Showing papers in "Tribology Transactions in 1968"

Evaluation of Lubricants Using Optical Elastohydrodynamics

Abstract: A system is described whereby a clear map is obtained of the contact between a metal (steel) ball rolling against a plate glass disk This is achieved by mounting the disk in an air bearing and coating its surface with a thin layer of chromium that partially reflects the light, allowing good interference patterns to be formed The effect of load (giving stresses to 100,000 psi) and speed and viscosity is demonstrated for a wide range of fluids A complete run can be carried out with at most 5 ml of sample It is shown that load hardly alters the film thickness in the middle of the contact but does affect the minimum film thickness, which is in the side lobes By using a calibrated oil the pressure-viscosity coefficients of the fluids can be determined The rate of shear is very high, between 01 and 40 million sec−1 and the flow orientation of polymer thickened oils is clearly marked as well as the molecular orientation postulated by Bondi For most fluids, except the polymer thickened oils and silicones,

A Study of Tricresyl Phosphate as an Additive for Boundary Lubrication

Abstract: A method of combining thin-layer chromatography with activation analysis to measure quantitatively the individual impurities in tricresyl phosphate (TCP) is described. The relative amounts and types of impurities found in commercial grades of TCP are discussed. Preparative thin-layer chromatography and iron powder chromatography are applied to produce TCP samples with known concentrations of several impurities. The use of the four-ball wear tester as a method of determining trends in wear values as a function of base stock and additive quality is demonstrated. The relationship of acid phosphate rather than TCP concentration to antiwear properties of compounded lubricants is suggested by transition load studies. Presented as an American Society of Lubrication Engineers paper at the ASLE/ASME Lubrication Conference held in Chicago, Illinois, October 17–19, 1967.

The Load-Carrying Mechanism of Organic Sulfur Compounds—Application of Electron Probe Microanalysis

Abstract: A detailed literature survey has shown that considerable controversy exists on the mode of action of organic sulfur compounds as load-carrying additives. Previous work by the authors, using four ball extreme-pressure and wear tests, has suggested that under mixed lubrication (antiwear) conditions, organic disulfides are adsorbed on to the metal surface with cleavage of the sulfur-sulfur bond to form an iron mercaptide layer. However, under more severe conditions such as exist in the extreme-pressure region, cleavage of the carbon-sulfur bond occurs to give an inorganic sulfur-containing layer. Thus the different relative performances of disulfides in the mixed lubrication and extreme-pressure regions are readily explained. This paper now presents the results of a detailed examination of the wear scars obtained with certain disulfides using an electron probe microanalyser. The results illustrate the use of this new technique for studying the nature of worn surfaces but, even more important, lend strong sup...

Oxidation Characteristics of MoS2 and Other Solid Lubricants

Abstract: Thermogravimetric oxidation data are presented for fifteen refractory metal dichalcogenides. Interpretation of these data is supported by oxidation thermograms of the chalcogens and the refractory metals and by X-ray diffraction analysis of the oxidized products. The effects of humidity, heating rate, and particle size on oxidation of the dichalcogenides are presented. Thermogravimetric analysis is shown to be helpful in detecting impurities, such as unreacted elements, in commercial samples. Some dichalcogenides are shown to retain the same relative oxidation stability, when bonded in thin films with a ceramic, as for pure powder samples. A table is presented summarizing these oxidation characteristics together with information from the literature on crystal structures, electrical resistivities, and densities. Presented as an American Society of Lubrication Engineers paper at the ASLE/ASME Lubrication Conference held in Chicago, Illinois, October 17–19, 1967.

The Influence of the Atomic Nature of Crystalline Materials on Friction

Abstract: Atom arrangement in crystalline materials, considering lattice, planes, structure and effect on mechanical properties related to friction

Fundamental Research on a Radial Face Seal

Abstract: Radial face seals generally speaking operate under full hydrodynamic lubricating conditions, but the mechanism of lubrication is not completely understood. In a primarily experimental investigation the author has attempted to establish a description of the basic lubricating mechanism in radial face seals. The experimental apparatus and measuring techniques are briefly described. The experimental results display a high degree of reproducibility. Dynamic measurements of film thickness reveal fluctuations at twice shaft speed frequency that are concluded to be due to surface waviness. This conclusion is corroborated by the topography of the sealing faces. At constant geometry the friction coefficient and film thickness appear to depend on two dimensionless numbers incorporating average face pressure, sealing pressure, viscosity and speed. A simplified theory that lakes into account the macroroughness of the sealing faces shows close correlation with the experimental data obtained. Having obtained a strong in...

The Wear of Electrodeposited Gold

Abstract: The wear and friction of pure gold and gold alloy electrodeposits were determined. These platings are widely used in sliding electric contacts and include golds hardened with silver, cadmium, nickel, cobalt, or cobalt and indium. In preliminary work, the microstructures, hardnesses, crystallographic orientations of the surface, and topographies of the golds were examined; these properties vary widely, and relationships among them are discussed. Sliding was with thick deposits to eliminate effects of substrate. The experimental method involved repeat-pass unidirectional sliding at 100g in a rider-flat apparatus with plated flats against wrought gold or gold-plated riders. Wear and friction are described for both as-plated samples, and to eliminate distinguishing surface textures, with flats abraded to a common roughness. Wear was found to be related to hardness, topography, and crystallographic orientation. A new result is that prow formation does not occur above a load-dependent critical roughness. For ab...

On the Effectiveness of Hollow Balls in High-Speed Thrust Bearings

Abstract: The geometry, kinematics, dynamics, and fatigue life of a thrust-loaded, angular-contact, ball bearing are investigated considering the inertial effects of hollow balls at shaft speeds corresponding 1 to 3 million Ndm. The data presented show the variation in these parameters and indicate that the effectiveness of hollow balls is governed by the combined condition of speed and axial load rather than speed alone. Presented at the 23rd ASLE Annual Meeting in Cleveland, May 6–9, 1968.

Wear of Unlubricated Steel Surfaces in Sliding Contact

Abstract: Observations have been made of the wear from an SAE 1113 steel pin specimen rubbing on a SAE 113 steel disk in a normal laboratory atmosphere in relation to normal load (0.5–10.4 lbf), slidinq speed (21–188 ft/sec), sliding distance and track history. As a function of sliding distance, three regions are observed; (i) initial severe wear, (ii) mild wear resultinq from the formation of oxide layers on both the pin specimen and transferred particles adhering to the track, (iii) a milder wear, due to the attainment of a uniform track condition. The wear rate measured in (ii) is observed to be proportional to normal load for constant (normal load)1/2 × (sliding speed) provided that the magnitude of this parameter is insufficient to cause periodic removal of the surface film. This conclusion is shown to be compatible with earlier theoretical predictions when the presence of an oxide layer was pre-supposed. Unlike the coefficient of friction which is primarily determined by the pin surface condition only, the pi...

Sliding Experiments with Polytetrafluoroethylene

Abstract: The sliding of polytetrafluoroethylene (PTFE) was experimentally examined with a sled type apparatus and with a conventional three pins-on-flat frictometer. Friction hysteresis and time-and speed-dependent phenomena were observed with both instruments and were compared. With the sled apparatus, the relation between friction and sliding speed of PTFE sliding on PTFE at different ambient temperatures was examined and is described. A study of the sliding surface of PTFE with the electron microscope was made. The initial results give clear photographic evidence in stereo that films and fibers of PTFE are stretched and drawn over relatively large distances across the topography of the sliding surface. In view of this and the viscoelastic nature of polymer deformation, the observed time and temperature dependence of friction becomes plausible. Presented at the ASLE Annual Meeting in Cleveland, May 6–9, 1968.

The Ball-on-Cylinder Test for Evaluating Jet Fuel Lubricity

Abstract: For evaluating the lubricating qualities of jet fuels, the ball-on-cylinder device appears to be particularly suitable. It can operate at low enough loads so that subtle differences in fuel quality can be detected. Examples are given of the effect of refining, the differences in additive action, the importance of test atmosphere, and the influence of temperature. Other test methods appear to be too severe for all-around fuels testing. Presented at the 23rd ASLE Annual Meeting in Cleveland, May 6–9, 1968.

Some Effects of Nonhydrocarbon Base Oil Constituents on the Friction and Surface Coating Formation Obtained with Three Additives

Abstract: The effects of antiwear, EP, and friction modifying additives on the friction of steel-on-steel are greater when blended in more highly refined base oils. To explain this observation, non-hydrocarbons (sulfur, nitrogen, and oxygen compounds) of the types either (a) initially present in less well-refined oils or (b) formed by oil oxidation during use, were added to base blends consisting of a chlorinated wax, a sulfurized terpene oil, or didodecyl phosphite in a highly refined mineral oil. The resulting changes in friction and surface-coating formation were measured as a function of the nonhydrocarbon concentration. The additive effects on friction were canceled selectively by some of the 34 nonhydrocarbons studied at concentrations that could be encountered in less well-refined oils, whereas pure hydrocarbon additions had little effect. Mechanisms for the observed friction and surface coating changes have been proposed. Presented as an American Society of Lubrication Engineers paper at the ASLE/ASME Lubri...

Surface Temperature and Its Relation to Periodic Changes in Sliding Conditions between Unlubricated Steel Surfaces

Abstract: The authors have previously observed periodic changes in the frictional force and wear rate in unlubricated sliding between SAE1113 steel surfaces. Also the steady-state value of the coefficient of friction, f, and the periodic time of surface breakdown, T, were observed to be continuous functions of (normal load, W)½ × (sliding speed, U). Theoretical considerations predict the increase in temperature, θF, at the contacting asperities to vary with f and to be a function of (W½U). Temperatures have been measured using both microhardness and coaxial thermocouple techniques. In the steady-state it has been found that the bulk surface temperatures, θB is a continuous function of (W½U) and hence f and T are expressible as functions of θB. Attempts to relate θB and θF are discussed. It is observed that during surface breakdowns, θB rises rapidly due to a sudden increase in f. It is concluded that this temperature increase promotes the formation of a new oxide surface layer and the return to steady-state conditi...

New Test Techniques for Evaluating the Compatibility of Materials with Liquid Oxygen under Impact

Abstract: The current drop-weight test methods for evaluating the compatibility of materials with liquid oxygen under impact are briefly discussed, with particular emphasis upon the characteristically poor repeatability of the “threshold value” impact sensitivity ratings yielded by these methods. It is pointed out that this trait is primarily due to the poor statistics of the test procedures used. It is further shown that impact sensitivity alone, even when measured by the most accurate and reliable technique, is not an adequate description of the potential fire or explosion hazard of a material; reaction intensity must also be considered. With this background, typical results from two new test techniques are presented and discussed. In one of these, impact sensitivity is measured in terms of the drop height at which a material has a 50% probability of reaction. In the other, reaction intensity is measured in terms of the maximum peak pressure of the air shock wave generated by the reaction. Presented at the 23rd A...

The Role of Diffusion in Corrosive Wear

Abstract: Oxygen diffusion through the lubricant film is an important factor in corrosive wear, a type of wear where the primary attack is the formation of iron oxide at the rubbing surface. Experimental data were obtained in a ball-on-cylinder device and quantitatively correlated with oxygen availability by a mathematical model. This model assumes two parallel surfaces separated by a small distance, one surface moving with respect to the other. The lubricant at the inlet is saturated with oxygen, which diffuses to the stationary surface to form iron oxide. The iron oxide is removed immediately by the rubbing motion. From the analysis the average clearance predicted was about 10 microinches, a reasonable figure. For the condition used experimentally, essentially all of the oxygen entering the system will diffuse to the surface and be consumed. Thus, differences in mass diffusivity are not important in determining the wear rate. The experimental observations, in agreement with the theoretical prediction, show that c...

The Effect of Clamping Stress Distribution on the Fretting Fatigue of Alpha Brass and Al-Mg-Zn Alloy

Abstract: This investigation shows that below a certain value of the maximum pressure in the region of contact, fatigue cracks are not initiated. This critical value of the maximum pressure is lower the greater the area of contact. In alpha brass the rate of crack initiation increases with increasing values of the maximum pressure, whereas in the Al-Mg-Zn alloy the rate of crack initiation decreases as the maximum pressure increases. Presented as an American Society of Lubrication Engineers paper at the ASLE/ASME Lubrication Conference held in Chicago, Illinois, October 17–19, 1967.

On the Separation Boundary Condition for Fluid Lubrication Theories of Journal Bearings

Abstract: Various boundary conditions of fluid lubrication theories have been presented for the trailing edge of the lubricant film of a journal bearing, but they do not seem to be clearly investigated physically in connection with the lubricant film rupture. The reverse flow and, hence, the separation of fluid are observed experimentally to cause the film rupture. This condition is brought to be the boundary condition of the bearing film rupture in this paper. By using this condition, the bearing characteristics, such as eccentricity, load capacity, and attitude angle, are investigated theoretically. The experimental results, obtained by using the transparent bearing for the direct observation of the bearing film behavior, agree well with the theoretical ones. Presented at the 23rd ASLE Annual Meeting in Cleveland, May 6–9, 1968.

The Observation of Individual Asperity Interactions in Lubricated Point Contact

Abstract: The elemental interactions between asperities of ball and flat surfaces in contact are described by considering these factors: (a) the influence of lubricant supply and distribution around the test balls on the kinematics of ball motion and surface velocities; (b) the microgeometry statistics of the contacting surfaces, defining the size, shape and distribution of individual asperities; (c) the (partial) elastohydrodynamic film formed in the Hertz contact area as it influences the average spacing between the contacting surfaces. By joint operation of these factors, individual asperity interactions take place and were observed by way of their effects on friction and their electrical conductivity behavior. On the basis of the observations, a tentative model of the asperity interactions is suggested.

Slow Speed Wear of Steel Surfaces Lubricated by Thin Oil Films

Abstract: Time rates of wear and distance rates of wear are presented as a function of calculated oil film thickness between two cylindrical steel rollers loaded to a maximum Hertz contact stress of 300,000 psi. Wear is divided into a constant wear mode and a transient wear mode depending on the oil film thickness. A negative slope of the curve representing the distance rate of wear versus oil film thickness explains the stabilizing effect on radial surfaces. A positive slope in a narrow range of oil film thickness causes a surface instability due to wear and surface rippling occurs. Transient wear occurs at the thicker oil films. When followed by zero wear rate surface oxide films develop. The total amount worn off during the transient varies greatly with the oil film thickness when using rollers of a given surface finish. Control of oil film thickness by either velocity or viscosity changes due to tempearture produces similar wear effects. Presented as an American Society of Lubrication Engineers paper at the ASL...

Preliminary evaluation of greases to 600 F and solid lubricants to 1500 F in ball bearings.

Abstract: Ball bearing test apparatus for evaluation of greases and solid lubricants at high temperatures

Chemical Interactions Involved in the Formation of Oxidation-Resistant Solid Lubricant Composites

Abstract: Solid lubricating compacts of tungsten diselenide-gallium alloys are currently under development for use as self-lubricating members in high speed-high temperature ball bearing systems. The material is of considerable interest due to the fact that it resists oxidation at temperatures three times higher than pure tungsten diselenide. This paper discusses initial studies of the physical and chemical changes that occur in these compacts during a heal-treating cycle required in their fabrication. Speculations regarding the mechanism responsible for their oxidation resistance are presented. Presented as an American Society of Lubrication Engineers paper at the Lubrication Conference held in Chicago, Illinois, October 17–19, 1967.

A Correlation of Bulk Moduli and P-V-T Data for Silicone Fluids at Pressures up to 500,000 psig

Abstract: The increased sophistication of hydraulic systems along with the advancement of elastohydrodynamics and high pressure metal forming techniques has created a need for more complete bulk moduli and P-V-T data. By correlation of the available data on silicones, a generalized relationship for this class of fluids is determined for bulk modulus as a function of pressure, temperature, and density of the fluid at atmospheric pressure and 77F. Thus, density and bulk modulus for most silicone fluids may be predicted at temperatures from 32F to 400F and pressures up to 500,000 psig. For most silicone fluids only the density at atmospheric pressure and 77F is needed beforehand. A few exceptions are listed for which the correlation is applicable with minor modifications. The average deviation of the predicted values of bulk moduli from the experimental data is 1%. Presented at the 23rd ASLE Annual Meeting in Cleveland, May 6–9, 1968.

Optimum Design of Gear Systems for Surface Durability

Abstract: This study deals with the development of a design system for evaluation of the significant parameters which optimize the performance of gear units for surface durability. A double reduction unit is considered for illustration. The results show the feasibility of automated design procedures for gear systems with regard to pitting, scoring, and wear. Presented at the ASLE Annual Meeting in Cleveland, May 6–9, 1968.

New Sulfide Addition Agents for Lubricant Materials

Abstract: Two sulfides, AsSbS4, and AsAsS4 were prepared by aqueous precipitation methods. Property studies covered lubricant characteristics, and comparisons were made with As2S3, As2S3, Sb2S3 and Sb2S3. The various compounds were examined as chemical addition agents for diester lubricating grease and organic resin solid film lubricants. Details are presented for lubricant formulation and preparation, as well as laboratory test methods. The single most significant result is the dual response of AsSbS4 to steel-steel and steel-molybdenum. Previous studies have shown that sulfur compounds as a class are preferential lubricants for molybdenum; however, a lubricating effect for steel by metallic sulfides has been essentially limited to MoS2. Presented at the ASLE Annual Meeting in Cleveland, May 6–9, 1968.

Viscoseal—Pressure Generation and Friction Loss under Turbulent Conditions

Abstract: A new theory is developed that predicts the sealing coefficient and the friction factor of a viscoseal under turbulent flow conditions. This theory, being a synthesis of Boon and Tal's laminar viscoseal theory and Ng, Pan, and Elrod's turbulent lubrication theory, shows very satisfactory correlation with available experimental data. The results have been given in simplified formulas such that they are readily usable for design purposes. At high Reynolds numbers the seal geometry has been optimized, although performance near the optimum is rather constant for rather different values of the geometrical parameters. Existing theories on the turbulent behavior of the viscoseal are briefly discussed. Presented at the 23rd ASLE Annual Meeting in Cleveland, May 6–9, 1968.

The Lubricating Performance of an “in Situ” Process MoS2 Film in Air and in Liquids

Abstract: The performance of a synthetic MoS2 film, produced by electrodeposition of molybdic oxide followed by a temperature-pressure H2S conversion to a molybdenum sulfide compound, is examined under extreme pressure conditions immersed in various fluids. Friction wear and EP characteristics, measured on various test machines, are compared to those of the fluids alone and also to conventional bonded films. The fluids examined include: mineral oil, jet fuel, hydraulic fluid, silicone fluid. The dry films include: burnished MoS2 powder, MIL-L-8937 resin bonded film, MIL-L-8129 silicate bonded film and the synthetic “in situ” MoS2 film. The performance of the synthetic MoS2 film on titanium and stainless steel is also examined. Presented as an American Society of Lubrication Engineers paper at the ASLE/ASME Lubrication Conference held in Chicago, Illinois, October 17–19, 1967.

Experiments with hydrodynamic journal bearings of various materials and designs in sodium at temperatures to 800 deg F

Abstract: Hydrodynamic journal bearings in liquid sodium, discussing stability characteristics of different geometries and wear at high temperatures

Propagation of Surface Disturbances on Radially-Loaded Disks

Abstract: An analysis is presented showing the manner in which an initial point disturbance on the surface of one disk of a pair of radially loaded disks rolling and sliding in contact will grow and propagate other surface disturbances on both disks. In the analysis it is assumed that an area becoming disturbed will be able to cause disturbances on surfaces which come into contact with it. The patterns of the disturbances formed have been compared with scuff patterns on pairs of failed disks, and significant similarities are shown. The number of disturbances and the spacing of the leading edges of the disturbances are similar to the number and spacing of the scuff marks. The analysis gives lengths of the disturbances somewhat longer than the scuff marks. It is concluded that the analysis is helpful in understanding failures on disks, and it can be extended to scuff propagation on gears. Presented as an American Society of Lubrication Engineers paper ASLE/ASME Lubrication Conference held in Chicago, Illinois, Octobe...

Wear Coefficient Correlation of Test Methods and Design Calculations for Solid Film Lubricants

Abstract: This paper presents a portion of the work done by the authors in developing a new approach to evaluation techniques for wear of solid film lubricants. The theory and experimental requirements are presented that are necessary to adapt the use of “wear coefficient” to the extremely thin films required for these materials. A method for correlation of wear data obtained on various testers is included. Experimental results have covered an environmental temperature range from —320F to 1100F. Design formulas for linear motion, journal, thrust, and spherical bearings have been derived to utilize experimental data in the estimation of hardware bearing wear. Presented at the 22nd Annual Meeting of the American Society of Lubrication Engineers held in Toronto, May 1–4, 1967.

Rarefied Gas Flow through Passages with Static Boundaries

Abstract: A resume of the current state-of-knowledge concerning rarefied gas flow through passages with static boundaries is presented. A brief development of the theoretical gas flow models which have been used for long tubes and annuli is included. These theoretical models have been developed to cover the flow regime extending from laminar continuum flow to free molecular flow. The analysis required to use these models is simple and straightforward. Experimental data are presented for the flow of argon through a long tube and for the flow of argon and xenon through annuli. The experimental values of mass flow rate per unit pressure drop as a function of Knudsen number are graphically presented for a long tube and for two annuli. Also presented on the same figures are the values predicted by the theoretical models. The agreement between theory and experiment for the complete regime between continuum and free molecular flow is very good. Presented at the ASLE Annual Meeting in Cleveland, May 6–9, 1968.