• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집B
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• pp.578-583
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• 2001

Chattering phenomenon is an abrupt relative vibration between the strip and rolls of rolling machine in working. It inevitably results from the progress of the degeneration in the mill facilities. This research was carried out in order to analyze the characteristic and find the cause of chatter mark in finishing mill and it was founded that major causes are facility character of driving part and special condition in case of excessive roll force.

• 대한기계학회논문집
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• 제16권7호
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• pp.1363-1372
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• 1992

본 연구에서는 고속 냉간 압연유를 개발하기 위한 기초 연구로써 압연유의 기본이 되는 기유의 종류와 압연유에 첨가되는 각종 첨가제중 고속, 고압하 압연에서 가장 문제가 되는 히트 스크래치를 방지하는 역할을 하는 극압제의 종류 및 함량이 압연유의 윤활성과 내소부성에 어떠한 영향을 주는가를 소다식 진자형 마찰계수 시험 기, Falex 시험기 그리고 Four Ball 시험기와 같은 실험실적 평가방법과는 달리 실제 롤과 스트립 사이의 접촉조건이 상사한 시험압연기를 사용한 윤활성 및 내소부성 평가 실험을 통하여 검토하였다. 본 평가 실험에 사용된 시험압연기는 압하배분, 압연 채 터링(chattering), 장력 제어, 압연윤활 특성, 압연재 형상 제어, 이주속 압연특성 등 을 시험할 수 있는 다목적 냉간압연기로써 그 구조와 제원을 Fig.1과 Table 1에 나타 내었다. 또한 극압제를 함우하고 있는 압연유와 스트립 표면간의 화학반응에 의한 극압막의 존재여부를 확인하기 위하여 EDS(energy dispersive spectrometer) 분석법과 ESCA (electron spectroscopy for chemical analysis) 분석법을 이용하여 분석하였다.

• 대한기계학회논문집A
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• 제36권4호
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• pp.429-435
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• 2012

압연공정 중에 작업롤은 스트립과의 지속적인 마찰에 의해 마모가 발생하여, 질량 불평형이 발생하게 된다. 이러한 작업롤의 질량 불평형을 고려한 압연기의 수학적 모델을 제안하였고, 이 모델은 실험에 의해 검증되었다. 작업롤은 편심을 가진 강체 로터로 가정되어, 질량 불평형의 채터 진동에 대한 영향을 분석하였다. 스핀들의 준평형 해석을 통해 계산된 조인트 힘은 압연기의 작업롤에 외력으로 작용시켰다. 압연기의 운동방정식을 직접적분법으로 풀어 과도 응답을 얻고 주파수 분석을 수행하였다. 편심은 수직 방향의 진동보다 수평 방향의 진동에 더 큰 영향을 끼쳤는데, 작업롤 반경의 1%의 편심거리도 수평 방향 채터 주파수의 진폭을 크게 상승시킬 수 있다는 것을 확인하였다.

• 한국분말재료학회지
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• 제16권1호
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• pp.33-36
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• 2009

In order to increase the magnetic loss for electromagnetic(EM) wave absorption, the soft magnetic $Fe_{73}Si_{16}B_7Nb_3Cu_1$(at%) alloy strip was used as the basic material in this study. The melt-spun strip was pulverized using an attrition mill, and the pulverized flake-shaped powder was crystallized at $540^{\circ}C$ for 1h to obtain the optimum grain size. The Fe-based powder was mixed with 2 wt% $BaTiO_3$, $0.3{\sim}0.6$ wt% carbon black, and polymer-based binders for the improvement of electromagnetic wave absorption properties. The mixture powders were tape-cast and dried to form the absorption sheets. After drying at $100^{\circ}C$ for 1h, the sheets of 0.5 mm in thickness were made by rolling at $60^{\circ}C$, and cut into toroidal shape to measure the absorption properties of samples. The characteristics including permittivity, permeability and power loss were measured using a Network Analyzer(N5230A). Consequently, the properties of electromagnetic wave absorber were improved with the addition of both $BaTiO_3$ and carbon black powder, which was caused by the increased dielectric loss of the additive powders.

• 한국경영과학회:학술대회논문집
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• 대한산업공학회/한국경영과학회 1996년도 춘계공동학술대회논문집; 공군사관학교, 청주; 26-27 Apr. 1996
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• pp.63-66
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• 1996

Cold rolling mill process in steel works uses stands of rolls to flatten a strip to a desired thichness. At Pohang Iron and Steel Company (POSCO) in Pohang, Korea, precalculation determines the mill settings before a strip actually enters the mill and is done by an outdated mathematical model. A corrective neural network model is proposed to improve the accuracy of the roll force prediction. Additional variables to be fed to the network include the chemical composition of the coil, its coiling temperature and the aggregated amount of processed strips of each roll. The network was trained using a standard backpropagation with 2,277 process data collected form POSCO from March 1995, then was tested on the unseen 200 data from the same period. The combined model reduced the prediction error by 55.4% on average.

• 대한조선학회지
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• 제19권4호
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• pp.39-45
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• 1982

A floating rig, which has been used to develop the ocean resources has a common characteristics with the catamaran ship that it is composed of the two simple hulls. So the motion responses of the floating rig can be predicted theoretically with the aid of the strip method as those of the catamaran. And for the strip method, the two-dimensional hydrodynamic coefficients are the most important inputs to predict the results accurately. In this report, a theoretical method is proposed for calculating two-dimensional hydrodynamic forces and moments acting upon arbitrary shaped twin-hull cylinders, which are forced to make a heaving, swaying and rolling oscillation about their mean position on the free surface of a finite depth water. The theoretical results by making use of the singularity distribution method are presented. The accuracy of the coefficients was confirmed to be reasonable by the comparison with the Ohkusu's results for two circular cylinders in an infinite depth water. The depth effects on two-dimensional hydrodynamic coefficients for two circular cylinders are also checked. In some range of wave numbers, large differences in the behavior of hydrodynamic coefficients between for a finite depth and for an infinite depth are shown.

• Corrosion Science and Technology
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• 제23권2호
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• pp.83-92
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• 2024

A hot-dip simulator was utilized to replicate abnormal coating buildup observed during line stops at galvanize lines, assessing the influence of processing conditions on buildup (up to 14 mm/side). Steel samples from 19 coils (comprising IF, BH, LCAK, HSLA, DP600-DP1180, Si: 0.006 - 0.8 wt%, P: 0.009 - 0.045 wt%) were examined to explore the phenomenon of heavy coating growth. It was discovered that heavy coating buildup (~3 mm/h) and rapid strip dissolution (~0.17 mm/h) in a GA or GI pot can manifest with specific combinations of steel chemistry and processing conditions. The results reveal the formation of a unique coating microstructure, characterized by a blend of bulky Zeta crystals and free Zn pockets/networks due to the "Sandlin" growth mechanism. Key variables contributing to abnormal coating growth include steel Si content, anneal temperature, dew point in heating and soaking furnaces, Zn pot temperature, Zn bath Al%, and cold-rolling reduction%. At ArcelorMittal Dofasco galvanize lines, an automatic online warning system for operators and special scheduling for incoming Si-bearing steels have been implemented, effectively preventing further heavy buildup occurrences.

• 한국항해학회지
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• 제18권2호
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• pp.19-40
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• 1994

Several factors can be chosen for evaluating seakeeping performance, such as deck wetness, propeller racing, slamming, rolling, vertical acceleration and vertical bending moment, in consi-deration of the safety of human being, cargo and ship. In fact, there are few developments for an evalua-tion method of seakeepting performance correponding with each ship's characteristics. The purpose of this paper is to develop an quantitative evaluation method of seakeeping performance according to ship types. The scope and the method of this study are as follow. (1) Obtain each response amplitude of ship's motion in waves by Ordinary Strip Method and apply it to short-crested, irregular wave for random process of the factors on seakeeping performance. (2) Define the evaluation index, the dangerousness, the maximum dangerousness and the evaluation diagram. (3) Figure out the different characteristics according to ship types by computer simulation of evaluating seakeeping performance. (4) Adopt vertical acceleration and one of rolling or lateral acceleration as the factors on seakeeping performance by clarifying the correlation of stochastic process. This study developed an evaluation method coincident with each ship's characteristics, and suggested a device for application to actual ship. This method might be useful in developing the practical system of seakeeping performance in accordance with ship types. The ship models for computer simulation are 175m container ship types, 93m tranning ship HANARA as passenger ship type, 259m bulk-carrier type and 164m pure car-carrier type.

• 한국정밀공학회지
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• 제14권12호
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• pp.73-85
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• 1997

The rolling force and roll deformation behavior in the twin roll type strip continuous casting process has been computed to estimate the thermal charcteristics of a caster roll. To calculation of rolling force, the relationship between flow stress and strain for a roll material and casting alloy are assumed as a function of strain-rate and temperature because mechanical properties of a casting materials depends on tempera- ture. The three dimensional thermal dlastic-plastic analysis of a cooling roll has also been carried out to obtain a roll stress and plastic strain distributions with the commercial finite element analysis package of ANSYS. Temperature fields data of caster roll which are provided by authors were used to estimated of roll deformation. Roll life considering thermal cycle is calculated by using thermal elastic-plastic analysis results. Roll life is proposed as a terms of a roll revolution in the caster roll with and without fine failure model on the roll surface. To obtain of plastic strain distributions of caster roll, thermomechan- ical properties of roll sleeve with a copper alloy is obtained by uniaxial tensile test for variation of temperature.

• 대한기계학회논문집
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• 제15권1호
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• pp.145-153
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• 1991

본 연구에서는 Toh가 개발하여 stretchforming에 응용한 강소성 대변형 이론 을 압연문제에 적용하여 강소성 대변형 유한요소 프로그램을 개발하는데 있다.