Advances in Bearing Lubrication and Thermal Sciences

This reprint focuses on the hot issue of bearing lubrication and thermal analysis, and brings together many cutting-edge studies, such as bearing multi-body dynamics, bearing tribology, new lubrication and heat dissipation structures, bearing self-lubricating materials, thermal analysis of bearing assembly process, bearing service state prediction, etc. The purpose of this reprint is to explore recent developments in bearing thermal mechanisms and lubrication technology, as well as the impact of bearing operating parameters on their lubrication performance and thermal behavior

Review and critical analysis: Rolling-element bearings for system life and reliability

A ball and cylindrical roller bearing technical specification which incorporates the latest state-of-the-art advancements was prepared for the purpose of improving bearing reliability in U.S. Army aircraft. The current U.S. Army aviation bearing designs and applications, including life analyses, were analyzed. A bearing restoration and refurbishment specification was prepared to improve bearing availability

Boundary Conditions for Elastohydrodynamics of Circular Point Contacts

The paper presents the solution of an elastohydrodynamic point contact condition using inlet and outlet lubricant entrainment with partial counter-flow. The inlet and outlet boundaries are determined using potential flow analysis for the pure rolling of contiguous surfaces. This shows that Swift–Stieber boundary conditions best conform to the observed partial counter-flow at the inlet conjunction, satisfying the compatibility condition. For the outlet region, the same is true when Prandtl–Hopkins boundary conditions are employed. Using these boundary conditions, the predictions conform closely to the measured pressure distribution using a deposited pressure-sensitive micro-transducer in a ball-to-flat race contact. Furthermore, the predicted conjunctional shape closely conforms to the often observed characteristic keyhole conjunction through optical interferometry. The combined numerical–experimental analysis with realistic boundary conditions described here has not hitherto been reported in the literature

Cutting torque and tangential cutting force coefficient identification from spindle motor current

This article presents an enhanced methodology for cutting torque prediction from the spindle motor current, readily available in modern machine tool controllers. This methodology includes the development of the spindle power model which takes into account all mechanical and electrical power losses in a spindle motor for high-speed milling. The predicted cutting torque is further used to identify tangential cutting force coefficients in order to predict accurately the cutting forces and chatter-free regions for milling process planning purposes. The developed model is compared with other studies available in the literature, and it demonstrates significant improvements in terms of the completeness and accuracy achieved. The developed model is also validated experimentally, and the obtained results show good compliance between the predicted and the measured cutting torque. The developed enhanced procedure is very appealing for industrial implementation for cutting torque/force monitoring and tangential cutting force coefficient identificatio

High Fidelity Model of Ball Screws to Support Model-based Health Monitoring

L'abstract è presente nell'allegato / the abstract is in the attachmen

Predicted and experimental performance of large-bore high-speed ball and roller bearings

The values of inner and outer race temperature, cage speed, and heat transferred to the lubricant or bearing power loss, calculated using the computer programs Shaberth and Cybean, with the corresponding experimental data for the large bore ball and roller bearings were compared. After the development of computer program, it is important that values calculated using such program are compared with actual bearing performance data to assess the programs predictive capability. Several comprehensive computer programs currently in use are capable of predicting rolling bearing operating and performance characteristics. These programs accept input data of bearing internal geometry, bearing material and lubricant properties, and bearing operating conditions. The programs solve several sets of equations that characterize rolling element bearings. The output produced typically consists of rolling element loads and Hertz stresses, operating contact angles, component speed, heat generation, local temperatures, bearing fatigue life, and power loss. Two of these programs, Shaberth and Cybean were developed

Model Specification for Rework of Aircraft Engine, Power Transmission, and Accessory/Auxiliary Ball and Roller Bearings

This document provides a model specification for the rework and/or repair of bearings used in aircraft engines, helicopter main power train transmissions, and auxiliary bearings determined to be critical by virtue of performance, function, or availability. The rolling-element bearings to be processed under the provisions of this model specification may be used bearings removed after service, unused bearings returned from the field, or certain rejected bearings returned for reinspection and salvage. In commercial and military aircraft application, it has been a practice that rolling-element bearings removed at maintenance or overhaul be reworked and returned to service. Depending on the extent of rework and based upon theoretical analysis, representative life factors (LF) for bearings subject to rework ranged from 0.87 to 0.99 the lives of new bearings. Based on bearing endurance data, 92 percent of the bearing sets that would be subject to rework would result in L(sub 10) lives equaling and/or exceeding that predicted for new bearings. The remaining 8 percent of the bearings have the potential to achieve the analytically predicted life of new bearings when one of the rings is replaced at rework. The potential savings from bearing rework varies from 53 to 82 percent of that of new bearings depending on the cost, size, and complexity of the bearin

Analysis of rolling contact spall life in 440 C steel bearing rims

The results of a two year study of the mechanisms of spall failure in the HPOTP bearings are described. The objective was to build a foundation for detailed analyses of the contact life in terms of: cyclic plasticity, contact mechanics, spall nucleation, and spall growth. Since the laboratory rolling contact testing is carried out in the 3 ball/rod contact fatigue testing machine, the analysis of the contacts and contact lives produced in this machine received attention. The results from the experimentally observed growth lives are compared with calculated predictions derived from the fracture mechanics calculations

Evaluation of rolling contact fatigue resistance for coated components

The thesis reviews and studies current evaluation mechanisms, techniques and machines for testing rolling contact fatigue failure resistance and load capacity of coated components. The thesis investigates both normal and accelerated rolling contact fatigue evaluation test mechanisms and their models, and evaluation test technique principles suitable to the appraisal of coated bearing components. A major contribution of the thesis is the design and development of a new rolling contact fatigue evaluation test machine for coated components. Tests of the rolling contact fatigue of coated bearing raceways under the oil lubricant, grease lubricant and no lubricant conditions, applying the new rolling contact fatigue evaluation mechanisms, evaluation technique principles and the new test machine, have been performed. The accelerated rolling contact fatigue tests of the coated bearing raceways use SiC powder in the oil lubricant.The new rolling contact fatigue test machine has been found suitable for evaluating the rolling contact fatigue resistance of components with superhard coatings. The accelerated rolling contact fatigue test method has been shown to give comparable rolling contact fatigue test results to those obtained in a normal rolling contact fatigue test, while being much faster. In the fatigue test, the cyclic maximum shear stress produces an initial fatigue crack near the substrate surface of the test bearing raceways. The observed phenomena are consistent with theory, although the location of the initial crack is much closer to the surface than would be predicted by a 'static' Hertzian analysis. Insufficient traction forces on the contact surface between the rolling elements of a test coated bearing makes gross skidding occur, leading to rapid wear, over-heating and final failure of the test coated bearing. The LSO fatigue life of the test coated bearing raceway tends to decrease with increase of the coating thickness and coating hardness of the test coated bearing raceway

Electrotribodynamics of ball bearings in electrical machines

The trend towards electrification presents new challenges in bearing design. One such consideration is the occurrence of electrical discharge contact pathways, which can lead to surface damage. The current study presents a novel comprehensive multiphysics model, incorporating bearing dynamics, mechanics of lubricated rolling element-to-races contacts and electrical contact model for both DC and AC voltages. The model also includes both electrical resistance and capacitance effects in the bearing contacts. Key bearing vibration frequencies such as cage frequency and the bearing base natural frequency along with the voltage supply frequency are observed as influential in the electric current discharge. The developed model enables the prediction of rhythmic fluting patterns commonly observed in the failed bearing applications subject to electrical discharge