• Journal of the Korean Society for Precision Engineering
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• v.33 no.1
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• pp.31-35
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• 2016

For reaction injection molding (RIM) polyurethane was mixed in the mixing head by impingement mixing, injected into the mold, and cured quickly, as soon as the mold is filled. The shape of the nozzle in the mixing head is critical to improve the quality of polyurethane. To achieve homogeneous mixing, an intensive turbulence energy in the mixing nozzle is essential. In this study, a mixing nozzle for RIM was designed, and mixing efficiency was investigated based on experiment. Experiments were conducted with different combinations of nozzle tips and exit diameter to measure the mixing efficiency by measuring jet force and investigating mixing image with high speed camera. Jet force increased gradually and reaches steady state conditions. The jet force depended on shape of nozzle tip and outlet sizes. These results suggest that optimized nozzle configurations are necessary for high efficiency mixing with RIM.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.05e
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• pp.40-43
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• 2003

전기방전에 대한 shed 재료의 열화내성과 우수한 발수성의 장기간 유지특성은 폴리머 애자의 장기성능에 있어서 가장 중요한 인자들이다. 애자 제조시 무결점 성형성 또한 중요한데 열화내성을 확보하기 위해 다량의 ATH의 첨가가 수반되기 때문에 적절한 process oil의 사용이 불가피하다. 사용하는 오일의 종류와 량에 따라 옥외절연물의 장기성능에 영향을 주는 표면발수성이나 방전내성은 크게 차이가 나는 것으로 밝혀지고 있다. 본 논문에서는 화학적 구조와 정도가 다른 몇 가지 실리콘 fluid들을 실리콘 고무에 처방하여 기본물성과 초고압 옥외절연물의 shed 재료로서 장기성능에 영향을 주는 방전열화내성과 표면발수성의 회복특성을 평가하였다. 실리콘 고무의 무결점 사출성형에 가소도가 중요한데 동일한 무기물 첨가조건에서 유사한 가소도를 갖게 하는데 필요한 량은 fluid들의 종류에 따라서 상당한 차이가 있었다. 특히 PDMS는 점도는 낮지만 분자량이 커서 많은 량이 첨가되어 기계적 특성저하가 크게 일어났다. 코로나 처리후 발수성 회복특성은 fluid들의 분자크기와 반응기의 종류에 따라 상당히 영향을 받았으며 분자가 클수록 초기회복속도는 다소 느려도 최종의 상시발수성은 다소 높게 유지되었으며 2일 이내에 거의 초기 접촉각으로 회복되었다. 내아크성은 무게손실이 적을수록 오차범위도 작은 안정된 특성을 보였으며 fluid들의 종류에 따른 무게손실의 차이는 크지 않았다. 트래킹 방전에 의한 무게 감소는 fluid의 분자가 크면서 페닐기를 가진 fluid들이 첨가된 고무가 우수한 특성을 보였다.

• Elastomers and Composites
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• v.34 no.3
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• pp.229-238
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• 1999

In this study, double bond, unsaturated group was introduced to the main chain of EVA by chemically treating EVA, nondiene polymer. Benzene sulfonic acid, ENB and DCPD were used as a third element. Also, from blending CR and SBR, conventional synthetic rubber we prepared vulcanizates and examined their physical properties. The datum lead to the following conclusion that some problems were modified; limited temperature in use and mechanical properties like hardness, tensile strength, tensile stress, and elongation rate of thermoplastic EVA, keeping the following advantages of original EVA; green strength, injection molding by Pressure, adhesion, tackiness, dimensional stability, and ozone resistance, etc. It is expected that continuous research of the modification between nondiene and diene polymer will improve what were shown disadvantages in synthetic polymer; processing, oxidation resistance, and adhesion. In addition, it will be possible to continue process of rubber products by utilizing possible fluidity for fusion of EVA.

• Transactions of Materials Processing
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• v.15 no.9 s.90
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• pp.667-672
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• 2006

Agglutination is one of the most commonly employed reactions in clinical diagnosis. In this paper, we have designed and fabricated nickel mold insert for injection molding of a microfluidic lab-on-a-chip for the purpose of the efficient detection of agglutination. In the presented microfluidic lab-on-a-chip, two inlets for sample blood and reagent, flow guiding microchannels, improved serpentine laminating micromixer(ISLM) and reaction microwells are fully integrated. The ISLM, recently developed by our group, can highly improve mixing of the sample blood and reagent in the microchannel, thereby enhancing reaction of agglutinogens and agglutinins. The reaction microwell was designed to contain large volume of about $25{\mu}l$ of the mixture of sample blood and reagent. The result of agglutination in the reaction microwell could be determined by means of the level of the light transmission. To achieve the cost-effectiveness, the microfluidic lab-on-a-chip was realized by the injection molding of COC(cyclic olefin copolymer) and thermal bonding of two injection molded COC substrates. To define microfeatures in the microfluidic lab-on-a-chip precisely, the nickel mold inserts of lab-on-a-chip for the injection molding were fabricated by combining the UV photolithography with a negative photoresist SU-8 and the nickel electroplating process. The microfluidic lab-on-a-chip developed in this study could be applied to various clinical diagnosis based on agglutination.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.16 no.6
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• pp.117-124
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• 2017

In this study, we investigated the optimization of process conditions by using the Six Sigma process, design of experiment (DOE) method and response surface method (RSM) to resolve dimensional deviation and appearance problems arising from the shortened process time of the mobile phone rear cover. The analysis of the trivial many was performed by 2-sample T-test and cooling time, and mold temperature and packing pressure were selected as the vital fews affecting the overall width of the product. The optimal conditions of the process were then studied using the DOE and the RSM. We analyzed the improvement effects by applying the selected optimal conditions to the production process and the results showed that the difference between the mean value and target value of the overall width stood at 0.01 mm, an improvement of 88.89% compared to current process that fell within the range of standard dimension. The short-term process capability stood at $4.77{\sigma}$, which implied an excellent technology level despite a decrease by $0.22{\sigma}$ compared to the current process. The difference in process capability decreased by $2.44{\sigma}$ to $0.41{\sigma}$, showing a significant improvement in management capability. Ultimately, the process time of the product was shortened from 18.3 seconds in the current process to 13.65 seconds, resulting in a 34.07% improvement in production yield.

• Elastomers and Composites
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• v.47 no.4
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• pp.336-340
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• 2012

Residual stress in the injection molded part is originated from thermal shrinkage and shear stress during injection molding process. There are many measurement methods of residual stress in the plastic part. Residual stress in opaque products can be measured by chemical cracking test. This method enables the solvent and specimen to react and to cause cracks. Cracks developed according to the level of residual stress. Thus the stresses in plastic part can be quantitatively measured by counting the number of cracks or measuring the size of cracks. Relationship between stress and number of cracks in a plastic specimen has been investigated in this study. Bergen jig was used to give a strain in the specimens those were molded using PC/PBT and PC/ABS. Solvent for the chemical cracking test was prepared using tetrahydrofuran and methyl alcol with the ratio of 1 to 3. Stresses in the specimen can be calculated by strains those were imposed by Bergen jig. Cracks were developed for stress higher than certain level. The number of cracks increased by second order function for stress.