The Vibration and Temperature Check of Bearings
Bearing vibration and temperature are two of the most important parameters to consider when working with rolling-element bearings. Bearings typically generate vibration due to their internal stresses, caused by external loads, misalignment and other factors. In addition, they typically increase in temperature related to the load, speed, lubrication and the physical condition of the bearings themselves.
Therefore periodic measurements of both vibration and temperature should be made for rolling-element bearings. This will provide a wealth of information about the bearing condition and its performance in operation. In this article, we will discuss the importance of vibration and temperature checks for bearings and look at the methods and tools available for carrying out these procedures.
Bearing Vibration
Vibration components of radial, axial and tangential movements can be detected and measured by attaching a vibration sensor such as an accelerometer to the bearing housing, shaft or bearing in order to detect the presence of vibration and frequency of the components present. Vibration measurements should preferably be taken in three planes - radial, vertical and axial (parallel to the shaft axis) - in order to determine the nature of bearing vibration.
The standards and information used to interpret the measurements can vary depending on the manufacturer and the type of bearing. As a general guide, rolling-element bearing vibration levels should typically be lower than 1 mm/s (0.04 inch/s) in radial, vertical and axial directions. Vibration levels above 1.5 mm/s (0.06 inch/s) in any direction may indicate that the bearings should be replaced or checked further.
Bearing Temperature
The temperature of the bearings can be a good indicator of bearing condition. Almost all bearings will have increased temperatures in operation - the amount of this increase depending on the load and speed applied to the bearing. Higher temperatures indicate more frictional losses and bearings running above their design limits, which may require adjustment in terms of speed, load or misalignment.
Temperature measurements should be taken at least periodically and compared to the manufacturer’s datasheet. Ideally, measurements should be taken before and after operation to get an indication of increased temperature due to the bearings running in service. Depending on the type of bearing and its application, temperature measurements should generally be below 65° C (150° F) in most cases.
Equipment for Vibration and Temperature Measurement
To make accurate vibration and temperature measurements for bearings, a suitable instrument is available. These instruments typically combine a vibration sensor and temperature probe into a single unit, making measurements in both directions relatively straightforward.
The vibration sensor is typically either an accelerometer or a proximity probe, depending on the application (see Figure 1). In both cases, the instrument should be attached to the bearing housing and connected to the instrument either via a wire or through a wireless Bluetooth connection.
The temperature probe is typically a thermocouple or thermistor, which is attached to the bearing inlet or outlet. These probes are connected to the instrument via a wire, giving a continuous readout of the temperature of the bearing during operation.
Conclusion
Vibration and temperature measurements of rolling-element bearings should be taken regularly in order to maintain an acceptable level of bearing performance and condition. With the right equipment, vibration and temperature checks of bearings are relatively straightforward and provide a wealth of information about bearing condition which can enable proactive maintenance planning. By conducting regular checks, bearing life can be extended and costs associated with bearing failure and premature replacement can be reduced.
