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TECHNICAL FORUM

J. of Lubrication Tech. 1972;94(2):107-111. doi:10.1115/1.3451643.
Abstract
Topics: Tribology
Commentary by Dr. Valentin Fuster

RESEARCH PAPERS

J. of Lubrication Tech. 1972;94(2):112-116. doi:10.1115/1.3451644.

The effect of ball bearing cross-sectional geometry (ring stiffness) on spalling fatigue life of bearings under heavy radial load was investigated experimentally. For a circular undercut design, the particular case tried, the fatigue life was significantly increased, supporting the proposal that an “undercut” below the raceway is desirable. Static load tests showed that force oscillations are reduced in the more flexible bearing. Hence bearing-induced vibrations should be reduced.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1972;94(2):117-122. doi:10.1115/1.3451647.

The series-hybrid bearing couples a fluid-film bearing with a rolling-element bearing such that the rolling-element bearing inner race runs at a fraction of shaft speed. A series-hybrid bearing was analyzed and experiments were run at thrust loads from 100 to 300 lb and speeds from 4000 to 30,000 rpm. Agreement between theoretical and experimental speed sharing was good. The lowest speed ratio (ratio of ball bearing inner-race speed to shaft speed) obtained was 0.67. This corresponds to an approximate reduction in DN value of 1/3 . For a ball bearing in a 3 million DN application, fatigue life would theoretically be improved by a factor as great as 8.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1972;94(2):125-130. doi:10.1115/1.3451652.

A theoretical analysis, based on boundary layer theory, is presented to predict the oil pumping ability of a tapered roller bearing. The momentum integrals for an assumed laminar boundary layer about the I.D. circumference of the outer race (cup) are derived and solved numerically. The resulting equations predict that the head, flow and viscous torque generated are dependent upon the bearing’s speed and geometry, as well as the viscosity and density of the oil in the bearing.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1972;94(2):131-135. doi:10.1115/1.3451655.

A laboratory study has been made of the lubrication and friction characteristics of a plastic on metal (Charnley-Muller) and a metal on metal (McKee-Farrar) total hip joint replacement prostheses. The results show the effect of lubricant, speed, and load on the performance of the joints. Under a 560 lb load the coefficient of friction of the plastic to metal joint was lower than that of the metal to metal at speeds up to the equivalent of fast walking. Bovine serum and synovial fluid, as well as human serum albumin were found to be good lubricants of both types of prostheses. The frictional force produced by the metal on metal prosthesis increased linearly with load, in both the dry and lubricated states. This was not the case with the plastic to metal joint. The results show that at low physiological loads the effort required to articulate the prostheses are comparable while at higher loads the friction force of the metal to plastic is significantly lower. Friction readings taken with no lubricant indicate the serious damage which would result in the human body if a metal to metal prosthesis became devoid of liquid. The load and speed behavior of the prostheses require different interpretation of the data than presently postulated.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1972;94(2):136-142. doi:10.1115/1.3451656.

Equations for the flow rate, load capacity, and friction torque for a conical hydrostatic bearing were developed. These equations were solved by a digital computer program to determine bearing configurations for minimum friction torque. Design curves are presented that show optimal bearing dimensions for minimum friction torque as a function of dimensionless flow rate for a range of dimensionless load capacity. Results are shown for both laminar and turbulent flow conditions. The results indicate the hydrostatic pocket friction is a significant portion of the total friction torque. However, the bearing dimensions for a minimum friction design are affected very little by inclusion of pocket friction in the analysis. For laminar flow the values of the outerland radius ratio X3 and outer bearing radius ratio X4 did not change significantly with increasing friction factor. For turbulent flow, the outer bearing radius ratio X4 did not change with increasing friction factor; therefore, the value determined for X4 in the laminar flow case is valid for all turbulent flows.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1972;94(2):143-150. doi:10.1115/1.3451660.

A roller bearing model, which includes the effects of full film lubrication at the race contacts, was developed for use in estimating cage slip, roller slip, film thickness, and cage forces for a given bearing geometry and operating condition. The model includes churning loss, cage pilot surface friction, roller pocket friction, cage unbalance as well as the drag due to the unloaded rolling elements. Roller skew and misalignment have been neglected, however these effects could be introduced if desired. The description of the lubricant film thickness, traction, and pressure forces are based upon assumptions introduced by Dowson, which reduce the complex numerical procedure required for a rigorous solution to the isothermal elastohydrodynamics problem to a set of nonlinear equations. A parametric study on a 1907 basic roller bearing is included to illustrate the use of such a model as a design tool.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1972;94(2):153-162. doi:10.1115/1.3451666.

To reduce the influence of misalignment (asymmetrical loading) on cylindrical roller bearings it is necessary to supplement the crown modifications of bearing elements. A unique hollow-ended roller design was developed for this purpose employing a three-dimensional finite element elasticity study to determine the stress state in the flexible rim section. The results when combined with the classical Hertzian contact stress distribution result in an accurate description of the shear stress field throughout the roller rim sections. Results of fatigue tests run under asymmetrically distributed loads supported the analytical efforts demonstrating significant improvements in L10 lives for the hollow-ended roller as compared to a solid roller. Peak stresses occurred in the vicinity of the contact area for both types of rollers with the solid exhibiting stresses 5 percent or more higher than those found in the hollow-ended type. Of equal importance, the observed failure mode for hollow-ended rollers under heavy load fatigue test conditions is one of conventional subsurface initiated O.D. spalling, thereby proving the rim design to be structurally sound.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1972;94(2):165-171. doi:10.1115/1.3451669.

Rolling-element fatigue tests were run with eight through-hardened bearing materials at 150 deg F. One-half in. dia balls of each material were run in five-ball fatigue testers. Care was taken to maintain constant all variables known to affect rolling-element fatigue life. The longest lives at 150 deg F were obtained with AISI 52100. Ten-percent lives of the other materials ranged from 7 to 78 percent of that obtained with 52100. A trend is indicated toward decreased rolling-element fatigue life with increased total weight percent of alloying elements. Three groups of 120-mm bore ball bearings made from AISI M-1, AISI M-50, and WB-49 were fatigue tested at an outer-race temperature of 600 deg F. The 10-percent lives of the M-50 and M-1 bearings exceeded the calculated AFBMA life by factors of 13 and 6, respectively. The bearings with WB-49 races showed lives less than AFBMA life. The results of the bearing tests at 600 deg F correlate well with the results of the five-ball fatigue data at 150 deg F.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1972;94(2):174-178. doi:10.1115/1.3451673.

Three test groups of 2.75 in. bore tapered roller bearings were manufactured from pilot heats of cold hearth electron beam remelted modified 4620 steel, a heat of standard consumable electrode vacuum remelted (CV) 4620 steel and from conventionally melted modified 4620 bearing steel. Bearing life tests were performed in a synthetic fluid and two mineral oils of different viscosity to determine the contact fatigue strength of the electron beam melted steel as compared to the CV steel and conventional steel. The electron beam and the consumable vacuum melted steel had equivalent contact fatigue strength in this initial appraisal. The CV steel had contact fatigue strength 4.5 to 9.8 times better than the conventional bearing steel.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1972;94(2):181-186. doi:10.1115/1.3451678.

A comprehensive analytical and experimental study of the effect of misalignment on load distribution and fatigue life of tapered roller bearings is presented. Included are the effects of truncation of crowned rollers and edge of contact stresses. Bearing life tests, involving approximately 500 bearings, were run at various loads and misalignments to obtain sufficient test data to substantiate the analytical results.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1972;94(2):188-192. doi:10.1115/1.3451682.

By the use of a new variational technique, the bearing profile which maximizes the load carrying capacity of an infinite length journal bearing is obtained. The lubricant is assumed to be incompressible and of constant viscosity. The flow is assumed to be laminar and the optimization is based upon a minimum film thickness. The solution obtained is a concentric step bearing with a film thickness ratio of 1.812 and a ridge to pad ratio of 0.328. It is mathematically shown by the use of the “nonlocal” formulation that this step profile does yield a maximum among all profiles sufficiently “close.”

Commentary by Dr. Valentin Fuster

DISCUSSIONS

Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster

TECHNICAL BRIEFS

Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster

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