• 소성∙가공
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• 제6권2호
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• pp.110-117
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• 1997

Sticking behavior under the hot rolling conditions for ferritic stainless steels have been studied. Sticking, which is a phenomenon that the naked metal exposed to the surface by scale breakaway during hot rolling sticks to the roll surface, was affected by both high temperature tensile strength and oxidation resistance of the steels. A steel having higher tensile strength and lower oxidation resistance exhibits better resistance to the sticking. It is due to that higher tensile strength increases localized deformation resistance and lower oxidation resistance creates lower friction between steel and roll by forming thicker scale as a lubricant during hot rolling. So, the sticking tends to occur more severely in the order of 430J1L, 436L, 430 and 409L. The most sensitive temperature to the sticking was found to be 90$0^{\circ}C$ for all grade of steels. It was also found that the high speed steel(HSS) roll compared to the Hi-Cr roll was more beneficial to prevent sticking. Because higher surface hardness of HSS roll compared to that of Hi-Cr roll provides less nucleation sites for sticking such as scratch on the roll surface.

• 대한금속재료학회지
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• 제46권9호
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• pp.593-603
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• 2008

In this study, effects of alloying elements on the sticking occurring during hot rolling of five kinds of ferritic STS430J1L stainless steels were investigated by analyzing high-temperature hardness and oxidation behavior of the rolled steels. Hot-rolling simulation tests were conducted by a high-temperature wear tester which could simulate actual hot rolling. The simulation test results revealed that the sticking process proceeded with three stages, i.e., nucleation, growth, and saturation. Since the hardness continuously decreased as the test temperature increased, whereas the formation of Fe-Cr oxides in the rolled steel surface region increased, the sticking of five stainless steels was evaluated by considering both the high-temperature hardness and oxidation effects. The addition of Zr, Cu, or Si had a beneficial effect on the sticking resistance, while the Ni addition did not show any difference in the sticking. Particularly in the case of the Si addition, Si oxides formed first in the initial stage of high-temperature oxidation, worked as initiation sites for Fe-Cr oxides, accelerated the formation of Fe-Cr oxides, and thus raised the sticking resistance by about 10 times in comparison with the steel without Si content.

• 한국재료학회지
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• 제29권10호
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• pp.647-655
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• 2019

In order to analyze the effect of hot asymmetric rolling on the microstructure and texture of aluminum alloy and to investigate the effect of the texture on the formability and plastic anisotropy of aluminum alloy, aluminum 6061 alloy is asymmetrically rolled at room temperature, $200^{\circ}C$, $350^{\circ}C$, and $500^{\circ}C$, and the results are compared with symmetrically rolled results. In the case of asymmetric rolling, the equivalent strain (${\varepsilon}_{eq}$) is greatest in the upper roll part where the rotational speed of the roll is high and increases with increasing rolling temperature. The increase rate of the mean misorientation angle with increasing temperature is larger than that during symmetrical rolling, and dynamic recrystallization occurs the most when asymmetrical rolling is performed at $500^{\circ}C$. In the case of hot symmetric rolling, the {001}<110> rotated cube orientation mainly develops, but in the case of hot asymmetric rolling, the {111}<110> orientation develops along with the {001}<100> cube orientation. The hot asymmetric rolling improves the formability (${\bar{r}}$) of the aluminum 6061 alloy to 0.9 and reduces the plastic anisotropy (${\Delta}r$) to near zero due to the {111}<110> shear orientation that develops by asymmetric rolling.

• 대한기계학회논문집
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• 제12권6호
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• pp.1217-1226
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• 1988

본 연구에서는 고속연속주조의 기초적 연구로서 벌징만을 선택하여 주조속도 의 변화에 의한 주편의 거동을 해석하기 위해 응력을 변형률, 변형률속도, 온도의 함 수로서 잡고 크리프 변형과 탄소성 변형을 동시에 고려한 모델을 도입하여 주편내에서 의 벌징량, 변형률 등의 상태를 밝히며, 고속주조에 있어서 고려해야 할 사항에 대하 여 고찰한다.

• 대한기계학회논문집B
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• 제31권2호
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• pp.173-180
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• 2007

A series of field tests were performed to develop aerodynamic characteristic evaluation method and countermeasure technology in conventional and high-speed railway. The strength of rolling stock-induced wind which affect the people and substructure in platform and nearby track were investigated. The slipstream of passing trains was measured by hot-wire array system. The speed of trains was 110 - 125km/h for conventional ones and 300km/h for high-speed ones. The streamlined shape trains cause about 50% smaller-scale slipstream compared to the non-streamlined ones.

• 대한금속재료학회지
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• 제46권11호
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• pp.737-746
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• 2008

Mechanisms of sticking phenomena occurring during hot rolling of a modified STS 430J1L ferritic stainless steel have been investigated in this study by using a pilot-plant-scale rolling machine. As the rolling pass proceeds, the Fe-Cr oxide layer formed in a reheating furnace is destroyed, and the destroyed oxides penetrate into the rolled steel to form a thin oxide layer on the surface region. The sticking does not occur on the surface region containing oxides, whereas it occurs on the surface region without oxides by the separation of the rolled steel at high temperatures. This indicates that the resistance to sticking increases by the increase in the surface hardness when a considerable amount of oxides are formed on the surface region, and that the sticking can be evaluated by the volume fraction and distribution of oxides formed on the surface region. The lubrication and the increase of the rolling speed and rolling temperature beneficially affect to the resistance to sticking because they accelerate the formation of oxides on the steel surface region. In order to prevent or minimize the sticking, thus, it is suggested to increase the thickness of the oxide layer formed in the reheating furnace and to homogeneously distribute oxides along the surface region by controlling the hot-rolling process.

• 공업화학
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• 제30권3호
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• pp.384-388
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• 2019

동절기 고속철도차량 하부 및 대차부에 부착된 설빙이 차량 운행 시 도상자갈구간(침목이 받는 차량 하중 전달 및 침목 고정을 위한 자갈 구간)에서 고속으로 낙하하여 자갈을 비산시켜 이로 인한 철도차량 구조물 및 시설물의 피해가 보고되고 있으며, 이는 고속철도 개통 이후 지속되고 있다. 이러한 문제점 해결을 위해 자갈의 비산을 방지하는 네트, 인력 제빙, 이동식 열풍기 등을 사용하고 있으나 효율성이 떨어진다. 기존보다 효율적인 제빙을 위해 화학적 제빙액에 대한 연구가 진행되고 있으며, 본 연구에서는 화학적 제빙액으로 사용되는 물질들의 융빙성능, 동점도, 증발성 등을 평가하여 고속철도차량 제빙용으로 최적의 물질을 찾고자 한다. 평가 물질로는 유기산염류 4종(개미산나트륨, 초산나트륨, 개미산칼륨, 초산칼륨)과 알코올류 2종(프로필렌글리콜, 글리세롤)을 대상으로 하였다. 이때, 실내 평가에서는 개미산칼륨, 초산칼륨, 프로필렌글리콜이 유사한 융빙성능을 보였으나, 모사 살포 시스템을 이용한 융빙성능 결과, 프로필렌글리콜이 가장 우수한 성능을 보였다. 이는 프로필렌글리콜의 동점도가 2.989029 St로 다른 물질 대비 높아 얼음에서 보다 오래 체류하여 제빙하기 때문이다. 또한, 개미산칼륨과 초산칼륨은 결정이 석출되어 차량외관에 악영향을 미치므로 사용에 어려움이 있다. 본 연구를 통해 프로필렌글리콜이 고속철도차량용 제빙액으로 최적의 물질임을 확인하였다.

• 제어로봇시스템학회논문지
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• 제15권6호
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• pp.634-640
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• 2009

The plate manufacturing processes are composed of the reheating furnace, finishing mill, cooling process and hot leveling. The finishing rolling mill (FM) as a reversing mill has produced the plate steel through multiple pass rolling. The automatic gauge control (AGC) is employed to maintain the thickness tolerance. The high grade products are forming greater parts of the manufacturing and customers are requiring strict thickness margin. For this reason, the advanced AGC method is required instead of the conventional AGC based on the PI control. To overcome the slow response performance of the conventional AGC and the thickness measurement delay, a fuzzy AGC based on the thickness deviation and its trend is proposed in this paper. An embedded controller with the fuzzy AGC has been developed and implemented at the plate mill in POSCO. The fuzzy AGC has dynamically controlled the roll gap in real time with the programmable logic controller (PLC). On line tests have been performed for the general and TMCP products. As the results, the thickness deviation range (maximum - minimum of the inner plate) is averagely from 0.3 to 0.1 mm over the full length. The fuzzy AGC has improved thickness deviation and completely satisfied customer needs.

• 제어로봇시스템학회논문지
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• 제14권2호
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• pp.191-196
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• 2008

This paper proposes a cooling stop temperature control(CSTC) concept which aims at obtaining the uniform temperature and quality of the material along the longitudinal and lateral direction of the strip. The CSTC is designed using the experimental CCT(Continuous Cooling Transformation), TTT(Time Temperature Transformation) curves and the temperature control model by the heat transfer governing equation, and the temperature control simulator. The cooling pattern and the rolling speed can be solved by the CSTC. It is shown through the field test of the hot strip mill of POSCO that the phase transformation ratio of the high carbon steel is considerably improved by the proposed temperature control.

• 한국산학기술학회논문지
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• 제18권1호
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• pp.609-617
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• 2017

철도는 전 세계적으로 매우 안전하고 중요한 운송 수단 중 하나이다. 그러나 철도시스템이 복잡도가 높아지고 주행거리 증가 등으로 인해 매년 사고가 지속적으로 발생하고 있다. 특히, 고속열차와 화물열차의 경우, 차축베어링 비정상 과열로 인하여 차축베어링의 기능이 소실되면 차축의 불균등한 하중을 초래한다. 따라서, 차축베어링의 비정상 과열은 심각한 사고 또는 차량 탈선의 원인이 될 수 있다. 이에 따라서 현재 고속열차 운행 중 차축의 비정상적인 발열을 검지하기 위하여 차축온도검지장치(Hot Box Detector, HBD)가 설치되어 운영되고 있다. 본 연구에서는 비정상 차축 과열 발생시, 이를 빠르고 효율적으로 검지하기 위하여 지수가중이동평균(EWMA) 기법을 적용한 차축온도 모니터링 방법을 제안하였다. 또한 제안한 방법에 대하여 통계적으로 설계하였다. 본 연구에서 제안하는 방법은 현재의 차축온도검지 모니터링 방법과 비교하여 비정상 과열의 발생에 대하여 더 좋은 성능으로 평가되었으며 그 수행도는 최대 170% 향상되었다.