• Proceedings of the Korean Fiber Society Conference
• /
• 2003.10a
• /
• pp.47-48
• /
• 2003

Dilute bubble suspensions are prepared by introducing carbon dioxide bubbles into polyol resin. The apparent shear viscosity is measured with a wide gap parallel plate rheometer. A numerical simulation for deformation of a single bubble suspended in a Newtonian fluid is conducted by using a finite volume method (FVM) where multigrid algorithms are incorporated. Transient and steady results of bubble deformation were obtained and were in good agreement with experimental results. At high capillary number, viscosity of the suspension increases as the volume fraction increases, while at low capillary number, the viscosity decreases as the volume fraction increases.

• Proceedings of the Korean Society for Agricultural Machinery Conference
• /
• 2003.02a
• /
• pp.315-320
• /
• 2003

식품의 가공 분야뿐만 아니라 제약 공정 등의 생물산업 분야에서는 유변학(Rheology)이 차지하고 있는 위치는 매우 중요하며 물질의 유변물성을 정확히 파악하지 않고서는 정밀도를 요하는 가공 공정을 이룰 수 없어 우수한 제품을 생산하기 어렵다. 특히 작품 압출 성형분야에서 생물고분자(biopolymer) 원료의 유변 물성은 압출 성형시 중요한 역학을 하며 더 좋은 압출 성형 장치의 설계와 압출 공정의 제어를 위해서는 원료에 패한 물리적 성질의 이해와 압출 성형 장치 내에서 일어나는 변화를 이해해야 한다. (중략)

• Polymer(Korea)
• /
• v.37 no.3
• /
• pp.399-404
• /
• 2013

In order to develop the blends with good long-term thermal stability and tensile elongation, the blends of polyphenylene sulfide (PPS) and 7 kinds of elastomer were tested. PPS/elastomer (90/10, 80/20, 70/30) blend samples were prepared by compression molding after twin screw extrusion or punching after sheet extrusion. Rheological, mechanical property and morphology of the blends were analyzed by capillary rheometer, UTM, impact tester, and SEM. For long-term thermal stability tests, the mechanical properties were measured again after the samples were stored in a convection oven for a week. The tensile strengths were almost same regardless of kinds of elastomer and the tensile elongation was the maximum for the PPS/m-EVA blend. As the content of elastomer increased, the elongation increased but delamination occurred at 30 wt% of elastomer content. The tensile strength increased but the elongation decreased seriously after thermal aging. Many problems related with PPS processing could be solved by adding a small amount of the elastomers partially compatibile with PPS and it would be applicable to develop various PPS grades.

• Elastomers and Composites
• /
• v.45 no.2
• /
• pp.122-128
• /
• 2010

We measured shear viscosity of copoly(styrene(St)/butyl methacrylate(BMA)) (co-PSB) particles, with a capillary rheometer at $170^{\circ}C$, prepared by suspension polymerization with hydrophobic silica as a stabilizer. co-PSB particles with the weight average molecular weights of lower than 74,800 g/mol displayed a Newtonian behavior at low shear rates. With the weight average molecular weight exceeding 136,800 g/mol, co-PSB particles showed shear thinning against shear rates and the absolute value of the slopes between shear viscosity vs. shear rate increased. When the ratio between St and BMA changed from 7/3 to 5/5 to 3/7, shear viscosity and glass transition decreased despite similar molecular weights. When the ratio was 1/9, it showed a large increase in initial shear viscosity despite reduced glass transition. Shear viscosity exhibited an increase in proportion to carbon black concentration. The effect of carbon black concentration on the shear viscosity of co-PSB composites was less pronounced compared to varying molecular weights and/or compositional ratio.

• Transactions of Materials Processing
• /
• v.23 no.1
• /
• pp.41-48
• /
• 2014

The light guide plate has become the major component for the backlight module in general information technology products (e.g. mobile phones, monitors, etc.). High speed injection molding has been adopted for thin walled LGP giving advantages such as weight, shape, size, and reduction in production costs. In the current study, the rheological characteristics of high liquidity plastic resin PC(HL8000) were measured using a capillary rheometer to improve the reliability of the numerical analysis for high speed injection molding. With the measured viscosity and PVT of PC(HL8000), numerical analysis of injection molding was conducted using the simulation software(Moldflow). Filling time and deflection were predicted and compared with those of traditional PC resins(H3000, H4000). The results show that PC(HL8000) has significantly different rheological characteristics during high speed injection molding. Hence proper properties of the resin should be used to improve the accuracy of numerical predictions.

• Journal of Powder Materials
• /
• v.23 no.2
• /
• pp.112-119
• /
• 2016

A powder injection molding process is developed and optimized for piezoelectric PAN-PZT ceramics. Torque rheometer experiments are conducted to determine the optimal solids loading, and the rheological property of the feedstock is evaluated using a capillary rheometer. Appropriate debinding conditions are chosen using a thermal gravity analyzer, and the debound specimens are sintered using sintering conditions determined in a preliminary investigation. Piezoelectric performance measures, including the piezoelectric charge constant and dielectric constant, are measured to verify the developed process. The average values of the measured piezoelectric charge constant and dielectric constant are 455 pC/N and 1904, respectively. Powder injection molded piezoelectric ceramics produced by the optimized process show adequate piezoelectric performance compared to press-sintered piezoelectric ceramics.

• The Korean Journal of Rheology
• /
• v.9 no.2
• /
• pp.73-80
• /
• 1997

분말 입자 형태가 다른 2가지 스테인레스 강(SUS 316L)분말과 조성이 다른 2가지의 결합제를 이용하여 분말충전율의 변화를 가지도록 제조된 5가지 분말사출재에 대한 Bagley 보정 실험을 실시하여 Bagley 보정값에 대한 온도, 분말충전율, 분말 입자 형태 그리고 결 합제의 영향을 조사하였다. Bagley 보정값을 구하기 위한 자료 처리를 하는 과정에서 길이 가 긴 모세관(L/D=60) 의 압력손실이 Thixotropy에 의해서 감소한 현상을 발견하였다. 이는 모세관 점성측정기를 이용한 분말사출제의 점도 측정시 길이가 긴모세관의 사용이 바람직하 지 못하다는 것을 나타낸다. 분말사출재의 Bagley 보정값에 대한 온도와 결합제의 영향은 매우 미약하게 나타났는데 특히 결합제의 영향은 거의 나타나지 않는 것을 발견하였다. 분 말충전율과 분말 입자 형태의 Bagley 보정값에 대한 영향은 매우 크게 나타났으며 분말충 전율이 증가할수록 Bagley 보정값이 증가하고 분말 입자의 형태가 불규칙한 분말을 사용한 분말사출재의 보정값이 구형의 분말에 비해 높은 보정값을 나타냈다. 실험결과에 대한 고찰 결과, 분말사출재의 모세관 입출구에서 압력손실의 주 원인은 분말 이자간 마찰과 충돌이라 고 판단되었다.

• Korea-Australia Rheology Journal
• /
• v.16 no.3
• /
• pp.153-160
• /
• 2004

Open microcellular foams having small-sized cell and good mechanical properties are desirable for many practical applications. As an effort to reduce the cell size, the microcellular foams combining viscosity improvers into the conventional formulation of styrene and water system were prepared via high internal phase emulsion polymerization. Since the material properties of foam are closely related to the solution properties of emulsion state before polymerization, the flow behavior of emulsions was investigated using a controlled stress rheometer. The yield stress and the storage modulus increased as viscosity improver concentration and agitation speed increased, due to the reduced cell size reflecting both a competition between the continuous phase viscosity and the viscosity ratio and an increase of shear force. Appreciable tendency was found between the rheological data of emulsions and the cell sizes of polymerized foams. Cell size reduction with the concentration of viscosity improver could be explained by the relation between capillary number and viscosity ratio. A correlative study for the cell size reduction with agitation speed was also attempted and the result was in a good accordance with the hydrodynamic theory.

• Elastomers and Composites
• /
• v.50 no.1
• /
• pp.49-54
• /
• 2015

Dynamically vulcanized PMMA/ACM (80 wt%/20 wt%) blend using DCP as a curing agent was prepared using internal mixer. The morphology, mechanical properties, optical properties, melt viscosity and die swell were characterized by using FE-SEM, tensile test, Izod impact test, dynamic mechanical analysis, ARES and capillary rheometer, respectively. The blends show a phase-separated morphology in which ACM are dispersed in PMMA matrix. Dynamically vulcanized blend exhibits higher mechanical properties, higher melt viscosity, and die swell as compared to simple blend. And, the dynamically vulcanized blend showed total transmittance of more than 75% and haze of higher than 90%, which enable it to find potential applications to fabricate an optical diffuser by extrusion process.

• Journal of the Korean Society for Precision Engineering
• /
• v.9 no.4
• /
• pp.109-117
• /
• 1992

Mixing of ceramic-binder system was investigated experimentally and theoretically for application to Ceramic Injection Molding. Polypropylene, stearic acid, and paraffin wax were selected as the binder system, and silicon nitride fine powders were selected as the ceramic material. Single screw ectruder was employed as the mixing equipment. Theoretical analysis was performed to investigate the mixedness of mixture quantitatively. The analysis predicted average residence time average total strain, and average shear stress as a function of screw speed for mixtures of different volume fraction. Qualitative mixedness of mixture and characteristics of mixing were investigated by using SEM and EPMA. In addition, rheological properties of the mixture were investigated by using a capillary rheometer to examine possibility of injection molding.