• 한국세라믹학회지
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• 제34권4호
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• pp.394-398
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• 1997

Mn-Zn ferrite powders were prepared by alcoholic dehydration, using coprecipitation method. Then the effects of organic dispersant and polymeric binder concentration on stability and casting of slurry were discussed. Citric acid, the organic dispersant and polyvinylacohol(PVA), the non-ionic binder, were selected as additives of slurry. With variation of concentration of water, citric acid and polyvinylalcohol(PVA), optimum forming conditions were determined from viscosity and density. To compare with dry process, density and microstructure of sintered body formed by uniaxial die pressing were observed.

• 대한치과기공학회지
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• 제23권2호
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• pp.203-210
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• 2002

This test is to conduct applied research the reaction area of the Ti-cast metal body which is made use of Dental Phosphate-silica alumina bonded investment material selling at a market, and the cooling method is how to effect on the acicular. The experimentation is as followings, 1. Experimental specimens After invest with Dental Phosphate-silica alumina bonded investment material, the $10{\times}10{\times}1.0mm^3$ wax pattern was casted by Dental high vacuum argon centrifugal casting machine. 2. Test We can analyze SEM/EDS, XRD utilize the fractography(an optical microscope). 3. Conclusion The pure cast metal body constituted of reaction products layer, stability layer and contamination layer. This pure cast have no connection with the cooling condition. The pure Titanium shows difference in a component distribution according to the cooling condition. Through this experimentation we can establish that acicular in the pure Ti-cast metal is consist of Hexagonal structure a=2.9505$\AA$, c=4.6826$\AA$.

• 한국전산유체공학회지
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• 제2권1호
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• pp.117-128
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• 1997

Effects of dam and weir on the fluid flow and behavior of inclusions in the continuous casting tundish have been studied using the CFD (Computational Fluid Dynamics) technique. Inclusions affecting the quality of steel products have been considered to be passive: the fluid flow has been obtained for unstaggered grid points defined on body-fitted generalized cuvilinear coordinates with no attention on inclusions, and the spatial propagation of inclusions has been determined by using the flow field data. The result show that the dam and weir direct the flow to the free surface and increase the residence time of inclusions significantly, and thereby that inclusions have much more chance to be floated to the free surface of the tundish where it is eliminated. It is also found that they offer more margin on the geometric design of exit nozzles connected to moulds. This finding is particularly important for twin casting operations where the quality of steel products from the two moulds be kept uniformly.

• 대한치과기공학회지
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• 제34권2호
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• pp.75-81
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• 2012

Purpose: All ceramic crown, made from zirconia instead of metal for core material, is recognized the best esthetical prosthesis. Recently, high-priced zirconia blocks and expensive CAD/CAM machines come into use for making zirconia core. In this study, slip casting process is adapted to evaluate the possibility of the recycling the remained parts of zirconia block after machining. Methods: Remained zirconia blocks were reduced to powders with zirconia mortar, and screened with 180 mesh sieve. Passed powders were ball milled under various conditions to obtain the optimum zirconia slip for casting. Solid casting method was used for casting the specimens with plaster mold. Formed specimens were dried and biscuit fired at $1,000^{\circ}C$ for 1 hour. Biscuit fired specimens were finished with exact shape of square pillar. Finished specimens were fired from $1,200^{\circ}C$ to $1,550^{\circ}C$ at $50^{\circ}C$ intervals for 1 hour. Linear shrinkage, apparent porosity, water absorption, bulk density, and flexural strength were tested. Microstructures were observed by SEM. Results: Above examinations indicated that the optimum firing temperture was $1,500^{\circ}C$, and when fired at this temperature for 1 hour, apparent porosity was 0% and flexural strength was 680MPa. SEM photomicrographs showed uniform 200~300nm grain size, which is equal with microcture of sintered commercial zirconia block. when compare 24% linear shrinkage of cast specimen with 20% linear shrinkage of CAD/CAM machined block, it was estimated that the size controlling of cast core was not so difficult. Conclusion: According to the all of this experimental results, the cast zirconia core produced from the remained parts of zirconia block was possible to use for all ceramic denture.

• 한국결정학회지
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• 제9권1호
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• pp.64-70
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• 1998

석탄회 70 wt%-점토 30wt%인 슬립으로부터 DCC(Direct Coagulation Casting)법을 이용하여 다공체를 제조하였다. 각각 1.55, 1.60, 1.65g/cm3의 비중을 갖는 슬립으로부터 제조한 다공체의 미세구조 관찰 및 기공크기 분포 측정을 통해 슬립의 비중이 기공크기 및 분포에 미치는 영향에 대해서 연구하였다. 슬립의 비중에 관계없이 평균기공의 크기는 약 2.5μm이었으며, 1.60g/cm3의 비중을 갖는 슬립으로부터 제조된 다공체의 미세구조 및 기공분포가 가장 균일하였다. 슬립비중 1.55g/cm3인 경우에는 고체의 양이 작아 겔화의 진행이 느려 기공분포가 넓어졌으며, 비중 1.65g/cm3인 슬립은 해교제의 첨가량이 많아 응집제 첨가시 점도의 변화가 매우 컸으며 불안정한 슬립 특성을 보였다.

• 대한임베디드공학회논문지
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• 제2권4호
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• pp.221-226
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• 2007

This paper propose a control network system based on IEEE1394 for a multi body robot control. The IEEE1394 has the characteristic of high speed(400Mbps), real-time, stability and plug&play. And IEEE1394 also supports freeform daisy chaining, branching and hot plugging, which reduce cabling complexity and make a system simple. Especially, multi host and broad casting support network data sharing method which is suitable for control network for multi body robot. Through experiment, we show that the proposed control network can interface 48 joints (BLDC motors, gears, and encoders) and four 6-axis force/torque sensors with 4Khz communication bandwidth, which is adequate for a multi body robot.

• 한국분말재료학회지
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• 제29권2호
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• pp.118-122
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• 2022

The synthesis of porous W by freeze-casting and vacuum drying is investigated. Ball-milled WO₃ powders and tert-butyl alcohol were used as the starting materials. The tert-butyl alcohol slurry is frozen at -25℃ and dried under vacuum at -25 and -10℃. The dried bodies are hydrogen-reduced at 800℃ and sintered at 1000℃. The XRD analysis shows that WO₃ is completely reduced to W without any reaction phases. SEM observations reveal that the struts and pores aligned in the tert-butyl alcohol growth direction, and the change in the powder content and drying temperature affects the pore structure. Furthermore, the struts of the porous body fabricated under vacuum are thinner than those fabricated under atmospheric pressure. This behavior is explained by the growth mechanism of tert-butyl alcohol and rearrangement of the powders during solidification. These results suggest that the pore structure of a porous body can be controlled by the powder content, drying temperature, and pressure.

• 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.

• 한국CDE학회논문집
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• 제12권1호
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• pp.50-57
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• 2007

In recent years, many robotics researches have been focused on developing human-friendly robots, that is, humanoid biped robots. The researches of humanoid robots include various areas such as hardware development, control of biped locomotion, artificial intelligence, human interaction, etc. The present work concerns the hardware development of a mid-size humanoid robot, BONOBO, focusing on rapid development of outer body parts with integrated application if CAD/CAM/CAE/RP. Most parts are three-dimensionally designed using 3D CAD, and effectively connected with CAE analyses using both kinematic simulation and structural analysis. In order to reduce lead time and investment cost for parts developments, Rapid Prototyping (RP) and CAM are selectively utilized for manufacturing body parts. These master parts are then replicated using the vacuum casting process, from which we can obtain plastic parts repeatedly. Through this integrated approach, the first prototype of BONOBO can be successfully developed with relatively low time and investment costs.

• 한국세라믹학회지
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• 제48권5호
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• pp.354-359
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• 2011

Silicon nitride ceramics were prepared by microwave gas phase reaction sintering. By this method higher density specimens were obtained for short time and at low temperature, compared than ones by conventional pressureless sintering, even though sintering behaviors showed same trend, the relative density of sintered body inverse-exponentially increases with sintering temperature and/or holding time. And grain size of ${\beta}$-phase of the microwave sintered body is bigger than one of the conventional pressureless sintered one. Also they showed good bending strengths and thermal shock resistances.