about a 3.5% error into the analysis, where the resulting contact area is under-estimated by that amount. Assuming that the thermal resistance across the metal and lubricant contact is small compared to the resistance generated due to the thermal constriction of ball to race geometry, the Yovanovich model can be used to estimate the lubricant area once the thermal conductance is measured across the bearing. Thus, the total lubricant area, A 0, can be determined. Based on the analysis method, the contact areas  due to the lubricant and the metal-to-metal Hertzian contact are shown in Table 3.3.1. The values  depicted represent the lubricant and metal contact area between the inner race and one ball. Note thatthe initial lubricant area is dependent on the amount applied to the bearing system before testing began. In this case, the 62-mm OD bearing had a larger relative lubricant amount in the ball-to-race pathway  than the smaller 28-mm OD bearing. In the next section, we’ll explore how the run-in process impacts  lubricant quantity in the ball-to-race contact. Table 3.3.1  Static Bearing Ball-to-Race Hertzian and Lubricant Area Before Run-In Bearing Details Area – (Inner Race) Bearing SizeOD  (mm)Load, P  (N)Hertzian  Contact  Area (mm2)Lubricant  Area  (mm2)Total  Area  (mm2)Lubricant/  Hertzian Area (%) Large bearing, steel 62 133 8.2E-02 45.E-02 53.E-02 550 Small bearing, steel 28 129 4.5E-02 11.E-02 15.E-02 245 3.4 Oil Lubricated Static Run-In Bearing Oiled bearings (small and large, steel) were then run-in in the following manner:  As the bearings turned  continuously at 6000 rpm, the conductance, temperatures, and heat generation were observed to gradually decrease. Changes were most pronounced early in the test and gradually decreased in intensity over time. Each bearing was considered to be completely run-in when no additional changes in these variables could be detected with additional operational time. Measurements of thermal conductance  resumed after bringing the bearing to rest (static conditions) and compared with the results before run-in conditions were established. Observations on the run-in process indicated that the larger bearing runs-in significantly faster. While the  small bearing took 5 days to run-in, the large bearing took significantly less time (less than 3 hours). It was not known exactly how long run-in conditions were reached for the largest 62-mm OD bearing tested because the thermal equilibrium in the test set up itself took 3 hours to occur and by then the bearing was run-in. A possible explanation for the much shorter run-in times for the larger bearing was that a much  larger centrifugal force on the larger 62-mm OD bearing caused more lubricant to be thrown out initially.   Table 3.4.1 shows the impact of a 6000-rpm run-in on lubricant in the ball-to-race pathway. The data  presented in the table represents the lubricant and metal contact area between the inner race and one ball, and provides a relative feel for the amount of lubricant present in the raceway. Before run-in, the lubricant area in the race for the large bearing was significantly larger than the small  bearing, but /g68/g73/g87/g72/g85 run-in, the reverse occurred. While the lubricant contact area size was initially larger in  the 62mm OD bearing, relatively, the lubricant was only 138% larger than its Herzian contact area  compared with 183% for the smaller 28mm OD bearing. This large decrease in lubricant was reflected in a large drop in thermal conductance measurements  described next. Figure 3.4.1 shows the bearing thermal conductance as a function of axial loads for a  28-mm OD bearing, both before and after run-in and Figure 3.4.2 depicts the results for the large 62-mmOD bearing.   120