• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.21 no.9
• /
• pp.1400-1413
• /
• 1997

Semi-solid forging(SSF) process of A356 aluminium alloy has been studied to assess the effect of process variables on the component integrity. Semi-solid material(SSM) was fabricated by mechanical and electro-magnetic stirring process. The fabricated SSM by using mechanical stirring process has been carried out on cooling rate of 0.022.deg. C/sec 0.0094.deg. C/sec and stirring speed n=600, 1000 rpm, respectively. The fabricated SSM by using electro-magnetic stirring process is supplied by Pechiney. The holding time and temperature in the semi-solid state before forging also affects the globular microstructure of alloy. Therefore, the influence of these two parameters is discussed in terms of the microstructure of alloy. The SSF process has been conducted with three different die temperatures($T_{die}$=250.deg. C, 300.deg. C, 350.deg. C) and two kinds of gate types(straight gate and orifice gate). This paper is to investigate the influence of gate shapes of die on filling phenomena in SSF process more deeply. The mechanical properties of forged components were also investigated for variation of process conditions such as die temperature, gate shape and SSM.

• Journal of Biomedical Engineering Research
• /
• v.16 no.1
• /
• pp.9-16
• /
• 1995

Biodegradable poly (I ,4-butanediol succinate) (PBS) was synthesized from 1,4-butanediol and succinic anhydride. The glass transition temperature of poly (I, 4-butanediol succinate) was revealed at $73^{\circ}C$. The crystallization and cold crystallization of the polymers were investigated as a function of holding time in melt state, cooling rate. reheating, and molecular weight. Chain scission and/or cmsslinking did not occur in the melt state at var.ious holding times. Slower scanning rate can allow more times for nucleation, rearrangement, and packing of the polymer chain, so the onset temperature of crystallization from the melt was increased. PBS crystallized from the melt was found to have spherulitic structure. The degradation behavior of PBS was studied under basic conditions and with microorganisms using the modified ASTM method. In the basic solution. PBS lost up to 85% of its mass within two days. Based upon visual observation, the crystalline structure of films composed of larger molecular weight polymers retained their crystallinity longer than similar structures in low molecular weight samples.

• 한국연소학회:학술대회논문집
• /
• 2006.04a
• /
• pp.69-74
• /
• 2006

An Experimental study was conducted on $CO_2$ recycle combustion heating system using pure oxygen instead of conventional air as an oxidant, which is thereby producing a flue gas of mostly $CO_2$ and water vapor($H_2O$) and resulting in higher $CO_2$ concentration. The advantages of the system are not only the ability to control high temperatures characteristic of oxygen combustion with recycling $CO_2$. but also the possibility to reduce NOx emission in the flue gas. A small scale industrial reheating furnace simulator and specially designed variable flame burner were used to characterize the $CO_2$ recycle oxy-fuel combustion, such as the variations of furnace pressure, temperature and composition in the flue gas during recycle. It was found that $CO_2$ concentration in the flue gas was about 80% without $CO_2$ recycle, but increased to $90{\sim}95%$ with $CO_2$ recycle. The furnace temperature and pressure was decreased due to recycle and the NOx emission was also reduced to maintain under 100ppm.

• Korean Journal of Materials Research
• /
• v.14 no.6
• /
• pp.379-388
• /
• 2004

To investigate the effect of D-ferrite on the hot workability and surface defect of STS 304 billets containing 3 wt. % Cu, microstructure observations and high temperature mechanical properties test were carried out for the specimens extracted mainly from raw or oxidized billets. It was found that the total $\delta$-ferrite content has little influence on the hot workability, even though the fracture cracks due to high temperature tension or compression test were initiated and propagated mostly along $\delta$/${\gamma}$ boundary in the specimens. On the other hand, it was supposed that the direct causes of surface defects in the wire rolled from the as-continuously cast billet were the grain boundary embrittlement arose from the deep diffusion of oxygen into the grain boundary, and the oxidation of $\delta$-ferrite connected by a grain boundary to the surface during the billet reheating process as well.

• Journal of Sensor Science and Technology
• /
• v.22 no.2
• /
• pp.124-129
• /
• 2013

In this paper, we manufactured the regenerated FBG by the thermal annealing of seed FBG based on UV irradiation. The writing conditions of regenerated FBGs were investigated in four types of optical fiber. FBGs written in $H_2$-free fiber were erased and not regenerated during the thermal annealing. FBG written in $H_2$ loaded Boron co-doped fiber was erased at the temperature of about $580^{\circ}C$ and regenerated about $590^{\circ}C$. However, the extinction of regenerated FBG started at the temperature over $900^{\circ}C$ and then FBG disappeared out. FBG written in $H_2$ loaded Ge high doped fiber was erased and regenerated around the temperature of $800^{\circ}C$ and maintained until the end of the thermal annealing. The reflection of the regenerated FBG was decreased about 12 dB and the center wavelength of the regenerated FBG was shifted about 0.7 nm compared with that of the seed FBG. The thermal characteristics of the regenerated FBG were analyzed by reheating from room temperature to $980^{\circ}C$. As results, the regenerated FBG had survived without a decrease of reflection and the thermal sensitivity was $15pm^{\circ}C$.

• Proceedings of the Materials Research Society of Korea Conference
• /
• 2011.10a
• /
• pp.29.1-29.1
• /
• 2011

The selective catalytic reduction (SCR) of $MnO_x$ with $NH_3$ is an effective method for the removal of $MnO_x$ from stationary system. The typical catalyst for this method is $V_2O_5-WO_3(MoO_3)/TiO_2$, caused by the high activity and stability. However, This catalyst is active within $300{\sim}400^{\circ}C$ and occurs the pore plugging from the deposition of ammonium sulfate salts on the catalysts surface. It needs to locate the SCR unit after the desulfurizer and electrostatic precipitator without reheating of the flue gas as well as deposition of dust on the catalyst. The manganese oxides supported on titania catalysts have attracted interest because of its high SCR activity at low temperature. The catalytic activity of $MnO_x/TiO_2$ SCR catalyst with different manganese precursors have investigated for low-temperature SCR in terms of structural, morphological, and physico-chemical analyses. The $MnO_x/TiO_2$ were prepared from three different precursors such as manganese nitrate, manganese acetate (II), and manganese acetate (III) by the sol-gel method and then it calcinated at $500^{\circ}C$ for 2 hr. The structural analysis was carried out to identify the phase transition and the change intensity of catalytic activity by various manganese precursors was analyzed by FT-IR and Raman spectroscopy. These different precursors also led to various surface Mn concentrations indicated by SEM. The Mn acetate (III) tends to be more suppressive the crystalline phase (rutile), and it has not only smaller particle size, but also better distributed than the others. It was confirmed that the catalytic activity of MA (III)-$MnO_x/TiO_2$ was the highest among them.

• Journal of the Korean Society for Heat Treatment
• /
• v.18 no.1
• /
• pp.3-11
• /
• 2005

Using various thermo-mechanical schedules characterized by varying reheating temperature, deformation temperature and strain, the austenite recrystallization and ferrite refinement of a Nb bearing low carbon steel(0.15C-0.25Si-1.11Mn-0.04Nb) were investigated. For single pass heavy deformations at $800^{\circ}C$, the 40% deformed austenite was not recrystallized while the 80% deformed one was fully recrystallized. Ferrite grains formed in the 80% deformed specimen was not very small compared with those in the 40% deformed specimen, which implied the recrystallized austenite was not more beneficial to ferrite refinement than the non-recrystallized one. In case of deformation in low temperature austenite region, a multi-pass deformation made finer ferrites than a single-pass deformation, as the total reduction was the same, due to more ferrite nucleation sites in the non-recrystallization of austenite for multi-pass deformation. When specimen was deformed at $775^{\circ}C$ that was $10^{\circ}C$ higher than $Ar_3$, the ferrite of about $1{\mu}m$ was formed through deformation induced ferrite transformation(DIFT), and the amount of ferrite was increased with increasing reduction. Dislocation density was very high and no carbides were observed in DIFT ferrites, presumably due to supersaturated carbon solution. By deformation in two phase(50% austenite+50% ferrite) region the very refined ferrite grains of less than $1{\mu}m$ were formed certainly by recovery and recrystallization of deformed ferrites and, a large portion of ferrites were divided by subgrain boundaries with misorientation angles smaller than 10 degrees.

• The Transactions of the Korean Institute of Electrical Engineers
• /
• v.38 no.4
• /
• pp.307-315
• /
• 1989

In this paper, we have analyzed the temperature variation trend of a slab on between the process of reheating furnace and the termination of roughing mill process during hot rolling process. 1) cooling by radiation and convection current in the air, 2) plastic deformation heat, 3) cooling by descaling water, 4) cooling by contact with rolling rolls and/or transmitting rolls. For the analysis, the factors have been adopted as the problems of the rolling process to be solved such that we have established an application technique in relation to the determination of boundary conditions on the slab surface. We have presented a procedure for an analysis of the cooling phenomenon treated as a problem of two-dimensional transient heat flow using finite difference equation and suggested techniques of implementing sequentialized rolling tasks in correlation with the procedure. From the result of simulation, it is shown that the difference between calculation value and measurement value is within the range of the industrial measurement error. Also, it is proved that the assumptions, conditions, and properties used in the computer simulation is appropriate by showing that the pattern of a drop in temperature at each rolling event is in accord with real circumstances.

• Preventive Nutrition and Food Science
• /
• v.10 no.1
• /
• pp.68-73
• /
• 2005

A significant number of cases of illness has been attributed to food consumption in restaurants, and as the number of meals eaten away from home continues to rise, the potential for large-scale, foodborne illness outbreaks will continue to increase. It is critical that hospitality and culinary arts students preparing for careers as professionals in foodservice establishments or restaurants have an appropriate understanding of food safety. The level of food safety knowledge was similar between hospitality and culinary arts students, and an analysis of 266 questionnaires indicated that specific areas, such as hand washing, cross contamination in refrigerator, reheating leftovers, refrigeration of cooked food within two hours, proper temperature of food storage, using of thermometers to monitor temperatures, proper egg handling, and possible food borne illness caused by fruits, should be the primary focus of educational resources. Student respondents showed a higher awareness level of responsibility in their roles for food safety, but more emphasis needs to be given to the correct understanding of food safety issues. Hospitality and culinary arts educators can use this precise information to develop food safety education materials and programs to assist in the prevention of foodborne illness and to knowledgeably educate their graduates about food safety.

• Ceramist
• /
• v.10 no.3
• /
• pp.67-74
• /
• 2007

Crystallisation kinetics of the erbium doped soda-tellurite glasses were studied using the differential thermal analysis (DTA) and differential scanning calorimetery (DSC) techniques. The DTA curves in the temperature range of 350 K to 650 K were obtained from isochronal heating rates, chosen in the range of 2 to 20 K/min. DSC isothermal curves were used to calculate the fraction of crystals formed on reheating. The apparent activation energies for devitrification were derived by measuring the shifts in the values of $T_g$ and $T_x$ with heating rates, using the Kissinger method. The derived values of apparent activation energies for isochronal and isothermal methods varied in the range of $190-204\;{\pm}\;5\;kJ\;mol^{-1}$. The X-ray powder diffraction analysis of heat treated and transparent samples showed the presence of nano-scale size sodium-tellurite crystals. These crystallites were found to have a strong influence on the full width of half maxima of the transition in $Er^{3+}:\;^4I_{13/2}{\rightarrow}^4I_{15/2}$, which extended from 70 nm in the vitreous materials to 132 nm in glass-ceramic materials.