• Journal of the Korean Society of Industry Convergence
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• v.25 no.2_2
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• pp.199-208
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• 2022

The steel wire or steel bar processing process applied to the manufacture of various bolts and power transmission shafts was improved by applying in-line phosphate film treatment technology. By applying a polymer lubricant for a non-reactive metal forming process and a non-reactive non-phosphorus lubricating coating agent, the film formation for each process time was comparatively analyzed and reviewed. Compared to the nine processes applied previously, the in-line phosphate film treatment technology applied with only two processes has been effectively improved in terms of reduction of treatment time, reduction of facility installation area, prevention of water pollution due to wastewater, and non-use of ozone-depleting substances. In addition, it was found that it can have an important effect on productivity improvement and price competitiveness from the simplification of quality control and process control as well as improvement of the working environment.

• Tribology and Lubricants
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• v.40 no.1
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• pp.17-23
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• 2024

This study analyzes the thermal effects on the performance of an air foil thrust bearing (AFTB) using COMSOL Multiphysics to approximate actual bearing behavior under real conditions. An AFTB is a sliding-thrust bearing that uses air as a lubricant to support the axial load. The AFTB consists of top and bump foils and supports the rotating disk through the hydrodynamic pressure generated by the wedge effect from the inclined surface of the top foil and the elastic deformation of the bump foils, similar to a spring. The use of air as a lubricant has some advantages such as low friction loss and less heat generation, enabling air bearings to be widely used in high-speed rotating systems. However, even in AFTB, the effects of energy loss due to viscosity at high speeds, interface frictional heat, and thermal deformation of the foil caused by temperature increase cannot be ignored. Foil deformation derived from the thermal effect influences the minimum decay in film thickness and enhances the film pressure. For these reasons, performance analyses of isothermal AFTBs have shown few discrepancies with real bearing behavior. To account for this phenomenon, a thermal-fluid-structure analysis is conducted to describe the combined mechanics. Results show that the load capacity under the thermal effect is slightly higher than that obtained from isothermal analysis. In addition, the push and pull effects on the top foil and bump foil-free edges can be simulated. The differences between the isothermal and thermal behaviors are discussed.

• The Journal of Korean Academy of Prosthodontics
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• v.41 no.2
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• pp.128-135
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• 2003

Statement of problem : Implant screw loosening remains a problem in implant prosthodontics. Some abutment screws with treated surfaces were introduced to prevent screw loosening and to increase preload. DLC(Diamond Like Carbon) film has similar properties on hardness, wear resistance, chemical stability, biocompatibility as real diamond materials. Purpose : The purpose of this study was to investigate the effect of lubricant layer on abutment screw and to discriminate more effective method between soft lubricant and hard lubricant to prevent screw loosening. Material and method : In this study, $1{\mu}m$ thickness DLC was used as protective, lubricating layer of titanium screws and 3 times removal torque was measured on the abutment screws to investigate the difference in 10 coated and 10 non-coated abutment screws. Results : The results indicated that the implants with DLC coating group were not more resistant to the applied force in screw loosening. At 32Ncm, the 3 times removal torque in DLC group were $27.75{\pm}2.89,\;25.85{\pm}2.35$ and $26.2{\pm}2.57$. The removal torque in no-coated abutment screws were $27.85{\pm}4.23,\;27.35{\pm}2.81$ and $27.9{\pm}2.31$, respectively. Conclusion : The lubricant layer used in this study was Diamond Like Carbon(DLC) and it have a properties of hard and stable layer. The DLC coating layer was hard enough to prevent distortion of screws in the repeated unscrewing procedure in clinical situation. The reduced friction coefficient in hard DLC layer was not effective to prevent screw loosening.

• Tribology and Lubricants
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• v.7 no.2
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• pp.28-35
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• 1991

3원통/링 마모시험기를 사용하여 윤활유 공급하에서 미끄럼 마모시험을 수행하였다. 엔진유에 첨가되는 대표적 첨가제인 ZDDP, 청정제, 분산제의 첨가제 3종과 모델 산호물로서 유성제인 스테아린산을 선택하여, 그 배합유의 마모방지특성을 조사하였다. 청정제 및 분산제 각각의 첨가에 의해 마모방지특성은 향상되었으나, 청정제 및 분산제를 동시에 첨가할 경우 마모방지성능의 향상효과는 없어졌다. 또한, 모델산화물인 스테아린산의 첨가로 인하여 ZDDP의 마모방지작용은 나빠지나, 청정분산제가 그 악영향을 억제하는 작용을 한다.

• Tribology and Lubricants
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• v.5 no.2
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• pp.87-93
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• 1989

The effect of the Concentration of solid lubricant, MoS$_2$ alone and in presence of other additives, ZDDP and DEP on the wear characteristics of liquid lubricants has been studied using the Four Ball Wear tester and Falex E.P. tester. On the basis of the experimental result, it showed that the concentration of MoS$_2$ and compatibility with other additives is very cbncerned with wear performance.

• Tribology and Lubricants
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• v.4 no.1
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• pp.30-35
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• 1988

Liquid crystals have some tribologically favorable lameliar structure. The Performance of ther mottopic liquid crystal was investigated under elastohydrodynamic condition in terms of traction and film thickness. It exhibited low traction and very thin film thickness, which were almost constant over the entire speed range measured. It was also found to have sealing effect like grease. This work has shown that there exists "potential" for using liquid crystals as lubricants.

• Proceedings of the SAREK Conference
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• 2005.06a
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• pp.69-69
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• 2005

• Tribology and Lubricants
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• v.4 no.2
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• pp.52-59
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• 1988

The purpose of this study is to establish a standard for proper selection of water soluble cutting fluids, such as Emulsion type, Semi-Synthetic type and synthetic type, by investigating cutting effects at the normal temperature(26$\circ$C) and cooling temperature(0$\circ$C) from the viewpoint of cooling and lubricant actions. This paper describes a relation among cutting force, surface roughness and cooled water soluble cutting fluids which are considered as effective restraints on Built up edge.

• Transactions of Materials Processing
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• v.11 no.6
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• pp.475-481
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• 2002

Tube hydroforming is a relatively new technology in comparison with conventional stamping process. Thus, there is no large knowledge base to assist the product and process designers, especially from the friction point of view. This paper covers the topic of friction and lubrication with regard to tube hydroforming. It presents the fact that frictional characteristic can have an effect on the formability of specific components. The presented concept describes the equipment which is required to determine the friction coefficient. Some example results of the friction and bulge test are shown.

• Tribology and Lubricants
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• v.10 no.2
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• pp.30-38
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• 1994

The thermohydrodynamic(THD) performance of a large tilting pad journal bearing is investigated both theoretically and experimentally. The theory takes into account the three dimensional variation of lubricant viscosity and eddy viscosity, and the inlet pressure. Owing to the inlet pressure effect, the film pressure and load capacity are increased but the mixing temperature and bearing surface temperature are decreased. The continuous distribution of the film pressure and film thickness and the bearing surface temperature are measured along with the shaft speed and the bearing load, and they are compared with the theoretical results. The results obtained by the experiment are in good agreement with those by the theory including the inlet pressure effect. It is suggested that the three dimensional turbulent THD analysis including the inlet pressure effect is very useful to predict the performance of the large tilting pad journal bearing more accurately.