열가압 및 열처리에 따른 IPS Empress 2 세라믹의 굴곡강도와 미세구조

Oh, Sang-Chun,Dong, Jin-Keun,Luthy, Heinz,Scharer, Peter 대한치과보철학회 2000 대한치과보철학회지 Vol.38 No.5

This investigation was designed to determine whether heat-pressing and/or simulated heat treatments affected the flexure strength and the microstructure of the lithium disilicate glass-ceramic in the IPS Empress 2 system. Four groups of the specimens were prepared as follows: group 1 - as-received material, group 2 - heat-pressed material; group 3 - heat-pressed and simulated initial heat-treated material; group 4 - heat-pressed and the simulated heat-treated material with full firings for a final restoration. The three-point bending test and the scanning elec-tron microscope (SEM) analysis was conducted for the purpose of this study. The flexure strength of group 2 was significantly higher than that of group 1. However, there were no significant differences in strength among group 2, 3, and 4, and between group 1 and 4. The SEM micrographs of the lithium disilicate glass-ceramic showed the closely packed, multi-directionally interlocking microstructure of numerous lithium disilicate crystals protruding from the glass matrix. The crystals of the heat-pressed materials (group 2, 3, and 4) were a little denser and about two times bigger than those of the as-received material (group 1). This change of microstructure is more obviously exhibited particularly between group 1 and 2. However, there was no a marked difference among group 2, 3, and 4 after the heat-pressing procedure. Although there were significant increase of the strength and some changes of the microstructure after the heat-pressing operation, the combination of the heat-pressing and the simulated subsequent heat treatments did not produce the increase of strength of IPS Empress 2 glass-ceramic.

핫프레스 공정 기반 CF-PEKK 복합재의 근적외선 고속가열에 의한 열적 열화 반응의 메커니즘 분석

이교문,박수정,박예림,박성재,김윤해 한국복합재료학회 2022 Composites research Vol.35 No.2

The application of infrared heating in the hot press forming of the thermoplastic composites is conducive to productivity with high-speed heating. However, high energy, high forming temperature, and high-speed heating derived from infrared heating can cause material degradation and deteriorate properties such as re-melting performance. Therefore, this study was conducted to optimize the process conditions of the hot press forming suitable for carbon fiber reinforced polyetherketoneketone(CF/PEKK) composites that are actively researched and developed as high-performance aviation materials. Specifically, the degradation mechanisms and properties that may occur in I9infrared high-speed heating were evaluated through morphological and thermal characteristics analysis and mechanical performance tests. The degradation mechanism was analyzed through morphological investigation of the crystal structure of PEKK. As a result, the size of the spherulite decreased as the degradation progressed, and finally, the spherulite disappeared. In thermal characteristics, the melting temperature, crystallization temperature and heat of crystallization tend to decrease as degradation progresses, and the crystal structure disappeared under long-term exposure at 460°C. In addition, the low bonding strength was observed on the degraded surface, and the bonding surfaces of PEKK did not melt intermittently. In conclusion, it was confirmed that the CF/PEKK composite material degraded at 420°C in the infrared high-speed heating. Furthermore, the spherulite experienced morphological changes and the re-melting properties of thermoplastic materials were degraded. 열가소성 복합재의 핫프레스 성형공정에서 근적외선 가열의 적용은 소재를 성형온도까지 고속가열함으로써 공정 전체의 생산성을 확보할 수 있으나, 고에너지, 높은 성형온도, 고속가열에 의해 소재의 열화가 발생하여 재용융 성능 등의 소재 특성이 저하될 수 있다. 이에 본 연구는 고성능 항공소재로 활발히 연구개발되고 있는Carbon fiber reinforced Polyetherketoneketone(CF/PEKK) 복합재에 적합한 핫프레스 성형공정의 최적화된 공정조건을 확립하기 위하여 근적외선 고속가열을 적용하였을 때, CF/PEKK 복합재에서 발생할 수 있는 열화 메커니즘과 그 특성을 형태학적, 열적 특성 및 기계적 성능 시험을 통해 평가하였다. 열화 반응에 따른 메커니즘 규명은 광학 현미경을 활용하여 PEKK의 결정구조의 형태학적 조사를 기반으로 분석하였다. 그 결과, 열화가 진행됨에 따라 구결정의 크기가 감소하며 최종적으로 완전 열화 시 구결정이 소멸되는 것을 확인하였다. 열적 특성은 용융온도, 결정화온도, 발열량이 열화가 진행됨에 따라 감소하는 경향이 관찰되며, 460oC 장시간 노출에서 결정구조가 소멸된 것을 확인하였다. 랩전단강도(Lap shear strength)시험 결과, 열화된 표면에서는 낮은 접합강도가 관찰되며, 접합면 분석에서 특정 면에서는 열에 의한 용융 특성이 나타나지 않았다. 결론적으로 CF/PEKK 복합재의 근적외선 고속가열 적용에 있어 특정 온도에서 열화 진행되며, 이에 구결정의 형태학적 변화와 열가소성 소재의 재용융 특성의 저하를 확인하였다.

도재용착용 비귀금속과 열가압성형도재의 전단결합강도 연구

김성수,김욱태,이명곤,Kim, Seong-Soo,Kim, Wook-Tae,Lee, Myung-Kon 대한치과기공학회 2011 대한치과기공학회지 Vol.33 No.1

Purpose: Heat pressed ceramics, used for all ceramic restorations, have the additional advantage of being technically less change through using of the lost-wax technique. Conceptually, combining the ceramic with the clinically proven reinforcing ability of a metal framework would be advantageous; however, cause of mismatching of fusion between ceramics and metal frameworks which from differences of casting temperature and coefficient of thermal expansion, pressed ceramics could not be used with a metal framework. The purpose of this study was to compare shear bond strength of press-to metal ceramic to porcelain fused non precious metal and feldspatic porcelain fused non precious metal. Methods: The 30 metal specimens were casted in a porcelain fused non precious metal nickel-chromium alloy. They were divided into 3 groups by surface treatment and applied ceramic: $125{\mu}m$ aluminium oxide sandblasting and veneered feldspatic porcelain (group FP), $125{\mu}m$ aluminium oxide sandblasting and had press-to-metal ceramic applied (group PC), porcelain bonder (gold bonder) fused on surface of metal specimens and had press-to-metal ceramic applied (group PCG). In each group 10 metal specimens were used. The press-to-metal ceramic applied 20 specimens had ash-free wax pattern applied, the metal-wax complexes invested, and were pressed with heat press ceramic. All specimens were subjected to shear bond strength test at a crosshead speed of 1.0 mm/min. Results: The results of measured in Mean SD and data were analyzed by one-way AVOVA (p= .05) and Tukey HSD test (p= .05).: group FP $16.090{\pm}1.841$ MPa, group PC $12.620{\pm}1.8256$ MPa, group PCG $10.920{\pm}0.9283$, significant differences between all groups (p < .05). Significant differences were found in each between group FP and group PC, group FP and group PCG (p < .05). Conclusion: The shear bond strength of press-to-metal ceramic to porcelain fused non precious metal was described higher in unused gold bonder group than used gold bonder groups.

Effects of Correction by Heating/Pressing on Mechanical Behavior of Steel Bridge Pier

Mikihito Hirohata,Takuya Morimoto,You-Chul Kim 한국강구조학회 2009 International Journal of Steel Structures Vol.9 No.1

A series of experiments was conducted in order to elucidate effects of correction by heating/pressing on mechanical behavior of steel bridge piers. Local buckling deformation of specimens due to loading considering the situation of an earthquake was corrected by heating/pressing, with or without water-cooling. Some out-of-plane deformations were inevitably left to avoid cracking in the welds. This geometric imperfection was defined as residual imperfection. After the correction, the same loading experiment was conducted. From the results, no deterioration was confirmed in mechanical properties of the steel even with water-cooling only if heating temperature was kept below A1 transformation temperature. Although it is ideal to have local buckling deformation repaired within the allowance of initial deflection in correction by heating/pressing, it was elucidated that making the residual imperfection mode opposite to local buckling mode was reasonable for guarantee of the maximum load of the corrected structure. A series of experiments was conducted in order to elucidate effects of correction by heating/pressing on mechanical behavior of steel bridge piers. Local buckling deformation of specimens due to loading considering the situation of an earthquake was corrected by heating/pressing, with or without water-cooling. Some out-of-plane deformations were inevitably left to avoid cracking in the welds. This geometric imperfection was defined as residual imperfection. After the correction, the same loading experiment was conducted. From the results, no deterioration was confirmed in mechanical properties of the steel even with water-cooling only if heating temperature was kept below A1 transformation temperature. Although it is ideal to have local buckling deformation repaired within the allowance of initial deflection in correction by heating/pressing, it was elucidated that making the residual imperfection mode opposite to local buckling mode was reasonable for guarantee of the maximum load of the corrected structure.

열 압착을 이용한 가식성 젤라틴 필름 제조

김의현(Eui Hyun Kim),송아영(Ah Young Song),민세철(Sea Cheol Min) 한국식품과학회 2022 한국식품과학회지 Vol.54 No.2

본 연구에서는 열 압착 공정을 이용하여 생고분자 가식성 FG 필름과 MG 필름을 제작하였고, 제조 공정 차이에 따른 필름의 형성, 표면 미세구조, 그리고 빛 투과도를 비교하기 위해 캐스팅 방법을 이용해서도 FG 필름을 제작하였다. 열 압착을 이용하여 FG와 MG로부터 연속적이고, 균일하며, 투명하고, 그리고 매끄러운 표면을 가진 필름을 제작할 수 있었다. 열 압착된 FG 필름은 열 압착된 MG 필름보다 빛 투과도와 인장 강도가 낮았으나, 육안 관찰 및 현미경을 이용한 표면 미세구조를 관찰 시 큰 차이를 확인할 수 없었으며, 수분 투과도와 필름의 명도 및 붉은 정도에서도 유의적인 차이가 보이지 않았다. 또한, 열 압착된 FG 필름이 캐스팅된 FG 필름보다 육안으로 보았을 때 더욱 투명하고 균일한 표면을 가진 것을 확인할 수 있었고, 투명도도 캐스팅된 FG 필름보다 높음을 알 수 있었다. 열 압착된 FG 필름이 캐스팅된 FG 필름보다 낮은 인장 강도와 높은 수분 차단 능력을 갖췄다. 열 압착된 FG 필름은 캐스팅된 FG 필름과 색도의 차이가 있었고, 캐스팅된 FG 필름보다 매끄럽고 균일한 표면 미세구조를 가진 것을 알 수 있었다. 본 연구의 결과는 열 압착 공정을 사용하는 산업적 생고분자 생산 시스템을 사용하여 우수한 수분 차단 능력을 갖춘 가식성 필름을 MG과 생선껍질로부터 얻어지는 FG을 이용해 제작할 수 있음을 보여주었다. In this study, edible films made of fish and mammalian gelatins were produced using heat pressing, and their physical properties were investigated. Transparent and smooth films were formed continuously and uniformly using a mixture of fish skin gelatin (FG) or mammalian gelatin (MG), glycerol, and water under the process of heat pressing at 90℃ and 20 MPa for 5 min. Heat-pressed FG films possessed lower light transmittance and tensile strength than heat-pressed MG films; however, their appearance, surface morphology, water vapor permeability, lightness, and redness were not different from those of heat-pressed MG films. Although heat-pressed FG films had lower tensile strength, they had a flatter and more uniform surfaces and demonstrated higher transparency and moisture barrier properties compared to the casted FG films. These results demonstrate the potential utility of heat pressing for the large-scale production of edible films using both FG and MG.

가압·가열 처리한 층층나무 적층재를 활용한 테이블 디자인 연구

신랑호,한태형,권진헌 한국가구학회 2012 한국가구학회지 Vol.23 No.1

In this study domestic thinning and small diameter woods of Giant dogwood (Cornus controversa Hemsl) was used. To increase the utilizability of wood, the utilizability was proposed after manufacturing laminated wood by pressing and heating. The physical and mechanical characteristics of Laminated wood were investigated and the color change was measured, using a Chromaticity coordinates, after being pressed at 10% (45 mm), 20% (40 mm), 30% (35 mm) for 5 minutes, using Stopper, and then heated at 180°C for 6, 12, 24 and 48 hours. The results were as follows. Wood density, compressive strength, MOR, MOE are increased with increasing pressing rate but decreased as heating time is increased after pressing. However, Color change is clear, dimensional stability is improved after pressing and heating.

열가압 성혈 글라스 세라믹의 파괴인성에 미치는 반복 열가압 성형의 영향

원대희 大韓齒科器材學會 2002 대한치과재료학회지 Vol.29 No.4

This study was performed to evaluate the effects of repeating the heat pressing procedure on the fracture toughness of heat-pressable glass-ceramics. Three commercially available ingots of Authentic(Ceramay GmbH), Empress and Empress 2(deutsche Ivoclar Dental GmbH) were used. Crystal phases of these glass-ceramics were investigated by means of X-ray diffraction analysis (XRD) and morphology and microstructure were studied using scanning electron microscopy (SEM). Fracture toughness was calculated using the length of radial crack formed on the Vickers-produced indentation crack by means of the indentation fracture method. According to the result of X-ray diffraction analysis, the test groups of Authentic and Empress did not show the change in crystal peak intensity, but the test group of Empress 2 showed increase in crystal peak intensity after repeating the heat pressing procedure. Fracture toughness values of the test groups of Authentic and Empress showed the aspect of increase after repeating the heat processing procedure but that of Empress 2 group showed decrease.

A Busbar Integrated SiC-based Converter with Embedded Heat-pipes

Yao Chang,Amir Sajjad Bahman,Haoze Luo,Wuhua Li,Xiangning He,Francesco Iannuzzo,Frede Blaabjerg 전력전자학회 2019 ICPE(ISPE)논문집 Vol.2019 No.5

In this paper, a bus-bar integrated packaging technology for press-pack power modules is proposed. The proposed packaging technology features high power-density, even pressure distribution among chips, and low stray parameters. The structure design and fabrication flow process are analyzed and experiments are made to verify the feasibility of proposed solution. The critical challenge about the package is related to thermal management. To reduce the thermal stress of chips, a heat-pipe integrated heatsink is developed and finite-element-method (FEM) simulations are used to evaluate the cooling performance of the proposed heatsink. The results demonstrate that the proposed heatsink has a relatively low cost and works effectively. It paves the way to better packaging design and more efficient thermal management method for high power devices.

전기방사법으로 제조한 PEI/PVdF 블렌드 웹의 물리적 특성에 대한 후처리 영향

석훈(Hoon Seok),박철민(Cheol Min Park),김동영(Dong Young Kim),조성무(Seong Mu Jo) 한국고분자학회 2012 폴리머 Vol.36 No.5

Polyetherimide(PEI)와 poly(vinylidene flouride)(PVdF) 폴리머들을 블렌딩하여 전기방사를 통해 웹을 제조하였다. 낮은 기계적 물성을 증대시키기 위해서 압착과 연신이라는 후처리 공정을 이용하였으며 후처리 공정이 기계적 물성에 미치는 영향을 조사하였다. 물리적 특성을 확인하기 위해 SEM, 인장 시험 측정기를 이용하여 측정하였다. 180 ˚C의 압착 온도에서 1/2, 1/3, 1/4, 1/5의 비율로 압착된 웹들은 초기 상태에 비해 대략 4~5배 가량 인장 강도가 증가하였으며, 이들을 220 ˚C의 온도에서 30~40% 연신함으로써 2~8MPa의 추가적인 인장 강도 증대를 보였다. Polyetherimide (PEI) and poly(vinylidene fluoride) (PVdF) blend web was prepared by electrospinning technique. In order to improve low mechanical properties, post processes like hot-pressing and heat-stretching were employed, and a study on the effects of post processes on their mechanical properties was performed. To confirm the physical properties of the web, scanning electron microscopy and tensile measuring instrument were used. The mechanical strength of webs pressed in the ratios of 1/2, 1/3, 1/4 and 1/5 at 180 ˚C were improved four-to-five times compared to pristine webs. Also they showed an additional increase by 2~8MPa, by heat-stretching 30 to 40% at 220 ˚C.

Generality Verification for Factors Dominating Mechanical Behavior under Compressive Loads of Steel Structural Members Corrected by Heating/Pressing

Mikihito Hirohata,You-Chul Kim 한국강구조학회 2008 International Journal of Steel Structures Vol.8 No.2

Factors dominating a mechanical behavior under compresive loads of stel structural members corrected by heating/presinghad been identified by using cruciform columns. These factors were geometric residual imperfection resulting from incompletecorrection by heating/presing and increase of yield stres due to large plastic deformation caused by local buckling and itscorection process. In this paper, in order to verify the generality of these factors, a series of experiments and the elastic-plasticlarge deformation analysis were carried out on box columns. From the results, the behavior under compresive loads such asgenerality of these dominant factors could be confirmed regardles of the structural shape of members.