• Corrosion Science and Technology
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• 제14권2호
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• pp.59-63
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• 2015

Airless spray which is widely used for painting to ship blocks and hull sides is the coating method for attaching atomized paint material to the substrate using spray tip nozzle with compressed air. When the paint material which has high solid contents such as epoxy primer paint is atomized by passing through spray tip nozzle with high pressure, the nozzle composed of tungsten carbide(WC) undergoes the erosive wear, leading to widening of nozzle hole. The deformation of nozzle hole induces improper spray pattern and coating failures such as finger pattern and sagging because the conditions of spray pump pressure and paint flow rate for developing full spray pattern are changed. In this study, an appropriate replacement cycle of spray tip was predicted by measuring the erosive wear tendency as increasing the spraying time of epoxy primer paint.

• Restorative Dentistry and Endodontics
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• 제47권3호
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• pp.29.1-29.10
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• 2022

Objectives: This study aimed to investigate the anti-erosive/abrasive effect of resin infiltration of previous deproteinized dentin. Materials and Methods: Dentin slabs were randomly assigned to 3 groups (n = 15): Control (no deproteinization; no resin infiltrant applied), RI (no deproteinization; resin infiltrant applied), and DRI (deproteinization; resin infiltrant applied). After undergoing the assigned treatment, all slabs were subjected to an in vitro cycling model for 5 days. The specimens were immersed in citric acid (0.05 M, pH = 3.75; 60 seconds; 3 times/day) and brushed (150 strokes). Between the challenges, the specimens were exposed to a remineralizing solution (60 minutes). The morphological alterations were analyzed by mechanical profilometry (㎛) and scanning electron microscopy (SEM). Data were submitted to one-way analysis of variance (ANOVA) and Tukey tests (p < 0.05). Results: Control and RI groups presented mineral wear and did not significantly differ from each other (p = 0.063). DRI maintained a protective layer preserving the dentin (p < 0.001). After erosive/abrasive cycles, it was observed that in group RI, only 25% of the slabs partially evidenced the presence of the infiltrating, while, in the DRI group, 80% of the slabs presented the treated surface entirely covered by a resin-component layer protecting the dentin surface as observed in SEM images. Conclusions: The removal of the organic content allows the resin infiltrant to efficiently protect the dentin surface against erosive/abrasive lesions.

• International Journal of Fluid Machinery and Systems
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• 제9권4호
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• pp.287-299
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• 2016

In China, agricultural irrigation water often contains a lot of suspended sediment which may cause the nozzle wear. In this study, a new numerical simulation combing the Discrete Phase Model and a remeshing algorithm was conducted. The geometric boundary deformation caused by the erosion wear, was considered. The weight loss of the nozzle, the node displacement and the flow field were investigated and discussed. The timestep sensitivity analysis showed that the timestep is very critical in the erosion modeling due to the randomness and the discreteness of the erosion behavior. Based on the simulation results, the major deformation of the boundary wall due to the erosion was found at the corners between outlet portion and contraction portion. Based on this remeshing algorithm, the simulated erosion weight loss of the nozzle is 4.62% less compared with the case without boundary deformation. The boundary deformation changes the pressure and velocity distribution, and eventually changes the sediment distribution inside the nozzle. The average turbulence kinetic energy at the outlet orifice is found to decrease with the erosion time, which is believed to change the nozzle's spray performance eventually.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2017년도 춘계학술대회 논문집
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• pp.132.2-132.2
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• 2017

플라즈마 전해 산화(Plasma Electrolytic Oxidation, PEO)는 Al, Ti, Mg 합금과 같은 경량 금속소재에 대한 표면처리기술로서 주목을 받고 있다. PEO 처리에 의해 표면에 치밀하게 형성되는 세라믹 산화층은 우수한 내식성, 내마모성을 보유하기 때문에, 이와 같은 특성이 요구되는 분야에 적용하기 위한 연구가 활발하다. 특히 PEO 세라믹 코팅층의 응착마모(adhesive wear)와 절삭마모(abrasive wear)에 관한 연구는 상당부분 이루어지고 있으나, 캐비테이션 침식과 같은 침식마모(erosive wear) 특성에 관한 연구는 부족한 실정이다. 본 연구에서는 알루미늄 합금 소지에 제작된 PEO 코팅층의 캐비테이션 손상 특성을 고찰하였으며, 전해액 조성이 PEO 코팅층의 미세조직과 캐비테이션 손상 특성에 미치는 영향을 살펴보았다. PEO 처리를 위해 사용된 소재는 상용 5083-O합금 판재로서 $2cm{\times}2cm$로 절단하여, 에머리페이퍼로 1000번까지 연마하여 사용하였다. 사용된 전해액은 증류수에 KOH(1 g/L)을 base로 하여 $Na_2SiO_3$(2 g/L)의 첨가유무를 변수로 하였다. 시편을 양극으로 하고 STS304를 음극으로 하여 각각 DC 전원 공급기의 +극과 -극에 연결하였으며, 정전류 조건에서 30분간 $0.1A/cm^2$의 전류밀도를 인가하였다. PEO 처리후 시편은 SEM, EDS, XRD를 이용하여 표면 특성 평가를 실시하였다. PEO코팅층의 캐비테이션 특성 평가는 초음파 진동식 캐비테이션 발생 장치를 이용하였으며, 캐비테이션 실험 후 시간에 따른 표면 거칠기의 변화 거동을 분석하였다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2003년도 춘계학술대회 논문집
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• pp.593-598
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• 2003

Ceramic plates containing many micro-holes are used in diverse applications such as MCP (Microchannel Plate). catalytic converters, filters, electrical insulators in integrated circuits, and so on. One of the efficient methods for machining many holes in ceramic plates is wet drilling of ceramic green bodies followed by sintering them. Since the strength of ceramic green bodies is much lower than the strength of sintered ceramic plate, ceramic green bodies can be drilled with high feed rate. The axial force during micro-drilling of ceramic green bodies increases rapidly at high feed rate, which induces the crack in workpiece. Therefore, the tool lift of micro-drill with respect to feed rate may be determined by the predicting increase of axial force. In this work, the axial force during micro-drilling was calculated using the chip flow model on the micro-drill tip. from which the tool life of diamond abrasive micro-drill during micro-drilling of ceramic green bodies was calculated.

• 한국분말재료학회지
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• 제15권6호
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• pp.509-513
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• 2008

High-pressure abrasive entrained jet have rapidly become important machining technology over the last two decades. However, suspension jet by high-pressure has been recently developed for packaging sawing. Ideally, diamond materials should be used for components in abrasive water-jet systems that are subject to high erosive conditions. Using the diamond orifices improve maintenance and extend wear part life. This paper gives insights to using an abrasive suspension jet with diamond orifice. The influences of orifice material and orifice design are evaluated.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2000년도 제32회 추계학술대회 정기총회
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• pp.304-309
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• 2000

Si$_3$N$_4$-6wt%Y$_2$O$_3$-lwt%Al$_2$O$_3$was prepared by hot pressed and gas pressure sintering to investigate the effect of microstructure on erosion behaviors. Hardness and fracture toughness were measured with prepared specimens to study the high temperature erosion properties. A gas blast type erosion tester was used In examine erosion behavior of the specimens up to 700$^{\circ}C$. In case of GPS silicon nitride, the erosion rate increases up to 500$^{\circ}C$ and decreases over 500$^{\circ}C$. Maximum erosion rate was observed at 300$^{\circ}C$ for HP silicon nitride. The principal factors affecting the high temperature erosive wear of brittle materials are largely dependent on high temperature properties of grain boundaries.

• 상하수도학회지
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• 제27권3호
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• pp.383-394
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• 2013

A sedimentation basin is used to remove suspended sediments which can cause abrasive and erosive wear on hydraulic turbines of hydropower plants. This sediment erosion not only decreases efficiency of the turbine but also increases maintenance costs. In this study, the three-dimensional numerical simulations were carried out on the overseas hydropower project. The simulations of flow and suspended sediment concentration were obtained using FLOW-3D computational fluid dynamics code. The simulations provide removal efficiency of a sedimentation basin based on particle sizes. The influence of baffles on the flow field and the removal efficiency of suspended sediments in the sedimentation basin has been investigated. This paper also provides the numerical simulations for sediment-induced density currents that may occur in the sedimentation basin. The simulation results indicate that the formation of density currents decreases the removal efficiency. When a baffle is installed in the sedimentation basin, the baffle provides intensive settling zones resulting in increasing the sediments settling. Thus the enhanced removal efficiency can be achieved by installing the baffle inside the sedimentation basin.

• 한국산학기술학회논문지
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• 제9권2호
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• pp.291-297
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• 2008

일방향 탄소섬유 강화 복합재료(CFRP)의 고체입자 마식 거동을 다양한 충돌각도 (${\alpha}$), 속도 (V) 및 섬유 방향 (${\beta}$)에 대하여 연구하였다. 실험결과 30o 충돌각도에서 최대 마식률을 나타내었고, 마식률은 멱함수 법칙 $E{\propto}\;V^n$에 따라 충돌속도에 크게 의존하였다. 본 연구에서는 이상의 결과로부터 일방향 탄소섬유 강화 복합재료의 마식률을 충돌속도, 충돌각도 및 섬유방향 각도로부터 예측하는 방법을 제안하였다.

• 대한소아치과학회지
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• 제31권4호
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• pp.555-563
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• 2004

치아침식증은 순수한 화학적 반응에 의한 치아 경조직의 소실로 정의된다. 침식의 원인요소로는 여러 가지가 이미 거론된 바, 최근에 들어서는 이 중 산성음식과 음료가 중요한 요소로 관심을 모으고 있다. 특히 최근 들어서는 다양한 산성 음료의 소비가 급증하는 추세이고, 성장기 어린이나 청소년이 이러한 음료를 선호하여 음용의 빈도가 우려할 만한 수준으로 치아침식증을 촉진할 것으로 생각된다. 이 중 유산균 발효유는 비교적 저렴하고 쉽게 접할 수 있으며, 어린이가 주 소비자라는 점, 그리고 유치와 새로 맹출한 영구치가 침식에 더욱 취약하다는 점에서 소아치과학 분야의 관심사가 되기에 충분하다고 사료되었다. 따라서 본 연구는 유산균 발효유에 의한 유치의 법랑질 침식 정도를 평가할 목적으로 시행되었다. 시판중인 4 종의 유산균 발효유를 선정하고 각각의 산도, 완충능 및 일부 무기이온 농도를 측정하였다. 그리고 40개의 유치 법랑질 시편을 4개 군으로 나누어 30분, 60분, 90분, 120분 동안 $20^{\circ}C$, 80ml의 각 시료에 담근 후 각 시간대별 법랑질의 침식정도를 알기 위해 표면미세경도를 측정하여 다음과 같은 결과를 얻었다. 1. 본 실험에 사용된 유산균 발효유의 산도는 평균 pH 3.77로서 치아침식증을 유발하기에 충분한 수준이었다. 2. 유산균 발효유에 대한 노출 후의 법랑질 표면경도는 대조군에 비해 모든 시료에서 낮아졌다(p<0.05). 노출시간에 따른 법랑질 표면경도의 변화는 모든 실험군에서 초기에는 급격히 낮아지다가 시간경과에 따라 그 정도가 덜해지는 양상을 보였다. 3. 법랑질이 시료에 노출된 30분에서 120분까지의 법랑질 표면경도 변화양상은 시료마다 유의한 차이를 보였다(p<0.05).