• Proceedings of the Korean Vacuum Society Conference
• /
• 1999.07a
• /
• pp.198-198
• /
• 1999

본 연구는 진공상태에서 단단한 물질로 된 diamond stylus로 단결정 MgO 표면에 마모(abrasion)가 할 때 발생되는 Photon emission(PHE), electron emission(EE), 마찰력을 시간의 함수로 동시에 측정하였다. 마모가 일어나는 동안 PHE 와 EE을 시간의 함수로 측정하면 마찰력 신호(signal)와 일치하지 않고 강한 fluctuation을 보여주고 있다. 마모를 가할 때 PHE와 EE의 signal은 wear 실험이 지속되는 동안은 force signal과 관계가 있다. 그러나 변형과 마찰력의 시간의 함수에는 관계하지 않음을 알 수 있다. 본 실험에서 사용된 실험장치는 PhE, EE, frictional force을 동시에 실할 수 있는 장치이다. 광자방출 실험은 공기 중에서도 할 수 있으나 전자방출은 진공에서 얻을 수 있으므로 1$\times$10-4pa하에서 실험하였다. 전자방출은 Channel electron multiplier(bias-100V)로 검출하였고, 광자 에너지는 Gencom photomultiplier를 사용하여 180~600nm의 photon을 측정하였다. 마모는 탐색기에 관계되는 접촉점의 움직임에 관계없이 실험하였다. 시료의 처리과정과 load속도에 따른 PhE, EE, data의 방출은 시료의 표면 상태에 따라 좌우되었다. cleaved 표면은 polished 표면보다 강한 emission을 나타내었다. 이것은 마찰이 표면 상태에 의존됨을 볼 수 있었다. 속도에 따라 emission이 증가하다가 ~0.5m/s이상에서 포화상태에 도달하였다. emission 측정은 열처리한 시료와 열처리 안한 시료를 비교하였다. 발광도(luminescence)는 주로 변형(deformation)에 의해 생겼으며, 전자 방출은 벽개(fracture)에 의해 발생됨을 알 수 있었다. 측정한 3개의 signal을 시간에 따라 분석하면 stick-slip-like 현상을 볼 수 있었다. 이것으로 보아 stick은 변형에 의해 생기고 ms 후에 벽개 현상이 발생됨을 볼 수 있다. 이러한 방출 현상은 마모시 일어나는 세라믹의 급격한 벽개 과정을 이해하는 데 많은 도움을 주었다. PhE와 EE signal은 다이아몬드 stylus로 단결정 MgO 기판에 마모를 가할 때 ms 단위로 검출 할 수 있었다. 방출과 마찰력은 표면조건, load, stylus velocity에 따라 변하였다. 마찰력, PhE, EE의 시간에 따른 분석에서 PhE는 변형 과정에 민감하며, EE는 stylus velocity에 의존하였다. 본 연구의 MgO 마찰 실험에서 표면 변화에 대한 정보를 얻을 수 있었다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2008.06a
• /
• pp.344-344
• /
• 2008

최근 들어, 압전 세라믹스 제조기술의 급속한 발전으로 기계, 전자뿐만 아니라 휴대용 전자기기의 초소형 적층형 압전모터 및 압전변압기 같은 고품질 압전소자의 개발에 있어 특히 소자의 소형화에 따라 나노크기의 분말제조가 연구의 주류를 이루고 있다. 현재 이러한 나노크기의 세라믹스 제조에 사용되는 방법으로는 화학적 공침법, 졸겔법, 수열반응, 그리고 고에너지 볼밀법등이 보고되고 있다. 볼밀링 공정은 세라믹제조 시 필수 불가결한 공정이나 일반적으로 미세화에 그 한계가 있어 $1{\mu}m$이하의 입자크기를 가지는 분말은 제조가 곤란한 것으로 인식되어 왔다. 그러나 고에너지 볼밀을 이용한 볼밀링은 원료의 변형, 파괴 등과 같은 원료의 물리적 변화 뿐만 아니라 원료를 구성하는 원자/분자 구조에 영향을 미쳐 원료의 화학적 특성의 변화를 유발한다. 이러한 화학적 특성의 변화는 이종 원료간의 화학 반응성을 향상시켜 밀링 중에 새로운 화학종의 생성을 유발하게 되는데 이러한 현상을 mechanochemical 효과라 한다. 이러한 mechanochemical 효과는 나노 분말 입자의 제조뿐만 아니라, 분자설계, 재료합성, 자원처리 및 리사이클링 등에도 그 적용이 시도되고 있다. 이러한 mechanochemical 효과를 이용하여 분말을 미세화 함으로써 저온 소결과 재료특성 향상을 기대해 볼 수 있다. 따라서, 이번 연구에서는 우수한 압전 특성을 가진 PMN-PNN-PZT조성을 가지고 시편을 제작하였으며, 고에너지 볼밀시간에 따라 그 압전 및 유전특성을 조사하였다.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
• /
• 1999.06a
• /
• pp.119-126
• /
• 1999

The rolling fatigue lives (RFL) of five kinds of silicon nitride balls were investigated. Four kinds of Si$_3$N$_4$ balls were fabricated using different raw materials, sintering aids and sintering conditions, Commercially available Si3N4 ball was also studied for comparison. All the balls were finished up to the dimensional accuracy of Grade 10 defined in KS B 2001 (Steel Balls for Ball Bearings) with a size of 9.525mm. RFL tests were then conducted under the initial theoretical maximum contact stress 6.38 GPa and the spindle speed 10,000 rpm. Gear oil was provided by oiled race as lubricant. The results of RFL test indicated the prerequisitic conditions for the long rolling life of Si$_3$N$_4$ball : (1) the high density, (2) mjcrostructures consisted of small uniformly distributed grains, (3) little glassy phase in grainboundary, and (4) little crystalline phase and secondary phase that induces residual thermal stress due to the differences of thermal expansion coefficient with Si$_3$N$_4$Phase.

• Tribology and Lubricants
• /
• v.14 no.2
• /
• pp.26-34
• /
• 1998

This paper presents a high-speed performance analysis of ball bearings with ceramic balls under thrust loads. The sliding velocity profiles between a ball and raceways were obtained by the 3-D quasi-dynamic equations of motion including both centrifugal force and gyroscopic moment derived by vector matrix algebra. The friction at the contact areas was obtained by the Bair-Winer's non-Newtonian rheological model and the Hamrock-Dowson's central film thickness in EHL analysis. The nonlinear equations were solved by the Newton-Raphson method and the underrelaxation iterative method. The friction torques and ball behaviors with various loads, ball materials, and contact angles were predicted by this model. It was shown that the friction torque was sensitive to thrust load and contact angle, and that the friction torque and the pitch angle of the bearing with ceramic balls are smaller than those of the bearing with steel balls.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 1995.10a
• /
• pp.841-845
• /
• 1995

In this study, a motor-integrated high-speed spindle system with .psi. 65mm*25,000rpm is developed by introducing the oil-jet lubrication method,ceramic angular contact ball bearing, a built-in motor and so on. And oil-jet lubrication experiments for evaluating the system performance are performed under various operation conditions. Especially, in order to establish the oil-jet lubrication conditions related to the development of a high-speed spindle system, the effects of oil supply rate and rotational spindle speed are investigated on the temperature rise, temperature distribution,motor current and so on.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 1995.10a
• /
• pp.846-851
• /
• 1995

A motor-integrated high-speed spindle system with .psi. 65*25, 000rpm is modeled for analytical and experimental studies related to the dynamic characteristics. And the systematic and rational identification processes for evaluating the material properties of spindle and built-in motor is introduced. The impulse excitation method is applied for the experimental model testing, and the dynamic characteristics of test model is theoretically analysed by using the finite element method based on Timoshenko theory. Especially, the experimental and theoetical results reveal that the test model under the required operational conditions has no critical problem for dynamic characteristics.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2002.07b
• /
• pp.549-552
• /
• 2002

$(SrBi_2Nb_2O_9)_{0.5}-(Bi_3TiNbO_9)_{0.5}$ ceramics were fabricated by the mixed-oxide method, and the structural and electrical properties with variation of ball-milling time were investigated. All SBN-BTN specimens showed the typical polycrystalline X-ray diffraction patterns without the presence of the second phase. The SBN-BTN specimen sintered at $1200^{\circ}C$ and ball-milled for 168h showed the average grain size of $16{\mu}m$. The dielectric constant and dielectric loss of the SBN-BTN specimen sintered at $1150^{\circ}C$ and ball-mill for 72h were 225, 0.4% at 1KHz, respectively.

• Journal of the Korean Society for Precision Engineering
• /
• v.15 no.5
• /
• pp.59-64
• /
• 1998

In this study, a motor-integrated high-speed spindle system with $\psi$65mm $\times$ 25,000rpm is developed by introducing the oil-jet lubrication method, ceramic angular contact ball bearings, a built-in motor and so on. And oil-jet lubrication experiments fur evaluating the system performance are performed under various operation conditions. Especially, in order to establish the oillet lubrication conditions related to the development of a high-speed spindle system, the effects of oil supply rate and rotational spindle speed are investigated on the temperature rise, temperature distribution, motor current and so on.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
• /
• 2004.10a
• /
• pp.326-333
• /
• 2004

This paper presents the structural characteristics analysis of a high-speed horizontal machining center with spindle speed of 50, 000rpm and feedrate of 120m/min. The spindle system is designed based on the built-in motor, angular contact ceramic ball bearings, oil-air lubrication and oil-jacket cooling method. The X-axis and Y-axis feeding systems are composed of the linear motor and linear motion guides, and the Z-axis feeding system is composed of the servo-motor, ball screw and linear motion guide. The structural analysis model of the high-speed horizontal machining center is constructed by the finite element method, and the validity of structural design is estimated based on the structural deformation of the high-speed horizontal machining center and spindle nose caused by the gravity and inertia forces.

• Tribology and Lubricants
• /
• v.15 no.2
• /
• pp.150-155
• /
• 1999

The rolling fatigue lives (RFL) of five kinds of silicon nitride balls were investigated. Four kinds of Si$_3$N$_4$balls were fabricated using different raw materials, sintering aids and sintering conditions. Commercially available Si$_3$N$_4$ball was also studied for comparison. All the balls were finished up to the dimensional accuracy of Grade 10 defined in KS B 2001 (Steel Balls fer Ball Bearings) with a size of 9.525 mm. RFL tests were then conducted under the initial theoretical maximum contact stress 6.38 GPa and the spindle speed 10,000 rpm. Gear oil was provided by oiled race as lubricant. The results of RFL test indicated the prerequisitic conditions for the long rolling life of Si$_3$N$_4$ball : (1) the high density, (2) microstructures consisted of small uniformly distributed grains, (3) little glassy phase in grainboundary, and (4) little crystalline phase and secondary phase that induces residual thermal stress due to the differences of thermal expansion coefficient with Si$_3$N$_4$phase.