How can the lubrication condition of bearings be monitored using ultrasound?

The lubrication condition of a bearing influences the mechanical processes within the bearing and therefore also the resulting structure-borne sound. Changes in these ultrasonic signals can therefore provide indications of changes in the lubrication condition.

Using the SONAPHONE with the BS20 or BS40 structure-borne sound sensors, these signals can be detected, made audible, and evaluated.

How is the condition assessed?

The structure-borne sound sensor is coupled to a suitable measurement point on the bearing or bearing housing. The SONAPHONE displays the detected ultrasonic signal, for example as a level curve and spectrogram, and also makes the signal audible.

The assessment can include:

• the ultrasonic level,
• changes in the level over time,
• the spectrogram,
• the audible ultrasonic signal,
• comparison with previous measurements on the same bearing.

Changes in the ultrasonic signal of a bearing may, among other things, indicate a change in its lubrication condition.

When is the BS20 or BS40 used?

The BS20 is particularly suitable for manual inspections. It is coupled to the measurement point using a suitable waveguide. A magnetic waveguide can also be used for recurring measurements. The BS20 additionally features an integrated infrared temperature sensor.

The BS40 is particularly suitable for recurring comparative and trend measurements. It can, for example, be attached to a defined measurement point using a magnetic base or permanently coupled via a screw connection for semi-stationary measurements.

Both sensors detect structure-borne sound signals and can therefore be used for bearing condition monitoring.

Why are comparable measurement conditions important?

The quality and comparability of a structure-borne sound measurement are significantly influenced by the measurement point and the way in which the sensor is coupled.

For recurring measurements, wherever possible, use:

• the same measurement point,
• the same sensor,
• the same accessories,
• the same coupling method,
• a comparable sensor position, and
• similar operating conditions.

Different accessories or coupling methods can influence the frequency response and therefore the measurement result.

Ultrasonic measurement supports condition-based monitoring and optimization of bearing lubrication. The required lubricant type and lubricant quantity must still be determined according to the specifications of the bearing, machine, or lubricant manufacturer.