Unf ortunately, there may be other contributions to bearing drag that are not accounted in the model (such  as ball speed variations or cage instabilities) . Unless they are recognized and quantified, these additional  sources of torque will be captured in the LQF, and may be misinterpreted as a value due to the presence  of additional lubricant . Due to these unpredictable contributors, the LQF is  often considered to be a “catchall” adjustment factor that includes both the lubricant and other unknown or un- modeled quantities.    Our purpose with the present report is to establish a n experimental and analytical  method for using heat  generation to determine LQF values, which then can be used in further analysis of bearing performance. In a future report, we will probe more deeply into the relationship between LQF and the actual quantity of lubricant in the critical rolling and sliding interfaces . This paper will explain the experimental and analytical  method behind quantifying LQF, and the resulting data collected for two different ball bearing types : 1) An  all-52100 steel angular contact 305-s ize ball bearing, and 2) A Silicon Nitride  – 52100 steel  hybrid angular  contact 305-s ize ball bearing 

Experimental Method of Determining Lubricant Quantity Factor    The LQF was determined experimentally by measuring heat generation and temperatures of an isolated bearing in a vacuum environment, where the inner race was moving at a constant 6000 rpm speed while  the outer race was held stationary . Both the  test rig’s  thermal and mechanical boundary conditions  were   monitored and set for a given test . A series of boundary conditions were varied to create a test matr ix and  resulting bearing  temperature and heat generation values were measured. The bearing and test conditions  were then modeled and LQF was correlated to the test data using computational bearing analysis software.  The influence of temperature and axial loads were then determined and compared for  the two different  bearing types . The next sections will describe the experiment, the test method and models required to  characterize LQF for the two bearings tested.  

Test Rig Overview   The test rig, originally designed to measure bearing thermal conductance [1], provided control of thermal  and mechanical loads while monitoring the heat generated by a single test bearing. All tests were conducted  in a vacuum environment .    Figure 1 is a photograph and schematic of the test stand, which is housed in a vacuum bell jar . The  hardware shown was used for  measuring heat generation of  the 305-size bearings tested . The thermal  system consists of a heat source and sink . Lamps generate a heat source that applies a thermal l oad on  the rotating shaft . Heat travels up the shaft, through the test bearing and transfers through the disk -shaped  Outer Heat Meter into a chiller -controlled heat sink on the perimeter of the Outer Heat Meter.    The mechanical controls include an applied axial load and a known and constant rotational speed. An axial  load is applied using the Axial Load Device which applies a controlled and constant measured load to the outer rim of the Outer Heat Meter . The load transfers to the test bearing that  is supported at the inner race  by the shaft . In this way, a controlled axial load is applied and held constant throughout the test . The speed  of the bearing is controlled by a vacuum motor that applies a constant and known rotational speed of the shaft and bearing inner race while the outer race is held stationary. The test is contained in a vacuum environment at pressures in the order  of magnitude of 1x10 -6 Torr.  

Testing Method   The control thermal and mechanical boundary condition variables include a known heat sink chiller temperature, a known axial load, rotational shaft speed, and a heat lamp voltage output . While we can  regulate the voltage to the heat source, the amount of heat input into the shaft is not controlled, although it is measured at steady state conditions so it is a known value. Thus, the test matrix includes the following:   1. Apply a range of axial loads   2. Apply a range of  thermal sink chiller temperatures   3. Apply a range of voltage to the heat lamps   4. All test data is collected at a constant shaft rotational speed of 6000 rpm   NASA/CP—2018-219887 544