• Tribology and Lubricants
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• 제39권3호
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• pp.111-117
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• 2023

This paper presents an experimental investigation of the tribological characteristics of PTFE composites filled with nano CuO particles under low sliding speed and load. All the specimens were prepared by sintering. Before sintering, the mixture of PTFE powder and CuO particles were mixed by a high-speed mixer using CuO volume fractions of 0.2 vol. % and 5 vol. %. Each mixture was sintered at 350 ℃ for 30 min on the steel disk. We conducted ball-on-disk sliding test an hour using a steel ball against PTFE composites, including pure PTFE. The load and sliding speed used was 2 N and 0.01 m/s, respectively. Adding nano CuO particles increases the friction coefficient because of the abrasiveness of hard nano CuO particles. The highest coefficient of frictions was obtained from 5 vol. % CuO. Conversely, the lowest wear of the composites was obtained from the 5 vol. % CuO nanocomposite. This study reveals that the addition of nano CuO particles can lower the wear of PTFE, despite an increase in the coefficient of friction. However, the coefficient friction is still moderate compared to other engineering polymers. In addition, the amount of CuO nano particles has to be optimized to reduce friction and wear at the same time.

• Tribology and Lubricants
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• 제14권2호
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• pp.26-34
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• 1998

This paper presents a high-speed performance analysis of ball bearings with ceramic balls under thrust loads. The sliding velocity profiles between a ball and raceways were obtained by the 3-D quasi-dynamic equations of motion including both centrifugal force and gyroscopic moment derived by vector matrix algebra. The friction at the contact areas was obtained by the Bair-Winer's non-Newtonian rheological model and the Hamrock-Dowson's central film thickness in EHL analysis. The nonlinear equations were solved by the Newton-Raphson method and the underrelaxation iterative method. The friction torques and ball behaviors with various loads, ball materials, and contact angles were predicted by this model. It was shown that the friction torque was sensitive to thrust load and contact angle, and that the friction torque and the pitch angle of the bearing with ceramic balls are smaller than those of the bearing with steel balls.

• International Journal of Air-Conditioning and Refrigeration
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• 제15권1호
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• pp.1-9
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• 2007

This study concerns the characteristics of helical flow in a concentric and eccentric annulus with a diameter ratio of 0.52 and 0.9, whose outer cylinders are stationary and inner ones are rotating. Pressure losses and skin friction coefficients have been measured for fully developed flows of water and 0.2% aqueous of sodium carboxymethyl cellulose (CMC), respectively, when the inner cylinder rotates at the speed of 0-500 rpm. The effect of rotation on the skin friction is significantly dependent on the flow regime. In all flow regimes, the skin friction coefficient is increased by the inner cylinder rotation. The change of skin friction coefficient corresponding to the variation of rotating speed is large for the laminar flow regime, whereas it becomes smaller as Re increases for the transitional flow regime and, then, it gradually approach to zero for the turbulent flow regime.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 한국윤활학회 1997년도 제25회 춘계학술대회
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• pp.33-40
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• 1997

This study was undertaken to investigate tribology characteristics of the alumina ceramics($Al_2O_3$) for the vauiation of ambient condition such as air and distilled water. The results obtained were as follows. As the sliding speed increases, the friction coefficient in the air decreased due to the reduction of sheafing stress caused by the heat accumulation of contact interface. And the friction coefficient in the distilled water decreased due to an activation of the tribochemical reaction. As the contact load increases, the friction coefficient is small in the air due to temperature rise of the contact interface. However, at the low speed side in the distilled water, the friction coefficient holds a large value due to decrease of the tribochemical reaction. The friction surface of ceramics can be protected in the air by the influence of the oxides tansfered from STB2 and also in the distilled water by the influence of the corrosive productive hydroxides.

• Proceedings of the KSME Conference
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• 대한기계학회 2000년도 춘계학술대회논문집A
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• pp.766-771
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• 2000

This study is mainly concerned with friction and wear properties for the piston ring of non-lubricating air compressor which made of PTFE-polyimide composites. At the PTFE and polyimide alone mixture specimens, PTFE80%-polyimide20%, which shows the lowest men friction coefficient and specific wear rate at 0.94m/s sliding speed. At each of carbon, copper and oxide lopper mixed with PTFE80%-polyimide20%. In case of copper10%, at 0.94m/s sliding speed, the mean friction coefficient shows 0.087, which is the lowest value in all specimens. In case of the specific wear rate, copper30% specimen shows the lowest value of $2.537E-5(mm^3/Nm)$ in all specimens.

• Tribology and Lubricants
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• 제8권2호
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• pp.20-25
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• 1992

Friction and wear behavior of hot isostatic pressed $Al_2O_3-TiC$ was experimentally examined. Pin-on-disk type friction and wear apparatus was designed and manufactured for the experiment. The experiments were conducted under unlubricated sliding motion in both low and high humidity for three kinds of sliding speed. $Al_2O_3-TiC$ and bearing steel were used as counterface materials. Friction coefficient, wear rate, and surface roughness were measured. Wear surface and wear debris were observed through optical microscope and SEM and analyzed by EDAX. The results showed that the counterface materials, the sliding speed, and the moisture at the sliding surface have significant influence on the friction coefficient and wear rate of $Al_2O_3-TiC$.

• KSTLE International Journal
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• 제9권1_2호
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• pp.17-21
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• 2008

The rolling piston type rotary compressor has been widely used for refrigeration and air-conditioning systems due to its compactness and high-speed operation. The present study is one of studies to maximize the advantages of refrigerant compressors. In addition, because friction characteristics of the critical sliding component is essential in the design of refrigerant compressors, the present study also analyzed the lubrication characteristics of a rotary compressor used for refrigeration and air-conditioning systems. In order to measure the friction force between the vane and the rolling piston, an experimental apparatus known as the Pin-on-Disk was used. Load is applied by the hydraulic servo valve controlling the pressure of the hydraulic cylinder. The results showed that the rotational speed of the shaft, the operating temperature, and the discharge pressure significantly influenced the friction force between the vane and the rolling piston.

• Journal of Surface Science and Engineering
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• 제41권4호
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• pp.156-162
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• 2008

Small FRP(fiber-reinforced polymer) fishing ships have numerous problems with the point of the environmental and recycling perspectives. In light of these aspects, aluminum can be used as a material for ship building. It is environmental friendly, easy to recycle, and provides a high added value to fishing boats. In this paper, we report on mechanical and electrochemical characteristics of welding parts for friction stir welded 5456-H116 Al alloy. In friction stir welded at various traveling speeds under the rotation speed of 500 RPM, the best characteristics presented in traveling speed of 15mm/min. The anodic polarizations of base metal and welding metal were observed tendency which current density from the open circuit potential suddenly increase. The cathodic polarization presented concentrated polarization caused by the dissolved oxygen reduction reaction and activation polarization caused by hydrogen generation. From result of Tafel analysis, the corrosion potential of 5456 alloy(Base metal) was lower than that of friction stir welded part, as were its corrosion current densities.

• International Journal of Advanced Culture Technology
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• 제3권1호
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• pp.161-168
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• 2015

This article aims to apply a friction stir spot welding for producing a lap joint of AA1100 aluminum alloy and SGACD zinc coated steel. The experiment was designed by MINITAB and then investigated the relation among the friction spot joint parameters. The experimental results are as follows. The friction spot joining could successively produce the lap joint of AA1100 aluminum alloy and SGACD zinc coated steel. Interaction between the rotate speed, the hold time and the tool insert speed affected to vary the tensile shear strength of the lap joint. The prediction of the optimized welding parameters that indicated the tensile shear strength of 1966 N was the rotated speed of 4000 rpm, the pin hold time of 6 sec, the pin insert rate of 6 mm/min with the S/N ratio of 66.56 that was higher than that of the total mean S/N ratio. The practical experiment of the predicted welding parameters indicated the tensile shear strength of 2165 N and had the S/N ratio of 66.70 that was higher than the predicted tensile shear strength.

• Journal of the Korean Society for Heat Treatment
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• 제32권3호
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• pp.124-130
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• 2019

Friction stir welding is one of the interesting welding methods for titanium and its alloy which proceeds with plastic flow due to thermo-mechanical stirring and friction heat. Solid-state welding can solve severe problems such as high-temperature oxidation, interstitial oxygen diffusion and grain coarsening by liquid-state welding. Dynamic recrystallization and grain refinement can vary significantly with the plunging load and rotational speed of tool during friction stir welding, and suitable process conditions must be optimized to obtain microstructure and better mechanical characteristics. Suitable FSW conditions were 1000 kg of plunging load and 200 rpm of rotational speed and it showed YS 270 MPa, UTS 332.1 MPa, and El 17.3%, which were very similar to those of wrought titanium sheet.