• Corrosion Science and Technology
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• v.14 no.2
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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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• v.47 no.3
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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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• v.9 no.4
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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.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2017.05a
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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.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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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.

• Journal of Powder Materials
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• v.15 no.6
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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.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2000.11a
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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.

• Journal of Korean Society of Water and Wastewater
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• v.27 no.3
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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.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.9 no.2
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• pp.291-297
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• 2008

The solid particle erosion behaviour of unidirectional carbon fiber reinforced plastic (CFRP) composites was investigated. The erosive wear of these composites was evaluated at different impingement angles ($30^{\circ}$, $45^{\circ}$, $60^{\circ}$, $90^{\circ}$), different impact velocities (40, 55, 60, 70m/s) and at three different fiber orientations ($0^{\circ}$, $45^{\circ}$, $90^{\circ}$). The erodent was SiC sand with the size $50-100{\mu}m$ of irregula. shapes. The result showed ductile erosion behaviour with maximum erosion rate at $30^{\circ}$ impingement angle. The fiber orientations had a significant influence on erosion. The erosion rate was strongly dependent on impact velocity which followed power law $E{\propto}\;V^n$. Based on impact velocity (V), impact angle (${\alpha}$) and fiber orientation angle (${\beta}$), a method was proposed to predict the erosion rate of unidirectional fiber reinforced composites.

• Journal of the korean academy of Pediatric Dentistry
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• v.31 no.4
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• pp.555-563
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• 2004

The pH of beverages is known to be low and have, therefore, been implicated in the increasing incidence of erosion. Erosion is believed to be the predominant cause of teeth wear in children and young adults, although there will always be a contribution from attrition and abrasion. The aim of the present study was to evaluate the effect of yogurt on the progression of erosive demineralization in human enamel using demineralization model in vitro. In 4 yogurts, available on the market, pH, buffering capacity and the concentrations of calcium, phosphate and fluoride were determined. The buffering effect was determined by titration with NaOH. 50 milliliters of each drink was then titrated with 1M sodium hydroxide, added in 0.5 milliliters increments, until the pH reached about 7. Human deciduous enamel(n=40) samples were divided into four groups and exposed to 80ml of the yogurt for 30,60, 90 and 120min. Enamel surface microhardness(VHN) was examined before and after each exposure. 1. The average PH of fermented milk was 3.77 and this pH value was acidic enough to cause tooth erosion. 2. All of the fermented milks were found to be erosive(p<0.05) 3. The teeth exposed to the fermented milk all showed erosion like lesions and microhardness measurements showed that enamel surface hardness decreased proportionately with increased time of immersion in all tooth specimen groups. 4. After immersion for 30 and 60 minutes, reduction rate of microhardness values was not significantly different between the groups(p>0.05). However, after 90 and 120 minutes, reduction rate of each group was significantly different(p<0.05).