• Tribology and Lubricants
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• v.31 no.3
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• pp.125-140
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• 2015

In this paper, we present the results of the wear analysis of journal bearings on a stripped-down single-cylinder engine during start-up and coast-down by motoring. We calculate journal bearing wear by using a modified specific wear rate considering the fractional film defect coefficient and load-sharing ratio for the asperity portion of a mixed elastohydrodynamic lubrication (EHL) regime coupled with previously presented graphical data of experimental lifetime linear wear in radial journal bearings. Based on the calculated wear depth, we obtain a new oil film thickness for every crank angle. By examination of the oil film thickness, we determine whether the oil film thickness at the wear scar region is in a mixed lubrication regime by comparing dimensionless oil film thickness, h/σ, to 3.0 at every crank angle. We present the lift-off speed and the crank angles involved with the wear calculation for bearings #1 and #2. The dimensionless oil film thickness, h/σ, illustrates whether the lubrication region between the two surfaces is still within the bounds of the mixed lubrication regime after scarring of the surface by wear. In addition, we present in tables the asperity contact pressure, the real minimum film thickness at the wear scar region, the modified specific wear rate, and the wear angle, α, for bearings #1 & #2. To show the real shape of the oil film at wear scar region, we depict the actual oil film thickness in graphs. We also tabulated the ranges of bearing angles related with wear scar. We present the wear volume for bearings #1 and #2 after one turn-on and turn-off of the engine ignition switch for five kinds of equivalent surface roughness. We show that the accumulated wear volume after a single turn-on and turn-off of an ignition switch normally increases with increasing surface roughness, with a few exceptions.

• Journal of the Society of Cosmetic Scientists of Korea
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• v.33 no.3
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• pp.197-201
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• 2007

Oil soluble licorice extract(licorice extract) is an officially approved cosmetic component as a whitening ingredient in Korea. The durability of licorice, during which the whitening effect can be maintained in optimum condition, must be accurately defined. Since the cosmetics durability under real condition is relatively longer than its development time. It is needed to predict the real durability interval from the experimental measurement under simulated operating conditions. We analyzed the relationship between the licorice lifetime and the high temperature condition by using Arrhenius equation. We have established the constant stress test with temperature of $50^{\circ}C$, $55^{\circ}C$, and $60^{\circ}C$ condition, within which no formulation change of licorice products is expected for the accelerated stress test. In this paper, the lifetime of licorice in cosmetics was defined as time period for its 10% contents reduction. We observed that the lifetime of licorice is 580 h at $50^{\circ}C$, 319 h at $55^{\circ}C$ and 166 h at $60^{\circ}C$. Using the above experimental data, we obtained the equation for the relationship between the licorice lifetime and temperature as follows; log(lifetime)=-35.0243 + 1.15322$\times$(11604.83/temperature). From this equation, the lifetime of licorice at $25^{\circ}C$ can be estimated as 26 months. The estimated result was verified by measuring full lifetime of licorice. In fact, there was no significant difference between the estimated lifetime and real measurement within 95 % significance level. This study can be applied to other useful cosmetic components for the fast estimation of the exact durability.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.65 no.9
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• pp.1518-1523
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• 2016

In this study, in order to understand the degradation characteristics of oil-paper insulation for power transformers and OF cables, tan delta was measured using cable model specimens with long-term accelerated thermal and electrical aging. In addition, to find out the degradation level due to the accelerated aging, tensile strengths of aged papers were measured. As a result, tan ${\delta}$ showed the characteristics of slight decrease at the first stage and then increase with the aging time, which could be analyzed due to the evaporation of remaining moisture and the change of aging rate with time. Also, the trend of tensile strengths with aging temperature and time was appeared to be exponentially decreased and by use of these data equivalent calculated lifetimes and accelerated aging factors were derived for each aging temperatures. After then, tan ${\delta}$ was analyzed with the equivalent operating years. For all different aging temperatures, the aged data were very well fit to the equivalent operating years and it is shown that tan ${\delta}$ was increased with the decrease of tensile strength.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.15 no.11
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• pp.1003-1008
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• 2002

In this paper, the estimation of lifetime with the various conditions of the interface between toughened epoxy and rubber which are consisting materials of underground power delivery system has been studied. After the measurement of the short time AC interfacial breakdown strength on macro interfaces at room temperature, the breakdown time at several voltages were measured under the constant voltages lower than the short time breakdown voltage. The long time breakdown voltage was calculated by using Inverse Power Law. Two types of interfaces was studied. One was the interface between toughened epoxy and EPDM(Ethylene Prorylene Diene Terpolymer). The other was the interface between toughened epoxy and silicon rubber. Interfacial pressure and roughness of interfaces was determined through the characteristic of short time AC interfacial breakdown strength. Oil condition was no oiled, low viscosity oiled and high viscosity oiled. High viscosity oiled interface between Toughened epoxy and silicon rubber had the best lifetime exponent, 20.69. and the breakdown voltage of this interface after 30 years was evaluated 19.27㎸.

• Elastomers and Composites
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• v.55 no.3
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• pp.199-204
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• 2020

Considering the immense applicability of isoprene rubbers, such as natural rubber (NR) and synthetic polyisoprene rubber (IR), attempts are being made to introduce more functionality within the rubber structure, e.g. epoxidation, to widen their technological viability. Epoxidation introduces polar epoxy bonds into the rubber molecular chain, resulting in enhanced intermolecular interactions among the rubber chains, increasing the oil resistance and air impermeability. Although there have been many reports on the epoxidation of NR in its latex form, there has been no such report using its solid form (or gum), which limits the epoxidation in terms of portability. Furthermore, the gum form has longer lifetime, while the latex form has limited lifetime for its efficient use. In this study, the epoxidation of natural rubber and polyisoprene rubber (using meta-chloroperoxybenzoic acid (mCPBA) as the epoxidizing agent) by dissolving their gum in hexane (i.e., the solution method) have been studied and compared. The effects of the amount of mCPBA, reaction time, and reaction temperature were investigated. The present process is easy and facilitates the epoxidation of rubbers in their solid form; therefore, it can be used for industrial upscaling of epoxidized rubber production.

• Journal of Advanced Marine Engineering and Technology
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• v.41 no.1
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• pp.44-49
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• 2017

In this research, a purifying system using a centrifugal filter equipped with a water separation component has been studied. Oil utilized for lubrication and cooling in marine engines becomes unable to achieve its original purpose over time as the accumulation of solid particles and water increases. Therefore, methods applying the Bernoulli equation to eliminate water in oil were investigated and proposed. As a result, a practical purifying system was designed and tested by an officially certified organization. The new purifying system is anticipated to contribute to the extension of the lifetime of oil in addition to damage reduction methods of mechanical parts.

• Membrane Journal
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• v.32 no.2
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• pp.83-90
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• 2022

Wastewater from refineries and petroleum plant lead to severe environmental pollution. There are various existing processes applied for oily water treatment, but membrane-based technology is one of the most efficient methods. Polymeric membranes prepared from organic materials for the separation of oil in water often face chronic problem of membrane fouling. Inorganic membranes are considered to be more efficient due to longer lifetime than organic membranes. Zeolite membranes have better chemical stability and long-term recyclability. The presence of hydrophilicity enhances the water flux of membrane. Ceramic membranes prepared from zeolites are another efficient class of inorganic membranes applied for oil water separation. This review is focused on oily wastewater separation based on zeolite membrane which classified into two categories, i) neat zeolite and ii) zeolite composites with other materials.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.915-922
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• 2017

The study on the thermal and oil resistance rubber composite, 2016. [6] predicted the lifetime of Fluorocarbon Rubber by accelerating aging at high temperature ($150^{\circ}C$, $175^{\circ}C$, $200^{\circ}C$). general rubber products are likely to exhibit different properties depending on the degradation factors such as temperature, humidity, ozone, light, emulsion, mechanical and electrical stress. To solve these problems, We compared the rate of change about tensile strength, elongation rate, volume change rate, weight change rate, thickness change rate, thermal conductivity in low temperature promoting aging on the basis of predictive lifetime of high temperature promoting aging. As a result of the review, the required life expectancy was satisfied, but there was a slight difference in the rate of change between the high-temperature promoted aging life result and the low temperature promoted aging life result. The cause was a reduction in "tensile strength / elongation" and an increase in "volume / weight / thickness" caused by the main chain decomposition of fluorine rubber due to aging at high temperature promoting aging. However, the low temperature promoting aging was caused by the curing reaction of fluorine rubber at $80^{\circ}C$. The tensile strength / elongation and volume / weight / thickness changes were small.

• Tribology and Lubricants
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• v.34 no.5
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• pp.197-207
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• 2018

Thermal deterioration of fuel due to long-term storage influences engine performance and causes malfunctions. Fuel stability is usually evaluated via heat resistance and thermal stability during a brief heat shock at high temperature; storage stability in this scenario means that there is very little change in the quality of the fuel during long-term storage. In addition, rubber-based products such as oil seals, O-rings, and rubber hoses can influence the quality of the fuel. When these rubber products are in contact with fuel, they can swell, mechanically weaken, and occasionally crack, thus leaking low molar weight rubber and additives including plasticizer and antioxidant into the fuel to degrade its properties and shorten its useful lifetime. This study determines the thermal stabilities of three kinds of synthetic fuels by evaluating their low temperature kinematic viscosities, chemical composition changes via GC analyses, gross heat of combustion, and color changes. We evaluate the compression set of O-rings by immersing one NBR and two FKM rubber O-rings in the three synthetic fuel samples in airtight containers at variable storage temperatures for six months; from this, we estimate the lifetimes of the O-rings using the Power law model. There were very little changes in the chemical compositions and gross heat of combustion after six months of the experiment. The lifetimes are thus dependent on the materials of the rubber products, and in particular, the FKM O-ring was calculated to have a theoretical lifetime of 200 to 5,700 years. These results indicate that the synthetic fuels maintain their physical properties even after long-term storage at high temperatures, and the FKM O-ring is suitable for long-term sealing of these fuels.

• Corrosion Science and Technology
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• v.14 no.2
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• pp.54-58
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• 2015

A heavy oil of low quality has been mainly used in the diesel engine of the merchant ship as the oil price has been significantly jumped for several years. Thus, a combustion chamber of the engine has been often exposed to severely corrosive environment more and more because temperature of the exhaust gas of the combustion chamber has been getting higher and higher with increasing of using the heavy oil of low quality. As a result, wear and corrosion of the engine parts such as exhaust valve, piston crown and cylinder head surrounded with combustion chamber are more serious compared to the other parts of the engine. Therefore, an optimum repair welding for these engine parts is very important to prolong their lifetime in a economical point of view. In this study, 1.25Cr-0.5Mo filler metal was welded with SMAW method in the forged steel which would be generally used with piston crown material. And the corrosion properties of weld metal, heat affected and base metal zones were investigated using electrochemical methods such as measurement of corrosion potential, anodic polarization curves, cyclic voltammogram and impedance etc. in 35% $H_2SO_4$ solution. The weld metal and base metal zones exhibited the highest and lowest values of hardness respectively. And, the corrosion resistance of the heat affected and weld metal zones was also increased than that of the base metal zone. Furthermore, it appeared that the corrosive products with red color and local corrosion like as a pitting corrosion were more frequently observed on the surface of the base metal zone compared to the heat affected and weld metal zones. Consequently, it is suggested that the mechanical and corrosion characteristics of the piston crown can be predominantly improved by repair welding method using the 1.25Cr-0.5Mo electrode.