• Advances in concrete construction
• /
• 제7권4호
• /
• pp.263-275
• /
• 2019

In the present work, Granulated Blast Furnace Slag (GBFS) and Fly ash (FA) were used as partial replacement of Natural Sand (NS) and Ordinary Portland Cement (OPC) by weight. One control mix, one with GBFS, three with FA and three with GBFS-FA combined mixes were prepared. Replacements were 50% GBFS with NS and 20%, 30% and 40% FA with OPC. Preliminary investigation on development of compressive strength was carried out at 7, 28 and 90 days to ensure sustainability of waste materials in concrete matrix at room temperature. After 90days, thermo-mechanical study was performed on the specimen for a temperature regime of $200^{\circ}-1000^{\circ}C$ followed by furnace cooling. Weight loss, visual inspection along with colour change, residual compressive strength and microstructure analysis were performed to investigate the effect of replacement of GBFS and FA. Although adding waste mineral by-products enhanced the weight loss, their pozzolanicity and formation history at high temperature played a significant role in retaining higher residual compressive strength even up to $800^{\circ}C$. On detail microstructural study, it has been found that addition of FA and GBFS in concrete mix improved the density of concrete by development of extra calcium silicate gel before fire and restricts the development of micro-cracks at high temperature as well. In general, the authors are in favour of combined replacement mix in view of high volume mineral by-products utilization as fire protection.

• 대한전기학회논문지
• /
• 제38권4호
• /
• pp.307-315
• /
• 1989

본 논문에서는 열간압연공정중 소재가 가열로에서 추출되어 조압연 공정을 마치기 까지 소재인 slab의 온도변화추이를 해석키 위하여 rolling process 상에서 온도에 영얄을 미치는 인자인 1) 대기중 복사 및 대류에 의한 냉각 2) 소성가공발열 3) descaling water에 의한 수냉각 4) rolling roll, 운반 roll과의 접촉냉각등 제요인에 관한 사항을 rolling process 상에서의 문제로 평가도입하여 해석하고저 하는 slab 표면에서의 경계조건 설정과 관련한 적용기법을 정립하였고 소재의 냉각 현상을 two dimensional transient heat flow문제로 취급, 유한차분방정식을 이용하여 해석하는 과정과 관련 rollinh작업을 sequence화 하여 적용하는 기법을 제시하였다. simulation 결과 계산치와 실계측편차 (${\pm}18^{\circ}C$)범위내에서 일치함을 제시하였고 또한 rolling event 별로 나타나는 온도하강 pattern이 실제의 압연상황과 잘 일치함을 제시하므로서 본 computer simulation 과정에서 적용한 가정, 조건, 물성치 등의 적정성 등을 입증하였다.

• 한국세라믹학회지
• /
• 제26권4호
• /
• pp.459-470
• /
• 1989

Single crystals of rare-earth iron garnets were grown from solutions of molten lead oxide, lead fluoride, baric oxide, iron oxide, and the oxides of yttrium, samarium orgadolinium. The crystals were grown by slow cooling technique. A convenient composition was 41.8mol% PbO, 20.59mol% PbF2, 8.23mol% B2O3, 20.00mol% Fe2O3 and 10.00mol% R2O3 where R is Y, Sm or Gd. For this experiment, platinum crucibles of size 20, 30cc and a vertical siliconit tube furnace were used. The precipitation temperature of YIG was observed in the range of 115$0^{\circ}C$-112$0^{\circ}C$ and the optimum growth conditions in this experiment were determined. The nucleation rate was controlled by the holding time after the fast colling, the growth rate by the slow cooling conditiions. The form of the grown YIG crystals showed a combination of {110} and {211}, and the size of the crystals grown in this experiment was up to about 9mm under the conditions of holding time 16hour, cooling rate 2$^{\circ}C$/hr. and temperature range 115$0^{\circ}C$-90$0^{\circ}C$. The precipitatin temperature of SmIG was observed in the range of 105$0^{\circ}C$-98$0^{\circ}C$ and the size of the crystals grown in this experiment was up to about 5mm under the conditiions of holding time 16hours, cooling rate 2$^{\circ}C$/hr. and temperature range 100$0^{\circ}C$-80$0^{\circ}C$.

• 대한금속재료학회지
• /
• 제49권1호
• /
• pp.58-63
• /
• 2011

The grain size and growth direction of a directionally solidified turbine blade were evaluated by the initial nucleation condition at the start block of directional solidification. The initial nucleation condition was controlled by inserting a Ni foil on the directional solidification plate of the directional solidification furnace. Fine grains with good orientation were obtained in the faster cooling condition at the start block. The nucleus number was compared with the cooling rate of the start block by electron back scattered diffraction (EBSD). DSC (differential scanning calorimeter) analysis was performed to compare the melting point and undercooling for nucleation of the coarse nuclei and fine nuclei of the start block. The faster cooling condition at the start block showed more undercooling for nucleation and smaller size of nuclei which resulted in a fine grain with good orientation in the directional turbine blade.

• 한국결정학회지
• /
• 제7권2호
• /
• pp.147-155
• /
• 1996

할로겐 램프를 열원으로 이용하는 결정성장장치인 부유대역융로를 제작하여 고온초전도체 Bi2Sr2CaCu2O8의 성장에 이용하였다. 제작된 결정성장장치는 할로겐 램프를 초점에 위치시키기 위한 holder unit, 1kW의 할로겐 램프로서 최대 1800℃까지 사용이 가능한 image furnace, 냉각장치, 원료 물질을 공급하는 feeding unit, 성장된 단결정을 인상하는 pulling unit, 그리고 2mm/hr - 40mm/hr의 속도로 상하 이동 및 15rpm -120rpm의 회전이 가능한 제어부 등으로 구성되었다. 300W의 할로겐 램프를 이용하여 Bi2Sr2CaCu2O8 fiber를 성장시켰으며 성장된 fiber는 XRD, SEM, EDS 등으로 분석하였다. 성장조건은 공기분위기에서 성장속도 3∼4mm/hr, 상·하부축 회전속도 20∼25 rpm이었으며 성장된 fiber는 Bi2Sr2CaCu2O8 기지 내에 (Sr,Ca)CuO2 및 (Sr,Ca)2CuO3의 2차상을 포함하고 있었다.

• 제어로봇시스템학회:학술대회논문집
• /
• 제어로봇시스템학회 2004년도 ICCAS
• /
• pp.1506-1510
• /
• 2004

A mobile robot system is developed to inspect the condition of industrial facilities under hot environment. The mobile robot is equipped with internal and external heat insulating material, an internal cooling mechanism, two CCD cameras, wireless communication devices for both the control and image signals, and an embedded controller. The portable controller is equipped with two joysticks for both the mobile robot and the inspection CCD camera, an LCD monitor, and several buttons. The developed mobile robot travels on the internal floor in hot furnaces by operators' joystick operation, captures the images of facilities in the furnaces using a zoom CCD camera, and sends the images to the portable controller through wireless communication. The mobile robot can be operated without any problem under hot environment less than 400$^{\circ}C$ in 30 minutes. This kind of automatic inspection mobile robot can be helpful to prevent significant troubles of industrial facilities without danger of human beings under harmful environment.

• 한국결정학회지
• /
• 제4권1호
• /
• pp.42-48
• /
• 1993

K6P4Ol3 응제를 사용하여 TSSG법에 의해 KTP(K Tiop04) 단결정을 성장시켰다. 가열로의 내부에 heatpipe와 복사방열판을 설치하여 도가니 내의 온도 안정성 및 균일도를 향상시켰다. 크고 양질의 단결정을 얻기 위한 목적으로 조업온도 구간,초기 냉각속도, 강제교반, 융제의 재사용과 같은 몇 가지 조업변수들에 따른 영향을 비교 고찰하였다. 본 융제의 조건하에서(0.6g KTP/lg flux), 초기 냉각속도가 0.1℃/hr 이하까지 느릴수록, 적절한 결정 회전이 수반될수록 양질의 단결정성장에 유리하였다. 최대 44 × 39 ×17체 크기의 KTP단결정을 얻을 수 있었으며, 단순가공 상태하에서도 21.3% SHG 변환효율을 나타내었다.

• 대한기계학회논문집
• /
• 제18권5호
• /
• pp.1227-1234
• /
• 1994

A cold spot temperature control system for the batch annealing furnace has been established in order to reduce energy consumption which is essential to improve productivity and stabilize the properties of products. A relationship between annealing cycle time and gas flow rate is developed and also for the variation of coil cold spot temperature with time during heating, and actual temperature measurements at mid-width of each coil during soaking. The results of the temperature variation effect on the cold rolled steel sheet batch annealing are as follows. (1) Cooling rate increasing gradually with increasing atmospheric gas flow, but heating rate is hardly increasing without atmospheric gas component change. (2) In case of short time heating, the slowest heating part is the center of B coil and in case of ling time heating, the low temperature point moves from the center of coil to inside coil. (3) The outside of top coil is the highest temperature point under heating, which becomes the lowest temperature point under cooling. (4) Soaking time determination depends on the input coil width, and soaking time for quality homogenization of 1214 mm width coil must be 2 hours longer than that of 914 mm width coil.

• 열처리공학회지
• /
• 제29권6호
• /
• pp.277-283
• /
• 2016

The influences of cooling pressure of quenching process on the mechanical properties such as hardness, impact endurance and anti-thermal fatigue behaviour of STD61 steel were investigated. The specimens were heat-treated using a vacuum furnace in which they were austenitized at $1,030^{\circ}C$ for 1hour under the pressure of $10^{-3}$ torr and cooled with quenching gas of various pressure, i.e. 1, 2 and 6 bar. According to the observation on the specimens prepared with quenching from austenizing temperature, the mechanical properties of the samples with higher quenching pressure were better than those of prepared at lower quenching pressure. The samples prepared with high quenching pressure showed the more homogeneous microstructure with finer carbides. The size of carbides such as VC and (Fe, Cr)C in quenched specimens decreased with increasing gas quenching pressure. It is considered that the rapid cooling with pressure may restrict the formation and growth of carbide.

• 한국정밀공학회지
• /
• 제27권8호
• /
• pp.76-83
• /
• 2010

Metallic sandwich panels with pyramidal truss structures are high-stiffness and high-strength materials with low weight. In particular, bulk structures have enough space for additional multi-functionalities. In this work, in order to fabricate 3-D structures efficiently, Layered Manufacturing Method (LMM) which was composed of three steps, including crimping process, stacking process and bonding process using rapid infrared brazing, was proposed. The joining time was drastically reduced by employing infrared brazing of which heating rate and cooling rate were faster than those of conventional furnace brazing. By controlling the initial cooling rate slowly, the bonding strength was improved up to the level of strength by conventional vacuum brazing. The observation of infrared brazed specimens by optical microscope and SEM showed no defect on the joining sections. The experiments of 1-layered pyramidal structures and 2-layered pyramidal structures subject to 3-point bending were conducted to determine structural advantages of multilayered structures. From the results, the multi-layered structure has superior mechanical properties to the single-layered structure.