Wave Journal Bearing with Compressible Lubricant—Part I: The Wave Bearing Concept and a Comparison to the Plain Circular Bearing

To improve hydrodynamic journal bearing steady-stale and dynamic performance, a new bearing concept, the wave journal bearing, was developed at the author's lab. This concept features a waved inner bearing diameter. Compared to other alternative bearing geometries used to improve bearing performance such as spiral or herringbone grooves, steps, etc., the wave bearing's design is relatively simple and allows the shaft to rotate in either direction. A three-wave bearing operating with a compressible lubricant; i.e., gas, is analyzed using a numerical code. Its performance is compared to a plain (truly) circular bearing over a broad range of bearing working parameters, e.g., bearing numbers from 0.01 to 100. The geometry of the wave bearing gives the bearing its high load; i.e., stiffness, and stability characteristics. The wave bearing's performance is dependent upon the amplitude of the wave and the position of the waves relative to the applied load. To maximize wave bearing performance, the waves' position relative to the applied load should be carefully selected. The wave journal bearing offers better stability than the plain circular bearing' under all operating conditions and all wave-load orientations. Specifically, an unloaded journal bearing can be made to run stably in any operating regime by incorporating the wave geometry.     

Thermohydrodynamic Analysis of a Journal Bearing in a Turbulent Flow Regime—Part II: Application to an Axial Groove Bearing

The governing equations developed in (1), where a perturbation method is applied in the equation of motion and the energy equation is linearized, are used to study journal bearings of finite length operating in turbulent flow regimes. The thermohydrodynamic solutions are obtained for a journal bearing with four axial grooves. Heshmat and Pinkus' mixing theory (2) is used to evaluate the inlet temperature of each sector. These governing equations are solved to yield pressure, mass-mean velocity and temperature distributions, the mixing temperature at the inlet and the flow rates at the entry and exit of each sector, and the fictional forces.     

Thermohydrodynamic Analysis of a Journal Bearing in a Turbulent Flow Regime—Part I: Theory

An attempt is made to formulate a thermohydrodynamic model of fluid-film lubrication that is valid in turbulent flow regimes. The model considers the flow to be a small perturbation of turbulent Couette flow. The modified Reynolds equation is obtained for the turbulent flow and the integro-differential energy equation makes the turbulence analysis easier by replacing the conductive terms in terms of the convective boundary conditions at two solid surfaces. Sample results applying the perturbation method agree well with available experimental data and theoretical methods.     

A Lubrication Deviation From the Classical EHL Theory by the Lubricant Viscoplasticity: Part II — Boundary of Lubrication Regimes

This paper distinguishes elastahydrodynamic lubrication (EHL) regimes in isothermal pure rolling case as three kinds according to lubricant rheology. In these regimes, the lubricants are respectively viscoelastic, viscoplastic, and non-continuum. Mathematical expressions are introduced ta describe the boundaries among these three regimes. H_c - r_it and U - W charts respectively plot the operational scopes of these lubrication regimes. The present study holds significance to understanding EHL film formation and more clearly embodies elastohydrodynamic film failure stage transitions.     

Influence of Pad Pivot Friction on Tilting-Pad Journal Bearing Measurements—Part II: Dynamic Coefficients©

This paper presents measured results for the dynamic stiffness and damping force coefficients for two tilting-pad journal bearings. Comparison between a bearing with spherical seated ball and socket pad pivots and one with line contact rocker-back pad pivots is made. The bearings tested were preloaded five pad designs with load directed on the pivots. The bearings have length to diameter ratios of 0.75, offset ratios of 0.50, preloads of about 0.320, a journal diameter of 70 mm, and radial machined pad clearances of 113.0 μm. Measurements were made for a range of speedload conditions encompassing a Sommerfeld number range of 0.1 to 2.0. Comparison of the principal stiffness and damping coefficients for the two bearings show the same trends. Nearly zero cross-coupled stiffness coefficients were measured for the bearing with rocker-back pad pivots. For the bearing with spherical seated pad pivots, non-dimensional cross-coupled stiffness coefficients for K_xy ranged from -1.2 to -0.9 and for K_yx ranged from -3.8 to 0.8. A hypothesis for increased pad pivot friction in the ball and socket is presented to explain the variation in cross-coupled stiffness coefficients between the two bearings.     

An Analysis of the Effect of Lubricant Supply Rate on the Performance of the 360° Journal Bearing

A theoretical study was made to determine the influence of lubricant supply rate on the performance of the 360° journal bearing for L/D = 1. The results are presented in chart form to facilitate their application to analysis and design.     

Effect Of Roller Profile On Cylindrical Roller Bearing Life Prediction—Part II Comparison of Roller Profiles

Four roller profiles used in cylindrical roller bearing design and manufacture were analyzed using both a closed form solution and finite element analysis (FEA) for stress and life. The analyzed roller profiles were flat, end tapered, aerospace, and fully crowned and loaded against a flat raceway. Four rolling-element bearing life models were chosen for this analysis: those of Weibull; Lundberg and Palmgren; Ioannides and Harris; and Zaretsky. The flat roller profile without edge loading has the longest predicted life. However, edge loading can reduce life by as much as 98 percent. The end-tapered profile produced the highest lives, but not significantly higher than those produced by the aerospace profile. The fully crowned profile produced the lowest lives. Except for the flat roller profile, the predicted lives with the FEA method exceed those with the closed form solution. The fatigue limit proposed by Ioannides and Harris equates to one-half the value of a compressive residual stress that may exist in a rolling bearing steel.     

EHL Performance of the Lubricant With Shear Strength: Part I — Boundary Slippage and Film Failure

This paper analytically investigates the isothermal line contact elastohydrodynamic lubrication of three lubricants with much different shear strengths under the nondimensional operating parameters of w = 2.15e-4 and U = 2.53e-10 applying the lubricant ideal viscoplastic rheological model. The boundary slippage of the low-shear-strength lubricant occurring in the EHL inlet zone was found and results in a much thinner film compared to the classical EHL theory prediction. The film boundary slippage and its growth with the slide/roll ratio variation of tile low-shear\- strength lubricant exhibit special phenomena, which are much different from those of the high-shear-strength lubricant. The easy occurrence of film failure in concentrated contact in the case of high sliding speed, heavy load, large slide/roll ratio, and low-shear-strength lubricant was concluded due to the severe friction heating on the surface conjunction and the lubricant thermal desorption on tile lubricant/surface boundary. The EHL film failure mechanism was further recognized.     

Measured Performance of a Highly Preloaded Three-Lobe Journal Bearing–-Part II: Dynamic Characteristics

The dynamic coefficients of a three-lobe bearing with a preload factor of 0.75 were determined. Principal and cross-coupled stiffness and damping coefficients were derived from measured responses to forced harmonic excitation. Three operating speeds were tested and, for each speed, the load was varied so that the Sommerfeld number ranged from 0.23 to 2.87. Three orbits were used for each test condition, which resulted in three data points for each condition. At each condition the nominal data points fell within the uncertainties of the data. Non-dimensionalized data at all three speeds were independent of any given Sommerfeld number; thus, the Reynolds number had little influence for the range of conditions tested. Data indicated that minimization of the uncertainties is possible with optimal orbit selection.     

Measured Performance of Tilting-Pad Journal Bearings over a Range of Preloads—Part II: Dynamic Operating Conditions

This article presents a comparison of the measured dynamic coefficients of five tilting-pad journal bearings with a range of preload factors. Each bearing had five shoes machined to a journal diameter of 70 mm, length-to-diameter ratio of 0.75, pivot offset ratios of 0.50, and a nominal assembled radial clearance of 81.3 μm. The rocker-backed tilt pads have nominal radial machined clearances of 176.8, 114.3, 91.4, 73.7, and 61.0 μm. These clearances constitute a range of preloads from ?0.333 to 0.540. Tested were both on-pad and between-pad orientations, with respect to applied forces. Dynamic coefficients are extracted from the test rig by applying sinusoidal synchronous forces and measuring the resulting relative journal-to-bearing motion. A range of speed-load conditions was used, resulting in a Sommerfeld number range of 0.1 to 4.5. Measured dynamic coefficients (nondimensional principal and cross-coupled stiffness and damping coefficients) show the influence of preload. For the speed and load conditions included herein, the dynamic coefficients were not strongly dependent on the preload factor. But very importantly the measured results demonstrate the reduced ability of tilting-pad journal bearings to satisfactorily operate in the negative preload regime for the bearings tested.     

A Theoretical Study of the Effect of Offset Loads on the Performance of a 120° Partial Journal Bearing

Reynolds' equation for a 120° partial journal bearing of the clearance type having an L/D ratio of 1 is solved numerically to determine the effect of positioning circumferentially the line of action of the load at various points along the bearing arc. The influence of the load position (α/β) on film thickness, eccentricity, journal position, friction, flow, temperature rise, and maximum film pressure is investigated and performance curves given. It is shown that the position of the load has a significant effect on bearing performance.     

Test of a Fluid-Film Wave Bearing at 350°C with Liquid Lubricants

A novel fluid-film wave bearing has been run at a higher temperature (350°C) than ever before with a perfluoropolyether (PFPE)-K liquid lubricant. Additionally, the wave journal bearing (45 mm diameter and 24 mm long) completed an 8-h endurance test at the NASA Glenn Research Center. The lubricant was PFPE-K XHT 500. After being maintained at 350° C for 8 h, the bearing temperature was raised to 356°C for the last 30 min of the run. The speed was 29,000 rpm and the load ranged from 2670 to 3560 N. The bearing was perfectly stable both dynamically and thermally. The observed temperature was more than 150°C above that run with current turbine engine lubricants. The use of high-temperature bearings as tested here would allow efficiency increases of more than 5% in aero or terrestrial turbine engines.     

Scuffing Behavior of Piston-Pin/Bore Bearing in Mixed Lubrication—Part II: Scuffing Mechanism and Failure Criterion

Surfaces and subsurfaces of test specimens that failed in scuffing were examined. A scuffing criterion is developed stating that scuffing failure would occur when the maximum surface tangential traction is larger than the modified shear strength. A scuffing uncertainty factor is introduced to reflect the influence of factors that affect wear and scuffing and the inaccuracy in modeling.     

A Mixed Lubrication Model for Journal Bearings with a Thin Soft Coating—Part I: Contact and Lubrication Analysis

Soft coatings are used extensively in industry for contact friction reduction, particularly during the running-in period. A numerical model is developed for contact and lubrication analysis of some soft coating coated bearings in mixed fluid lubrication. The model is applied to determine oil film thickness, contact pressure, and the friction coefficient of the coated bearings in contact with a hard journal surface. The contact of tin-coated 339 Al-Si alloy bearings with case hardened steel is analyzed using the developed model.     

Test Results of Key and Spherical Pivot Five-Shoe Tilt Pad Journal Bearings—Part II: Dynamic Measurements

Tests were conducted to measure the dynamic characteristics for two types of five-shoe tilt pad journal bearings having a load between pads configuration. Dynamic measurements of the two bearings are presented for 5000, 7000 and 12,000 rpm, and unit loads ranging from 126 kPa to 1724 kPa. Comparisons are made between the measured data and the theoretical prediction. Test data includes fluid film stiffness and damping, with calculated uncertainties and the measured radial stiffness of the pivots. The measured dynamic characteristics show the bearings differ with respect to stiffness and damping, while the measured radial pivot stiffnesses were nearly identical     

A Mixed Lubrication Model for Journal Bearings with a Thin Soft Coating—Part II: Flash Temperature Analysis and its Application to Tin Coated Al-Si Bearings

Flash temperature has a profound influence on the tribological behavior of contact surfaces. An asperity flash temperature model is developed for journal bearings with a thin soft coating. The asperity flash temperature of tin coated 339 Al-Si alloy bearings in contact with case hardened steel journals is analyzed. Factors influencing the flash temperature are discussed. Correlations of the flash temperature with asperity roughness parameters, such as the RMS roughness and skewness values, are explored. It was found that the maximum rise in temperature increased as the roughness and skewness increased.     

Coloured adaptive structured Petri-net Part II: deduction of the structured graph from the pregraph and application — modelling of a flexible workshop

In Part II of this paper, the authors describe the transformation of the pregraph into a structured coloured Petri-net. This step illustrates the different elementary processes as sequential control systems of the workshop and communications and binding types between these processes.     

Comparison of the Dynamic Behavior and Lubrication Characteristics of a Reciprocating Compressor Crankshaft in Both Finite and Short Bearing Models©

The compression force of refrigerant gas, the viscous and inertial force of the piston, and the centrifugal force of balancer weight induce rotating whirl of the crankshaft in a small reciprocating compressor. It is necessary to develop an analytical model for the accurate prediction of dynamic behavior of the compressor mechanism having coupled characteristics between the piston and crankshaft. The reciprocating compression mechanism is dynamically modeled by considering the viscous frictional force of a piston and the variation in the contact length of the piston-cylinder system, and then numerical analysis is performed for the coupled dynamic behavior of the piston and crankshaft. For the accurate predictions of the dynamic behavior and characteristics of lubrication of the crankshaft-journal bearing system, a finite bearing model is adopted. In addition, the dynamic trajectory and characteristics of lubrication of the crankshaft such as power consumption and oil leakage are compared between the finite bearing model and the short bearing approximation. The influences of the variation in the radial clearance of the journal bearings, lubricant viscosity, and mass and mass moment of inertia of the piston and connecting rod on the dynamic behavior and characteristics of lubrication such as power consumption and oil leakage are investigated.     

Solid Lubrication of Silicon Nitride with Cesium-Based Compounds: Part II — Surface Analysis

Energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and Auger electron spectroscopy (AES) were used to characterize the wear surfaces of selected samples from Part 1 of the authors study. Results are presented for films generated on silicon nitride (Si₃N₄) originally coated with cesium oxytrithiotungstate (Cs₂WOS₃), cesium sulfate (Cs₂SO₄), and a hydrated cesium silicate (Cs₂O·3SiO₂·nH₂O), all applied in a sodium silicate binder (Na₂SiO₃). Results show the presence of mostly Si, O, and Cs within the wear tracks of post-tested specimens. In some cases, W and S were not detected on samples that originally contained these elements, suggesting that decomposition had taken place. To simulate the reactions that might occur in a tribo-contact, mixtures of Si₃N⁴ and Cs₂WOS₃ powders were heated in air to 700°C and analyzed using XPS and Bremsstrahlung-excited AES. It was found that Cs₂WOS₃ accelerates the formation ofSiO₂ on Si₃N₄ under static conditions. These results support our hypothesis that high temperature chemical reactions between the cesium-containing compounds and the Si₃N₄ surface form a lubricious cesium silicate film. A mechanism is proposed based on the glass-modifying tendency of alkali metals and the hot-corrosion of Si₃N₄     

Exploring Operation Mechanisms of the Flexible Metal-to-Metal Face Seal: Part II—Scoring and Leakage Analysis

The numerical model previously developed in Part I was applied to analyze the contact wetness, oil exchange rate, and surface temperature distributions within the sealing band of the flexible metal-to-metal face seal (FMMFS). The analysis showed that the above three parameters were essentially critical to the seal scoring and leakage. Both macro- and microgeometries of the FMMFS contribute to variations of seal performance.