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In the first part of this series, we covered the reasons why lubrication is necessary for anti‐friction bearings and the duties that the lubricant has to perform. We will…
In the first part of this series, we covered the reasons why lubrication is necessary for anti‐friction bearings and the duties that the lubricant has to perform. We will now consider the lubricant itself.
SELECTING the correct bearing for any particular application involves more than the determination of the correct type and size. It is true that the calculation of the nominal working life will give an indication of the operational life before failure, but this calculation only takes into account the fatigue life of the material. If this theoretical life is to be obtained—and perhaps exceeded—then additional factors must be taken into account when initially designing the bearing arrangement. Lubrication and protection from the operating environment are two very important considerations.
The effects of space environment on friction and wear and on the selection of lubricants and self‐lubricating materials for spacecraft mechanisms are discussed, with special emphasis on the ultrahigh vacuum of space. Experimental studies have demonstrated the feasibility of using selected oils and greases to lubricate lightly loaded ball bearings without replenishment for periods of over one year under the following conditions of operation : speeds of 8,000 rpm, temperatures of 160 to 200°F., and vacuum of 10–8 torr. Over one‐half year of successful operation has been achieved under similar operating conditions with self‐lubricating retainers of reinforced Teflon, provided that the loads were light. Bonded films of molybdenum disulfide have given shorter lifetimes and poor repro‐ducibility. Metal‐to‐metal slip‐ring contacts introduce excessive electrical noise into circuits when operated in vacuum of 10–7 torr. The noise (as well as the friction and wear) can be markedly reduced by providing a small amount of oil vapor, sufficient to maintain a pressure on the order of 10–6 torr, or by incorporating molybdenum disulfide into the brush material.
New, undestroyed greases of the same brands as those used in a field test, described in Part 1, were examined using conventional methods, such as the SKF V2F test, the…
New, undestroyed greases of the same brands as those used in a field test, described in Part 1, were examined using conventional methods, such as the SKF V2F test, the roll stability test (ASTM D‐1831), the Grease Worker (ASTM D‐217), the torque test (ASTM 1478‐91), bleeding measurements ( IP 121), yield stress measurements, the 4‐ball test (ASTM D 2266‐86), base oil viscosity measurements, thickener content and the cone penetration test (ASTM D217‐88). The greases have also been tested with several new test methods developed at the University. A specification for relevant testing methods was drawn up and the connections between the tested parameters were investigated. It was found that the mechanical stability could be predicted with a combination of ASTM D‐1831 and the limiting shear stress coefficient γ. This coefficient is capable of predicting wear. It was found that the bearing temperature could be predicted by using the base oil viscosity.
OVER the years lithium soap greases have earned a reputation of providing excellent service under a wide variety of operating conditions. Since their introduction in the early 1950s, lithium soap greases have served the market well, being especially suitable for both automotive and industrial multipurpose applications. Their performance has enabled them to grow in commercial importance to the point where they now account for over half the grease volume manufactured in the United States.
Describes the structure and rheological characteristics of soap based greases and how the thickener retains the oil phase. Illustrates the thixotropic behaviour and effect…
Describes the structure and rheological characteristics of soap based greases and how the thickener retains the oil phase. Illustrates the thixotropic behaviour and effect of time of shearing on friction, film thickness, noise energy loss in grease lubricated contacts. Shows how friction can be less with grease than with oil.
This paper aims to carry out tribological experiments to explore the applications of femtosecond laser surface texturing technology on rock bit sliding bearing to enhance…
This paper aims to carry out tribological experiments to explore the applications of femtosecond laser surface texturing technology on rock bit sliding bearing to enhance the lifetime and working performance of rock bit sliding bearing under high temperature and heavy load conditions.
Surface textures on beryllium bronze specimen were fabricated by femtosecond laser ablation (800 nm wavelength, 40 fs pulse duration, 1 kHz pulse repetition frequency), and then the tribological behaviors of pin-on-disc configuration of rock bit bearing were performed with 20CrNiMo/beryllium bronze tribo-pairs under non-Newtonian lubrication of rock bit grease.
The results showed that the surface texture on beryllium bronze specimens with specific geometrical features can be achieved by optimizing femtosecond laser processing via adjusting laser peak power and exposure time; more than 52 per cent of friction reduction was obtained from surface texture with a depth-to-diameter ratio of 0.165 and area ratio of 5 per cent at a shear rate of 1301 s−1 under the heavy load of 20 MPa and high temperature of 120°C, and the lubrication regime of rock bit bearing unit tribo-pairs was improved from boundary to mixed lubrication, which indicated that femtosecond laser ablation technique showed great potential in promoting service life and working performance of rock bit bearing.
Femtosecond laser-irradiated surface texture has the potential possibility for application in rock bit sliding bearing to improve the lubrication performance. Because proper micro dimples showed good lubrication and wear resistance performance for unit tribo-pairs of rock bit sliding bearing under high temperature, heavy load and non-Newtonian lubrication conditions, which is very important to improve the efficiency of breaking rock and accelerate the development of deep-water oil and gas resources.
– This paper aims to study the impact of surface texture on grease-lubricated journal bearing, load-carrying capacity, friction and friction coefficient.
This paper aims to study the impact of surface texture on grease-lubricated journal bearing, load-carrying capacity, friction and friction coefficient.
The paper opted for a basic application research using the commercial CFD software FLUENT 14.0.
The load-carrying capacity can be enhanced if the surface texture is introduced from a suitable position. The textural shape has a more significant effect on the friction and load-carrying capacity than the friction coefficient. The rheological parameters of grease affect the load-carrying capacity in the same way, i.e. the load increases with the increase in the rheological parameters. With the decrease in the value of cavitation pressure, the cavitation area reduces but the dynamic pressure area gets enlarged.
Because of the chosen research method, the research results may lack the analysis of experiments.
The research results can be applied to the domain in the high-speed spindle and lubricated multibody system.
The investigation on the performances of grease-lubricated journal bearing with surface texture would be significant.
The Eastern Region of British Railways are evaluating, on the tortuous 10 mile route between Liverpool Street and Chingford, methods of reducing flange wear on the wheels of multiple unit passenger trains. Among the greasing systems being studied is the Enots‐Vogel equipment designed for greasing both inner and outer faces of wheel flanges and supplied by Enots Ltd., Aston Brook Street, Birmingham 6. Equipment of this type has been in use on European railways for some time but only for the treatment of the outer faces of wheel flanges (this is because of a basic difference in railroad design practised there—in Europe check rails are, in general, only installed as parts of points, but in Britain they are often laid on curves so that check rail mileage often represents a significant proportion of total track mileage).