Browsing by Author "Kim, Eun-Hee"

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    Development of A New Coating System for The High Functional Mold in Thin-wall Casting
    (2014) Kim, Eun-Hee; Jung, Yeon-Gil; Lee, Je-Hyun
    A new inorganic binder system has been developed to prepare the mold having a high strength for the thin-walled casting. To increase the fracture strength at high temperature, a large amount of inorganic binder should be converted into glass phase and the generated glass phase has to be homogeneously coated on the surface of starting particles. In this work, two types of process were employed to investigate the coating and glassification efficiencies of inorganic precursor. In the first process (process I), the green body consisting of starting powder and organic binder was dipped in the inorganic precursor solution. In the second process (process II), the starting powder was coated by inorganic precursor, and then the organic binder was used to form the green body. The mold sample prepared using process II showed the higher strength value than that using process I, owing to the inclement effect on the glassfication efficiency by the loss of inorganic precursor in process I. The prepared real mold was perfectly produced and the casted product showed a clean surface without defects such as dross, nonmetallic inclusions, and crack. Consequently, the new inorganic binder system could be applied for preparing the mold for the thin-wall casting having high mechanical properties.
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    Improvement in the hygroscopicity of inorganic binder through a dual coating process
    (Elsevier, 2019-10) Choi, Hyun-Hee; Kim, Eun-Hee; Lee, Hye-Ju; Kim, Bong-Gu; Jung, Yeon-Gil; Zhang, Jing; Mechanical Engineering and Energy, School of Engineering and Technology
    The use of an anti-absorbent is proposed in this work to reduce the hygroscopicity of the inorganic binder in the casting mold, in which the anti-absorbent is coated on the mold prepared with an inorganic binder. Three types of polymers were used to select material with optimal water resistance. Polystyrene (PS) and polyvinyl alcohol (PVA) were used as a water-insoluble polymer and water-soluble polymer, respectively. In addition, polyurethane (PU) prepolymer has intermediate properties between PS and PVA. PVA and PU prepolymer were used for comparative testing with PS. For this testing process, the prepared green body was dipped into a solution of inorganic binder precursor mixed with tetraethyl orthosilicate (TEOS, SiO2 precursor) and sodium methoxide (NaOMe, Na2O precursor), and then dipped into a solution of coating reagent after a drying process. Thus, these series of coating processes in a green body is called a dual coating process. Finally the sample was heat-treated at 1000 °C to generate a glass phase by an organic–inorganic conversion process. In the sample prepared with PS, the highest contact angle and a high firing strength were exhibited, independent of polymer concentration, while the sample coated with PVA showed lower green and firing strengths. When prepolymer, PU, was applied, the green strength was remarkably improved, showing lower firing strength compared with that of PS. The green and firing strengths were optimized through the dual coating process with PS. Moreover, the moisture-proof effect of the dual coating process was verified through the moisture steam test.