• Journal of the Korean Society for Precision Engineering
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• v.15 no.2
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• pp.28-34
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• 1998

Powder metallurgy processes are able to form Net-Shape products and have been widely used in the production of automobile parts to improve its productivity. However, because of pores in powder products, the toughness of powder products are generally poor. Therefore, forged products are used in parts which suffer severe fatigue loads. In this paper, the choice of powder materials and production processes such as mixing, compaction, sintering, heat treatment to produce automobile spline hub are studied. Three type of materials are selected and processed and its microstructure and properties are investigated by tensile test, compression ring test, and impact test. Materials and processing methods are selected from the results. Finally, experimental spline hubs are manufactured by selected processes from selected powders and proved by torsional durability test.

• Journal of Animal Reproduction and Biotechnology
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• v.34 no.4
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• pp.305-310
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• 2019

Embryos produced with serum show the alterations in their ultrastructure, impaired compaction, abnormal blastulation, aberrant mRNA expression profiles and large calf syndrome with greater incidences of stillbirths and deaths after birth. The aim of the present study was to describe in vitro embryo production by analyzing embryo production, fetal production and pregnancy rate in free-serum medium. The OPU-IVP data used in this study from 2016. Approximately, sixteen cows (Hanwoo), which belonged to the Institute of Gyeongsang National University, were used. Two experimental group is used in this study. Serum groups were conducted in March to July and free-serum group was conducted in September to December. The recovered cumulus-oocyte complexes were morphologically classified to four grades based on the compaction of cumulus cells layers and homogeneity of the cytoplasm. The number of oocyte was significantly greater in serum groups than that in free-serum groups (29.61 ± 0.63 vs. 15.6 ± 0.62; p < 0.05). Between serum and free-serum groups indicate that average of 1st and 2nd grade oocytes were no difference (2.38 ± 1.67 vs. 2.38 ± 1.48; p > 0.05), but number of 3rd and 4th grade oocytes were greater in serum groups than that in free-serum groups (7.31 ± 7.64 vs. 5.60 ± 6.29; p < 0.05). Embryo cleaved competence was higher in rate in free-serum groups than that in serum groups (62.1% vs. 58.3; p < 0.05). However, blastocyst developmental rate was no difference between serum and free-serum groups (33.1% vs. 43.5%; p < 0.05). 986 recipients were used for embryo transfer. Pregnancy rate was indicated that between serum and free-serum group was no difference (54.6% vs. 56.3%; p < 0.05). In conclusion, we developed the free-serum system for production of in vitro bovine embryos in order to meet the developmental and qualitative requirements for large scale commercial use.

• Nuclear Engineering and Technology
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• v.54 no.5
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• pp.1909-1913
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• 2022

This work shows the technical feasibility to obtain uranium tetrafluoride through an electrochemical mercury cell. This technique represents a custom scaling-up methodology from our previous studies to obtain UF₄ using the dropping mercury electrode cell. The UF₄ products were obtained from natural UF₆ gas, which was hydrolyzed to obtain a 50 g/L UO₂F₂ solution. The electrolysis cell was made using a mercury reservoir, to reach UF₄ production rates of 1 Kg UF₄/day. This custom design allowed a stable UF₄ production thanks to the mercury cathode, which do not permit the accumulation of solid products in its surface. The cell was tested using current densities from 5.000 to 17.500 A/m² and temperatures from 25 to 65 ℃. The maximum current efficiency achieved under these conditions was 80%. The UF₄ powders possessed spherical morphology, with diameters between 20 and 80 ㎛. Compared to the SnCl₂ precipitation, this process did not allow preferential growth of the precipitates. This improved the compaction of the UF₄ - Mg powders mixtures, with densities between 3.0 and 3.5 g/cm³. The purity of the UF₄ products was over 98%.

• Journal of the Korean Ceramic Society
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• v.42 no.9 s.280
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• pp.618-623
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• 2005

HTGR (High Temperature Gas-Cooled Reactor) is highlighted to next generation power plant for producing the clean hydrogen gas. In this study, the spherical $UO_2$ kernel via $UO_3$ gel particles was prepared by the sol-gel process. Raw material of slightly Acid Deficient Uranyl Nitrate (ADUN) solution, which has pH = 1.10 and $[NO_3]/[U]$ mole ratio = 1.93, was obtained from dissolution of $U_3O_8$ powder with conc.-$HNO_3$. The surface of these spherical $UO_3$ gel particles, which was prepared from the broth solution, consisted of 1 M-uranium, 1 M-HMTA, and urea, were covered with the fine crystallite aggregates, and these particles were so hard that crushed well. But the other $UO_3$ gel particles prepared with the broth solution, consisted of 2 M-uranium, 2 M-HMTA, and urea, have soft surface characteristics and an amorphous phase. This type of $UO_3$ gel particles is some chance of doing possibility of high density from the compaction. The amorphous $UO_3$ gel particles was converted to $U_3O_8$ and then $UO_2$ by calcination at $600^{\circ}C\;in\;4\%\;-\;H_2\;+\;N2$ atmosphere.

• International Journal of Highway Engineering
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• v.19 no.2
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• pp.67-74
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• 2017

PURPOSES : The objective of this study is to ascertain the curing period of cementless cold central plant recycled asphalt base-layer, using mechanical analyses and specimen quality tests on the field. METHODS : Cold central plant recycled asphalt base-layer mixture was produced in the plant from reclaimed asphalt, natural aggregate, filler for the cold mix, and the modified emulsion AP using asphalt mix design and plant mix design. In order to examine the applicability of the curing period during the field test, the international standards for the possibility of core extraction and the degree of compaction and LFWD deflection were analyzed. Moreover, Marshall stability test, porosity test, and indirect tensile strength test were performed on the specimens of asphalt mix and plant mix design. RESULTS : The plant production process and compaction method of cementless cold central plant recycled asphalt base-layer were established, and the applicability of the optical moisture content for producing the mixture was verified through the field test. In addition, it was determined that the core extraction method of the conventional international curing standard was insufficient to ensure performance, and the LFWD test demonstrated that the deflection converges after a two-day curing. However, the back-calculation analysis reveals that a three-day curing is satisfactory, resulting in a general level of performance of dense asphalt base-layer. Moreover, from the result of the specimen quality test of the asphalt mix design and plant mix design according to the curing period, it was determined that the qualities satisfied both domestic and international standards, after a two-day curing. However, it was determined that the strength and stiffness after three-day curing are higher than those after a two-day curing by approximately 3.5 % and 20 %, respectively. CONCLUSIONS:A three-day curing period is proposed for the cementless cold central plant recycled asphalt base-layer; this curing period can be demonstrated to retain the modulus of asphalt-base layer in the field and ensure stable quality characteristics.

• Journal of the Korean Geotechnical Society
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• v.40 no.2
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• pp.81-93
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• 2024

In Korea, numerous large-scale infrastructure construction projects and housing site developments are being undertaken. However, due to limited land availability, sourcing high-quality backfill materials that meet the standards for railroad and road embankment compaction and mechanically stabilized earth (MSE) retaining wall construction poses significant challenges. Concurrently, there has been an increase in structural failures of many MSE retaining walls, attributed primarily to reduced bearing capacity and impaired drainage performance, resulting from inadequate backfill compaction. This study aimed to analyze the structural performance and safety of an MSE retaining wall using recycled soil as backfill. We conducted small-scale model tests utilizing 3D printing technology combined with two-dimensional numerical analysis. The study quantitatively evaluated the MSE retaining wall's performance concerning the recycled soil mixing ratio and reinforcement installation methods. Furthermore, the utility of 3D printing was confirmed through the production of an experimental wall designed to facilitate easy reinforcement attachment, mirroring the conditions of actual MSE retaining wall construction.

• Journal of the Korea Furniture Society
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• v.10 no.1
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• pp.95-102
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• 1999

The objective of this paper was the development of boards made from waste newspapers. The boards were produced from particle ONP(old newspaper) to reduce energy consumption in the board production process. ONP boards bonded with polyurethan adhesives(PU) were produced on a laboratory scale, and their physical and mechanical properties were examined. The average density of the ONP was $0.48g/cm^3$, and the densities of the boards were $0.50-0.90g/cm^3$. Therefore, th compaction ratios of the boards were in the range of 1.04-1.88. The results obtained were as follows: 1) An increase in board density results in a corresponding improvement in bending properties. 2) An increase in board density results in increased thermal conductivity. 3) In this research, ONP board can be used only for interior applications. To gain exrerior applications, the dimensional stability properties(thickness swelling and water absorption) need to be improved.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1995.03a
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• pp.31-40
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• 1995

Powder metallurgy process has many advantages such as hight efficientyof material, mass productivity and complex shape production with good mechanical properties. Among the powder forming processes, incremental forging allows the consolidation to be achieved with amaller force then those required by conventional forging. In particular the proces known as rotary forging is an unique and prodominant process known as rotary forging is an unique and prodominant process in which the working constraints approximate to those in normal closed die forging. This study is concerned with the powder compaction by rotary forging process. An experimental rotary forging press with 500kN load capacity has been developed, which is equippe dwith the rotational conicla die inclined to the central axis of the press at arbitrary angle. It is found that the highly densified P/M parts can be obtained by rotary forging process and the material properties are superior to those of the conventrional sintered parts. The detailedcomparision of the mechanical properties by rotary forging process with those by conventional process are given.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 1999.10a
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• pp.90-94
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• 1999

Waste gypsum is produced about 2.6million tons per year as a by-product in the process of TiO$_2$production. Geotechnical properties such as natural water content, specific gravity, Atterberg limits were determined to figure out the engineering characteristics waste gypsum. Grain-size distribution, compaction, CBR tests, and unconfined compression test for various mixing ratios between waste gypsum and decomposed granite soil 8t dredged soil. The environmentally adverse effect for mixed specimen with waste gypsum is far below than those of regulatory requirement.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.735-736
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• 2006

Organically bonded P/M mixes have been developed to improve the stability of dimensional properties by reducing the segregation of the mix constituents and improving the filling characteristics. Robustness and reliability are key factors for the promotion of P/M as cost effective substitute of competing manufacturing technologies. Based on the production of four different belt pulleys, this paper presents the achievement of reduced weight scatter and close dimensional control realizable by using a $Starmix^{TM}$ that is organically bonded.