• Tribology and Lubricants
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• v.24 no.6
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• pp.349-354
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• 2008

An inter-propellant seal (IPS) for high thrust turbopump is designed. With given operating conditions and requirements, the inter-propellant seal is designed to satisfy the leakage characteristics which is less than 0.1% of normal flow rate of pumps. A numerical analysis is developed to predict the leakage flow rate. The results show that the maximum leakage of LOX and kerosene are less than 0.1% of normal flow rate of pumps, respectively. Based on the numerical analysis results, the detail of IPS is performed. Finally a prototype of IPS is manufactured to perform sets of performance tests in the near future.

• Tribology and Lubricants
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• v.18 no.2
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• pp.127-132
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• 2002

The Taguchi method, a robust experimental design, was used to optimize manufacturing parameters of a brake lining during hot pressing and heat treatment. A friction material containing 15 ingredients was employed fur this experiment and friction and wear tests were carried out by using a pad-on-disk type tribotester. Sixteen brake linings with different manufacturing conditions were examined according to a parameter design. From the results of the signal-to-noise (S/N) ratio and the analysis of variance (ANOVA), the cause and effect of the manufacturing parameters on physical properties (hardness and porosity) and friction and wear characteristics of brake linings was obtained.

• Tribology and Lubricants
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• v.15 no.2
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• pp.131-140
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• 1999

This study dealt with some problems occurred in spectrometric oil analysis that has been popularly used for a machine condition monitoring in various fields of industry. One of the problems is that spectrometric technique could not analyze contaminants of large particle (larger than 10 $\mu\textrm{m}$) in lubricating oils. This limitation caused a serious problem in analyzing lubricated machine conditions since wear debris of large size represents better critical machine conditions. In this work, this problem was found to be solved by using a filtration method prior to spectrometric analysis. Another problem could be that spectrometric analysis is incapable of identifying contaminants. This nay mislead the result seriously in practice. This problem was surveyed by analyzing both various types of industrial lubricants and laboratory simulation tests, and the solutions to the problem were suggested in this work.

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

• Tribology and Lubricants
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• v.16 no.3
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• pp.173-181
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• 2000

Friction, wear and corrosion characteristics of various MoS$_2$ bonded film lubricants were investigated to apply them to automotive wheel joints. MoS$_2$ bonded film lubricants were formulated by combinations of several additives and binders, and they were coated onto the pre-treated surfaces of specimens. Friction and wear characteristics were evaluated with Falex pin & vee-block test and LFW-1 block-on-ring test. For the corrosion resistant characteristics of the films, salt solution spray corrosion tests were performed. Results showed that MoS$_2$ bonded films containing both inorganic and organic corrosion-resistant additives yielded a synergy effect on anti-corrosion resistance. Also, binders having the better water-proof and thermal stability showed the lower friction and higher corrosion resistance.

• Tribology and Lubricants
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• v.13 no.3
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• pp.28-32
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• 1997

Indentation, scratch and sliding tests were carried out in this paper to predict the critical loads and the failure modes of TiN-coated specimen. The test specimens were S20C steels with three different substrate hardness, roughness and coating thickness. The scratch test shows that the coating thickness has more dominant effect on the critical load of coated disk than the hardness and the roughness. Using the percent contact load, the ratio of sliding load to the critical scratch load, the cycles to failure are measured to predict the wear-life of TiN film. On the wear-life diagram the percent loads and the cycle to failure show the good linear relation on semi-log coordinate. With decreasing loads, the diagram shows the wear-limit at which the coated disk survives more than 4000 cycles.

• Tribology and Lubricants
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• v.13 no.3
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• pp.42-47
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• 1997

Three kinds of the sialon ceramics with and without TiN additions were prepared by hot pressing to investigate the effect of microstructure on erosion behaviors. Hardness and fracture toughness were measured with prepared specimens to study the effect of additives on the mechanical properties. A gas blast type erosion tester was employed to examine erosion behavior of the specimens up to $600^{\circ}C$. Erosion tests showed an increase of erosion rate up to 40$0^{\circ}C$ and a gradual decrease of erosion rate up to 50$0^{\circ}C$ for all kinds of sialon. The results also showed that erosion rates of the sialons were controlled better by microstructural factors than by mechanical properties including fracture toughness and hardness.

• Tribology and Lubricants
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• v.16 no.3
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• pp.194-200
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• 2000

In order to evaluate the effect of Nb on wear properties of high speed steel(HSS) by powder metallurgy, niobium-alloyed HSS have been prepared by adding 0%, 1%, 3% and 5%Nb to HSS of 6%W-5%Mo-4 %Cr-5%V-5%Co. Sliding wear tests were conducted at various sliding speed conditions under the constant pressure using a pin-on-disc type machine. The results of this study show that the wear resistance of HSS by powder metallurgy was increased by the addition of Nb within the range of sliding speed used in this experimental study. However, the amount of Nb did not improve the wear resistance. It may be due to the thermal stability of carbide and high temperature properties of the matrix containing Nb comparing to that without Nb.

• Tribology and Lubricants
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• v.11 no.4
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• pp.35-44
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• 1995

Within the practical ranges of speed and load, the formation of transfer films and the consequent effects on the friction and wear behavior of ceramic materials during repeated pass sliding contact were studied. These tests were done using $Al_{2}O_{3}$, SiC and $Si_{3}N_{4}$ with the cylinder-on-flat test configuration. The three pairings behaved differently, even if some wear mechanisms were common to the three systems. The $Al_{2}O_{3}$ pair showed the least wear in overall conditions, followed by the $Si_{3}N_{4}$ pair in harder sliding conditions. The wear of SiC was very high at severe loading. In case of $AL_{2}O_{3}$ and $Si_{3}N_{4}$, the transfer film, whenever formed, is strongly attached, enough to resist being wiped off by the slider. As a consequence, the formation of this f'fim leads to a decrease in the wear rate because of the protecting role of the film. The presence of the film at the contact interface also results in high friction. Also, the wear rate of each ceramics is related to the frictional power provided by load, speed and friction.

• Tribology and Lubricants
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• v.17 no.4
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• pp.276-282
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• 2001

Nano adhesion between SPM (scanning probe microscope) tips and 075 (octadecyltrichlorosilane) SAM (self-assembled monolayer) was experimentally studied. Tests were performed to measure the nano adhesion and friction in both AFM(atomic force microscope) and LFM(lateral force microscope) modes in various conditions of relative humidity. OTS SAM was formed on Si-wafer (100) surfaces, and Si$_3$N$_4$ tips of different radius of curvature were used. When the surface was hydrophobic, the adhesion and friction forces were found lower than those of bare Si-wafer. Results also showed that micro-adhesion force increased as the relative humidity and the tip radius of curvature increased. The main parameter for affecting the micro-adhesion was found absorbed humidity on the contact surface. These results were discussed with the JKR model and a capillary force caused by absorbed water.