• Title/Summary/Keyword: Cold pressing

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Adaptability of zirconia core fabricated by cold isostatic pressing (냉간 정수압 성형법으로 제작된 지르코니아 코어의 적합도에 관한 연구)

  • Seo, Yoon-Jeong;Yun, Kwi-Dug;Kim, Hyun-Seung;Park, Sang-Won
    • The Journal of Korean Academy of Prosthodontics
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    • v.48 no.2
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    • pp.143-150
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    • 2010
  • Purpose: The purpose of this study is to fabricate the new zirconia block (CNU block) and to evaluate fit of core and porcelain veneered zirconia crown. Material and methods: The experimental blocks were fabricated from the commercial ytrria-stabilized zirconia powder (KZ-3YE Type A). The powder was uniaxial pressing and the green bodies were conducted using the Cold Isostatic Pressing. The zirconia blocks were presintered at $1040^{\circ}C$ and the final sintering was performed at $1450^{\circ}C$. The Kavo Everest ZS $blank{(R)}$ (KaVo, Biberach/ $Ri{\beta}$.) was used as a control group. The linear shrinkage of CNU block and Kavo block were compared. Twenty-one cores for porcelain veneered crowns were fabricated with CAD/CAM system ($Everest{(R)}$, Biberach/ $Ri{\beta}$.). Group I; seven cores fabricated from Kavo blocks, Group II; seven cores fabricated from CNU blocks, Group III; seven cores from CNU blocks and porcelain veneering for crowns. All specimens were cemented and sectioned into two planes; diagonal and bucco-lingual. The measurement of the marginal, internal, and occlusal fit was carried out using SEM ($S-4800^{(R)}$) at $30{\times}$. The results were analyzed by one-way ANOVA test. Results: The linear shrinkage of the CNU block and the KaVo block was 19.00% and 20.09%. The marginal gap of cores ($29.67{\pm}6.58{\mu}m$) fabricated from CNU blocks showed significantly smaller than that of the cores of Kavo blocks ($36.84{\pm}7.18{\mu}m$) (P < .05). The internal gaps of the porcelain veneered crowns ($32.23{\pm}6.33{\mu}m$) were larger than those of the other two groups ($37.57{\pm}6.81{\mu}m$ and $38.14{\pm}6.81{\mu}m$). Conclusion: No statistically significant difference was found in between experimental groups and control group. The experimental groups in marginal gap showed significantly smaller than the control group.

Fabrication of bi-axially textured Ni tapes for YBCO coated conductors by a cold rolling process and heat treatment of Ni powder compacts (니켈 분말 성형체의 냉간압연과 열처리로 제조된 YBCO coated conductor용 양축 정렬된 니켈 테이프)

  • 이동욱;지봉기;임준형;정충환;주진호;박순동;전병혁;홍계원;김찬중
    • Progress in Superconductivity and Cryogenics
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    • v.4 no.2
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    • pp.16-20
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    • 2002
  • Bi-axially textured Ni tapes for YBCO coated conductors were Prepared by cold rolling and heat treatment of Ni Powder compacts. The Ni powder used in this study was 5 urn in particle size and 99.99 % in purity. The process of this study consists of filling of hi powder into a rubber mold, cold-isostatically Pressing and sintering of the powder compacts at 110$0^{\circ}C$ for 6h in 96 % Ar - 4 % H$_2$ atmosphere. The sintered compacts were cold rolled with a 5 % step reduction ratio into a 100 micron-thick tapes and then heat-treated at 100$0^{\circ}C$ for various time periods. The (200) texture of Ni tape was successfully developed through the recrystallization heat treatment of the cold rolled Ni tapes. At 100$0^{\circ}C$, the degree of texture of the heat-treated Ni tapes seems not to be significantly affected by the heat-treatment time. The short heat treatment of S min was sufficient to develop the complete (200) cube texture. The degree of in-Plane and out-of-plane texture of the prepared Ni tapes was 8-10$^{\circ}$. The heat treated Ni tapes consisted of equiaxed grains with a size 50-70 microns. and the AFM sol-face roughness was as smooth as 3 nm.

Correlation of the 2223 percentage before the first intermediate pressing and the transport property of the fully processed Bi-2223/Ag tapes

  • Jiang, C.H.;Yoo, J.M.;Ko, J.W.;Kim, Y.K.;Chung, H.S.
    • Progress in Superconductivity
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    • v.4 no.1
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    • pp.94-98
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    • 2002
  • Two kinds of multifilament Bi-2223/Ag tapes, which are different in the precursor calcination temperatures, were heat treated for different time (12, 20, 30, 50, 70, or 100 h) firstly to obtain varied B2223 contents, and then followed by the same pressing and sintering cycles. The relation of the 2223 phase contents after the first sintering and the transport property of the fully processed tapes was studied. The results show that 75-80% 2223 phase formed in tapes before the first cold pressing is beneficial to get a high $I_{c}$ in the final tapes. Compensating the total heat treatment time of the tapes first sintered for 20 h to the same length as that first sintered for 50 h in the subsequent sintering stages, different $I_{c}$ enhancements were observed in these two tapes. No improvement on $I_{c}$ was found in the tape made from the powder calcined at higher temperature, whereas for the tape prepared with the lower temperature calcined powder, the $I_{c}$ was increased to the same level as that first sintered for 50 h. The 2223 contents before the intermediate mechanical work is related to the residual reactants, especially to the liquid phase, which is of vital importance to the phase conversion and healing microcracks, meanwhile, to the size and distribution of the non-superconducting secondary phases. The lower temperature calcined powder resulted in slow formation of 2223 phase, but also provided more reactants and liquid phase for the further phase conversion, as a consequence, for the Improvement of $I_{c}$. c/.

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Solid state reactive sintering of cold pressed thermoelectric Mg3Sb2 (냉간 압축 성형한 Mg3Sb2 열전재료의 고상 반응 소결)

  • Kim, In-Ki;Jang, Kyung-Wook;Oh, Han-Jun
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.24 no.4
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    • pp.176-182
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    • 2014
  • We intended to prepare $Mg_3Sb_2$ compound bodies through solid state reactive sintering after cold-pressing mixtures of elementary Mg and Sb powders and investigated the crystal phases of the sintered bodies according to Mg/Sb mole ratios and reaction temperatures. The $Mg_3Sb_2$ bodies sintered at the temperatures of 773~843 K showed typical crystalline phases of $Mg_3Sb_2$ compounds, but their diffraction angles in XRD patterns were slightly different along with the vertical axis of the bodies obtained. All the bottom parts of the sintered $Mg_3Sb_2$ bodies were composed of the typical crystalline phases of $Mg_3Sb_2$ compounds and their diffraction angles were completely in accord with those of the ${\alpha}-Mg_3Sb_2$ phase, when Mg : Sb = 3.15 : 1.85 at 823 K, or when the Mg moles were greater than or equal to 3.10 at 843 K. It was considered that the slightly remaining Mg phases were formed by precipitation from ${\alpha}-Mg_3Sb_2$ phases during the solidification process of liquid phase.

Microstructures of Powders and Additively Manufactured Objects of an Alloy Tool Steel for Cold-Work Dies (냉간금형용 합금공구강 분말 및 적층조형체의 미세조직)

  • Kang, Jun-Yun;Yun, Jaecheol;Kim, Hoyoung;Kim, Byunghwan;Choe, Jungho;Yang, Sangsun;Yu, Ji-Hun;Kim, Yong-Jin
    • Journal of Powder Materials
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    • v.24 no.3
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    • pp.202-209
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    • 2017
  • A cold-work tool steel powder is used to fabricate 3-dimensional objects by selective laser melting using a high-pressure gas atomization process. The spherical powder particles form continuous carbide networks among the austenite matrix and its decomposition products. The carbides comprise Nb-rich MC and Mo-rich $M_2C$. In the SLM process, the process parameters such as the laser power (90 W), layer thickness ($25{\mu}m$), and hatch spacing ($80{\mu}m$) are kept fixed, while the scan speed is changed from 50 mm/s to 4000 mm/s. At a low scan speed of 50 mm/s, spherical cavities develop due to over melting, while they are substantially reduced on increasing the speed to 2000 mm/s. The carbide network spacing decreases with increasing speed. At an excessively high speed of 4000 mm/s, long and irregularly shaped cavities are developed due to incomplete melting. The influence of the scan pattern is examined, for which $1{\times}1 mm^2$ blocks constituting a processing layer are irradiated in a random sequence. This island-type pattern exhibits the same effect as that of a low scan speed. Post processing of an object using hot isostatic pressing leads to a great reduction in the porosity but causes coarsening of the microstructure.

Try out and Analytical Researches on Quenching Process of Coupled Torsion Beam Axle using Boron Steel Tube (보론강을 이용한 CTBA의 후열처리 공정 실험 및 해석)

  • Yoon, S.J.;Park, J.K.;Kim, Y.S.;Suh, C.H.;Lee, K.H.;Kim, R.Y.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2009.10a
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    • pp.181-184
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    • 2009
  • The hot press farming process, which is the press hardening of steel parts using cold dies, can utilize both ease of shaping and high strength due to the hardening effect of rapid quenching during the pressing. In this study, a thermo-elastoplastic analysis of the hot press forming process using the finite element method was performed in order to investigate the deformation behavior and temperature history during the process and the mechanical properties of the pressed parts.

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Fabrication and Optical Properties of Inorganic Electroluminescent Devices (무기전계발광 디스플레이 소자 제작 및 광학 특성 연구)

  • Lee, Jun-Young;Hwang, Jin-Ha
    • Journal of the Korean Ceramic Society
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    • v.46 no.3
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    • pp.317-322
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    • 2009
  • Statistical designs of experiments were applied in order to understand the effect of processing variables on the brightness of inorganic electroluminescent displays. The main effects and interaction of phosphor and dielectric layers are estimated to be statistically significant. Additional improvement was made on removing the pores in the thick films, using the defoaming in pastes and cold isostatic pressing in bonding the top and bottom parts of the inorganic electroluminescent devices. Such optimization contributed to the reduction in the corresponding threshold voltage and enhancement in the brightness.

The Effects of Number and Location of Finger Joints on the Bending Strength of Glue Laminated Wood for Green Wood Building (핑거접합부의 수량 및 배치가 생태목조건축용 집성재의 휨강도에 미치는 영향)

  • So, Won-Tek
    • Journal of the Korea Furniture Society
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    • v.18 no.1
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    • pp.20-30
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    • 2007
  • This experiment was carried out to investigate the effects of number and location of finger joints on the bending strength of glue-laminated lumbers. Urea resin adhesives were used in this experiment and the resin content was 70% for cold pressing. The lamina were edge-jointed and end-jointed. The specimen were composed of one or three layers. The obtained results are summarized as follows; The effects of finger joints on the decrease of bending strength of glue laminated woods were different according to the number and location of finger joints. The decrease of MOR was highest on the middle position of laminated woods. The effects of several arrangements of finger joints on the bending strength of glue laminated woods showed on Figure 7 and 8. The variance of thickness-laminating on the bending strength of glue laminated woods were larger than those of width-laminating.

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Analysis of Densification Behavior of Magnesium Powders in Extrusion using the Critical Relative Density Model (임계상대밀도모델을 이용한 마그네슘분말의 압출공정 치밀화 거동)

  • Yoon, Seung-Chae;Chae, Hong-Jun;Kim, Taek-Soo;Kim, Hyoung-Seop
    • Journal of Powder Materials
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    • v.16 no.1
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    • pp.50-55
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    • 2009
  • Numerical simulations of the powder extrusion need an appropriate pressure-dependent constitutive model for densification modeling of the magnesium powders. The present research investigated the effect of representative powder yield function of the critical relative density model. We could obtain reasonable physical properties of pure magnesium powders using cold isostatic pressing. The proposed densification model was implemented into the finite element code. The finite element analysis was applied to simulation of powder extrusion of pure magnesium powder in order to investigate the densification and processing load at room temperature.

Measurement of Absorbed Dose for High Energy Electron using $CaSO_4:Tm$ - PTFE TLD (고에너지 전자선의 흡수선량 측정에 있어서 TLD의 유용성)

  • Park, Myeong-Hwan;Kim, Do-Sung
    • Journal of radiological science and technology
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    • v.23 no.1
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    • pp.97-101
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    • 2000
  • In this study, the highly sensitive $CaSO_4:Tm$-PTFE TLDs has been fabricated for the purpose of measurement of high energy electron. $CaSO_4:Tm$ phosphor powder was mixed with polytetrafluoroethylene(PTFE) powder and moulded in a disk type(diameter 8.5 mm. thickness $90\;mg/cm^2$) by cold pressing. The absorbed dose distribution and ranges for high energy electron were measured by using the $CaSO_4:Tm$-PTFE TLDs. The ranges determined were $R_{100}=14.5mm$, $R_{50}=24.1mm$ and $R_P=31.8mm$, respectively and the beam flatness, the variation of relative dose in 80% of the field size, was 4.5%. The fabricated $CaSO_4:Tm$-PTFE TLDs nay be utilized in radiation dosimetry for personal, absorbed dose and environmental monitoring.

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