Showing papers in "Tribology Transactions in 1990"

The Effect of Anion Vacancies on the Tribological Properties of Rutile (TiO2-x), Part II: Experimental Evidence

Abstract: Friction and wear tests were completed with the (001) and (110) planes of single crystal rutile (TiO 2-x ) specimens sliding against selected ceramic counterfaces, in well-defined crystallographic directions. The purpose of the experiments was to investigate the environmental influences on anion vacancy formation, as related to a recent hypothesis connecting oxygen substoichiometry with predictable variations in the tribological properties of rutile. The data were obtained with two, entirely different test machines operating at various loads, speeds, temperatures, sliding directions and durations, as well as test specimen atmospheres. The results independently confirmed the predicted, anion vacancy-controlled formation of certain low and high lattice (strain) energy crystallographic shear systems (i.e., Magneli phases) and that their generation is overwhelmingly environment-dependent. The stoichiometry-controlled lattice energy of these rutile phases influences the surface and bulk shear strength (τS) of ...

Abrasion and erosion of WC-Co with controlled microstructures

Abstract: The influence of microstructure on room-temperature abrasive and erosive wear resistance of selected WC-Co materials was examined. Cermets containing 6 and 12 w/o Co were processed under controlled conditions to produce materials with three WC grain sizes: fine—0.8 μm; medium—1.4 μm; or coarse—2.7 μm. The hardness, fracture toughness and microstructural parameters of the resulting six grades were determined. Diamond abrasive wear tests showed that the wear resistance of these WC-Co materials to abrasion depends more strongly on the WC grain size than on the cobalt content, while the wear resistance to Al2O3-particle gas-jet erosion shows a strong dependence on the cobalt content and less on WC pain size. Presented at the 44th Annual Meeting in Atlanta, Georgia May 1–4, 1989

Acidic Attack of Perfluorinated Alkyl Ether Lubricant Molecules by Metal Oxide Surfaces

Abstract: The reactions of linear perfluoropolyalkylether (PFAE) lubricants with alpha-Fe203 and Fe203-based solid superacids were studied. The reaction with alpha-Fe203 proceeds in two stages. The first stage is an initial slow catalytic decomposition of the fluid. This reaction releases reactive gaseous products which attach the metal oxide and convert it to FeF3. The second stage is a more rapid decomposition of the fluid, effected by the surface FeF3. A study of the initial breakdown step was performed using alpha-Fe203, alpha-Fe203 preconverted to FeF3, and sulfate-promoted alpha-Fe203 superacids. The results indicate that the breakdown reaction involves acidic attack at fluorine atoms on acetal carbons in the linear PFAE. Possible approaches to combat the problem are outlined.

Analysis of Crankshaft Bearings Using a Mass Conserving Algorithm

Abstract: A mass conserving algorithm (Elrod algorithm) which uses the Jakobsson, Floberg, and Olsson cavitation boundary conditions has been implemented to analyze crankshaft bearings. The main and connecting rod bearings of a typical automotive engine are considered. Some sample steady-state results are presented. The inverse problem (given the load, find the journal orbit) is solved for real engine loads. Comparisons are made with a non-conservative algorithm based on the Reynolds boundary condition. Significant differences in the cavitation zones and oil flows are observed between the two algorithms. In all cases, the oil flow into the bearing is found to match the oil flow out of the bearing for the Elrod algorithm. Presented at the 44th Annual Meeting in Atlanta, Georgia May 1–4, 1989

Measurement and Calculation of the Dynamic Operating Characteristics of the Five Shoe, Tilting Pad Journal Bearing

Abstract: This paper presents results from an experimental and theoretical investigation of the dynamic characteristics of the tilting pad journal bearing. The five shoe bearing, of nominal diameter 76.2 mm and Lid ratio 0.75, has been loaded statically “between pads” The dynamic characteristics were measured for shaft speeds of 15, 30, 45 and 60 Hz and for loads that ranged between 1.7 and 4.5 kN. The theoretically derived stiffness and damping coefficients were calculated from a model which accounts for both thermal and elastic effects in the bearing. After the inclusion of shaft flexibility in the analysis of the measured dynamic coefficients, correlation between the experimental and theoretical results was found to be satisfactory. Presented at the 35th STLE/ASME Tribology Conference in Fort Lauderdale, Florida October 16–19, 1989

Experimental Study of the Effects of Surface Roughness on Friction

Abstract: Experimental verification of lubrication theories for surface roughness effects is lacking. We have conducted an experimental study using riblet tapes to generate repeatable surfaces on the test samples. A computer-assisted pin-on-disk tribometer was developed to measure the friction of the test samples. To study the effects of roughness height and lay orientation on friction, machined samples and. samples with different riblet tapes mounted longitudinally and transversely were tested. Our results show that lower roughness height yields lower friction, and that transverse roughness has lower friction than longitudinal roughness. The surface roughness effects become increasingly significant as the film thickness decreases. These findings substantiate earlier theoretical studies. A flow visualization system for the tribometer was also developed to observe flow characteristics of different surface roughnesses. Presented at the 35th STLE/ASME Tribology Conference In Fort Lauderdale, Florida October 16–19, 1989

Non-Newtonian Effects of Multigrade Oils on Journal Bearing Performance

Abstract: This study is aimed at predicting the non-Newtonian effects of multigrade oils on journal bearing performance. The governing differential equation, similar to the Reynolds equation, is derived using a general apparent-viscosity function as the constitutive equation in order to be able to accommodate different rheological equations. Treatment of the non-Newtonian effects is confined to nonlinear viscous behavior. Oil elasticity and normal stress effects are not considered. The problem formulation resembles that of the THD problem, and the governing differential equation contains non-Newtonian factors based on the cross-film integrals of viscosity. The problem is solved by the finite difference technique, and the results show reasonable agreement with the experimental data available in the literature. In order to represent the rheology of multigrade engine oils, a new non-linear viscous constitutive equation is proposed. This equation is fitted to experimental data on the rheology of two multigrade engine o...

Analysis of Distortions of Cylinders and Conformability of Piston Rings

Abstract: A criterion for piston ring conformability to distorted cylinders is described. The criterion allows one to quantify magnitudes and order of bore distortions regarding the piston ring conformability. By comparing magnitudes of distortions which are critical relative to conformability with the magnitudes of actual distortions, determined through Fourier analysis of bore profile, the quality of piston ring/cylinder interface (expressed in terms of conformability/non-conformability of the piston rings) can be evaluated. The criterion was developed based upon the understanding that curvatures of the bore profile and of the piston ring running band are equal at full conformability of the ring to the cylinder bore. A description of the bore profile by random function was instrumental in development of the criterion and yielded opportunity for the presentation of the piston ring conformability problem in a statistical aspect that is important for quality control operations. The critical-to-conform-ability values...

Cavitation Regimes in Squeeze Film Dampers and Their Effect on the Pressure Distribution

Abstract: High speed motion pictures have revealed several operating regimes in a squeeze film, damper. Pressure measurements corresponding to these distinct regimes were made to examine their effect on the performance of such dampers. Visual observation also revealed the means by which the pressure in the feed groove showed higher amplitudes than the theory predicts. Comparison between vapor and gaseous cavitation are made based on their characteristic pressure wave, and the effect this has on the resultant force in the squeeze film. Presented at the 44th Annual Meeting in Atlanta, Georgia May 1–4, 1989

On Reciprocating Elastomeric Seals: Calculation of Film Thicknesses Using the Inverse Hydrodynamic Lubrication Theory

Abstract: The elastohydrodynamic lubrication (EHL) problem of an axi-symmetric, elastomeric, reciprocating seal may be considered as one of a heavily loaded line contact with only small piezo-viscous effects. A method is presented to calculate the overall film thickness for the stationary, isothermal situation with sufficient lubricant supply and negligible surface roughness effects. It applies the inverse theory to the frictionless dry contact pressure distribution, considering the influence of the boosting action in the entry zone of the film. Its validity is shown for the isoviscous EHL of the Hertzian contact. The finite element method (FEM) may be used to calculate the contact situation of mounted and pressurized seals. Important aspects of such calculations are discussed. To calculate film thicknesses using such FEM results, a computer program PROGRES was written. Good correspondence between the predictions of PROGRES and experimental outstroke film thicknesses are obtained for a rectangular rod seal with rou...

Decomposition of Perfluoroalkylpolyethers (PFPE) in Ultra-High Vacuum Under Sliding Conditions

Abstract: Reactions of perfluoroalkylpolyethers (PFPE: Fomblin, Demnum and Krytox) were studied during the sliding contact of stainless steel specimens under ultrahigh vacuum conditions. All three fluids reacted with the steel specimens during sliding. Fomblin, which has acetal linkages, decomposed under the sliding conditions generating gaseous products, (COF2 and fluorinated carbons) which were detected by a quadrupole mass spectrometer. Gaseous products were not detected for the Demnum and Krytox fluids. The amount of gaseous products from Fomblin increased with increasing sliding speed. At the end of the sliding experiments, the wear scar and deposits on the specimens were examined by small spot size XPS. The oxide layer on the specimen surface was removed during sliding, and metal fluorides were formed on the worn surface. The surface of the wear scar and deposits were covered with adsorbed PFPE. Based on these results, it was concluded that the decomposition reaction on Fomblin was initiated by contacting the fluid with a fresh metal surface which was formed during sliding.

Accuracy Evaluation of Experimentally Derived Dynamic Coefficients of Fluid Film Bearings Part I: Development of Method

Abstract: The goal of many experimental studies of fluid film bearings is the determination of the eight linearized stiffness and damping coefficients. These coefficients cannot be measured directly; they are derived from a series of other measurements. In many cases, the coefficients are found by applying known steady-state sinusoidal loads to excite a journal on a rigid rotor and measuring the resulting displacement, velocity, and acceleration orbits. This paper relates how uncertainties in these measurements affect the accuracy of the derived coefficients. The analysis can also be used for the proper selection of test procedures and transducers to measure the primary variables and estimate results beforehand. For an example case, it was found that bearing coefficients are entirely subject to test conditions, meaning not only sensor accuracy but where in an orbit data is taken. Stiffness coefficients had about an order of magnitude less uncertainty in their evaluation (∼3 percent) than the damping coefficients (∼...

A thermodynamic approach to viscosity

Abstract: For use in elastohydrodynamic systems, the ideal lubricant is generally one which forms a thick separating film between the rubbing surfaces over a wide range of operating conditions This implies a fluid with a low temperature-viscosity coefficient and a high pressure-viscosity coefficient Unfortunately, there is a braod correlation between these two values for liquids This paper derives and then verifies, using experimental data, an expression for this correlation based upon the assumption that viscosity is a thermodynamic property of state From the resultant expression, the factors that contribute to a high ratio of pressure- to temperature-viscosity coefficient are identified and discussed by reference to a range of lubricant structures Other implications of viscosity being a property of state are also considered Presented as a Society of Tribologists and Lubrication Engineers paper at the ASME/STLE Tribology Conference In Baltimore, Maryland, October 16–19, 1988

Tribology studied using atomically smooth surfaces

Abstract: An investigation is reported of the boundary layer friction resulting from films of nonpolar liquid lubricants, 1 to 6 layers of molecules thick. The liquids were confined between parallel step-free single crystals of muscovite mica. The apparent dynamic viscosity at 1 Hz (shear rate less than 250 sec−1) was considerably enhanced over that of the isotropic liquids and increased substantially with increasing net normal pressure. A transition to a solid-like response occurred with increasing net normal pressure, without discernible change in thickness. Investigations of the critical shear stress to accomplish sliding showed a buildup of this static friction over times from minutes to hours. For films of hexadecane, the pressure coefficient of the critical shear stress was approximately 2 to 20, depending on the equilibration time allowed at each normal pressure. The tribological behavior of these lubricant films did not appear to reflect material properties of the lubricants as such, but rather to stem, fro...

A Mechanism of Vapor Effect on Friction Coefficient of Molybdenum Disulfide

Abstract: Molybdenum disulfide single crystals, compressed single crystals and pellets were friction tested in vacuum, air and water. The friction coefficient of MoS2 single crystal was hardly affected by air or water. In the case of the compressed MoS2 single crystals or MoS2 pellets, the friction coefficient became higher in the order of vacuum, air and water. When a large quantity of water was charged into compressed MoS2 single crystals or MoS2 pellets, the friction coefficient decreased to that obtained in a vacuum. These phenomena were explained by the surface tension of the condensed water in wedge-shaped cavities. Presented at the 35th STLE/ASME Tribology Conference in Fort Lauderdale, Florida October 16–19, 1989

Structure of Films Formed During the Deposition of Lubrication Molecules on Iron and Silicon Carbide

Abstract: The structure of films formed on iron foil and silicon carbide wafers during high temperature (700 degrees C) deposition of two lubricants, tricresol phosphate (TCP) and poly phenyl ether (PPE), were studied using scanning and transmission electron microscopy, energy dispersive x-ray analysis, x-ray diffraction, and rate measurements. It was found that on iron foils, TCP decomposes and some of the molecular fragments which remain interact chemically with the iron. A two-layer structure forms. The bottom layer apparently consists of fairly large oriented cementite (Fe3C) crystals. The top layer contains particles of iron phosphide structures. In thicker films, other iron carbides, iron phosphides, and iron-phosphate crystals are also present. The size, chemical content, and degree of crystallinity of the particle structures was found to change with depth of deposit. The rate of deposition declined with time, and this correlated with a decline in the iron concentration near the surface, suggesting that iron...

Modifying the Lambda Ratio to Functional Line Contacts

Abstract: Lambda ratio, the lubricant film thickness divided by the composite roughness within an operating rolling element bearing, has been recognized for more than 25 years as an important contact parameter related to bearing performance, primarily fatigue life. This paper considers a simplified method of functional filtering within a bearing contact that provides a more appropriate composite roughness for a wider range of bearing sizes and loadings. The concept was tested with a series of regression models of standard and modified lambda ratios, including the uncoupled lambda parameters. The models were rated using three different statistical indices to assess how each model accounted for the variation present in a large collection of bearing test data. Presented at the 35th STLE/ASME Tribology Conference In Fort Lauderdale, Florida October 16–19, 1989

Wear of Ceramic Cutting Tools in Ni-Based Superalloy Machining

Abstract: The machining performance of monolithic and composite silicon nitride and Al2O3-based cutting tools in continuous turning of Inconel 718 was examined. The character of tool wear has been found to vary, depending on the feed rate and cutting speeds. At a lower cutting speed, of 120 m/min, tool life is restricted by depth-of-cut notching, while at high cutting speeds (300 m/min), tools fail due to nose wear and fracture. The sensitivity of monolithic Si3N4 and Al2O3 to depth-of-cut notching was found to he significantly reduced with the addition of SiC whiskers, and to a lesser extent with TiC particulates. The ceramic composites also exhibited resistance to nose and flank wear that was higher than that of the monoliths. The internal stress distribution for the cutting tool has been calculated using the finite element method and is the basis for explaining fracture beneath the rake face. Cutting tool wear results are discussed in terms of chemical and mechanical properties of the ceramic tool material, abra...

Oil Film Thickness in an Elastic Connecting-Rod Bearing: Comparison Between Theory and Experiment

Abstract: The minimum oil film thickness in a dynamically loaded connecting-rod, big-end bearing of a high-speed gasoline engine has been studied experimentally and theoretically. The theoretical calculations were carried out for both rigid and elastic bearings. The theory is also used to explore the effects on the experimental results of a mechanical scissor linkage and of the assumption that there is no distortion or cavitation. Comparisons are made between the theory and. experiment of the effects of crankshaft speed and lubricant viscosity. Presented at the 44th Annual Meeting in Atlanta, Georgia May 1–4, 1989

On the Frictional Instabilities in a Cylindrical Roller Bearing

Abstract: Computer simulations of a high-speed cylindrical roller bearing, as obtained by the computer code ADORE, are used to correlate bearing performance to the frictional behavior at the roller/race and cage contacts. It is shown that an optimum traction-slip relation at the roller/race contacts may be determined to produce minimum race wear and heat generation in the bearing. Unlike the well defined circular cage mass center whirl orbits commonly seen in ball bearings, no significant cage whirl was found in a lightly loaded cylindrical roller bearing over the range of frictional parameters considered. Presented at the 44th Annual Meeting in Atlanta, Georgia May 1–4, 1989

Effect of Surface Roughness on Pressure Spike and Film Constriction in Elastohydrodynamically Lubricated Line Contacts

Abstract: In this paper a full numerical solution for the partial elastohydrodynamic lubrication in heavily loaded line contacts is obtained by using a Newton-Raphson iterative technique presented by Houpert and Hamrock (9). The results obtained from present work confirm the major conclusions by Path and Cheng (3), and by Zhu and Cheng (6), and demonstrate the effects of surface roughness on the pressure spike and the lubricant film constriction. Presented at the 44th Annual Meeting in Atlanta, Georgia May 1–4, 1989

Influence of Normal Force and Frequency in Fretting

Abstract: The contact conditions for fretting between spherical caps are reviewed. In particular, the relations between critical displacement and tangential force amplitudes for incipient slip on one hand, and normal force and frequency on the other, are analyzed. Experiments are carried, out with a testing apparatus, specially designed for fretting under controlled conditions within wide intervals of testing parameter values. An austenitic stainless steel and a Cu-3%Si alloy are investigated. It is confirmed that the critical tangential force is proportional to the normal force, and that the critical displacement is proportional to the 213 power of the normal force for two different frequencies, 300 and 800 Hz. The observed amplitude values are significantly higher than the theoretical values for the higher frequency. The frequency dependence is discussed. Presented at the 35th STLE/ASME Tribology Conference In Fort Lauderdale, Florida October 16–19, 1989

Characterization of Tricresylphosphate Lubricating Films by Micro-Fourier Transform Infrared Spectroscopy

Abstract: The characterization of tricresylphosphate (TCP) lubricating film by use of micro-Fourier Transform Infrared Spectroscopy (μ-FTIR) is reported. The study uses a combination of test methods to establish the qualitative sequence of chemical reactions that result in the formation of the observed anti-wear film. A four-ball wear tester, using a 6 μl test procedure, was used to generate the tribochemical films. A static pressurized Differential Scanning Calorimeter (DSC) was used at several temperatures to obtain TCP-iron reaction products similar to those formed under rubbing conditions. The wear contact temperatures can be estimated by comparison of the μ-FTIR spectra of the static reaction products to the spectra from the wear tests conducted at room temperature. The combination of the FTIR and DSC proved to be a powerful, rapid and reliable analytical tool. The use of DSC as a static reactor and the four-ball wear tester as a sequential test procedure provided the necessary materials for FTIR analyses. The...

Effects of Organic Molybdenum Compounds on the Friction and Wear Observed with ZDP-Containing Lubricant Blends

Abstract: Combining an organic molybdenum compound with a zinc dialkyl dithiophosphate (ZDP) antiwear additive can significantly reduce kinetic friction at loads in the antiwear regime as determined in laboratory, 4-ball wear tests. Both molybdenum dithiophosphates and dithiocarbamates are effective. The friction and wear benefits are independent of the ZDP present. Adding a high total base number (TBN) metallic detergent can greatly enhance the high load antiwear behavior of the three component blend whereas lower TBN detergents do not. Unfortunately, ashless dispersants can destroy the observed benefits. The performance improvements obtained with organic additives could not be duplicated by adding specific inorganic solids, either singly or in combination. Presented at the 35th STLE/ASME Tribology Conference in Fort Lauderdale, Florida October 16–19, 1989

Vapor phase deposition on high temperature surfaces

Abstract: Vapor phase deposition was studied at temperatures ranging from 500°C to 900°C. This study was carried out to determine the mechanism of deposition of tricresyl phosphate (TCP) from the vapor phase on chromium-nickel alloy, hot pressed silicon carbide, and hot pressed silicon nitride substrates under different atmospheres including an inert carrier gas and an inert gas plus oxygen. The deposited films were studied using scanning electron microscopy (SEM), optical microscopy, and an electrobalance to analyze the surface topography and calculate the deposition rate. From the data obtained using nickel-chromium alloy substrates, kinetic analysis were made using the Avrami equation from which the specific reaction rate constant (K), and the apparent activation energy (Ea) were determined. This analysis suggests that chemisorption is the rate controlling step. Presented at the 35th STLE/ASME Tribology Conference in Fort Lauderdale, Florida October 16–19, 1989

Dry friction of oxide ceramics against metals : the effect of humidity

Abstract: Reciprocating friction experiments were conducted to determine the effect of humidity on the friction characteristics of oxide ceramics slid against pure metals. Aluminum oxide and zirconium oxide had similar friction properties against metals. The friction coefficients of the oxide ceramics were affected by the type of metal (the chemical activity of the metal) and the relative humidity (RH). Especially in highly humid air, the friction coefficients were well correlated with the Gibbs free energy of ionization of the metals; that is, the more active metals showed higher friction coefficients. This result was considered to be attributable to the metal oxides caused by an oxidizing atmosphere (highly humid air). Another experiment in which Ti specimens with preoxidized surfaces were slid on the ceramic specimens was carried out, and the enhancing effect of the surface metal oxides on adherence characteristics was confirmed. On the other hand, the lubricative effect of water adsorbed on the surfaces of the ...

Solid lubrication of ceramic surfaces by IAD-silver coatings for heat engine applications

Abstract: In this study, we investigated the tribological characteristics of alumina ceramics that were coated with silver by means of ion-assisted deposition (IAD). Tests were performed at temperatures up to 400°C on an oscillating-slider wear test machine as a partial simulation of a ring/cylinder system. The results showed that higher test temperatures caused greater wear damage and increased friction of uncoated alumina. At 400°C, the wear rates of the alumina-alumina test pairs were eight to ten times higher than those of specimens tested at room temperature. The steady-state friction coefficients of the uncoated alumina were also rather high, typically ranging from 0.8 to 1.1. In contrast, the wear rate of I AD-silver -coated flats was negligible and the wear rate of counterface pins sliding against these coated flats was reduced by factors ranging from 4 to 73 depending on test temperature. Friction was also reduced to about one-half to one-third that of uncoated pairs. Surface and structure analytical inves...

Accuracy Evaluation of Experimentally Derived Dynamic Coefficients of Fluid Film Bearings Part II: Case Studies

Abstract: Six case studies are presented on the predicted uncertainties of derived bearing coefficients resulting from uncertainties in experimentally measured displacements, velocities, accelerations, and forces. In a previous paper the full set of equations, including eight linearized bearing coefficients, were derived from which bearing coefficients can be calculated based on measured quantities. Different algorithms for obtaining and reducing data are developed and presented for the cases. To demonstrate the method, bearings with known coefficients are chosen and uncertainties are theoretically applied to the measurements. The “measured” coefficients are then predicted and compared to the known values. In the first two cases the full set of equations is used for a three-lobe bearing with different excitation orbits. For case 3 the full set of equations is used for a tilt pad bearing with no cross-coupled terms. In case 4 the equations are rewritten with no cross-coupled terms for the same tilt pad bearing; for ...

Zinc Dialkyldithiophosphate Oxidation by Cumene Hydroperoxide: Kinetic Studies by Raman and 31P NMR Spectroscopy

Abstract: The oxidation of zinc dialkyldithiophosphates (ZDDPs) by cumene hydroperoxide in cyclohexane is studied by Raman and 31P NMR spectroscopy. The reaction proceeds in two main stages: oxidation of ZDDP to basic ZDDP, and oxidation of basic ZDDP to other products. Observation of phosphorus-containing reaction products by the two techniques yields approximate rate coefficients for the two stages. 31P NMR spectra of the basic ZDDP peak at high resolution gives evidence of the progressive break up of this cluster molecule, by loss of (RO)2PS2 coordinating groups, as the oxidation proceeds.

Digital Control of Magnetic Bearings Supporting a Multimass Flexible Rotor

Abstract: This paper considers the characteristics of magnetic bearings used to support a three mass flexible rotor operated at speeds up to 14,000 RPM. The magnetic components of the bearing are of a type reported in the literature previously, but the earlier analog controls have been replaced by digital ones. Analog-to-digital and digilal-ln-analog converters and digital control software were installed in a PC. This PC-based digital controller was used to operate one of the magnetic bearings on the test rig. Basic proportional-derivative control was applied to the bearings, and the bearing stiffness ami damping characteristics were evaluated. Particular attention is paid to the frequency dependent behavior of the stiffness and damping properties, and comparisons are made between the actual controllers and ideal proportional-derivative control. Presented at the 44th Annual Meeting in Atlanta, Georgia May 1–4, 1989