Showing papers in "Tribology Transactions in 1979"

Elastohydrodynamic Film Thickness Measurements of Artificially Produced Surface Dents and Grooves

Abstract: Elastohydrodynamic (EHD) film thickness measurements using optical interferometry have been made of artificially produced dents and grooves under rolling and sliding conditions. These measurements are compared to stylus traces of the dent and groove profiles to determine the local deformation associated with micro-EHD pressure generation. The surface geometry associated with the dents and grooves is seen to become intimately involved in the lubrication process itself, creating local pressure variations that substantially deform the local surface geometry, particularly under sliding conditions. The rolling results have implications concerning surface initiated fatigue and the sliding results show clearly the EHD surface interactions that must occur prior to scuffing failure. Presented as an American Society of Lubrication Engineers paper at the ASLE/ASME Lubrication Conference in Minneapolis, Minnesota, October 24–26, 1978

Stiffness and Damping Coefficients for the Five-Pad Tilting-Pad Bearing

Abstract: Stiffness and damping coefficients are presented for the 5-pad tilt-pad bearing for various preloads, offsets, length to diameter ratios and pad loadings (on and between pad) Finite elements and the pad assembly method are used to calculate these coefficients and the effects of the unloaded pads are included Design curves suitable for tilt-pad bearings in widespread industrial use are presented Presented as an American Society of Lubrication Engineers paper at the ASLE/ASME Lubrication Conference in Kansas City, Missouri, October 3–5, 1977

A Thin-Film Test for Measurement of the Oxidation and Evaporation of Ester-Type Lubricants

Abstract: A new thin-film oxidation test has hen developed for the quantitative evaluation of aircraft gas turbine (ester) lubricants. Problems associated with diffusion limitation are minimized by the use of a small sample (20-200 μL) with a relatively large fixed area of fluid-gas contact. Analysis with gel permeation chromatography (GPC) gives a semi-quantitative measurement of additive depletion, and measures the quantity of original fluid reacted and the quantities of oxidized products formed. By a careful calibration under a nitrogen atmosphere, the volatility loss is measured and calculated independently of the oxidation reaction. Test repeatability is excellent. The system is adaptable for a wide range of time-temperature studies and allows the duplication of system conditions in conditions in equipment, such as in the aircraft gas turbine lubrication system. A wide variety of catalytic surfaces typical of those found in structural and bearing portions of the lubrication system can be duplicated. The overal...

Friction and Wear Behavior of Single-Crystal Silicon Carbide in Sliding Contact with Various Metals

Abstract: Sliding friction experiments were conducted with single-crystal silicon carbide in contact with various metals. Results indicate the coefficient of friction is related to the relative chemical activity of the metals. The more active the metal, the higher the coefficient of friction. All the metals examined transferred to silicon carbide. The chemical activity of the metal and its shear modulus may play important roles in metal-transfer, the form of the wear debris and the surface roughness of the metal wear scar. The more active the metal, and the less resistance to shear, the greater the transfer to silicon carbide and the rougher the wear scar on the surface of the metal. Hexagon-shaped cracking and fracturing formed by cleavage of both prismatic and basal planes is observed on the silicon carbide surface. Presented at the 33rd Annual Meeting in Dearborn, Michigan, April 17–20, 1978

Some Chemical Effects in Boundary Lubrication Part I: Base Oil-Metal Interaction

Abstract: Base fluid-metal interactions of a super-refined paraffinic mineral oil were studied. Wear debris from a Shell Four-ball wear tester was analyzed. Based on the amount of iron distributed among used oil, organic solid, iron particles, and iron oxides, one is able to interpret the wear phenomenon in terms of mechanical and chemical processes. Oxygen concentration at the wear junction controls the type of the chemical interactions between the metal and the lubricant. These chemical reactions appear to be controlled by the thermal gradient at the junction; catalytic effects by the metal are insignificant. Presented as an American Society of Lubrication Engineers paper at the ASLE/ASME Lubrication Conference in Kansas City, Missouri, October 3–5, 1977

Prediction of the Bulk Temperature in Spur Gears Based on Finite Element Temperature Analysis

Abstract: The temperature distribution in spur gears operating in a state of thermal equilibrium is solved by using a finite element method. The effects of various dimensionless parameters on bulk temperature are shown. A table is provided which can be used to predict the bulk temperature on gear teeth, once the heat transfer coefficients and frictional heat input is estimated. Theoretical results for estimating heat transfer coefficients and frictional heat are also summarized. Presented as an American Society of Lubrication Engineers paper at the ASLE/ASME Lubrication Conference in Kansas City, Missouri, October 3–5, 1977

Geometry Effects in Tilting-Pad Journal Bearings

Abstract: A theoretical study has been undertaken to show the influence of bearing geometry on the steady-state and dynamic behavior of tilling-pad journal bearings. The computer model used takes into account a different viscosity on each pad, turbulence in the oil film and pad inertia. The geometric changes considered include the pad clearance and the bearing clearance, the length/diameter ratio, the number of pads, and the orientation of the bearing with respect to the load direction. The major operating characteristics which have been examined are oil film thickness, pad temperature, power loss, and oil film stiffness and damping. The basic form of bearing against which changes in geometry are compared has 5 centrally pivoted pads with a length/diameter ratio of 0.4. The bearing diameters considered in the theoretical study are 160 mm and 400 mm. Comparisons with experiment are also made for bearings having diameters of 160 mm and 430 mm. Presented at the 33rd Annual Meeting in Dearborn, Michigan, April 17–20, 1978

The Chemical Degradation of Ester Lubricants

Abstract: Gel permeation chromatography is shown to be a valuable technique for analysis of the oxidation and thermal degradation products of various types of esters. Esters potentially useful as synthetic lubricant basestocks, such as tridecyl pelargonate (a mono-ester), di-2-ethylhexyl sebacate (a diester) and trimethylolpropane triheptanoate (a neopentyl polyolester) form products of up to 50 000 molecular weight when oxidized at high temperatures. The oxidation products have been separated by molecular weight using preparative gel permeation chromatography (GPC) and then have been analyzed spectrographically. The polymeric products of oxidation show similar chemical bond structure for the various types of esters studied. The importance of oxygen and metal catalysis on product formation is demonstrated. The influence of steel surfaces on the products of oxidation suggests a tribochemical reaction resulting in the ultimate formation of a “friction polymer.” Presented at the 33rd Annual Meeting in Dearborn, Michig...

The Effects of Antioxidant Reactions on the Wear Behavior of a Zinc Dialkyldithiophosphate

Abstract: A systematic study of the wear behavior of a synthetic hydrocarbon bare oil as a function of time and concentration of added zinc di-n-octyldithiophosphate, ZDTP, has been carried out utilizing the 4-ball apparatus. A comparative study was made using ZDTP which had been reacted with a known concentration of peroxy radical species. Wear rates manifested, by the reacted, ZDTP at concentrations near 10−4 M total ZDTP were considerably higher than those observed with unreacted ZDTP at the same concentrations. Moreover, the observed wear rates were found to be quantitatively related to amounts of unreacted ZDTP as measured by a new peroxy radical litration method. These findings are consistent with the view that the products derived from the anti-oxidant reactions of ZDTP in lubricants are ineffective as antiwear agents. Presented at the 33rd Annual Meeting in Dearborn, Michigan, April 17–20, 1978

Friction, Deformation and Fracture of Single-Crystal Silicon Carbide

Abstract: An investigation was conducted to determine the nature of the deformation and fracture of silicon carbide and its effects on friction properties. Friction experiments were conducted with hemispherical and conical diamond riders sliding on the basal plane of silicon carbide. The results indicate that, when deformation is primarily elastic, the friction does not depend on crystallographic orientation and there is no detectable fracture or crocking. When, however, plastic deformation occurs, silicon carbide exhibits anisotropic friction and deformation behavior. Surface fracture crack patterns surrounding wear tracks are observed to be or three types. The crack-geometries of two types are generally independent of orientation, the third crack, however, depends on the orientation. All surface cracks extend into subsurface. Anisotropic friction, deformation and fracture on the basal plane are primary controlled by the slip system {101¯0} ⟨112¯0⟩ and a cleavage of {101¯0}. Presented as an American Society of Lub...

The Influence of High Pressure Oil Seals on Turbo-Rotor Stability

Abstract: The use of ring type oil seals in modern turbo-compressors is a standard design procedure which has evolved as a result of experimental testing and field experience. Originally, major concerns were inner-seal leakage and losses associated with the fluid-film friction in the seal oil film. More recent applications of oil seals have been in compressors which run in excess of double the first shaft bending peak response speed. This fact has focused attention on the hydrodynamic characteristics of the oil seals. This paper presents a method of analyzing high-pressure ring type oil seals which enables the design engineer to determine the seals' influence on rotor-bearing stability. The results of the analysis are used in a multi-mass flexible rotor stability analysis to show how the oil seals can produce a zone of shaft-whip instability in high-speed turbo-compressors. Experimental results are presented which clearly indicate the presence of shaft whip instability before oil seal modifications and its total ab...

Self-Protection of High Wear Materials

Abstract: Thick intermediate films or third bodies with high load-carrying capacity are generated through wear by different materials. A balance thus naturally exists between the material wear rate and the protection afforded by these compacted wear debris films. The length of a specimen situated parallel to the sliding motion or wear debris transport direction, necessarily plays a role different from its width. For the same unit, loading material wear protection increases with length and is independent of width. The wear problem can, therefore, be approached with two-dimensional models. Debris motion explains why wear data obtained with the same materials on machines with specimens of different shapes are difficult to correlate. Presented as an American Society of Lubrication Engineers paper at the ASLE/ASME Lubrication Conference in Kansas City, Missouri, October 3–5, 1977

A Study of Sealing Phenomena on Oil Seals

Abstract: It will be 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 phenomena of an oil seal in this paper, the suction volume per an unit time, [Qbar] of lubricating oil instead of air is used as a means of estimating the sealing status. It becomes clear that there is the relation, [Qbar]αG1/2 , wherein G is nondimensional parameter of oil seal, and that suction coefficient of oil, K (=[Qbar]/uD2 G1/2 , wherein u and D are sliding velocity of between shaft and seal and shaft outer diameter, respectively, depends on the sealing characteristic constant, Φ, the surface roughness of the rotating shaft and its eccentricity. Presented as an American Society of Lubrication Engineers paper at the ASLE/ASME Lubrication Conference in Kansas City, Missouri, October 3–5, 1977

Performance of a Large Thrust Bearing with Minimized Thermal Distortion

Abstract: Designs are needed for large, heavy duty tilting-pad thrust bearings to minimize the load and thermal distortions of sliding surfaces which adversely effect bearing performance. A new bearing construction is proposed in this paper, aimed at reducing thermal distortion. The effects of the thermal distortion on proposed design are analyzed with a simplified model and a significant improvement in bearing performance in comparison to a conventional bearing, is confirmed in tests. Presented as an American Society of Lubrication Engineers paper at the ASLE/ASME Lubrication Conference in Kansas City, Missouri, October 3–5, 1977

Surface Temperature Measurements in Rolling and Sliding EHD Contacts

Abstract: A number of devices in which concentrated contact conditions occur have relatively small amounts of slip or none at all. A knowledge of contact temperatures developed under these conditions is essential to understanding the lubricant rheology and also the fluid film failure. In this study, moving surface temperature measurements in rolling and sliding EHD point contacts were made using an available infrared technique. Film thickness and traction have also been measured. Slide-to-roll ratios of −2 to +2 have been studied. By using a different kinematic configuration, stationary surface temperatures have also been measured. It has been shown that, while surface temperature rises in the low slip region are relatively small, stationary surface temperatures are significantly higher than the moving surface temperatures. Flash temperature theory has been extended to cover the combined rolling and sliding conditions. Correlation between the predicted and the measured values has also been performed. Presented at t...

Friction and Fracture of Single-Crystal Silicon Carbide in Contact with Itself and Titanium

Abstract: An investigation was conducted to examine the friction properties and mechanical behavior of single-crystal silicon carbide (0001) surface sliding against itself and against polycrystalline titanium. The results indicate hexagon-shaped pits of silicon carbide and the formation of platelet hexagon-shaped wear debris of silicon carbide due to cleavages of both prismatic and basal planes as a result of silicon carbide sliding against itself. The fracturing of silicon carbide also occurs near the adhesive bond to titanium. The wear debris produced by brittle fracture plows the titanium and transfers to it. Further, the silicon carbide wear debris, which adhered and transferred to titanium, plows the silicon carbide surface and transfers back to it

Ferrographic Analysis of Wear Debris Generated in Accelerated Rolling Element Fatigue Tests

Abstract: Ferrographic analysis was used to determine the types and quantities of wear particles generated during accelerated rolling contact fatigue tests. The NASA five-ball rolling contact fatigue tester was used. Ball specimens were made of AMS 5749, a corrosion resistant, high-temperature bearing steel. The lubricant was a super-refined naphthenic mineral oil. Conditions included a maximum Hertz stress of 5.52 × 109 Pa and a shaft speed of 10 000 rpm. Four types of wear particles were observed; normal rubbing wear particles, fatigue spall particles, spheres, and friction polymer. Presented as an American Society of Lubrications Engineers paper at the ASLE/ASME Lubrication Conference in Kansas City, Missouri, October 3–5, 1977

Tribochemical Surface Reaction and Lubricating Oil Film

Abstract: A radioactive tracer technique was used to investigate a tribo-chemical surface reaction obtained by a thrust collar type friction Machine. Radioactive dibenzyl disulfide labeled with sulfur-35 was used as an additive. Steel and copper disks were used as friction specimens. Radioactive copper sulfide on the friction surface was quantitatively measured with a G-M tube, and a kinetical analysis of the reaction was carried out. The friction coefficient decreased linearly depending on the amount of surface produced on the friction surface. This dependency was accompanied by adsorption of dibenzyl disulfide, which made a more effective lubricating oil film and was enhanced by the sulfide on the friction surface. The results of kinetical analysis were explained effectively by considering the oil film behavior related to the adsorptive action of the surface sulfide. Presented as an American Society of Lubrication Engineers paper at the ASLE/ASME Lubrication Conference in Kansas City, Missouri, October 3–5, 1977

Analysis of Step Journal Bearings—Infinite Length, Inertia Effects

Abstract: This paper analyzes infinitely long centered and eccentric step journal bearings using finite elements. Step inertia and turbulence effects are included. The analysis is verified by comparison with other theoretical and experimental results for centered step bearings. Results of a parametric study for the centered case considering both turbulence and step inertia effects predict optimum step geometrics similar to those predicted by pure laminar theory. Neglecting the pressure drop due to inertia forces at the step, but including the effects of turbulence around the bearing, produces errors less than 10 percent in both load capacity and dynamic coefficients for Reynolds numbers less than 1500. This analysis concludes that finite length step bearings with oil lubricants may be adequately analyzed without taking into account step inertia effects. Presented at the 33rd Annual Meeting in Dearborn, Michigan, April 17–20, 1978

Coastdown Time as a Mechanical Condition Indicator for Vertical Axis Motors with Grease-Lubricated Ball Bearings

Abstract: A technique is presented to assess the mechanical condition of vertical axis electric motors equipped with grease-lubricated ball bearings by comparing observed and predicted rotor coastdown times. A theoretical expression for calculating the coastdown time required, as input, a relationship between rotor torque and rotational speed. Torque values derived from existing theory in the literature proved unsatisfactory. Experiments were conducted on four electric motors with varying bearing size and preload, blade configuration and grease lubricant properties to refine the input criteria. Substitution of these empirically derived torque values into the expression then gave acceptable results. Deviation of actual coastdown times from those predicted indicates a probable mechanical problem and need for investigation. Presented at the 33rd Annual Meeting in Dearborn, Michigan, April 17–20, 1978

An Analysis of Alkyl and Aryl Zinc Dithiophosphate-Type Lubricating Oil Additives By Liquid Chromatography and Infrared Spectroscopy

Abstract: An analytical method was developed for the estimation of the alkyl-to-aryl ratio of organo zinc dithiophosphate additives in finished lubricants based upon concentrating the active ingredients by liquid chromatography followed by infrared spectroscopic measurements. Presented as an American Society of Lubrication Engineers paper et the ASLE/ASME Lubrication Conference in Minneapolis, Minnesota, October 24–26, 1978

Modified face seal for positive film stiffness

Abstract: The object of the invention is to improve the film stiffness of a face seal without increasing the sealing and dam area. The improved sealing apparatus (16) has a primary seal ring (20) in the form of a nose piece. A spring (24) forces a sealing surface (28) on the seal ring into sealing contact with a seat (18) to form a face seal. A circumferential clearance seal is formed in series with this face seal by a lip (34) on the nose piece. The width of the surface (36) of the lip is substantially the same as the width of the sealing surface (28) on the face seal. Also the clearance between the surface (36) on the lip and the shaft (10) is substantially the same as the spacing between the face sealing surfaces (28 and 30) on the face seal when the shaft is rotating. The circumferential clearance seal restricts the flow of fluid from a main cavity (14) to an intermediate cavity (32) with a resulting pressure drop. The hydrostatic opening face is strongly dependent on the face seal clearance, and the desired axial stiffness is achieved.

A Simplified Model of Elastohydrodynamic Lubrication of Rollers—The Central and Exit Solution

Abstract: The purpose of the study is to find a simple model to serve as a tool for later studies of thermal effects, roughness effects and thermal instability problems in elastohydrodynamic lubrication. The Grubin model has the required simplicity but, unfortunately, it cannot reproduce the entry and exit conditions well enough. A modification of the theory suggested by Grubin himself considerably increases the fidelity of the solutions, particularly in the central and exit regions of the contact. The modification and the effects resulting from it, particularly with respect to thermal effects are discussed.

Pseudo-Random Binary Sequence Forcing in Journal and Squeeze-Film Bearings

Abstract: The need is established for the experimental determination of linearized bearing oil-film coefficients. General methods of dynamic testing are discussed and previous attempts to measure bearing coefficients are reviewed. Three criteria for assessing the suitability of any test procedure for estimating linear bearing coefficients are formulated and used to show that improved techniques are still required. A new test procedure using pseudo-random binary sequence forcing is described and is shown to possess several attractive advantages compared with more traditional methods of dynamic testing. The method is applied to determine the linear characteristics of a prototype squeeze-film bearing and some experimental results are presented. Presented at the 33rd Annual Meeting in Dearborn, Michigan, April 17–20, 1978

The Wear of Aluminum-Bronze on Steel in the Presence of Aviation Fuel

Abstract: A study has been made of the action of a commercially available corrosion inhibitor added to hydrofined aviation fuels in reducing the wear of aluminum bronze sliding on KE180, 13 percent chromium steel. From measurements of friction and wear and an extensive examination of surfaces using Auger electron spectroscopy, a surface model has been proposed which elucidates the mechanism of wear protection. Presented as an American Society of Lubrication Engineers paper at the ASLE/ASME Lubrication Conference in Kansas City, Missouri, October 3–5, 1977

Calculation of Elastic Contact Stresses for Rough-Curved Surfaces

Abstract: Statistical theories of rough elastic contact have previously been developed for the contact of spheres and of parallel cylinders, and have predicted stress distributions significantly different from those of the classical Hertzian theory. The theories characterize the surface in terms of three surface parameters describing, respectively, the roughness, density and radius of curvature of the asperities. In this paper, a procedure is described for quantifying these theories by obtaining the surface parameters from the spectral-moment approach to surface description; the only surface measurement needed is one of roughness. The procedure is illustrated by two numerical examples relating to the contact of a rocker arm with a pushrod and to a journal bearing. In the case of the rocker and pushrod, no significant difference from the smooth-surface results is found. In the case of the journal bearing, however, the maximum stress is calculated to be 36 percent less, and the nominal contact width 2.2 times more, t...

Static and dynamic performance characteristics of an orifice-compensated hydrostatic journal bearing

Abstract: The fluid film lubrication equation for a zero-speed, orifice-compensated, multipocket hydrostatic journal bearing is solved by a finite element method for determining its steady-state performance and the dynamic stiffness and damping coefficients. These coefficients of the film influence the response of the shaft-bearing system. Performance data have been computed for a four-pocket bearing of L/D = 1.0, with various orifice design parameters and eccentricity ratios. For stability studies, critical mass for the linearized system has been determined by Routh's criterion. By discretizing time and using the Runge-Kutta method, motion trajectories of the journal center have been theoretically determined for a small arbitrary initial disturbance.

Bearing Performance Investigations Through Speed Ratio Measurements

Abstract: The performance of ball bearings and their lubricants were studied by monitoring the speed ratio (the ratio of ball pass to shaft speed). Bearing speed ratio measurements were found to provide new insights into bearing and lubricant performance. This paper presents a summary of the development of the theoretical speed ratio equations, describes a unique measurement technique for measuring and monitoring the speed ratio, and presents several applications. Highlighted are experiments revealing the tendency for greases to promote varying degrees of slippage and skidding at the ball-raceway contacts. Presented at the 33rd Annual Meeting in Dearborn, Michigan, April 17–20, 1978

Analytical Dynamics of Partial Journal Bearings with Applications

Abstract: A variational approach has been employed to solve Reynolds' equation for a finite length partial journal bearing. The pressure, is obtained as a doubly infinite sine series and the load capacity can be expressed, for some bearings, as a simple sum of coefficients. Applications include a 60 degree, L/D = 0.5 partial are bearing and a L/D = 1.5 plain journal bearing for which both the half Sommerfeld and Reynolds' boundary conditions are employed. Presented as an American Society of Lubrication Engineers paper at the ASLE/ASME Lubrication Conference in Kansas City, Missouri, October 3–5, 1977