When radial load applied to the bearings was high, ball excursion occurring in the retainer ball-pockets became large due to ball-speed-variation (BSV). Such BSV was also caused by inclination of the outer race to the shaft (tilted misalignment). If pocket clearance was smaller than maximum ball excursion, large force was imposed on the ball-retainer contact, resulting in retainer damage. The objective of this experimental and analytical research was to determine the effect of tilted misalignment on the tribo-characteristics of 40-mm-bore ball bearings in liquid hydrogen. The bearings used a retainer having elliptical-shaped ball pockets to restrain the ball-retainer contact due to high BSV. Various ball-pocket clearances (1.75, 1.95, 2.15 mm) were tested under high tilted misalignment conditions in a level of 1.9-3.5 × 10^-3 mm/mm at speeds up to 50,000 rpm and thrust loads of 590-2,650 N. Testing showed that, the retainer having a pocket clearance of 2.15 mm, the clearance of which was possibly larger than the maximum ball excursion emphasized by high tilted misalignment, enabled to stabilize the bearing torque and the bearing temperature at a speed of 50,000 rpm. Based on the results, the threshold of the ball-retainer contact occurred by tilted misalignment was discussed.

View full abstract

The influence of trace water and oxygen in a hydrogen environment on the sliding behavior of pure iron was studied using a newly developed pin-on-disk apparatus in a vacuum chamber equipped with an advanced gas replacement system. The hydrogen environment in the siding tests contained 0.5 to 95 ppm water and 0.07 to 2 ppm oxygen; a turbo-molecular pump was used for evacuation and a chemical filter for reducing water and oxygen in the hydrogen gas supplied to the chamber. The concentrations of water and oxygen in the hydrogen overflow from the chamber were determined using moisture and oxygen sensors, respectively. Other potential contaminant gases were analyzed using a quadrupole mass spectrometer during evacuation and were found to be insignificant. The amount of wear and the appearance of wear debris as well as the sliding surfaces were significantly different for the different concentrations of water and oxygen. The roles of these gasses are discussed.

View full abstract

This study investigated the effect of a particle diameter and a weight fraction of RB ceramics particles on friction and wear of polyamide 66 composites filled with RB ceramics particles (PA66/RB ceramics composites) sliding against a bearing steel ball under dry condition. RB ceramics particles with a mean diameter of 3, 30, and 150 μm were used as the filler. Weight fractions of RB ceramics particles were 10, 30, and 50 mass% for the mean diameter of the particles of 3 μm, and 30, 50, and 70 mass% for the mean diameters of 30 and 150 μm. The smaller mean diameter and the higher weight fraction of RB ceramics particles provided lower friction coefficients and lower specific wear rates with the PA66/RB ceramics composites. The composite with a mean diameter and a weight fraction of RB ceramics particles of 30 μm and 70 mass% took the lowest friction coefficient of 0.27 among the composites. The composite with a mean diameter and a weight fraction of RB ceramics particles of 3 μm and 50 mass% took the lowest specific wear rate of 1.3 × 10^-9mm²/N among the composites, which was equivalent to the specific wear rate of RB ceramics disk.

View full abstract

A general analysis has been done to investigate the dynamic performance and stability of short wave journal bearing. Reynolds equation is solved for unsteady-state operations. The unsteady analysis has been used to determine the rotor dynamic coefficients for various eccentricity ratios and wave eccentricity ratios. These coefficients has been used to determine the stability parameters such as critical mass and whirl ratio to show that wave bearing provides better stability at higher speed than circular bearing.

View full abstract

The load-dependent frictional performance of vitamin E-blended ultrahigh molecular weight polyethylene (UHMWPE) in serum lubricant was examined. The UHMWPE specimens were slid against the surface of Co-28Cr-6Mo alloy by using a pin-on-disk friction test apparatus. The frictional performance of vitamin E-blended UHMWPE differed from that of virgin UHMWPE under 30 MPa loading, while little difference was observed under 3 MPa loading. The friction force of vitamin E-blended UHMWPE showed a lower value in initial friction and a higher value in steady state friction, and the variability of friction force in the transition process was relatively small. Frictional performance similar to that of the vitamin E-blended UHMWPE was observed as a result of applying vitamin E to the sliding surface of virgin UHMWPE. These results suggest that the frictional performance of vitamin E-blended UHMWPE in serum lubricant is affected by the presence of vitamin E on the sliding surface under high compressive load.

View full abstract

Gear teeth wear, in most cases, by a smooth process giving initially good contact conditions, followed by a very slow and gradual process. Further, continuous progression of tooth wear may cause unfavorable changes of surface topography, thereby, giving rise to worsened contact situations. The metal removed from the worn teeth surfaces enter into the machine system and can, in turn, cause failure of other components, finally resulting in a severe form of tooth failure. The causes and subsequent prevention of the damage due to wear can be studied by oil/wear particle analysis of lubricants under operating conditions. This paper describes the results of experimental studies performed for evaluation of lubricant film thickness, wear particle analysis based on their morphology, metal composition analysis of lubricants using X-ray fluorescence, atomic absorption spectrometry (AAS) and Energy dispersive spectrometry (EDS). These results have been correlated with wear.

View full abstract

In order to study the fracto-emission mechanism, measurements of impact-induced fracto-emission (FE) of negatively charged particles from a soda-lime silicate glass were conducted at different impact energies, with simultaneous observation of the fracture mode by high-speed photography. The FE signals and their integrated values during the impact period were found to be dependent on the impact energy, E. For E ≤ 150 mJ, surface damage occurred around the impact track and the maximum fracto-emission signal was observed just after the indenter contacted the glass surface. The integrated FE signal intensity I_FE increased according to a 0.60 power law for the impact energy. For E > 150 mJ, the glass body broke into several pieces and the integrated signal intensities were greater than those for the surface fractures. The I_FE values increased according to a 0.84 power law for the impact energies. The FE signal patterns were compared with the high-speed camera photo-sequences. The dependence of I_FE on E could be explained in terms of the relationship between the line crack length at the indention and the impact energy. The FE signals during impact were attributed to the contact electric potential of the indenter and the glass surface, crack generation, and the scattering of fragments.

View full abstract

The friction and wear properties of a sintered porous Cu alloy impregnated with either Thermo-Reversible Gel-Lubricant (TR Gel-Lube) or base fluid (PAO) were investigated. Friction tests were conducted under a wide range of normal loads (0.98 N, 9.8 N, and 19.6 N) and sliding velocities (0.2 m/s, 0.5 m/s, 1.0 m/s, and 2.1 m/s), using a high-carbon chromium steel (JIS-SUJ2) bearing ball with 8 mm diameter as a ball specimen. The friction coefficients of the sintered Cu alloy impregnated with TR Gel-Lube were lower than those of the alloy impregnated with the base fluid under a wide range of normal loads and sliding velocities. Particularly, the friction coefficient of the sintered Cu alloy impregnated with TR Gel-Lube had extremely low value - less than 0.05 at high normal load and high sliding velocity. The specific wear rates of the sintered Cu alloy impregnated with base fluid and that impregnated with TR Gel-Lube had low values - less than 10-8 mm2/N under a wide range of normal loads and sliding velocities. There was no significant difference in wear rates between the two impregnants.

View full abstract