• 한국표면공학회지
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• 제41권6호
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• pp.292-300
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• 2008

Dental implant system is composed of abutment, abutment screw and implant fixture connected with screw. The problems of loosening/tightening and stability of abutment screw depend on surface characteristics, like a surface roughness, coating materials and friction resistance and so on. For this reason, surface treatment of abutment screw has been remained research problem in prosthodontics. The purpose of this study was to investigate the stability of TiN and WC coated dental abutment screw, abutment screw was used, respectively, for experiment. For improving the surface characteristics, TiN and WC film coating was carried out on the abutment screw using EB-PVD and sputtering, respectively. In order to observe the coating surface of abutment screw, surfaces of specimens were characterized, using field emission scanning electron microscope(FE-SEM) and energy dispersive x-ray spectroscopy(EDS). The stability of TiN and WC coated abutment screw was evaluated by potentiodynamic, and cyclic potentiodynamic polarization method in 0.9% NaCl solution at $36.5{\pm}1^{\circ}C$. The corrosion potential of TiN coated specimen was higher than those of WC coated and non-coated abutment screw. Whereas, corrosion current density of TiN coated screws was lower than those of WC coated and non-coated abutment screw. The stability of screw decreased as following order; TiN coating, WC coating and non-coated screw. The pitting potentials of TiN and WC coated specimens were higher than that of non-coated abutment screw, but repassivation potential of WC coated specimen was lower than those of TiN coated and non-coated abutment screws due to breakdown of coated film. The degree of local ion dissolution on the surface increased in the order of TiN coated, non-coated and WC coated screws.

• 대한치과보철학회지
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• 제42권6호
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• pp.628-640
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• 2004

Statement of problem. Wear as a result of repeated closing/opening cycles may decrease the friction coefficient of screw head, threads, and other mating components and, consequently, resistance to opening gradually decreases. It may cause screw loosening, which is one of the most common failures in implant prosthesis. Purpose. The purpose of this study is to evaluate the changes on the head and thread surface of the abutment screws after repeated closing and opening through the examination of tested screws in SEM(scanning electron microscope). Materials and methods. Five species of abutments were selected (3i-three, Avana-two) respectively by two pieces. The implant fixtures were perpendicularly mounted in liquid unsaturated polyesther(Epovia, Cray Valley Inc.) with dental surveyor. Each abutment was secured to the implant fixture by each abutment screw with recommended torque value using a digital torque controller. The abutment screws were repeatedly tightened and removed 20 times with a digital controller. FESEM (field emission scanning electron microscope, Netherland, Phillips co., model:XL 30 SFEG) was used to observe changes of each part caused by repeatedly closing/opening expeiment. First, the Photomicrographs of pre-test screws provided by each manufacturer were taken. The changes of each screw were investigated after every fifth closing and opening experiment with FESEM. Scaning electron microscope photomicrographs of each screw were taken four times. Results. As the number of closing and opening was increased, the wear or distortion of hexed or squared slot that contacted with the driver tip was more severely progressed. Wear or distortion of hexed slot was more severe than that of squared slot and it was more remarkable in the titanium screw than in the gold screw. All the tested screws showed that the width in the crest of their screw thread decreased gradually as the test was proceeded. Conclusions. Conclusively, we recommend the clinical use of gold screw, a periodic exchanges of abutment screws and avoiding repeated closing/opening unnecessarily. We also suggest a more careful manipulation of the abutment screw and screw-driver and using of abutment screw with an acute-angled slot design rather than an obtuse-angled one. Finally, it is suggested that the new slot design and the surface treatment for enduring wear or distortion should be devised.

• 한국산학기술학회논문지
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• 제17권4호
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• pp.319-324
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• 2016

입도분포가 다양한 입자크기로 이루어져 있는 지반은 일반적으로 지반의 강도가 좋다. 입도분포가 다양하지 않음에도 충분한 지지력을 가지고 있는 지반이 더러 있는데, 이러한 지반의 특징은 Gap 입도로 분포되어 있다는 것이다. 이를 바탕으로 유추하여보면 입자의 크기가 다양하지 않더라도 적절한 입도의 배치를 통해 강한 지반이 조성될 수 있음을 알 수 있다. 이 연구에서는 임의로 조성한 Gap 입도시료와 well, uniform 입도시료와의 내부마찰각의 변화에 대하여 고찰하였다. 큰 입자와 작은 입자 크기의 비율에 따라서 시료를 조성한 후 직접전단시험을 수행하여 지반의 강도정수를 구하고 결과를 비교 분석하였다. 연구결과 시료의 입자크기비와 내부마찰각을 연관시킬 수 있었으며 입도의 분포가 Gap이라고 하더라도 주어진 조건에서 가장 큰 입자 크기비를 가지고 있는 시료가 다양한 입도분포의 시료보다 큰 마찰력을 가질 수 있음을 알 수 있었다. 또한 중간입자크기를 가지고 있는 시료로 조성한 uniform시료보다도 같은 입자 크기의 Gap 입도 시료가 더 큰 강도를 지니고 있었다. 비교적 간단한 입도의 조정만으로도 대상 지반의 강도를 추가적으로 증대시킬 수 있는 공법개발의 기초를 확립하였다.

• 한국주조공학회지
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• 제11권6호
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• pp.475-481
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• 1991

In this study the fabrication technology and mechanical properties of AC8A/$Al_2O_3$ Composites by squeeze casting process were investigated to develope for application as the piston materials that require good friction, wear resistance, and thermal stability. AC8A/$Al_2O_3$ composistes without a porosity and the break of preform were fabricated at the melt temperature of $740^{\circ}C$, the preform temperature of $500^{\circ}C$, and mold temperature of $400^{\circ}C$ under the applied pressure of $1200kg/cm^2$ as the results of the observation of microstructures. As the results of this study, the tensile strength of AC8A/$Al_2O_3$ composites was not increased linearly with $Al_2O_3$ volume fraction and so it seemed not to agree with the rule of mixture, which had been used often in metal matrix composite. Also the tensile strength after thermal fatigue test was little different from that before the test. Consequently it was thought that AC8A/$Al_2O_3$ composites fabricated under our experimental conditions had a good thermal stability and subsequently a good interface bonding. Wear rate(i.e., volume loss per unit sliding distance) of AC8A/$Al_2O_3$ composites was decreased with $Al_2O_3$ volume fraction and the sliding speed at both room temperature and $250^{\circ}C$ and so there was a good correlation between wear rate and hardness. Also the wear rate of AC/8A20% $Al_2O_3$ composities was obtained the value of $1.65cm^3/cm$ at sliding speed of 1.14m/sec as compared with about $3.0\;{\times}10^{-8}cm^3/cm$ hyereutectie Al-Si alloy(Al-16%Si-2%Cu-1%Fe-1%Ni), which applied presently for piston materials. The wear behavior of $Al_2O_3$ composites was observed to a type of abrasive wear by the SEM view of wear surface.

• Composites Research
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• 제29권1호
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• pp.24-32
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• 2016

본 연구에서는 3D 아이소파라메트릭 쉘요소 모델을 사용하여 전단농화유체(STF: shear thickening fluid)가 함침된 케블라 페브릭(Kevlar fabric) 복합재의 방탄성능에 대하여 해석을 수행하였다. 다양한 적층복합재(12, 18, 20, 24-layer)를 대상으로 탄두 초기속도에 따른 충돌 후 속도(Residual velocity)를 측정하여 실험치와 비교하였다. SFT가 함침된 복합재의 방탄 성능의 효과를 검증하기 위하여 다양한 속도영역에서 STF가 함침된 것과 함침 되지 않은 것의 방탄성능을 비교하였다. STF가 함침된 케블라 페브릭은 450 m/s 이하의 저속에서는 비교적 큰 마찰효과를 일으키며 고속에서는 STF가 함침된 Kevlar fabric의 마찰효과는 기대할 수 없는 수준으로 오히려 역효과를 일으키는 것을 확인할 수 있었다. 연구를 통해 STF가 함침된 케블라 페브릭의 특성을 퇴화 3D 쉘 요소를 사용하여 효과적으로 모사할 수 있었으며, 실험 치와의 결과 비교를 통하여 그 유효성을 검증하였다.

• 대한치과보철학회지
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• 제44권2호
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• pp.229-242
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• 2006

Statement of problem: In order to increase preload with reducing the friction coefficient, abutment screws coated with pure gold and Teflon as dry lubricant coatings have been introduced. But the reported data indicate that if screw repeated tightening and loosening cycle, an efficiency of increasing preload was decreased by screw surface wearing off. Purpose: This study was to evaluate the influence of tungsten carbide/carbon coating, which has superior hardness and frictional wear resistance, on the preload of abutment screws and the stability of coating surface after repeated closures. Material and method: The rotational values of abutment screws and the compressive forces between abutment and fixture were measured in implant systems with three different joint connections, one external butt joint and two internal cones. Moreover the stability and the alteration of coating surface were examined by comparison of the compressive force and the removable torque values during 10 consecutive trials, observation with scanning electron microscope and analyzed the elemental composition with energy dispersive x-ray spectroscopy Results and conclusion: 1. Application of coating resulted in significant increase of compressive force in all implant systems(P<.05). The increasing rate of compressive force by coating in external butt joint was gloater than those in internal cones (P<.05). 2. Coated screw showed the significant additional rotation compared to non-coated screw in all implant systems (P<.05). There were no significant differences in the increasing rate of rotation among implant systems (P>.05). 3. Removable torque values were greater with non-coated screw than that with coated screw (P<.05). 4. Coated screw showed insignificant variations in the compressive forces during 10 consecutive trials(P>.05) 5. After repeated trials, the surface layer of coated screw was maintained relatively well. However surface wearing and irregular titanium fragments were found in non-coated screw.

• 한국표면공학회지
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• 제39권4호
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• pp.179-189
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• 2006

High velocity oxygen fuel(HVOF) thermal spray coating of WC-Co powder is one of the most promising candidate for the replacement of the traditional hard chrome plating and ceramics coating because of the environmental problem of the very toxic $Cr^{6+}$ known as carcinogen and the brittleness of ceramics coating. WC-Co micron and nano powder were coated by HVOF thermal spraying method for the study of durability improvement of the high speed spindle. Coatings were planned by Taguchi program for the four spray parameters of spray distance, flow rates of hydrogen, oxygen and powder feed rate. Optimal coating process was obtained by the studies of coating properties such as porosity, surface roughness, micro hardness, and micro structure. WC-Co micron and nano powder were coated on the Inconel 718 substrate by the optimal coating process obtained in this study. The wear behaviors were studied by the sliding wear tester at room temperature and at an elevated temperature of $500^{\circ}C$ for the application to high speed spindle. Sliding wear test was carried out for four most promising hard coatings of chrome coating, ceramics coatings such as $A1_2O_3,\;Cr_2O_3$ and HVOF Co-alloy T800 for the comparison of their wear behaviors. HVOF WC-Co coating was better than other coatings showing highest micro hardness of 1400 Hv and comparable friction coefficients with others. HVOF WC-Co coating is a strong candidate for the replacement of the traditional hard chrome plating for the high speed spindle.

• 한국축산시설환경학회지
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• 제11권1호
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• pp.11-16
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• 2005

1. 구획이 작고 논두렁이 많은 논의 볏짚 수집에 적합한 1축롤 구동 래핑암회전식 트랙터 3점히치 장착형 원형베일 래퍼를 개발하였다. 2. 2개의 구동롤을 구동하는 래핑암 회전식원형베일래퍼는 베일 적재시 베일에 변형이 발생하였으며 작업시 무게중심이 높아 기체 흔들림이 있었으나 시작기는 베일적재시 롤이 수평직선운동을 하여 베일의 변형이 적었으며 무게중심이 낮아 작업 안정성이 다소 높은 것으로 평가되었다. 3. 베일적재시에 두 개의 적재롤이 자유회전을 하여 적재시의 베일과 롤의 마찰저항을 구름저항으로 바꿈으로써 베일의 변형이 생기지 않았으며 베일을 회전시키기 위한 구동롤의 토크를 기존의 2축롤 구동식은 12 kgf-m 이었으나 새로 개발한 1축롤 구동식은 6 kgf-m로 낮았다. 4. 구동롤 토크가 낮아 1축롤 구동으로 베일래핑작업이 가능하였으며 기계구조를 단순화 킬 수 있었다. 5. 기존 회전테이블식에 비해 작업능률을 $45\%$ 향상, 작업비용은 $17\%$ 절감할 수 있었다.

• 해양환경안전학회지
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• 제25권5호
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• pp.609-616
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• 2019

선박에 파울링이 발생되면 운항 중 선박의 저항이 증가하게 되고 이로 인해 연료 소모량도 높아지게 된다. 또한 파울링의 제거에 많은 시간이 필요하게 되어 전체적으로 선박의 유지보수 비용이 증대되는 문제점이 있다. 이러한 문제점을 해결하고 환경오염을 방지하기 위해 주석과 같은 독성 물질을 포함하지 않는 자기연마형 방오도료를 개발하고 있다. 이와 같은 종래기술은 해수와의 마찰이나 진동이 많이 발생하는 운항 중에는 연마기능이 촉진되어 방오성능이 증대되나, 정박 중과 같이 실제로 파울링이 심화되는 경우에는 해수의 흐름이 없어 연마기능이 저하되어 방오성능이 떨어지는 문제점이 있다. 이러한 문제점을 해결하기 위해 선체의 진동 및 해수의 흐름이 없어서 연마 기능이 저하되는 정박 중에도 진동을 부여하여 연마 기능의 저하를 방지하는 제품을 개발하였다. 개발된 초음파 방오장비의 성능의 신뢰성을 위해 파형발생기의 반복성을 확인하였고 장치의 파울링 제거효율의 정성적인 경향은 시편을 통해 파악하였다. 실험 결과 주파수와 진폭의 반복성의 변동계수 값은 평균 0.2 %, 4.0 %를 나타냈고 시편의 파울링 발생량은 No.5 시편에서 73.3 g으로 가장 많았고 파울링 제거효율은 장치를 설치하지 않은 시편과 비교하여 평균 93.2 % 값을 확인할 수 있었다.

• 한국표면공학회지
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• 제55권6호
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• pp.390-397
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• 2022

Parylene-C which was mainly used for industries such as electronics, machinery and semiconductors has recently been in the spotlight in the medical field due to its properties such as corrosion resistance and biocompatibility. In this study we intend to derive a plan to improve the bonding strength of Parylene-C coating with the SUS304 base material for medical use which can be applied to various medical fields such as needles, micro needles and in vitro diagnostic device sensors. Through plasma pretreatment the bonding strength between Parylene-C and metal materials was improved. It was confirmed that the coated surface was hydrophobic by measuring the contact angle and the improvement of the surface roughness of the sample manufactured through CNC machining was confirmed by measuring the surface roughness with SEM. Through the above results, it is thought that it will be effective in increasing usability and reducing pain in patients by minimizing friction when inserting medical devices and in contact with skin. In addition it can be applied to various application fields such as human implantable stents and catheters, and is expected to improve the performance and lifespan of medical parts.