• Journal of the Korean Society of Safety
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• v.24 no.1
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• pp.1-6
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• 2009

In machining of ceramic materials, they are very difficult-to cut materials because of there high strength and hardness. Machining of ceramics are characterized by cracking and brittle fracture. Generally, ceramics are machined using conventional method such as grinding and polishing. However these processes are generally costly and have low MRR(material removal rate). This paper focuses on machinability evaluation of machinable ceramics for products with CNC machining center. Thus, in this paper, experiment applying cutting parameters is performed based on experimental design method. A design and analysis of experiments is conducted to study the effects of these parameters on the surface roughness by using the S/N ratio, analysis of ANOVA, and F-test. And multiple linear regression analysis is applied to compare experimental with predicted data in consideration of surface roughness. Cutting parameters, namely, feed, cutting speed and depth of cut are used to accomplish purpose of this paper. Required experiments are performed, and the results are investigated.

• Korean Journal of Metals and Materials
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• v.49 no.12
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• pp.989-994
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• 2011

Samples with compositions of 80 wt% Mg-14 wt% Ni-6 wt% $Fe_2O_3$ (named $Mg-Ni-Fe_2O_3$), and 78 wt% Mg-14 wt% Ni-6 wt% $Fe_2O_3-2$ wt% CNT (named $Mg-Ni-Fe_2O_3-CNT$ ) were prepared by reactive mechanical grinding. Hydriding and dehydriding properties and effects of CNT addition on the hydriding and dehydriding rates of $Mg-Ni-Fe_2O_3$ were then investigated. Activation of the $Mg-14Ni-6Fe_2O_3$ sample was completed after three hydriding (under 12 bar $H_2$)-dehydriding (under 1.0 bar $H_2$) cycles at 573 K. The addition of CNT to the $Mg-14Ni-6Fe_2O_3$ sample made the activation process unnecessary, with a small decrease in the hydrogen-storage capacity.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.21 no.3
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• pp.22-28
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• 2022

In the semiconductor and display component industries, the use of ceramic materials, which are high-strength materials, is increasing for ensuring durability and wear resistance. Among them, alumina materials are used increasingly. Alumina materials are extremely difficult to process because of their high strength; as such, research and development in the area of mineral material processing is being promoted actively to improve their processing. In this study, the processability of an electrodeposition tool is investigated using the electrodeposition method to smoothly process alumina materials. Furthermore, processing is conducted under various processing conditions, such as spindle speed, feed speed, and depth of cut. In addition, the processing characteristics of the workpiece are analyzed based on the tooling.

• The Journal of Korean Academy of Prosthodontics
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• v.62 no.2
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• pp.113-122
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• 2024

The gradual teeth wear with age is a natural phenomenon, but excessive wear beyond physiological levels can lead to vertical dimension loss, occlusal imbalance, temporomandibular joint disorders, and periodontal disease. In such cases, prosthodontic restoration becomes necessary emphasizing the importance of appropriate vertical dimension increase and stable occlusion in central relation (CR). In this case, a 74-year-old patient with clenching and grinding habit had severe teeth wear and after assessing interocclusal distance, wear degree, pronunciation, and facial profile, it was decided to perform full-mouth fixed prosthesis restoration with a 4 mm vertical dimension increase. And the significantly displaced Maximum Intercuspal Position (MICP) caused by parafunctional movements was re-established as a stable mutually protective occlusal relationship at centric relation and after a successful 4 months adaptation to provisional restorations, the final prosthesis was fabricated. During 4months of observation periods, stable occlusion in central relation and mutual protection occlusal relationships were maintained and the patient was satisfied with function and aesthetics, leading to this report.

• Journal of the Korean Recycled Construction Resources Institute
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• v.6 no.2
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• pp.103-111
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• 2011

This study examined rheological properties of blast furnace slag and ash paste that are widely used as cement concrete for mineral admixture in current. In that way rheological properties of the paste of mineral admixture only was examined. The result of this study were as follow: In order to analyze that the rheological properties of the mineral admixture only, fine particles were produced with grinding machine to 3 particle sizes. These powders in general from the result of comparison with and analysis of rheological properties and the coefficient n and De values. The result that ash powder was higher in plastic viscosity and yield stress than Slag powder, and with the same n value, ash powder showed higher plastic viscosity and yield stress than Slag powder. But Slag powder in particle size distribution showed a sensitive tendency on changing in rheological properties.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.53-58
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• 2002

Electrical insulation and mechanical properties of the plasma sprayed oxide ceramic coatings were studied before and after the sealing treatment of the ceramic coatings. Plasma sprayed A1$_2$O$_3$-TiO$_2$ coating as the reference coating was sealed using three commercial sealants based on polymer. Penetration depth of the sealants to the ceramic coating was evaluated directly from the optical microscope using a fluorescent dye. It is estimated that the penetration depth of the sealants to the ceramic coating is from 0.2 to 0.5 mm depending on the sealants used. The preliminary test results with a DC puncture tester imply that the dielectric breakdown voltage mechanism of plasma sprayed ceramic coatings has been determined to be a corona mechanism. Dielectric breakdown voltage of the as-sprayed and as-ground samples have shown a linear trend with regard to the thickness showing an average dielectric strength of 20 kV/mm for the thickness scale studied. It is also shown that grinding the coating before sealing and adding fluorescent dye do not agent the penetration depth of sealants. All of the microhardness, two-body abrasive wear resistance, bond strength, and surface roughness of the ceramic coating after the sealing treatment are improved. The extent of improvement is different from the sealants used. However, three-point bending stress of the ceramic coating after the sealing treatment is decreased. This is attributed to the reduced micro-crack toughening effect since the cracks propagate easily through the lamellar of the coating without crack deflection and/or branching after the sealing treatment.

• Journal of the Korean Ceramic Society
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• v.40 no.7
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• pp.620-624
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• 2003

LiCo$_{y}$Mn$_{2-y}$O$_4$ samples were synthesized by calcining a mixture of LiOH.$H_2O$, MnO$_2$ (CMD) and CoCO$_3$ calcining at 40$0^{\circ}C$ for 10 h and then calcining twice at 75$0^{\circ}C$ for 24 h in air with intermediate grinding. All the synthesized samples exhibited XRD patterns for the cubic spinel phase with a space group Fd(equation omitted)m. The electrochemical cells were charged and discharged for 30 cycles at a current density 600 $mutextrm{A}$/$\textrm{cm}^2$ between 3.5 and 4.3 V. As the value of y increases, the size of particles becomes more homogeneous. The first discharge capacity decreases as the value of y increases, its value for y=0.00 being 92.8 mAh/g. The LiMn$_2$O$_4$ exhibits much better cycling performance than that reported earlier. The cycling performance increases as the value of y increases. The efficiency of discharge capacity is 98.9％ for y=0.30. The larger lattice parameter for the smaller value of y is related to the larger discharge capacity. The more quantity of the intercalated and the deintercalated Li in the sample with the larger discharge capacity brings about the larger capacity fading rate.ate.

• Resources Recycling
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• v.33 no.2
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• pp.37-45
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• 2024

Molybdenum is used in various industries because of its high heat and corrosion resistance. It was selected as a critical mineral in Korea. However, there have been recent challenges in production because of the increased depth and decreased grade of molybdenum veins. Consequently, it is necessary to enhance the effectiveness of the molybdenum beneficiation process. In this study, a basic evaluation of beneficiation characteristics was conducted to enhance the effectiveness of the domestic molybdenum ore beneficiation process. The properties of the beneficiation process were assessed using mineralogical analysis, work index, and flotation kinetics. The results revealed that the allowable particle size of the molybdenum ore for liberation was ~100 ㎛. In addition, the work index was calculated to be 14.57 kWh/t. The operating conditions in the flotation units were achieved by determining the optimal flotation time for each process based on flotation kinetics. Finally, the characteristics of molybdenum ore beneficiation provided in this study can be utilized to diagnose the grinding and flotation processes of large-scale molybdenum beneficiation plants.

• Journal of the Korean Society of Industry Convergence
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• v.25 no.5
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• pp.799-810
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• 2022

Welding work is a production work method widely used throughout the industry, and various types of welding technologies exist. In addition, many methods are being studied to automate these welding operations using robots, but in the ship manufacturing field, welding such as painting, cutting, and grinding is also the most common operation, but the manual operation ratio is higher than in other industries. Such a high manual labor ratio in the field of ship manufacturing not only causes quality problems and production delays according to the skill of workers, but also causes problems in the supply and demand of manpower. Therefore, this paper analyzed the reason why the automation rate is low in welding work at ship manufacturing sites compared to other industries, and analyzed the production process and field environment for small and medium-sized ship manufacturing companies that repeatedly manufactured with a small quantity production method. Based on the analysis results, it is intended to propose a robot system that can easily move between workplaces and secure uniform welding quality and productivity by collaborating simple welding tasks with humans. Finally, the simulation environment is constructed and analyzed to secure the suitability of robot system application to current production site environment, work process, and productivity, rather than to develop and apply the proposed robot system. Through such pre-simulation and robot system suitability analysis, it is expected to reduce trial and error that may occur in actual field installation and operation, and to improve the possibility of robot application and positive perception of robot system at ship manufacturing sites.

• Journal of Conservation Science
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• v.21
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• pp.5-20
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• 2007

The stone artifacts in Bronze age from the Hyocheon sites in the Gwangju, Korea were studied on the basis of material characteristics and provenance presumptions. The use and rock names of the artifacts are a stone shovel by andesite, the stone grinding pestle by pyrophyllite, the stone sickle by schist and four stone semifinished artifacts by slates. Andesitic stone shovel could be observed easily around the Hyocheon relic site. But, rocks of the stone grinding pestle, the stone sickle, the stone arrowhead and the stone semifinished artifacts could be confirmed typical occurrences of the all kinds of rocks around the Hwasun coal mine area above 10km from the site. These are made the coupled samples with each stone artifact to the same kinds of raw material rocks based on analysis of the lithology and geochemistry. As a result a geochemical evolution trends of both a stone artifact and the rock showed very similar patterns based on normalization using the behavior, enrichment, compatibility and incompatibility of the elements. Therefore, the source rock of the stone shovel was convey from Mudeung mountain possible interpreted that the domestic-type artifacts are distributed in the vicinity of the Hyocheon site. On the other hand, the stone grinding pestle, the stone sickle, the stone arrowhead and the stone semifinished artifacts were convey from the Hwasun coal mine area possible foreign-type stone artifacts interpreted that the source rocks. Consequently, in the foreign-type stone artifacts are should archaeologic research which it can examine various possibilities clearly that the possibility to coming the introduction with the mankind migration, diffusion to dealings of tribe, the captured enemy equipment through the war and the trade with the behavior of the materials.