• Journal of the Korean Society of Manufacturing Process Engineers
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• v.14 no.6
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• pp.111-121
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• 2015

The objective of this study is to develop an automatic object changer unit to improve changing process problems existing in the conventional horizontal machining center. In order to perform this objective, an upward and downward traverse unit was designed. This unit consists of a motor, reducer, chain and sprocket wheel, and an upper and lower base. This automatic object changer unit performs a sliding contact motion in a purpose built and designed frame. Constraint conditions for the upward and downward traverse unit were first designed. Then, an operation mechanism was designed and introduced as the sum of the kinetic energy for the sprocket wheel and the upper and lower base and which was based on the moment of inertia, which is the kinetic energy of the converted upward and downward traverse unit in the side of the reducer. The paper covers the design of th e Automatic Pallet Changer for th e machining center.

• Journal of Power System Engineering
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• v.20 no.1
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• pp.50-56
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• 2016

This paper handled an investigation on the turbulent flow characteristics of three-dimensional small-size axial fan(SSAF) according to operating loads. Also, it was carried out by unsteady-state, incompressible and three-dimensional large eddy simulation(LES). The downstream flow type of SSAF is changed from axial flow to radial flow around the beginning of stall region at the aerodynamic performance curve. Axial mean velocity component largely grows around blade tip at the operating point of A to D, but transverse and vertical mean velocity components as well as Reynolds shear stresses highly develop around blade tip at the operating point of E to H. On the other hand, the peak value of turbulent kinetic energy developed around blade tip shows the highest at the operating point of E.

• KSTLE International Journal
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• v.1 no.2
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• pp.113-117
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• 2000

The rotary-vane compressor has become one of the most successful types of compressors because of its mechanical reliability, compactness, and adaptability to moderately high-speed operation in virtually an unlimited range of sizes. However recently, the depletion of the ozone layer due to the current refrigerant(R22) has been getting worse, and it is one of the world's pressing issues. In this paper, we will discuss the use of R410a in the compressor of a room air-conditioner as an alternative refrigerant and air-conditioning system to R22, since R410a has greater refrigerant characteristics than R22. Miniaturization of the rotary compressor for the new refrigerant and air-conditioning system is also possible, which reduces the prime cost of production, hence R410a is naturally a better refrigerant. But to apply the new HFC refrigerant system in refrigeration and air-conditioning systems, a significant redesign of the current refrigerant system is also required, because as the refrigeration changes, lubrication characteristics vary. Close attention must be paid to friction force and energy loss due to friction and wear at many sliding areas.

• Journal of Mechanical Science and Technology
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• v.20 no.11
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• pp.1980-1992
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• 2006

Nucleate pool boiling experiments were performed using pure R11 for various surface angles under constant heat flux conditions during saturated pool boiling. A 1-mm-diameter circular heater with an artificial cavity in the center that was fabricated using a MEMS technique and a high-speed controller were used to maintain the constant heat flux. Bubble growth images were taken at 5000 frames per second using a high-speed CCD camera. The bubble geometry was obtained from the captured bubble images. The effects of the surface angle on the bubble growth behavior were analyzed for the initial and thermal growth regions using dimensional scales. The parameters that affected the bubble growth behavior were the bubble radius, bubble growth rate, sliding velocity, bubble shape, and advancing and receding contact angles. These phenomena require further analysis for various surface angles and the obtained constant heat flux data provide a good foundation for such future work.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2002.05a
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• pp.125-128
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• 2002

The automotive industry have made an effort to reduce the weight of vehicle structures with increased safety, while initial model of the final product does not contain any prehistoric effects in a design stave. It takes lots of time to calculate forming effects that have great influences on the energy absorption of structures. In this paper, finite element inverse analysis is adopted to calculate forming effects, such as thickness variation and effective plastic strain as well as an initial blank shape with small amount of computation time. Crash analysis can be directly performed after inverse analysis of the forming process without remeshing scheme. The direct mesh mapping method is used to calculate an initial guess from the sliding constraint surface that is extracted from the die and punch set. Analysis results show that energy absorption of structures is increased with consideration of forming effects and finite element inverse analysis is usefully applicable to calculate forming erects of vehicle structures for the crash analysis.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.994-995
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• 2006

The microstructure of the extruded Al-20Si bars showed a homogeneous distribution of eutectic Si and primary Si particles embedded in the Al matrix. The grain size of ${\alpha}-Al$ varied from 150 to 600 nm and the size of the eutectic Si and primary Si in the extruded bars was about 100 - 200 nm. The room temperature tensile strength of the alloy with a powder size $<26{\mu}m$ was 322 MPa, while for the coarser powder ($45-106{\mu}m$) it was 230 MPa. With decreasing powder size from $45-106{\mu}m$ to $<26{\mu}m$, the specific wear of all the alloys decreased significantly at all sliding speeds due to the higher strength achieved by ultrafine-grained constituent phases. The fracture mechanism of failure in tension testing and wear testing was also studied.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2000.11a
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• pp.332-340
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• 2000

Friction properties of automotive brake pads containing different types of abrasivess were investigated. Five different abrasives, including o-quartz, magnesia, magnetite, alumina, zircon, were employed in this investigation and size effects of the abrasives on friction characteristics were also studied using 1, 50, 140$\mu\textrm{m}$ size zircon. Experimental results showed that the hardness and size of these abrasive particles were strongly related to friction behaviors and wear mechanisms. Harder and smaller abrasives showed higher friction coefficient and more wear. The surfaces of friction materials with different sizes of abrasives showed that two different modes of abrasion (two-body and three-body abrasion) appeared during sliding. Considering the above results, abrasive materials were thought to destroy transfer film and the extent of the destruction depends on the types and sizes of abrasive particles. A mechanism of the wear mode transition (two-body to three body abrasive motion) was suggested considering the binding energy and friction energy in terms of abrasive particle size.

• Tribology and Lubricants
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• v.30 no.6
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• pp.378-383
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• 2014

This study predicts the of the hysteretic friction of a rubber block sliding on an SMA asphalt road. The friction of filled rubber on a rough surface is primarily determined by two elements:the viscoelasticity of the rubber and the multi-scale perspective asperities of the road. The surface asperities of the substrate exert osillating forces on the rubber surface leading to energy dissipation via the internal friction of the rubber when rubber slides on a hard and rough substrate. This study defines the power spectra at different length scales by using a high-resolution surface profilometer, and uses rubber and road surface samples to conduct friction tests. I consider in detail the case when the substrate surface has a self affine fractal structure. The theory developed by Persson is applied to describe these tests through comparison with the hysteretic friction coefficient relevant to the energy dissipation of the viscoelastic rubber attributable to cyclic deformation. The results showed differences in the absolute values of predicted and measured friction, but with high correlation between these values. Hence, the friction prediction model is an appropriate tool for separating the effects of each factor. Therefore, this model will contribute to clearer understanding of the fundamental principles of rubber friction.

• Earthquakes and Structures
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• v.19 no.6
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• pp.459-469
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• 2020

An external prestressed steel-bar truss unit was developed as a new strengthening technology to enhance the seismic performance of an in-plane masonry wall structure while taking advantage of the benefits of a prestressed system. The presented method consists of six steel bars: two prestressed vertical bars to introduce a prestressing force on the masonry wall, two diagonal bars to resist shear deformation, and two horizontal bars to maintain the configuration. To evaluate the effects of this new technique, four full-scale specimens, including a control specimen, were tested under combined loadings that included constant-gravity axial loads and cyclic lateral loads. The experimental results were analyzed in terms of the shear strength, initial stiffness, dissipated energy, and strain history. The efficiency of the external prestressed steel-bar truss unit was validated. In particular, a retrofitted specimen with an axial load level of 0.024 exhibited a more stable post behavior and higher energy dissipation than a control specimen with an observed complete sliding failure. The four vertical bars of the adjacent retrofitting units created a virtual column, and their strain values did not change until they reached the peak shear strength. The shear capacity of the masonry wall structure with external prestressed steel-bar truss units could be predicted using the model suggested by Yang et al.

• Polymer(Korea)
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• v.32 no.4
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• pp.397-402
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• 2008

Perfluoropolyether(PFPE) has been widely applied in industry because of its very excellent properties of very high contact angle and low surface energy, good lubricant property and antifouling property. But the difficulty to synthesize PFPE has limited the research on this field. In this study, the novel silicon-containing oligomer with perfluoropolyether moiety was synthesized, and the structure was characterized by $^{19}F$-NMR and $^1H$-NMR. The surface properties of contact angle, sliding angle, and soil release property were investigated. The results show that PFPE in this study can be utilized as an anti-smudge coating material because it shows lower sliding angle and better soil release property than commercial products.