• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.05a
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• pp.94-97
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• 2009

Cast defect in large steel ingots are estimated in quality and compared each other cast conditions on simulation results by now. The cast defects, micro-crack, shrinkage, pin hole which are predictable in simulation with a reasonable accuracy. In this study, 15 ton steel ingot casting was simulated for solidification model and cast defect prediction. And the real cast was carried out in a foundry for the compeer to the simulation results, the cast defect prediction. Also, the quantity of predicted defect was tried to measuring with the defect mach counting for the various simulated cast conditions. The defect quantity work was used to find the optimized cast condition in DOE(design of experiment) procedure.

• Transactions of Materials Processing
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• v.19 no.3
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• pp.173-178
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• 2010

A die cast impeller blade has been developed in the effort on cost reduction in marine equipment industry. The purpose of this work is to optimize the die casting process using Taguchi's design of experiment for minimizing the internal defect of the die cast impeller blade. The experiments were preformed using the numerical simulation based on the L18 orthogonal array. As a results, the internal defect size of the die cast impeller blade for optimal design was controlled less than 1mm.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.05a
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• pp.91-93
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• 2009

A large steel ingot needs to be larger and larger in size and an ultra high clean, no defect in quality with a low hot top ratio for the resent heavy industry. The demands are very difficult to achieve simultaneously because of their contradictive effect to each other in results. In this study, 30ton steel ingot was cast in a foundry with an optimized design parameter of cast mold and cast process conditions for the low hot top ratio, 12%. The cast ingot was analyzed in macro defect, segregations, and cleanness. No macro defect was founded in central surface of the ingot. The degree of segregation and cleanness are in the controlled range with a sound quality.

• Journal of Korea Foundry Society
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• v.22 no.6
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• pp.309-314
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• 2002

The effect of mold density and evacuation on surface defect of high chromium cast iron upon EPC process was investigated. Under evacuation of $0.1{\sim}0.3$ atm, surface defects were carbon defect, burn on and misrun. Carbon defect was augmented by increasing mold density from 0.011 g/$cm^3$ to 0.03 g/$cm^3$ under evacuation of $0.1{\sim}0.3$ atm, but carbon defect was decreased by increasing evacuation from 0.1 to 0.3 atm. Burn-on wasn't found under evacuation of 0.1 atm regardless of mold density, but burn-on was augmented by increasing evacuation from 0.2 to 0.3 atm and decreased by reducing mold density. Misrun was only found under 0.1 atm evacuation and 0.011 g/$cm^3$ mold density.

• Journal of the Korean Society for Heat Treatment
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• v.12 no.1
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• pp.40-46
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• 1999

Rotary bending fatigue tests were carried out to investigate the improvement of fatigue limit in annealed and austempered spheroidal graphite cast iron. Main results obtained are as follows. (1) The tensile strength(hardness) of Series C is higher than that of Series B, and fatigue limits are 245MPa in Series C, 230MPa in Series B and 195MPa in Series A, respectively. (2) The fatigue limits of Series B and Series A are mainly governed by the resistance to fatigue crack initiation. Whereas, the fatigue limit of Series C is governed by the resistance to fatigue crack initiation and growth. The defect size and the resistance to crack initiation and growth should be considered to clarify the fatigue properties in spheroidal graphite cast iron. (3) Improvement of fatigue limit by half-austempering is more reasonable than that of full-austempering treatment in multi defective materials as spheroidal graphite cast iron.

• Journal of Ocean Engineering and Technology
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• v.23 no.2
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• pp.81-86
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• 2009

Infrared thermography was used to determine the location, size, and depth of defects under the surface of M.C nylon. Defects were created in a specimen by back-drilling circular holes. These defects were located at the maximum temperature difference that occurred. The sizes of the defects could be calculated by means of the full width at half of the maximum temperature difference. The depth of a defect could be calculated by the peak time and the maximum temperature difference. The maximum temperature difference between a defect and normal part was decreased with the depth of the defect. And the peak time also slowly appeared with the depth of the defect.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.65 no.11
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• pp.1937-1942
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• 2016

Unlike oil immersed transformers, cast-resin transformers have the solid insulator 'epoxy resin' in sealed structure. Therefore, they reveal a lot of limitations in checking aging conditions and predicting an accident. This study analyzed the characteristics of Cast-resin transformers by the measurement distance and measurement sensitivity with a corona defect sample, using antenna sensor. Therefore, the experiment has proven that the antenna sensor-based measurement method proposed in this study is able to detect the insulation defect location of the cast-resin transformer, unlike conventional measurement methods. It is expected that the result of this study will be used to develop a new type of measuring method in order to measure insulation defects and to use in safety inspection of domestic cast-resin transformers.

• Journal of Mechanical Science and Technology
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• v.14 no.10
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• pp.1021-1027
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• 2000

In this study, fatigue tests were performed to examine the effects of micro drill hole on fatigue limit of as cast and austempered ductile cast iron (ADI) using the rotary bending fatigue tester. As results, micro drill holes ($diameter{\leq}0.4mm$) did not influence the fatigue limit of ADI, compared to annealed ductile cast iron; the critical defect size of crack initiation, in ADI was larger than as cast. If the ${\sqrt{area}}$ of micro drill hole and graphite nodule in ADI are comparable, crack initiates at the graphite nodule. When the ruggedness developes through austempering treatment process, microstructure on crack initiation at micro drill hole is tougher than that of as cast ductile cast iron.

• Journal of the Korean Society for Precision Engineering
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• v.14 no.9
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• pp.30-36
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• 1997

In this study, the development of an aluminum forged piston was tried to substitute the cast piston, in which there were internal defects such as blow hole and shrink pipe. A gasoline engine piston was chosen as an example for developing the forged piston. Before aluminum forging, model, material (plasticine) test was carried out to investigate the forgeability and internal flow pattern of the forged piston at room temperature. From the result of model material test, an aluminum piston to be forged was redesigned. The aluminum pistion was forged in hot process. The quality of a forged piston was compared with that of a cast piston in the point of mechanical properties, internal defect and microstructure. It was proved that the forged piston was superior to the cast piston.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.35 no.6
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• pp.594-602
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• 2022

Cast-resin transformers are widely installed in various electrical power systems because of their low operating cost and low influence on external environmental factors. However, when they have an internal defect during the manufacturing process or operation, a partial discharge (PD) occurs, and eventually destroys the insulation. In this paper, a Rogowski-type PD sensor was studied to replace commercial PD sensors used for the insulation diagnosis of power apparatus. The proposed PD sensor was manufactured with four different types of PCB-based winding structures, and it was analyzed in terms of the detection characteristics for standard calibration pulses and the changes of the output voltage according to the distance. The output increased linearly in accordance with the applied discharge amount. It was confirmed that the hexagon structure sensor had the highest sensitivity, because the winding cross-sectional area of the sensor was larger than others. In addition, as the distance from the defect increased, the output voltage of the sensors decreased by 7.32% on average. It was also confirmed that the attenuation rate according to the distance decreased as the input discharge amount increased. For the application of this new type sensor, PD electrode system was designed to simulate the void defect. Waveforms and PRPD patterns measured by the proposed PD sensors at DIV and 120% of DIV were the same as the results measured by MPD 600 based on IEC 60270. The proposed PD sensors can be installed on the inner wall of the transformer tank by coating its surfaces with a non-conductive material; therefore, it is possible to detect internal defects more effectively at a closer distance from the defect than the conventional sensors.