• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.6 no.4
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• pp.439-452
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• 1994

One of the chlorofluorocarbon compounds. R-12 deplete atmospheric ozone. It leads to international agreement to reduce CFC production. R-134a has similar thermodynamic properties to CFC-12. It has zero ODP(Ozone Depletion Potential). This Paper focuses on the lubricating oils for using with R-134a PAGs(Polyalkylene Glycol's) and esters are primary lubricants that are now being tested for use with R-134a Because of extreme polarity of R-134a. there are many problems in the selection of lubricating oil. This investigation analyzes compressor working conditions and calculates wear parts friction for simulation testing. Miscibility and material compatibility is proved by sealed glass tests. Friction was tested on the closed type pin on disk wear tester. This equipment simulates actual refrigerating compressor. Environment controlled test made more reliable result than field test Conventional oils(mineral oils, Alkylbenzene, PAO(Polyalpha Olefin) are immiscible with R-134a. PAGs and ester oils are miscible with R-134a. Friction coefficient is similar to conventional system(mineral oil/R-12 systems) at operating condition. At start & stop condition, PAGs/R-134a system has high friction coefficient. It provide reliable result on the lubricity, miscibility, material compatibility of R-134a with these new lubricants. It suggests proper selection of refrigeration oil that may improve compressor durability of performance.

• The Journal of Korean Academy of Prosthodontics
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• v.53 no.1
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• pp.74-80
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• 2015

When oral cancer is occured, one may experience problems such as lip defect, necrosis of periodontal tissue and cervical caries caused by radiotherapy. According to ADI (Association of dental implantology), recent radiotherapy on jaw bone could be a relative contraindication of implant treatment. Due to this controversy, in most cases, treatment is done with removable dentures rather than implants. Especially, lip defect caused by an oral cancer operation have a serious repercussion on the retention of the denture. In this case report, patient with upper lip cancer had undergone resection primarily and secondary radiotherapy was done periodically. As a result, upper teeth of patient were extracted gradually and lower teeth showed very poor periodontal status. Therefore, Polident$^{(R)}$ denture adhesive cream (GlaxoSmithKline, London, England) was applied on maxillary complete denture to overcome reduced retention due to the lip defect and double crown RPD with friction pin was applied on the mandible successfully for two years.

• The Journal of Korean Academy of Prosthodontics
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• v.56 no.4
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• pp.368-374
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• 2018

In this case, the patient was restored with gold Hader bar mandibular implant overdenture using two implants about 10 years ago, and the retentive force was lost due to severe wear of the bar due to 3.5 years use. The overdenture was repaired using a Locator attachment, but the male part was completely worn after 6.5 years use. Finally, we used a hybrid telescopic double crown with a friction pin to fabricate a new implant overdenture, which was observed for 2 years and showed excellent prognosis. So, we describe the cause of failure of each attachment (Gold Hader bar, Locator) in two implant overdentures and report on the advantages and disadvantages of double crown implant overdenture and the conditions for success.

• Composites Research
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• v.23 no.2
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• pp.10-16
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• 2010

$Al_2O_3$ fiber and SiC particle hybrid metal matrix composites (MMCs) were manufactured by squeeze casting method investigated for their tribological properties. The pin specimens had different ratios of fiber to particle content but their total weight fraction was constant at 20 wt. %. Tribological tests were performed with a pin-on-disk friction and wear tester. The investigation of the dry tribological characteristics of hybrid MMCs were carried out at room temperature and elevated temperature of$100^{\circ}C$ and$150^{\circ}C$. The morphologies of worn surfaces were examined by scanning electron microscope (SEM) to observe tribological characteristics and investigate wear behavior. The results revealed that the wear resistance improved with the content of SiCp increased of the planar random (PR) MMCs at room temperature. At the elevated temperature, it revealed that the wear resistance of normal (N) MMCs was superior to that of the PR-MMCs due to PR-fibers were easily pulled out holistically from the worn surface. Meanwhile, the coefficient of friction decreased with the temperature increasing.

• Journal of Dental Rehabilitation and Applied Science
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• v.34 no.4
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• pp.317-323
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• 2018

When oral cancer develops in the maxilla, oro-nasal communication occurs after surgical treatment including removal of the primary site. Restoration through an obturator is necessary to prevent food from storing due to non-oral opening, and to ensure proper pronunciation and aesthetic restoration. In this case, the patient was treated with right hemi-maxillectomy due to oral cancer and has residual abutment and poor periodontal support due to the effect of head and neck radiotherapy. The obturator was treated with a hybrid telescopic double crown denture. Reporting a successful prognosis in 18 months of follow-up.

• Tribology and Lubricants
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• v.35 no.1
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• pp.1-8
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• 2019

Demand for plastic gears are increasing in many industries due to their low production cost, light weight, applicability without lubricant, corrosion resistance and high resilience. Despite these benefits, utilizing plastic gears is limited due to their poor material properties. In this work, DLC coating was applied to improve the tribological properties of polyamide66 gear. 0 V, 40 V, and 70 V of negative bias voltages were selected as a deposition parameter in DC magnetron sputtering system. Pin-on-disk experiment was performed in order to investigate the wear characteristics of the gears. The results of the pin-on-disk experiment showed that DLC coated polyamide66 with 40 V of negative bias voltage had the lowest friction coefficient value (0.134) and DLC coated PA66 with 0 V of negative bias voltage showed the best wear resistance ($9.83{\times}10^{-10}mm^3/N{\cdot}mm$) among all the specimens. Based on these results, durability tests were conducted for DLC coated polyamide66 gears with 0 V of negative bias voltage. The tests showed that the temperature of the uncoated polyamide66 gear increased to about $37^{\circ}C$ while the DLC coated gear saturated at about $25^{\circ}C$. Also, the power transmission efficiency of the DLC coated gear increased by about 6% compared to those without coating. Weight loss of the polyamide66 gears were reduced by about 73%.

• The Journal of Korean Academy of Prosthodontics
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• v.57 no.1
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• pp.24-30
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• 2019

The successful results of the treatment using a double crown denture have been reported in several papers for some of the few remaining teeth in patient. In particular, double crown dentures may be an alternative to treatment in cases where the periodontal status is poor and clasp type removable partial dentures are inappropriate (crown/root ratio > 1). In this case, the patient visited clinic with a chief complaint of difficulty in mastication due to loss of posterior teeth and overall teeth mobility. After teeth with severe periodontitis were extracted, treatment plan of mandible is Kennedy class I removable partial denture (RPD) and treatment plan of maxilla is hybrid telescopic double crown RPD with a friction pin. Patient is well adapted after the prosthetic treatment and we report due to achieving satisfactory results in pronunciation, mastication, retention and aesthetics.

• Transactions of the Society of Information Storage Systems
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• v.3 no.3
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• pp.129-134
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• 2007

Boron nitride (BN) is a highly attractive material for wear resistant applications of mechanical components. BN is super hard and it is the second hardest of all known materials. It also has a high thermal stability, high abrasive wear resistance, and in contrast to diamond, BN does not react with ferrous materials. The motivation of this work is to investigate the tribological properties of BN for potential applications in ultra-precision components for data storage, printing, and other precision devices. In this work, the wear characteristics of BN thin films deposited on DLC or Ti buffer layer with silicon substrate using RF-magnetron sputtering technique were analyzed. Wear tests were conducted by using a pin-on-disk type tester and the wear tracks were measured with a surface profiler. Experimental results showed that wear characteristics were dependent on the sputtering conditions and buffer layer. Particularly, BN coated on DLC layer showed better wear resistant behavior. The range of the wear rates for the BN films tested in this work was about 20 to $100{\mu}m^3$/cycle.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.467-470
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• 2004

Diamond-Like Carbon (DLC) thin film is a semiconductor with high mechanical hardness, low friction coefficient, high chemical inertness, and optical transparency. DLC thin films have widespread applications as protective coatings and solid lubricant coatings in areas such as Hard Disk Drive (HDD) and Micro-Electro-Mechanical-Systems (MEMS). In this work, the wear characteristics of DLC thin films deposited on silicon substrates using a DC-magnetron sputtering system were analyzed. The wear tracks were measured with an Atomic Force Microscope (AFM). To identify the sp2 and sp3 hybridization of carbon bonds and other bonds Raman spectroscopy was used. The structural information of DLC thin films was obtained with Fourier transform infrared spectroscopy and wear tests were conducted by using a micro-pin-on-reciprocator tester. Results showed that the wear characteristics were dependent on the sputtering conditions. The wear rate could be correlated with the bonding state of the DLC thin film.

• Transactions of Materials Processing
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• v.17 no.5
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• pp.343-349
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• 2008

The wear between piston ring face and cylinder liner is an extremely unpredictable and hard-to-reproduce phenomenon that significantly decreases engine performance. This study will discuss characteristics of wear between hard and soft piston ring coatings with running surface of cylinder liner. Detailed tribological analysis by using Pin-on-Disk(POD) testing machine describes the lubricity mechanism between piston ring coatings and cylinder liner at different temperature with and without oil. The effect of surface roughness of the cylinder liner on the friction coefficient and wear amount of piston ring coatings will also be analyzed. To simulate scuffing mechanism between piston ring and cylinder liner, accelerated lab testing was performed. This study will provide the data from tribological testing of hard and soft piston ring coatings against cylinder liner. Furthermore, the microstructures and morphological features of the surface and the near-surface materials during wear will be investigated. From the scuffing test by using POD testing machine, scuffing mechanisms for the soft and hard coating will be analyzed and experimentally confirmed.