• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.10
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• pp.844-848
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• 2012

Encapsulant curing in terms of convection oven leads to thermal induced stress due to nonuniform thermal conductivity in LED package. We have adopted infrared (IR) light for silicone curing in order to release the stress. The light uniformity irradiated on an encapsulant surface is confirmed to be uniform by optical simulation. Shear strength of die paste using IR compared to convection oven is increased 19.2% at the same curing time, which indicates curing time can be shortened. The indentation depth difference between center and edge of silicone encapsulant in terms of convection oven and IR are 14.8% and 3.4%, respectively. Curing by IR also shows 2.3% better radiant flux persistency rate of LED at $85^{\circ}C$ after 1,000 h reliability test compared to convection curing.

• Journal of the Korea Concrete Institute
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• v.17 no.4 s.88
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• pp.551-558
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• 2005

The setting and hardening of concrete is accompanied with nonlinear temperature distribution caused by development of hydration heat of cement. Especially at early ages, this nonlinear distribution has a large influence on the crack evolution. As a result, in order to predict the exact temperature history in concrete structures it is required to examine thermal properties of concrete. In this study, the convection heat transfer coefficient which presents thermal transfer between surface of concrete and air, was experimentally investigated with variables such as velocity of wind, curing condition and ambient temperature. At initial stage, the convection heat transfer coefficient is overestimated by the evaporation quantity. So it is essential to modify the thermal equilibrium considered with the boiling effect. From experimental results, the convection heat transfer coefficient was calculated using equations of thermal equilibrium. Finally, the prediction model for equivalent convection heat transfer coefficient including effects of velocity of wind, curing condition, ambient temperature and boiling effects was theoretically proposed. The convection heat transfer coefficient in the proposed model increases with velocity of wind, and its dependance on wind velocity is varied with curing condition. This tendency is due to a combined heat transfer system of conduction through form and convection to air. From comparison with experimental results, the convection heat transfer coefficient by this model was well agreed with those by experimental results.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2022.04a
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• pp.131-132
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• 2022

Looking at recent construction cases at winter construction sites, there is a risk that heat sources such as kerosene fans and fossil fuels (brown coal, molded carbon) used in concrete will cure rapidly, so in situations where further curing is impossible after formwork removal, the outer wall and the entire slab are exposed to rapid external deterioration, resulting in delays in concrete strength expression and until collapse accidents. In this study, we applied kerosene fans and tropical circulating electric heat fans mainly used as curing heat sources at construction sites, comparative analysis. also verified the performance of structures during concrete curing due to thermal convention / circulation performance, concrete demand strength expression, and implementation of electric heat fans by heavy disaster methods.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2020.11a
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• pp.109-110
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• 2020

In This study, we tried to review an efficient curing method in consideration of safety and constructability among the problems of winter construction. In other words, as a result of the mock-up test, the measured value of carbon monoxide was 0 ppm in the case of an electric hot air fan. Since there is no carbon monoxide, problems such as suffocation are expected to be solved. In terms of temperature characteristics, electric hot air fans exhibited high thermal efficiency performance with a slight difference in upper/lower temperatures compared to the existing ones. In the future, we plan to conduct thermal efficiency evaluation through actual site performance verification. We will propose an efficient curing method through applicability evaluation.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2021.11a
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• pp.192-193
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• 2021

Recently, the need to strengthen the Air Environment Conservation Act and secure alternative heat sources during the winter by carbon neutrality policies has been raised. Accordingly, winter construction, which has safety and quality measures, is emerging as an essential factor. It is believed that eco-friendly tropical type electric hot air heaters will be able to solve most of the problems of winter construction at construction sites, especially prevention of suffocation and fire accidents. In addition, as a result of on-site performance verification, it has secured more than the same performance as the existing curing method, and the curing technology can create an eco-friendly and pleasant working environment while considering safety and construction.

• Macromolecular Research
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• v.16 no.6
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• pp.561-566
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• 2008

NR composites with different curing systems were aged thermally at 60, 70, 80, and $90^{\circ}C$ for 2-185 days in a convection oven, and the changes in the crosslink density were investigated as a function of the accelerated thermal aging. The overall crosslink densities increased with increasing aging time irrespective of the aging temperatures and curing systems. The changes in crosslink density were enhanced by increasing the aging temperature. The degree of the increased crosslink density was in the following order: "the conventional cure system > the semi-EV system > the EV system". For short term thermal aging, the change in crosslink density with the aging time was complicated, particularly for low temperature aging. The activation energies of the change in crosslink density with thermal aging using the conventional and semi-EV cure systems increased and then remained relatively constant with increasing aging time, whereas that of the specimen with an EV cure system tended to increase linearly. The experimental results were explained by the dissociation of the existing polysulfidic linkages and the formation of new cross links through the crosslinking-related chemicals remaining in the sample.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.249-252
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• 2008

In recent large-scale structures, as mass concrete type structure is frequently applied to the building, temperature crack due to hydration heat needs to be considered. Since a volume change is internally or externally restricted in a mold after placing concrete, temperature crack of mass concrete takes place. By this reason, the reduction method to control this crack is required. In this study, low heat mixture and hydration heat difference is used to execute the analysis of hydration heat, considering the changes of heat transfer coefficient according to curing conditions and block placement of mass concrete. For the analytical modelling, original portland cement and concrete of low heat mixture are placed in the upper and lower payer, respectively. A convection boundary condition is fixed because mass concrete of block placement is characterized by the difference of mold form and curing condition. Through the analysis results considering the changes of low heat mixture, block placement, and heat transfer coefficient, we check out the temperature and stress distribution and analyze the temperature crack reduction effect.

• Journal of the Korea institute for structural maintenance and inspection
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• v.14 no.1
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• pp.156-164
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• 2010

A total of 6 stepwise constructions were made for building the floating mass concrete foundation. The optimal curing strategies and specialized construction guidelines were adoptively extracted from the 1.5m cube mock-up test prior to the main concrete work. Two different thermal crack index(TCI) calculations from current construction manual exhibit relatively low values as comparing the measured temperature data. This implies that the hydration-induced cracking could be developed in parts of concrete mass. However, the controversial phenomenons in reality were observed. No significant surface cracks are detected at the successive construction stages. Thereby, this paper raises the question regarding on the existence of characteristic length with varying size and shape of a target specimen which are missing in the current construction manual. The isothermal core area and high thermal gradient area in the edge volume should be identified and be introduced to TCI calculation for the purpose of an accuracy.