• Journal of Technologic Dentistry
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• v.42 no.2
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• pp.113-120
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• 2020

Purpose: This study is to compare and analyze the shrinkage of the specimen after UV irradiation of UV cured resin at 5, 15, and 30 minutes. Methods: A cylindrical UV cured specimen was produced using a stainless steel mold. UV cured resin specimens were prepared in three groups: 5 minutes cured (5M), 15 minutes cured (15M), and 30 minutes cured (30M). The measurement was made in total 3rd. The measurement was made in total 3rd. The primary measurement was made after 24 hours using a digital measuring instrument. The 2nd and 3rd measurements were deposited in a constant temperature water bath and the shrinkage was measured. The measured data was calculated by referring to the ASTM C326 linear measurement calculation method. T-test and One-way ANOVA were performed to test the significance between groups. The post-test was conducted with Tukey (α=0.05). Results: When the inner diameter and the outer diameter of the three groups not placed in the water bath were compared and analyzed, the contraction was the smallest at 6.8% in the 5M group, and the contraction was the largest at 7.3% in the 30M group. In the outer diameter, the contraction of the 5M group was the smallest at 3.5%, and the contraction of the 30M group was the largest at 4.5%. Shrinkage decreased in all three groups immersed in a water bath for 3-7 days. Conclusion: In the UV cured resin specimen, the shrinkage increased as the amount of UV irradiation increased.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.14 no.3
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• pp.9-14
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• 2015

The Direct Metal Tooling (DMT) process is a kind of additive manufacturing processes, which is developed using various commercial steel powders, such as P20, P21, SUS420, and other non-ferrous metal powders. The DMT process is a versatile process that can be applied to various fields, such as the molding industry, the medical industry, and the defense industry. Among them, the application of the DMT process to the molding industry is one of its most attractive and practical applications, since the conformal cooling channel cores of injection molds can be fabricated at a slightly expensive cost by using the hybrid fabrication method of DMT technology compared with parts fabricated with machining technology. The main objectives of this study are to provide various characteristics of the parts made using the DMT process compared with the same parts machined from bulk materials and evaluate the performance of the injection mold equipped with a conformal cooling channel core fabricated using the hybrid method of the DMT process.

• Journal of Korea Foundry Society
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• v.34 no.3
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• pp.100-106
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• 2014

In recent years, Mg and its alloys have attracted a great deal of attention due to their low density, relatively excellent castability, and straightforward recyclability. Mg alloys have been widely applied to various industrial fields, and are representatively used in automotive and electronic parts. According to previous researches, the electrical conductivity of Mg alloys greatly decreases with increasing Al content. However, with the addition of Zn and/or Cu, the electrical conductivity of Mg alloys is maintained or slightly increased, and improved mechanical properties are obtained as well. On this basis, Mg-Zn-Cu alloys have been investigated in the present study with a focus on the effect of adding Zn and Cu on the electrical conductivity. The Zn and Cu contents ranged from 4 to 6wt.% and 0 to 1.5wt.%, respectively. Ternary Mg-Zn-Cu alloys have been prepared by gravity casting in a steel mold. In the as-casting condition, the electrical conductivity of Mg-Zn-Cu alloys showed a linear increasing trend with decreasing Zn and increasing Cu contents. Furthermore, impact values of Zn = -1.5 and Cu = 2.5 were determined for these alloys by electrical conductivity tests.

• Journal of the Korean Society for Nondestructive Testing
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• v.33 no.1
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• pp.73-79
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• 2013

In this study, NIMAX material has been processed using the three-dimensional measuring instrument and white light interferometer. they were tested to roundness and surface roughness and results are as follows: As for a cutting characteristic, it indicated that F4 showed a lower result than 2F showed due to the high hardness of the material and showed a good result when spindle rotation speed and tool feed were low. As for the measurement of roundness through 3-Dimensional measuring machine, it indicated that 4F showed a good result like the condition of cutting component and that roundness showed a good result when spindle rotation speed of 1,700 rpm and tool feed speed of 85 mm/min were applied. As for the surface roughness of processing surface, Surface roughness showed better 4F than 2F and conditions of spindle rotation speed 1,700 rpm, tool feed rate 55 mm/min showed good results in the Ra $0.4025{\mu}m$.

• Journal of the Korean Society for Heat Treatment
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• v.24 no.3
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• pp.127-132
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• 2011

The silicon-containing Diamond-like Carbon (Si-DLC) film as an low friction coefficient coating has especially treated a different silicon content by plasma-enhanced chemical vapor deposition (PECVD) process at $500^{\circ}C$ on nitrided-STD 11 mold steel with (TMS) gas flow rate. The effects of variable silicon content on the Si-DLC films were tested with relative humidity of 5, 30 and 85% using a ball-on-disk tribometer. The wear-tested and original surface of Si-DLC films were analysed for an understanding of physical and chemical characterization, including a changing structure, via Raman spectra and nano hardness test. The results of Raman spectra have inferred a changing intra-structure from dangling bonds. And high silicon containing DLC films have shown increasing carbon peak ratio ($I_D/I_G$) values and G-peak values. In particular, the tribological tested surface of Si-DLC was shown the increasing hardness value in proportional to TMS gas flow rate. Therefore, at same time, the structure of the Si-DLC film was changed to a different intra-structure and increased hardness film with mechanical shear force and chemical reaction.

• Journal of the korean academy of Pediatric Dentistry
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• v.25 no.2
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• pp.259-267
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• 1998

For more than two decades, many investigators have tried a variety of methods for delivering antimicrobial agents to the oral cavity with the objective of eliminating mutans streptococci. In the belief that the effectiveness of chemotherapy might be improved by a more effective delivery system, the intention of the present study was to exploit a new drug delivery system delivering chlorhexidine to the oral cavity. The vehicle delivering chlorhexidine tested in this study was self-curing acrylic resin(polymethyl methacrylate). The powder of the acrylic resin was polymerized with the 5 different liquid preparations, in which $Chlorzoin^{(R)}$ was mixed with five different monomer/Chlorzoin ratios immediately prior to the polymerization, in a stainless steel mold ($40mm{\times}40mm{\times}2mm$). A total of 50 cured resin specimens were divided into 5 groups according to the different monomer preparations. Every specimen was soaked in an airtight container filled with distilled water (100 ml) and then kept in an incubator at $37^{\circ}C$. The solutions (0.8 ml) were collected from the container at every 24 hours, and the amount of released chlorhexidine in the solutions was measured in an ultraviolet spectrophotometer at 250nm. The container was refilled with distilled water every after measurement. This procedure was repeated for 14 days. It was found that chlorhexidine was continuously released from all of the 50 specimens during the experimental period. And it was noted that the pattern of chlorhexidine release was a type of sustained-release preparation, that is, the amount of the released chlorhexidine at the first day in all 5 groups was high (p<0.0001), and then the release was decreased during the rest of the experimental period (p<0.001).

• Restorative Dentistry and Endodontics
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• v.27 no.3
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• pp.239-248
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• 2002

이 연구의 목적은 와동의 형태가 굴곡강도와 탄성계수 등 복합레진의 물리적 성질에 미치는 영향을 평가하는 것이다. 복합레진은 Clearfil$^{TM}$ AP-X(Kuraray, Japan)와 Esthet-X$^{TM}$(Dentsply, USA)가 이용되었으며, 상아질 접착제는 Clearfil$^{TM}$ SE Bond(Kuraray, Japan)와 Prime & Bond NT$^{TM}$(Dentsply, USA)를 사용하였다. 대조군의 시편은 split steel mold(25mm$\times$2mm$\times$2mm) 내에 상기 2종류의 복합레진을 충전하여 2개의 대조군 시편을 제작하였으며, 2.4 및 3.4의 C-factor를 부여하기 위한 유리 모형와동을 제작하고, 와동 내에 상기 2종류의 복합레진을 충전하기 전 유리와동의 내면은 sandblasting 처리하고 각각의 복합레진과 동일회사 제품의 상기 상아질 접착제로 처리한 후, 복합 레진을 각각 충전하여 4개의 실험군을 제작하였다. 제작된 실험군 시편은 저속 diamond saw로 충전된 복합레진 부위의 중심부를 통과하도록 절단하여 레진기둥(25mm$\times$2mm$\times$2mm)이 되도록 제작하였다. 제작된 시편을 37$^{\circ}C$의 증류수에 24시간 동안 보관 후, 만능시험기(EZ Test, Shimadzu, Japan)를 이용하여 분당 1mm의 crosshead speed로 3점 굴곡강도를 측정하였다. 또 Linometer(R&B, Korea)를 이용하여 복합레진의 중합수축량을 측정하였으며 굴곡강도측정 후 시편의 파단면은 주사전자현미경(S-2300, Hitachi, Japan)을 이용하여 관찰하였다. 실험결과의 통계분석은 95% 수준의 one-way ANOVA/Tukey's test를 이용하여 결과를 얻었다. 실험에 이용된 2종류 복합레진의 굴곡강도와 탄성계수는 C-factor치 증가에 따라 감소하였으며, 파단면 또한 C-factor의 증가에 따라 더 불규칙해지는 양상을 나타내었다. 본 실험의 결과 hybrid형 복합레진이 micro-hybrid형 복합레진에 비해 C-factor의 영향을 더 많이 받는 것으로 나타났으며, 와동의 C-factor증가가 굴곡강도나 탄성계수와 같은 복합레진의 물리적 성질을 저하시킨다는 것을 의미하였다.

• Korean Journal of Materials Research
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• v.24 no.1
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• pp.53-59
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• 2014

The corrosion resistance of submerged entry nozzle (SEN) materials were investigated for high-class steel manufacturing. Composite samples were fabricated by mixing $ZrO_2$, $Al_2O_3$, MgO, mullite, spinel, and carbon. The raw materials were mixed with attrition milling, compacted in a uniaxial pressure of 200MPa and calcined at $1000^{\circ}C$ for 3 h in $N_2$ atmosphere. The bulk density and apparent porosity of the calcined samples were measured by the liquid displacement method in water using Archimedes's principle. The corrosion resistance of the samples were measured by cup test with mold powder at $1550^{\circ}C$ for 2 h. The microstructure and elemental analysis of samples were observed by scanning electron microscopy (SEM), energy dispersive spectrum (EDS), and X-ray diffraction pattern (XRD). The XRD result shows that the starting raw materials were crystalline phase. The microstructure of fabricated specimen was investigated before and after corrosion tests at $1000^{\circ}C$ and $1550^{\circ}C$ for 2h. $ZrO_2$-C composite showed good resistance in the slag corrosion test. Among the composite oxide materials, $ZrO_2-Al_2O_3$-C and $ZrO_2$-MgO-C showed better resistance than $ZrO_2$-C in the slag corrosion test. The diameter variation index of $ZrO_2$-C refractory was 16.1 at $1000^{\circ}C$ for 2 h. The diameter variation index of the $ZrO_2-Al_2O_3$-C refractory was larger than that of the $ZrO_2$-C refractory at $1550^{\circ}C$ for 2 h.

• Restorative Dentistry and Endodontics
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• v.40 no.3
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• pp.209-215
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• 2015

Objectives: The aim of this study was to evaluate the fluoride release of conventional glass ionomer cements (GICs) and resin-modified GICs. Materials and Methods: The cements were grouped as follows: G1 (Vidrion R, SS White), G2 (Vitro Fil, DFL), G3 (Vitro Molar, DFL), G4 (Bioglass R, Biodinamica), and G5 (Ketac Fil, 3M ESPE), as conventional GICs, and G6 (Vitremer, 3M ESPE), G7 (Vitro Fil LC, DFL), and G8 (Resiglass, Biodinamica) as resin-modified GICs. Six specimens (8.60 mm in diameter; 1.65 mm in thickness) of each material were prepared using a stainless steel mold. The specimens were immersed in a demineralizing solution (pH 4.3) for 6 hr and a remineralizing solution (pH 7.0) for 18 hr a day. The fluoride ions were measured for 15 days. Analysis of variance (ANOVA) and Tukey's test with 5% significance were applied. Results: The highest amounts of fluoride release were found during the first 24 hr for all cements, decreasing abruptly on day 2, and reaching gradually decreasing levels on day 7. Based on these results, the decreasing scale of fluoride release was as follows: G2 > G3 > G8 = G4 = G7 > G6 = G1 > G5 (p < 0.05). Conclusions: There were wide variations among the materials in terms of the cumulative amount of fluoride ion released, and the amount of fluoride release could not be attributed to the category of cement, that is, conventional GICs or resin-modified GICs.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.5
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• pp.2993-2999
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• 2015

Steel companies are applying Ni-B or Ni-Co alloy plating to protect the surface of Continuous casting mold, and they are using saccharin polish which causes crack on plating layer due to sulfur in saccharin. It is considered that the Ni-S compound causes the cracking and additional tensile stresses. The Ni-Mn-B ternary alloy plating was developed for suppression of crack by forming Mn-S compound before Ni-S compound is formed, but there were no domestic or international standard on the Ni-Mn-B alloy plating. Therefore, reliability evaluation standard was established to evaluate the newly developed Ni-Mn-B plating. To develop accelerating life testing method, FMEA(Failure Mode & Effective analysis) was used to analyze the cause of the main failure in plating. The Ni-Mn-B reliability standard included accelerating life test method, and it was categorized by the fundamental performance test, environment test, and accelerated life test, and was designed to guarantee 1 000 hours of B10 life with 80 % reliable level.