The measurement of the running torque of oil and grease lubricated instrument ball bearings under combined radial and axial loads

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Virginia Polytechnic Institute

Although many studies have been made on the operating characteristics of instrument bearings, most were conducted at two rpm or less and with thrust load only. A study by H.H. Mable tested the running torques of radially loaded bearings from 1,000 to 40,000 rpm. The purpose of this investigation was to study the running torques of R-3 size instrument ball bearings at speeds up to 40,000 rpm while under combined radial and axial load.

Much of this investigation was devoted to the construction of an accurate torque sensing device. The method employed relied on the amplification of strain gage signals by a strain gage indicator and an x-y plotter. The strain gages were used to detect the strain at the base of a small beam that prevented rotation of the outer race.of a test bearing while the inner race was driven at test speed by an air turbine. The accumulated data was the result or 30 test series, with each series being constituted of a test sample of six ball bearings.

From the study, it was consluded that the strain gage method of torque sensing accurately measured the running torque of R-3 size ball bearings at ambient temperatures. It was also concluded that the effect of axial loading or an R-3 ball bearing loaded with 47 grams radially is negligible until the axial: load equals o.r exceeds the radial loading.

By comparing lubricants, it was concluded that grease lubricated ball bearings demonstrate running torques approximately twice as great as bearings lubricated with a similar weight of oil.