Showing papers in "Tribology Transactions in 1980"

Viscosity pressure correlation of liquids

Abstract: A single correlation was obtained to predict Newtonian viscosity-pressure coefficients of mineral oils, resin and polymer blends, pure hydrocarbons, and nonhydrocarbons. The correlation has been tested for a temperature range from 0°c (32 °F) to 135°C (275 °F). The empirical correlation makes use of atmospheric viscosity and density at the temperature of interest and viscosity-temperature property (mo) of the fluids. When the correlation was compared with other leading correlations, it was shown to require less physical-property data, apply to n wider range of chemical compositions, cover a wider range in fluidity, and provide greater accuracy. The correlation is presented in the form of a polynominal equation. Presented at the 34th Annual Meeting in St. Louis, Missouri, April 30-May 3, 1979

Friction and Wear at High Sliding Speeds

Abstract: Sliding tests have been carried out using a variety of soft metal and nonmetal pins on a rotating steel disk at speeds up to 150 m/s. A new high-speed friction apparatus in which the normal force, the friction force and the friction coefficient are recorded, was used. In general, the wear rate increased drastically, and the friction coefficient decreased moderately as the sliding speed was raised, these changes being especially pronounced when pin materials of low melting temperature were used. The friction data are in good agreement with those obtained by others using the pin-on-disk geometry. However, although in many cases the interface reached the melting temperature of the lower melting sliding material, the very low friction coefficient values of under 0.05 reported by some investigators were not reached. Presented at the 34th Annual Meeting in St. Louis, Missouri, April 30-May 3, 1979

Analysis of Step Journal Bearings—Finite Length, Stability

Abstract: The finite length pressure dam step bearing is analyzed neglecting step inertia effects, but including the effects of turbulence over the entire bearing surface. Load curves for sample step bearing designs are given along with stiffness and damping coefficients. Bearing stability threshold curves for various pressure dam bearing geometries are compared to plain journal, two-axial groove and grooved lower-half bearings. The optimum Sommerfeld number range for designing a pressure dam bearing to increase stability is S > 2.0. At S values of this order, the recommended film thickness ratio for favorable stability is between 3.0 and 6.0 with the step located at 145° in the direction of rotation from the positive horizontal axis. Presented as an American Society of Lubrication Engineers paper at the ASLE/ASME Lubrication Conference in Minneapolis, Minnesota, October 24–26, 1978

Gas Path Sealing in Turbine Engines

Abstract: A survey of gas path seals is presented with particular attention given to sealing clearance effects on engine component efficiency The effects on compressor-pressure ratio and stall margin are pointed out Various case-rotor relative displacements, which affect gas path seal clearances, are identified Forces produced by nonuniform sealing clearances and their effect on rotor stability are discussed qualitatively, and recent work on turbine-blade-tip sealing for high temperatures is described The need for active clearance control and for engine structural analysis is discussed The functions of the internal-flow system and its seals are reviewed Presented as an American Society of Lubrication Engineers paper at the ASLE/ASME Lubrication Conference in Minneapolis, Minnesota, October 24–26, 1978

Surface Chemistry of Some Antiwear Additives as Determined by Electron Spectroscopy

Abstract: A scanning Auger microprobe (SAM) investigation was performed to determine the spatial distribution of species produced during boundary lubrication at a steel-on-steel interface. Some correlations were made with the severity of wear as determined by a modified cup-block ASTM-EP lubricant test. Tested extreme-pressure (EP) additives include zinc di-isodecyldithiophosphate (ZDP), hexadecyl diethyldithiocarbamate (HDDC), and benzyl disulfide (BD). Presented at the 34th Annual Meeting in St. Louis, Missouri, April 30–May 3, 1979

The Preparation and Nature of Surface Films from Zinc Dialkyldithiophosphate

Abstract: An Amsler wear-testing machine has been modified to accept mechanisms by which the nominal line-contact between a rotating disk and a stationary flat plane can be traversed slowly along the plane. Lubricant reaction films formed at the contact are thus made available over an area of about 9 × 6 mm2. It has been found that the most uniform films are produced by maintaining a constant coefficient of friction during the traverse. Running-in of the disk is also beneficial. More extensive coverage is obtained by repeating the traverse over a given block. At least two types of film are produced with zinc dialkyldithiophosphates (ZDTPs): a thiophosphate film and a ferrous sulfide film. The latter is associated with localised high-wear score marks. Most films appear to be patchy. Thiophosphate film formed from s-butyl ZDTP additive comprises patches separated by almost bare metal whereas the film from n-butyl ZDTP is more continuous. The results are discussed in relation to the interpretation of analytical and ph...

The Effect of Grooving and Bore Shape on the Stability of Journal Bearings

Abstract: The stability thresholds of four basic journal bearing types are found. Increasing groove size (up to 90°) is found to exert a strong destabilizing effect. Increasing aspect ratio (L/D) also has a destabilizing effect. The stability of each type was found to improve progressively with preload. The influence of bore shape was found to be less important than groove size, α, or preload, δ. For fixed values of α, δ and L/D, the bore shapes in increasing order of stability were found to be: circular, lemon bore, offset halves, three lobe. Some variations on the three-lobe design are investigated. Presented at the 34th Annual Meeting in St. Louis, Missouri, April 30-May 3, 1979

An Analysis of Sealing Characteristics of Oil Seals

Abstract: The authors have studied fundamentally and experimentally the explanation of the sealing mechanism of oil seals. It will be generally noticed that the suction of air occurs to the rubbing portion of the lip of an oil seal which is operating under sealing condition. For the purpose of studying sealing characteristics of an oil seal in the authors' investigations, the volume, [Qbar], of transferred lubricating oil instead of air is used as a means of estimating the sealing status. The authors have clarified that there exists the relation, [Qbar]/uD2∞G1/2, wherein G, u and Dare nondimensional parameter of oil seals, sliding velocity of between shaft and seal and shaft outer diameter, respectively, and that suction coefficient of oil, K (=[Qbar]/uD2G1/2), is dependent on the sealing characteristic constant, Φ, the surface roughness and the lip material of seals. In this paper, it becomes clear that there exists the relation, K = Ko + α(Φnor - Φcon), wherein Φcon are the values estimated by f/G1/3 in the case ...

Performance of End-Face Seals with Diametral Tilt and Coning–Hydrodynamic Effects

Abstract: Hydrodynamic effects in end-face seals with diametral tilt and coning are analyzed. A closed-form solution for the axial separating force and the restoring and transverse moments is presented that covers the whole range from zero to full angular misalignment at various degrees of coning. Both low-pressure seals with cavitating flow and high-pressure seals with full fluid film are considered. The effect of coning is to reduce the axial force and the restoring and transverse moments compared to their magnitude in flat-face seals. Strong coupling between diametral tilt and transverse moment is demonstrated. This transverse moment which is entirely due to hydrodynamic effects can be the source of dynamic instability in the form of seal wobble.

Boundary Lubrication, Thermal and Oxidative Stability of a Fluorinated Polyether and a Perfluoropolyether Triazine

Abstract: Boundary lubricating characteristics, thermal stability and oxidation-corrosion stability were determined for a fluorinated polyether and a perfluoropolyether triazine. A ball-on-disk apparatus, a tensimeter and oxidation-corrosion apparatus were used. Results were compared to data for a polyphenyl ether and a C-ether. The polyether and triazine yielded better boundary lubricating characteristics than either the polyphenyl ether or C-ether. The polyphenyl ether had the greatest thermal stability (443°C) while the other fluids had stabilities in the range 389° to 397°C. Oxidation-corrosion results indicated the following order of stabilities: perfluoropolyether triazine > polyphenylether > C-ether > fluorinated polyether. Presented at the 34th Annual Meeting in St. Louis, Missouri, April 30–May 3, 1979

Simulation of the Lubrication of Isotropically Rough Surfaces

Abstract: The lubrication of area-distributed isotropic rough surfaces is studied by a Monte Carlo method. Small square elements of isotropically rough bearing surfaces are considered. Inside such an element, the film height values have a prescribed probability density distribution, but are generated in a random sequence. Mean unit flow and friction in the elements are determined by applying Reynolds' and solving it numerically by a finite-difference technique. The boundary conditions are provided by generating typical pressures along the elements edges. Accuracy in the computations is ensured by describing each basic valley-ridge trace by a minimum of 16 point values. The results demonstrate that isotropic roughness enhances pressure flow (compared with smooth bearings of the same nominal profile). A rough moving surface enhances shear flow while stationary roughness reduces it. However, quantitatively the results deviate from all current theories, including the one previously put forward by the author. The findin...

Stiffness and Damping Coefficients for Finite Length Step Journal Bearings

Abstract: Stiffness, damping and rigid rotor stability curves are presented for 13, finite-step (pressure dam), journal bearings of different geometries. Step inertia effects are neglected, but the axial and circumferential effects of turbulence over the entire bearing surface are included. Experimental results are compared to a theoretical stability analysis for a single-mass, flexible rotor. Good correlation is obtained between the predicted theoretical stability threshold speed and the experimental threshold speed for three test cases. Presented at the 34th Annual Meeting in St. Louis, Missouri, April 30-May 3, 1979

Elastohydrodynamic Lubrication of Grease-Lubricated Rolling Bearings

Abstract: The lubricant film thickness of grease-lubricated, cylindrical roller thrust bearings was measured, using a capacitance type displacement probe. For comparison, the same tests were also performed with the bearings lubricated with mineral oils. The film thickness and friction torque as a function of rotational speed were determined both under fully flooded and starved lubrication conditions. The test results show that the lubricant film thickness in grease-lubricated bearings is influenced by the base oil, and the thickener. Presented as an American Society of Lubrication Engineers paper at the ASLEIASME Lubrication Conference in Minneapolis, Minnesota, October 24–26, 1978

The Effect of Surface Roughness on the Wear of Low-Density Polyethylene

Abstract: The wear of low-density polyethylene on steel was studied as a function of the roughness of the steel surface and the sliding speed. The wear rate was found to increase as the speed and roughness increased. The mechanism of wear on surfaces with an Ra roughness of 0.065 μm was shown by SEM photos to be film formation and subsequent film breakup and debris formation. On surfaces with an Ra of 1.16 μm roughness, wear was primarily abrasive as evidenced by large wear particles and minimal film formation. The effect of sliding speed was to accelerate the film formation or abrasive wear rather than alter the wear mechanism. The tendency for film formation was correlated with the surface parameters of skewness and kurtosis. Presented at the 34th Annual Meeting in St. Louis, Missouri, April 30–May 3, 1979

Lubricant Degradation and Wear III. Antioxidant Reactions and Wear Behavior of a Zinc Dialkyldithiophosphate in a Fully Formulated Lubricant

Abstract: Earlier model systems studies have shown that the products of the antioxidant reactions of a zinc Dialkyldithiophosphate (ZDTP) with peroxy radicals are ineffective as antiwear agents. Now a similar study has been carried out with a fully formulated synthetic hydrocarbon/ester engine oil aged in fleet tests. The results are consistent with those reported earlier and indicate that the previous conclusion can be extended to a fully formulated lubricant in service. It was found that base stocks containing esters can exhibit increased wear upon addition of ZDTP. However, this can be suppressed by other oil additives. A study of the wear behavior of admixtures of a ZDTP and a hindered phenol reacted with peroxy radicals showed that the hindered phenol did not protect the ZDTP from degradation by antioxidant reactions, a result consistent with analysis of IR spectra presented in the accompanying paper (1). Presented at the 34th Annual Meeting in St. Louis, Missouri, April 30–May 3, 1979

Improved Performance of Film-Riding Gas Seals Through Enhancement of Hydrodynamic Effects

Abstract: Basic components of a spiral-groove, face-type gas seal are shown. Analyses of flow, of thermal environment and heat transfer were made to improve stability, decrease sensitivity to contaminants and reduce leakage. Analysis suggested reduced film thickness and the advantages of spiral-groove design over Rayleigh pad design for thin gas film operation. Experimental program started with static leakage tests to verify pressure deflections at various pressures; a 1000 h dynamic test followed where 114.3 mm (4.5 in.) diameter seals ran successfully at pressures up to 6.2 MPa (900 psig) and speeds up to 73.66 m.s.−1 (14 500 fpm). Presented as an American Society of Lubrication Engineers paper at the ASLE/ASME Lubrication Conference in Minneapolis, Minnesota, October 24–26, 1978

The Accuracy of the Narrow Seal Approximation in Analyzing Radial Face Seals

Abstract: The accuracy of the narrow seal approximation which enables closed form analytical solutions for radial face seals is examined in this paper. Both hydrostatic and hydrodynamic effects in a flat, misaligned seal are considered. Analytical, results obtained from a simplified Reynolds equation, based on the neglect of circumferential pressure gradient and seal curvature, are compared with accurate results from numerical solution of the complete Reynolds equation. The agreement between the approximate and accurate solutions is quite reasonable over a wide range of a seal's inner-to-outer radius ratio. For radius ratios greater than 0.8, the accuracy of the narrow seal approximation is better than 1 percent over most of the range of angular misalignment. Presented as an American Society of Lubrication Engineers paper at the ASLE/ASME Lubrication Conference in Minneapolis, Minnesota, October 24–26, 1978

The Relation Between Pressure and Temperature in Rolling-Sliding EHD Contact

Abstract: A surface pressure/temperature transducer has been used to measure contact zone pressure and temperature distribution between a pair of steel disks. In addition, traction/slip curves have been generated for the same conditions. Data for oils representing a broad range of lubricant types are presented. They are (1) Synthetic paraffinic lubricant (2) Traction fluid (synthetic hydrocarbon) (3) Polyphenyl ether (4) MIL-L-23699 lubricant. The experimental conditions include two loads (0.7 and 1.1 GPa), one speed (220 inls; 5.6 m/s), and a range of slip conditions from 0–23 percent. Very large peak temperatures, up to 200°C above ambient, were observed during the experiments. The highest peak temperatures were observed for rolling-sliding conditions with the traction fluid, but even for pure rolling conditions, temperature rises of 30°C were measured. Presented at the 34th Annual Meeting in St. Louis, Missouri, April 30–May 3, 1979

Lubricant Degradation and Wear II. Antioxidant Capacity and IR-Spectra in Systems Containing Zinc Dialkyldithiophosphates

Abstract: As an extension of earlier work, a systematic study was made of the changes in the antioxidant capacity and infrared spectra of zinc dialkylthiophosphate in model systems and in a fully formulated lubricant aged in laboratory and fleet tests. The reaction of peroxy radicals with a zinc dialkyldithiophosphate in the model systems results in a decay of the P = S absorbance to approximately 40 percent of its initial value. The P=S absorbance is linearly related to the remaining antioxidant capacity of the solutions. For the fully formulated lubricant containing a second ldquo;ashless” antioxidant, the P=S decays to a much lower value approaching zero as the antioxidant capacity approaches a value of about 20 percent of its initial value. A study of the behavior of a zinc dialkyldithiophosphate in admixtures with hindered phenol reveals that the zinc dialkyldithiophosphate was not protected from antioxidant reactions by the hindered phenol, a result which is consistent with results obtained with the fully for...

Failure of Thin Film Lubrication—Function-Oriented Characterization of Additives and Steels

Abstract: The lubrication condition of sliding concentrated steel contacts can be described in terms of transition diagrams, relating the mode of lubrication [i.e. (partial) elastohydrodynamic (EHD), boundary and virtually unlubricated] to load, speed and temperature. Addition of 1 wt. percent zincdialkyldithiophosphate (ZDP) to mineral oil is found to increase the load-carrying capacity of both the EHD and the boundary film, provided that the lubricant contains free oxygen. Under argon cover, the beneficial effects of ZDP are lost. Addition of 1 wt. percent dibenzyldisulfide (DBDS) affects only the load-carrying capacity of the boundary lubricant film. This effect is maintained under argon cover. Increasing the percentage of chromium in the steel from 1.5 wt. percent to 5.6 wt. percent (simultaneously adding up to 1 wt. percent Mo and V), seriously impairs the load-carrying capacity of the boundary lubricant film, while that of the EHD film remains virtually unaffected. On the other hand, an increase in the amount...

Experimental Study of Three Journal Bearings with a Flexible Rotor

Abstract: The unbalance response and stability of a simple flexible rotor was tested over a speed range with three different types of journal bearings: axial groove, pressure dam and tilting pad. Measurements were made of total rotor response, synchronous response and frequency spectrums at various running speeds and at selected locations along the shaft. Axial groove bearings were better for low-speed use and near the critical speed but oil whip occurred at approximately twice the first rotor critical speed. Two sets of pressure dam bearings with different geometries were tested and both controlled vibrations at the critical speed. Whip occurred at twice and thrice the critical speed for the two pressure dam bearings. Tilting-pad beatings exhibited large vibration amplitudes near the critical speed, but did not go into oil whip at speeds up to three times the first rotor critical speed. Presented at the 34th Annual Meeting in St. Louis, Missouri, April 30-May 3, 1979

A Mixed Friction Hydrostatic Mechanical Face Seal Model with Thermal Rotation and Wear

Abstract: A mixed friction model is presented for the mechanical face seal. The model considers load sharing between mechanical and fluid hydrostatic pressures and the friction that results. Thermal rotation resulting from friction heating is included. Equilibrium solutions are presented which show a strong influence of thermal rotation on initial seal performance. A wear model shows that seal faces wear parallel after a period of steady operation in spite of initial taper. The model can be used to simulate seal performance over a period of time and under variable operating conditions. Presented at the 34th Annual Meeting in St. Louis, Missouri, April 30-May 3, 1979

The Role of Surface Chemistry in Lubrication and Scuffing

Abstract: Since the advent, of railways, the main work in lubrication has been towards understanding the formation of the oil film. The emphasis is now changing. Interest, is concentrated on film breakdown. While hydrodynamic theory can calculate the film thickness between surfaces, it cannot predict the critical, oil-film thickness for failure. This is the task of surface chemistry and metallurgy. In this paper, the factors involved in failure are described, in particular the importance of physisorption and chemical reaction, or chemisorption, is emphasized. A mechanism of scuffing based, on the residence time of molecules is advanced. Presented at the 34th Annual Meeting in St. Louis, Missouri, April 30-May 3, 1979

Magnetic Fluid Seals for Special Applications

Abstract: Three magnetic fluid seals custom engineered to meet specific application objectives are discussed. These seals are: a belt edge seal, a large diameter seal and a centrifugal seal. Extensive experimental data were acquired on the first two seals to determine their performance characteristics. Some of these test results are compared with the theoretical expectations. Numerical computations are made on the centrifugal seal to Predict its sealing capabilites. Presented at the 34th Annual Meeting in St. Louis, Missouri, April 30-May 3, 1979

Surface Roughness Considerations in Metalworking

Abstract: The inadequacy of average roughness values such as AA and RMS for describing surface topography in metalworking is discussed. It is suggested that an expression involving asperity height, asperity form and roughness direction is needed. Surface roughness considerations in metalworking differ from those in bearing lubrication because of metal hardness changes and plastic deformation which occur in the former. This makes the roughnesses of the opposing surfaces dependent on one another in metalworking and thus complicates the analysis considerably. While many of the contact area distributions in metalworking are Gaussian, examples are shown for metal rolling where divergence from Gaussian is pronounced. A discussion of the effects of roughness directionality upon oil film thickness in metalworking indicates a strong dependence between these two parameters. Presented as an American Society of Lubrication Engineers paper at the ASLE/ASME Lubrication Conference in Minneapolis, Minnesota, October 24–26, 1978

The Wear of the Noble Metals

Abstract: Using a pin-on-disk apparatus, experiments were carried out to determine the wear coefficients of the nine elemental metals which form little or no oxide in air (ruthenium, rhodium, palladium, silver, rhenium, osmium, iridium, platinum, gold) when sliding against each other. The tests mere unlubricated in air at room temperature. It was found that the lowest wear coefficients involved hexagonal metals and incompatible metal pairs. For pairs of metals differing in hardness, the ratio of wear volumes of the two metals was the inverse of the ratio of penetration hardness. In general, the scatter of wear volumes was far lower than that observed in previous tests using oxide-forming metals, in which cases the oxide layers were perturbing factors. The test results suggest that the current practice of using alloys based on gold, platinum and palladium in sliding electric contacts is not optimum, and that combinations involving rhodium and ruthenium deserve consideration. Presented as an American Society of Lubri...

The friction and wear of metals and binary alloys in contact with an abrasive grit of single-crystal silicon carbide

Abstract: Sliding friction experiments were conducted with various metals and iron-base binary alloys (alloying elements Ti, Cr, Mn, Ni, Rh and W) in contact with single crystal silicon carbide riders. Results indicate that the friction force in the plowing of metal and the groove height (corresponding to the wear volume of the groove) decrease linearly as the shear strength of the bulk metal increases. The coefficient of friction and groove height generally decrease, and the contact pressure increases with an increase in solute content of binary alloys. There appears to be very good correlation of the solute to iron atomic ratio with the decreasing rate of change of coefficient of friction, the decreasing rate of change of groove height and the increasing rate of change of contact pressure with increasing solute content. These rates of change increase as the solute to iron atomic radius ratio increases or decreases from unity.

Development of Surface Coatings for Air-Lubricated, Compliant Journal Bearings to 650°C

Abstract: Surface coatings for an air-lubricated, compliant journal for an automotive gas turbine engine were tested to find those capable of withstanding temperatures of either 540°C (1000°F) or 650°C (1200°F). Also, the coatings have to be capable of surviving the start-stop sliding contact cycles prior to rotor lift-off and at touchdown. Selected coating combinations were tested in start-stop tests at 14 kPa (2 psi) loading for 2000 cycles at room and maximum temperatures. Specific coating recommendations are: Cdo and graphite on foil versus chrome carbide on journal up to 370°C (700°F); NASA PS-120 (Tribaloy 400, silver, and CaF2) on journal versus uncoated foil up to 540°C (1000°F); and chemcially adherent Cr2O3 on journal and foil up to 650°C (1200°F). The chemically adherent Cr2O3 coating system was further tested successfully at 35 kPa (5 psi) loading for 2000 start-stop cycles. Presented as an American Society of Lubrication Engineers paper at the ASLE/ASME Lubrication Conference in Minneapolis, Minnesota,...

The Effect of Periodic Loading on the Shear Strength Properties of Thin Organic Polymeric Films

Abstract: The paper commences with a description of a technique used to obtain the shear strength properties of thin (ca 100nm) solid polymeric films. The effect of velocity in this sliding experiment is rationalized in terms of the contact time in which a load is applied to an element of material and the shear strain rate in the film. The velocity range that may be employed is small in order to minimize the effects of frictional heating which somewhat restricts the investigation of the relative influences of these two parameters. A new experimental technique is described that may be used in conjunction with the conventional sliding system so as to elucidate uniquely the contact time effect. The method involves modulating the normal load with a small sinusoidal component, and while the experiment has not been analyzed rigorously, the accumulated data suggest that the response of the polymer film is dependent on the period in which it is loaded and that retardation in compression occurs with all polymer films to var...

End-Face Seal Deflection Effects—The Problems of Two-Component Stationary or Rotating Assemblies

Abstract: Component deformations have a significant effect on performance of high-pressure, end-face seals. Deflection analysis is necessary for prediction, control and understanding, but is often complicated by existing arrangements of support for seal faces. The common commercial design for both a stationary and a rotating seal face is the two-component assembly. A method for treating the effects of changes of pressure, general temperature and steady frictional heating is presented. Deflection sensitivities of a two-component assembly are expressed as ldquo;influence coefficients,” evaluated by finite element analysis of multiple load cases. The importance of radial Coulomb friction due to differential shrinkage at the interface of n two-component assembly is highlighted. Such friction gives rise to undesirable performance hysteresis. Once ldquo;influence coefficients” for a particular end-face seal have been evaluated by the method outlined in this report, the effect of various shape and material changes can be ...