 에너지는 SIT-II의 경우 $186^{\circ}C$의 한계발화온도와 104.5kJ/mol의 활성화 에너지를 구하였다. 기존에 구하여진 IF-SIT결과 값과 비교하였을 때 무한평판의 두께 3cm, 5cm, 7cm에 대해 각각 한계발화온도가 $199.5^{\circ}C,\;188.5^{\circ}C,\;180.5^{\circ}C$이고, 167.4kJ/mol의 활성화 에너지 값을 지니므로, SIT-II로 구하여진 겉보기 활성화 에너지는 IF-SIT로 구하여진 값 보다 낮게 나타났으며, 이 값은 일반 Cellulose의 활성화 에너지 값 보다 도 더 낮은 것으로 나타났다.

• 대한환경공학회지
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• 제38권8호
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• pp.428-434
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• 2016

본 연구에서는 하수 내 인 제거 시 티타늄계열 응집제의 인 제거특성을 알아보기 위해 알루미늄계열 응집제와 비교하였다. Jar-tester를 이용하여 다양한 OH/Ti 몰비(B값)의 응집제를 투여하여 실험을 진행하였다. 초기 인 농도가 증가할수록 처리 후 $PO_4-P$ 농도가 0.2 mg P/L 이하에 도달하기 위한 [Ti]/[P]는 감소하였다. T-P 제거효율은 응집제 주입량이 증가할수록 높아졌지만, 최고 제거효율에 도달한 후에는 B값에 관계없이 감소하였다. 반면에 $PO_4-P$ 제거율은 최고점에 도달한 후 B값에 상관없이 일정하게 유지하는 경향이 나타났다. 동일한 인 제거효율에서 Ti계열 응집제의 주입량은 Al계열 응집제보다 약 2배정도 높았다. 또한, Ti계열 응집제의 B값에 따라 인제거효율에 영향을 미쳤다.

• 설비공학논문집
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• 제22권6호
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• pp.383-391
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• 2010

In this study, HFC152a, HFC134a/HFC152a and HC290/HFC134a/HFC152a mixtures are studied for the supplementary and alternative refrigerants for HFC134a used in automobile air-conditioners. Due to the high global warming potential of HFC134a, it has to be phased out in the long run. Thermodynamic performance of these refrigerants are measured in a bench tester of 3.5 kW capacity with an open type compressor under both summer and winter conditions. Test results show that the coefficient of performance (COP) and capacity of pure HFC152a and HFC134a/HFC152a mixture are 9.1~12% and 7% higher than those of HFC134a. As for the HC290/HFC134a/HFC152a, the COP is up to 9.5% higher than that of HFC134a with 1~2% of HC290 while that is up to 6.1% lower than that of HFC134a with 5% HC290. The capacity of the ternary mixture, however, is 8.6% higher than that of HFC134a at all compositions tested. The compressor discharge temperatures of all refrigerants tested are $6{\sim}10^{\circ}C$ higher than that of HFC134a. For all refrigerants, the amount of charge is reduced up to 32% due to the decrease in liquid density. Overall, these refrigerants provide good performance with reasonable energy savings with less environmental problem and thus can be used as long term alternatives for automobile air-conditioners.

• 보건교육건강증진학회지
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• 제13권2호
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• pp.167-183
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• 1996

Human teeth vary widely in color. Practitioner and patients are concerned with preventing and correcting discolored or dark teeth to achieve and maintain stain-free, white teeth. Tooth brushing cannot alter tooth color but it can remove adhering films and stains. The esthetics of natural dentition can be improved by bleaching and this process can be applied to intrinsically and extrinsically stained teeth. The need for a brighter, more attractive smile has made rapid growth in the market for tooth whiteners. There is no doubt these products work as whiteners, at least on mild to moderate stains, but the safety of these products are unclear. In this experiment, the effect of tooth whitener application on the color and microhardness of extracted human enamel was measured. RMS, RMT and NWT were used as tooth whiteners, and tooth paste(ETQ) and hydrogen peroxide solution(HPO) were used as controls. 35 caries-free extracted human molars were embedded and polished with the exposed enamel diameter of 4 mm. The tooth whiteners and control agents were applied according to the manufacturers' instructions or clinically simulated procedures for eight weeks, and measurements were repeated every two weeks. Value(L＊) difference was measured using Differential Colorimeter(Model TC-6FX, Denshoku Co., Japan), and microhardness was measured using microhardness tester(Mitsuzawa Seiki Co., Japan). The results were as follows; 1. After application of agents for eight weeks, the Vickers hardness increased significantly in the ETQ, RMS and RMT application group(p〈0.01), and that decreased significantly in NWT application group(p〈0.01), but in HPO application group there was no significant change. The change in microhardness was greatest in NWT application group(p〈0.01). 2. After application of tooth whiteners and controls for eight weeks, the value change of toothpaste application group was significantly lower than those of other agents groups(p〈0.01), and there was no significant difference in value(L＊) change among tooth whitener groups(p〉0.01). 3. The application of tooth paste and paste type tooth whitener made gradual value change, but hydrogen peroxide gel type tooth whitener and hydrogen peroxide solution made rapid value change during initial application period.

• Tribology and Lubricants
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• 제34권2호
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• pp.49-54
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• 2018

Hydraulic reciprocating seal has been widely used to prevent fluid leakage in hydraulic systems. Also, hydraulic reciprocating seal plays a significant role to provide lubricant film at contacting interface to minimize tribological problems due to sliding with counter material. To predict lifetime of hydraulic reciprocating seal, quantitative understanding of wear characteristics with respect to operating conditions such as normal force and sliding speed is needed. In this work, effect of sliding speed on wear of polyurethane (PU) hydraulic reciprocating seal were experimentally investigated using a pin-on-disk tribo-tester. The wear characteristics of PU specimens were quantitatively determined by comparing the confocal microscope data before and after test. It was found that the wear rate of PU specimens decreased from $4.9{\times}10^{-11}mm^3$ to $1.1{\times}10^{-11}mm^3/Nm$ as sliding speed increased from 120 mm/s to 940 mm/s. Also, it was observed that the friction decreased slightly as the sliding speed increased. Improvement of lubrication state with increasing sliding speed was likely to be responsible for this enhanced friction and wear characteristics. This result also suggests that decrease in sliding distance between PU elastomer and counter materials at lower sliding speed is preferred. Furthermore, the quantitative assessment of wear characteristics of PU specimen may be useful in prediction of lifetime of PU hydraulic reciprocating seal if the allowed degree of wear for failure of the seal is provided.