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연속주조와 열간압연의 직결화에 관한 Slab 의 온도거동
윤우석,강신언 대한금속재료학회(대한금속학회) 1995 대한금속·재료학회지 Vol.33 No.12
In order to realize hot direct rolling(HDR) process, it is prerequisite to produce high temperature slabs by the continuous casting process. For this purpose, two-dimensional mathematical model has been used to estimate the change in slab temperature from the meniscus to the edge heater. The secondary cooling patterns have been modified to obtain slabs with high temperature via slab surface temperature measurements and thermal analysis of the slabs. The effect of the thermal insulator on slab temperature has been studied to find out the optimum condition for obtaining slabs with higher temperature. As means to investigate the temperature profile of slab in the edge heater and to validate mathematical model, temperature of slab with embedded thermocouples was measured in the edge heater. Based on the above temperature controlling methods, the HDR has been operated successfully.
박슬래브 연속주조에서 깔대기형 주형동판의 크랙 발생에 관한 연구
尹禹錫,朴重吉 대한금속재료학회 2001 대한금속·재료학회지 Vol.39 No.12
The formation of copper plate crack in thin slab funnel mold was investigated using metallographic studies and mathematical models. X-ray analyses of crack surface revealed that relatively brittle compound was formed in the copper matrix at high temperature where crack initiated. The scale deposition at cooling slot of copper plate below the meniscus was found after casting, which hindered the heat transfer between solidified shell and copper plate. To calculate the heat transfer in the mold at the high casting speed, new heat flux equation was made using measured average heat fluxes at different casting speed. Two dimensional heat transfer and stress analysis were done to investigate the temperature and stress fields associated with cracks. The high temperature during casting, and high tensile stress of copper plate after casting were found in the funnel transition region just below the meniscus, due to geometrical effect and uneven distance between hot face and cooling slot tip of copper plate. The tension bolt was removed to verify the stress concentration relief at funnel transition region and crack was decreased after test.
윤우석,정진오 順天大學校 1990 論文集 Vol.9 No.1
ㅁIn order to estimate the exact condition of the internal crack formation in continuously cast slabs, we calculate the bulging, roll misalignment, unbending strains developed in cast slabs considering steel grade, casting speed, equipment conditions and compare the total strain with the critical strain for internal crack. The cracking condition in cast slabs could be explained well using the ratio of total strain to critical strain.
유한요소법에 의한 알루미늄 봉 수냉시의 응력 발생 해석
이동녕,윤우석 대한금속재료학회(대한금속학회) 1988 대한금속·재료학회지 Vol.26 No.4
The stress distributions in an aluminum rod developed during guenching in 43℃ water from the temperature of 600℃ have been calculated using finite element method. In calculating the transient temperature field, the heat flux between the water arid the rod surface was calculated using the heat transfer coefficient. The stress and strain distributions were calulated using the thermo-elastoplastic model. The effect of creep was neglected because the rod, diameter of which was 5㎝, was exposed for a time period which is too short for the development of significant creep strains. At the beginning of cooling, compressive stresses were developed in the core, while tensile stresses in the surface layer. The stress disturbance occured 2 to 4 seconds after quenching, during which the largest temperature gradient developed, and finally the tensile stresses developed in the core while the compressive stresses in the surface layer.
연속주조시 주형 내 용강유동에 미치는 EMBR 의 영향
이창현,윤종규,윤우석,문기현,차필령 대한금속재료학회(대한금속학회) 1998 대한금속·재료학회지 Vol.36 No.10
In order to solve problems involved with the curved type continuous caster and high speed casting by controlling the steel flow in the mold, the electromagnetic mold brake ruler (EMBR) using a static magnetic field was installed at No. 2 continuous casting plant of POSCO Kwangyang Works. Numerical modelling and plant tests were carried out to optimize the core type and operation condition of the EMBR. The core "Type A" located near the SEN outlets and shaped simple linear, had a detrimental effect on the slab quality. However, the core "Type B" located below the SEN with a magnetic insulator at the core center, reduced the defects of slab, especially at high throughput casting conditions. The optimum range of the surface velocity was found to be in 12∼20 ㎝/sec for reducing both the sub-surface and internal defects of slabs by plant tests with EMBR. The EMBR has been operated with the optimum magnetic density to preserve this surface velocity for each casting width and casting speed.
김경현,이동녕,오규환,윤우석 대한금속재료학회(대한금속학회) 1994 대한금속·재료학회지 Vol.32 No.4
A two dimensional finite element model has been developed to calculate the temperature and stress distribution in a continuously cast beam blank. In the stress analysis, a thermo-elasto-plastic model was employed. The effects of a mold and the friction between a mold and beam blank were examined. The beam blank was found to deform asymmetrically during solidification due to its complicated geometry. Thermal stresses were developed at the initial stage, but decreased as solidification proceeded. The maximum tensile stress was found to develop parallel to the surface of a fillet under the constraint of a mold without friction, But the maximum tensile stress shifted toward the web with increasing friction.