Temperature Measurement in Fluid Film Bearings



Temperature Measurement
Any change in load, shaft speed, oil flow, oil inlet temperature, or bearing surface finish affects bearing temperature. In turn, excessively high temperatures in the shoe babbitt metal can lead to costly bearing failures caused by wiping of the babbitt.

As you would expect, computer programs are available which analyze oil film pressure, oil temperature, oil viscosity, and shoe deflection. However, these programs yield temperature predictions which are dependent upon several assumptions regarding film shape, hot oil carry-over, and average viscosity.

Fortunately, a more reliable method of assessing bearing performance exists. Kingsbury offers shoes with built-in temperature sensors so you can continually monitor the shoe's surface temperature. This way, metal temperature (the most accurate indicator of the bearing condition) is known at a glance. Remember, discharge oil temperature is indicative only of the inlet oil temperature and the friction power loss in the bearing.

How the Temperature Sensor Works
The temperature sensor, whether it is a thermocouple or a resistance temperature detector (RTD), measures the metal temperature between the shoe's center and trailing edge, where the highest, most critical temperature reading occurs. The sensor can be epoxied in the shoe body or at the 75/75 position. The sensor is located 75% of the shoe length in the direction of rotation from the leading edge, and the 75% of the shoe width measured radially outward from the shoe's inner diameter.

Note: Temperature sensors should not be embedded in the babbitt, because babbitt surface distortions could occur.

Design Option: Temperature sensors can be mechanically mounted to facilitate replacement. Spring loaded sensors, dual elements, and other types of special sensors are also available.

Grooves can be provided in the shoes and base ring to accommodate the lead wire between the sensing element and the wire exit for the bearing housing.

Note: The load direction and shaft rotation must be defined accurately. Temperature varies across and through the shoe, so the sensor must be located properly. For these reasons, we have developed standard sensor locations, such as the 75/75 position for thrust bearings.