The lubricant on thin-film disks is a key material for disk durability. Bonded lubricant layer remains on disk surfaces after solvent rinsing which removes mobile lubricant. To improve disk durability, lubricant treatments comprising heat treatment and UV irradiation, have been studied. Both of them increase bonded lubricant thickness but the bonded lubricant characteristics are not well understood. In this study, disks with only the bonded lubricant remaining after rinsing were prepared. Results of pin-on-disk wear tests and surface tension measurements on these disks showed that “bonded lubricant” could be moved by mechanical sliding and that the smaller the surface tension, the lower the pin wear.
This paper presents results of a theoretical analysis to determine the leakage flow and dynamic characteristics of circumferential wave geometry annular seals using turbulent lubrication theory. Turbulent lubrication equations based on an eddy viscosity model have been used to develop the turbulent Reynolds equation. Convective fluid inertia effects have been incorporated using the perturbation approach in turbulent lubrication. To determine the dynamic characteristics i.e. stiffness, damping and whirl ratio, perturbation theory for small amplitude vibration of the journal center has been adopted. In general, it has been found that circumferential wave geometry improves the performance of the annular seal at higher speeds and increases in the L/D and taper ratios.
In this study, five kinds of thermoplastic resin/RB ceramics composite materials were developed, and their tribological properties were investigated under dry and oil lubricated conditions. RB ceramics particles with mean diameter of 150 μm were compounded with five kinds of thermoplastic resins (PA66, PA11, PBT, POM, and PP). These compounds were formed into disk geometry by injection molding. A weight fraction of RB ceramics particles were 50 wt% for POM, 60 wt% for PA11 and PBT, and 70 wt% for PA66 and PP. Friction coefficients of the thermoplastic resin/RB ceramics composites were lower than those of the neat thermoplastic resins under dry condition, and those were much lower at low sliding velocities under oil lubricated condition. A stable value of friction coefficient against sliding velocity variation was also obtained for the thermoplastic resin/RB ceramics composites as compared with the neat thermoplastic resins under both dry and oil lubricated conditions. Furthermore, a remarkable reduction of specific wear rate was achieved for the newly developed composites as compared with the neat resins under dry condition (67-98% reduction) and oil lubricated conditions (68-99% reduction). These results would suggest that RB ceramics particles can be applied as filler for polymer composites providing both low friction and high wear resistance.
Ni-Cr alloy sliding tests in the atmosphere at 1000 °C which is higher than the temperatures used in the conventional research were carried out and observed the process in which glazed oxide layer is formed on the wear track. By the analysis of the element distribution on the cross-section of the glazed oxide layer formed on the wear track after the friction had been reduced, we have clarified that the glazed oxide layer formation process is the same as the process found by the conventional research. Furthermore, the discharge of wear particle necessary for the formation of glazed oxide is further promoted at 1000 °C and therefore glazed oxide begins to form on the comparatively early stage, thereby showing low friction and low wear.
Surface texturing is considered to be an effective means of enhancing the properties of a tribological contact not only in a normal uni-directional sliding condition but also in fretting under lubricated conditions. Well-regulated “micro dimples” were formed on a flat surface using the method of micro fabrication. In this study, a bearing steel (HV760) was used for the specimens with ball-on-flat configuration. The frictional force and relative movement between the specimens were measured simultaneously during fretting with a frequency 7.35 Hz, for fretting up to 2 × 105 cycles under a lubricated condition of 350 neutral oil (typically used for grease lubricated contacts). The normal load, and fretting stroke were varied in the range of 4.9 N to 22.1 N, 12 μm to 215 μm respectively. The initial running-in process (namely, the phenomenon of a significant reduction in the coefficient of friction seen in the early stages of fretting) was the main focus of the study, with comparisons being made between specimens with flat surfaces. The main findings were that a micro texturing surface resulted in a reduced number of cycles to complete the running-in process (when compared to the flat surface), but that the wear scar was wider in the micro texturing surface. It is proposed that the micro texturing surface provides a less stiff contact than the flat surface and that the lubricant can become entrapped in the dimples in the contact, and thus provide enhanced entrainment of the lubricant into the contact.
The success of a spacecraft mission depends to a great extent on the performance of the moving mechanical systems. The most common mode of failure in these systems is tribological. Tribological failures occur mainly due to non availability of lubricant at the working zone of the bearings as a result of degradation, evaporation and creep. The life of these moving mechanical systems could be extended, if lubricant is replenished by some means. This paper describes the development of a positive lubrication system named as command lubrication system (CLS). This is an active lubrication system which when actuated by external commands delivers lubricant to the bearings. It is actuated only when there is a demand for lubricant indicated by increase in frictional torque or bearing temperature. The outstanding feature of this system is that the lubricant is stored under ambient pressure and hence less chance of leakage. The CLS can solve the lubrication problem of spacecraft systems which require very long mission life of more than 20 years. It is also suitable to tribosystems in terrestrial devices.
We have a problem of fish adhering to the metal grids of grill during grilling fish strongly. This problem is difficult to be solved because the grids of grill coated the fluorine resin which was used generally could be disintegrated at more than 300 °C. This adhesion mechanism is so complicated phenomena. As a usual, the maximum peeling force to peel off fish from the grids is the parameter to evaluate the adhesion properties of grids. However, such maximum peeling force is not basic data with physical meaning because it depends on the sequence of peeling fish. Therefore we proposed a new evaluation method. We focused on the adhesion of fish protein against a rod specimen. We poured the fish protein on a plate specimen, put a rod specimen on them and heated them in an electric furnace. One minute later, we pulled up an end of the rod specimen in the constant speed. During this experiment, we measured the peeling force and the displacement of the end of the rod specimen. After this experiment, we observed the plate specimen with SEM and EDS to evaluate the contact area at the interface between the rod specimen and denatured fish protein.
Fretting wear is often the case when ball-and-roller bearings oscillate under grease lubrication. Against the backdrop of fretting wear on the wheel bearings of automobiles caused by rail transportation, the ASTM D4170 fretting test method was developed to evaluate the fretting protection property of lubricating grease. The ASTM test is conducted under a fixed load, but the load condition for industrial machines usually fluctuates. Currently, there is no international standard to evaluate the fretting wear under fluctuating load. In this study, using thrust ball bearings the authors examined 14 kinds of commercially produced greases and three kinds of originally prepared greases on fretting protection evaluation under both the ASTM test and the impact fretting test. Consequently, the authors found out the inversion of the order of fretting protection superiority between the ASTM test and the impact fretting test. As for the kinematic viscosity of base oil of grease, the amount of wear of ASTM test increases with increasing the kinematic viscosity, on the other hand the wear of impact fretting test decreases with increasing the kinematic viscosity.
The durability of a hybrid ceramic 25-mm-bore ball bearing having a single outer land-guided retainer was evaluated and improved in liquid hydrogen at speeds up to 120,000 rpm (120,000 min-1) (3 million DN) by comparing the propagation of superficial thermal microcracks on Si3N4 balls at various speeds. To select a tough Si3N4 ball capable of restraining crack propagation, bearing tests were conducted for three kinds of the Si3N4 balls with different jet-cooling systems. The test results showed that the Si3N4 ball having high fracture toughness as well as high thermal shock resistance could restrain the propagation of wide-ditch microcracks. With regard to the jet-cooling system, four nozzles were better than two nozzles with increasing jet speed. Furthermore, the jet flow aimed at the retainer was superior to that aimed at the inner race, and its result indicated that microcracks might be generated at the trace in contact with the outer raceway under insufficient cooling conditions with a large centrifugal force. Thus, decreasing the maximum contact stress of the outer race to 2.0 GPa by a limited race curvature of 0.51 could restrain the propagation of superficial microcracks.