• Polymer(Korea)
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• v.32 no.6
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• pp.501-508
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• 2008

Small injection molded articles such as lens and mobile product parts are usually molded in multi-cavity mold. The problem occurring in multi-cavity molding is flow unbalance among the cavities. The flow unbalance affects the dimensions and physical properties of molded articles. First of all, the origin of flow unbalance is geometrical unbalance of the delivery system. However, even the geometry of the delivery system is well balanced, cavity unbalance occurs. This comes from the temperature distributions in the cross-section of runner. Temperature distribution depends upon injection speed because heat generation near runner wall is high at high injection speed. Among the operational conditions, injection speed is the most significant process variable affecting the filling unbalances in multi-cavity injection molding. In this study, experimental study of flow unbalance has been conducted for various injection speeds and materials. Also, the filling unbalances were compared with CAE results. The dimensions and weights of multi-cavity molded parts were examined. The results showed that the filling unbalances vary according to the injection speeds and resins. Subsequently, the unbalanced filling and pressure distribution in the multi-cavity affect the dimensions and physical states of molded parts.

• The korean journal of orthodontics
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• v.34 no.1 s.102
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• pp.83-91
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• 2004

This study was performed to examine treatment efficiency and patient discomfort rate according to used handpiece speed in clean-up technique. Brackets were bonded to extracted human premolar(50 teeth). After debonding, 50 extracted human premolar were divided Into each two groups(low speed handpiece group with tungsten carbide bur and high speed handpiece group with ultra-fine diamond finishing bur) of 25 according to used handpiece speed in clean-up technique. In clean-up procedure, teeth vibration and pulp thermal changes were measured. After clean-up procedure, the enamel surfaces of randomly selected 10 teeth from each two groups were taken by SEM and evaluated. The findings of this study were as follows ; 1. During resin removal, tooth vibrations of various amplitude in low speed handpiece group were more than those of high speed handpiece. 2. The pulpal thermal changes of high speed handpiece group were significantly higher than those of low speed handpiece group, also the resin removal time in high speed handpiece group was almost as twice as in low speed handpiece group. 3. The figures of SEM to enamel surfaces after resin removal showed that notches and resin remnants in high speed handpiece group were more than those in low speed handpiece group.

• Journal of the Korean Wood Science and Technology
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• v.33 no.3 s.131
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• pp.30-37
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• 2005

This study aimed at offering basic data to develop a new use of sawdust and rice husk. Research investigated the variation of density, weight loss and dimensional decreasing rate by the percentage of resin impregnation and carbonization temperature of ceramics, which were formed by the percentage of resin impregnation of 40~80% and carbonization of $600{\sim}1200^{\circ}C$ with board impregnated with phenolic resin made from sawdust and rice husk. The results of this study were as follows:1) As the percentage of resin impregnation increased, the thickness shrinkage and weight loss were decreased; on the other hand, density and modulus of rupture increased. Meanwhile, the carbonization temperature at $1200^{\circ}C$ showed the highest values, as the density was $0.81g/cm^3$ and the bending strength was $77.9kgf/cm^2$ in the percentage of resin impregnation at 70%. 2) As the carbonization temperature grew higher the linear shrinkage, thickness shrinkage and weight loss increased while the density increased until the carbonization temperature of $1000^{\circ}C$; but then decreased slightly at $1200^{\circ}C$.

• Composites Research
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• v.31 no.1
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• pp.12-16
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• 2018

Composite material and mold steel can be expanded differently with the temperature gradients during the forming process because their coefficients of thermal expansions are not the same. Therefore, in order to manufacture the product with accuracy, it is necessary to verify that the forming pressure on the surface of the composite material is maintained to the required level from the material supplier. In this paper, the pressure between the composite material and mold due to the temperature difference was predicted by finite element analysis and the accuracy of predicted value was verified by measuring the thermal expansions of mold steel by the ruler. The predicted value by finite element analysis is closely in agreement with one by the experiment within the required tolerance value of ${\pm}0.05mm$.

• Restorative Dentistry and Endodontics
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• v.26 no.5
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• pp.387-392
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• 2001

When cavity floor is near the pulp, polymerization of light-activated restorations results in temperature increase. This temperature increase cause by both the exothermic reaction process and the energy absorbed during irradiation. Therefore instating base is required. Most frequently used insulating base is glass ionmer. The purpose of this study was to evaluate intrapulpal temperature changes of glass ionomer according to various curing intensity and curing time. Caries and restoration-free mandibular molars extracted within three months were prepared Class I cavity of 3$\times$6mm with high speed handpiece. 1mm depth of dentin was evaluated with micrometer in mesial and distal pulp horns. Pulp chambers were filled with 37.0$\pm$0.1$^{\circ}C$ water to CEJ. Chromium-alumina thermocouple was placed in pulp horn for evaluating of temperature changes. glass ionomer material was placed in 2mm. total curing time was 40s: continuous 40s, intermittent 20s, intermittent 10s. Glass ionomer material was cured with 300mW/$\textrm{cm}^2$, 550mW/$\textrm{cm}^2$ light curing unit. The results were as follows : 1. Temperature in pulp increased as curing unit power is increased. 2. Temperature in pulp more increased continuous emission than intermittent emission.

• Proceedings of the KAIS Fall Conference
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• 2010.11a
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• pp.301-304
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• 2010

본 논문에서는 다수 캐비티 금형의 러너 내 불균일한 전단분포로 인해 발생되는 충전불균형에 따른 치수정밀도, 기계적 강도 등 물성의 차이가 발생되는 문제점을 해소하기 위해서 수지가 처음 분기되는 2차 러너의 구조에 변화를 주어 다수 캐비티 사출성형에서 충전균형을 위한 러너시스템을 제시하였다. 이 러너시스템은 전단률차이에 의한 즉, 온도가 불균일한 수지의 흐름을 혼합함으로써 수지의 흐름을 균일하게 하여 충전균형을 이루도록 하였다. PP수지를 대상으로 각 캐비티 간 균형충전에 대해 이 러너시스템이 효과가 있는지 검증하기 위해 CAE프로그램(Moldflow)을 이용한 유동해석을 통해 그 효과를 나타내 보았다.

• Proceedings of the Korea Water Resources Association Conference
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• 2012.05a
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• pp.260-264
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• 2012

전 지구적으로 지구온난화로 인해 기후변화가 일어나고 있으며 이에 대해 다양한 방면에서 기후변화에 대한 대응, 적응, 극복을 위한 연구가 활발히 진행되고 있다. 선진국에서는 일찍이 기후 변화관련 영향을 정량적으로 평가하고 치수정책에 반영하고자 노력하고 있으며, 우리나라의 경우도 2000년에 들어서 기후변화 관련 연구를 본격적으로 시작하였다. 지난 100년 동안 한반도 기온은 약 $1.7^{\circ}C$ 상승하여 세계온도의 증가율에 비해 2.3배 상승하였고, 최근 50년 동안 우리나라 강수량을 분석한 결과 전국적으로 강수일수는 감소하고 일강수량 80mm 이상인 호우발생 빈도는 증가하는 것으로 나타났다. 또한, 남부지역에서는 연강수량이 7% 증가하고 연 강수일수는 14% 감소하며 강수강도는 18% 증가하는 것으로 분석되었다. 이상의 결과를 종합해 볼 때, 우리나라는 기후변화의 영향으로 강우일수는 감소하고 연강우량은 증가하는 것을 알 수 있으며, 이는 곧 강우강도가 강해짐에 따라 홍수와 가뭄의 발생가능성이 증가될 것으로 예상된다. 따라서 본 연구에서는 기후변화에 따른 홍수와 가뭄 발생에 대응하기 위한 기초자료를 제공하고자 지석천 유역의 기후변화 시나리오에 따른 유출량 변화를 모의하였으며, 이를 위해 분포형 장기 강우-유출모형인 SWAT(Soil And Water Assessment Tool)모형을 이용하였다. 기후변화 시나리오 자료는 국내 기상청에서 제공하는 수평격자 27km의 고해상도 RCM A1B 시나리오 자료를 사용하였으며, 1971~2010년 기간의 기후변화 시나리오 자료를 지석천 유역에 인접한 광주기상청 실측 기상자료와 비교하여 편이보정 후 2011~2100년 기간의 유출량을 모의하였다. 유출량 모의값에 대한 검 보정을 위하여 지석천유역의 하류지점인 남평지점의 실측 유량을 이용하여 검 보정을 실시하였으며, 2002~2005년 기간의 자료를 이용하였다. 검 보정 결과 2002~205년 기간 동안의 유출량 모의값은 실측유량값과 유사한 경향을 나타내었으며 본 연구의 목표인 2011~2100년까지의 유출량은 기후변화 시나리오의 내용과 비슷한 첨두유량이 증가함을 나타내었다.

• Korean Journal of Materials Research
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• v.2 no.4
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• pp.298-305
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• 1992

The carbonization behaviors of CFRP fabricated with 2D-woven fabric and matrix phenolic resin have been studied. The changes in dimension were observed in the temperature range of 365-37$0^{\circ}C$ in the thickness direction, 118-12$0^{\circ}C$ in the normal direction each other by TMA analysis. Observation with the optical microscope shows that the formed cracks and pores during the fabrication of CFRP were propagated with the increase of pyrolysis temperaure. New cracks and pores were formed in the pyrolysis temperature range of 400-50$0^{\circ}C$ In line with the formation and propagation of cracks, porosity was increased and density was decreased rapidly in the pyrolysis temperature range of from 40$0^{\circ}C$ to 70$0^{\circ}C$. Therefore heating rate in the carbonization process need to be controlled carefully by intervals.

• Elastomers and Composites
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• v.42 no.4
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• pp.201-208
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• 2007

In this study, the thermal shrinkage and expansion stresses of filled NR and SBR vulcanizates were measured to investigate the dimensional stability at an elevated temperature. When a rubber sample was held at constant pre-strain, a thermal stress developed upon heating due to the entropic consideration. The peak shrinkage stress of carbon black or silica filled NR decreased with increasing filler content. In SBR compounds, however, the peak shrinkage stress of SBR with 30 phr filler content was higher than that of unfilled compounds. The expansion stress of carbon black filled NR was changed little, but that of filled SBR increased with increasing the filler content. The peak expansion stress of silica filled NR and SBR vulcanizates increased with increasing silica content.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.9
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• pp.991-997
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• 2011

This paper deals with the basic principles and procedures involved in the steam-chest molding process used for manufacturing expanded polypropylene (EPP) bead foam. Steam-chest molding is an integral process for EPP technology. However, little research has been carried out on the processing conditions for steam-chest molding this process. The characteristics of EPP foam are energy absorption, multiple-impact protection, low weight, structural strength, and durability. In this study, the steam pressure in steam-chest molding was varied to determine the optimum conditions for manufacturing EPP foam. Moreover, annealing was performed after EPP-foam molding to prevent the shrinkage of the steam-molded product. It was possible to verify the mechanism of foam shrinkage by observing the change in weight with time at different annealing temperatures. Moreover, a tensile test and scanning electron microscopy (SEM) analysis were performed to support these experimental results. The dimensional stability of each molded product was investigated at different steam pressures.