• Journal of the Korean Society for Precision Engineering
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• v.33 no.5
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• pp.419-425
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• 2016

A powder spreading phenomenon is one of disadvantageous characteristics of the powder bed fusion process using electron beams. The powder spreading phenomenon can be controlled using a pre-heating process of metallic powders. The aim of this paper was to investigate the preheating process of Stellite21 powder using electron beams. Powder spreading experiments were performed to examine the influence of process parameters on the spreading behaviors of Stellite21 powder. Powder heating experiments were carried to investigate the effects of the focusing current of the electron beam on the quality of the heated region. Using the results of the powder spreading and heating experiments, an appropriate combination of process parameters was obtained. The pre-heating experiment of Stellite21 was performed using the estimated combination of process parameters. The results of preheating experiments showed that the preheated Stelllite21 layer with desired characteristics can be created when the estimated combination of process parameters is applied.

• Journal of the Korean Society of Safety
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• v.29 no.4
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• pp.61-72
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• 2014

The aim of this study is to define the condition of optimal pre-treatment for preferable activated carbon fibers (ACFs), which are based on rayon fibers. This paper shows the ideal path of ACFs preparation process; implies that rayon fibers are pre-treated by various solvents with different times before the heating process. The pre-treated rayon fibers finally turned into desirable rayon fiber-based ACFs through optimal pre-treatment condition by heating processes. The thermal analysis method of pre-treated rayon fibers by thermo-gravimetry analyser (TGA) is an idealized tool, which analyzes the best thermal condition of pre-treatment process. Surface morphologies of resulting rayon fibers based ACFs were examined by scanning electron microscope(SEM). The results of TGA and SEM analyses show that the optimal pre-treatment condition for preparing ACFs was clearly defined, in terms of thermal stability and surface morphology.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.266-267
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• 2006

We present a systematic study of the heating and pre-sintering behavior of porous copper powder metal compacts. We employ a TE102 single mode microwave system to position the samples in the separated electric field (E) or magnetic field (H) anti-node of the cavity. We observe significant differences in the heating, pre-sintering, and microstructure evolution of the samples due to the individual fields. We note that sample history (whether heated first in the E-field or H-field) greatly effects a difference in heating trends and subsequent heating behavior and does not appear to be solely a thermal process.

• Journal of the Korea Organic Resources Recycling Association
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• v.23 no.4
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• pp.63-73
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• 2015

This study was carried out to evaluate the change of heating value of cow manure by applying pre-treatment process. Three types of treatment precess; Composting, Dry anaerobic digestion and Physical compression were applied as a pre-treatment method. Composting and anaerobic digestion of cow manure were cause of caloric value reduction of the cow manure. The heating value of cured compost was 5% lower than that of initial composting material. The heating value of dry anaerobic digestion residue was 25.7% lower than that of fresh cow manure. By physical compression of cow manure, heating value and VS/TS ratio (Volatile solids/Total solids ratio) of compressed cow manure were higher than that of fresh cow manure. On the other hand, heating value and VS/TS ratio of leachate generated by compression process were lower than those of fresh cow manure.

• Journal of Institute of Control, Robotics and Systems
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• v.14 no.6
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• pp.543-547
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• 2008

In the paper, we develop the ultrasonic bonding technique for LCD driver chips having small size and high pin-density. In general, the mounting technology for LCD driver ICs is a thermo-compression method utilizing the ACF (An-isotropic Conductive Film). The major drawback of the conventional approach is the long process time. It will be shown that the conventional ACF method based on thermo-compression can be remarkably enhanced by employing the ultrasonic bonding technique in terms of bonding time. The proposed approach is to apply the ultrasonic energy together with the thermo-compression methodology for the ACF bonding process. To this end, we design a bonding head that enables pre-heating, pressure and ultrasonic excitation. Through the bonding experiments mainly with LCD driver ICs, we present the procedures to select the best combination of process parameters with analysis. We investigate the effects of bonding pressure, bonding time, pre-heating temperature before bonding, and the power level of ultrasonic energy. The addition of ultrasonic excitation to the thermo-compression method reduces the pre-heating temperature and the bonding process time while keeping the quality bonding between the LCD pad and the driver IC. The proposed concept will be verified and demonstrated with experimental results.

• International Journal of Highway Engineering
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• v.18 no.2
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• pp.73-82
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• 2016

PURPOSES: The national highways and expressways in Korea constitute a total length of 17,951 km. Of this total length of pavement, the asphalt pavement has significantly deteriorated, having been in service for over 10 years. Currently, hot in-place recycling (HIR) is used as the rehabilitation method for the distressed asphalt pavement. The deteriorated pavement becomes over-heated, however, owing to uncontrolled heating capacity during the pre-heating process of HIR in the field. METHODS: In order to determine the appropriate heating method and capacity of the pre-heater at the HIR process, the heating temperature of asphalt pavement is numerically simulated with the finite element software ABAQUS. Furthermore, the heating transfer effects are simulated in order to determine the inner temperature as a function of the heating system (IR and wire). This temperature is ascertained at $300^{\circ}C$, $400^{\circ}C$, $500^{\circ}C$, $600^{\circ}C$, $700^{\circ}C$, and $800^{\circ}C$ from a slab asphalt specimen prepared in the laboratory. The inner temperature of this specimen is measured at the surface and five different depths (1 cm, 2 cm, 3 cm, 4 cm, and 5 cm) by using a data logger. RESULTS: The numerical simulation results of the asphalt pavement heating temperature indicate that this temperature is extremely sensitive to increases in the heating temperature. Moreover, after 10 min of heating, the pavement temperature is 36%~38% and 8%~10% of the target temperature at depths of 25 mm and 50 mm, respectively, from the surface. Therefore, in order to achieve the target temperature at a depth of 50 mm in the slab asphalt specimen, greater heating is required of the IR system compared to that of the gas. CONCLUSIONS : Numerical simulation, via the finite element method, can be readily used to analyze the appropriate heating method and theoretical basis of the HIR method. The IR system would provide the best heating method and capacity of HIR heating processes in the field.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.19 no.4
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• pp.52-57
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• 2020

The frequency of the manufacturing and modification of automotive press dies via overlay welding has recently increased, but the welding quality depends on the operator skills and the working conditions. Therefore, this study presents a way to improve the overlay welding quality regardless of the operator skills. Three welding conditions with different pre- and post-heating treatments were tested on some specimens; the weld surface quality was analyzed by examining the cutting face. The results demonstrated the best quality of the weld surface that was heated before and after the welding.

• Journal of Nutrition and Health
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• v.36 no.10
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• pp.1071-1082
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• 2003

The objective of this study was to evaluate and improve the microbiological quality of HACCP application in school foodservice operations. The microbiological quality of foods and utensils were evaluated two times at each critical control point (CCP) with 3M petrifilm in five Daegu elementary schools. Two processes were evaluated: Heating process and after-heating process. The CCPs of the heating process were receiving, cooking and serving temperatures. The CCPs of the after-heating process were personal hygiene, cross contamination avoidance and serving temperature. After the first experiment, 31 employees of five schools were classroom educated, trained on-site, and pre- and post-tested on HACCP-based sanitation with the goal of improving the microbiological quality of the foodservice. Scores representing knowledge of holding, thawing, washing, food temperature, sanitizing and food-borne illness increased after education. In the heating process, internal food temperatures in the first and second experiments were higher than 74$^{\circ}C$, the holding temperature in the first experiment was less than 6$0^{\circ}C$. In the second experiment, the serving temperature improved to a satisfactory level. The microbiological quality in the second experiment improved by decreasing the time from cooking to serving. In the after-heating process, the ingredients were boiled before being cut in the first experiment. In the second experiment, ingredients were cut before being boiled, improving microbiological quality. Also in the second experiment, cooking just before serving food improved its microbiological quality through time-temperature control. These results strongly suggest it is essential to measure microbiological quality regularly and to educate employees on HACCP continuously, especially time-temperature control and cross contamination avoidance in order to improve foodservice quality.

• Corrosion Science and Technology
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• v.20 no.2
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• pp.69-76
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• 2021

In this work, we have performed a corrosion failure analysis of a leaking tube connected to an upper header of a condensate pre-heater in a heat recovery steam generator. It was revealed that the leakage position in the tube was the location where the materials were easily vulnerable due to tensile residual stresses induced by the material manufacturing process and welding process. In addition to an imbalance in the module induced by temperature difference during operation of the pre-heater, the weight of the modules and thermal fatigue provoked a type of stress of tensile-tensile fatigue on the tube. Thus, the leakage position of the pre-heater was exposed to the tensile stress on the inner surface of the tube facing the gas, which rendered the unstable oxide layer susceptible to corrosion and the formation of pits on the water side. The cracks propagated along with the degraded microstructure in a transgranular cracking mode under fatigue loading and finally resulted in water leakage.

• Journal of Biomedical Engineering Research
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• v.43 no.4
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• pp.219-229
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• 2022

In this study, we propose a miniaturized micro-ceramic heater device. After screen-printing a silver paste between pre-sintered two aluminum oxide plates to integrate a heating circuit, the device was fabricated through a low-temperature sintering process. In order to configure the optimal heating circuit integration condition, the output current evaluation and heating test were performed according to the number of screen prints of the silver paste at various voltages. A silver paste-based heating circuit printed with a line width of 200 ㎛ and a thickness of 60 ㎛ was successfully integrated on a pre-sintered alumina substrate through a low-temperature sintering process. In the case of the 5 times printed device, the thermal response showed a response rate of 18.19 ℃/sec. To demonstrate feasibility of the proposed device in the medical field, such as bio-tissue suturing and hemostasis, a voltage was applied to pig tissue in the device to test tissue change due to heat generated from the device. These results show the possibility that the proposed small ceramic heater could be used in the medical field based on its excellent temperature response.