• Journal of the Korean Society for Precision Engineering
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• v.30 no.3
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• pp.278-283
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• 2013

While Built-in Spindle is working in machining center, the tool is changed by ATC(Automatic Tool Changer) automatically. However, impurities could be stacked in front of spindle because of chips formation while machining, and positional error between spindle and tool could be generated. Compressed air holes are necessary for removal of the impurities. But, the diameter and number of compressed air hole are different for each built-in spindle in market. In this paper, flow analysis is carried out to find out the efficient figuration of the compressed air hole by using velocity and pressure distributions.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2000.05a
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• pp.1021-1026
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• 2000

The thermal characteristics of high-speed air spindle system with built-in motor are studied. Experiment and finite element method analysis obtain temperature rise and temperature distribution of housing. For the analysis three-dimensional model is built and temperature rise and distribution in thermal steady state are computed for each rotational frequency. Generally. It is said that the heat generation of air bearing is negligible. But it is certain that the heat generation of air bearing can not be negligible especially in high-speed conditions Frequency response test for air spindle system is executed. In case that the heat generation of air spindle system is high, natural frequency of the system becomes lower when it reaches thermal steady-state and it means that the stiffness of air hearing becomes smaller due to the change of bearing clearance. It is shown that the temperature rise of all spindle system causes thermal expansion md induces the variation of hearing clearance. In consequence the st illness of air bearing becomes smaller.

• Prospectives of Industrial Chemistry
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• v.23 no.4
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• pp.20-29
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• 2020

최근 미세먼지가 사회적 이슈가 됨에 따라 지하철 시스템의 공기 질에도 많은 관심이 쏠리고 있다. 지하철 미세먼지는 지상과 달리 폐쇄적인 환경이라는 특징이 있는데, 이로 인해 발생 및 유입된 미세먼지는 지하철 시스템에 축적된다. 지하철 미세먼지의 대부분을 차지하는 미세마모입자들은 철 성분을 주축으로 다양한 중금속 성분을 포함하므로 인체에 해롭다. 본 기고문에서는 이러한 지하철 미세먼지 및 미세마모입자에 대한 기본 지식과 미세마모입자의 주된 발생원인 휠-레일 접촉 미세먼지발생 연구에 대해 소개하고자 한다. 연구 결과들은 지하철 공기 질 향상을 위해 미세마모입자 발생 저감에 기여할 것으로 기대된다.

• Journal of Advanced Marine Engineering and Technology
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• v.38 no.4
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• pp.418-423
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• 2014

Small hydropower has been considered as a solution to resolve the problem of exhaustion of fossil fuel and industrial pollution. In this study, we developed and tested a Cross-Flow Turbine with two guide vanes to optimize the small hydropower for the site condition with large fluctuation of head and flow rate. Furthermore, in the condition of constant inlet head, CFD analysis was carried out to analyze the effect of air suction and valve position on the performance characteristics. The results showed that the air suction can minimize the hydraulic loss caused by the Recirculation flow in the runner passage and flow impact on main shaft so that it can increase the turbine efficiency and output power.

• Proceedings of the Korean Society For Composite Materials Conference
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• 1999.11a
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• pp.134-138
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• 1999

For the stable operation of high speed aerostatic spindle, the low rotational inertia and high damping ratio of spindle shafts as well as high fundamental natural frequency are indispensable. Conventional steel spindles are not appropriate for very high speed operation because of their high rotational inertia and low damping ratio. In this study, the composite spindles with aerostatic bearing were designed and manufactured with carbon fiber/epoxy composite. The fundamental natural frequency of the composite spindle was evaluated through the modal testing.

• Proceedings of the Membrane Society of Korea Conference
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• 1994.10a
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• pp.34-35
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• 1994

기체혼합물의 분리및 정제기술은 에너지 절약의 관점과 새로운 기능성 고분자의 개발로 고분자막에 의한 분리법이 관심을 끌게되었다. 공기로부터 산소부화, 방사성 크세논 및 크립론의 제거, 제련소 폐가스증의 수소분리, 천연가스로부터 헬륨의 회수분야등은 실제로 산업적으로 실용화되고 있다. 그러나 고분자막은 일반적으로 투과성과 선택성이 서로 상반되는 경향을 나타내므로, 투과성과 분리성이 좋은 기능성 고분자막의 개발에 다양한 연구가 필요로 하고있다. 본 연구에서 사용한 PTFE(polytetrafluoroethylene)는 결정성 고분자로서 넓은 온도범위에서 낮은 마찰계수, 우수한 전기적 절연특성, 강한 Carbon-fluorine 겹합에 기인한 높은 열적 안정성, 화확적 불활성때문에 공업용 고분자 재료로서 독특한 위치를 차지하고 있다. 최근에 미국과 일본을 주축으로 상용화딘 공기전지(Zinc-air battery)는 PTFE막의 뛰어난 소수성과 화학적 저항성으로 수은 전지의 대체품으로 주목받고 있는데, 장기 방전시 성능 저하가 따르므로 막을 통한 산소투과성을 방전에 필요한 최소값으로 감소시키는 것이 중요한 과제가 되고있다.

• Korean Journal of Construction Engineering and Management
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• v.7 no.2 s.30
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• pp.109-117
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• 2006

Recent rapid changes such as construction market reduction, lowest bidding system of construction cost, five days per week system, and post-construction sale system are inevitably accelerating the competitiveness between construction companies. Those rapid changes of construction environment require construction companies, which are main participants of construction industry, to adapt to the changes and more to lead new construction environment. However, there are many construction uncertainties which could delay construction completion. Without the proper identification of construction uncertainties, structured strategy establishment and management of construction schedule, the competitive advantages of construction duration could not be made. Thus this paper limited the research boundary to construction duration competitiveness instead of general strategy establishment. Recognizing the importance of proper calculation of construction duration, requirements of construction duration reduction and limited researches related to construction schedule strategy, we established the 25 strategies for construction duration competitivenss by internal and external construction environment analysis and SWOT analysis, and then elicited the first considerations to accomplish the strategies through concensus of all the staffs by questionnaire, brainstroming and face-to-face interviews.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.13 no.5
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• pp.38-48
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• 2004

Recently the use of high-speed equipment in machine-tool industry has greatly increased, which requires the development of prognostics and prediction methods on the design stage. Conversion of the test/experiments stage from real to virtual reality will not only significantly reduce the design and manufacturing cost, but will also increase design quality. This paper shows how it is possible to develop the automated system for the design calculations of the air-bearing spindles. First, the general calculation method is introduced. It contains several steps, namely, geometry identification, pressure calculation, stiffiness calculation, dynamics characteristics calculation. For geometry identification reducing spindle shaft to rings was proposed, which helps to automate the calculation process. For pressure calculation the Peshti method was implemented. For stiffiness calculation the analysis was made, which shown the necessity of correct calculation step selection. Then the system of ordinary differential equations containing influence coefficients was evolved, which is used for trjectories calculation. The graphical representation of the calculation results shows the dynamic behavior of the spindle unit concerning various working conditions. Finally, this automated system is illustrated by an example of the air-bearing spindle calculation.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.998-1002
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• 2003

This paper investigates the characteristics of stiffness and load in the thrust bearing of spindle which could be changeable according to the groove shape of inlet, in order to design a high-stiffness air bearing by selecting a optimal groove shape. In experiments, dead weight and displacement sensor are used to measure the load carrying capacity and the stiffness respectively. Various shapes and different depth of groove of self-restrictor are used as experimental conditions. Comparative study between the theoretical value and the practical one by measuring the value of stiffness and load of the thrust bearing is performed.

• Journal of the Korean Society for Precision Engineering
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• v.12 no.8
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• pp.86-91
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• 1995

Recently, motor integrated spindle is often used in a high speed spindle system of machine tools in order to increase machining speed. The important problem in high speed motor integrated spindle is to reduce thermal effect occured by motor and ball bearings. In this study, the effect of heat transfer from motor is investigated. The experimental equipment is composed with oil-air lubrication method, air cooling system and angular contact ball bearings. The results show that the thermal effect in motor is larger than in ball bearing until DmN 8000,000 with air cooling.