Bearing responsibility

Rolling bearings are among the most important components in most machines with moving parts; they play an essential role in these systems by reducing rotational friction, supporting radial and axial loads, and ensuring that the machine continues to perform at its optimum level. 

Exacting demands are made on the load carrying capability of bearings, as well as their running accuracy, noise levels, friction and frictional heat, life and reliability. Therefore, it is natural that rolling bearings should have come to play such a prominent part, and that over the years they have been the subject of extensive research and continuous improvements.

Despite careful design and manufacture, as well as testing the bearing in the application, however, sometimes a bearing does not last for its required service life. Failures cause economic losses due to production downtime, consequential damage of adjacent parts, and the cost of repairs.

When a bearing does fail, it is critical to determine the cause so appropriate modifications can be made. Premature bearing failure can occur for a variety of reasons with each failure leaving its own special imprint on the bearing. The good news is that by examining a failed or damaged bearing, it is possible in most cases to establish the root cause and define corrective actions to prevent a recurrence.

Warning signs

There are a variety of reasons that bearings fail, but impending failure is often preceded by signs that the machine is not performing at its optimum. Clues to potential problems can include noise, vibration and excessive heat.

For example, metal-to-metal contact can lead the bearings to run hot and cause premature wear, leading to higher noise levels. Any misalignment of the shaft relative to the housing or the housing seal can cause a non-contact or gap type seal to rub. This condition can elevate temperatures, increase noise levels and accelerate wear during the initial running-in period. It also compromises sealing integrity.

Another example is high temperatures which can alter the physical properties of the ring and ball materials. The resulting loss in hardness can then reduce the bearing capacity causing early failure.

Contaminants can also damage the bearing contact surfaces, increasing noise and vibration levels. Denting of the bearing contact surfaces can occur when solid contaminants are left in the bearing housing from a previous failure, from wear of other components such as gears, or from contaminated lubricant. This can increase temperature, noise and vibration levels.

A common method used to try to identify deterioration or damage in a bearing is listening. Bearings that are in good condition produce a soft purring noise. Grinding, squeaking and other irregular sounds usually indicate that the bearings are in poor condition, or that something is wrong.

The need for vibration monitoring comes from three fundamental facts:

•    All machines vibrate.

•    The onset of a mechanical problem is generally accompanied by an increase in vibration levels.

•    The nature of any faults can be determined from the vibration characteristics.

It is also important to monitor the operating temperature at bearing positions. If the operating conditions have not been altered, an increase in temperature is often an indication of imminent bearing damage. However, keep in mind that a natural temperature rise lasting one or two days normally occurs immediately after first machine start up and after each re-lubrication when using grease.

Please can you put the following in a box headed:

Causes of excessive noise, vibration and high temperatures

Noise

•    Metal-to-metal contact

•    Contamination

•    Too loose fits

•    Surface damage

•    Rubbing

Vibration

•    Metal-to-metal contact

•    Contamination

•    Too loose fits

•    Surface damage

Heat

•    Lubrication problem

•    Sealing conditions

•    Insufficient clearance in operation

•    Improper bearing loading