• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.7 s.178
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• pp.1712-1720
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• 2000

• Tribology and Lubricants
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• v.6 no.1
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• pp.57-67
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• 1990

For increasing the performance of Machine tools, the improvement of the static and dynamic characteristics of spindle bearing is important. In this paper are the static characteristics, the pressure distribution, friction force and outlet flow rate, and the dynamic characteristics stiffness and damping coefficient, of a cylindrical hydrostatic journal bearing with multi oil pockets are analyzed.

• Journal of the Korean Society of Industry Convergence
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• v.23 no.6_2
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• pp.971-977
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• 2020

In this paper, We propose a portable electrostatic meter which can measure high voltage static electricity caused by friction to prevent fire or explosion accidents in grinding, crushing, power injection, transport, filling, dust removal, painting, and foreign matter removal processes. The proposed device not only shows static electricity strength in 4 steps with respect to distance and voltage but also gives warning with a buzzer, on process facilities that are likely to generate high voltage static electricity due to friction. The device is implemented by filtering the signal detected by the wireless antenna, amplifying the signal by 6 times, and passing the signal through the integrator circuit. Tests are carried out with an electrostatic discharge simulator. And the results show that 4 LEDs are turned on at the distance of 10cm, 3 LEDs at 12cm, 2 LEDs at 13cm, and 1 LED at 15cm, when a fixed voltage of 500V is given. And also, the tests show that the static electricity can be detected at 5cm on 100V, 10cm on 200V, 15cm on 500V, 20cm on 1000V, and 25cm on 1500V. We expect to reduce accidents caused by static electricity by allowing safety managers on fields where fire or explosion accidents can happen to monitor static electricity.

• Tribology and Lubricants
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• v.23 no.6
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• pp.278-282
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• 2007

Friction characteristics of a low-steel friction material were examined to investigate creep groan phenomena. The amount of three ingredients (steel fiber, $ZrSiO_4$, cashew) were changed to produce test specimens using a constrained mixture design. Tribological properties of the friction material specimens were obtained by using a 1/5 scale dynamometer. Results showed that the amount of three different ingredients strongly affected the level of friction coefficient and the difference between the static friction coefficient and the kinetic friction coefficient $({\Delta}{\mu}).\;ZrSiO_4$ and steel fiber tended to increase the average friction coefficient and aggravated the stick-slip phenomena suggesting high creep groan propensity. On the other hand, cashew tended to decrease average friction coefficient and ${\Delta}{\mu}$.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.7 s.238
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• pp.938-946
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• 2005

Friction is a dominant nonlinear factor in servomechanisms, which seriously deteriorates system accuracy. A friction compensator is indispensable to fabricate high-performance servomechanisms. In order to compensate for the friction in the servomechanism, identification of the friction elements is required. To estimate the friction of the servomechanism, an accurate linear element model of the system is required first. Tn this paper, a nonlinear friction model, in which static, coulomb and viscous frictions as well as Stribeck effect are included, is identified through the describing function approximation of the nonlinear element. A nonlinear element composed of two relays is intentionally devised to induce various limit cycle conditions in the velocity control loop of the servomechanism. The friction coefficients are estimated from the intersection points of the linear and nonlinear elements in the complex plane. A Butterworth filter is added to the velocity control loop not only to meet the assumption of the harmonic balance method but also to improve the accuracy of the friction identification process. Validity of the proposed method is confirmed through numerical simulations and experiments. In addition, a model-based friction compensator is applied as a feedforward controller to compensate fur the nonlinear characteristics of the servomechanism and to verify the effectiveness of the proposed identification method.

• Tribology and Lubricants
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• v.26 no.4
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• pp.230-239
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• 2010

Mechanical face seal installed in boiler feedwater pump prevents leakage of working fluid using thin fluid film between stator and rotor. If the leakage of working fluid exceeds the allowable volume, serious malfunction of boiler feedwater pump will be happen. The thinner fluid film exists between stator and rotor, the less working fluid leaks out. However, if the thickness of fluid film is not enough, the wear of seal face will be increased. And it causes the decrease in life of mechanical face seal. Therefore appropriate design is necessary to maximize the performance and life of mechanical face seal. In this study, numerical analysis using finite volume method was conducted to investigate the static characteristics of wavy mechanical face seals which have 4 different wavy surface profiles on rotor. As a result, opening force, leakage volume of working fluid and friction torque were obtained. For the same minimum film thickness, the static characteristics of mechanical face seal were affected by the wavy surface profile which can change the thickness of working fluid film and pressure distribution.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.05a
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• pp.748-752
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• 2004

Fluid dynamic bearings (FDBs) have been replacing ball bearings of the HDD spindle motor very rapidly. But there are several demerits of HDB, such as high friction torque, variable viscosity of the fluid lubricant depending on operating temperature, low stiffness, and etc. Eccentricity is one of the major parameters which affects the static and dynamic characteristics. As the static eccentricity is larger, the stiffness and the damping coefficients become bigger. But friction torque is relatively unaffected by the static eccentricity. This research proposes a new type of journal bearing with asymmetric journal grooves which results in better dynamic characteristics. The static and dynamic characteristics of the new journal bearing are investigated by solving the Reynolds' equation with FEM, and the transient analysis is performed to predict the dynamic behavior of rotor by solving the equations of motion of a HDD spindle system with Runge-Kutta method. The result shows that the proposed Journal bearings have much bigger stiffness and damping coefficients compared with the conventional symmetric ones. And consequently, it has smaller whirl radius and tilting angle.

• Transactions of the Korean Society of Automotive Engineers
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• v.14 no.4
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• pp.59-67
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• 2006

Recently, application of friction welded SUH35/SUH3 is increasing in the manufacturing process of automotive engine valves For securing its reliability and a reasonable strength evaluation method, it is necessary to assess stress singularity under the residual stress condition on the friction welded interface between dissimilar materials. In this paper, strength evaluation method of friction welded materials was investigated by boundary element method and static tensile testing. An advanced method of quantitative strength evaluation for SUH35/SUH3 friction welded material is to be suggested by establishing fracture criterion by using stress singularity factors.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 1999.10a
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• pp.371-376
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• 1999

Stick-slip friction is present to some degree in almost all actuators and mechanisms and is often responsible for performance limitations. Simulation of stick-slip friction is difficult because of strongly nonlinear behavior in the vicinity of zero velocity. A straightforward method for representing and simulating friction effects is presented. True zero velocity sticking is represented without equation reformulation or the introduction of numerical stiffness problems. Stick-slip motion is investigated experimentally, and the fundamental characteristics of the stick-slip motion are clarified. Based on these experimental results, the characteristics of static in the period of stick and kinetic friction in the period of slip are studied concretely so as to clarify the stick-slip process.

• Transactions of the Korean Society of Automotive Engineers
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• v.14 no.5
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• pp.164-171
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• 2006

Application of friction welding is increasing in the manufacturing process of machine elements in many industry fields. To establish a reasonable strength evaluation method and fracture criterion, it is necessary to analyze stress singularity under the residual stress condition on friction welded interface between dissimilar materials. In this paper, a method to establish fracture criterion on interface of friction welded dissimiliar materials was investigated by using the boundary element method BEM and static tensile testing. A quantitative fracture criterion for friction welded dissimilar materials is suggested by using stress singularity factor, $\Gamma$.