• Tribology and Lubricants
• /
• v.34 no.6
• /
• pp.209-216
• /
• 2018

Sapphire is a substrate material that is widely used in optical and electronic devices. However, the processing of sapphire into a substrate takes a long time owing to its high hardness and chemical inertness. In order to process the sapphire ingot into a substrate, ingot growth, multiwire sawing, lapping, and polishing are required. The lap grinding process using pellets is known as one of the ways to improve the efficiency of sapphire substrate processing. The lap grinding process ensures high processing efficiency while utilizing two-body abrasion, unlike the lapping process which utilizes three-body abrasion by particles. However, the lap grinding process has a high material removal rate (MRR), while its weakness is in obtaining the required surface roughness for the final polishing process. In this study, we examine the effects of free abrasives in lap grinding on the material removal characteristics of sapphire substrate. Before conducting the lap grinding experiments, it was confirmed that the addition of free abrasives changed the friction force through the pin-on-disk wear test. The MRR and roughness reduction rate are experimentally studied to verify the effects of free abrasive concentration on deionized water. The addition of free abrasives (colloidal silica) in the lap grinding process can improve surface roughness by three-body abrasion along with two-body abrasion by diamond grits.

• The Journal of Korean Academy of Prosthodontics
• /
• v.49 no.4
• /
• pp.308-315
• /
• 2011

Purpose: The purpose of this study was to colorimetrically evaluate the masking effect of different opacity of ingots on the final shade of IPS Empress Esthetic$^{(R)}$ laminate veneer restorations using the CIE $L^*a^*b^*$ system. Materials and methods: Six porcelain disks of IPS Empress Esthetic$^{(R)}$ system (translucency: E 01, E 03, E 0C-1, E TC-1, E TC-2, E TC-3) were fabricated with 7 mm in diameter and 0.6 mm in thickness. Six extracted human incisors (shade: A1, A3, A4, B2, B3, C3) were used as the abutment specimens. The incisors were prepared using a diamond wheel and made with a flat labial surface on the middle 1/3. For each combination of different shades of abutments and copings, the change in color was measured with a colorimeter. CIE $L^*a^*b^*$ coordinates were recorded for each specimen. Color differences (${\Delta}E$) were calculated. Descriptive statistical analysis was done. Results: ${\Delta}E$ values were significantly affected by coping translucency and abutment shade (P<.05). The color differences (${\Delta}E$) of laminate veneers among abutments with A3, B3, C3, and A4 shade were mostly below 2.7 which was within the clinically acceptable range, while color differences between A4 and B2, A3 and B2, and A1 and A4 showed more than 2.7. Conclusion: The final color of IPS Empress Esthetic$^{(R)}$ laminate veneers were significantly influenced by translucency of the coping and shade of abutment teeth. The large value difference of abutment teeth limited the masking ability by laminate veneers.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
• /
• v.3 no.2
• /
• pp.95-104
• /
• 2005

Effects of the aluminum melting temperature, melting time and a kind of flux agents on the distribution of surrogate nuclide were investigated in the electric furnace at the aluminum melting including surrogate radionuclides(Co, Cs, Sr) in order to establish the fundamental research of the melting technology for the metallic wastes from the decommissioning of the TRIGA research reactor. It was verified that the fluidity of aluminum melt was increased by adding flux agent but it was slightly varied according to the sort of flux agents. The results of the XRD analysis showed that the surrogate nuclides move into the slag phase and then they were combined with aluminum oxide to form more stable compound. The weight of the slag generated from aluminum melting test increased with increasing melting temperature and melting time and the increase rate of the slag depended on the kind of flux agents added in the aluminum waste. The concentration of the cobalt in the ingot phase decreased with increasing reaction temperature but it increased in the slag phase up to 90$\%$according to the experimental conditions. The volatile nuclides such as Cs and Sr considerably transferred from the ingot phase to the slag and dust phase.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.24 no.2
• /
• pp.47-53
• /
• 2014

Three kinds of crystalline silicon have been used for the solar cell grade. First of all, single crystalline silicon is the main subject to enhance the production yield. Most of the efforts are focused on the control of the melt-crystal interface shape affected by the crystal-crucible rotation rate. The main subject in the multi-crystalline silicon ingot is the contamination control. Faster Ar gas flow above the melt surface will lower the carbon contamination in the crystal. And also, twin boundary electrically inactive is found to be more effective than grain boundary for the improvement of the MCLT. In the case of mono-like silicon material, propagation of the multi-crystalline silicon growing from the inner side crucible is the problem lowering the portion of the single crystalline part at the center of the ingot. Crystal growing apparatus giving higher cooling rate at the bottom and lower cooling rate at the side crucible was suggested as the optimum solution obtaining higher quality of the mono-like silicon ingot. Proper application of the seeds at the bottom of the crucible would be one of the solutions.

• Korean Journal of Materials Research
• /
• v.3 no.3
• /
• pp.253-260
• /
• 1993

High strength and fracture toughness of Al-Li-Cu alloy(2090 Al alloy) have been achieved by the improvement of melting and casting, extrusion and heat treatment techniques. To establish the sucessful process for semi-industrial scale ingot(20Kg) the following areas have been investigated: (1) Improvement of melting and casting techniques for ingot by introducing atmospheric modifications, vacuum and rotary degassing, and deslagging. (2) The effect of heat treatment on mechanical properties (3) Mechanical characterization by tensile test, fracture toughness test and fatigue crack propagation test. High mechanical properties were found to be intimately related with ingot soundness. Tensile strength of final products varied from 534MPa to 566MPa in peak aged condition while elongation/ductility ranged from 9.0% to 11.9%. From the fracture toughness test with using compact tensile specimen, plane strain fracture toughness($K_{Ic}$) appeared to be 39MPa${\surd}$m in peak aged condition and 23MPa${\surd}$ m in underaged condition. When load ratios of 0.1, 0.3 and 0.5 were given ${\Delta}K_{th}$ was 6.0MPa${\surd}$ m, 5.3MPa${\surd}$ m and 4.3MPa${\surd}$ m respectively.

• Korean Journal of Heritage: History & Science
• /
• v.50 no.1
• /
• pp.4-17
• /
• 2017

In this research, the chemical composition of the iron artifacts from the late 6th-century to early 7thcentury Baekje remains in Gwanbuk-ri, Buyeo, specifically of the nine iron artifacts including slags, furnace walls and ingot iron excavated in the District "Na", were examined by observing their chemical compounds and microstructures. As a result, GB1 and GB6 were determined to be proto-reduction lumps whereas GB2, GB3, GB4 and GB5 were determined to be tempered slags, respectively. Also, he furnace wall GB7 were containing mullite and cristobalite, which are high temperature index minerals, The extrusion temperature was found out to be about $1200{\sim}1300^{\circ}C$, and it is most likely that the smelting temperature in the furnace was in that temperature range. GB8 ingot iron was determined to be a forged ironware. This ingot iron was an intermediary product for making ironware and its nonmetallic inclusions displayed similar microstructure and contents compared to the forged iron. Because of the existence of proto-reduction lumps and forged iron, the iron making facility located in District "Na" most likely had a small-scale iron making facility that handled iron bloom smelting and refining processes.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2012.05a
• /
• pp.147-148
• /
• 2012

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2003.05a
• /
• pp.221-224
• /
• 2003

In the open die forging process, it is difficult to optimize process parameters such as die shape, initial ingot size, feeding pitch, rotation angle and other process parameters in the operational environments. Therefore in this study, 3D finite element analysis has been performed to obtain optimal process condition for open die forging process. FEM analyses at various feeding pitches and rotation angles provide process conditions to make round bar having precise dimensional accuracy.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 1991.04a
• /
• pp.68-76
• /
• 1991

최근 열간압연의 공정이 단순하고 회수율이높은 CC재 (연속 주조재)가 IC재 (Ingot 주조재)에 비해 냉간압연 재료의 주종을 이루고있으며, Roll 조도의 급속한 저하로 슬립현상과 채터링현상 등이 발생한다. 본 연구에서는 Work Roll 마멸 및 조도 저하에 큰 영향을 미치는 (1) 압연 가공길이 및 (2) 실험 재료의 종류에 따른 영향과 (3) 압연하중에 의한 Roll 조도변화를 실제 압연가공을 통하여 분석하고, (4) 알미늄 산화 게재물의 영향과 전사율을 연구하고저 한다.

• 전기의세계
• /
• v.21 no.1
• /
• pp.17-21
• /
• 1972

Electrical resistivity and switching phenomena in glass semiconductor of AsTe and AsTeGa is studied. Samples sliced from ingot which is air quenched or water quenched, show high resistivity at room temperature. The resistivity of the AsTe and AsTeGa is 1*10$^{6}$ .ohm.-cm and 5*10$^{6}$ .ohm.-cm at 27.deg. C. Switching phenomena take place in thin the thick samples. Holding voltage is different with the thickness of the samples and the characteristics of switching in the thin and thick samhles are similar. When square wave pulse voltage is applied, delay time is detected to 5.mu.sec by oscilloscpoe.