• The Journal of Korean Academy of Prosthodontics
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• v.41 no.5
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• pp.596-605
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• 2003

Statement of problem : IPS Empress2 system was developed and used in prosthodontic treatment, but the cost of ingot is expensive for wide application. Purpose : This study was to investigate the possibility on recycling of IPS Empress 2 ceramic for wide application of IPS Empress 2 ceramic in prosthodontic treatment. Material and Method : 1st, 2nd and 3rd pressed disc-shaped($10{\times}1.5mm$) IPS Empress 2 specimens were made with IPS Empress ingot(200, Ivoclar, Liechtenstein) and pressing furnace(IPS Empress EP 500, Ivoclar, Liechtenstein). Vicker's surface hardness and fracture toughness, acid resistance, and pressing accuracy of IPS Empress 2 ceramic were measured and analyzed. Surface hardness was measured by microhardness tester(MTX 70. Matsuzawa, Japan), before and after surface treatment with 0.5% hydrofluoric acid and carbonic acid(Coca cola) for evaluation of acid resistance. Results : The surface hardness of 1st pressed specimen was the higher(5.11 GPa) than those of 2nd pressed(4.89 GPa) and 3rd pressed specimen(4.86 GPa), and the fracture toughness of 1st pressed ($1.58MPam^{1/2}$) and 2nd pressed specimen($1.51MPam^{1/2}$) were higher than that of 3rd pressed specimen($1.39MPam^{1/2}$). The changes of surface hardness of 1st, 2nd, and 3rd pressed specimens after treatment with fluoric acid were 0.17, 0.06, 0.05 (GPa) respectively, and those of 1st, 2nd, and 3rd pressed specimens after treatment with carbonic acid were 0.07, 0.00, 0.05(MPa) respectively. The pressing accuracy of 1st,2nd and 3rd specimen were 77.22%, 85.681%, and 75.05%. The pressing accuracy of 2nd pressed specimen was higher than that of the 3rd specimen. Conclusion : The changes of physical properties according to recycling of IPS Empress 2 from this study were insignificant. Therefore the possibility of recycling of IPS Empress 2 can be suggested from the results.

• Journal of the Korean Magnetics Society
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• v.13 no.4
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• pp.182-186
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• 2003

A new axial pressing method using pulse magnetizing field was studied to improve the remanence of Nd-Fe-B sintered magnets. In order to make near-net shape green compacts of butterfly, disk, or coin magnets, conventional axial-type pressing has been normally used. However, compared to the transverse-type pressing, it is not possible to obtain higher remanence by this method because the magnetic alignment of powder begins to deteriorate when the density of green compacts increases over a critical value. On the other hand, we found that an axial pressing under pulse magnetizing field was very effective to increase the degree of magnetic alignment of powder, yielding remanences even higher than those obtained by the transverse pressing. In this study, it was revealed that appropriate tapping density and how to apply pulse magnetic held were important to improve the grain alignment and thus remanence of Nd-Fe-B sintered magnet.

• Journal of Powder Materials
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• v.16 no.2
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• pp.85-90
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• 2009

Magnesium and its alloys are attractive as light weight structural/functional materials for high performance application in automobile and electronics industries due to their superior physical properties. In order to obtain high quality products manufactured by the magnesium powders, it is important to control and understand the densification behavior of the powders. The effect of the sheath surrounding the magnesium powders on the plastic deformation and densification behavior during equal channel angular pressing was investigated in the study by experimental and the finite element methods. A modified version of Lee-Kim's plastic yield criterion, notably known as the critical relative density model, was applied to simulate the densification behavior of magnesium powders. In addition, a new approach that extracts the mechanical characteristics of both the powder and the matrix was developed. The model was implemented into the finite element method, with which powder compaction under equal channel angular pressing was simulated.

• Transactions of the Korean Society of Automotive Engineers
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• v.16 no.4
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• pp.69-74
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• 2008

The heat generated by the brake system of vehicles results in reduction of friction force on the brake surface and vibration during a braking. To solve these problems, extensive research for the brake shape has been conducted such as drilling cooling holes on the brake disc, accommodating ventilated holes and etc. In this study, we suggest the circumferential pressing type brake disc in order to improve its cooling performance. In order to compare the cooling-down efficiency between the conventional side-pressing type and the circumferential-pressing type, we adopted the FMVSS 105-77 as thermal analysis conditions and This newly proposed concept has been verified using Thermal-structure Coupled Field Analysis along with comparative analysis with the existing ventilated disk.

• Journal of Powder Materials
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• v.18 no.2
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• pp.176-180
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• 2011

Study of the main properties of PVDF films produced by two processing technologies such as hot pressing from a melt or solution casting was the aim of this paper. All samples were prepared of as-received PVDF powder. First group of samples was prepared by the hot pressing. Second group of samples was prepared by the solution casting method. PVDF powder was dissolved in dimethylformamide. To characterize properties of samples, different experimental methods such as FRA (dielectric spectroscopy), IR-spectroscopy and DSC/TGA analysis were used in this work. It was found that IR-spectra of both studied groups do not change compared to that for virgin PVDF powder. It confirms that molecular structure is practically independent on the processing technology of samples. The only difference has been found that new band centered at $1723\;cm^{-1}$ appears for samples prepared by the hot pressing method. This absorption band is related with formation of C=C bonds in samples prepared by the hot pressing method in contrast both to PVDF powder and samples prepared by the solution casting method.

• Journal of the Korean Ceramic Society
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• v.31 no.2
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• pp.177-184
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• 1994

AlN-BN ceramics with BN contents in the range of 10 to 40 wt% were prepared by hot pressing using no additive, or 3 wt%, Y2O3 or CaO, which are common densification aids for AlN. And their machinability, bend strength, and microstructures were investigated. Both the main and radial cutting forces decreased with increasing BN content in all three kinds of samples. For the BN contents of 30 wt% or above, the cutting forces were lower than that of a mild steel tested at a same condition. Especially in the case of main forces, the values were less than a quarter of that of a mild steel, indicating excellent machinability. Bend strength (when the tensile surfaces of specimens were perpendicular to the hot pressing direction) also decreased with BN content mainly due to the much lower Young's modulus of BN compared to AlN. With the composition of 30 wt% BN at which the AlN-BN ceramics started to show better machinability than a mild steel, the bend strength was 150 to 160 MPa, which is greater than that of machinable glass-ceramics of a mica system. With tensile surfaces parallel to the hot pressing direction, however, the bend strength obtained for the samples processed with the sintering acids showed low values (about 40 MPa), since most BN particles had such orientation that their cleavage planes (i.e., basal planes) were perpendicular to the pressing direction.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.20 no.6
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• pp.785-792
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• 2011

Equal channel angular(ECA) pressing is the established processing technique in which a polycrystalline metal is pressed through the die to achieve a very high plastic strain. Therefore, the capability to produce an ultra-fine grain size in the materials is provided. To investigate that mechanical properties at elevated temperature have the ultrafine grain ECA pressing, experiments were conducted on an Al-4.8% Mg-0.07% Mn-O.06% Si alloy. After having been solution treated at 773K for 2hrs, the billet for ECA pressing was inserted into the die. And it was pressed through two channel of equal to cross section intersecting at a 90 degree angle. The billet can be extrude repeatedly because of 1:1 extrusion ratio. Since the billet is passed through the cannel for 2 times, a large strain is accumulated in the alloy. The tensile tests on elevated temperature were carried out with initial strain rate of $10^{-3}s^{-1}$ at eight temperature distributed from 293K to 673K.

• Proceedings of the KSME Conference
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• 2000.11a
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• pp.747-753
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• 2000

There has been a number of investigations in recent years reporting the results obtained on the structure and properties of metals deformed to severe plastic deformation (SPD). Being deformed to SPD, ultra-fine grains (UFG) are usually formed, and UFG structure exhibits fundamental differences in original physical properties. One method often used to obtain SPD is equal channel angular pressing (ECAP). In order for this technique to be exploited, it is important to understand the deformation behavior during the ECAP processing and relationship to the configuration of die. The finite element method (FEM) has been used to investigate this issue. It has been found that the plastic deformation is sensitive to the channel angle and material properties and is not uniform across the width of the specimen and the pressing load is relative to deformation during the ECAP processing.

• Journal of the Korean Wood Science and Technology
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• v.21 no.4
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• pp.64-72
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• 1993

Mechanical properties of 15 mm thick, three-layer particleboard were studied by varying resin content, specific gravity, mat moisture content, pressing time and pressing temperature. Based on the results of the study, Multiple regression models were developed to estimate the mechanical properties of three-layer particleboard. The results of this study showed the mechanical properties of particleboard were highly related with resin content. specific gravity and mat moisture content in decending order. The mechanical properties were able to estimated as the linear function of resin content and specific gravity. However, the effects of change in mat moisture content on the mechanical properties showed a non-linear pattern. The mechanical properties curves over mat moisture content reached peaks at 15 %, and then decreased at 18 % and 21 % of mat moisture contents. On the other hand, the effects of pressing time and pressing temperature on the mechanical properties of particleboard were not significant.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.32 no.4
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• pp.1-9
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• 2000

As the speed of the paper machine and printing press increases, the dependency of the production efficiency upon the frequency of web break increases. It is believed that flaw or crack that presents in paper is one of the most important for web break. Runnability of papers on the paper machine could be evaluated by measuring fracture toughness. In this paper the effect kof beating and pressing on the runnability was investigated using handsheets made from softwood bleached kraft pulp beaten to different freeness. Pressing pressure was also varied to obtain different levels of sheet consolidation. Density, tensile strength, and J-integral of the handsheets were evaluated. For measuring J-integral either a single specimen method or RPM method was employed. Results showed that the density and tensile strength were improved as beating and pressing increased because of increased interfiber bonding. J-integral increased with beating until the CSF reached 400mL. No significant difference in J-integral, however, was observed afterward with the increase of beating. And it appeared to be due to acceleration of the stress concentration around the crack that exists on the fiber wall of the sheet when cracks exists.