• Transactions of Materials Processing
• /
• v.16 no.3 s.93
• /
• pp.172-177
• /
• 2007

The process design for large-scale ring rolling of Ti-6Al-4V alloy was performed by calculation method, processing map approach and FEM simulation. The ring rolling design includes geometry design and optimization of process variables. The calculation method was used to make geometry design such as initial billet and blank sizes, and final rolled ring shape. A commercial FEM code, SHAPE-RR was used to simulate the effect of process variables in ring rolling on the distribution of the internal state variables such as strain, strain rate and temperature. In order to predict the forming defects during ring rolling and the formation of over-heating above $\beta$-transus temperature due to deformation heating, the process-map approach based on Ziegler's instability criterion was used with FEM simulation. Finally, an optimum process design to obtain sound Ti-6Al-4V rings without forming defects was suggested through combined approach of Ziegler's instability map and FEM simulation results.

• Journal of Korea Foundry Society
• /
• v.18 no.5
• /
• pp.450-461
• /
• 1998

The optimal reheating conditions to apply the thixoforging and semi-solid die casting process were investigated by changing the reheating time, the holding time, the reheating temperatures, the capacity of the induction heating system, and the adiabatic material size. In the case of solid fraction fs=50% (for semi-solid die casting), the microstructure of SSM (specimen size:$d76{\times}l90$) at the condition of the first elevating time of 4 min, holding time of 1 min and holding temperature of $350^{\circ}C$, the second elevating time of 3 min, holding time of 3 min and holding temperature of $575^{\circ}C$, the third elevating time of 1 min, holding time of 2 min and holding temperature of $584^{\circ}C$, capacity of Q=8.398KW is obtained with globular microstructure and finest. In addition, in the case of solid fraction fs=55% (for thixoforging), the SSM (specimen size:$d76{\times}l90$) at the condition of the first elevating time of 4 min, holding time of 1 min and holding temperature of $350^{\circ}C$, the second elevating time of 3 min, holding time of 3 min and holding temperature of $570^{\circ}C$, the third elevating time of 1 min, holding time of 2 min and holding temperature of $576^{\circ}C$, capacity of Q=12.04KW is obtained with the finest globular microstructure. We saw that the most important factor in a three-step reheating process is the final holding time.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.19 no.2
• /
• pp.683-688
• /
• 2018

In this study, we analyzed the heat generation state of a flat heating element by using image processing technology in conjunction with carbon fiber. The flat heating element is manufactured by chopping the carbon fiber to a small size and bonding it again using a dispersing agent. The solution of carbon fiber, bound together using the dispersant, is then filtered onto the nonwoven fabric. The last step is to obtain flat carbon fibers in the form of nonwoven fabrics for the purpose of drying the filtered carbon fibers. In the flat heating element, electricity may be applied to the carbon fiber on the surface produced in this manner. In this study, the flat heating element was analyzed by four methods. The analysis of the heat generation characteristics and heating rate of the flat heating element confirmed that the fabricated sheet heating element corresponds to a normal army. The analysis of the insulation coating and flat heating element module, which can be used for actual product manufacturing, involves two dimensional image analysis using image processing technology. The thermal image analysis of the flat heating element is a programming technique that not only analyzes the heat generation state in both two and three dimensions, but also displays the upper and lower 15 to 20% ranges of temperature corresponding to the heat generation in the image. In the final analysis, it is possible to easily find the erroneous part in the manufacturing process by directly showing the state of the fabricated flat heating element on the screen. By combining this image analysis method of the flat heating element with the existing method, we were able to more accurately analyze the heat generation state.

• Journal of the Korean Ceramic Society
• /
• v.33 no.9
• /
• pp.1057-1063
• /
• 1996

Y2O3-CeO2-ZrO2 powders were prepared from water-soluble salts using a coprecipitation method. The forming process of oxide and the characteristics of the calcined powders treated in different drying conditions were investigated. The oxidation was occurred at the temperature of around 40$0^{\circ}C$ and the main crystallization of ZrO2 around $600^{\circ}C$. On calcination at $600^{\circ}C$ heating lamp-dried powders consisted of agglomerates of globular morphology with average agglomerate size of 2.27${\mu}{\textrm}{m}$ and specific surface area of 68.3m2/g and spray dried powders contained dense spheric particles with average agglomerate size of 1.35${\mu}{\textrm}{m}$ and specific surface area of 11.0m2/g which exhibited low agglomeration tendency. Removal of the water by a freeze-drying technique produced calcined powders containing flake-like secondary particle structures with wide agglomerate size distri-bution of 0.1-60${\mu}{\textrm}{m}$ and specific surface area of 24.5${\mu}{\textrm}{m}$. The 20 MPa-pressed density (36.8-41.4% T,D) of calcined powders did not nealy depend on drying methods whilst compaction ratio of calcined powders derived from freeze-drying was the highest ( 6.24) among three drying methods. On continuous heating up to 150$0^{\circ}C$ the sinterability of calcined powders derived from heating lamp-drying was superior to those derived from spray-and freeze-drying. The final sintered density of calcined powders was the highest (96% T,D at 150$0^{\circ}C$) in case of heating lamp-drying.

• Journal of the Korean Institute of Intelligent Systems
• /
• v.5 no.1
• /
• pp.33-42
• /
• 1995

A practical application of a fuzzy-neuro controller is described for an air-conditioning system. Air-handing units are being widely used for improving the performance of central air-conditioning systems. The fuzzy-neuro control system has two controlled variables, temperature and humidity and three control elements, cooling, heating, and humidification. In order to achieve high efficiency and economical contorl, especially in large offices and industrial buildings, two controllable parameters, temperature and humidity, must be adequately controlled by the three final controlling elements. In this paper a fuzzy-neuro control system is described for controlling air-conditioning systems efficiently and economically. Simulation results confirmed that the fuzzy neuro control system is effective for this multivariable system.

• Journal of the Korean Institute of Navigation
• /
• v.18 no.4
• /
• pp.147-154
• /
• 1994

A practical application of a fuzzy control system is described for an air-conditioning system. Air-hadling units are being widely used for improving the performance of central air-conditioning systems. The fuzzy control system has two controlled variables, temperature and humidity, and three control elements, cooling, heating, and humidification. In order to achieve high efficiency and economical control, especially in large offices and industrial buildings, two controllable parameters, temperature and humidity, must be adequately controlled by the three final controlling elements. In this paper a fuzzy control system was described for controlling air-conditioning systems efficiently and economically.

• Journal of the Korean Society of Food Science and Nutrition
• /
• v.35 no.7
• /
• pp.881-885
• /
• 2006

The product formation and changes in color of glucose/glutamine model system were investigated in relation to heating temperature and time. The mixtures of glucose and glutamine in equal molar ratio were heated at 125, 150 and $175^{\circ}C$ for 10, 20 and 30 minute, respectively. Acetic acid, butanoic acid, 2-butenoic acid, di-(2-cthylhexyl)phthalate, 2,3-dihydro-3,5-dihydroxy-6-methly-4H-pyran-4-one and 5-hydroxymethylfurfural were identified as a major compounds, and 1,3-dimethylbenzene, 2-ethylhexanol, furfural, 5-methylfurfural, 2-pyrrolidinone, and 2,6-di(t-butyl)-4-hydroxy-4-methyl-2.5-cyclohexadien-1-one as 6 minor compounds by using GC/MS. The contents of acetic acid, 2-ehylhexanol and 2-pyrrolidinone increased with increased heating temperature and time, whereas the formation of the other 9 compounds increased up th heating conditions of $150^{\circ}C$ for 10 or 20 min or $175^{\circ}C$ for 10 min, and decreased dramatically with heating above those conditions. Color parameter $L^*$ decreased with increasing heating conition, resulting in dark brown color in final products. Changes of redness parameter $a^*$ and yellowness $b^*$ showed similar to those of the contents of 9 compounds mentioned as above.

• Journal of Electrical Engineering and Technology
• /
• v.6 no.4
• /
• pp.543-550
• /
• 2011

Conductive SiC-$ZrB_2$ composites were produced by subjecting a 40:60 (vol%) mixture of zirconium diboride (ZrB2) powder and ${\beta}$-silicon carbide (SiC) matrix to spark plasma sintering (SPS). Sintering was carried out for 5 min in an argon atmosphere at a uniaxial pressure and temperature of 50 MPa and $1500^{\circ}C$, respectively. The composite sintered at a heating speed of $25^{\circ}C$/min and an on/off pulse sequence of 12:2 was denoted as SZ12L. Composites SZ12H, SZ48H, and SZ10H were obtained by sintering at a heating speed of $100^{\circ}C$/min and at on/off pulse sequences of 12:2, 48:8, and 10:9, respectively. The physical, electrical, and mechanical properties of the SiC-$ZrB_2$ composites were examined and thermal image analysis of the composites was performed. The apparent porosities of SZ12L, SZ12H, SZ48H, and SZ10H were 13.35%, 0.60%, 12.28%, and 9.75%, respectively. At room temperature, SZ12L had the lowest flexural strength (286.90 MPa), whereas SZ12H had the highest flexural strength (1011.34 MPa). Between room temperature and $500^{\circ}C$, the SiC-$ZrB_2$ composites had a positive temperature coefficient of resistance (PTCR) and linear V-I characteristics. SZ12H had the lowest PTCR and highest electrical resistivity among all the composites. The optimum SPS conditions for the production of energy-friendly SiC-$ZrB_2$ composites are as follows: 1) an argon atmosphere, 2) a constant pressure of 50 MPa throughout the sintering process, 3) an on/off pulse sequence of 12:2 (pulse duration: 2.78 ms), and 4) a final sintering temperature of $1500^{\circ}C$ at a speed of $100^{\circ}C$/min and sintering for 5 min at $1500^{\circ}C$.

• Journal of Forest and Environmental Science
• /
• v.32 no.4
• /
• pp.323-328
• /
• 2016

Thermal stability and rheological behaviors of Ricinodendron heudelotii wood were investigated. Thermogravimetric analysis conducted at a heating rate of $10^{\circ}C/min$ from 20 to $600^{\circ}C$ in a nitrogen atmosphere indicated that there was no variation in the decomposition of the onset and final temperature for all the polymers. The thermal behaviours were investigated at a temperature range from 130 to $0^{\circ}C$ at $3^{\circ}C/min$, multi-frequencies of 0.1-10 Hz using dynamic mechanical analysis. N-methyl-2-pyrolidone saturated specimens were tested while submerged under the same solvent. Polymers decomposition pattern during thermogravimetric analysis are similar in the radial position of the wood. The glass transition temperature (Tg) of R. heudelotii is $45{\pm}1^{\circ}C$ at 0.1 Hz. The Tg differs from the innerwood to outerwood. The Tg showed that N-methyl-2-pyrolidone saturated R. heudelotii would require low energy consumption during chemi-thermomechanical pulping.

• Journal of the Korean Wood Science and Technology
• /
• v.26 no.3
• /
• pp.1-8
• /
• 1998

Western redcedar timber, 26 by 26cm in cross section and by 200cm long, was dried in a laboratory radio-frequency/vacuum kiln under 65torr of ambient pressure and a fixed frequency of 6.78MHz for the potential rapidly dry large timber. All process data were collected and saved in a computer through a data acquisition system. The temperature in the middle of timber was higher than temperature at the quarter point of timber length and thickness. Temperature gradients developed in the longitudinal and transverse direction of timber. The pressure in the middle of timber was higher than pressure at the quarter point of timber length. The pressure in the middle of timber was lower in the early stage of drying, and higher in the latter stage of drying than pressure at the quarter point of timber thickness. Power density was very highest during heating period and then gradually decreased. The drying curve was approximately linear and the total drying time was 27 hours from an initial moisture content(MC) of 48.6 percent to a final Me of 19.2 percent with only a few mild internal checks in the middle location of timber.