• Journal of the Korean Wood Science and Technology
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• 제43권5호
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• pp.672-681
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• 2015

As a part of abating the formaldehyde emission of amino resin-bonded wood-based composite panels, this study was conducted to investigate hydrolytic stability of urea-melamine-formaldehyde (UMF) resin depending on various hydrolysis conditions and hardener types. Commercial UMF resin was cured and ground into a powdered form, and then hydrolyzed with hydrochloric acid. After the acid hydrolysis, the concentration of liberated formaldehyde in the hydrolyzed solution and mass loss of the cured UMF resins were determined to compare their hydrolytic stability. The hydrolysis of cured UMF resin increased with an increase in the acid concentration, time, and temperature and with a decrease in the smaller particle size. An optimum hydrolysis condition for the cured UMF resins was determined as $50^{\circ}C$, 90 minutes, 1.0 M hydrochloric acid and $250{\mu}m$ particle size. Hydrolysis of the UMF resin cured with different hardener types showed different degrees of the hydrolytic stability of cured UMF resins with a descending order of aluminum sulfate, ammonium chloride, and ammonium sulfate. The hydrolytic stability also decreased as the addition level of ammonium chloride increased. These results indicated that hardener types and level also had an impact on the hydrolytic stability of cured UMF resins.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2016년도 추계 학술논문 발표대회
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• pp.15-16
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• 2016

Ways to efficiently manufacture gloss exposed mass concrete at an inexpensive price, in other words, ways to paste transparent transfer paper onto the surface of a combined mold has been designated as New Technology Article 191 by the Ministry of Land, Infrastructure and Transport. But if the difference in the coefficient of linear expansion between the mold's and transfer paper's material causes temperature to rise or fall, a wrinkly surface can appear. Therefore this study, by experimentally comparing the deformation characteristics between the mold material and transfer paper material upon changes in temperature, seeks to serve as a basic reference point for selecting the optimal transfer paper for different mold types. Study results revealed that for molds, polyester resin transfer paper is optimal, and for aluminum molds, acrylic resin transfer paper is.

• Design & Manufacturing
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• 제13권4호
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• pp.17-22
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• 2019

Currently, studies on weight reduction and fuel efficiency increase are the most important topics in the automotive industry and many studies are under way. Among them, weight reduction is the best way to raise fuel efficiency and solve environmental pollution and resource depletion. Materials such as aluminum, magnesium and carbon curing materials can be found in lightweight materials. Among these, research on improvement of bonding technology and manufacturing method of materials and improvement of material properties through study of ultrahigh strength steel sheet is expected to be the biggest part of material weight reduction. As the strength of the ultra hight strength steel sheet increases during forming, it is difficult to obtain the dimensional accuracy as the elastic restoring force increases compared to the hardness or high strength steel sheet. It is known that the spring back phenomenon is affected by various factors depending on the raw material and processing process. We have conducted analytical evaluations and studies to analyze the springback that occurs according to the cross-sectional shape of the ultra high tensile steel sheet.

• Tribology and Lubricants
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• 제11권5호
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• pp.40-46
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• 1995

This study concerns the design and development of the non-vibrating capacitance probe which could be used as a non-contact sensor for tribological wear. This device detects surface charge through temporal variation in the work function of a material. Experiments are performed to demonstrate the operation of the probe on a roating aluminum shaft. The reference electrode of the probe, made of lead, is placed adjacent (< 1.25-mm distance) to the shaft. Both surfaces which are electrically connected, form a capacitor. An artificial spatial variation in the work function is imposed on the shaft surface by coating a segment along the shaft circumference with a colloidal silver paint. As the shaft rotates, the reference electode senses changing contact potential difference with the shaft surface, owing to compositional variation. Temporal variation in the contact potential difference induces a current through the electrical connection. This current is amplified and converted to a voltage signal by an electoronic circuit with an operational amplifier. The magnitude of the signal decreases asymptotically with the electrode-shaft distance and increases linearly with the rotational frequency. These results are consistent with the theoretical model. Potential applications of the probe on wear monitoring are proposed.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1994년도 추계학술대회 논문집
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• pp.571-576
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• 1994

In recent years, ultrasonic has been widely applied in measurement and industrial fields and its application range has been expanded as a result of continuous research and development. Wire Bonding Machine, an instrument fabricating semi-conductor, makes use of ultrasonic bonding method. In order to improve the currently used wire bonding machine using ultrasonic energy, technical accumulation is needed steadily through development of exciting device of ultrasonic composed of piezoelectic vibrator and horn. This study investigates the design conditions affecting the dynamic characteristics through the theoretical and experimental analysis of piezoelectric vibrator and horn, The study conducts separately the system identification of piezoelectric vibrator in time domain and the modal analysis of horn in frequency domain. In theoretical model, the integrated modeling is conducted via a combination of dynamic identification of piezoelectric vibrator and theoretical analysis of horn. Hence comparison is made for theoretical and experimental results of the dynamic characteristics of the ultrasonic transducer composed of piezoelectric vibrator and horn. Form the results of this study we develop the design technique of ultrasonic transducer using dynamic characteristic analysis and propose the possibility of ultrasonic welding considering the optimal condition of the natural frequency and vibration mode of horn.

• 한국펄프종이공학회:학술대회논문집
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• 한국펄프종이공학회 2006년도 PAN PACIFIC CONFERENCE vol.2
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• pp.387-390
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• 2006

Cationic rosin sizes are prepared by premixing extremely pure ployaluminum chloride (PAC) and dispersed rosin size (DRS). It turned out that zeta potential and particle size of the sizing agents took a big change by Plus90 analyzer's and FTIR analyzer's analysis. It turned out that -C=O and -COOH of the DRS have both chemical reaction with PAC to form the muti-hydroxyl aluminum rosin acid and that the cationic rosin sizes modified by PAC has dissymmetric and symmetric flexible vibration two absorbing peaks of the groups (its absorbing peaks $at1596cm^{-1}\;and\;1425cm^{-1}$). By DRS reacting with PAC, zeta potential of the resin size varied from negative to cationic. $Al_{2}O_{3}/rosin=1:0.3$, zeta potential of premixed admixture is tiptop28.8mv, When joined continuously PAC, zeta potential of cationic rosin sizes descend on the contrary.

• 공업화학
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• 제1권2호
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• pp.176-181
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• 1990

탄소섬유/알루미늄 복합 재료의 계면 전단 강도를 향상시키기 위하여 탄소섬유 표면을 $400-600^{\circ}C$의 온도 범위에서 황화수소 기체로 처리하였다. 처리 탄소섬유 표면의 변화를 주사 전자 현미경과 X-선 광전자 스펙트럼에 의해 관찰하고 분석하여 표면 처리 탄소섬유의 표면에 황 화합물이 존재하는 것을 확인하고, 표면처리 탄소섬유의 탄소 및 탄소의 함량 변화를 조사하였다. 탄소섬유 표면의 황화수소 기체 처리의 최적 온도는 $550^{\circ}C$였고, 처리 탄소섬유 표면의 황 화합물은 disulfide, $(S)_n$ 및 thiophene의 형태를 이루고 있었다. 처리 탄소섬유는 처리 온도 $400-600^{\circ}C$의 범위에서 5% 정도의 인장 강도 저하를 나타냈다.

• 한국정밀공학회지
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• 제23권5호
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• pp.44-50
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• 2006

This paper describs about the technique of ultra-precision machining for an infrared(IR) camera aspheric mirror. A 200 mm diameter aspheric mirror was fabricated by SPDTM(Single Point Diamond Turning Machine). Aluminum alloy as mirror substrates is known to be easily machined, but not polishable due to its ductility. Aspheric large reflector without a polishing process, the surface roughness of 5 nm Ra, and the form error of ${\lambda}/2\;({\lambda}=632.8\;nm)$ for reference curved surface 200 mm has been required. The purpose of this research is to find the optimum machining conditions for cutting reflector using Al6061-T651 and apply the SPDTM technique to the manufacturing of ultra precision optical components of Al-alloy aspheric reflector. The cutting force and the surface roughness are measured according to each cutting conditions feed rate, depth of cut and cutting speed, using diamond turning machine to perform cutting processing. As a result, the surface roughness is good when feed rate is 1mm/min, depth of cut $4{\mu}m$ and cutting speed is 220 m/min. We could machined the primary mirror for IR camera in diamond machine with a surface roughness within $0.483{\mu}m$ Rt on aspheric.

• 한국표면공학회지
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• 제51권1호
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• pp.34-39
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• 2018

Steel crucible used for molten Al has a problem of very limited lifetime because of the interaction between Fe and molten Al. This study was performed to improve the lifetime of steel crucible for molten Al by coating metallic Al and by further anodizing treatment to form thick and uniform anodic oxide films. The lifetime of the steel crucible was improved slightly by Al coating from 30 to 40 hours by metallic Al coating and largely to 120 hours by coating the surface with anodic oxide film. The improved lifetime was attributed to blocking of the reaction between Fe and molten Al with the help of anodic oxide layer with more than 20 um thickness on the crucible surface. The failure of the steel crucible arises from the formation of intermetallic compounds and pores at the steel/Al interface.

• 한국표면공학회지
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• 제44권4호
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• pp.125-130
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• 2011

$Cr_2AlC$ compounds were synthesized by hot pressing, and oxidized between 900 and $1200^{\circ}C$ in air for up to 50 hours. They oxidized to a thin $Al_2O_3$ layer containing a small amount of $Cr_2O_3$with the liberation of carbon as CO or $CO_2$ gases. The consumption of Al to form the $Al_2O_3$ layer led to the depletion of Al and enrichment of Cr just below the $Al_2O_3$ layer, resulting in the formation of an underlying $Cr_7C_3$ layer. As the oxidation temperature and time increased, the $Cr_7C_3$ oxide layer and the underlying $Cr_7C_3$ layer thickened. The oxidation resistance of $Cr_2AlC$ was generally good due to the formation of the $Al_2O_3$ barrier layer.