• 한국분말재료학회지
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• 제17권4호
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• pp.312-318
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• 2010

High speed steels (HSS) were used as cutting tools and wear parts, because of high strength, wear resistance, and hardness together with an appreciable toughness and fatigue resistance. Conventional manufacturing process for production of components with HSS was used by casting. The powder metallurgy techniques were currently developed due to second phase segregation of conventional process. The powder injection molding method (PIM) was received attention owing to shape without additional processes. The experimental specimens were manufactured with T42 HSS powders (59 vol%) and polymer (41 vol%). The metal powders were prealloyed water-atomised T42 HSS. The green parts were solvent debinded in normal n-Hexane at $60^{\circ}C$ for 24 hours and thermal debinded at $N_2-H_2$ mixed gas atmosphere for 14 hours. Specimens were sintered in $N_2$, $H_2$ gas atmosphere and vacuum condition between 1200 and $1320^{\circ}C$. In result, polymer degradation temperatures about optimum conditions were found at $250^{\circ}C$ and $480^{\circ}C$. After sintering at $N_2$ gas atmosphere, maximum hardness of 310Hv was observed at $1280^{\circ}C$. Fine and well dispersed carbide were observed at this condition. But relative density was under 90%. When sintering at $H_2$ gas atmosphere, relative density was observed to 94.5% at $1200^{\circ}C$. However, the low hardness was obtained due to decarbonization by hydrogen. In case of sintering at the vacuum of $10^{-5}$ torr at temperature of $1240^{\circ}C$, full density and 550Hv hardness were obtained without precipitation of MC and $M_6C$ in grain boundary.

• Composites Research
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• 제12권5호
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• pp.31-39
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• 1999

최근에 플라스틱 복합재료는 고강도, 초경량이라는 재료의 우수한 성질과 높은 생산성으로 인해서 그 활용도가 급속히 증가하고 있고, 그 중 섬유강호 플라스틱 복합재료는 가장 각광받는 재료중 하나이다. 본 연구에서는 연속섬유강화 플라스틱 복합재료를 열간 압축성형법을 이용하여 성형조건을 변화시켜 성형한 후 성형품의 성형성에 대하여 연구하였다. 연속섬유강화 플라스틱 복합재료를 압축 성형할 때 발생하는 문제점은 유동 속도차에 의한 섬유와 모재간의 분리현상이다. 이 분리현상으로 인해 성형품은 불균질해지고 이방성이 되어 기계적 특성 등에 영향을 받는다. 그러므로 분리에 영향을 미치는 섬유구조 및 기하하적 형상 등 성형조건을 연구할 필요가 있다. 니들펀칭 횟수 NP=0 punches/$\textrm{cm}^2$인 경우 성형시 모재와 강화재간의 분리현상이 증가하여 성형품의 성형성에 큰 영향을 미친다. 또한 펀치의 반경 rp=1mm일 경우 압축성형에 의한 큰 형상변화에 의하여 역시 분리현상이 증가한다. 본 논문에서는 성형공정 인자들이 제품의 성형성에 어떠한 영향을 미치는지 알아보기 위하여 연속섬유강화 플라스틱 복합재료를 니들펀칭 횟수를 변화시켜 복합판을 제작한 후, 펀치의 반경을 변화시켜 고온 압축성형 하였을 때 일어나는 불균질도와 성형품의 두께를 측정하여 비교하고, 이에 미치는 금형 코너부의 반경 및 니들펀칭 횟수의 영향에 대해서 검토한 결과를 보고한다.

• Korean Chemical Engineering Research
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• 제58권1호
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• pp.44-51
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• 2020

n-Methylimidazole, acetonitrile, benzylbromide 및 sodiumhexafluoroantimonate를 이용하여 염기성 촉매 1-benzyle-3-mehyl-imidazolium hexafluoroantimonate (BMH)를 합성하고, tetramethyl biphenol (TMBP)과 epichlorohydrine을 이용하여 결정성 바이페닐 에폭시를 합성하여 FT-IR과 ¹H-NMR으로 구조를 분석하였다. 합성한 촉매 BMH의 경화 거동을 고찰하기 위하여 0 ℃에서 250 ℃까지 5 ℃/min의 속도로 승온시키면서 에폭시 수지에 대하여 BMH의 질량비를 0.5, 1.0, 2.0 wt.%로 변화시켜 시차주사 열량계(differential scanning calorimeter, DSC)로 분석하였다. 그 결과, BMH 촉매는 비스페놀 A형 에폭시와 양이온 중합체의 단계적 가열과정에서 빠른 경화 특성을 보였다. 또한 합성한 바이페닐 에폭시는 일정한 온도에서 급격히 점도가 낮아지는 특성과 바이페놀의 강직한 골격구조를 가지는 특성을 가지고 있기 때문에 결정성 구조 및 고내열성을 요구하는 반도체용 봉지재료의 대표격인 epoxy molding compound (EMC)의 원료로서의 적용 가능성을 고찰하였다. 그 결과, 본 연구에서 개발한 바이페닐 에폭시는 결정성 구조로 이루어진 것을 확인하였으며, 경화제로 페놀 노볼락수지와 고온에서의 경화반응 시, BMH 촉매 존재 시에는 150 ℃ 근처에서 경화반응이 관찰되어 EMC의 원료로 사용될 수 있음을 확인하였다.

• 한국신뢰성학회지:신뢰성응용연구
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• 제7권4호
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• pp.173-181
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• 2007

Out door exposure to daylight and weather climate conditions can cause adverse effect on the properties of automotive plastic materials. The effects of sunlight exposure, especially ultra violet (UV) radiation, can break down the chemical bonds in a polymeric material. This degradation process is called photo-degradation and ultimately leads to color changes, cracking, chalking, the loss of physical properties and deterioration of other properties. To explore the effect of sunlight exposure on the automotive materials, this study investigated photo-oxidation degree and surface property change of molding parts by analytical methods. For the further study, accelerated weathering test methods are proposed, which can correlate with out door weathering, to predict long term performance of automotive plastic materials.

• 소성∙가공
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• 제17권7호
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• pp.496-500
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• 2008

Plastics is commonly used in consumer electronics because of it is high strength per unit mass and good productivity. But plastic parts are usually distorted after injection molding due to the residual stress after filling, packing, cooling process, and etc. And plastic material is to be deteriorated according to various temperature conditions and operating time, which can be characterized by stress relaxation and creep. The viscoelastic behavior of plastic materials in time domain can be expressed by the Prony series of the commercial code, ABAQUS. In the paper, the process to predict the post deformation under cyclic thermal loadings was suggested. The process was applied to the real panel, and the deformation predicted by the analysis was compared with that of real test, which showed the possibility of applying the suggested process to predict the post deformation of plastic product under thermal loadings.

• 한국표면공학회지
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• 제35권3호
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• pp.113-120
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• 2002

Injection molded plastic parts have many surface defects. These include a weld line, sink mark, flow mark, gloss, shading, scratching etc. Because these surface faults are not aesthetically acceptable, plastic parts are produced through painting or texturing. The purpose of this paper is to develop paintless molded parts using a flow control method. Computer aided injection mold filling simulations were used in order to minimize the number of defects from injection molding. Based on the numerical results, FR(Flame Retardant) HIPS was developed and the guidelines for part design, mold design, and the processing conditions were established. The effects of cost savings, improvements in productivity, and recycling were considered by reducing the number of surface faults and eliminating the painting process.

• 한국정밀공학회지
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• 제15권12호
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• pp.97-105
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• 1998

The fiber oriented condition inside fiber reinforced composite material is a basic factor of mechanical properties of composite materials. It is very important to meausure the fiber orientation angle for the determination of molding conditions, mechanical characteristics, and the design of composite materials. In the work, the fiber orientation distribution of simulation figure plotted by PC is measured using image processing in order to examine the accuracy of intersection counting method. The fiber orientation function measured by intersection counting method using image processing is compared with the calculated fiber orientation function. The results show that the measured value of fiber orientation function using intersection counting method is lower than the calculated value, because the number of intersection between the scanning line and the fiber with smaller fiber aspect ratio is counted less than with larger fiber aspect ratio.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1995년도 추계학술대회 논문집
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• pp.659-663
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• 1995

The fiber oriented conditied inside fiber reinforced composite material is a basic factor of mechanical properties of composite materials. It is very important to measure the fiber orientation angel for the determination of molding conditions, mechanical charactistics, and the design of composite materials. In the work, the fiber orientation distribution of simulation figure plotted by PC is measured using image processing in order to examine thr accuracy of intersection counting method. The fiber orientation function measured by intersection countingmethod using image processing is compared with the calculated fiber orientation function. The results show that the measured value of fiber orientation function using intersection counting method is lower than the calculated value, because the number of intersection between the secant line and the fiber with smaller fiber aspect ratio is counted less than with larger fiber aspect ratio.

• Tribology and Lubricants
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• 제5권2호
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• pp.94-100
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• 1989

Friction and Wear behavior of continuous graphite fiber composites was studied for different fiber orientations against the sliding direction. The effect of fiber orientation on friction and wear of the composite and on the deformation of the counterface was investigated experimentally. Pin on disk type testing machine was built and employed to generate the friction and wear data. A graphite fiber composite plate was produced by the bleeder ply molding in an autoclave and machined into rectangular pin specimens with specific fiber orientations, i.e., normal, transverse, and longitudinal directions. Three different wear conditions were employed for two different periods of time, 24 and 48 hours. The wear track of the worn specimens and the metal counterface was examined with a scanning electron microscope (SEM) to observe the damaged fibers on the surface and wear film generation on the counterface. Wear mechanism of the composite during sliding wear is proposed based on the experimental results.

• 소성∙가공
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• 제15권1호
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• pp.42-46
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• 2006

For mass production, usually injection mold has multi-cavity which is filled through geometrical balanced runner system. Despite geometrical balanced runner system, filling imbalances between cavity to cavity have always been observed. These filling imbalances are one of the most significant factors to affect quality of plastic parts. Filling imbalances are results from non-symmetrical shear rate distribution within melt when it flows through tile runner system. It has been possible to decrease filling imbalance by optimizing processing conditions, but it has not completely eliminated this phenomenon during injection molding processing. This paper presents a solution for these filling imbalances by using Runner Core pin (RC pin). The Runner Core pin which is developed in this study creates a symmetrical shear distribution within runner. As a result of using Runner Core pin, a remarkable improvement in reducing filling imbalances was confirmed.