• Tribology and Lubricants
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• 제19권1호
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• pp.21-25
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• 2003

The 440C stainless steel is used for ball bearings and bevel gears in the control rod drive mechanism for the integral reactor, SMART. The friction characteristics of 400C stainless steel a investigated in sliding motion using the reciprocating tribometer which can simulate the operating conditions of the control rod drive mechanism. Highly purified water is used as lubricant, and the water is heated and pressurized in the autoclave. Friction force on the reciprocating specimens is measured by the load cells and transformed into friction coefficient. It is verified that frictional characteristic of the 440c steel is not drastically changed up to operating temperature and variation of friction coeffcient at operating temperature from room temperature to 160$^{\circ}C$ is within 5%.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 한국윤활학회 2001년도 제33회 춘계학술대회 개최
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• pp.96-99
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• 2001

The fatigue life of support bearings is one of the most critical factors for the performance of a control rod driving mechanism. They are operated at high temperature and high pressure and especially lubricated with dramatically low viscosity water. The support bearing is made of standardized 440C stainless steel, and it supports thrust load including the weight of the driving system and external force. Friction and wear characteristics of this material operating under severe lubrication condition is not well known yet, although it is expected to be changed with respect to temperature and boundary pressure. So the friction characteristics are investigated in sliding conditions using the reciprocating tribometer which can simulate the operating conditions. Highly purified water is used as lubricant, and the water is heated up and pressurized. Friction farce on the reciprocating specimens is monitored by the load cells. The results of the experiments are presented in this paper.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 한국윤활학회 2001년도 제34회 추계학술대회 개최
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• pp.267-272
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• 2001

The effect of characteristic of surface roughness and roughness patterns on frictioin was studied experimentally in boundary lubrication with reciprocating tribometer. Roughness was changed from Ra=0.2 $\mu\textrm{m}$ to Ra=1.2 $\mu\textrm{m}$. Three roughness patterns-transverse, oblique, longitudinal- were tested for various load. Ra=1.0 $\mu\textrm{m}$ roughness showed lower friction coefficient and transversal pattern showed lower friction and high scuffing load in the test conditions.

• Proceedings of the KSME Conference
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• 대한기계학회 2001년도 춘계학술대회논문집A
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• pp.151-156
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• 2001

Experimental frictional and wear characteristics of silicon graphite materials is studied in this paper. Those specimens are lubricated with high temperature and highly pressurized water to simulate the same operating condition for the journal bearing and the thrust bearing on the main coolant pump bearing in the newly developing nuclear reactor named SMART(System-integrated Modular Advanced ReacTor). Operating condition of the bearings is realized by the tribometer and the autoclave. Friction coefficient and wear loss are analyzed to choose the best silicon graphite material. Pin on plate test specimens are used and coned disk springs are used to control the applied force on the specimens. Wear loss ana wear width are measured by a precision balance and a micrometer. The friction force is measured by the strain gauge which can be used under high temperature and high pressure. Three kinds of silicon graphite materials are examined and compared with each other, and each material shows similar but different results on frictional and wear characteristics.

• Transactions of Materials Processing
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• 제24권6호
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• pp.405-410
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• 2015

Sheet-forming of Mg alloys is conducted at elevated temperatures (250℃) due to the low formability at room temperature. The high-temperature process often gives rise to surface damage on the alloy (i.e. galling.) In the current study, the frictional characteristics of DLC coating slid against an AZ31 Mg alloy at various temperatures were investigated. The coating has been used widely for low-friction processes. Dry-sliding friction and galling characteristics of an AZ31 Mg alloy (disk), which slid against uncoated and a DLC-coated STD-61 steel (pin), were investigated using a reciprocating-sliding tribometer at room temperature and 250℃. To represent the real sliding phenomena during a sheet metal forming process, single-stroke tests were used (10mm stroke length) rather than a reciprocating long sliding-distance test. The DLC coating suppressed adhesion between the alloy and the tool steel at room temperature, and exhibited a low friction coefficient. However, during sliding at 250℃, severe adhesion occurred between the two surfaces, which resulted in a high friction coefficient and galling.

• Tribology and Lubricants
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• 제39권2호
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• pp.43-48
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• 2023

In this study, we investigate the tribological behavior of AISI 304 stainless steel pairs under deionized water and hexagonal boron nitride (h-BN) water dispersion lubrication. The specimen friction and wear properties are evaluated using a reciprocating ball-on-flat tribometer. The coefficient of friction remains nearly constant throughout the test under both lubricant conditions. The wear depth of the specimens under h-BN lubrication is smaller than that under deionized water lubrication, indicating the inhibition behavior of h-BN nanolubricants on direct metal-metal contacts. Optical micrographs and stylus profilometer measurements are performed to evaluate the severity of damage caused by the sliding motion and to determine the wear morphology of the specimens, respectively. The results show that h-BN nanolubricants does not have a significant effect on the friction behavior but demonstrates reduced wear owing to their trapping effect between the sliding interfaces. Moreover, scanning electron microscopy and energy-dispersive X-ray spectroscopy images of the specimens were acquired to confirm the trapping effect of h-BN between the sliding interfaces. The results also suggest that the trapped lubricants can distribute the contact pressure, reducing the wear damage caused by the metal-metal contact at the interface. In conclusion, h-BN nanolubricants have potential as an anti-wear additive for lubrication applications. Further investigation is needed to provide direct evidence of the trapping effect of h-BN nanoparticles between the sliding interfaces. These findings could lead to the development of more efficient and effective lubricants for various industrial applications.

• Tribology and Lubricants
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• 제18권3호
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• pp.211-218
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• 2002

The effect of characteristic of surface roughness and roughness patterns on friction was studied experimentally in boundary lubrication with reciprocating tribometer. Roughness was changed from Ra=0.2($\mu\textrm{m}$)to Ra=1.2($\mu\textrm{m}$). Three roughness pattern-transverse, oblique, longitudinal- were tested for various load and velocity. The experimental results show that the scuffing resistance of surfaces with transversal roughness pattern is higher than that of surface with longitudinal and obliq pattern. under the conditions of the roughness values of Ra=0.2, 0.5,1.0 and 1.2. surfacer roughness (Ra) was decreased with the normal load increased before scuffing occurred. oblique pattern and longitudinal pattern with Ra=0.2 and Ra=1.0 was higher scuffing load under low sliding velocity, but with Ra=0.5 was higher scuffing load under high sliding velocity.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 한국윤활학회 2003년도 학술대회지
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• pp.105-111
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• 2003

The valve train system of engines has long been a sensitive area with respect to wear performance because of the high contact loads and surface sliding speeds encountered. In particular, wear problems of load-carrying components in relative motion, such as cam and tappet in valve train system have made troubles. To overcome these problems, combination of proper materials is important, as well as selecting of high wear performance materials. This paper presents the experimental result of friction and wear properties of ca/tappet materials. To investigate friction and wear properties for several combinations of materials, using commonplace tribometer(Plint 77, reciprocating type), we make a selection of a optimum material combination.

• Tribology and Lubricants
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• 제21권6호
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• pp.278-282
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• 2005

Deep groove ball bearing is installed in a control element of an integral nuclear reactor, where water is used as coolant and lubricant. This bearing is made of STS440C stainless steel for the raceways and the balls to use in radioactive environment and water. It is known that the retainer design affects ball bearing operability and endurance life, however there is no verified retainer design and material for water lubricated ball bearing. Four kinds of retainers are manufactured for the endurance test of water lubricated deep groove ball bearing. Three of them are commercially developed types and the other is designed for this research. It is verified that ball bearings with steel pressed and general plastic retainer can not survive to required life in the water, however bearings with machined type and cylinder type retainer can survive. This proves that one of the major design parameters for water lubricated ball bearing is retainer type and material. In this paper, experimental research of endurance test for water-lubricated ball bearing are reported.

• Advances in materials Research
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• 제5권3호
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• pp.193-203
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• 2016

Compared to metal-to-metal tribology, polymer tribology presents further complexity as it is more prone to be influenced by operating conditions. Over the past two decades, progress in the field of wear of polymers has led to the establishment of more refined wear mechanisms. The current paper establishes the link between different load parameters and the wear rate of polymers, based on experimental investigations. A pin-on-plate reciprocating tribometer was used to examine the wear behaviour of polyamide sliding against a steel counterface, under constant and fluctuating loads, in dry conditions. In addition, the influence of controlled imperfections in the polymer surface upon its wear rate were examined, under cyclic and steady loading, in order to better understand surface fatigue wear of polymers. The imposed imperfections consisted of vertical artificial deep crack (slit) perpendicular or parallel to the direction of sliding. The study concludes with the followings findings; in general, wear of polymers shows a significant tendency to the type of applied load. Under cyclic loads, polymers show an increase in wear rate compared to those tested under static loads. Such increase was found to increase with the increase in cyclic load frequency. It is also demonstrated that surface cracks results in higher wear rates, particularly under cyclic loads.