• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.855-859
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• 2005

Carbon fiber polymeric composites have been widely used in bearing materials under high pressure without oil-lubrication due to their self-lubricating characteristics. However, the severe wear of carbon composite surface occurs due to the generation of wear debris when the pressure applied on the composite surface is higher than the critical value of composite surface. In this work, in order to remove wear debris continuously during sliding operation, composite specimens with many micro-grooves on their sliding surfaces were devised. To investigate the effect of wear debris on the tribological behavior of carbon/epoxy composites, dry sliding tests were performed with respect to applied pressure using the composite specimens with and without micro-grooves. From the measurement of friction coefficients and wear rates, a model for the effect of wear debris on the friction and wear of composites was proposed.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.1261-1264
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• 2005

Recently, as researches and developments for milli-structure and micro machine are actively progressing, manufacturing technologies and skills for tiny small machine parts are getting more important. So, we have been trying to cut using high revolution air bearing spindle and micro-endmill, and studying for magnitude of cutting force, cutting force wave form and surface roughness. We figured out that in 60,000rpm is so slow that cutting is not perfact. Chatter occured to $2\mu{m}/rev\;at\;80,000rpm\;and\;4.4\mu{m}/rev$ at 100,000rpm. We confirmed that spindle run out increased surface roughness at high revolution.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.2
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• pp.130-137
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• 2004

A dynamic model of railway reducer is developed by the lumped parameter method. The model accounts for shafts, bearings flexibilities, gyroscopic effects and the force couplings among the transverse and torsion motions due to gearing. Vibration/noise analysis as well as strength of gear teeth, and bearing life are considered. Excitation forces of railway reduction are considered as the mass unbalance of the rotors, misalignment and a function of gear transmission error which comes from the modified tooth surface. A campbell diagram, in which the excitation sources caused by the mass unbalance of the rotors, misalignment and the transmitted errors of the gearing are considered, shows that, at the operating speed, there are not the critical speed. The program which can be used to analyze and predict vibration/noise characteristics by mass unbalance, misalignment and gear transmission error of railway reduction is developed with this system model.

• Tribology and Lubricants
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• v.16 no.6
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• pp.409-414
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• 2000

The friction and wear behaviors of MoS$_2$ coatings were investigated by using a pin and disk type tester. The experiment was conducted by using silicon nitride as pin material and MoS$_2$-on-bearing steel as disk material under different operating conditions that include linear sliding velocities in the range of 22-66 ㎜/sec, normal loads varying from 9.8 N to 29.4 N, corresponding to maximum contact pressures of 1.18-2.83 GPa and atmospheric conditions of high vacuum, medium vacuum, ambient air. The results showed that low friction coefficient of the coating has been identified in high vacuum and that friction coefficient and wear volume increased with increasing normal load. Also at high load conditions, the friction coefficient and wear volume increased with increasing sliding velocity.

• Journal of the Korean Society for Precision Engineering
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• v.17 no.2
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• pp.161-168
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• 2000

In this paper, machining characteristics of glass for HDD media are researched. Nowadays HDD media are used globally as a data storage device. In generally, it is machined by the lapping. But the lapping process time is long and the productivity is low. In this reason, 1 examined the possibility of ELID grinding of glass fur HDD media. If the machining process of HDD media can be changed to ELID grinding, a product cost will be largely saved. The machines used in this experiment were a special rotary type grinder and a normal rotary grinder. The one has an air bearing spindle, the other has not. Experimental results show the possibility of highly efficient grinding and mirror surface can be achieved by the ELID grinding.

• Journal of the Korean Society for Precision Engineering
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• v.17 no.6
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• pp.192-198
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• 2000

This paper presents multi degree analysis of self-exited vibration of grinding system including spindle and workpiece rotational effect. The governing equations are derived by applying the finite element method to structure of spindle and workpiece rotor and by estimating the grinding force. Vibration analysis is carried out for external cylindrical plunge grinding. Displacement of workpiece and grinding force is simulated with machining time. Using this model, effects of characteristics of spindle bearing and major grinding conditions on chatter growth rate are predicted. Some of results are compared with those of other previous model and show good agreements.

• Transactions of the Korean Society of Mechanical Engineers
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• v.7 no.2
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• pp.186-192
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• 1983

The purpose of this study is to determine the general frequency expression for a rotating shaft of uniform cross section, supported by two bearings, and carrying flywheel at the free end. The bearing spacing and the ratio of the weight of flywheel to the total distributed weight are used as parameters. The data have thus been reduced to dimensionless form so that the results are generally applicable for this type of rotor. Frequencies for the first three modes of vibration are determined. Experimental investigation with rotor/flywheel model confirmed the critical speed frequencies lie between analytical models with simply supported-simply supported boundary conditions and spring supported-spring supported boundary conditions.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2001.05a
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• pp.221-224
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• 2001

The dynamic characteristics of a hydraulic press for micro-stamping are investigated by Finite Element Analysis. This machine requires high precision in producing milli-structure of electric products such as TFT-LCD back-up light reflector. First, the modal analysis of the parts and the assembly of the hydraulic press is performed. Then, the sensitivity analysis is carried out. The results show that the bearing stiffness and the base mounting stiffness affect the specific mode shapes.

• ALGAE
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• v.20 no.4
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• pp.305-314
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• 2005

5 Haptophyta 2 Chrysophyta and 1 Prasinophyta species of scale-bearing nanoflagellates were collected in coastal water of Korea and identified by examination of their scales with Field Emission Scanning Electron Microscope (JSM-6700F). These included Chrysochromulina ahrengoti, C. simplex, C. spinifera, Prymnesium parvum, P. patelliferum, Mamiella gilva, Paraphysomonas imperforata and Pa. vestita. The surface of cells covered with unmineralised scales (5 Haptophyte and 1 Prasinophyta species) or silica scales (2 Chrysophyta species). Scale-covered flagella are found in the 1 Prasinophyta species. One of the main structural characteristics of Haptophyte is the haptonema, a filiform organelle which occurs together with the two flagella. It may be long and coiling upon irritation as in Chrysochromulina, or short and noncoiling as in Prymnesium.

• Journal of the Korean Society of Safety
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• v.29 no.5
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• pp.74-81
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• 2014

This study proposes an advanced type of a micropile system. The proposed micropile system consists of perfobond ribs installed steel rod to improve shear capacity between the thread and the grout, and partially expanded drill holes to increase resistance capacity between the grout and the ground. This study contains experimental evaluations on the proposed micropile system to verify the shear capacity of perfobond rib installed on the steel rod and the load-carrying capacity of shear key created by the partially expanded drill hole. Push-out tests were conducted on a rolled screw thread and steel rods which perfobond ribs are installed instead of rolled screw, in order to compare their load-carrying capacity and behavioral characteristics. As a result, it was confirmed that the perfobond-rib steel rods show much superior structural behavior in terms of initial stiffness, ultimate load, and ductile behavior.