Showing papers in "Journal of Lubrication Technology in 1982"

Ball bearing lubrication: The elastohydrodynamics of elliptical contacts

Abstract: The history of ball bearings is examined, taking into account rollers and the wheel in the early civilizations, the development of early forms of rolling-element bearings in the classical civilizations, the Middle Ages, the Industrial Revolution, the emergence of the precision ball bearing, scientific studies of contact mechanics and rolling friction, and the past fifty years. An introduction to ball bearings is presented, and aspects of ball bearing mechanics are explored. Basic characteristics of lubrication are considered along with lubrication equations, the lubrication of rigid ellipsoidal solids, and elastohydrodynamic lubrication theory. Attention is given to the theoretical results for fully flooded elliptical hydrodynamic contacts, the theoretical results for starved elliptical contacts, experimental investigations, the elastohydrodynamics of elliptical contacts for materials of low elastic modulus, the film thickness for different regimes of fluid-film lubrication, and applications.

Some Observations in High Pressure Rheology of Lubricants

Abstract: Experimental data are presented on viscosity, elastic shear modulus, and limiting shear stress of 12 liquid lubricants. It is shown that transition histories do affect the limiting shear stress of the materials in the form of isothermal compression resulting in a lower density and lower limiting stress than isobaric cooling. The measured limiting shear stress agrees with EHD traction data at slide-to-roll ratios of 0.1 or more. In pressure viscosity measurements of the polymer solutions, it is found that for some temperatures, the pressure viscosity coefficient of the blend is slightly less than that of the base, which results in the crossing of the viscosity-pressure isotherms at high pressures.

Abrasive Wear Mechanisms in Steels

Abstract: Abrasive wear tests have been carried out on three steels and a number of pure metals using a pin-on-drum instrument. Each steel was tested at several different hardness levels attained by varying the heat treatment and while the results show a relationship between abrasion resistance and hardness, this was not the linear relationship found by Kruschov and others. Single point scratch experiments and scanning electron microscopy were carried out in an attempt to elucidate the wear mechanisms in these different materials and from the results a model is suggested to account for the observed wear behavior.

Observation of Pressure Variation in the Cavitation Region of Submerged Journal Bearings

Abstract: Visual observations and pressure measurements in the cavitation zone of a submerged journal bearing are described. Tests are run at speeds of 1840 and 3000 rpm, and at each speed, four different levels of the ambient supply pressure are applied, ranging from 13.6 KPa to 54.4 KPa. A strong reverse flow is detected inside the cavitation area adjacent to its downstream end, and significant pressure variations on the order of 50 KPa are found inside the cavitation region at the downstream portion of its circumferential extent. Results indicate that the assumption of a constant cavitation pressure is incorrect in the case of enclosed cavitations, and it is postulated that oil which is saturated with air under atmospheric pressure becomes oversaturated in the subcavity pressure loop.

Regimes of Traction in Concentrated Contact Lubrication

Abstract: Experimental evidence is presented for the existence of three regimes of traction in concentrated contacts. Data are obtained in a rolling contact simulator by varying the lubricant, temperature, rolling speed, load and surface roughness at a fixed slide-to-roll ratio. At lower thicknesses the mixed regime is encountered, and traction is increased due to asperity interaction, while at higher film thicknesses, the lubricant pressure is distributed over a greater area than the Hertzian region, resulting in a lower average pressure and reduced traction.

The Effects of Ion Implantation on Friction and Wear of Metals.

Abstract: : The effect of ion implantation on the friction and wear behavior of metals was investigated. Experiments were conducted with iron, titanium, and copper implanted with nitrogen ions, iron implanted with aluminum ions, and copper implanted with zinc ions. The significant reduction in friction and wear of the iron and titanium systems is attributed to a hard layer formed during the ion implantation process. This hard layer minimizes plowing and subsurface deformation and hence reduces the delamination wear process, i.e. crack nucleation, crack propagation, and the formation of delamination wear sheets. A finite element model of an elastic semi-infinite solid under the contact of a stationary rigid asperity showed that the hard layer does not change the subsurface stress distribution by supporting the load, but rather that this thin layer decreases the plowing component of friction. The model predicts that this decrease in the friction coefficient in turn, substantially reduces subsurface deformation and thus wear. The implanted copper specimens which did not appear to have a hard surface layer showed little improvement in their tribological behavior over the unimplanted copper.

Single Pass Rub Phenomena—Analysis and Experiment

Abstract: An experimental and analytical investigation is presented of contact phenomena for the case of a fully-dense copper gas path seal segment which is rubbed by a single steel blade tip at room temperature. The experiments were executed on a pendulum-type test device, with forces, rub energy, surface temperature and residual deformation being determined for each single-path rub test. The thermal and mechanical factors influencing single-pass rub surface temperatures were modeled analytically. It is found that large plastic strains occurred on or near the contact surface of the copper rub specimens. A study of the influence of various material properties on surface temperature showed that increased thermal conductivity of the stationary component played a role in lowering contact temperatures. Increased thermal conductivity of the moving blade tip component and increased thermal diffusivity of the stationary material also had a beneficial effect.

Effect of Surface Roughness on Elastohydrodynamic Line Contact

Abstract: A numerical solution of an elastohydrodynamic lubrication (EHL) contact between two long rough surface cylinders is obtained. A simultaneous solution of an elasticity equation and the Reynolds equation for two partially lubricated rough surfaces is used to obtain a theoretical solution of pressure distribution, elastohydrodynamic load and film thicknesses for given speeds. A theoretical solution is also found for lubricants with pressure dependent viscosity, material properties of cylinders, and surface roughness parameters. Elastic deformation is found from hydrodynamic and contact pressure using plane strain analysis, and results indicate that for a constant central film thickness, increasing the surface roughness decreases the EHL load and there is little variation in minimum film thicknesses as the surface roughness is increased.

The Effects of Artificially-Produced Defects on the Film Thickness Distribution in Sliding EHD Point Contacts

Abstract: The effects of artificially produced dents and grooves on the elastohydrodynamic (EHD) film thickness profile in a sliding point contact were investigated by means of optical interferometry. The defects, formed on the surface of a highly polished ball, were held stationary at various locations within and in the vicinity of the contact region while the disk was rotating. It is shown that the defects, having a geometry similar to what can be expected in practice, can dramatically change the film thickness which exists when no defects are present in or near the contact. This change in film thickness is mainly a function of the position of the defects in the inlet region, the geometry of the defects, the orientation of the defects in the case of grooves, and the depth of the defect relative to the central film thickness.

Dynamics of Rotor Bearing Systems Supported by Floating Ring Bearings

Abstract: A general analysis and computational method is presented for calculating the unbalance and self-excited response of high-speed rotor-bearing systems. The analysis is applied to the calculation of the transient response of a rotor supported by two floating ring bearings. Included in the analysis are rotor gyroscopic moments as well as the flexibility of the shaft. Emphasis is placed on determining rotor whirl orbits as influenced by rotor unbalance, the phase angle of the unbalance masses, the clearances of the bearings, the viscosity of the lubricant, and the shock loads that the rotor may be subjected to. It is found that the rotor-bearing system normally operates in an unstable mode in the linear stability sense. However, the nonlinear forces developed by the fluid films of the floating ring bearing will bring the rotor-bearing system to whirl at a limit cycle well within the clearance circles. It is also shown that the rotor assembly will undergo a conical motion when the rotor and wheel configuration is asymmetrical.

Dynamic Analysis of Noncontacting Face Seals

Abstract: The dynamic behavior of a noncontacting coned face seal is analyzed taking into account various design parameters and operating conditions. The primary seal ring motion is expressed by a set of nonlinear equations for three degrees of freedom. These equations, which are solved numerically, allow identification of two dimensionless groups of parameters that affect the seal dynamic behavior. Stability maps for various seals are presented. These maps contain a stable-to-unstable transition region in which the ring wobbles at half the shaft frequency. The effect of various parameters on seal stability is discussed and an empirical expression for critical stability is offered.

Effects of Ultra-Clean and Centrifugal Filtration on Rolling-Element Bearing Life

Abstract: Fatigue tests were conducted on groups of 65-millimeter bore diameter deep-groove ball bearings in a MIL-L-23699 lubricant under two levels of filtration. In one test series, the oil cleanliness was maintained at an exceptionally high level (better than a class "000" per NAS 1638) with a 3 micron absolute barrier filter. These tests were intended to determine the "upper limit" in bearing life under the strictest possible lubricant cleanliness conditions. In the tests using a centrifugal oil filter, contaminants of the type found in aircraft engine filters were injected into the filters' supply line at 125 milligrams per bearing-hour. "Ultra-clean" lubrication produced bearing fatigue lives that were approximately twice that obtained in previous tests with contaminated oil using 3 micron absolute filtration and approximately three times that obtained with 49 micron filtration. It was also observed that the centrifugal oil filter had approximately the same effectiveness as a 30 micron absolute filter in preventing bearing surface damage.

Stability and Unbalance Response of Large Turbine Bearings

Abstract: Different bearing types frequently used in turbine practice are studied for both stability and unbalance response by linear and nonlinear analysis. The bearing configurations studies are: plain circular, three-axial groove, elliptical, three-lobe, and the three-pocket type. For the film force calculation, the Reynolds equation was solved by finite difference techniques using the effective viscosity concept. The bearing unbalance response was investigated for two values of out-of-balance loads: small unbalance which corresponds to an inaccurate balancing of rotors, and large unbalance representative of some emergency conditions in turbomachineries (blade loss, for example.) In the nonlinear analysis, the effect of energy dissipation in the film by the dynamic motion on the effective viscosity was investigated. The principal results show that all parameters which stabilize the bearing increase the bearing sensitivity to large unbalances. The bearings are ranked as follows in the order of increasing resistance to unbalance loading: three pockets, three-axial groove, offset three lobe, elliptic, circular. A quite different classification was obtained for the stability characteristics where the circular bearing was one of the least stable bearings.

Analysis of Starvation Effects on Hydrodynamic Lubrication in Nonconforming Contacts

Abstract: Numerical methods were used to determine the effects of lubricant starvation on the minimum film thickness under conditions of a hydrodynamic point contact. Starvation was effected by varying the fluid inlet level. The Reynolds boundary conditions were applied at the cavitation boundary and zero pressure was stipulated at the meniscus or inlet boundary. The analysis is considered valid for a range of speeds and loads for which thermal, piezoviscous, and deformation effects are negligible. It is applied to a wide range of geometries (i.e., from a ball-on-plate configuration to a ball in a conforming groove). Seventy-four cases were used to numerically determine a minimum-film-thickness equation as a function of the ratio of dimensionless load to dimensionless speed for varying degrees of starvation. From this, a film reduction factor was determined as a function of the fluid inlet level. Further, a starved fully flooded boundary was defined and an expression determining the onset of starvation was derived. As the degree of starvation was increased, the minimum film thickness decreased gradually until the fluid inlet level became critical. Reducing the fluid inlet level still further led to a sharp decrease in the minimum film thickness. An expression determining the critically starved fluid inlet level was derived. The changes in the inlet pressure buildup due to changing the available lubricant supply are presented in the form of three-dimensional isometric plots and also in the form of contour plots.

The Wear of High Molecular Weight Polyethylene—Part II: The Effects of Reciprocating Motion, Orientation in the Polyethylene, and a Preliminary Study of the Wear of Polyethylene Against Itself

Abstract: The wear of ultra-high molecular weight polyethylene against relatively smooth, dry stainless steel takes place by the same basic wear mechanisms whether unidirectional or reciprocating motion is used, but reciprocating motion produces slightly less wear overall. The effect of molecular orientation in the polyethylene has been studied and it has been shown that orientation perpendicular to the wearing surface is undesirable, whereas orientation parallel to the wear surface is mildly beneficial. The wear of polyethylene against itself is relatively severe and is largely determined by the temperatures reached by the rubbing surfaces.

Spherical Roller Bearing Analysis

Abstract: This paper documents the analytic foundation and software architecture for the computerized mathematical simulation of spherical roller bearing behavior, with emphasis on the mechanical aspects of bearing operation at a given temperature. The resulting software, SPHERBEAN (SPHERical BEaring ANalysis), permits isothermal investigation of spherical bearing performance under axial, radial, or combined loading. The analysis considers elastohydrodynamic (EHD) and hydrodynamic (HD) lubrication loads, roller tilt and skew, roller speeds, and mounting fits. Sample problems illustrating program use are presented.