• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2001.11a
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• pp.364-373
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• 2001

This paper describes the variation of lubricant's temperature effects on elastohydrodynamic lubrication. The Newton-Raphson technique was used to solve the simultaneous system of Reynolds and elasticity equations. To show effects of lubricant's temperature, average temperature across the oil film was calculated using the energy equation. Pressure distribution, film shape, and temperature distribution were obtained for fully flooded conjunctions, and various dimensionless speed parameters while load and material parameters were held constant. Minimum film thickness were obtained for various material properties while load and velocity were held constant. It is drawn that the thermal effects have a strong influence on a minimum film thickness under high rolling velocity and slip ratio.

• Tribology and Lubricants
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• v.10 no.4
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• pp.75-81
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• 1994

In load sharing model, the load is supported by the contacting asperities and the lubricants. The asperity contact area of two sliding surfaces are relatively very small as compared with the apparent contact area. The asperity contact pressure is relatively higher than the lubricant pressure. With the combined effect of asperity and lubricant pressure, the surface roughness and temperature rise must be considered to calculate the lubricant film thickness of the line-contact bearing.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1998.10a
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• pp.212-218
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• 1998

This paper presents a study of the elastohydrodynamic lubrication of elliptical contacts where lubricant entrainment coincides with the major axis of the Hertzian contact ellipse. A finite difference method and the Newton-Raphson method are applied to analyze the problem. Film contours and pressure distributions are compared with the results for lubricant entrainment coincides with the minor axis. Variations of the minimum and central film thicknesses with the radius ratio are also examined. Therefore, the present numerical scheme can be used generally in the analysis of the EHL of elliptical contacts where the lubricant entraining vector did not coincide with either of the principal axis of the conjunction.

• Tribology and Lubricants
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• v.35 no.5
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• pp.300-309
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• 2019

Gas foil thrust bearings (GFTBs) support axial loads in oil-free, high speed rotating machinery using air or gas as a lubricant. Due to the inherent low viscosity of the lubricant, GFTBs often have super-laminar flows in the film region at operating conditions with high Reynolds numbers. This paper develops a mathematical model of a GFTB with turbulent flows and validates the model predictions against those from the literature. The pressure distribution, film thickness distribution, load carrying capacity, and power loss are predicted for both laminar and turbulent flow models and compared with each other. Predictions for an air lubricant show that the GFTB has high Reynolds numbers at the leading edge where the film thickness is large and relatively low Reynolds numbers at the trailing edge. The predicted load capacity and power loss for the turbulent flow model show little difference from those for the laminar flow model even at the highest speed of 100 krpm, because the Reynolds numbers are smaller than the critical Reynolds number. On the other hand, refrigerant (R-134a) lubricant, which has a higher density than air, had significant differences due to high Reynolds numbers in the film region, in particular, near the leading and outer edges. The predicted load capacity and power loss for the turbulent flow model are 2.1 and 2.3 times larger, respectively, than those for the laminar flow model, thus implying that the turbulent flow greatly affects the performance of the GFTB.

• Journal of the Korean Society of Propulsion Engineers
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• v.17 no.3
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• pp.15-20
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• 2013

The graphites as airtight structure seals prevent high-pressure and high-temperature gas from flowing into actuator of propulsion system and generate lubricant film during wear procedure to assist lubricant and sealing. In this study, the tribological characteristics of the graphite in high-temperature are evaluated. In order to evaluate the tribological characteristics of high density graphite(HK-6), variables which are temperature, sliding speed and contact load are set. this study suggest optimized environment conditions through the wear properties of graphite. Consequeantly, high temperature is better than at room temperature to generate lubricant film, so that friction coefficient of graphite is lower at high temperature than at room temperature.

• Tribology and Lubricants
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• v.15 no.3
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• pp.248-256
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• 1999

Many tribological components in automobile engine undergo high load and sliding speed with thin film thickness. The lubrication characteristics of the components are regarded as ether hydrodynamic lubrication or boundary lubrication, whereas in a working cycle they actually have both characteristics. Many modem engine lubricants have various additives for better performance which make boundary film formation even under hydrodynamic lubrication regime. Conventional Reynolds equation with the viewpoints of continuum mechanics concerns only bulk viscosity of lubricant, which means that its simulation does not give insights on boundary lubrication characteristics. However, many additives of modern engine lubricant provide mixed modes of boundary lubrication characteristics and hydrodynamic lubrication. Especially, high molecular weight polymeric viscosity index improvers form boundary film on the solid surface and cause non-Newtonian fluid effect of shear thinning. This study has performed the investigation about journal bearing system with the mixed concepts of boundary lubrication and hydrodynamic lubrication which happen concurrently in many engine components under the condition of viscosity index improver added.

• Tribology and Lubricants
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• v.14 no.3
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• pp.39-45
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• 1998

Reynolds equation, which describes behavior of fluid film in journal bearings, basically satisfies mass conservation. But, boundary conditions usually used with this equation, e.g. half Sommerfeld or Reynolds boundary conditions, cannot fulfill this natural law of conservation. In the case of connecting rod bearing, where applied load is dynamic and its magnitude is relatively large, such unrealistic boundary conditions have serious influence on calculation results, especially on lubricant flow rate or power disspation which are important parameters in thermal analysis. In this paper, mass-conserving boundary condition was applied in the finite element analysis of connecting rod bearings. Lubricant flow rate and power dissipation rate were calculated together with journal center locus, minimum film thickness and maxmium film pressure. These computation results were compared with those of the case of Reynolds boundary condition. Balance between inlet and outlet flow rate was well achieved in the case of mass-conserving boundary condition.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.356-356
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• 2007

Plasma immersion ion beam deposition (PIIBD) technique is a cost-effective process for the deposition of diamond like carbon thin film, the possible solid lubricant on large surface and a complex shape. We used PIIB process for the preparation of DLC thin film on $Al_2O_3$ with deposition conditions of deposition temperature range $200^{\circ}C$, working gas pressure of 1.310-1Pa. DLC thin films were coated by $C_2H_2$ ion beam deposition on $Al_2O_3$ after the ion bombardment of SiH4 as the bonding layer. Energetic bombardment of $C_2H_2$ ions during the DLC deposition to ceramic materials generated mixed layers at the DLC-Si interface which enhanced the interface to be highly bonded. Wear test showed that the low coefficient of friction of around 0.05 with normal load 2.9N and proved the advantage of the low energy ion bombardment in PIIBD process which improved the tribological properties of DLC thin film coated alumina ceramic. Furthermore, PIIBD was recognized as a useful surface modification technique for the deposition of DLC thin film on the irregular shape components, such as molds, and for the improvement of wear and adhesion problems of the DLC thin film, high temperature solid lubricant.

• Tribology and Lubricants
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• v.8 no.2
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• pp.14-19
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• 1992

rate of growth of "protective" films of oxides and compounds derived from the lubricant. The protection afforded by the films is strongly dependent on lubricant and steel composition, initial composite surface roughness and the load/speed sequence or history in the early stages of sliding. The protective films, formed by chemical and mechanical action between lubricant and mating surfaces, delayed the surface roughening and offered higher load capacity. Given the great number of variables involved it is not possible to follow more than a few of the chemical changes on surfaces at the end of experiments. Ellipsometry was therefore used to monitor the formation and loss of dual protective films in real time, and also to find the effect of protective films on scuffing and break-in depending on lubricant conditions.

• Tribology and Lubricants
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• v.36 no.6
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• pp.365-370
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• 2020

Recently, additive manufacturing (AM) technology has been applied to various industries such as automotive, aviation, medical, and electronics. Most prior studies are limited to the mechanical properties of printed materials, and few studies are being conducted on their tribological characteristics. However, the friction and wear characteristics of the material should be studied in order to utilize the components manufactured using AM technology as mechanical parts. In this study, the friction and wear characteristics of acrylonitrile-butadiene-styrene (ABS)-like resin printed with stereo lithography apparatus (SLA) 3D printing are evaluated according to the viscosity of silicon oil lubricant using a ball-on-disk experiment. Lubricants with a viscosity of 500, 1000, and 2000 cSt are prepared for the experiment. If silicon oil lubricants are used during the ball-on-disk test, the coefficient of friction (COF) and wear rates are significantly reduced, and the higher the viscosity of the lubricant, the lower will be the COF and wear rates. It is also verified that the temperature of the specimen owing to friction also decreases according to the viscosity of the lubricant. This is because of the silicon oil film thickness, and the higher the viscosity of the lubricant, the thicker will be the oil film. More studies on the tribological characteristics of 3D printing materials and suitable lubricants will be required to use 3D printed parts as mechanical elements.