Study on the running torque of angular contact ball bearings subjected to angular misalignment

Angular misalignment is unavoidable in most applications of rolling-element bearings. The goal of this study is to examine the effects of angular misalignment on the running torque of angular contact ball bearings. A computational method to calculate the running torque of misaligned angular contact ball bearings was introduced. Then, the effects of angular misalignment, along with radial and axial loading, on the running torque of angular contact ball bearings were investigated for two representative preloading methods: constant-force preload and constant-displacement preload. The simulation results showed that (1) the angular misalignment, irrespective of bearing loading, significantly increases the angular contact ball bearing running torque when the constant-displacement preload method was implemented, and (2) the angular misalignment has an insignificant effect on the angular contact ball bearing running torque when the constant-force preload method was adopted. Furthermore, an extensive simulation was performed to examine the effect of load-induced angular misalignment on the running torque of angular contact ball bearings implemented in a geared shaft system. The simulation results showed that the radial load-induced angular misalignment requires additional running torque to the actual rotor-bearing systems, especially when using the constant-displacement preload.

Calculation of Friction Coefficients in Journal Bearings to Determine the Turning Gear Motor Power

Steam turbine turning gear is a gear train, driven by electric motor, which is used to drive the rotor at a given speed and capable of breaking away the turbine and its load equipment from a standstill. Steam turbine rotor trains are supported by journal bearing which require lube oil for cooling. The normal turning gear operation requires that lube oil and the lift oil systems must be in-service in order to reduce the friction coefficient at the journal bearings during breakaway. The rotor train breakaway and running torque is the resisting moments at each of the journal bearings. The resisting moments at each journal bearing are functions of bearing loading, pad type, journal diameter and friction. Therefore, it is important to determine the static and dynamic coefficient of friction in journal bearings of the rotor system to design the turning gear motor power. In the present work, a detailed study has been made for calculating the static and dynamic friction coefficients in the bearings and validated the values with experiments for designing a suitable motor to run the rotor of a steam turbine.

Running Torque of Ball Bearings With Polymer Lubricant (Running Torque Formulas of Deep Groove Ball Bearings Under Axial Loads)

A running torque analysis was performed on axially loaded deep groove ball bearings lubricated with a polymer lubricant. The analysis included a Type I and a Type II bearing. The Type I bearing has a stamped steel riveted cage with its cavity packed with the polymer lubricant. The ball surface, except for the contact points of the ball and the raceways, was covered with the polymer lubricant. The Type II bearing had the polymer lubricant packed only on the riveted parts of the cage; the balls were not covered with the polymer lubricant. The analysis was applied to a 6206 deep groove ball bearing axially loaded in a range typical of preloads applied in actual application to this size bearing to establish bearing tare torque. The results were compared to an available database. The running torque formulas for deep groove ball bearings with polymer lubricant under axial load were proposed as the sums of the running torque caused by the shearing resistance of the mineral oil between the bearing rings and the polymer lubricant, the elastic hysteresis, the differential slip, the spinning friction of the balls, the elastohydrodynamic lubrication (EHL) viscous rolling resistance, and the friction between the balls and the polymer lubricant (or the cage). The effects of the sources of the running torque were investigated. In the case of the Type I bearing, the running torque caused by the friction between the balls and the polymer lubricant, the EHL viscous rolling resistance, and the shearing resistance of the mineral oil between the bearing rings and the polymer lubricant significantly affect the running torque. In the case of the Type II Bearing, the running torque caused by the EHL viscous rolling resistance and the shearing resistance of the mineral oil between the bearing rings and the polymer lubricant significantly affect the running torque. A reasonable correlation exists between the analysis and the database. However, the analysis needs to be further validated with bearing data from different size deep groove ball bearings run under varying loads and speeds.

Testing and Comparative Evaluation of Space Shuttle Main Engine Flowmeter Bearings

This paper provides a summary of testing of Space Shuttle Main Engine (SSME) flowmeter bearings and cage material. This testing was conducted over a several month period in 2004 at the Marshall Space Flight Center (MSFC). The test program’s primary objective was to compare the performance of bearings using the existing cage material and bearings using a proposed replacement cage material. In order to meet the test objectives for this program, a flowmeter test rig was designed and fabricated to measure both breakaway and running torque for a flowmeter assembly. Other test parameters, such as motor current and shaft speed, were also recorded and provide a means of comparing bearing performance. The flowmeter and bearings were tested in liquid hydrogen to simulate the flowmeter’s operating environment as closely as possible. Based on the results from this testing, the bearings with the existing cage material are equivalent to the bearings with the proposed replacement cage material. Therefore, the new cage material is a suitable replacement for the existing cage material.