• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.15 no.2
• /
• pp.133-140
• /
• 2002

This paper aims to investigate the effect of silicone oils as processing agent affecting the loss and recovery of hydrophobicity. The recovery of hydrophobicity was evaluated by the measurement of the surface electrical resistivity and the contact angle on the SIR surface. Two kinds of silicone oils (1 and 2) having different molecular weight were selected under a consideration of hydrophobicity and processability. SIR specimens were exposed to corona discharges in air and the specimens were analyzed with contact angle and surface resistance measurements. It was observed that the contact angle and the surface resistivity of SIR increase gradually with testing time. The fast recovery of hydrophobicity of SIR, expressed by the increment of contact angle and surface resistivity, was showed in SIR2 containing silicone oil 2.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 1999.11a
• /
• pp.501-504
• /
• 1999

The polymer insulators which are installed on outdoor have a great advantage than porcelain and 71ass, due to suppression of leakage current, light weight, low cost, etc. It needs variable evaluation methods for application of these insulators on service. The analysis of measuring leakage current is useful for ageing diagnosis because of monitoring in real-time. In this paper, we look over the recovery of hydrophobicity of silicone rubber in mini salt-fog chamber with leakage current monitoring. also, we understand the relation of between hydrophobicity and leakage current and discuss on method of leakage current monitoring.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2005.07a
• /
• pp.288-289
• /
• 2005

As high temperature superconductor applications became a reality due to increase in coated conductor performance, it is important to understand their stability behavior to design safe electrical power systems. We have experimentally studied the dependence of quench and recovery characteristics of coated conductors on the amplitude of current and duration time. The sample used in the present study is stabilized with stainless steel. Stability tests of 3 cm long sample were performed in a liquid nitrogen bath cooling condition by applying a short period over current pulses for 50 and 100 ms, with amplitude up to ~ 6 times of the critical current. The transport current that follows before and after the current pulse was fixed about ~85% the critical current. We analyzed the quench recovery using the current voltage characteristic.

• Transactions of Materials Processing
• /
• v.20 no.6
• /
• pp.456-460
• /
• 2011

A major source of difficulty in die design for high strength steel is the high level of elastic recovery during unloading. The degree of elastic recovery is affected by factors such as material strength, bending angle, punch's corner radius and sheet thickness. Finite Element Method was used in the present work to quantitatively analyze the elastic recovery for various combinations of these parameters. In some cases elastic recovery happened in reverse direction. This phenomenon, which we call spring-go, was explained via changes in stress distribution in the panel occurring in the forming process.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.25 no.10
• /
• pp.529-533
• /
• 2013

Heat-recovery ventilators are being adopted in most newly built apartment houses for energy reduction and indoor environment improvement. In winter, however, the dew condensation resulting from the difference between the indoor and outdoor temperatures may reduce the ventilator's performance and threaten the health of indoor residents. This study analyzes the occurrence of dew condensation according to the ventilator's operational conditions and the changes of temperature and products. The experimental results show that condensations is formed at $26^{\circ}C$ and 60%R.H, which is an unfavorable climatic condition, and when the damper is not closed tightly. Therefore it is important to ensure damper performance to prevent back flow.

• Geomechanics and Engineering
• /
• v.4 no.2
• /
• pp.121-134
• /
• 2012

The paper presents the results of identification, monotonous and cyclic triaxial tests on a potentially liquefiable soil from the Guadeloupe island. The material is a very soft clayey soil whose susceptibility to liquefaction is not clear when referring to index properties such as grain size distribution, plasticity, etc. The classifications found in the literature indicate that the material has rather a "clay-like" behaviour, i.e., is not very susceptible to liquefaction, but its properties are very close to the threshold values given by the authors. Cyclic triaxial tests carried out on the material under different conditions show that liquefaction is possible for a relatively important level of cyclic deviator or number of cycles. The second part of the paper is devoted to the study of the recovery of the soil after liquefaction and possibly reconsolidation. For the specimens tested without reconsolidation, that simulated the soil immediately after an earthquake, the recovery is nearly non-existent but the drop in pore pressure during extension results in a small available strength. On the contrary, after reconsolidation, the increase in strength of the liquefied specimens is quite large, compared to the initial state, but with unchanged failure envelopes.

• Korean Journal of Materials Research
• /
• v.19 no.12
• /
• pp.661-666
• /
• 2009

Froth flotation has been carried out in order to produce roasting-molybdenite concentrate from molybdenite ore in the Shin-yeomi mine. In our study, roasting-molybdenite (Mo 0.43%) from Shin-yeomi mine was recovered by varying the conditions of regrinding time, dosage of collector and alkalinity. Liberation and flotation efficiency more were effective at regrinding time of six minutes than at single grinding. Mo recovery curves increased considerably as dosage of kerosene increased, whereas Mo grade curves decreased gradually. The separation efficiency of molybdenite was effective when the dosage of collector (kerosene) was adjusted to 300 g/t. The molybdenite concentrate was agglomerated in the range of pH 5-7 and its separation efficiency increased to pH 9-10. The concentrate of 49.5% Mo grade ($MoS_2$, 82.6%) with 81.5% recovery from Shin-yeomi molybdenite ores was obtained under conditions of 20% pulp concentration, 300 g/t kerosene 325 g/t frother (AF65), 2.5 kg/t depressant ($Na_2SiO_3$), pH 9-10 and four cleaning times. In the future, a trial run that can separate up to 50% Mo grade from Shin-yeomi molybdenite ores will be performed.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.13 no.7
• /
• pp.636-641
• /
• 2000

The purpose of this study is assessing the characteristics of surface aging and recovery of hydrophobicity for silicone rubber which takes a great interest as outdoor insulation recently subjected to the combined stressed of salt fog and AC power. The methods for assessing are contact angle ATR-FRIR, AFM and XRD. In addition salt fog method is adopted as the artificial contamination experiment and AC power is applied 24 hour on and 24 hour off repeatedly for 5 cycles. The results suggest that degraded surface was more rough than virgin but was restored water repellency through the off cycle. It was due to not only the formation of fractal surface but also maintenance of hydrophobic surface by diffusion of low molecular oil. Although surface recovers initial hydropohbicity there are possibilities of decreasing electrical performance due to irreversable changes such as depolymerization of surface and loss of filler particles. This fact is confirmed by surface conductivity measurement showing that the degradation is significant and the recovery of hydrophobicity is imperfect as the energized cycle increases.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2007.11a
• /
• pp.474-475
• /
• 2007

Wire electrical explosion(WEE) has been used for the production of fine metal particles. In WEE, electrical powder was stored and compressed into capacitor and released to produce fine particles through evaporation and condensation. In this study, the effect of applied voltage on the size of copper powders was investigated. High tension was added up to the explosion device by dividing 4 steps. At voltages lower than 5.2 kV, the fraction of powders finer than $44{\mu}m$ was almost negligible. The effectiveness of explosion increased sharply with increased voltage over 5.8 kV. At the highest voltage of 6.4 kV, more than 80% of explosion products were finer than $44{\mu}m$.

• Resources Recycling
• /
• v.30 no.3
• /
• pp.70-81
• /
• 2021

This study evaluated the recyclability of waste plastics in used coffee capsules disposed of as municipal waste. For recycling, a new material separation process was developed to remove the coffee grounds through primary crushing, washing, sieving, and secondary crushing, followed by corona discharge electrostatic separation. Furthermore, for the under 10 mm size fraction samples, the aluminum removal and the plastic recovery were 95.4% and 98.3%, respectively, under optimal conditions. In addition, for the 15 mm fraction samples, the aluminum removal and the plastic recovery were 91.3% and 97.2%, respectively. To evaluate the recyclability of the separated waste plastics, the samples were pelleted, and their material properties were analyzed. No hazardous substances were detected, and the results were similar to those for homo-PP. Therefore, it was confirmed tha t sufficient functiona lity existed a s recycled PP. However, owing to the da rk color of the pellets, limited applications to black or dark products are expected.