• 한국재료학회지
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• 제13권5호
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• pp.292-296
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• 2003

In an attempt to enhance phase transformation and homogenization of Mn-doped $FeSi_2$, mechanical alloying of elemental powders was applied. Cold pressing and sintering in vacuum were carried out to produce a dense microstructure, and then isothermal annealing was employed to induce a phase transformation to the $\beta$-$FeSi_2$semiconductor. Phase transitions in this alloy system during the process were investigated by using XRD, EDS and SEM. As-milled powders after 100 h of milling were shown to be metastable state. As-sintered iron silicides consisted of untransformed mixture of $\alpha$-$Fe_2$$Si_{5}$and $\varepsilon$-FeSi phases. $\beta$-$FeSi_2$phase transformation was induced by subsequent isothermal annealing at $830^{\circ}C$, and near single phase of $\beta$-$FeSi_2$was obtained after 24 h of annealing. Thermoelectric properties in terms of Seebeck coefficient, and electrical conductivity were evaluated and correlated with phase transformation. Seebeck coefficient electrical resistivity and hardness increased with increasing annealing time due to $\beta$ phase transformation.

• 공업화학
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• 제29권1호
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• pp.43-48
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• 2018

본 연구에서는 PCC (precipitated calcium carbonate) 제조에 있어 칼슘이온 추출 최적화를 위하여 추출 용제, 용제의 농도, 추출원의 투입량, 전처리 공정 등 다양한 추출 조건에 따른 실험을 수행하였다. 칼슘추출원으로 CaO를 사용하였으며, 칼슘이온의 추출량과 CaO의 입자크기를 확인하기 위하여 ICP와 SEM 분석을 수행하였다. 그 결과 2 M의 hydrochloric acid를 용제로 사용한 경우 100%의 칼슘이온이 추출되었으며, 추출원의 최적 투입량은 6 g으로 확인하였다. 반면 반응시간, 반응온도, 입자 분쇄 및 열처리 공정은 칼슘이온 추출량에 큰 영향이 없음을 확인하였다.

• 한국가구학회지
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• 제25권1호
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• pp.45-54
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• 2014

Wood cutting utilizing CNC art in the field of furniture design industry, art, education are diverse. However, there is lack of data in the case for wood cutting, such as cutting conditions and wood cutting. So this article is to establish furniture design processing using CNC. The researchers investigated the processed products using CNC, the data of the web site and CNC relevant articles, then organized its impact on the furniture industry today. History and definition of CNC have studied for a discussion of the advantages and disadvantages. Then, the researchers analyzed the cases to investigate the wood cutting conditions, was applied to the fabrication of furniture domestic and foreign. CNC organized systematically design information through the computer So, it allowed to reduce the repetitive behavior that has to work hand in the furniture manufacture existing. CNC has made it possible to design a fine complex in furniture design industry. So it became possible to make a new representation and production of various forms. Material about CNC are mostly for milling machine and shelves for metal processing. So, the researchers investigated and precautions general content of wood cutting. The enhanced understanding to investigate an example that is applied outside the country, is used to analyze the expression various techniques CNC. It is difficult to obtain accurate data processing, it has various characteristics in the same timber, Future research is about analyzing type applications and CNC machining range at the time of processing the various wood.

• 한국분말재료학회지
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• 제22권4호
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• pp.283-288
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• 2015

Two sintering methods of a pressureless sintering and a spark-plasma sintering are tested to densify the Fe-TiC composite powders which are fabricated by high-energy ball-milling. A powder mixture of Fe and TiC is prepared in a planetary ball mill at a rotation speed of 500 rpm for 1h. Pressureless sintering is performed at 1100, 1200 and $1300^{\circ}C$ for 1-3 hours in a tube furnace under flowing argon gas atmosphere. Spark-plasma sintering is carried out under the following condition: sintering temperature of $1050^{\circ}C$, soaking time of 10 min, sintering pressure of 50 MPa, heating rate of $50^{\circ}C$, and in a vacuum of 0.1 Pa. The curves of shrinkage and its derivative (shrinkage rate) are obtained from the data stored automatically during sintering process. The densification behaviors are investigated from the observation of fracture surface and cross-section of the sintered compacts. The pressureless-sintered powder compacts show incomplete densification with a relative denstiy of 86.1% after sintering at $1300^{\circ}C$ for 3h. Spark-plasma sintering at $1050^{\circ}C$ for 10 min exhibits nearly complete densification of 98.6% relative density under the sintering pressure of 50 MPa.

• 대한기계학회논문집A
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• 제41권3호
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• pp.199-204
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• 2017

현재 진동이 심한 산업현장에서 많은 종류의 풀림방지 너트가 사용되고 있다. 왜냐하면 진동의 풀림은 큰 사고를 유발할 수 있기 때문이다. 하지만 대부분의 풀림방지너트는 복잡한 가공과정을 거치기 때문에 가격 경쟁력에서 불리하다. 때문에 본 연구에서는 가공이 쉬운 새로운 유형의 커브드 너트를 개발 하고자 한다. 탄성에너지와 너트의 풀림메커니즘 사이의 탄성에너지를 연구하고 분석한 뒤, 나사의 풀림테스트를 한다. 커브드 너트는 기존너트에 밀링 공구를 이용하여 수직으로 한번 또는 두 번 너트의 밑면을 가공한다. 결과적으로 너트의 탄성에너지가 클수록 너트의 풀림을 막게 된다. 본 연구에서는 NAS3350의 진동테스트 장비를 이용하여 시험을 하고 결과를 분석한다.

• 한국분말재료학회지
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• 제23권2호
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• pp.108-111
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• 2016

$Y_2O_3-H_3BO_3:Eu^{3+}$ powders are synthesized using a mechanical alloying method, and their photoluminescence (PL) properties are investigated through luminescence spectrophotometry. For samples milled for 300 min, some $Y_2O_3$ peaks ([222], [440], and [622]) and amorphous formations are observed. The 300-min-milled mixture annealed at $800^{\circ}C$ for 1 h with Eu = 8 mol% has the strongest PL intensity at every temperature increase of $100^{\circ}C$ (increasing from 700 to $1200^{\circ}C$ in $100^{\circ}C$ increments). PL peaks of the powder mixture, as excited by a xenon discharge lamp (20 kW) at 240 nm, are detected at approximately 592 nm (orange light, $^5D_o{\rightarrow}^7F_1$), 613 nm, 628 nm (red light, $^5D_o{\rightarrow}^7F_2$), and 650 nm. The PL intensity of powder mixtures milled for 120 min is generally lower than that of powder mixtures milled for 300 min under the same conditions. PL peaks due to $YBO_3$ and $Y_2O_3$ are observed for 300-min-milled $Y_2O_3-H_3BO_3$ with Eu = 8 mol% after annealing at $800^{\circ}C$ for 1 h.

• 한국분말재료학회지
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• 제24권2호
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• pp.128-132
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• 2017

Harmonic structure materials are materials with a core-shell structure having a shell with a small grain size and a core with a relatively large grain size. They are in the spotlight because their mechanical properties reportedly feature strength similar to that of a sintered powder with a fine grain size and elongation similar to that of a sintered powder with a coarse grain size at the same time. In this study, the tensile properties, microstructure, and stretch-flangeability of harmonic structure SUS304L made using powder metallurgy are investigated to check its suitability for automotive applications. The harmonic powders are made by mechanical milling and sintered using a spark plasma sintering method at 1173 K and a pressure of 50 MPa in a cylindrical die. The sintered powders of SUS304L having harmonic structure (harmonic SUS304L) exhibit excellent tensile properties compared with sintered powders of SUS304L having homogeneous microstructure. In addition, the harmonic SUS304L has excellent stretch-flangeability compared with commercial advanced high-strength steels (AHSSs) at a similar strength grade. Thus, the harmonic SUS304L is more suitable for automotive applications than conventional AHSSs because it exhibits both excellent tensile properties and stretch-flangeability.

• 대한치과기공학회지
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• 제40권1호
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• pp.17-25
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• 2018

Purpose: When casting of ceramics, proper amount of deflocculant was added for disperse the particles in slip. In this study, examined the optimum amount of APMA(ammonium polymethaacrylate) water as deflocculant for casting the zirconia. Methods: The 100 g of zirconia powder were ball milled with 300 g zirconia ball, 90 g of distilled water, and APMA water in polyethylene pot for 24 hours. The amount of APMA water were added as deflocculant from 0.5 to 0.9 g at an intervals of 0.1 g. The viscosity of slip with no deflocculant showed 1362c.p. and the minimum viscosity with 580c.p. obtained when the slip contained 0.7% of deflocculant. Bar type specimens were casted with plaster mold and biscuit fired at $1100^{\circ}C$ for 1 hours. Biscuit fired specimens were finished with $60mm(L){\times}14mm(W){\times}10mm(H) bar$. Finished specimens were 2nd fired at $1500^{\circ}C$ for 1 hour. Results: Regardless the addition of deflocculant, all 2nd fired specimens showed 0% of apparent porosity and water absorption. The specimens with no deflocculant showed 24% of drying shrinkage and 27.4% firing shrinkage. On the other hand, The specimens with deflocculant showed 17.4% of drying shrinkage and 17.6% firing shrinkage regardless the amount of deflocculant. The maximum bulk density with $6.09g/cm^3$ obtained when the specimens casted with 0.7~0.9% of deflocculant contained slips. Bend strength of specimen with no deflocculant showed 680 MPa and the maximum bend strength with 814 MPa obtained when the specimen casted with 0.7% of diflocculant contained slip. Conclusion : It was found that the particle shape of the powder according to the dispersing agent is added, the particle size, sintering temperature and affect the particle size distribution, sintering time, sintering atmosphere, such a great influence on the sintering.

• 한국분말재료학회지
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• 제20권3호
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• pp.215-220
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• 2013

In the present work, 6061 Al-$B_4C$ sintered composites containing different $B_4C$ contents were fabricated and their characteristic were investigated as a function of sintering temperature. For this, composite powders and their compacts with $B_4C$ various contents from 0 to 40 wt.% were fabricated using a planetary ball milling equipment and cold isostatic pressing, respectively, and then they were sintered in the temperature ranges of 580 to $660^{\circ}C$. Above sintering temperature of $640^{\circ}C$, real density was decreased due to the occurrence of sweat phenomena. In addition, it was realized that sinterability of 6061Al-$B_4C$ composite material was lowered with increasing $B_4C$ content, resulting in the decrease in its real density and at the same time in the increment of porosity.

• 실천공학교육논문지
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• 제7권2호
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• pp.119-123
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• 2015

ABS 소재는 가공이 쉽고 충격과 열에 대한 내성이 강해 가전제품뿐만 아니라 자동차용 내외장재 금속 대체용으로도 많이 사용되고 있다. 이러한 특성으로 ABS의 수요가 늘어감에 따라 ABS를 이용한 가공교육도 그 중요성이 커지고 있다. 그 교육의 일환으로 전국 기능대회 및 지방 기능대회 금형 가공 부분에서 ABS 소재가 쓰이고 있다. 이때 ABS 소재를 이용한 가공에 있어서 ABS 소재를 고정하는 바이스의 힘은 가공 후 최종 형상에 영향을 미치게 된다. 하지만 가공 교육 작업 주의사항이나 지시사항 등에 이에 관한 정확한 명시가 되어있지 않은 상황이다. 따라서 이번 연구에서는 ABS 소재를 이용한 가공 교육에 있어서 교육에 사용하는 기초 형상에 대한 바이스의 고정시키는 힘이 가공 후 최종 형상에 미치는 영향을 알아보고, ABS 소재의 가공 교육 시 적합한 바이스 주의사항을 제시하고자 한다.