• 제목/요약/키워드: rheological processes

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Polymer Materials Design for Good Processability of Polymer Processing

  • Koyama, Kiyohito
    • 한국고분자학회:학술대회논문집
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    • 한국고분자학회 2006년도 IUPAC International Symposium on Advanced Polymers for Emerging Technologies
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    • pp.135-136
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    • 2006
  • The shear flow properties have been reported in many cases by manufactures and fabricators. Only this characteristic is sometimes insufficient for the processings to provide a complete picture of the relationship between the processability and the flow behavior when underwent free-surface processes in which the shape and thickness of the extrudate are determined by the rheological properties of the melt, the die dimensions etc. In this paper the methodology of control of elongational flow is discussed in terms of relaxation time control of the polymer melts.

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Rheological Perspectives on Direct Printing Processes

  • 안경현
    • 한국재료학회:학술대회논문집
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    • 한국재료학회 2011년도 춘계학술발표대회
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    • pp.1.2-1.2
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    • 2011
  • With recent advances in materials and products, materials processing experiences new challenges. More particles and polymers in material side and thinner and faster deformations in processing side. It happens in most emergying industries such as manufacturing of batteries, solar cells, multi-layer chips, displays, printed electronics, to list a few. In most cases, they are manufactured by coating or printing process, which is defined as a process in which gas is replaced by liquid on a substrate. In this sense, casting, inkjet printing, and roll-to-roll printing are all included. The printing process consists of three unit processes. As the materials used in the above mentioned applications typically contain a large amount of particles with polymers and solvents, they continuously change microstructures during preparation, flow, and even drying. However, little is known about the flow characteristics of such complex fluids and less is known about how to design and control the process. Therefore, for better control of the process and for better quality of the product, we need to understand the flow characteristics of these complex fluids under extremely fast flow environment.

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가압회전식 장비를 이용한 A356 합금의 미세조직과 재가열 특성 (Characteristics of Microstructure and Reheating of A356 Aluminum Alloy by Pressure Rotation Equipment)

  • 서판기;고재홍;강충길
    • 한국소성가공학회:학술대회논문집
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    • 한국소성가공학회 2005년도 추계학술대회 논문집
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    • pp.227-230
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    • 2005
  • Many rheocasting processes had been proposed because of the difficulty of recycling, the limit of material, and the high cost of raw material in thixocasting. But, these rheocasting processes also had disadvantages such as the high initial Investment cost and the lower mechanical properties than thixocasting. In this study, a continuous fabrication of rheological material with pressure rotation equipment was newly devised to overcome the disadvantages of rheocasting process. In order to investigate the thixoformability, reheating experiments were carried out with the material fabricated by the newly devised equipment. Morphological characteristics between mechanical stirring and reheating were compared.

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Rheology of PP/Clay Hybrid Produced by Supercritical $CO_2$ Assisted Extrusion

  • Lee, Sang-Myung;Shim, Dong-Cheol;Lee, Jae-Wook
    • Macromolecular Research
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    • 제16권1호
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    • pp.6-14
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    • 2008
  • Polypropylene (PP)-layered silicate nanocomposites were developed using a new processing method involving a supercritical carbon dioxide ($scCO_2$)-assisted co-rotating twin-screw extrusion process. The nanocomposites were prepared through two step extrusion processes. In the first step, the PP/clay mixture was extruded with $CO_2$ injected into the barrel of the extruder and the resulting foamed extrudate was cooled and pelletized. In the second step, the foamed extrudate was extruded with venting to produce the final PP/clay nanocomposites without $CO_2$. In this study, organophilic-clay and polypropylene matrix were used. Maleic anhydride grafted polypropylene (PP-g-MA) was used as a compatibilizer. This study focused on the effect of $scCO_2$ on the dispersion characteristics of the clays into a PP matrix and the rheological properties of the layered silicate based PP nanocomposites. The dispersion properties of clays in the nanocomposites as well as the rheological properties of the nanocomposites were examined as a function of the PP-g-MA concentration. The degree of dispersion of the clays in the nanocomposites was analyzed by X-ray diffraction and transmission electron microscope. Various rheological properties of the nanocomposites were measured using a rotational rheometer. In the experimental results, the $scCO_2$ assisted continuous manufacturing extrusion system was used to successfully produce the organophilic-clay filled PP nanocomposites. It was found that $scCO_2$ had a measurable effect on the clay dispersion in the polymer matrix and the melt intercalation of a polymer into clay layers.

폴리카보실란 전구체의 용매 처리에 따른 열적 및 유변학적 특성 분석 (Thermal and Rheological Characterizations of Polycarbosilane Precursor by Solvent Treatment)

  • 송예은;주영준;신동근;조광연;이두진
    • Composites Research
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    • 제35권1호
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    • pp.23-30
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    • 2022
  • 폴리카보실란은 탄화규소 섬유 방사와 세라믹 제조를 위해 필요한 중요한 전구체이며, 이 전구체는 제조방법 및 공정에 따라 고내열성 및 내산화성 및 연속적인 탄화규소 섬유 생산 능력이 달라진다. 탄화규소 섬유는 폴리카보실란의 합성, 정제 및 분자구조제어기술, 그리고 이를 이용한 용융방사 및 안정화, 열처리 공정을 통해 제조된다. 본 논문에서는 폴리카보실란 전구체를 다양한 용매처리를 통하여 전구체 내에 존재하는 미반응물 및 저분자량의 정제효과를 파악하였으며, 또한 다양한 온도에서의 열처리에 따른 폴리카보실란 전구체의 중합 및 네트워크 재배열에 의한 변화에 대해 열적 분석을 실시하였다. 특히, 폴리카보실란 전구체의 유변물성 특성을 통해 용매처리 및 열처리에 따른 복합점도 및 구조적 배열의 변화를 분석하였다.

LPBF용 타이타늄 합금 분말의 유변특성에 대한 입자 구형도의 영향 (Effect of Particle Sphericity on the Rheological Properties of Ti-6Al-4V Powders for Laser Powder Bed Fusion Process)

  • 김태윤;강민혁;김재혁;홍재근;유지훈;이제인
    • 한국분말재료학회지
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    • 제29권2호
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    • pp.99-109
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    • 2022
  • Powder flowability is critical in additive manufacturing processes, especially for laser powder bed fusion. Many powder features, such as powder size distribution, particle shape, surface roughness, and chemical composition, simultaneously affect the flow properties of a powder; however, the individual effect of each factor on powder flowability has not been comprehensively evaluated. In this study, the impact of particle shape (sphericity) on the rheological properties of Ti-6Al-4V powder is quantified using an FT4 powder rheometer. Dynamic image analysis is conducted on plasma-atomized (PA) and gas-atomized (GA) powders to evaluate their particle sphericity. PA and GA powders exhibit negligible differences in compressibility and permeability tests, but GA powder shows more cohesive behavior, especially in a dynamic state, because lower particle sphericity facilitates interaction between particles during the powder flow. These results provide guidelines for the manufacturing of advanced metal powders with excellent powder flowability for laser powder bed fusion.

측방향하중(側方向荷重)에 의한 벼줄기의 역학적특성(力學的特性)에 관한 연구(I) -이완거동 분석- (Study on the Mechanical Properties of the Rice Plants Subjected to Radial Load -Analysis of Relaxation Behavior-)

  • 허윤근
    • Journal of Biosystems Engineering
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    • 제18권4호
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    • pp.402-409
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    • 1993
  • During all mechanical processes rice plants are subjected to verious forces such as natural load of wind and mechanical load of agricultural machines. A force is always accompanied by deformation, which must be either sufficiently great for pressing or sufficiently slight in order to avoid damage. The mechanical behavior of the rice plants is determined by three variables : force, deformation and time. And they must be studied using rheological methods to determine their viscoelastic properties. This study is conducted to experimentally determine the mechanical and rheological properties of the rice stalks subjected to radial load. The force relaxation tests are performed under constant deformation, during which the reduction of forces over time is measured. The mechanical models were developed from the abtained data. The results were as follows : 1. The relaxation behavior of a rice stalk in radial compession may be described by a generalized Maxwell model consisting of 3 Maxwell elements in parallel. 2. Relaxatiom intensity always decreased with increased time of relaxation. 3. The rate of deformation has a significant effect on the relaxation behavior. having increasing pattern with an increase in rate of deformation. 4. The relaxation intensity and residual deformation increased with increased initial load. 5. The relaxtion of the intermediate portion of stalk was bigger tham that of the upper and lower portions.

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Rheology of flocculated kaolinite dispersions

  • McFarlane A.J.;Addai-Mensah J.;Bremmell K.
    • Korea-Australia Rheology Journal
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    • 제17권4호
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    • pp.181-190
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    • 2005
  • Rheological characterisation of flocculated kaolinite pulps has been undertaken to elucidate particle interactions underpinning the dewatering behaviour induced by flocculation with polyethylene oxide (PEO), anionic polyacrylamide (PAM A) and their blends. Shear yield stress $(\tau_y)$ analysis indicated that polymer mediated particle interactions were markedly amplified upon shear of PEG based pulps. In contrast, PAM A based pulps showed a significant decrease in yield values upon shear. Steady stress measurements analysed using a modified Ellis model indicated subtle differences between the respective linear viscoelastic plateaus of the pulps. Furthermore, modified shear thinning behaviour was evident in PEG based pulps. Estimation of elastic and viscous moduli (G', G') was made using dynamic stress analysis for comparison with values determined from vane measurements. Despite a noticeable difference in the magnitude of G' between the two methods, similar trends indicating sheared PEG-based pulps to be more elastic than PAM based pulps, were observed. Floc microstructural observations obtained in support of rheological properties indicate that PEG flocculant induces significantly more compact particle aggregation within the clay pulps under shear consistent with the yield stress data, in contrast to PAM A, or indeed unsheared PEG based pulps. Consequentially, sheared PEG based pulps show significantly improved dewatering behaviour. The implications of the results, potential benefits and drawbacks of flocculation with PEG and PAM A are discussed with respect to improvements in current dewatering processes used in the minerals industry.

Effect of Activation Energy and Crystallization Kinetics of Polyethylenes on the Stability of Film Casting Processes

  • Lee, Joo-Sung;Cho, Joon-Hee
    • Korea-Australia Rheology Journal
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    • 제21권2호
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    • pp.135-141
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    • 2009
  • Effect of activation energy and crystallization kinetics of polyethylenes (PEs) on the dynamics and stability has been investigated by changing rheological properties and crystallization rate in film casting process. The effect of changes of these properties has been shown using a typical example of short-chain branching (SCB) in linear polyethylenes. SCBs in linear polymers generally lead to the increase of the flow activation energy, and to the decrease of the crystallization rate, making polymer viscosity lower in the case of equivalent molecular weight. In general, the increment of the crystallinity of polymers under partially crystallized state helps to enhance the process stability by increasing tension, and lower fluid viscoelasticity possesses the stabilizing effect for linear polymers. It has been found that the fluid viscoelasticity plays a key role in the control of process stability than crystallization kinetics which critically depends on the cooling to stabilize the film casting process of short-chain branched polymers operated under the low aspect ratio condition.

압전작동기를 이용한 고주파수 젯팅 디스펜서의 성능 특성 (Performance Characteristics of High Frequency Jetting Dispenser Featuring Piezoactuator)

  • 윤보영;구오흥;홍승민;손정우;최승복
    • 한국소음진동공학회:학술대회논문집
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    • 한국소음진동공학회 2007년도 추계학술대회논문집
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    • pp.595-600
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    • 2007
  • This paper presents a new jetting dispenser driven by a piezoelectric actuator at high operating frequency to provide very small dispensing dot size of adhesive in modern semiconductor packaging processes. After describing the mechanism and operational principle of the dispenser, a mathematical model of the structured system is derived by considering behavior of each component such as piezostack and dispensing needle. In the fluid modeling, a lumped parameter method is applied to model the adhesive whose rheological property is expressed by Bingham model. The governing equations are then derived by integrating the structural model with the fluid model. Based on the proposed model, dispensing performances such as dispensing amount are investigated with respect to various input trajectories.

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