• Tribology and Lubricants
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• v.15 no.4
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• pp.321-327
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• 1999

An experimental study was performed to discover the effect of adsorbed moisture on the rolling resistance behavior of pure silver-coated 52100 bearing steel. Plasma surface modifications were performed on the silver-coated specimen to change the wetting characteristics. Experiments using a thrust ball bearing-type rolling test-rig were performed under vacuum, dry air and various humidity conditions. Results showed that the changes in the wetting characteristics influenced remarkably on the silver particle agglomeration and resulted in the different behavior of rolling resistance with humidity.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.14 no.6
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• pp.37-44
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• 2005

This paper presents fabrication techniques of the optical fiber position sensor (or spindle state monitoring. These include selection of components such as optical fibers, a laser-diode, a photo-diode, and op-amp IC of the signal process circuit. We also describe electric runout problem. The fabricated sensor has a linearity of $1.7\%$ FSO in the air gap range $0.1\~0.6mm$, a resolution of $0.37{\mu}m$ and a bandwidth of 6.3kHz. Finally, we have successfully operated a magnetic bearing spindle system using the sensors.

• Tribology and Lubricants
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• v.35 no.1
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• pp.59-64
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• 2019

When slipping occurs between two materials, the coefficients of friction must be considered because these values determine the overall efficiency of the machine or slip characteristics. Therefore, it is important to find the coefficient of friction between two materials. This paper focuses on obtaining the coefficient of friction between an aiming bolt and a retainer located in the headlamps of a vehicle. This bolt supports the headlamp, and if the bolt is loosened by external vibration, the angle of the light will change and block the vision of pedestrians or other drivers. In order to study these situations, the coefficient of friction between aiming bolts and retainers needs to be measured. In addition, the coefficient of friction of materials used in the headlamp should be obtained. To determine these two factors, a new device is designed for two cases: surface-surface contact and surface-line contact. To increase reliability of the results, the device is designed using an air-bearing stage which uses compressed air as lubricant to eliminate the friction of the stage itself. Experiments were carried out by applying various vertical forces, and the results show that the coefficient of friction can be measured consistently. The procedure for designing the device and the results are discussed.

• Tribology and Lubricants
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• v.14 no.2
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• pp.35-41
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• 1998

The $WS_2$ solid lubricant synthesized through the vapour phase transport method was coated on the commercial bearing steel (SUJ 2) substrate, and the tribological behaviour of the lubricant was investigated using a ball-on-disk type tester. The $WS_2$ powder was spray-coated at room temperature using compressed air, and the change of friction coefficient was examined in various conditions, i.e., specimen configuration, atmosphere (air and nitrogen), applied load and rotating speed. $WS_2$ coated ball and disk showed the optimum friction coefficient of 0.07 and wear life of 45,000 cycles in the nitrogen atmosphere under 0.3 kgf and 100 rpm, whereas relatively high coefficient of 0.13 and reduced wear life of 4,000 cycles were observed in air atmosphere. The effect of rotating speed on the friction coefficient was not observed both in nitrogen and in air atmospheres. This confirmed that the spray-coated $WS_2$ solid lubricant was effective in reducing the friction coefficient and improving wear life in nitrogen atmosphere, and the oxygen and moisture existing in air could seriously deteriorate the lubrication effect of $WS_2$ coating layer.

• Tribology and Lubricants
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• v.35 no.5
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• pp.310-316
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• 2019

This paper presents two methods for designing a high-speed air spindle operated over the rotational speed of 50,000 rpm. The first method is an approximate method, which assumes a symmetric spindle shape even though it is not symmetric in reality. The second is an analysis of rotordynamics using beam and solid models. The approximate method can be used to calculate the bearing load capacities, stiffness and damping coefficients, stability of the shaft system, and response of the forced excitation from the unbalanced mass. Designers can use this method to determine the dimensions of the desired spindle at the first stage of the design. The more detailed behavior of the spindle can be calculated using the rotordynamics theory using beam and solid models based on the Finite Element Method. In this paper, a spindle, with two air bearings, one motor at the end, and two air thrust bearings, is newly developed. The solutions from the two rotordynamics theories are compared with the solution obtained using the approximate method. The three calculations are in agreement, and the procedure for the design of a spindle system, supported on the externally pressurized air bearings, ispresented and discussed.

• The KSFM Journal of Fluid Machinery
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• v.10 no.3 s.42
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• pp.47-54
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• 2007

A rotordynamic analysis was performed with a dry vacuum pump, which is a major equipment in modem semiconductor and LCD manufacturing processes. The system is composed of screw rotors, lobes picking air, helical gears, driving motor, and support rolling element bearings of rotors and motor. The driving motor-screw rotor system has a rated speed of 6,300rpm, and was modeled utilizing a rotordynamic FE method for analysis, which was verified through the results of its 3-D finite element model. As loadings on the bearings due to the gear action were significant in the system considered, each resultant bearing load was calculated determinately and indeterminately by considering the generalized forces of the gear action as well as the rotor itself. Each resultant bearing loading was used in calculating each stiffness of rolling element bearings. Design goals are to achieve wide separation margins of critical speeds and favorable unbalance responses of the rotor in the operating range. Then, a complex rotordynamic analysis of the system was carried out to evaluate its forward synchronous critical speeds, whirl natural frequencies and mode shapes, and unbalance responses under various unbalance locations. Results show that the entire system is well designed in the operating range. In addition, the procedure of rotordynamic analysis for dry vacuum pump rotor-bearing system was proposed and established.

• Journal of the Korean Society for Precision Engineering
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• v.10 no.4
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• pp.104-108
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• 1993

The linear length measurements are most frequently performed and should be most accurate among other parts in dimensional metrology. We developed the linear measuring system using a laser interferometer to improve the accuracy and to shorten the calibration time. The uncertainty of the system is 0.01 .mu. for 500mm steel gage block. The range of the measurement and resolution of the system are 1000mm and 0.01 .mu. m, respectively.

• International Journal of Highway Engineering
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• v.7 no.4 s.26
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• pp.79-89
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• 2005

Field and laboratory investigations were performed for concrete pavement of the Yeongdong Expressway located in western part of the Kangwon Province where lots of the substantially large spatting distresses were found. The spatting distresses were investigated to the naked eye in the field, and splitting tensile strength, air void, and neutralization tests were performed for the cores obtained from the pavement. In addition, load transfers at joints and dynamic bearing capacities at slab centers were measured to identify the lowering of the structural capability of the pavement. It was judged that the investigated concrete slabs were affected by freezing and thawing action because the air voids of the cores were substantially low. Therefore, it was concluded that the low air voids affected the lots of the large spatting distress in the pavement located in the region of cold winter.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.13 no.4
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• pp.160-169
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• 1999

Linear pulse rootor (LPM) be suitable a field where smooth linear rootion of high precision is required, because it's structured with minute teeth pitch in airgap of between and stator and roover(forcer). Force and position of LPM are effected sensitively by the teeth pitch, air gap, permanent magnet and excitation current. So, LPM is much important to analyze the force characteristics. llis paper was awlied to perrreance roothed for force calculation at airgap. The airgap of LPM is maintained from the pressure generated by an air-bearing. Simplified airflow and permeance methods will be used to calculate the air gap under static conditions. Therefore, the maximum available force is then derived using the coenergy method with variable air gap, also normal force and linear thrust was acquired from variable minute displacement 1[mm]. 1[mm].

• Journal of the Korea Institute of Military Science and Technology
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• v.24 no.5
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• pp.467-474
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• 2021

A study on optimal shape selection of a mechanical fastening for the repair of crack defect of ROK Air Force F-5 fighter wing was conducted. The crack defect occurred in the spar of the wing, and the technical manual does not specify the repair method. However, ROK Air Force decided to develop a repair technology for this defect in consideration of various logistic conditions. Three repair shapes for the proper repair were devised and the finite element analysis was performed to examine the structural safety of these three connection members. As a result of the structural safety review, two connection members except one were structurally safe with safety margins over zero because the calculated stress values were at or below the yield strength level. Therefore, two connection members were determined to be able to use for repair under the condition that the aircraft operated within the design limit load. The results of this study would be very useful if the same defect occurs in long-term aircraft operated by the ROK Air Force.