• Elastomers and Composites
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• 제54권4호
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• pp.330-334
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• 2019

Cryogenic crushing techniques have been employed for recycling waste rubber articles and for extracting residual organic additives present in rubber samples. Rubber particulate derived from tire tread abrasion is one of the key components of road dust. Therefore, in this work, we prepared rubber particulates using a cryogenic crusher and characterized their shapes as well as size distributions according to the type of rubber. The rubber particulates exhibited uneven surfaces with the presence of some small pieces. The order of the particle size distribution was observed to be: NR > BR > SBR. Subsequently, carbon black was added; this led to a decrease in the particle size and the shape becoming rougher. The crushed particulates of the carbon black-filled samples comprised agglomerated shapes of small pieces, which were similar in shape to that of wear debris in tire tread. It was discovered that crosslink density was one of the principal factors that led to the formation of small crushed particulates. The small particulates obtained by cryogenic crushing can be utilized as model rubber particulates for researching micro dust.

• Elastomers and Composites
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• 제55권3호
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• pp.184-190
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• 2020

In the wet master batch process, process oil is used to improve the workability of silica-SBR. The process oil expands the polymer and provides lubrication to soften the stiff rubber chain. However, addition of excess process oil can interfere in the crosslinking reaction between rubber molecules and reduce the crosslinking density of silica-SBR. Controlling the amount of process oil is an important aspect for properly controlling the workability and crosslinking density of silica-SBR. In this study, silica-SBR was prepared by adjusting the amount of process oil to confirm its effect on silicaSBR. Vulcanization characteristics of silica-SBR were examined using a moving die rheometer. Dynamic viscoelasticity was measured using a dynamic mechanical thermal analyzer, and the mechanical properties were investigated using the universal testing machine according to ASTM D412. As a result, all silica-SBR compounds with 10 to 40 phr of process oil have effects of improving the processability and the silica dispersibility. Also, the optimum condition was determined when 10 phr of processed oil was added because the abrasion resistance was improved 65% compared to that at 40 phr.

• 한국표면공학회지
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• 제52권4호
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• pp.187-193
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• 2019

Electroless Ni-P coatings are widely used in the chemical, mechanical, and electronic industries because of their excellent wear and abrasion resistance. In this study, the effect of $TiO_2$ particles of composite coating was investigated. To improve the corrosion resistance, electroless $Ni-P-TiO_2$composite coating was studied by varying the $TiO_2$ content. The morphology and phase structure of $Ni-P-TiO_2$ composite coatings were analyzed by scanning electron microscopy(SEM), X-ray diffractometry(XRD) and X-ray photoelectron spectroscopy(XPS). The result showed that $Ni-P-TiO_2$composite coating is composed of Ni, P, Ti and O. It exhibits an amorphous structure, high hardness and good corrosion resistance to the substrate. $Ni-P-TiO_2$ composite coatings have higher open circuit potential than that of the substrate, which obtained at $TiO_2$ content of 5.0 g/L optimal integrated properties.

• 한국기계가공학회지
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• 제20권10호
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• pp.1-8
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• 2021

Cylinder liners used in diesel engines of combat equipment are prone to cavitation due to wet cooling. The damage caused by erosion and corrosion due to cavitation has a fatal effect on the performance and lifespan of a diesel engine. Therefore, a study was conducted to improve the durability of cylinder liners. Two surface treatment techniques were proposed: nitriding and chrome plating. It was observed that the amount of erosion on the surface of nitride-treated cylinder liners was high because the surface-treated part eroded due to its weak impact resistance against the bubble explosion generated by cavitation. In contrast, the chrome-plated cylinder liner had a lower amount of erosion among the specimens subjected to the accelerated test. These results verified that the resistance of chrome-plated liners against cavitation is high. Therefore, it can withstand the impact of bubble explosion. If the chrome plating thickness is set with reference to the KS standard, an exceptional durability of abrasion, wear resistance, and corrosion resistance can be obtained. If the thickness is set between 120~250㎛, it is expected that the durability of the cylinder liner can be improved. Although a recovery method for corroded cylinder liners is suggested, the proposed method has an inherent risk of crack generation. Therefore, further research is required to solve this problem.

• 한국표면공학회지
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• 제52권3호
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• pp.156-162
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• 2019

Electroless Ni-P coatings are widely used in the chemical, mechanical, and electronic industries because of their excellent wear and abrasion resistance. In this study, The influence of pH values on properties of Ni-P-PTFE composite coatings was investigated. To improve mold lubrication, Ni-P-PTFE composite coatings at different pH value were studied. The morphology and phase structure of Ni-P-PTFE composite coatings were analyzed by scanning electron microscopy(SEM) and X-ray diffractometry(XRD). The result showed that Ni-P-PTFE composite coating is composed of Ni, P and PTFE. It exhibits an amorphous structure and good Corrosion Resistance to the substrate. Ni-P-PTFE composite coatings have higher open circuit potential than that of the substrate, which obtained at pH value of 5.0 optimal integrated properties.

• 한국기계가공학회지
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• 제21권2호
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• pp.123-129
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• 2022

Quartz (SiO2) has high abrasion and heat resistances and excellent chemical and mechanical properties; therefore, it is used in various industries, such as machinery, chemistry, optics, and medicine. Quartz is a high-hardness and brittle material and is classified as the topmost difficult-to-cut material, which is because of the cracking or chipping at the edge during processing. Corner wear, such as cracks and chippings that occur during cutting, is a major cause for the deterioration in the machining quality. Therefore, many researchers are investigating various techniques to process quartz effectively. However, owing to the mechanical properties of quartz, most studies have been conducted on grinding, micromachining, and microdrilling. Few studies have been conducted on quartz processing. The purpose of this study was to analyze the machining characteristics according to the machining factors during the slot machining of quartz using a cubic boron nitride (CBN) tool and to select the optimal machining conditions using the Taguchi method. The machining experiment was performed considering three process variables: the spindle speed, feed rate, and depth of cut. The cutting force and surface roughness were analyzed according to the processing conditions.

• 한국해양환경ㆍ에너지학회지
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• 제12권3호
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• pp.143-150
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• 2009

선박의 주기관이나 발전기관 등 디젤기관에서 사용하는 연료유는 원유를 정제해서 사용하고 있다. 석유화학공업에서 원유로부터 양질의 고급 휘발유를 많이 생산하기 위하여 촉매를 사용하는 유동접촉분해(FCC) 방법을 채택하여 원유를 분리하고 있다. 유동접촉분해 시 촉매의 주성분은 Si와 Al이며, 그 외에 Fe, Zn, Ti 등의 기본금속과 알칼리 금속 및 Ce, Nd, Ni, V 등의 희유금속이 함유되어 있다. 만일 선박에 사용되는 연료유에 이러한 성분의 촉매가 많이 혼입되어 Al, Si, Ni, V이나 Fe 등의 성분이 과다하게 되면 기관 부속품 마모가 아주 심하게 되고, 기관전체를 사용하지 못하게 되어 대형 해양 선박사고가 발생 할 수 있다. 다시 말해, 이런 성분이 많이 함유된 연료유를 기관에 사용하는 경우 연료펌프, 연료분사밸브, 실린더라이너, 피스톤링의 마모가 심하게 발생하게 된다. 따라서 이러한 사고를 예방하기 위하여 사고 발생현황에 대한 정확한 원인을 규명하고 밝히는 것이 중요하다. 아울러 그 사고의 원인이 자연적인 마모, 경년변화인가 또는 외적인 요인에 의한 사고인가에 따라 보험 보상 대상여부가 판명될 수 있어, 연료유로 인한 사고 원인규명은 아주 중요한 업무이다. 본 논문에서는 연료유 관련 사고가 발생한 선박을 대상으로 사고유형, 사고원인 및 예방법에 대한 검토를 하고 향후 선박의 디젤엔진에서 저질연료유 사용에 따른 문제점을 개선하도록 제시하고자 한다.

• 대한소아치과학회지
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• 제31권4호
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• pp.685-695
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• 2004

복합레진은 치질과 우수한 결합력을 가지며 심미적인 이유로 치과의 대표적 수복재로 자리잡고 있다. 그러나 저작력에 따른 마모와 구강내 환경에서의 수분흡수에 따른 가수분해가 복합레진의 강도약화를 야기하고 있다. 실험에 사용된 복합레진은 현재 임상에서 많이 사용되고 있는 Point4, Tetric flow, Heliomolar flow, Filtek supreme 이다. 각 제품의 화학적 분해와 마모도를 평가하기 위해 각각 10개의 시편을 제작하여 그 중 5개는 $37^{\circ}C$의 수중하에 1Kg의 하중을 가하여 10,000 cycle동안의 마모도를 측정하였다. 나머지 5개 시편은 무게 측정을 한 후 0.1N NaOH용액, 3ml에 저장하여 $60^{\circ}C$에서 보관한 후 2주 후 제거하여 1.23% HCl로 2시간 동안 중화하고 증류수로 세척한 후 $60^{\circ}C$에서 건조하였다. 무게 손실, 분해층 깊이 및 시편내의 Si의 농도 변화. 최대 마모 깊이를 근거로 평가하여 다음과 같은 결과를 얻었다. 1. 각 제품의 무게 손실량은 Heliomolar flow, Filtek supreme, Point4, Tetric flow 순이었으며 Heliomolar flow, Filtek supreme을 제외한 다른 제품간에는 유의한 차이를 보였다(P<0.05). 2. 각 제품의 표면하 분해층 깊이는 Filtek supreme, Heliomolar flow, Tetric flow, Point4 순이었으며 Heliomolar flow, Tetric flow을 제외한 다른 제품간에는 유의 한 차이를 보였다(P<0.05). 3. 각 제품으로부터 용출된 Si은 Filtek supreme, Heliomolar flow, Point4. Tetric flow 순이었으며 Point4, Tetric flow을 제외 한 다른 제품간에는 유의한 차이를 보였다(P<0.05). 4. 최대마모깊이 측정시 Heliomolar flow, Point4, Filtek supreme, Tetric flow 순이며 0.1N NaOH 용액에 보관한 레진의 마모깊이가 물에 보관한 레진에 비해 증가한 양상을 보였다. 5. 주사전자현미경 관찰시 NaOH 용액에 보관한 후 레진 기질과 충전제 사이의 결합의 파괴를 관찰할 수 있었으며, 공촛점 레이저 현미경 관찰시 NaOH 용액에 보관한 후 수복재의 기질과 충전제 사이의 파괴양상인 분해층 깊이를 관찰할 수 있었다.

• 대한정형도수물리치료학회지
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• 제5권1호
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• pp.75-80
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• 1999

The Taekwondo being a martial sports, there are higher chances for the injury to occur than the non martial sports. Therefore, this study analyze the frequency, the area, the type, and the condition of the injury which are prone to occur in the Taekwondo matches; it is to help the Taekwondo players in prevention of the injury and in treatment. The subjects of this study were the 48 players (male 24, female 24) who participated in the final selection contest of the national team player on March 9 to 12, 1993. The data of the injury were obtained from the medical recoder staff and were analyzed to the frequency of the injury per match, the vulnerable area of the injury, the type of injury, and the condition of the injury with a gender difference. There were 24 matches for the male and 24 matches for the female, total 48 matches. Therefore, the total participation number of the players are the double of the match number. 1. The frequency of the injury per match was 18.3%(11/60) for male and 23.1%(12/52) for women. 2. The areas of the injury were ankle 36.4%(4), foot 18.2%(2), knee 18.2%(2), lower leg 18.2%(2), wrist 9.1%(1) in male; foot 33.4%(4), ankle 16.7%(2), knee 16.7%(2), lower back 16.7%(2), lower leg 8.3%(1), face 8.3%(1) in female. 3. The types of the injury were contusion 45.5%(5), sprain 27.3%(3), abrasion 9.1%(1), laceration 9.1%(1), tendon rupture 9.1%(1) in male; contusion 33.3%(4), sprain 33.3%(4), abrasion 16.7%(2), subcutaneous hemorrhage 8.3%(1), dislocation 8.3%(1) in female. 4. The condition of the injury were the unblocked attack 36.4%(4), attacking kick 27.3%(3), blocking a kick 18.2%(2), attacking punch 9.1%, impact with surface 9.1%(1) in male; attacking kick 33.3%(4), unblocked attack 25%(3), blocking a kick 25%(3), attacking punch 8.3%(1), impact with surface 8.3%(1) in female. This study shows that the injury from the Taekwondo matches occurred most in the lower extremity joints and the foot, and shows that the most of the injury types were contusion and sprain. Therefore, it is believed to be helpful to wear the proper fitting ankle or the knee protector and using other protective equipment to prevent the sports injury in the Taekwondo matches.

• 터널과지하공간
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• 제23권3호
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• pp.180-191
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• 2013

본 연구는 백운광산지역에 부존하는 대리석을 효율적으로 채석하고자 새로이 도입한 체인쏘머신(chain saw machine)의 적용성과 작업 효율을 분석함으로써 최적의 채석 방안을 도출하고자 하였다. 절단 효율에 큰 영향을 미치는 채석대상암석의 물리적 특성을 파악한 결과, 국내 타 지역에서 산출되는 대리석의 물성과 유사한 수준을 보이고 있으며 등방적 성질을 지니고 있어 산업용 석재로서 유리한 것으로 나타났다. 부존 대리석이 석재로서 가지는 중장기 품질을 확인하기 위해 내부식성, 마모율 등의 시험을 수행한 결과, pH 5.6의 인공강우를 50회 적용한 이후부터 시험편의 무게와 탄성파속도가 감소하였으며 마모율은 22.67%로 나타났다. 채석장 현장에서 시험운행 중인 체인쏘머신의 작업별 소요시간과 절단속도를 분석하여 단위작업을 9가지로 분류하였고 각 단위작업별 소요시간을 도출하였다. 이를 토대로 현장에 실제 적용 가능한 2가지 작업패턴에 대한 작업소요시간을 비교한 결과 장비 본체이동을 최소화하여 절단순서를 결정한 패턴 B가 원석의 외곽면을 우선 절단하도록 절단순서를 결정한 패턴 A보다 약 6%의 작업시간 단축을 나타내었다. 절단패턴 분석과 함께 백운광산의 광체를 3차원으로 모델링하고 대상암석의 부존조건을 고려한 채석 계획안을 제시하였다.