• 한국화재소방학회:학술대회논문집
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• 한국화재소방학회 1997년도 International Symposium on Fire Science and Technology
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• pp.289-296
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• 1997

This paper discribes an experimental explosion risk assessment study on refrigerators containing flammable hydrocarbon refrigerant. A refrigerator used in this study is a larder fridge type, 215 liter in volume. The hydrocarbon refrigerant used in the refrigerator is iso-butane(C$_4$H$_{10}$). For the explosion safety assessment of the refrigerator, temperature of compressor, cooling air circulation fan motor, defrost heater and inner lamp were measured during the operation. And to confirm the ignitablity of flammable gas by the electric spark of the switches of the refrigerator, ON-OFF test of all switches were conducted with compulsorily near the stoichiometric concentration atmosphere of iso-butane-air mixture. As the result of experiment above mentioned and another experiment for the explosion safety assessment, we can conclude that explosion hazard in connection with the use of hydrocarbon refrigerant was few.w.

• Design & Manufacturing
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• 제8권2호
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• pp.37-40
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• 2014

A discharge electrode plays a role of shaving off workpiece with spark generated by current in discharge machining. Accordingly, for the discharge electrode, an electrode with excellent wear resistance is necessary. Generally, Graphite and Cu are used as the materials of the electrode, and recently Cu-W is mainly used as an electrode with excellent wear resistance. However, the form of the electrode generally used is produced mostly using cutting work, so a lot of costs incur if several similar forms are needed. Thus, this study developed a Cu-W electrode using Metal Injection Molding (MIM) process to produce similar forms with excellent productivity and a great quantity of electrodes in a similar form in discharge machining and carried out a discharge machining test. In developing an electrode applying MIM, predicting contraction of a product in a sintering process, a mold expansion ratio of 1.29486 was given, but the actual product showed a percentage of contraction 24% to 32%, which showed a difference of 3% to 5%. In addition, to verify wear resistance of the discharge electrode, abrasion loss was measured after the discharge.

• 한국정밀공학회지
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• 제10권1호
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• pp.42-51
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• 1993

Recently, WC-Co have some excellent properities as the material for the mechanical component such as metallic moulding parts, ball dies parts, and punch parts. This paper describes the surface roughness and grinding force caused by experimental study on the surface grinding of WC-Co with ultra-precision like a mirror shape using diamond wheel. Also, some investigations are carried out using WA grinding wheel to increase improved ground surface roughness such as polishing, lapping effect. Some important results obtained here are summarized as follow. 1) Within this experimental grinding condition, we can be obtained $R_{max}.\;2\mu\textrm{m}\;R_a\;0.3\mu\textrm{m}$ whichare the most favourable ground surface roughness using #140 diamond wheel, and improved surface roughness values about 20 .approx. 25% throughout 5 times sparkout grinding 2) The value of surface roughness is Rmax. $0.49\mu\textrm{m},\;R_a\;0.06\mu\textrm{m}$ using #600 diamond wheel. 3) The area of no rack zone is less than $F_{n}$ 0.27N/mm, Ft 0.009N/mm

• 한국분말재료학회지
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• 제24권2호
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• pp.122-127
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• 2017

Fe-6.5 wt.% Si alloys are widely known to have excellent soft magnetic properties such as high magnetic flux density, low coercivity, and low core loss at high frequency. In this work, disc-shaped preforms are prepared by spark plasma sintering at 1223 K after inert gas atomization of Fe-6.5 wt.% Si powders. Fe-6.5 wt.% Si sheets are rolled by a powder hot-rolling process without cracking, and their microstructure and soft magnetic properties are investigated. The microstructure and magnetic properties (saturation magnetization and core loss) of the hot-rolled Fe-6.5 wt.% Si sheets are examined by scanning electron microscopy, electron backscatter diffraction, vibration sample magnetometry, and AC B-H analysis. The Fe-6.5 wt.% Si sheet rolled at a total reduction ratio of 80% exhibits good soft magnetic properties such as a saturation magnetization of 1.74 T and core loss ($W_{5/1000}$) of 30.7 W/kg. This result is caused by an increase in the electrical resistivity resulting from an increased particle boundary density and the oxide layers between the primary particle boundaries.

• 한국분말재료학회지
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• 제26권5호
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• pp.383-388
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• 2019

To improve the mechanical properties of aluminum, graphene has been used as a reinforcing material, yielding graphene-reinforced aluminum matrix composites (GRAMCs). Dispersion of graphene materials is an important factor that affects the properties of GRAMCs, which are mainly manufactured by mechanical mixing methods such as ball milling. However, the use of only mechanical mixing process is limited to achieve homogeneous dispersion of graphene. To overcome this problem, in this study, we have prepared composite materials by coating aluminum particles with graphene by a self-assembly reaction using poly vinylalcohol and ethylene diamine as coupling agents. The scanning electron microscopy and Fourier-transform infrared spectroscopy results confirm the coating of graphene on the Al surface. Bulk density of the sintered composites by spark plasma sintering achieved a relative density of over 99% up to 0.5 wt.% graphene oxide content.

• 한국분말재료학회지
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• 제24권4호
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• pp.302-307
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• 2017

In this study, Fe-Cu-C alloy is sintered by spark plasma sintering (SPS). The sintering conditions are 60 MPa pressure with heating rates of 30, 60 and $9^{\circ}C/min$ to determine the influence of heating rate on the mechanical and microstructure properties of the sintered alloys. The microstructure and mechanical properties of the sintered Fe-Cu-C alloy is investigated by X-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM). The temperature of shrinkage displacement is changed at $450^{\circ}C$ with heating rates 30, 60, and $90^{\circ}C/min$. The temperature of the shrinkage displacement is finished at $650^{\circ}C$ when heating rate $30^{\circ}C/min$, at $700^{\circ}C$ when heating rate $60^{\circ}C/min$ and at $800^{\circ}C$ when heating rate $90^{\circ}C/min$. For the sintered alloy at heating rates of 30, 60, and $90^{\circ}C/min$, the apparent porosity is calculated to be 3.7%, 5.2%, and 7.7%, respectively. The hardness of the sintered alloys is investigated using Rockwell hardness measurements. The objective of this study is to investigate the densification behavior, porosity, and mechanical properties of the sintered Fe-Cu-C alloys depending on the heating rate.

• 한국분말재료학회지
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• 제18권3호
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• pp.290-296
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• 2011

Titanium carbonitride is more perspective materials compared to titanium carbide. It can be used in tool industry and special products because of its higher strength, abrasive wear-resistance and especially its strong chemical stability at high temperatures. We produced STS+TiCxNy composite by the spark plasma sintering for higher strength and studied the characteristics. The planar and cross-sectional microstructures of the specimens were observed by scanning electron microscopy. Characterizations of the carbon and nitride phases on the surface of composite were carried out using an X-ray diffractometer. During annealing TiCxNy particles diffusion into STS 430 was observed. After annealing, sintering isolations between particles were formed. It causes decreasing of mechanical strength. In addition when annealing temperature was increased hardness increased. Heterogeneous distribution of alloying elements particles was observed. After annealing composites, highest value of hardness was 738.1 MHV.

• 수산해양기술연구
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• 제21권2호
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• pp.157-166
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• 1985

가변 압축비 기관(C. F. R.)에 ionization gap probe를 피스톤 및 실린터 헤드 sleeve에 설치하여 화염거동에 대하여 실험한 결과는 다음과 같다. 1) 혼합연료에서 화염전파속도는 메타놀 함량에 따라 증가한다. 2) 혼합연료에서 메타놀 percent가 증가하면 에너지 소모비 (Btu/HP-hr)가 감소하여 열효율은 증가한다. 3) 당량비가 일정하면 평균유효압력은 메타놀 량이 증가할수록 감소한다. 4) 순수한 가솔린 및 혼합연료는 점화진각이 클수록 NO 하(X) 방출량은 증가하고 희박 혼합기 영역에서 NO 하(X) 방출량은 최대가 된다. 또 RG50/M40/THF10/W1의 연료에서는 당량비가 0.95이하에서는 당양비가 낮을수록, 점화진각이 높을수록 NO 하(X) 방출량은 증가하고, 0.95 이상에서는 당량비와 점화진각이 클수록 방출량은 감소한다. 5) CO, HC의 최소값은 메타놀 함유량이 높을수록 감소한다.

• International Journal of Automotive Technology
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• 제2권1호
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• pp.1-7
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• 2001

This paper presents further investigation into the effect of over-expansion cycle in a spark-ignition engine. On the basis of the results obtained in previous studies, several combinations of late-closing (LC) of intake valve and expansion ratio were tested using a single-cylinder production engine. A large volume of intake capacity was inserted into the intake manifold to simulate multi-cylinder engines. With the large capacity volume, LC can decrease the pumping loss and then increase the mechanical efficiency. Increasing the expansion ratio from 11 to 23.9 with LC application can produce about 13% improvement of thermal efficiency which was suggested to be caused by the increased cycle efficiency. The decrease of compression ratio from 11 to 5.5 gives little effect on the thermal efficiency if the expansion ratio could be kept constant. Thus, the expansion ratio is revealed to be a determining factor for cycle efficiency, while compression ratio is no more important, which suggests the usefulness of controlling the intake charge with intake valve closure timing. These were successfully explained by simple thermodynamic calculation and thus the mechanism could be verified by the estimation.

• 한국재료학회지
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• 제25권8호
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• pp.386-390
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• 2015

Fe-base superalloy powders with $Y_2O_3$ dispersion were prepared by high energy ball milling, followed by spark plasma sintering for consolidation. High-purity elemental powders with different Fe powder sizes of 24 and 50 mm were used for the preparation of $Fe-20Cr-4.5Al-0.5Ti-O.5Y_2O_3$ powder mixtures (wt%). The milling process of the powders was carried out in a horizontal rotary ball mill using a stainless steel vial and balls. The milling times of 1 to 5 h by constant operation (350 rpm, ball-to-powder ratio of 30:1 in weight) or cycle operation (1300 rpm for 4 min and 900 rpm for 1 min, 15:1) were applied. Microstructural observation revealed that the crystalline size of Fe decreased with an increase in milling time by cyclic operation and was about 15 nm after 3 h, forming a FeCr alloy phase. The cyclic operation had an advantage over constant milling in that a smaller-agglomerated structure was obtained. The milled powders were sintered at $1100^{\circ}C$ for 30 min in vacuum. With an increase in milling time, the sintered specimen showed a more homogeneous microstructure. In addition, a homogenous distribution of Y-compound particles in the grain boundary was confirmed by EDX analysis.