• 소성∙가공
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• 제18권4호
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• pp.290-295
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• 2009

The roll gap set-up in the finishing mill is one of the most important technologies in the hot plate rolling process. As the target thickness can be obtained by the correct set-up of the roll gap, improving the roll gap set-up technology is very critical for plate thickness accuracy. The main cause of thickness variation in hot plate mills is the non-uniform temperature distribution along the length of the slab. The objective of this study is to adjust the roll gap set-up for the thickness accuracy of plate in hot rolling process considering top-end temperature drop. Therefore this study has concentrated on determining the correct amounts of thickness variation according to top-end temperature drop and roll gap to compensate thickness variation. The control method of roll gap set-up which can improve the thickness accuracy was proposed. The off-line simulation of compensated roll gap significantly decreases top-end thickness variation.

• 한국산학기술학회논문지
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• 제21권7호
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• pp.577-582
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• 2020

발전소에서 생산된 전기는 여러 단계의 변전과정을 거쳐 소비자에게 전달된다. 이 때 각 소비자에게 적합한 전압으로 송전하기 위해 초기 송전단계 및 산업단지 및 공장과 같은 고전압이 필요한 경우에 사용되는 초고압변압기는 권선 단부에서 고압의 불평등 전계가 형성되어 절연파괴의 위험을 내재하고 있다. 초고압변압기는 전압의 승압과 강압을 위해 권선, 철심이 가장 중요한 부품이다. 특히 권선의 경우 전압이 직접 인가되면서 전압의 크기를 변환하는데 핵심적인 역할을 한다. 이때 권선 단부는 그 형상에 의해 불평등 전계가 형성되고 특히 권선의 모서리에 높은 전계 스트레스가 발생한다. 이러한 불평등 전계에 의한 권선 단부의 전기적 응력을 분산하기 위하여 정전링을 사용하는데 이 정전링은 권선 상·하단 단부에 설치된다. 이러한 정전링을 설계하기 위해서는 다양한 변수를 고려하여야 하지만 그 중 정전링 곡률, 정전링 표면의 절연지 두께, 권선과 권선사이에 설치되는 배리어 수, 배리어 두께가 정전링에 발생되는 전계 스트레스에 어떠한 영향을 미치는지 유한요소법(Finite Element Method)을 통해 확인하였고 그 결과를 통해 정전링 설계 시 고려해야 할 사항을 제안하였다.

• 열처리공학회지
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• 제22권1호
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• pp.16-22
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• 2009

The rolling process is an efficient and economical approach for the manufacturing of plate metals. In the rolling process, the temperature variation is very critical for plate thickness accuracy. The main cause of thickness variation in hot plate mills is the non-uniform temperature distribution along the length of the slab. Also the exit plate thickness is mainly affected by the rolling conditions such as mill modulus, plate thickness and plate width. Hence the thickness variation in top-end is also dependent on these factors. Therefore this study has concentrated on determining the correct amounts of thickness variation due to top-end temperature drop and process parameters.

• 한국CDE학회논문집
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• 제3권1호
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• pp.1-14
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• 1998

This paper introduces non-manifold offsetting operations, which add or remove a uniform thickness from a given non-manifold model. Since these operations can be applied to not only solids but also wireframe or sheet objects, they are potentially useful for pipeline modeling, sheet metal and plastic part modeling, tolerance analysis, clearance checking, constant-radius rounding and filleting of solids, converting of abstracted models to solids, HC too1 path generation and so on. This paper describes mathematical properties and algorithms for non-manifold offsetting. In this algorithm, a sufficient set of tentative faces are generated first by offsetting all or a subset of the vertices, edges and faces of the non-manifold model. And then they are merged into a model using the Boolean operations. Finally topological entities which are within offset distance are removed. The partially modified offsetting algorithms for wireframes or sheets are also discussed in order to provide more practical offset models.

• Structural Engineering and Mechanics
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• 제43권1호
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• pp.89-103
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• 2012

In this study, the stability of laminated homogeneous and non-homogeneous orthotropic truncated conical shells with freely supported edges under a uniform hydrostatic pressure is investigated. It is assumed that the composite material is orthotropic and the material properties depend only on the thickness coordinate. The basic relations, the modified Donnell type stability and compatibility equations have been obtained for laminated non-homogeneous orthotropic truncated conical shells. Applying Galerkin method to the foregoing equations, the expression for the critical hydrostatic pressure is obtained. The appropriate formulas for the single-layer and laminated, cylindrical and complete conical shells made of homogeneous and non-homogeneous, orthotropic and isotropic materials are found as a special case. Finally, effects of non-homogeneity, number and ordering of layers and variations of shell characteristics on the critical hydrostatic pressure are investigated.

• 반도체디스플레이기술학회지
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• 제22권4호
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• pp.19-25
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• 2023

With an attempt to investigate the correlation between the internal pressure distribution of slit nozzle and the thickness uniformity of slot-coated thin films, we have performed computational fluid dynamics (CFD) simulations of slit nozzles and slot coating of high-viscosity (4,800 cPs) polydimethylsiloxane (PDMS) using a gantry slot-die coater. We have calculated the coefficient of variation (CV) to quantify the pressure and velocity distributions inside the slit nozzle and the thickness non-uniformity of slot-coated PDMS films. The pressure distribution inside the cavity and the velocity distribution at the outlet are analyzed by varying the shim thickness and flow rate. We have shown that the cavity pressure uniformity and film thickness uniformity are enhanced by reducing the shim thickness. It is addressed that the CV value of the cavity pressure that can ensure the thickness non-uniformity of less than 5% is equal to and less than 1%, which is achievable with the shim thickness of 150 ㎛. It is also found that as the flow rate increases, the average cavity pressure is increased with the CV value of the pressure unchanged and the maximum coating speed is increased. As the shim thickness is reduced, however, the maximum coating speed and flow rate decrease. The highly uniform PDMS films shows the tensile strain as high as 180%, which can be used as a stretchable substrate.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2006년도 춘계학술대회 논문집
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• pp.295-299
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• 2006

The inner-structure bonded(ISB) sheet metal is defined as a composite sheet metal which has middle layer of truss-structure between two skin sheets. The characteristics such as ultra-light weight, high rigidity, high strength, etc are required especially for automobile parts. The characteristic of ISB sheet metal depends on inner-structure pattern or method of bonding. Pyramid type of crimped expanded metal is used for inner-structure and both of resistance welding and adhesive bonding are applied to make a specimen. As a result of compression test, it is appeared that forming limit is 10% reduction in thickness under a load of 8kgf per unit element(one inner-structure). In case of uniaxial tensile test the non-uniform surface integrity rather than the buckling of inner-structure happened at a load of 450kgf, which indicates elongation of 7.2% and thickness reduction of 13%. The eye-inspection method was applied to examine the defects occurring on the specimen during stretch forming. In case of biaxial stretch forming only the non-uniform deformation on the surface of a skin sheet could be observed. The forming limit in stretching of ISB sheet metal with the hemi-spherical punch of 150mm in diameter was 3mm in forming depth and 5% reduction in thickness.

• 반도체디스플레이기술학회지
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• 제22권4호
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• pp.32-37
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• 2023

For the potential applications in large-area OLED lightings, hydrogen fuel cells, and secondary batteries, we have performed an intermittent coating of high-viscosity polydimethylsiloxane using roll-to-roll slot die coater. During intermittent coating, dead zones inevitably appear where the thickness of PDMS patch films becomes non-uniform, especially at the leading/trailing edge. To reduce it, we have coated the PDMS patches by varying the process parameters such as the installation angle of the slot die head, coating speed, and patch interval. It is observed that the PDMS solution flows down and thus the thickness profile is non-uniform for horizonal intermittent coating, whereas the PDMS solution remaining on the head lip causes an increase in the PDMS thickness at the leading/trailing edges for vertical intermittent coating when the coating velocity is low. As the coating speed increases, however, the dead zone is shown to be reduced. It is addressed that the overall dead zone (the dead zone at the leading edge + the dead zone at the trailing edge) is smaller with horizontal intermittent coating than with vertical intermittent coating.

• Structural Engineering and Mechanics
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• 제62권5호
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• pp.587-593
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• 2017

The objective of this analytical study is to calculate the elasto-plastic stresses of Functionally Graded (FG) hyperbolic disc subjected to uniform temperature. The material properties (elastic modulus, thermal expansion coefficient and yield strength) and the geometry (thickness) of the disc are assumed to vary radially with a power law function, but Poisson's ratio does not vary. FG disc material is assumed to be non-work hardening. Radial and tangential stresses are obtained for various thickness profile, temperature and material properties. The results indicate that thickness profile and volume fractions of constituent materials play very important role on the thermal stresses of the FG hyperbolic discs. It is seen that thermal stresses in a disc with variable thickness are lower than those with constant thickness at the same temperature. As a result of this, variations in the thickness profile increase the operation temperature. Moreover, thickness variation in the discs provides a significant weight reduction. A disc with lower rigidity at the inner surface according to the outer surface should be selected to obtain almost homogenous stress distribution and to increase resistance to temperature. So, discs, which have more rigid region at the outer surface, are more useful in terms of resistance to temperature.

• Journal of Electrical Engineering and Technology
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• 제11권4호
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• pp.1035-1041
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• 2016

Internal cracks in products are invisible and can lead to fatal crashes or damage. Since X-rays can penetrate materials and be attenuated according to the material’s thickness and density, they have rapidly become the accepted technology for non-destructive inspection of internal cracks. This paper presents a robust crack filter based on local gray level variation and multiscale analysis for automatic detection of cracks in X-ray images. The proposed filter takes advantage of the image gray level and its local variations to detect cracks in the X-ray image. To overcome the problems of image noise and the non-uniform intensity of the X-ray image, a new method of estimating the local gray level variation is proposed in this paper. In order to detect various sizes of crack, this paper proposes using different neighboring distances to construct an image pyramid for multiscale analysis. By use of local gray level variation and multiscale analysis, the proposed crack filter is able to detect cracks of various sizes in X-ray images while contending with the problems of noise and non-uniform intensity. Experimental results show that the proposed crack filter outperforms the Gaussian model based crack filter and the LBP model based method in terms of detection accuracy, false detection ratio and processing speed.