• Journal of Mechanical Science and Technology
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• 제18권10호
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• pp.1849-1858
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• 2004

For examining friction-factor characteristics of round-hole pattern surfaces which are usually applied on damper seals, flat plate test apparatus is designed and fabricated. The measurement method of leakage and pressure distribution along round-hole pattern specimen with different hole area is described and a method for determining the Fanning friction factor is discussed. Results show that the round-hole pattern surfaces provide a much larger friction factor than smooth surface, and the friction factor vs. clearance behavior yields that the friction factor generally decreases as the clearance increases unlike the results of Nava's flat plate test. As the hole depth is decreased, the friction factor is increased, and maximum friction factor is obtained for 50% of hole area. Since the present experimental friction factor results show coincident characteristics with Moody's friction factor model, empirical friction factors for round-hole pattern surfaces are obtained by using the Moody's formula based on curve-fit of the experimental data. Results of Villasmil's 2D CFD simulation support the present experimental test result.

• 한국유체기계학회 논문집
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• 제6권3호
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• pp.15-20
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• 2003

For measuring friction factor of artificially-roughened surfaces which are usually applied to damper seals, flat plate test apparatus is designed and fabricated. The measurements of leakage flow and pressure distribution through round-hole patterned specimen with different hole areas are described, and a method is discussed for determining the friction factor experimentally. Results show that the friction factor of the round-hole patterned surface is bigger than that of smooth surface, and increases as increasing the hole area. A empirical friction factor model for the round-hole patterned surface can be descrived by the Moody's friction factor formula.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2002년도 유체기계 연구개발 발표회 논문집
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• pp.465-470
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• 2002

For measuring friction-factor of artificially-roughened surfaces which are usually applied on damper seals, flat plate test apparatus is designed and fabricated. the measurement of leakage and pressure distribution through round-hole pattern specimen with different hole area is described and a method is discussed for determining the friction-factor experimentally. Results show that the friction-factor of the round-hole pattern surfaces is bigger than that of smooth surface and increases as increasing the hole area. A empirical friction factor model for round-hole pattern surface is defined as the Moody's friction factor formula.

• Tribology and Lubricants
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• 제19권6호
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• pp.349-356
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• 2003

A damper floating ring seal with round hole pattern surfaces is suggested for better leakage control. The flat plate test of the round hole pattern surfaces has been performed to yield an empirical friction factor model. The exact predictions of the lock­up position of the damper floating ring, the leakage performance, and the rotordynamic coefficients of the seal are necessary to evaluate the rotordynamic performance of the turbo pump unit. The governing equations including the empirical friction factor model for round hole pattern surfaces are solved by the Fast Fourier Transform method. The lock­up position, leakage flow rate, and rotordynamic coefficients are evaluated according to the geometric parameters of the damper floating ring seal. Theoretical results show that the damper floating ring seals yield less leakage and better rotordynamic stability than the floating ring seal with a smooth surface.

• Journal of the Korean Wood Science and Technology
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• 제40권1호
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• pp.44-52
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• 2012

낙엽송 원통형 원주목에 대하여 수증기댐처리와 코팅처리를 실시하여 오-븐건조 하면서 건조속도, 재내의 수증기압 및 재온분포 및 건조할렬 등을 조사한 결과는 다음과 같다. 생재에서 난방된 실내의 이용함수율 수준인 함수율 약 8%까지 건조하는데 72~144시간 소요되었다. 무처리재와 코팅처리재는 전 건조기간에 걸쳐 통공층의 온도가 통피층의 온도보다 항상 높은 분포모형을 보인 반면, 수증기댐처리재의 경우 통피층의 온도가 통공층보다 높거나 같은 분포를 보였다. 수증기댐처리재와 코팅처리재의 경우는 거의 전 건조기간에 걸쳐 통피층의 수증기압이 통공층 보다 큰 분포를 보였다. 총체적으로 할렬발생 정도는 미약하였으며 할렬개수는 코팅처리재, 수증기댐처리재, 무처리재의 순으로 양호한 것으로 나타났다.

• Journal of the Korean Wood Science and Technology
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• 제42권2호
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• pp.101-111
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• 2014

In this study the effect of heartwood-coating (HCO), vapor-dam (VD), bark-remaining (BR) and bark-remaining-coating (BRC) treatments on the air circulating oven-drying characteristics of Japanese larch hollowed round-post was evaluated. The drying times of the hollowed round-posts for control, VD, HCO and BR specimens were 72, 168, 204 and 240 hours, respectively, from the initial MC to about 8% MC, which was recommended as the indoor in-use MC. The temperature in the hole of the VD specimen was lower than that of wood and the difference between air temperature in the hole and wood temperature became large during drying period. The vapor pressure of air in the hole was higher than that of inside wood for all specimens except VD specimen. The surface checks on all specimens were observed in increasing order of BR, BRC, UC, HCO and VD specimens.

• Journal of the Korean Wood Science and Technology
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• 제40권2호
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• pp.61-70
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• 2012

In this study the effect of heartwood-coating (HCO), vapor-dam (VD), bark-remaing (BR) and bark-remaining- coating (BRC) treatments were evaluated during air circulating oven-drying of hollowed round-post of Korean red pine. Hollowed round-post could be dried from the green condition to approximately 6% MC within 84 to 156 hours for the UC, HCO and VD specimens and it took 72 to 240 hours to about 8% MC, which is recommended as the indoor in-use MC. The temperatures in the hole of the Control (UC) and HCO specimens constantly showed a higher-leveled distribution pattern than those inside wood. The vapor pressure in the hole of the UC, HCO and BR specimens was higher than that inside wood and showed difference as highest value of about 20 mbar. The surface checks of all specimens were mild and were observed in increasing order of BRC, BR, UC, VD and HCO specimens.

• 한국정밀공학회지
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• 제16권10호
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• pp.94-100
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• 1999

Micro-EDM is widely used in machining of miro-parts such as micro-shafts and micro-holes. In order to select proper machining conditions and to reduce the machining time, it is necessary to understand machining characteristics under various machining conditions. Micro-hole machining tests were performed with round shape electrodes with different capacitances and voltages of the power source. The effects of the electrode rotational speed and diameter on the machining rate were also observed. From the experimental results, it was found that capacitance and voltage have significant effects on machining rate and the machined surface integrity. With higher capacitance and higher voltage, higher machining rate was observed together with poorer surface integrity. The electrode diameter was also found to have an effect on the machining rate and electrode wear.

• 한국기계가공학회지
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• 제8권2호
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• pp.46-52
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• 2009

Drilling operation is such an important machining process, which has been wildly applied to the industry, occupied over 30% of whole industry. However, there are many aspects of drilling process should be improved, such as increases of thrust force, surface roughness, and roundness, ect. In this study, we are aiming to reduce the thrust force, surface roughness, and roundness in drilling process. For this purpose, multi facet drills (MFD) of three types that are modified from standard drill (STD) are developed. The first type is multi stair drill (MSD) with shape of stair on relief plane. The second type is rough facet drill (RFD) with shape of round on relief plane. The third type is rough flute drill (RFLD) with shape of round on flute plane. For three types of MFD, we were carried out performance evaluation from the perspective of thrust force, surface roughness and roundness of machined hole. From obtained result, we could confirmed that performance of rough flute drill (RFLD) type is most excellent.

• 한국정밀공학회지
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• 제10권1호
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• pp.70-76
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• 1993

Burnishing, as a micro plastic working, is a finishing process used in conjuction with or in replacement of reaming, honing, lapping, and/or grinding. The tool which is a smooth, round steel ball slightly larger than the bore is pushed through pre-machined hole, leaving a closely controlled finish. The major application of the processes is to improve the geometric and mechanical properties of surface such as (1) dimensional accuracy, (2) surface roughness, (3) bearing ratio, (4) surface hardness, (5) wear resistance, (6) fatigue and corrosion resistance, etc. Therefore, this study carried out some experiments to illustrate the theoretical formula and to investigate surface accuracy (e.g. variation of diameter, surface roughness, bearing ratio) in accordance with the applied burnishing load.