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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Investigations of lubricant rheology as applied to elastohydrodynamic lubrication

Traction prediction in sliding elastohydrodynamic (EHD) contacts was examined along with an elastohydrodynamic lubrication simulation of the effects of load and speed on temperatures in the EHD contact. An existing shear stress theory and lubricant rheological model were studied and evaluated by applying them to traction prediction. Results obtained using measured film thickness and surface temperature data, were compared with measured traction values. The infrared technique for measuring temperatures in an EHD contact was further developed and ball surface and fluid temperatures are reported for sliding speeds of 0.35 to 5.08 m/s at 0.52 to 2.03 GN/sq m maximum pressure and surface roughnesses of .011 to .381 micrometers c.1.a. The relationship between asperity interaction, as measured by relocation surface profilimetry and high frequency temperature measurements, and the ratio of film thickness to surface roughness was also studied.

Kunz, R. K.↗
NASA NTRS1976

Oil-air mist lubrication as an emergency system and as a primary lubrication system

The feasibility of an emergency aspirator once-through lubrication system was demonstrated as a viable survivability concept for Army helicopter mainshaft engine bearings for periods as long as 30 minutes. It was also shown in an experimental study using a 46-mm bore bearing test machine that an oil-air mist once-through system with auxiliary air cooling is an effective primary lubrication system at speeds up to 2,500,000 DN for extended operating periods of at least 50 hours.

Loomis, W. R.↗
NASA NTRS1978

Investigations of lubricant rheology as applied to elastohydrodynamic lubrication

Measurements of lubricant shear rheological behavior in the amorphous solid region and near the liquid-solid transition are reported. Elastic, plastic and viscous behavior was observed. A shear rheological model based on primary laboratory data is proposed for concentrated contact lubrication. The model is a Maxwell model modified with a limiting shear stress. Three material properties are required: low shear stress viscosity, limiting elastic shear modulus, and the limiting shear stress the material can withstand. All three are functions of temperature and pressure. In applying the model to EHD contacts the predicted response possesses the characteristics expected from several experiments reported in the literature.

Bair, S.↗
NASA NTRS1984

Simulation of lubricating behavior of a thioether liquid lubricant by an electrochemical method

An electrochemical cell was constructed to explore the possible radical anion forming behavior of a thioether liquid lubricant. The electrochemical behavior of the thioether was compared with the electrochemical behavior of biphenyl, which is known to form radical anions. Under controlled conditions biphenyl undergoes a reversible reaction to a radical anion, whereas the thioether undergoes an irreversible reduction yielding several products. These results are discussed in relation to boundary lubrication.

Morales, W.↗
NASA NTRS1986

Simulation of lubricating behavior of a thioether liquid lubricant by an electrochemical method

An electrochemical cell was constructed to explore the possible radical anion forming behavior of a thioether liquid lubricant. The electrochemical behavior of the thioether was compared with the electrochemical behavior of biphenyl, which is known to form radical anions. Under controlled conditions biphenyl undergoes a reversible reaction to a radical anion, whereas the thioether undergoes an irreversible reduction yielding several products. These results are discussed in relation to boundary lubrication.

Morales, W.↗
NASA NTRS1988

Lubricating properties of molybdenum disulfide. Part 3: Performance of molybdenum disulfide-containing oils in fluid lubrication

The lubricating properties of a straight mineral oil with and without MoS2 powder were studied. Bearing testers of thrust-collar type and of journal bearing type were used for thin- and fluid-film conditions, respectively. The effectiveness of the MoS2 powder in the oil differed depending on the conditions of the rubbing surfaces. For fluid film conditions, considerable effects of the MoS2 were observed, in contrast to the thin-film cases. The addition of MoS2 powder was effective only when the lubricant film was formed between surfaces thickly enough to allow the inflow of MoS2 particles.

Soda, Norimune↗
NASA NTRS1980

High temperature self-lubricating coatings for air lubricated foil bearings for the automotive gas turbine engine

coating combinations were developed for compliant surface bearings and journals to be used in an automotive gas turbine engine. The coatings were able to withstand the sliding start/stops during rotor liftoff and touchdown and occasional short time, high speed rubs under representative loading of the engine. Some dozen coating variations of CdO-graphite, Cr2O3 (by sputtering) and CaF2 (plasma sprayed) were identified. The coatings were optimized and they were examined for stoichiometry, metallurgical condition, and adhesion. Sputtered Cr2O3 was most adherent when optimum parameters were used and it was applied on an annealed (soft) substrate. Metallic binders and interlayers were used to improve the ductility and the adherence.

Bhushan, B.↗
NASA NTRS2005

Ball Bearings Equipped for In Situ Lubrication on Demand

In situ systems that provide fresh lubricants to ball/race contacts on demand have been developed to prolong the operational lives of ball bearings. These systems were originally intended to be incorporated into ball bearings in mechanisms that are required to operate in outer space for years, in conditions in which lubricants tend to deteriorate and/or evaporate. These systems may also be useful for similarly prolonging bearing lifetimes on Earth. Reservoirs have been among the means used previously to resupply lubricants. Lubricant- resupply reservoirs are bulky and add complexity to bearing assemblies. In addition, such a reservoir cannot be turned on or off as needed: it supplies lubricant continuously, often leading to an excess of lubricant in the bearing. A lubricator of the present type includes a porous ring cartridge attached to the inner or the outer ring of a ball bearing (see Figure 1). Oil is stored in the porous cartridge and is released by heating the cartridge: Because the thermal expansion of the oil exceeds that of the cartridge, heating causes the ejection of some oil. A metal film can be deposited on a face of the cartridge to serve as an electrical-resistance heater. The heater can be activated in response to a measured increase in torque that signals depletion of oil from the bearing/race contacts. Because the oil has low surface tension and readily wets the bearing-ring material, it spreads over the bearing ring and eventually reaches the ball/race contacts. The Marangoni effect (a surface-tension gradient associated with a temperature gradient) is utilized to enhance the desired transfer of lubricant to the ball/race contacts during heating. For a test, a ball bearing designed for use at low speed was assembled without lubricant and equipped with a porous-ring lubricator, the resistance heater of which consumed a power of less than 1 W when triggered on by a torque-measuring device. In the test, a load of 20 lb (.89 N) was applied and the bearing was turned at a rate of 200 RPM. The lubricator control was turned on at the beginning of the test, turned off for about 800 seconds, then turned on again. As shown in Figure 2, the controlled lubricator stabilized the torque in a low range, starting immediately after initial turn-on and immediately after resumption of the lubricator control.

Marchetti, Mario↗
NASA NTRS1965

Dry film lubricants

The Space Age has necessitated accelerated development of many technologies which have direct application to commercial, earthbound hardware. One striking example is dry film lubrication. The stimulus for the development of dry film lubricants was provided by the unsatisfactory condition created when commercial liquid lubricants were exposed to the multiple environs of space. In the search for a satisfactory solution to lubrication in space, dry films were investigated. The dry film lubrication concept has proven most desirable for space, and a natural fallout is the potential shown by such films for consumer item application. On the acceptance that the coefficient of friction of dry films is not equivalent to that of a liquid lubricant under ideal conditions, this paper discusses how the ideal condition for liquid lubrication is rarely achieved in practical applications. Comparisons are made between the performance of dry film and liquid lubricants as a function of temperature, environmental pressure, and life. Furthermore, consideration is given to the comparative costs of liquid versus dry film lubricants to show the practicality and desirability of dry film lubrication to consumer items. Although no data on the performance of consumer items lubricated with dry films are presented, the comparisons clearly establish the potential of dry film lubricants in a competitive consumer market.

SOLID LUBRICANT↗
NASA NTRS1984

Status and New Directions for Solid Lubricant Coatings and Composite Materials

At one time, solid lubricants were used almost entirely in aerospace applications. Today there is a pronounced trend to use them over a much broader range of applications. For example, self-lubricating polymer-based composites have displaced traditional oil-lubricated, metallic composites for many journal bearings and thrust, washers in applications as diverse as earthmoving machinery and snow blowers to aircraft applications. For moderate temperatures below 200° C, glass filament-wound epoxy bearings with PTFE lubricating liners are useful; for temperatures up to 350° C, graphite fiber reinforced polyimide bearing materials are finding applications. Molybdenum disulfide, graphite, and PTFE are the most widely known and used solid lubricants, and there is increasing interest in the relatively new solid lubricant graphite fluoride. Advanced technology engines such as the adiabatic diesel and the small, efficient gas turbine have severe lubrication and wear problems at temperatures beyond the capabilities of any of these lubricants. Here, self-lubricating ceramics and inorganic composites for use at I000° C or higher are of interest. However, perhaps the most significant new direction for solid lubricant coatings and self-lubricating composites is their steadily increasing use in dry bearings for large volume, moderate temperature applications. This can be attributed to their simplicity of use (no supporting lubricant system needed), light weight, convenience, and general cost effectiveness.

Harold E Sliney↗
NASA NTRS1991

Effect of two synthetic lubricants on life of AISI 9310 spur gears

Spur-gear fatigue tests were conducted with two lubricants using a single lot of consumable-electrode vacuum-melted (CVM) AISI 9310 spur gears. The gears were case carburized and hardened to Rockwell C60. The gear pitch diameter was 8.89 cm. The lot of gears was divided into two groups, each of which was tested with a different lubricant. The test lubricants can be classified as synthetic polyol-ester-based lubricants. One lubricant was 30 percent more viscous that the other. Both lubricants have similar pressure viscosity coefficients. Test conditions included a bulk gear temperature of 350 K, a maximum Hertz stress of 1.71 GPa at the pitch line, and a speed of 10,000 rpm. The surface fatigue life of gears tested with one lubricant was approximately 2.4 times that for gears tested with the other lubricant. The lubricant with the 30 percent higher viscosity gave a calculated elastohydrodynamic (EHD) film thickness that was 20 percent higher than the other lubricant. This increased EHD film thickness is the most probable reason for the improvement in surface fatigue life of gears tested with this lubricant over gears tested with the less viscous lubricant.

Townsend, Dennis P.↗