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나사 풀림 방지를 위한 걸림턱 구조의 와셔 개발 및 성능 비교
오영탁(Young-Tak Oh),김기대(Gi-Dae Kim) 한국기계가공학회 2020 한국기계가공학회지 Vol.19 No.8
In this study, hole-boss locking washers were developed to prevent vibrational loosening, and a benchmark test was conducted to compare these washers with existing wedge locking washers, which are imported and high-priced. The developed washers consist of an upper washer with bosses and a lower washer with holes, and the bosses are caught in the holes so that the bolt is not loosened. Additionally, the top side of the upper washer and the underside of the lower washer have small wedges perpendicular to the direction of the bolt loosening, suppressing slips. A test by the Korea Test Laboratory indicated that the ratio of the loosening torque to the joining torque is greater than 70%, confirming that the developed washers have a sufficiently high anti-loosening performance. A Junker test apparatus was manufactured for the testing of vibrational loosening and a test comparison between the proposed washers and the existing wedge locking washers shows that the proposed washers have a slower reduction in the clamping force and a higher loosening-resistance in a vibrational circumstance compared with the wedge locking washers. These results indicate that the developed washers demonstrate a high performance and boast price competitiveness.
국내 논토양 및 밭토양 중 농약유래 잔류성유기오염물질의 노출량 평가
임성진,오영탁,노진호,김승용,주형곤,이민호,윤효인,최근형,류송희,박병준,Lim, Sung-Jin,Oh, Young-Tak,Ro, Jin-Ho,Kim, Seung-Yong,Joo, Hyeong-Gon,Lee, Min-Ho,Yoon, Hyo-In,Choi, Geun-Hyoung,Ryu, Song-Hee,Park, Byung-Jun 한국환경농학회 2017 한국환경농학회지 Vol.36 No.3
BACKGROUND:This study was conducted to investigate residual organochlorine pesticides (ROCPs) in agricultural soils and crops. Agricultural soil samples and crop samples were collected from 93 cities and counties. METHODS AND RESULTS: Extraction and clean-up for the quantitative analysis of ROCPs were conducted by the modified quick, easy, cheap, effective, rugged, and safe (QuEChERS) method. Recovery and limit of detection (LOD) of ROCPs in agriculturalsoils and crops were 76.5-103.0 and 75.2-93.2%, 0.01-0.08 and $0.10-0.15{\mu}g/kg$, respectively. Detected ROCPs in agricultural soils were ${\alpha}$-endosulfan, ${\beta}$-endosulfan, and endosulfan sulfate, the residue were 2.0-12.0, 1.2-53.1, and $2.2-329.8{\mu}g/kg$, respectively. But these pesticides in all green perilla leaf and green pepper samples were not detected. CONCLUSION: These results showed that ROCPs residues in agricultural soils were not as high as crop safety threatening.
김기대(Gi Dae Kim),오영탁(Young Tak Oh) 한국생산제조학회 2005 한국생산제조학회지 Vol.14 No.6
During stereolithography processes, one of the main sources of dimensional error of prototype is the distortion effect owing to the shrinkage of resin. In this study, the effects of dimension of specimen, such as length, width, and thickness, on the curl distortion is examined. During the SL processes, the variation of curl distortion error is measured according to the number of layers. Through this study, it is verified that there is a big difference of the distortion error in both direction and magnitude between before and after the supports are removed. It is also observed that end profile of the test part and the upper side around the border are also distorted due to the shrinkage of the resin.