How do you know when to stop lubricating a bearing? For some technicians, it seems like they only stop pumping once grease flows out on the ground. Too much grease, too little grease! What's a poor bearing to do?

According to most bearing manufacturers, over lubrication is a major cause of bearing failure. Over lubrication causes excessive loading which overheats the bearing, melting the lubrication, which in turn causes it to be thrown from the bearing - creating a lack of lubrication condition. This often results in bearing failure. If there is no release for the excessive grease, the pressure will cause a bearing failure. There have even been instances of electric motor a cavity being so full of grease; a short was created causing the entire motor to fail.

Most over lubrication is caused by lack of training, lack of awareness and lack of a written procedure. Some grease guns are calibrated for measured grease delivery and other feature digital gauges to track delivery.

Recently, acoustic or ultrasonic lubrication methods have become popular and offer an opportunity to prevent over lubrication. In some cases, proactive condition based lubrication is replacing the old time based lubrication procedures.

These devices "listen" to the sound of the bearing. Put simply, a properly lubricated bearing provides a smooth rushing sound heard the amplified audio signal in noise blocking headsets. Some units also feature digital meters to measure or trend sound level readings.

When a bearing lacks lubrication, a much rougher sound is detected and a technician can actually monitor the audiometer reduction and the sound level smoothing out as the grease comes into contract with the bearing.

There are two primary technologies available to accomplish the task of condition based lubrication monitoring. The first is a sonic or audible sound device. This device features a simple yet rugged stinger type metal contact probe connected to a grease gun mounted amplifier and control unit. Noise isolating headphones are supplied to block out ambient plant noise. This is the most popular unit as it is low cost, designed for ease of use (the only adjustment is volume) and can stand up to the most demanding environments.

The other unit's feature high frequency ultrasonic sensors, which also have numerous other plant applications, to detect, amplify and then translate or heterodyne the sound level into audible sounds, also heard through noise attenuating headsets. These devices are usually more sophisticated and include digital meters, data logging and software. They are multi-application instruments and are also used for leak detection, steam trap and valve testing as well bearing monitoring.

Both of these technologies have tremendous application, however, be cautioned as to the new sound monitoring procedure. I have read some manufacturers recommendations that would actually lead to over lubrication, even as you monitor the application of grease! Be sure and request a written procedure that the device manufacturer stands behind. It is a good idea to check with your bearing supplier as well as warranty issues may come into play and you want to ensure you remain covered.

Units are available in prices ranging from under $2,000 to well over $10,000. Training is usually offered by the vendor although a few independent training offerings are also available.