• Journal of the Korean Society for Heat Treatment
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• v.24 no.4
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• pp.209-216
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• 2011

Surface coatings were prepared on SKD11 core mold steel by plasma electrolytic oxidation (PEO). The coatings were investigated about the formation condition of core mold steel. SKD11 were coated by PEO in a mix solution of Sodium Aluminate $NaAlO_2$ (10 g/l), Sodium Silicate powder $Na_2SiO_3$ (0.5 g/l), Sodium tungstate dihydrate $Na_2WO_42H_2O$ (0.5 g/l) at less than $30^{\circ}C$. The electrical condition were voltage : 500~600 V; Pulse : 600~1800 Hz; current density 15~20 $A/dm^2$ various time : 3 min~40 min. The coatings surface morphology, cross-section, friction coefficient, hardness were investigated. The PEO coatings on SKD11 core mold steel showed the extended service life.

• Journal of the Korean institute of surface engineering
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• v.50 no.6
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• pp.480-485
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• 2017

Soft mold imprinting method that uses nanostructured polymer mold was investigated for anti-reflection film fabrication. The nanostructured soft mold was polyethylene terephthalate(PET) irradiated by oxygen ion beams. The collisional energy transfer between oxygen ion and the polymer surface induced cross-linking and scission reactions, resulting in self-organized nanostructures with regular patterns of the wavenumber of $5{\mu}m^{-1}$. Post processes including ultra-violet curable resin coating and delamination fabricated anti-reflection films. The imprinted resin surface also showed the consistent wavenumber, $5{\mu}m^{-1}$. Pristine PET, oxygen ion beam treated PET, and imprinted replica sample showed total transmittance of 91.04, 93.25, and 93.57-93.88%, respectively.

• Journal of Korea Foundry Society
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• v.27 no.2
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• pp.88-94
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• 2007

General criteria for the risering design of steel castings and commercial codes for the flow and solidification analysis were used to design the optimized risering in V-process. Three type of specimens were chosen including thin plates and a thick disc. Sided riser installed in the front of a plate casting was effective to prevent the shrinkage defects and to increase the casting yield ratio. Exothennic sleeve and chill were also effective. It was possible to apply the general criteria for the risering design of steel castings to V-process. Temperature of a mold surface was expected to rise over $1,000^{\circ}C$ in the temperature calculation considering radiation effect of molten metal in the mold. Since weakening temperature of the vinyl used in V-process is about $70^{\circ}C$, it should be emphasized that a proper coating of the vinyl film is necessary to prevent the possibility of burning out of the vinyl by the molten metal.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.18 no.6
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• pp.629-635
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• 2009

In this research, KP-4, one of the plastic mold steels, was coated with the AlTiN from one layer to four layers by the PVD method in the $\Phi$ 8mm cemented carbide ball end mill. Coated KP-4 was processed with various conditions. For example, slope of $15^{\circ}$, $30^{\circ}$ and $45^{\circ}$ the spindle rotation speed was changed from 10,000rpm to 16,000rpm, the tool feeding speed was changed from 1,300mm/min to 1,700mm/min, the depth of cut was also changed from 0.3mm to 0.9mm, and etc. Cutting component force according to the coating layer number, and surface roughness were studied. The cutting component force showed a good agreement better the up ward direction than the down ward direction under all experimental conditions. In case of the condition per the material shape, it was lessen when the tool have larger angle because the average effective diameter of the tool is larger. The surface roughness showed good condition in case of the up ward than the down ward direction. And, in the 3rd layer of AlTiN coating, it showed the most suitable condition.

• Journal of the Korean Society for Heat Treatment
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• v.35 no.5
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• pp.262-269
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• 2022

In order to process materials such as engineering plastics, which are difficult to mold due to their high strength compared to conventional polymer materials, it is necessary to improve the hardness and strength of parts such as screws and barrels of injection equipment in extrusion system. High-velocity oxygen fuel (HVOF) process is well known for its contribution on enhancement of surface properties. Thus in this study, using the HVOF process, WC coating layers of different thicknesses were bonded to the surface of S30C substrate by controlling the movement speed of the spray nozzle and each property was evaluated to decide the optimization condition. Through the results, the thickness of WC coating layer increased from 0 to 200 ㎛ maximum, along with the decrement of nozzle movement speed and the surface hardness get increased. Especially, the coated layer with the thickness over 180 ㎛ under the nozzle speed 500 mm/s had high hardness than thinner layer. In addition, the amount of wear consumed per unit time was also significantly reduced due to the formation of the coating layer.

• Journal of the Korea Institute of Building Construction
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• v.10 no.5
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• pp.137-143
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• 2010

This research is a comparative analysis of the surface gloss of concrete depending on the coating material added to the cast, and includes analyses of the surface gloss of specimens made of cement mortar, with and without the addition of superplasticizer. In terms of coating material, the 7th material, which is part of a liquid packaging material, was shown to have the highest gloss, and was followed by the 3rd material, which uses transparent film. As the level of gloss is shown to vary depending on the material used for the coating film, it can be interpreted that the surface gloss can differ depending on surface particles and chemical composition factors. To make a concrete surface smooth, it is more effective to use a coating material with impermeability and a highly dense surface.

• Journal of the Korean Society of Visualization
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• v.5 no.1
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• pp.3-8
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• 2007

We present simple methods for fabricating high aspect-ratio polymer nanostructures on a solid substrate by rigiflex lithography with tailored capillarity and adhesive force. In the first method, a thin, thermoplastic polymer film was prepared by spin coating on a substrate and the temperature was raised above the polymer's glass transition temperature ($T_g$) while in conformal contact with a poly(urethane acrylate) (PUA) mold having nano-cavities. Consequently, capillarity forces the polymer film to rise into the void space of the mold, resulting in nanostructures with an aspect ratio of ${\sim}4$. In the second method, very high aspect-ratio (>20) nanohairs were fabricated by elongating the pre-formed nanostructures upon removal of the mold with the aid of tailored capillarity and adhesive force at the mold/polymer interface. Finally, these two methods were further used to fabricate micro/nano hierarchical structures by sequential application of the molding process for mimicking nature's functional surfaces such as a lotus leaf and gecko foot hairs.

• KOMUNHWA
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• no.66
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• pp.87-112
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• 2005

Stain removal on ivory has been, for a long time, considered an undesirable treatment in conservation field because ivory is hygroscopic and anisotropic, having different physical properties in different directions. Cyclododecane, which sublimes at room temperature, has been investigated for its use in conservation field since 1995, as a reversible temporary consolidant, sealing agent or coating, water repellent, and barrier layer. This research aims to remove stains on ivory, temporarily protecting the none-stained area or painted area from methanol, acetone or the aqueous cleaning system using cyclododecane as a hydrophobic sealing agent. This research also aims to obtain information regarding whether cyclododecane can be safely and effectively used on archaeological wet ivory. Melted cyclododecane and saturated solutions of cyclododecane in mineral spirits, and hexanes were applied to ivory samples. Application methods, working properties of cyclododecane on ivory, and effect of cyclododecane coating on moisture content of wet ivory were evaluated. The sealing layer formed by molten cyclododecane or by saturated cyclododecane solution in hexane or saturated cyclododecane solution in mineral spirits did not form a secure contact with the surface of the highly polished ivory. The sealing formed with two different layers, in which saturated cyclododecane solution in hexane was applied initially and then molten cyclododecane was applied over the first layer, was found to securely protect the painted area. When the wet samples were kept in 100% RH environments for a month, active mold growths were observed except in the samples sealed with molten cyclododecane. In conclusion, cyclododecane was an efficient hydrophobic sealing agent to protect painting area while cleaning stains on ivory. It also prevented mold growing on wet ivory and wet bone. Evenness of cyclododecane film on ivory will be determined in UV light. Analytical techniques will include visual observation, polarized light microscopy, Scanning Electron Microscope, and Gas Chromatography.

• Korean Journal of Materials Research
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• v.31 no.11
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• pp.601-607
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• 2021

Laser cladding a surface treatment process that grants superior characteristics such as toughness, hardness, and corrosion resistance to the surface, and rebuilds cracked molds; as such, it can be a strong tool to prolong service life of mold steel. Furthermore, compared with the other similar coating processes - thermal spray, etc., laser cladding provides superior bonding strength and precision coating on a local area. In this study, surface characteristics are studied after laser cladding of low carbon steel using 18%Cr-2.5%Ni-Fe powder (Rockit404), known for its high hardness and excellent corrosion resistance. A diode laser with wavelength of 900-1070 nm is adopted as laser source under argon atmosphere; electrical power for the laser cladding process is 5, 6, and 10 kW. Fundamental surface characteristics such as crossectional microstructure and hardness profile are observed and measured, and special evaluation, such as a soldering test with molten ALDC12 alloy, is conducted to investigate the corrosion resistance characteristics. As a result of the die-soldering test by immersion of low carbon alloy steel in ALDC12 molten metal, the clad layer's soldering thickness decreases.

• Korean Journal of Food Science and Technology
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• v.29 no.5
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• pp.1033-1037
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• 1997

The occurrence of mold growth due to moisture migration in a composite chocolate product filled with marshmallow during storage was investigated. The correlation between water activities and water contents of dark chocolate coating and filling marshmallow at $25^{\circ}C$ was well applied to Kuhn's equation. The marshmallow was found to be more hydrogroscopic than the chocolate. Since the moisture transferred from marshmallow to chocolate, the water activity of marshmallow decreased from 0.88 to 0.80 and that of chocolate increased from 0.22 to 0.76 at $25^{\circ}C$ for 30 days. This water activity, 0.76, can allow mold growth. A mold was isolated on the surface of a composite chocolate product at $25^{\circ}C$after 3 months and then was identified as Aspergillus repens. Growth experiments at varied water activities with A. repens were performed. When the water activity in a chocolate solid medium increased from 0.73 to 0.93, the occurrence time of mold growth decreased from 62 to 15 days. These results suggested that the occurrence of mold growth was due to the increased water activity of the chocolate resulting from the moisture transfer from filling marshmallow dark to chocolate coating.