• 한국주조공학회지
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• 제41권3호
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• pp.241-251
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• 2021

7000계 알루미늄 합금은 다른 Al 합금에 비해 강도가 우수하여 주목을 받고있으며, 7000계 알루미늄 빌렛은 일반적으로 Direct-Chill (DC) 주조 공정을 통해 제조된다. DC 주조 공정으로 제조된 알루미늄 빌렛의 표면 결함은 주로 Exudation과 Meniscus freezing 현상과 관련이 있으며, 이는 합금 성분, 주조 속도 및 주조 온도의 영향을 받는다. 특히, 7000계 알루미늄 합금은 응고 과정에서 응고 온도 범위가 넓어 주조 결함이 발생하기 쉽다. 본 연구에서는 DC 주조 공정에 의해 제조된 Al-8Zn-2Mg-2Cu 합금 빌렛에 대한 표면 결함 변화에 대하여 조사하였다. 빌렛의 표면은 "Wavy" 또는 "Dot" 표면으로 관찰되었다. Wavy 표면은 낮은 주조 속도(200mm/min)와 온도(655℃)에서 Meniscus freezing 현상에 의해 형성되었으며, Concave 영역에서 Meniscus freezing 현상으로 인한 조성작 과냉으로 인해 미세한 수지상 조직이 관찰되었다. 반면에, 주조 온도가 높은 조건(675℃)에서는 Dot 표면이 기공 형성에 의해 형성되었으며, 높은 주조 속도(230mm/min)에서 제조된 Dot 표면을 갖는 빌렛에서는 높은 금속 수두압에 의해 Exudation 층이 형성되었다. Exudation 층의 Dot 영역과 Smooth 영역은 각각 미세한 수지상 형태와 주상정 형태의 조직이 관찰되었으며 이는 Dot 영역에서 가스 기공의 형성에 의한 결과이다.

• Journal of Electrical Engineering and Technology
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• 제10권3호
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• pp.971-982
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• 2015

In order to improve the quality of the billet continuous casting, a two-phase orthogonal power supply (TPOPS) for electromagnetic stirrer is researched, which is composed of three-phase PWM rectifier and three-leg inverter. According to the power analysis of system, the ripple of dc-link voltage is analyzed and its analytical expression is derived. In order to improve the performance of electromagnetic stirring, an integrated control method with feedforward control is proposed for PWM rectifier to suppress the fluctuations of dc-link voltage and provide a stable dc source for inverter. According to the simplified equivalent model, a composite current control method is proposed for inverter. This proposed method can combine the merits of feedforward control with feedback control to effectively improve the dynamic output performance of TPOPS. Finally, a 300kVA prototype of TPOPS is developed, and the results have verified the analysis and control method.

• Macromolecular Research
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• 제12권3호
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• pp.303-310
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• 2004

We have prepared an aqueous dispersion of poly(aniline-dodecyl benzene sulfonic acid complex) (PANI-DC) that has an intrinsic viscosity (〔η〕) near 1.3 dL/g using aniline as a monomer, dodecyl benzene sulfonic acid(DBSA) as a dopant/emulsifier, and ammonium peroxodisulfate(APS) as an oxidant. We found that the electrical conductivity of a PANI-DC pellet was 0.7 S/cm. A waterborne-polyurethane (WBPU) dispersion, obtained from isophorone diisocyanate/polytetramethylene oxide glycol/dimethylol propionic acid/ethylene diamine/triethylene amine, was used as a matrix polymer. We prepared blend films of WBPU/PANI-DC with variable weight ratios (from 99/1 to 66/34) by solution blending/casting and investigated the effects that the PANI-DC content has on the mechanical and dynamic mechanical properties, hardness, electrical conductivity, and antistaticity of these films. The tensile strength, percentage of elongation, and hardness of WBPU/PANI-DC blend films all decreased markedly upon increasing the PANI-DC content. The antistatic half-life time ($\tau$$\sub$$\frac{1}{2}$/) of pure WBPU film was about 110 s, but we found that those of WBPU/ultrasound-treated PANI-DC blend films decreased exponentially from 1.2 s to 0.1 s to almost 0 s upon increasing the PANI-DC content from 1 wt% to 15 wt% to > 15 wt%, respectively.

• 한국산업융합학회 논문집
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• 제24권5호
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• pp.589-596
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• 2021

In this study, the optimum gating system was designed, and the two zinc alloy worm gears were manufactured in single process by applying a symmetrical gating system with 2 runners. The SRG ratio is set to 1 : 0.9 : 0.6, and the cross-sectional shapes such as sprue, runner and gate are designed. In order to determine whether the design of the gating system is appropriate, casting analysis was carried out. It takes 4.380 s to charge the casting 100%, 0.55 to 0.6 m/s at the gates and solidification begins after the casting is fully charged. The amount of air entrapment is 2% in the left gear and 6% in the right gear. Hot spots occurred in the center hole of the gear, and pores were found to occur around the upper part of the hole. Therefore, the design of the casting method is suitable for worm gears. CT analysis showed that all parts of worm gear were distributed with fine pores and some coarse pores were distributed around the central hole of worm gear. The yield strength and tensile strength were 220 MPa, 285 MPa, and the elongation rate was 8%. Vickers hardness is 82 HV.

• E2M - 전기 전자와 첨단 소재
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• 제9권2호
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• pp.138-145
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• 1996

A multilayer piezoelectric transformer (MPT) which generates a high voltage dc power with low driving voltage and high voltage setup ratio was made by the tape casting method. The measured electrical characteristics of the MPT agreed with the results simulated from the equivalent circuit of the MPT. With increasing the number of layer in the MPT, the resonance curve of the input cur-rent revealed an asymmetry due to the increasing input capacitance, while that of output dc voltages revealed symmetry. The MPT which has very thin layer was excellently characterized as low driving voltage and high voltage setup ratio. The output dc voltage is nonlinearly influenced by the number of layer in the MPT.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2008년도 추계학술대회 논문집
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• pp.452-455
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• 2008

In the present study, blow forming characteristics of commercially roiled AZ31 alloy sheets were investigated. Two different kinds of AZ31 sheets were originally fabricated by using direct casting and strip casting methods respectively. Both sheets have similar grain sizes of about $7{\mu}m$ with a relatively equiaxed structure after rolling. A series of tensile tests were carried out to get flow behavior in terms of temperature and strain rate. Also, grain size effect was investigated by annealing as-received sheet at elevated temperatures. Elongation increased with temperature increment as well expected. However, the differences in tensile test condition did not give much difference in elongation even at the temperature range where a large elongation would be expected with such as fine grain of $7{\mu}m$. Blow forming experiments showed that forming condition did not result in higher difference in dome height. However, the interesting feature from this study was that formability of this AZ31 alloy got different with stress condition. Firstly, biaxial stress condition might result in lower temperature and strain rate dependencies compared to uniaxial tension results for both DC and SC sheets. Secondly, DC showed slower grain growth in uniaxial tension than in biaxial stress state while SC has much higher grain growth rage in uniaxial tension than in bulging.

• 한국전산유체공학회지
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• 제10권1호
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• pp.56-62
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• 2005

Large eddy simulation of vortexing flow of molten steel in the continuous casting mold with and without DC magnetic field was conducted. The influence of the position of magnetic field to the residence time and depth of the vortex was analyzed. The mechanism of the influence of magnetic field to the vortexing flow was found. The computational results show that the vortexing flow is the result of shearing of the two un-symmetric surface flows from the mold narrow faces when they meet adjacent to the SEN; the un-symmetric flow for turbulent vortex is caused by turbulent energy of the fluid and that for biased vortex is caused by biased flow and the turbulent energy of fluid; with the moving of the magnetic field from the centerline of the outlet of the SEN to the free surface, the surface velocity is decreased gradually and the depth of the turbulent vortex and the biased vortex is decreased, the residence time is increased with the magnetic field moves from DL=120mm to DL=60mm and then decreased; the turbulent vortex and the biased vortex can be eliminated when the magnetic field is located at the free surface.

• 한국주조공학회지
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• 제41권3호
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• pp.252-259
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• 2021

산업용으로 활용되는 많은 알루미늄 합금에 마그네슘 성분이 포함되어 있다. 이들 알루미늄 합금에 첨가된 마그네슘 원소는 알루미늄의 강도를 향상시키는 역할을 하지만, 제조 과정 중 산화 경향이 크기 때문에 제품의 품질과 특성을 저해하는 원인이 된다. 마그네슘이 주요 합금원소인 5천계 알루미늄 전신재 합금의 경우, 높은 산화성으로 인하여 마그네슘 함량은 약 5wt% 이내에서만 활용된다. 본 연구에서는 산화 경향이 억제된 것으로 알려진 ECO-Mg 모합금을 이용하여 5wt% 이상의 높은 마그네슘 함량을 포함하는 새로운 합금, ECO-Amag6~9 (6~9wt%Mg 함유) 합금을 제조하고 그 특성을 평가하였다. ECO-Almag6~9 합금은 높은 Mg 함량에도 깨끗한 용탕 품질이 확보되어 양산용 DC 주조기를 이용한 빌렛 제조 및 압출이 가능하였다. 또한 높은 Mg 함량으로 인해기존 산업용 5xxx계 합금에 비해 높은 강도와 연성을 보여 산업적 활용성이 높을 것으로 기대된다.

• 한국산업융합학회 논문집
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• 제24권5호
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• pp.597-608
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• 2021

The control head components used in small military vessels are designed to be domestically produced, prototypes, structural analysis, and casting methods are designed and cast. The control head assembly consists of a lever, an aluminum outside cover, Middle, front gear cover, back gear cover, and a zinc worm gear. In order to reverse the design of each component, 3D scanning device was used, 3D modeling was performed by CATIA, and prototype productions were carried out by 3D printer. In order to reduce the cost of components, gating system is used by gravity casting method. The SRG ratio of 1:0.9:0.6 was set by applying non-pressurized gating system to aluminum parts, 1:2.2:2.0 and pressurized gating system to zinc parts, and the shapes of sprue, runner and gate were designed. The results of porosity were also confirmed by casting analysis in order to determine whether the appropriate gating system can be designed. The results showed that all parts started solidification after filling completely. ANSYS was used for structural analysis, and the results confirmed that all five components had a safety factor of 15 more. All castings are free of defects in appearance, and CT results show only very small porosity. ZnDC1 zinc alloy worm gear has a tensile strength of 285 MPa and an elongation of 8%. The tensile strength of the four components of A356 aluminum alloy is about 137-162 MPa and the elongation is 4.8-6.5%.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1995년도 하계학술대회 논문집 B
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• pp.995-998
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• 1995

As the modern industrial processes become more complex, it is getting more difficult to model and control the processes. Naturally, an advanced type of DCS(Distributed Control System) with higher level functions is being sought Advanced DCS is a DCS with advanced functions such as fault diagnosis, GPC(Generalized Predictive Control), NN(Neural Network), and Fuzzy Control. In this thesis, we have studied a fuzzy control algorithm for realizing an advanced DCS. Its algorithm is implemented in a form of function code which is a process control language, being used by the industrial engineers. To verify the realized function code of the fuzzy control, the function code is applied to a continuous casting process of the Pohang Iron & Steel Works in Kwangyang. The rules of the fuzzy control were collected via interviews of the field operators and their operation documents. Finally, usability of the function code of the fuzzy control is shown via simulation for the continuous casting process model.