A temperature sensor mounted at the 75/75 position can provide the critical shoe temperature for that one, fixed location, but cannot indicate the temperature pattern over the entire shoe surface. In order to demonstrate the localized nature of the critical temperature region, we rely on isotherms (lines of constant temperature) based upon an array of 9 thermocouples evenly distributed across the shoe surface, plus a tenth thermocouple at the 75/75 location. The sensors are embedded in the babbitt material, approximately 0.03" (0.76 mm) below the shoe working surface. Values from all ten thermocouples are curve-fit in the circumferential and radial directions to obtain intermediate temperature values at other locations on the shoe. These combined measured and intermediate temperatures are plotted as isotherms in the accompanying illustrations.
Measured temperatures will vary according to:
Beyond the shoe's center, the thermal gradient becomes much steeper and more indicative of the actual oil film thickness.
Sometimes, thermal crowning and load distortions produce a distinct hot spot such as that shown at 6000 RPM, 500 PSI (3.45 MPa), with a temperature above 270°F (132°C).
Important: In a region of high oil film pressure, such a critical temperature is much more dangerous than a hot spot developing at a trailing edge for 6000 RPM, 300 PSI (2.07 Mpa), where the parabolic pressure distribution falls to zero.
By varying some of the factors which influence shoe temperature, we can evaluate overall bearing temperature performance based upon that change. For example, we have been able to measure the effects of reducing shoe thickness and using a smaller shoe support in our bearings. For results of these comprehensive tests, contact our Engineering Department.