• Title/Summary/Keyword: self-lubricant

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Lubrication Analysis of the Grooved Journal Bearing Lubricated with Pressurized High Temperature Water (고온/고압 환경 하에서 물로 윤활되는 그루브 저어널 베어링의 윤활 해석)

  • 이재선;박진석;김종인
    • Tribology and Lubricants
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    • v.18 no.2
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    • pp.105-108
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    • 2002
  • Specially designed grooved journal bearings are installed in the main coolant pump for SMART (System-integrated Modular Advanced ReacTor) to support radial load on the rotating shaft. The canned motor type main coolant pumps are arranged vertically on the reactor vessel and filled with circulating primary coolant which is pure water. The main coolant pump bearings are lubricated with this coolant without any other external lubricant supply. Because lubricating condition is too severe for this bearing to generate proper hydrodynamic film, investigation of lubrication characteristics of the journal bearing is important to satisfy life constraint of whole pump system, and the results will be applied to the analysis of dynamic characteristics of the shaft system. The bearing is made of silicon graphite which has self$.$lubricating effect. A lubrication analysis method is proposed for this vertically grooved journal bearing in the main coolant pump of SMART, and lubricational characteristics of the bearings are examined in this paper.

All-Organic Nanowire Field-Effect Transistors and Complementary Inverters Fabricated by Direct Printing

  • Park, Gyeong-Seon;Seong, Myeong-Mo
    • Proceedings of the Korean Vacuum Society Conference
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    • 2013.02a
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    • pp.632-632
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    • 2013
  • We generated single-crystal organic nanowire arrays using a direct printing method (liquidbridge- mediated nanotransfer molding) that enables the simultaneous synthesis, alignment and patterning of nanowires from molecular ink solutions. Using this method, single-crystal organic nanowires can easily be synthesized by self-assembly and crystallization of organic molecules within the nanoscale channels of molds, and these nanowires can then be directly transferred to specific positions on substrates to generate nanowire arrays by a direct printing process. The position of the nanowires on complex structures is easy to adjust, because the mold is movable on the substrates before the polar liquid layer, which acts as an adhesive lubricant, is dried. Repeated application of the direct printing process can be used to produce organic nanowire-integrated electronics with twoor three-dimensional complex structures on large-area flexible substrates. This efficient manufacturing method is used to fabricate all-organic nanowire field-effect transistors that are integrated into device arrays and inverters on flexible plastic substrates.

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The Assessment of Ceramic Wear by the Parameter Scf (Scf 파라메타에 의한 세라믹 마멸 평가)

  • 김상우;김석삼
    • Tribology and Lubricants
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    • v.12 no.1
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    • pp.56-65
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    • 1996
  • The result of wear test for ceramic materials was assessed by Scf parameter to verify the usefulness of the proposed Scf parameter. Friction and wear tests were carried out with ball on disk type. The materials used in this study were HIPed Alumina $(Al_2O_3)$, Silicon carbide (sic), Silicon nitride $(Si_3N_4)$ and Zirconia $(ZrO_2)$. The tests were carried out at room temperature with self mated couples of ceramic materials under lubricated condition. Turbine oil was used as a lubricant. In this test, increasing the load, specific wear rates and wear coefficients of four kinds of ceramic materials had a tendency to increase. The wear coefficients of ceramic materials were in order of $Al_2O_3, SiC, Si_3N_4, ZrO_2$. Worn surfaces investigated by SEM had residual surface cracks and wear particles caused by brittle fracture. As the fracture toughness of ceramic materials was higher, wear resistance more increased. The roughness of worn surface had correlation with wear rate. The wear rate(W$_{s}$) and Scf parameter showed linear relationship in log-log coordinates and the wear equation was given as $W_s = 5.52 $\times$ Scf^{5.01}$.

Performance Evaluation of PTFE Oil-seal for Automotive Engine Front Part (자동차 엔진 프론트부의 PTFE 오일씰의 성능평가)

  • Choi, Hyun-Jin;Park, Chul-Woo;Lee, Jong-Cheol;Kim, Jong-Gab;Choi, Seong-Dae
    • Transactions of the Korean Society of Automotive Engineers
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    • v.19 no.2
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    • pp.66-71
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    • 2011
  • This study analyzed the mechanical characteristics and evaluated their subsequent performance for two types of seals which reinforced characteristics with lower friction and anti-wear functions among the foremost important features in the automotive engine seals; one with the addition of glass fiber to PTFE(Polytetrafluoro ethylene); the other with the addition of self-lubricant molybdenumin addition to the glass fiber. Based on the configuration design of seal installed to the front part in the automotive engine, this study carried out interpretations on the stress and reaction for those two types of oil seals to compare the maximum stress and contact load generated from the seal steel, rubber and PTFE lip. This study also verified the stress concentration and anti-wear performance through the coefficient of friction, torque and durability test by producing two types of PTFE seals actually.

Role of Charges of the Surface-grafted Polymer Chains for Aqueous Lubrication at a Nonpolar Interface

  • Ron, Troels;Madsen, Jan Busk;Nikorgeorgos, Nikolaos;Lee, Seunghwan
    • Tribology and Lubricants
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    • v.30 no.5
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    • pp.247-255
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    • 2014
  • Charged polymer chains, i.e., polyelectrolytes, are known to show superior aqueous lubricating properties compared to those of neutral polymer chains, especially in brush conformation. This is primarily because of the incorporation of a large amount of counterions within the polymer layers and the consequently increased osmotic pressure. However, this effect is active only when the polymer chains remain immobilized even under tribostress, which is not realistic for high-contact pressure tribological applications, especially when they are irreversibly immobilized on tribopair surfaces. In contrast, with free polymers, which can be included as surface-active additives in the base lubricant (water), long-term lubricating performance based on "self-healing" properties is readily expected. In order to assess whether the superior aqueous lubricating properties of polyelectrolyte chains are valid for free polymers too, this study reviews recent studies on the tribological properties of many charged biopolymer and synthetic copolymers at a nonpolar, hydrophobic interface. In contrast to the irreversibly immobilized polyelectrolyte chains, free polyelectrolyte chains show inferior aqueous lubricating properties compared to their neutral counterparts owing to charge accumulation and the consequently impeded surface adsorption on the nonpolar surface. Nevertheless, bovine submaxillary mucin (BSM), a representative biopolymer, shows a sufficiently effective surface adsorption and aqueous lubricating capabilities even at neutral pH without losing the polyanionic characteristics.

Manufacture of High Density Graphite Using Coal Tar Pitch (석탄계 피치를 이용한 고밀도 흑연 제조)

  • Cho, Kwang-Youn;Kim, Kyung-Ja;Riu, Doh-Hyung;Lim, Kwang-Hyun;Kim, Jung-Il;Shin, In-Cheol;Lim, Yun-Soo;Joo, Heyok-Jong
    • Journal of the Korean Ceramic Society
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    • v.43 no.12 s.295
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    • pp.839-845
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    • 2006
  • Graphite has hexagonal closed packing structure with two bonding characteristics; (1) van der waals bonding between c axis, and (2) covalent bonding in the a and b axis. The weak van der waals bonds cause self-lubricant property, and the strong covalent bonds cause excellent electric and thermal conductivity. Furthermore, graphite is chemically very inert because of the material composed of only carbon elements. Thus, graphite is very useful for mechanical sealing materials. However, Graphite have porous microstructure because starting materials of graphite produce many volatile during the manufacturing processes. This causes low density of graphite, which is unsuitable for the mechanical sealing materials. Thus, further impregnation process is generally needed to enhance the graphite density. In this work, high density graphite is prepared with the principle of densification when coke and pitch binder, prepared from thermal treatment of coal tar pitch, become dehydrogenation during graphitization or carbonization.

Computer Simulation of Deformation in a Rubber Boots for Translation and Rotation of CV-joint for Automobile

  • Lee, Min-A;Lyu, Min-Young
    • Elastomers and Composites
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    • v.55 no.2
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    • pp.88-94
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    • 2020
  • Automobile industry, along with the automobile steering system, is rapidly changing and developing. The constant velocity joint transmits power to the wheels of vehicles without changing their angular velocity based on the movement of the steering wheel. Moreover, it controls their movement to act as a buffer. In order to prevent the excessive increase in temperature caused by the movement of vehicles, boots are attached to the constant velocity joint and lubricant is injected into the boots. The boots maintain the lubrication and protect the constant velocity joint from sand, water, and so on. As the wheels of the vehicle rotate, the boots are acted upon by forces such as bending, compression, and tension. Additionally, self-contact occurs to boots. Therefore, their durability deteriorates over time. To prevent this problem, polychloroprene rubber was initially used however, it was replaced by thermoplastic polyester elastomers due to their excellent fatigue durability. In this study, the structural analysis of boots was conducted. The results showed the deformation patterns of the boots based on the translation and rotation of the constant velocity joint. Moreover, it confirmed the location that was vulnerable to deformation. This study can be used to potentially design high-quality constant velocity joint boots.

Micro/Nanotribology and Its Applications

  • Bhushan, Bharat
    • Tribology and Lubricants
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    • v.11 no.5
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    • pp.128-135
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    • 1995
  • Atomic force microscopy/friction force microscopy (AFM/FFM) techniques are increasingly used for tribological studies of engineering surfaces at scales, ranging from atomic and molecular to microscales. These techniques have been used to study surface roughness, adhesion, friction, scratching/wear, indentation, detection of material transfer, and boundary lubrication and for nanofabrication/nanomachining purposes. Micro/nanotribological studies of single-crystal silicon, natural diamond, magnetic media (magnetic tapes and disks) and magnetic heads have been conducted. Commonly measured roughness parameters are found to be scale dependent, requiring the need of scale-independent fractal parameters to characterize surface roughness. Measurements of atomic-scale friction of a freshly-cleaved highly-oriented pyrolytic graphite exhibited the same periodicity as that of corresponding topography. However, the peaks in friction and those in corresponding topography were displaced relative to each other. Variations in atomic-scale friction and the observed displacement has been explained by the variations in interatomic forces in the normal and lateral directions. Local variation in microscale friction is found to correspond to the local slope suggesting that a ratchet mechanism is responsible for this variation. Directionality in the friction is observed on both micro- and macro scales which results from the surface preparation and anisotropy in surface roughness. Microscale friction is generally found to be smaller than the macrofriction as there is less ploughing contribution in microscale measurements. Microscale friction is load dependent and friction values increase with an increase in the normal load approaching to the macrofriction at contact stresses higher than the hardness of the softer material. Wear rate for single-crystal silicon is approximately constant for various loads and test durations. However, for magnetic disks with a multilayered thin-film structure, the wear of the diamond like carbon overcoat is catastrophic. Breakdown of thin films can be detected with AFM. Evolution of the wear has also been studied using AFM. Wear is found to be initiated at nono scratches. AFM has been modified to obtain load-displacement curves and for nanoindentation hardness measurements with depth of indentation as low as 1 mm. Scratching and indentation on nanoscales are the powerful ways to screen for adhesion and resistance to deformation of ultrathin fdms. Detection of material transfer on a nanoscale is possible with AFM. Boundary lubrication studies and measurement of lubricant-film thichness with a lateral resolution on a nanoscale have been conducted using AFM. Self-assembled monolyers and chemically-bonded lubricant films with a mobile fraction are superior in wear resistance. Finally, AFM has also shown to be useful for nanofabrication/nanomachining. Friction and wear on micro-and nanoscales have been found to be generally smaller compared to that at macroscales. Therefore, micro/nanotribological studies may help def'me the regimes for ultra-low friction and near zero wear.

Effects of Increasing Ambient Temperatures on the Static Load Performance and Surface Coating of a Gas Foil Thrust Bearing (외기 온도 증가가 가스 포일 스러스트 베어링의 하중지지 성능과 표면 코팅에 미치는 영향)

  • Hyunwoo Cho;Youngwoo Kim;Yongbum Kwon;Tae Ho Kim
    • Tribology and Lubricants
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    • v.40 no.3
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    • pp.103-110
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    • 2024
  • Gas foil thrust bearings (GFTBs) are oil-free self-acting hydrodynamic bearings that support axial loads with a low friction during airborne operation. They need solid lubricants to reduce dry-friction between the runner and top foil and minimize local wears on their surfaces during start-up and shutdown processes. In this study, we evaluate the lift-off speeds and load capacity performance of a GFTB with Polytetrafluoroethylene (PTFE) surface coating by measuring drag torques during a series of experimental tests at increasing ambient temperatures of 25, 75 and 110℃. An electric heat gun provides hot air to the test GFTB operating in the closed booth to increase the ambient temperature. Test results show that the increasing ambient temperature delays the lift-off speed and decreases the load capacity of the test GFTB. An early developed prediction tool well predicts the measured drag torques at 60 krpm. After all tests, post inspections of the surface coating of the top foil are conducted. Scanning electron microscope (SEM) images imply that abrasive wear and oxidation wear are dominant during the tests at 25℃ and 110℃, respectively. A quantitative energy dispersive spectroscopy (EDS) microanalysis reveals that the weight percentages of carbon, oxygen, and nitrogen decrease, while that of fluorine increases significantly during the highest-temperature tests. The study demonstrates that the increasing ambient temperature noticeably deteriorates the static performances and degrades the surface coating of the test GFTB.

The Effect of Si Content on the Tribological Behaviors of Ti-Al-Si-N Coating Layers (Ti-Al-Si-N 코팅막의 마모거동에 미치는 Si 함량의 영향)

  • Jin, Hyeong-Ho;Kim, Jung-Wook;Kim, Kwang-Ho;Yoon, Seog-Young
    • Journal of the Korean Ceramic Society
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    • v.42 no.2 s.273
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    • pp.88-93
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    • 2005
  • Ti-AI-Si-N coating layers were deposited on WC-Co substrates by a hybrid system of arc ion plating and sputtering techniques. The coatings were prepared with different Si contents to investigate the effect of Si content on their mechanical properties and microstructures. The dry sliding wear experiments were conducted on Ti-AI-Si-N coated WC-Co discs at constant load, 3N, and sliding speed, 0.1 m/s with two different counterpart materials such as steel ball and zirconia ball using a conventional ball-on-disc sliding wear apparatus. In the case of steel ball, the friction coefficient of Ti-AI-Si-N coating layers became lower than that of Ti-AI­N coating layers. The friction coefficient decreased with increasing of Si content due to adhesive wear behavior between coating layer and steel ball. On the contrary, in the case of zirconia ball, the friction coefficient increased with increasing of Si content, indicating that abrasive wear behavior was more dominant when the coating layers slid against zirconia ball.