• 설비공학논문집
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• 제14권12호
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• pp.1039-1046
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• 2002

To investigate the characteristics of orifice as an expansion devices, the experimental apparatus was made and experiments are being peformed using R22 and R290. The main idea of this control method of refrigerant flow rate with coupled orifices is to control the ON/OFF state of T and Ball type orifice corresponding to the subdivided region of thermal load. When system requires minimum thermal load, both T and Ball type orifices are closed, but refrigerant can flow through small hole of T type orifice. In regular thermal load, when ball type orifice is closed, T type orifice is opened and mass flow rate increase more than OFF state of T type orifice, due to large diameter. In maximum thermal load, both T and Ball type orifices are open and the much refrigerant can flow. The flow characteristics on T type orifice and parallel-combined orifice are obtained in the subdivided region of thermal load.

• Journal of Mechanical Science and Technology
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• 제18권2호
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• pp.230-239
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• 2004

A compact model approach of a network of spring elements for elastic loading is presented for the thermal deformation analysis of BGA package assembly. High-sensitivity moire interferometry is applied to evaluate and calibrated the model quantitatively. Two ball grid array (BGA) package assemblies are employed for moire experiments. For a package assembly with a small global bending, the spring model can predict the boundary conditions of the critical solder ball excellently well. For a package assembly with a large global bending, however, the relative displacements determined by spring model agree well with that by experiment after accounting for the rigid-body rotation. The shear strain results of the FEM with the input from the calibrated compact spring model agree reasonably well with the experimental data. The results imply that the combined approach of the compact spring model and the local FE analysis is an effective way to predict strains and stresses and to determine solder damage of the critical solder ball.

• 대한기계학회논문집A
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• 제20권1호
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• pp.154-162
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• 1996

Ball screws are commonly used in linear motion feeding systems of various machine tools and automated systems. They are known to have relatively little backlash, high precision and efficiency compared to ordinary lead screws. Furthermore, the effectiveness of ball screw has made it the preferred choice of many newly developed high speed precision feeding units. The motivation of this work is to establish the groove edsigh basis of ball screws for the reduction of contact fatigue failure. In most instances, fatigue failure between ball and shaft groove is due to excessive contact pressure. Especially, the excessive load is causative of plastic flow below the contact surface, which can contribute to surface failure. But, in spite of small load, if groove conformity rate is large, contact pressure is increased and internal shear stress reach the yield value of the material. In such a point, the authors deal with design procedure for deciding the permissible conformity rate of a ball screw groove with the computational evaluation of contact pressure and maximum shear stress.

• 한국정밀공학회지
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• 제16권2호통권95호
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• pp.123-129
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• 1999

Ball-end milling process is widely used in the die and mold manufacturing because of suitable one for the machining of free-form surface. During the process, the pencil cutting operation can be adopted before finish cut to eliminate overload in uncut area caused by large diameter of ball-end mill. The ball-end mill cutter for the pencil cutting is easily deflected by cutting force due to the long and thin shape, and the tool deflection in pencil cutting is one of the main reason of the machining errors in a free-form surface. The purpose of this study is to find the characteristics of deflected cutter trajectory by constructing measurement system with eddy-current sensor. It was found that the severe reduction of corner radius produced the overcut during the plane cutting. Up cutting method induced the overcut both plane and slope cutting, but down cutting one induced the undercut. From the experiments, down cutting with upward cutting path can generate the small undercut surface.

• Advances in nano research
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• 제14권5호
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• pp.409-419
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• 2023

Tracking the motion of tennis balls is a challenging task in using cameras around the tennis court. The most important instance of the tennis trajectory is the time of impact and touch the court which in some cases could not be detected precisely. In the present study, we aim to present a novel design of tennis balls equipped with nano-sensors to detect the touch of the ball to the court. In the impact instance, tennis ball receives significant acceleration and change in the linear momentum. This large acceleration could deform a small-beam structure with piezoelectric layer to produce voltage. The voltage could further be utilized to produce infrared waves which could be easily detected by infrared detection sensors installed on the same video cameras or separately near the tennis court. Therefore, the exact time of the impact could be achieved with higher accuracy than image analyzing method. A detailed dynamical property of such sensors is discussed using nonlinear beam equations. The results show that within the acceleration range of tennis ball during an impact, the piezoelectric patches of the nano-sensors in the tennis ball could produce enough voltages to propagate infrared waves to be detected by infrared detectors.

• 생물환경조절학회지
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• 제10권2호
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• pp.88-94
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• 2001

Ash ball 배지의 이화학적특성과 사용배지의 염류집적 및 제거효과를 펄라이트 및 입상암면과 비교하였다. ash ball의 가비중, 진비중, 공극율은 각각 0.93 g.$cm^{-3}$, 2.29 g.$cm^{-3}$, 40.6%, 59.4%로서 그중 가비중은 펄라이트 및 입상암면에 비해 현저히 높았고 가공율은 낮았다. 배지의 포화수분함량(saturation moisture capacity)은 ash ball이 52%, 펄라이트가 71%, 입상암면이 90%로 나타났고, 배수 1시간 후 수분율은 ahs ball이가 21%, 펄라이트가 27%, 입상암면이 80%로 낮아졌다. Ash ball의 입도별 수분율은 소립(3~5 mm)이 대립 (7~15mm)에 비해 5% 정도 높았다. Ash ball의 배드내 수분율은 수직 및 수평방향의 분포가 균일하여 수분확산성이 좋은 것으로 나타났다. ash ball의 pH는 7.6으로 약염기성을 나타내었다. 배지를 침지한 배양액의 pH는 7.6으로 약염기성을 나타내었다. 배지를 침지한 배양액의 pH는 다소 증가하는 경향을 보였으며 EC는 거의 변호가 없었으며, 배지내 무기이온의 흡착은 ash ball과 입상암면은 인산의 흡착이 비교적 많았다. 토마토 재배에 사용된 ash ball의 염류집적은 펄라이트와 비슷하였고 8회 정도의 침수처리로 배지표면에 흡착된 무기염을 대부분 제거할 수 있었다. 위의 결과로부터, ash ball 배지는 보수력은 다소 낮지만 통기성 및 수분확산성이 우수하여 배지내의 수분조절이 용이한 배지임을 알 수 있었다.

• 한국세라믹학회지
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• 제43권9호
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• pp.519-526
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• 2006

A full-factorial design of experiments with three input factors and two levels for each factor including center points was utilized for the preparation and characterization of twelve types of $BaTiO_3$ slips for tape casting. Ceramic powders with different particle sizes, different milling methods such as high energy milling and conventional ball milling, and two types of dispersant with different polymeric species were chosen as input factors in order to investigate their effects on slip and on green tape properties. Tape casting, a small rectangular-shaped K-square preparation, characterization and quantitative data analysis using statistical software were followed. Ceramic powder was the most significant among three input factors for the output responses of slip viscosity and green tape density, showing more favorable results with large particles than with very fine ones. In addition, high energy milling for only 30 min was more efficient than 24h of conventional ball milling in terms of powder dispersion and milling. The optimum condition based on the experimental results was a slip exposed to high energy milling with large ceramic particles along with a methylethyl acetate dispersant.

• 한국CDE학회논문집
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• 제10권5호
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• pp.375-379
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• 2005

Durability of rubber dust cover in the ball joint for automotive suspension parts is analyzed by FEM and compared with experimental data. Upper open area of ball joint is sealed by dust cover for preventing outflow of the lubricating oil and intrusion of send, dust, water, etc. This rubber cover undergoes repeated loadings such as tension and compression while the car is running. Analysis about rubber material needs to consider every kinds of nonlinearities arise in finite element analysis, which are geometric nonlinearity due to large displacement and small strain, materially nonlinearity and nonlinear boundary condition such as contact. The deformation behavior of dust cover is analysed by using the commercial finite element program MARC. In the study, this program could solve these kinds of nonlinear analysis accurately. Finite element model of dust cover is considered as 3-dimensional half model based on 2-dimensional axisymmetric model. Material property of rubber is modeled by Ogden model and input data for calculation takes form uniaxial tension test of rubber specimen. The final object of the study is obtaining the design specification of dust covers and the result of analysis should be a useful data to design of rubber cover.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2002년도 춘계학술대회 논문집
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• pp.778-781
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• 2002

Durability of rubber dust cover in the ball joint for automotive suspension parts were analyzed by FEM and compared with experimental data. Upper open area of ball joint is sealed by dust cover for preventing outflow of the lubricating oil and intrusion of send, dust, water, etc. This rubber cover undergoes repeated loadings such as tension and compression while the car is running. Analysis about rubber material needs to consider every kinds of nonlinearities arise in finite element analysis, which are geometric nonlinearity due to large displacement and small strain, materially nonlinearity and nonlinear boundary condition such as contact. So in the study, the deformation behavior of dust cover was analysed by using the commercial finite element program MARC. This program could solve these kinds of nonlinear analysis accurately. Finite element model of dust cover is considered as 3-dimensional half model based on 2-dimensional axisymmetric model. Material property of rubber was modeled by Ogden model and input data for calculation takes form uniaxial tension test of rubber specimen, The final object of the study is obtaining the design specification of dust covers and the result of analysis should be a useful data to design of rubber

• 대한환경공학회지
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• 제22권6호
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• pp.1139-1148
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• 2000

산업 폐기물 중 다량으로 발생하는 제강슬래그의 재활용을 위하여 -14/+24mesh 정도 크기의 슬래그를 미분말로 분쇄시 최적 조건을 조사하고 경제적인 분쇄조건을 확립하기 위하여 요구되는 동력을 산출하였다. 이를 위한 분쇄조건으로 ball mill의 회전속도, 분쇄시간, ball의 충진량, 시료의 충진량과 크기 등을 선정하였고 이에 대한 분쇄효율을 산출하였다. 본 연구에서는 임계회전속도의 79% 정도에 해당되는 값이 최적의 회전속도인 것으로 조사되었다. 분쇄시간에 따른 분쇄정도는 일반적으로 시간이 증가함에 따라 증가하는 것으로 나타났지만 분쇄 초기에 비해 분쇄가 더 진행될수록 분쇄효율은 감소하는 것으로 나타났다. Ball의 충진율은 mill내부 용량의 50%인 경우에 최척의 분쇄효율을 보였고, 시료의 충진량과 크기에 따른 입도초사 실험 에서는 시료의 충진량이 적고 원시료의 크기가 작을수록 분쇄정도는 증가하였다. 위의 결과에 의해 Bond의 식을 사용하여 동력효율을 계산한 결과 분쇄시간이 길수록 그리고 회전속도가 최적인 조건에서 동력효율이 가장 크게 나타나고 있음이 관찰되었다.