• 대한기계학회논문집
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• 제16권2호
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• pp.348-355
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• 1992

Casting structures and properties are determined by the solidification speed in the metal mold. The heat transfer characteristics of the interface between the mold and the casting is one of the major factors that control the solidification speed. According to Sully's research, the thermal resistance exists due to the air-gap formation at the mold-casting interface during the freezing process and the interface heat transfer coefficient is used to describe the degree of it. In this study, one-dimensional Stefan problem with air-gap resistance in the cylindrical geometry is considered and heat transfer characteristics is numerically examined. The temperature distribution and solidification speed are obtained by using the modified variable time step method. And the effects of the major parameters such as mold geometry, thermal conductivity, heat transfer coefficient and initial temperature of casting on the thermal characteristics are investigated.

• 한국주조공학회지
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• 제18권3호
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• pp.246-253
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• 1998

Precision metal mold casting process is a casting method manufacturing mechanical elements with high precision, having heavy/light alloys as casting materials and using permanent mold. To improve dimensional accuracy and the final mechanical properties of the castings, the solidification speed and the cooling rate of the casting should be controlled with the optimum mold cooling system, and moreover, to obtain more accurate control of the whole process interfacial heat transfer characteristic at the mold/casting interface must be studied in advance. In the present study, aluminum alloy casting system with metal mold equipped with electrical heating elements and water cooling system was designed and the temperature histories at points inside the metal mold were measured during the casting process. The heat transfer phenomena at the mold/casting interface was characterized by the heat flux between solidifying casting metal and metal mold, and the heat flux history was obtained using inverse heat conduction method. The effect of mold cooling condition upon the heat flux profile was examined, and the analysis shows that the heat flux value has its maximum at the beginning of the process.

• 대한기계학회논문집
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• 제16권6호
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• pp.1205-1215
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• 1992

본 연구에서는 1차원 상변화문제를 확장하여 사각형 주형내에서의 접촉열저항 을 고려한 2차원 상변화문제를 해석하고자 한다.즉 고상/액상 경계면인 상변화면을 추적하기 위하여 온도수식법(temperature formulation method)을 적용시 나타나는 복 잡성을 극복하기 위하여 제시된 엔탈피법을 이용하여 순수물질의 경우 뿐만 아니라 2상영역이 존재하는 합금에서의 온도분포, 상변화면의 이동속도 및 총응고에 소요되는 시간등의 열적특성을 해석하며, 또한 이러한 열적특성에 영향을 미치는 매개변수를 도출하고자 주형의 형상, 주형 외벽에서의 열전달계수, 접촉 열전달계수, 주형의 열전 도계수 및 주물의 초기온도등의 변화에 따른 효과를 고찰한다.

• 대한치과기공학회지
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• 제32권4호
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• pp.297-305
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• 2010

Purpose: The purpose of this study was to observe the change of metal-mold reaction and surface roughness in titanium casting specimens for phosphate-silica alumina bonded investment with mold temperatures. Methods: The metal-phosphate silica alumina bonded mold interface reaction and surface roughness of titanium casting specimens according to mold temperatures were investigated. The Specimens were analysed by scanning electron microscopy and surface roughness tester. Results: The oxidation behavior indicated by the growth of oxide thickness. The titanium-oxide layer were consisted two layer of a porous external and a dense internal one. The reaction layer and surface roughness increased with increasing investment material temperature. Conclusion: In this work, The most suitable mold temperature in casting of pure titanium was $200^{\circ}C$.

• 설비공학논문집
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• 제11권6호
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• pp.891-897
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• 1999

The heat transfer characteristics at the interface between the mold and the casting is one of the major factors for the solidification speed which determines the casting structures. The thermal resistance exists due to air gap formation at the mold/casting interface during the freezing process. In this study one dimensional Stefan problem with the air-gap resistance in the cylindrical mold is considered and the heat transfer characteristics is numerically examined by using the enthalpy method which is convenient in solving the Stefan problem with mushy zone. The present results agreed very well with those of previous papers. The effects of major parameters such as thermal conductivity, heat transfer coefficient of mold, on the thermal characteristics are investigated.

• 한국분말재료학회지
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• 제18권2호
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• pp.141-148
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• 2011

Carbon material shows relatively high strength at high temperature in vacuum atmosphere and can be easily removed as CO or $CO_2$ gas in oxidation atmosphere. Using these characteristics, we have investigated the applicability of carbon mold for precision casting of high melting point metal such as nickel. Disc shape carbon mold with cylindrical pores was prepared and Ni-base super alloy (CM247LC) was used as casting material. The effects of electroless Nickel plating on wettability and cast parameters such as temperature and pressure on castability were investigated. Furthermore, the proper condition for removal of carbon mold by evaporation in oxidation atmosphere was also examined. The SEM observation of the interface between carbon mold and casting materials (CM247LC), which was infiltrated at temperature up to $1600^{\circ}C$, revealed that there was no particular product at the interface. Carbon mold was effectively eliminated by exposure in oxygen rich atmosphere at $705^{\circ}C$ for 3 hours and oxidation of casting materials was restrained during raising and lowering the temperature by using inert gas. It means that the carbon can be applicable to precision casting as mold material.

• 한국주조공학회지
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• 제10권6호
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• pp.495-502
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• 1990

A basic heat flow model has been developed to estimate the heat transfer coefficient at the casting/mold interface during squeeze casting. Based on the measured temperature profiles in squeeze casting of Al-4.5%Si alloy, heat transfer coefficients which vary with time were calculated by numerical method. The influences of the load and the amount of fraction solid on the heat transfer coefficient have also been studied. Using the calculated heat transfer coefficient two dimensional solidification analysis in the squeeze casting process was carried out by the finite difference method, and the results were in good agreement with the experiments. It may be concluded that heat flow analysis in the squeeze casting process with accurate heat transfer coefficient at the casting /mold interface is important for a proper design of cooling in die and finally for improving productivity and die life as well.

• 소성∙가공
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• 제8권3호
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• pp.289-289
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• 1999

This paper describes the investment casting of TiAl alloys. The effects of mold material and mold preheating temperature for the investment casting of TiAl on metal-mold interfacial reaction were investigated by means of optical micrography, hardness profiles and an electron probe microanalyzer. The mold materials examined were colloidal silica bonded ZrO₂, ZrSiO₄, A1₂O₃and CaO stabilized ZrO₂. When compared with conventional titanium a1loy, the high aluminum concentration of TiAl alloys helps to lower their reactivity in the molten state. The A1₂O₃mold is a promising mold material for the investment casting of TiAl in terms of the thermal stability, formability and cost. Special attention need to be paid to thermal stability and mold preheating when developing the investment calling of TiAl alloys.

• 한국주조공학회지
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• 제14권6호
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• pp.558-565
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• 1994

The horizontal continuous casting process with the heated mold was applied to obtain the unidirectionally solidified rods($4{\sim}8mm$ dia.) of pure copper with good surface quality. The results could be summarized as follows. 1. The unidirectional solidification of pure copper rods with good surface(mirror surface) quality could be obtained by placing the S/L interface inside the heated mold cavity even though the cast copper rods were covered with thin copper oxide layer. 2. The casting speed for 4mm dia. rods with mirror surfaces was affected significantly by the mold-cooler distance rather than the cooling flow rate when other casting conditions were fixed. 3. The casting speed was the main factor affecting the oxidation of copper during the continuous casting and the thickness of copper oxide layer decreased almost linearly as the casting speed increased.

• 보존과학회지
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• 제37권4호
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• pp.340-356
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• 2021

We have tried the experimental research of lost-wax casting to reconstruct Gilt-Bronze Pensive Bodhisattva; preliminary and reconstruction experiment based on ancient texts. Main object to reconstruct is Korean National Treasure No.83, Gilt-Bronze Pensive Bodhisattva (Maitreya), then we measure alloy ratio and casting method based on the scientific analysis. Other impurities were removed from the base metal components(copper : tin : lead) and their ratio was set to 95.5 : 6.5 : 3 where the ratios for tin and lead were increased by 2.5% each. The piece-mold casting method was used, and piece-mold casting experiments were carried out twice in this study but supplementary research on piece-mold casting was necessary. The microstructure was confirmed to be typical cast microstructure and the component analysis result was similar to that of the prior study. Analysis of the chemical composition is confirmed to copper, tin, lead, and zinc, and the chemical composition of the matrix was 87.8%Cu-7.5%Sn-2.7%Pb-2.1%Zn, and similar to previous experimental research. Also resulted in the detection of small impurity in Zn. Analysis of the mould revealed that the mould was fabricated by adding quartz and organic matter for structural stability, fire resistance, and air permeability. We expect that our research will contribute to provide base data for advanced researches in future.