• 한국주조공학회지
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• 제14권1호
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• pp.45-51
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• 1994

The possibility of using bulk talc as molding material was reviewed and tested with the measurement of thermal properties and computer simulations. The measured thermal conductivity and heat diffusivity($k{\rho}c$) of talc were $2.4W/m^{\circ}C$ and $6.6{\times}10^6J^2/m^4^{\circ}C^2s$, respectively. Thermal properties of talc could be ranked between those of sand mold and iron mold. Talc transforms into cristobalite and enstatite at $910^{\circ}C$, During the transformation volume and structure change, cracks appear on the surface and distortion occurs. Therefore talc can be used for molding material below $910^{\circ}C$ if carefully treated. Computer simulation was carried out to test whether talc insert could promote directional solidification in sand mold and iron mold. In sand mold, it was possible to achieve directional solidification of thin plate casting with the length to thickness ratio of 15, if both iron insert and talc insert were used. In iron mold, it was possible to achieve directional solidification only with talc insert.

• 한국주조공학회지
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• 제31권4호
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• pp.212-217
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• 2011

The effects of alloying element and grain refinement on the tensile properties of magnesium alloy poured into sand mold were investigated. The strength of magnesium alloy was greatly increased by the addition of aluminium and that was increased with the increased aluminum content added up to 8.10 wt% and decreased beyond that. Even though the strength of Mg-8.10 wt%Al alloy was rather decreased by the addition of zinc, that was increased with increased zinc content added up to 0.50 wt% and decreased with the increased one beyond that. The maximum tensile strength was obtained with 0.50 wt%Mn added. The strength and elongation were simultaneously increased with grain refinement and the optimum amount of strontium addition for this was 0.30 wt%. The optimum chemical composition was obtained and the yield strength, tensile strength and elongation of the alloy with this composition were 90.2, 176.3MPa and 4.43%, respectively.

• 한국주조공학회지
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• 제25권1호
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• pp.40-50
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• 2005

A series of heavy section ductile cast iron ingots with the cube length of 250mm were systematically investigated as functions of casting parameters of sand casting. Abnormal graphite formation was specially observed with the variation of Si content and Bi or Sb addition. Effects of chilling during casting and adaptation of riserless system were also examined, and proved to be effective for the prevention of both shrinkage and abnormal graphite such as chunky one. The formation of chunky graphite was effectively prevented by low Si content despite the promotion of pearlite matrix structure. The ferritic matrix was encouraged to form by high Si content and chunky graphite formation was effectively suppressed by the addition of Bi and Sb. Bi addition, however, was not good enough to control the microstructure owing to the sensitive cooling rate dependent inoculation behavior and relative low ability of nodulization. Sb addition, on the other hand, was proved to be effective for the microstructural control and enhancement of various mechanical properties such as strength, elongation, and impact energy. It may be suggested that optimized casting parameters should be applied to produce heavy section ductile cast iron with reliability.

• 한국유기농업학회지
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• 제22권4호
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• pp.731-742
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• 2014

본 연구는 다비 재배를 하고 있는 비모란선인장 재배토양에 친환경 부산물비료인 지렁이분변토를 혼합 재배할 때 구경, 구고, 자구수 및 토양 화학적 특성에 미치는 영향을 조사하여, 재배기간 동안 충분한 영양을 공급할 수 있고 생산량을 확보할 수 있는 적정 혼합비율을 규명하였다. 수출용 접목선인장인 비모란 선인장(대목: 9 cm 접수: $1.5{\times}1.3cm$ 접목묘) '이홍' 품종을 2013년 6월부터 12월까지 서울시 서초구 내곡동 서울특별시 농업기술센터 플라스틱하우스 내에서 수행하였다. 농가에서 재배하고 있는 모래와 비료를 50:50으로 혼합한 것을 대조구로 하고, 모래와 음식물쓰레기를 먹이로 하여 생산한 지렁이분변토의 혼합비율을 80:20, 60:40, 40:60, 20:80, 0:100으로 한 5조합의 pH는 7.1-7.4로 거의 비슷하게 조사되었는데 비모란선인장 재배의 적정 pH가 6.5-7.5로 적합한 범위였다. 유기물함량은 지렁이분변토 혼합비율이 높아짐에 따라 증가하였지만 관행처리구 55 mg/kg보다는 32-43 mg/kg으로 낮게 조사되었다. 치환성양이온함량은 혼합비율이 증가함에 따라 높아졌지만 관행처리구보다 $K^+$, $Na^+$, $Mg^{2+}$ 양이 적었으나 $Ca^{2+}$의 함량은 관행처리구는 $9.1cmol^+/kg$이나 지렁이분변토 혼합시 $11.5-33.7cmol^+/kg$으로 높게 조사되었다. 지렁이분변토 혼합비율에 따른 비모란선인장 이식 3개월 후 구경을 조사한 결과 대조구 31.39 mm 보다 지렁이분변토 혼합처리구가 32.46-37.59 mm로 유의성 있는 차이를 보였다. 이식 5개월 후 비모란선인장 생육특성을 조사한 결과 구경은 32.63 mm 보다 지렁이분변토처리구가 32.49-37.59 mm로 혼합비율이 증가함에 따라 유의성 있게 신장하였다. 구고는 대조구의 경우 2.63 mm이고 지렁이분변토 혼합비율에 따라 2.79-3.16 mm로 유의성 있게 조사되었다. 자구수가 많이 생기는 것은 농가에는 매우 유리한 상황인데 대조구는 2.7개이고 지렁이분변토 혼합비율이 높아짐에 따라 3.2-8.3개로 조사되어 고도로 유의하였다. 특히 지렁이분변토 80%와 100% 처리구에서 6.2개와 8.3개로 조사되어 대조구보다 2.5배 이상 증가하였는데 비모란선인장 재배농가에서 단기간 자구생산에 활용할 수 있을 것으로 사료되었다. 지렁이분변토 40%와 60% 혼합처리의 경우 자구수가 4.5와 4.8개로 대조구보다 많이 조사되었으며, 토양배수에도 문제가 없었고 이끼가 발생하는 현상도 없었다. 비모란선인장 생육특성을 조사해본 결과 지렁이분변토 40% 및 60% 혼합비율이 생육에 효율적이라고 판단되었다.

• 한국주조공학회지
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• 제26권1호
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• pp.17-26
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• 2006

The substitution of cooling method from water quenching to air cooling after solution heat treatment was aimed for the development of a convenient and economical heat treatment process of duplex stainless steels without deterioration of mechanical and corrosion resistant properties for the industry. In order to achieve this goal, the mechanical properties and corrosion properties of a ASTM A890-4A duplex stainless steel were systematically investigated as functions of casting condition and cooling method after solution heat treatment. A 3-stepped sand mold and a permanent Y-block mold were used to check the effects of solidification structure and cooling rate after solution heat treatment. The microstructural characteristics such as the ferrite/austenite phase ratio and the precipitation behavior of ${\sigma}$ phase and carbides were investigated by combined analysis of OM and SEM-EDX with an aid of TTT diagram. Hardness and tension test were performed to evaluate the mechanical properties. Impact property at $-40^{\circ}C$ and corrosion resistance were also examined to check the possibility of the industrial application of this basic study. Throughout this investigation, air-cooling method was proved to effectively substitute for water-quenching process after the solution heat treatment, when the duplex stainless steel was sand mold cast with a thickness below 15 mm or permanent mold cast with a thickness below 20 mm.

• 한국주조공학회지
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• 제11권1호
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• pp.54-62
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• 1991

A computer program which consists of pre-processor, main solidification simulator and post-processor has been developed for three dimensional solidification analysis of steel castings. The pre-processor is used for mesh generation in a small personal computing system. The modified finite difference method is adopted for the main solidification simulation algorithm. The post -processor graphically presents the simulation results and shows the formation of shrinkage defects. Several experiments on large steel castings in sand mold were carried out. The temperature variations in casting and mold with time are measured experimentally, and the results are compared with calculation results. Several numerical examples for the prediction of shrinkage cavity in large steel casting of SC42 and SCNCrM2 alloys are compared with experimental results. The effect of sleeve and chills on solidification patterns are also studied. Formation of shrinkage defects for the three cases of experimental castings are relatively well predicted by present model.

• 한국재료학회지
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• 제32권12호
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• pp.538-544
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• 2022

In existing ceramic mold manufacturing processes, inorganic binder systems (Si-Na, two-component system) are applied to ensure the effective firing strength of the ceramic mold and core. These inorganic binder systems makes it possible to manufacture a ceramic mold and core with high dimensional stability and effective strength. However, as in general sand casting processes, when molten metal is injected at room temperature, there is a limit to the production of thin or complex castings due to reduced fluidity caused by the rapid cooling of the molten metal. In addition, because sodium silicate generated through the vitrification reaction of the inorganic binder is converted into a liquid phase at a temperature of 1,000 ℃. or higher, it is somewhat difficult to manufacture parts through high-temperature casting. Therefore, in this study, a high-strength ceramic mold and core test piece with effective strength at high temperature was produced by applying a Si-Na-Ti three-component inorganic binder. The starting particles were coated with binary and ternary inorganic binders and mixed with an organic binder to prepare a molded body, and then heat-treated at 1,000/1,350/1,500 ℃ to prepare a fired body. In the sample where the two-component inorganic binder was applied, the glass was liquefied at a temperature of 1,000 ℃ or higher, and the strength decreased. However, the firing strength of the ceramic mold sample containing the three-component inorganic binder was improved, and it was confirmed that it was possible to manufacture a ceramic mold and core via high temperature casting.

• Advances in concrete construction
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• 제9권3호
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• pp.227-234
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• 2020

Raw perlite is a volcanic alumino-silicate and is used as aggregate in the construction industry. The high silica and alumina contained in the raw perlite allows the production of geopolymer mortar with the help of alkaline solutions. In this study, different geopolymer mortars are obtained by mixing ground perlite (GP), sodium hydroxide (NaOH), water and CEN standard sand and the strength and microstructure of these mortars are investigated. Mortar specimens are placed in the oven 24 hours after casting and kept at different temperatures and times, then the specimens are cured under laboratory conditions until the day of strength tests. After curing, unit weight, ultrasound pulse velocity, flexural and compressive strengths are determined. Experimental results indicate that the mechanical properties of the mortars enhance with increasing oven-curing period and temperatures as well as increasing NaOH molarity. In addition, SEM/EDS and XRD analyses are performed on the mortar specimens and the results are interpreted.

• Computers and Concrete
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• 제20권3호
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• pp.311-318
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• 2017

This paper investigates the utilization of waste tyre crumb rubber as the fine aggregate in precast concrete Paving block (PCPB). PCPB's are generally preferred for city roads, pedestrian crosswalk, parking lots and bus terminals. The main aim of this paper is to evaluate the mechanical properties of wet cast PCPB containing waste tyre crumb rubber. The mechanical properties were investigated using a density, compressive strength, split tensile strength and flexural strength tests at 7, 28 56 days according to the IS 15688:2006 and EN1338. The wet cast method was followed for producing PCPB samples. The fine aggregate (river sand) was replaced with waste tyre crumb in percentage of 5%, 10%, 15%, 20% and 25% by volume. All the test results were compared with the conventional PCPB (Without rubber). The test results indicate its feasibility for incorporating waste tyre crumb rubber in the production of PCPB by the wet cast method.

• 한국주조공학회지
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• 제20권6호
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• pp.407-418
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• 2000

The effect of various factors on the results of degassing of AC4C aluminum alloy melt by using rotary degasser were investigated. The difference between the effects of nitrogen gases of commercial pure and high purity grades on the degassing results was not significant. The optimum degassing condition was obtained. The effect of holding and degassing temperature was not significant, either. The result of degassing was deteriorated by the modification treatment of eutectic silicon, meanwhile improved by the grain refining. The effect of the latter was stronger than that of the former when the melt was treated simultaneously. The volume fractions of hydrogen porosity of the castings obtained from the molds with water moisture such as natural and green sand molds were much higher than those from the molds without that such as pep-set and $CO_2$ molds.