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Results for “Lubricants”

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 1,513 records · Page 84

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NASA NTRS1975

Effect of starvation on film thickness and traction under elastohydrodynamic rolling and sliding conditions

Traction measurements under starved elastohydrodynamic conditions were obtained for a point-contact geometry. Simultaneous measurements of the film thickness and the location of the inlet lubricant boundary were made. Optical interferometry was used to measure film thickness. The thickness of a starved film for combined rolling and sliding conditions varies with the location of the inlet boundary in the same way as previously found for pure rolling conditions. When the fluid velocity distribution is calculated in the inlet region by a Reynolds lubrication analysis, backflow is seen to occur over a portion of the inlet region. Backflow is essential for the establishment of a flooded condition. The location of certain fluid velocity conditions within the inlet region, as suggested in the literature, does not adequately describe the onset of starvation. For the same slide-roll ratio a starved film was observed to possess greater traction than a flooded film. Traction measurements under starved conditions were also compared with those under flooded conditions for equivalent shear rates in the Hertzian region. When the shear rates within the Hertzian region were low and the film was severely starved, the measured tractions were lower than expected. This may be due to large shear stresses developed by the large pressure gradients that are generated in the inlet region when it is severely starved.

Wedeven, L. D.↗

NASA NTRS1976

Dynamic sealing principles

The fundamental principles governing dynamic sealing operation are discussed. Different seals are described in terms of these principles. Despite the large variety of detailed construction, there appear to be some basic principles, or combinations of basic principles, by which all seals function, these are presented and discussed. Theoretical and practical considerations in the application of these principles are discussed. Advantages, disadvantages, limitations, and application examples of various conventional and special seals are presented. Fundamental equations governing liquid and gas flows in thin film seals, which enable leakage calculations to be made, are also presented. Concept of flow functions, application of Reynolds lubrication equation, and nonlubrication equation flow, friction and wear; and seal lubrication regimes are explained.

Zuk, J.↗

NASA NTRS1976

Surface tension propellant control for Viking 75 Orbiter

The paper describes the selection, development and qualification of the surface tension system and includes results of low-g drop tower tests of scale models, 1-g simulation tests of low-g large ullage settling and liquid withdrawal, structural qualification tests, and propellant surface tension/contact angle studies. Subscale testing and analyses were used to evaluate the ability of the system to maintain or recover the desired propellant orientation following possible disturbances during the Viking mission. This effort included drop tower tests to demonstrate that valid wick paths exist for moving any displaced propellant back over the tank outlet. Variations in surface tension resulting from aging, temperature, and lubricant contamination were studied and the effects of surface finish, referee fluid exposure, aging, and lubricant contamination on contact angle were assessed. Results of movies of typical subscale drop tower tests and full scale slosh tests are discussed.

Dowdy, M. W.↗

NASA NTRS1977

Adhesion and friction of iron and gold in contact with elemental semiconductors

Adhesion and friction experiments were conducted with single crystals of iron and gold in contact with single crystals of germanium and silicon. Surfaces were examined in the sputter cleaned state and in the presence of oxygen and a lubricant. All experiments were conducted at room temperature with loads of 1 to 50 grams, and sliding friction was at a sliding velocity of 0.7 mm/min. Results indicate that the friction nature of metals in contact with semiconductors is sensitive to orientation, that strong adhesion of metals to both germanium and silicon occurs, and that friction is lower with silicon than with germanium for the same orientation. Surface effects are highly sensitive to environment. Silicon, for example, behaves in an entirely brittle manner in the clean state, but in the presence of a lubricant the surface deforms plastically.

Buckley, D. H.↗

NASA NTRS1977

Computer program for flat sector thrust bearing performance

A versatile computer program is presented which achieves a rapid, numerical solution of the Reynolds equation for a flat sector thrust pad bearing with either compressible or liquid lubricants. Program input includes a range in values of the geometric and operating parameters of the sector bearing. Performance characteristics are obtained from the calculated bearing pressure distribution. These are the load capacity, center of pressure coordinates, frictional energy dissipation, and flow rates of liquid lubricant across the bearing edges. Two sample problems are described.

Presler, A. F.↗

NASA NTRS1978

Thermal performance of shaft bearing system

Computer program calculates loads, torques, temperature, and fatigue life of multibearing shaft system operating with either wet or dry friction. Program is also capable of predicting system reactive to termination of lubricant supply to bearings and other lubricated mechanical elements.

Crecelius, W.↗

NASA NTRS1978

Techniques used for limiting degradation products of polymeric materials for use in the space environment

Techniques are discussed for limiting or controlling the degradation products (outgassing) of polymeric materials in the space environment. One technique, now ASTM E-595-77, is used to screen out those materials which lose greater than 1% Total Mass Loss when in vacuum for 24 hours at 125 C and which have more than 0.10% Collected Volatile Condensable Materials condensing on a collector surface at 25 C. Examples of silicone materials which are high and low in outgassing are given. The numerous mechanical motions in spacecraft experiments require liquid lubricants which also might degrade in space. Labyrinth seals and barrier films are utilized to limit the degradation of or from these lubricants. A recoverable in-flight experiment has been proposed for making definitive measurements of how effective these techniques are in limiting the amounts and escape paths of outgassed molecules.

Vest, C. E.↗

NASA NTRS1978

Cantilever mounted resilient pad gas bearing

A gas-lubricated bearing is described, employing at least one pad mounted on a rectangular cantilever beam to produce a lubricating wedge between the face of the pad and a moving surface. The load-carrying and stiffness characteristics of the pad are related to the dimensions and modulus of elasticity of the beam. The bearing is applicable to a wide variety of types of hydrodynamic bearings.

Etsion, I.↗

NASA NTRS1978

A study of various synthetic routes to produce a halogen-labeled traction fluid

Several synthetic routes were studied for the synthesis of the compound 1, 1, 3-trimethyl-1, 3-dicyclohexyl-2 chloropropane. This halogen-labeled fluid would be of use in the study of high traction lubricants under elastohydrodynamic lubrication conditions using infrared emission spectroscopy. The synthetic routes included: dimerization of alpha-methylstyrene, methanol addition to alpha-methylstyrene, a Wittig reaction, and an organometallic approach. Because of steric hindrance and competing reactions, none of these routes were successful.

Jones, W. R., Jr.↗

NASA NTRS1979

Method of making bearing materials

A method is described for making a composite material which provides low friction surfaces for materials in rolling or sliding contact. The composite material which is self-lubricating and oxidation resistant up to and in excess of about 930 C is comprised of a metal component which lends strength and elasticity to the structure and a fluorine salt component which provides oxidation protection to the metal but may also enhance the lubrication qualities of the composite.

Sliney, H. E.↗

NASA NTRS1979

Operating characteristics of a large-bore roller bearing to speeds of 3 times 10 to the 6th power DN

A 118-millimeter-bore roller bearing was studied parametrically at speeds from 10,000 to 25,500 rpm. The bearing had a round outer ring (not preloaded), and provisions were made for lubrication and cooling through the inner ring. In some tests the outer ring was also cooled. The bearing ran successfully at 300,00 DN with very small evidence of cage slip. Load, which was varied from 2200 to 8900 newtons (500 to 2000 lb), had no effect on bearing temperature or cage slip over the speed range tested. Bearing temperature varied inversely with cage slip for all test conditions. Cooling the outer ring decreased its temperature but increased the inner-ring temperature. Heat rejected to the lubricant (power loss within the bearing) increased with both shaft speed and total oil flow rate to the inner ring.

Schuller, F. T.↗

NASA NTRS1977

Scanning and focusing mechanisms of METEOSAT radiometer

Two mechanisms, both of screw-jack type are described. The scanning mechanism, an oil lubricated and sealed unit drives and accurately positions the telescope of the METEOSAT radiometer. The dry lubricated focusing mechanism is used to adjust the focus of this telescope. The METEOSAT program is nearly completed, and the first flight model will be launched at the end of the year.

Jouan, J.↗

NASA NTRS1978

Evaluation of SHABERTH: A bearing simulation computer program

To investigate lubrication effects on bearing thermal performance, an investigation was performed to determine the feasibility of using the SKF program SHABERTH for simulating the performance of cryogenically lubricated ball bearings. As a part of this study, the particular application chosen for SHABERTH was to simulate the performance of the Space Shuttle main engine turbo-pump and pre-burner bearing system.

Source record↗

NASA NTRS1979

Slicing of Silicon into Sheet Material: Silicon Sheet Growth Development for the Large Area Silicon Sheet Task of the Low Cost Silicon Solar Array Project

Testing of low cost low suspension power slurry vehicles is presented. Cutting oils are unlikely to work, but a mineral oil with additives should be workable. Two different abrasives were tested. A cheaper silicon carbide from Norton gave excellent results except for excessive kerf loss: the particles were too big. An abrasive treated for lubricity showed no lubricity improvement in mineral oil vehicle. The bounce fixture was tested for the first time under constant cut rate conditions (rather than constant force). Although the cut was not completed before the blades broke, the blade lifetime of thin (100 micrometer) blades was 120 times the lifetime without the fixture. The large prototype saw completed a successful run, producing 90% cutting yield (849 wafers) at 20 wafers/cm. Although inexperience with large numbers of wafers caused cleaning breakage to reduce this yield to 74%, the yield was high enough that the concept of the large saw is proven workable.

Fleming, J. R.↗

NASA NTRS1979

Surface temperatures and glassy state investigations in tribology, part 2

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. The maximum yield shear stress (limiting shear stress) is a function of temperature and pressure and is believed to be the property which determines the maximum traction in elastohydrodynamic contacts such as traction drives. A shear rheological model based on primary laboratory data is proposed for concentrated contact lubrication. The model is 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.

Bair, S. S.↗

NASA NTRS1979

Comparison of predicted and measured elastohydrodynamic film thickness in a 20-millimeter-bore ball bearing

Elastohydrodynamic film thicknesses were measured for a 20-mm bore ball bearing using the capacitance technique. The bearing was thrust loaded to 90, 445, and 778 N (20, 100, and 175 lb). The corresponding maximum contact stress on the inner race was 1.28, 2.09, and 2.45 GPa (185 000, 303,000, and 356, 000 psi). Test speeds ranged from 400 to 15,000 rpm. Measurements were taken with four different lubricants: (1) synthetic paraffinic; (2) synthetic paraffinic with additives; (3) synthetic type II aircraft oil; and (4) synthetic cycloaliphatic hydrocarbon traction fluid. The test bearing was mist lubricated. Test temperatures were 27, 65, and 121 C (80, 150, and 250 F). The measured results for the various test parameters were compared to theoretical predictions from computer programs. Also the data were plotted on dimensionless coordinates and compared to several classical isothermal theories.

Coy, J. J.↗

NASA NTRS1979

Surface temperatures and glassy state investigations in tribology

The limiting shear stress shear rheological model was applied to property measurements pursuant to the use of the constitutive equation and the application of the constitutive equation to elastrohydrodynamic (EHD) traction. Experimental techniques were developed to subject materials to isothermal compression which is similar to the history the materials were subjected to in EHD contacts. In addition, an apparatus was developed for measuring the shear stress-strain behavior of solid lubricating materials. Four commercially available materials were examined under pressure. They exhibit elastic and limiting shear stress behavior similar to that of liquid lubricants. The application of the limiting shear stress model to traction predictions was extended employing the primary materials properties measured in the laboratory. The shear rheological model was also applied to a Grubin-like EHD inlet analysis for predicting film thicknesses when employing the limiting shear stress model material behavior.

Bair, S.↗

NASA NTRS1979

NASA gear research and its probable effect on rotorcraft transmission design

The results of the NASA gear research is reviewed as well as those programs which are presently being undertaken. Research programs studying pitting fatigue, gear steels and processing, life prediction methods, gear design and dynamics, elastohydrodynamic lubrication, lubrication methods and gear noise are presented. The impact of advanced gear research technology on rotorcraft transmission design is discussed.

Zaretsky, E. V.↗