• Journal of Technologic Dentistry
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• v.29 no.2
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• pp.129-140
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• 2007

The purpose of this study was to evaluate the titanium castability (internal porosity) between pressure type casting machine & centrifugal casting machine with air-vent or not. Internal porosity is a well-known problem in dental titanium casting, resulting in inferior mechanical properties of dental restorations. To evaluate the castability, the square plate was chosen. 40 plate patterns($20{\times}20{\times}1.8mm$)were attached to funnel-shaped sprue. Then 20 plate patterns were attached air-vent. They were invested in titanium investment material and cast in a pressure type casting machine(20castings) and centrifugal casting machine(20castings). Each group were divided with air-vent(10castings) or not(10castings). The titanium castings were evaluated by radiographic photograph for the location of the internal porosities. The percentage porosity of each specimen was determined using standardized digital radiographs. The results were analyzed with analysis of variance and t-test for paired comparison between two groups.

• Nuclear Engineering and Technology
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• v.54 no.2
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• pp.709-731
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• 2022

Loss of fracture resistance due to thermal aging degradation is a potential limiting factor affecting the long-term (80+ year) viability of nuclear reactors. To evaluate the effects of decades of aging in a practical time frame, accelerated aging must be employed prior to mechanical characterization. In this study, a variety of chemically and microstructurally diverse austenitic stainless steels were aged between 0 and 30,000 h at 290-400 ℃ to simulate 0-80+ years of operation. Over 600 static fracture tests were carried out between room temperature and 400 ℃. The results presented include selected J-R curves of each material as well as K_0.2mm fracture toughness values mapped against aging condition and ferrite content in order to display any trends related to those variables. Results regarding differences in processing, optimal ferrite content under light aging, and the relationship between test temperature and Mo content were observed. Overall, it was found that both the ferrite volume fraction and molybdenum content had significant effects on thermal degradation susceptibility. It was determined that materials with >25 vol% ferrite are unlikely to be viable for 80 years, particularly if they have high Mo contents (>2 wt%), while materials less than 15 vol% ferrite are viable regardless of Mo content.

• Journal of Korea Foundry Society
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• v.41 no.2
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• pp.127-131
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• 2021

Based on its good compatibility with high-temperature environments, the Ti-48Al-2Cr-2Nb alloy is used for high-temperature materials of industrial equipment. In this study, a Ti-48Al-2Cr-2Nb alloy turbocharger turbine wheel was fabricated by a vacuum centrifugal casting method. The conditions that prevent misrun defects of the turbocharger turbine wheel blade from centrifugal casting using alumina molds were investigated. The microstructure of the alloy prepared by vacuum centrifugal casting was studied by means of optical microscopy (OM), with a micro-Vickers hardness analyzer (HV), by X-ray diffraction (XRD) and by SEM-EDS. The HV and SEM-EDS examinations of the as-cast Ti-48Al-2Cr-2Nb alloy showed that the thickness of the oxide layer (α-case) was typically less than 50 ㎛. At a high preheating temperature of 1,100℃, a moderate RPM of 260, and with an alumina mold with a large gate size, there were almost no misrun defects. Therefore, it was confirmed that a Ti-48Al-2Cr-2Nb alloy turbocharger turbine wheel with fewer misrun defects could be achieved through a high preheating temperature, a moderate RPM, a large gate size and an alumina mold to suppress the formation of alpha-case components.

• Journal of Korea Foundry Society
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• v.14 no.6
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• pp.566-575
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• 1994

The effects of varying the pouring temperature and the die preheating temperature in producing centrifugally cast HP alloy modified with Nb was evaluated on the basis of the resultant macrostructure, microstructure and hardness of these castings. Increased die preheating temperatures and pouring temperatures resulted in an increase in the thickness of the columnar dendritic zone, the primary and secondary dendrite arm spacing and the thickness of the zone of porosity at the casting I.D.(inner diameter). Lower die preheating temperature and pouring temperatures result in increased grain fineness and an increased zone of equiaxed grains. A higher hardness was achieved toward the casting O.D.(outer diameter) compared to the casting I.D., attributable to alloy segregation toward the casting I.D. and segregation differences resulting from reduced solidification cooling rates toward the casting I.D. Also, a higher hardness was realized at the cold end of the casting attributed to a more uniform distribution of carbides.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.4
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• pp.179-185
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• 2004

Surface finish technology is highly demanded in the wide field of industry applications from ultra-precision parts to rough casting parts. Therefore, many kinds of surface finish technologies have been developed for each purpose. Because surface of a car's wheel cast is very rough it becomes the reason of the corrosion. This surface is coated to complement such problem but because surface is rough, the result of coating is not good and the coated metal peels off well. Therefore before the wheel is coated, it is necessary to grind the surface. In this study, we devised the plant to apply a barrel machining to improve the surface roughness and enhance the productivity. Also we could obtain the optimum barrel machining conditions for the proper surface roughness.

• Journal of Korea Foundry Society
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• v.11 no.6
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• pp.482-490
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• 1991

This study presents the wear characteristics of Ti alloys (Pure Ti, Ti-6Al-4V, Ti-5Al-2.5Sn) fabricated by centrifugal precision casting in an Ohara dental titanium casting machine. It was found that the hardness of the surface region is higher than that of the interior region. It is considered that the oxygen adsorption in the surface region during casting, leads to the interstitial solid solution hardening. Wear resistance incerases in the order of pure Ti, Ti-6Al-4V, Ti-5Al-2.5Sn alloys. The interior hardness value increases in the same order. The specific wear rate increases with applied load and increases monotonously with sliding speed. The Fe transfer from the counterpart material was observed on the worn surface of the Ti-5Al-2.5Sn alloy. Oxidative wear occurs at low sliding speeds and mechanical fracture wear occurs at high sliding speeds.

• Journal of Korea Foundry Society
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• v.36 no.6
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• pp.202-207
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• 2016

The effects of Fe and Si additions on the microstructures and mechanical properties of aluminum bronze have been investigated. In a bar-type specimen cast in a die mold, the addition of Fe promoted the dendritic solidification of the ${\alpha}$ phase. The hardness values increased slightly in the Fe-added specimen with heat treatment, while these values was increased significantly in the specimens with Si or with combined additions of Fe and Si. When a centrifugal casting bush with combined addition of Fe and Si was heat treated, the FeSi compound within the matrix was finely dispersed, and was observed to be the origin of cup-cone type conical dimple failure in the tensile fracture surface. The mechanical properties of the heat treated centrifugal casting bushes, whose nominal alloy compositions were (Cu-7.0Al-0.8Fe-3.0Si)wt%, exhibited tensile strength of $703-781N/mm^2$, elongation of 6.6-11.7% and hardness of Hv 222.6-249.2. These high values of strength and elongation were attributed to the strengthening of the matrix due to the combined addition of Fe and Si, and to precipitation of fine the FeSi compound.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.20 no.8
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• pp.1546-1552
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• 2016

In addition, because it uses preheating to dissolve an alloy in general, it is hard to regulate the appropriate melting temperature of the alloy and brewing time and shows the defect of the supplementation thing due to the super-heating. Once the alloy is molten and then most of the casting by attaching a sight glass or non-contact temperature sensor is suitable casting temperature the operator pressing a button to generate a centrifugal force to inject the molten alloy into a crucible in the casting ring. These results, and most of the cast temperature is too high or too low to generate a lot of casting defects do not get into a uniform cast body. In this paper, we developed a dental casting machine for high frequency using a single temperature sensor which can measure the actual temperature of the alloy than the temperature of the external non-contact measurement using a temperature sensor.

• Journal of the Korean institute of surface engineering
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• v.50 no.5
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• pp.386-391
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• 2017

Two kinds of steels whose compositions were Fe-34.4Cr-14.5Ni-2.5Mo-0.4W-0.4Mn-0.5Si-(0.009 or 0.35)S (wt.%) were centrifugally cast, and oxidized at $900^{\circ}C$ for 50-350 h in order to find the effect of sulfur on the high-temperature oxidation of Fe-34.4Cr-14.5Ni-2.5Mo-0.4W-0.4Mn-0.5Si-(0.009 or 0.35)S (wt.%) alloys. These alloys formed oxide scales that consisted primarily of $Cr_2O_3$ as the major oxide and $Cr_2MnO_4$ as the minor one through preferential oxidation of Cr and Mn. They additionally formed $SiO_2$ particles around the scale/alloy interface as well as inside the matrices. The high affinity of Mn with S led to the formation of scattered MnS inclusions particularly in the 0.35S-containing cast alloy. Sulfur was harmful to the oxidation resistance, because it deteriorated the scale/alloy adherence so as to accerelate the adherence and compactness of the formed scales.

• Journal of Korea Foundry Society
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• v.41 no.6
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• pp.550-557
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• 2021

With the advent of the fourth industrial revolution, the interest in the internet of things (IoT) in manufacturing is growing, even at foundries. There are several types of process data that can be automatically collected at a foundry, but considerable amounts of process data are still managed based on handwriting for reasons such as the limited functions of outdated production facilities and process design based on operator know-how. In particular, despite recognizing the importance of converting process data into big data, many companies have difficulty adopting these steps willingly due to the burden of system construction costs. In this study, the field applicability of IoT-based devices was examined by manufacturing devices and applying them directly to the site of a centrifugal foundry. For the centrifugal casting process, the temperature and humidity of the working site, the molten metal temperature, and mold rotation speed were selected as process parameters to be collected. The sensors were selected in consideration of the detailed product specifications and cost required for each process parameter, and the circuit was configured using a NodeMCU board capable of wireless communication for IoT-based devices. After designing the circuit, PCB boards were prepared for each parameter, and each device was installed on site considering the working environment. After the on-site installation process, it was confirmed that the level of satisfaction with the safety of the workers and the efficiency of process management increased. Also, it is expected that it will be possible to link process data and quality data in the future, if process parameters are continuously collected. The IoT-based device designed in this study has adequate reliability at a low cast, meaning that the application of this technique can be considered as a cornerstone of data collecting at foundries.